jimmy kim - qut · jimmy kim principal supervisor: dr. poologanathan keerthan associate supervisor:...
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DEVELOPMENT OF MODULAR BUILDING
SYSTEMS MADE OF INNOVATIVE STEEL
SECTIONS AND WALL CONFIGURATIONS
Jimmy Kim
Principal Supervisor: Dr. Poologanathan KEERTHAN
Associate Supervisor: Prof. Mahen MAHENDRAN
Submitted in fulfilment of the requirements for the degree of
Master of Philosophy (Engineering)
School of Civil Engineering and Built Environment
Faculty of Science and Engineering
Queensland University of Technology
2019
Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations i
Keywords
Case Study, Cold-Formed Steel Sections, Fire Performance, Light Gauge Steel Framed
(LSF), Modular Building Systems (MBS), Prefabrication, Rivet-Fastened Rectangular
Hollow Flange Channel Beam (Rivet-Fastened RHFCB), Stiffened Channel Sections,
Thermal Modelling.
ii Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Abstract
Modular building systems and the modular construction techniques are construction
technologies that show promising capabilities to deliver construction results far
superior to those of traditional construction methods. This developing technology
exhibits the potential to provide results far superior to those otherwise obtained using
traditional construction methods including time, costs and waste savings. These
savings are attributed to its systematic, controlled and integrated processes that allow
project activities to be completed simultaneously. The modular construction process
follows that individual volumetric building units (modules) are constructed off-site in
a factory setting, transported to site and then assembled together in an arrangement
that constitutes a building structure.
The modular construction method is recognized as an emerging technology with the
industry still developing and refining this technology. The full potential of the modular
construction technology has yet to be completely realised with shortcomings and
drawbacks limiting their capabilities. The examination of real-world modular
construction projects has revealed shortcomings to be: poor structural-efficient designs
of the modular building systems (strength-to-weight performance), lack of control of
construction tolerances, impractical designs resulting in increased assembly efforts
and lack of measures to address fire-resisting performance.
To address these issues, this study has been performed to further the understanding of
modular construction and propose solutions to address the several recognised
shortcomings. Modular building systems have been thoroughly examined to establish
an understanding of their complex technology. Current cold-formed steel technologies
have been reviewed, particularly the Rivet-Fastened RHFCB section which is later
introduced as an innovative design to address the shortcomings of modular building
systems.
The study provides a comprehensive execution of case studies to analyse and pinpoint
the drawbacks and shortcomings of modular construction seen in real world projects.
These case studies have also examined current developing technologies that have been
developed to address these shortcomings.
Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations iii
The development of several wall systems is presented and introduced as innovative
designs to address the shortcomings of structural efficiency and fire-resisting
protective measures. These wall systems differ between each other through their
arrangements of gypsum plasterboard layers and cavity insulation. They are then
analysed through finite element modelling to predict their fire-resisting performance.
Each wall system configuration proved to provide superior fire-resisting performance
when compared to the standard wall system. Among the systems considered,
Configuration 5 demonstrated the best performance. Configuration 5 consisted of a
discontinuous arrangement of cavity insulation and back-blocking boards on either
side of the steel studs in the form of Gypsum Plasterboard.
The innovative concepts presented in this study are then combined to present a
conceptual design proposal of a modular building system. The proposed modular
building system took the form of a corner supported module and incorporated the rivet-
fastened RHFCB as the edge beams and joists to increase the structural efficiency.
Stiffened channel sections line the walls to provide greater structural stability and a
double Gypsum Plasterboard setting is adopted in the roof and floor systems for fire-
resisting measures. Several wall systems are proposed with each highlighting their
advantages and appropriate applications. Simple connections are adopted throughout
the system to minimize assembly efforts. The proposed design then concludes with
concepts to adopt for application in multi-storey modular building systems.
In summary, this study has introduced modular building systems and the modular
construction method. This promising technology has the capability to deliver
construction results far superior to those attained through traditional construction
methods, although it is still developing and has yet to realise its full potential. The
shortcomings and drawbacks of this technology are pinpointed, and innovative ideas
and designs are introduced to address these. This study concludes that with further
investigation, the full potential of the modular construction method can be achieved.
iv Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table of Contents
Keywords .................................................................................................................................. i
Abstract .................................................................................................................................... ii
Table of Contents .................................................................................................................... iv
List of Figures ......................................................................................................................... vi
List of Tables ......................................................................................................................... xiii
List of Abbreviations .............................................................................................................. xv
Statement of Original Authorship ......................................................................................... xvi
Acknowledgements .............................................................................................................. xvii
Chapter 1: Introduction .................................................................................... 19
1.1 Background .................................................................................................................. 19
1.2 Context ......................................................................................................................... 28
1.3 Aim .............................................................................................................................. 28
1.4 Significance, scope and definitions .............................................................................. 29
1.5 Thesis outline ............................................................................................................... 30
Chapter 2: Literature Review ........................................................................... 31
2.1 Introduction .................................................................................................................. 31
2.2 Cold-Formed Steel ....................................................................................................... 31
2.3 Structural Design of Cold-Formed Steel Structures ..................................................... 36
2.4 The Rivet-Fastened Rectangular Hollow Flange Channel Beam ................................. 40
2.5 Modular Building Systems ........................................................................................... 44
2.6 Findings, Summary and Implications .......................................................................... 79
Chapter 3: Case Studies..................................................................................... 85
3.1 Introduction .................................................................................................................. 85
3.2 461 Dean, New York City. ........................................................................................... 85
3.3 SOHO Apartments, Darwin ......................................................................................... 94
3.4 Octavio’s and Pascual’s Affordable Steel Concept .................................................... 100
3.5 The Verbus System .................................................................................................... 110
3.6 Double Skin Steel Panel Wall System ....................................................................... 117
3.7 VectorBloc Connection System ................................................................................. 121
3.8 Connector System for Building Modules by Verbus Systems ................................... 125
3.9 Conclusion ................................................................................................................. 130
Chapter 4: Thermal Modelling of Light Gauge Steel Framed Wall Systems
Proposed for Modular Building Systems ............................................................. 131
4.1 Introduction ................................................................................................................ 131
Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations v
4.2 Innovative LSF Wall System Configurations .............................................................133
4.3 Thermal Properties......................................................................................................136
4.4 Method of Numerical Studies .....................................................................................138
4.5 Results ........................................................................................................................140
4.6 Conclusion ..................................................................................................................146
Chapter 5: Conceptual Design of an Improved Modular Building System 147
5.1 Introduction ................................................................................................................147
5.2 Design Considerations ................................................................................................147
5.3 Design Inputs ..............................................................................................................149
5.4 Proposed Modular Building System Conceptual Design ...........................................153
5.5 Multi-Storey Configurations .......................................................................................170
5.6 Conclusion ..................................................................................................................173
Chapter 6: Conclusions ................................................................................... 174
6.1 Conclusions ................................................................................................................174
6.2 Literature Review .......................................................................................................175
6.3 Case Studies ................................................................................................................176
6.4 Thermal Modelling of Light Gauge Steel framed Wall Systems Proposed for Modular
Building Systems ........................................................................................................177
6.5 Proposed Conceptual Design ......................................................................................178
6.6 Recommendations and Future Research .....................................................................179
Bibliography ........................................................................................................... 181
vi Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
List of Figures
Figure 1-1: A three-dimensional steel-framed modular building system being
hoisted into place (TLG Modular Building Solutions, n.d.). ....................... 20
Figure 1-2: A two-dimensional structural steel frame being erected (Reardon,
David, & Downton, 2013). ........................................................................... 20
Figure 1-3: The Nicholson of Melbourne, Australia (Archi Channel, n.d.). .............. 21
Figure 1-4: Standard cold-formed steel sections and shapes. .................................... 22
Figure 1-5: Hollow Flange Beam Profile and Dimensions (Dempsey, 1990). .......... 23
Figure 1-6: Profile of the LiteSteel Beam (Steau, 2014). ........................................... 24
Figure 1-7: The manufacturing process of the LiteSteel beam (LiteSteel
Technologies America LLC, 2006). ............................................................ 25
Figure 1-8: Applications of LiteSteel Beams (LiteSteel Technologies America
LLC, 2010) and (Building Design & Construction, n.d.). ........................... 26
Figure 1-9: Rendered images of the Rivet-Fastened RHFCB. ................................... 26
Figure 1-10: Profile of the Rivet-Fastened Rectangular Hollow Flange Channel
Beam (Steau, 2014). ..................................................................................... 27
Figure 2-1: The structural frame of this residential structure consists of cold-
formed steel members (All Steel House Frames, n.d.). ............................... 32
Figure 2-2: Cold-formed steel decking overlayed by reinforced concrete in a
composite floor system (Luke Allen, 2014). ................................................ 32
Figure 2-3: Peter Naylor's advertisement titled "Portable Iron Houses for
California" (Browning, 1995). ..................................................................... 33
Figure 2-4: The cold roll-forming process (Chicago Roll Company, n.d.). ............... 34
Figure 2-5: The press braking method (ThomasNet.com, 2012). .............................. 35
Figure 2-6: The standard I-section is composed of two flange elements and a
single web element. ...................................................................................... 36
Figure 2-7: The ‘chequer board’ wave like pattern of local buckling
deformation (Quimby, 2014). ...................................................................... 37
Figure 2-8: Shear buckling of a lipped channel section (Hancock & Pham,
2013). ........................................................................................................... 38
Figure 2-9: Distortional buckling of a channel section (Keerthan, 2010). ................. 38
Figure 2-10: Lateral distortional buckling of a channel section (Keerthan,
2010). ........................................................................................................... 38
Figure 2-11: Lateral torsional buckling of a channel section (Keerthan, 2010). ....... 39
Figure 2-12: The improved flange design of the Rivet-Fastened RHFCB. ............... 41
Figure 2-13: RHFCB1 and RHFCB2 (Poologanathan & Mahendran, 2015). ........... 42
Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations vii
Figure 2-14: Varying failure modes encountered by Steau et al. (2015).
*Modified from Steau et al. (2015).............................................................. 44
Figure 2-15: Degree of prefabrication (Smith, 2011). ............................................... 45
Figure 2-16: Nonsuch House (centre structure) as seen on London Bridge
(Landow, 2012). ........................................................................................... 46
Figure 2-17: The Balloon Frame system is composed of wooden members
(Egonarts, 2014). .......................................................................................... 47
Figure 2-18: St Mary's Catholic Church (Goodman Theatre, n.d.). ........................... 47
Figure 2-19: Advertised image of Manning's Portable Cottages (McDonald,
n.d.). ............................................................................................................. 48
Figure 2-20: Autumn 1958 cover print of the Modular Quarterly, showing the
first officially recognised Modular Assembly (Wall, 2013). ....................... 49
Figure 2-21: A full modular hospital being constructed (Steelconstruction.info,
n.d.). ............................................................................................................. 51
Figure 2-22: A modular structure comprising of a primary steel frame and
supported on a podium (ArcelorMittal et al., 2008). ................................... 52
Figure 2-23: A four-sided steel module with load-bearing walls (ArcelorMittal
et al., 2008). ................................................................................................. 53
Figure 2-24: Design details of a typical four-sided steel module (M. Lawson,
2007). ........................................................................................................... 54
Figure 2-25: An intermediate SHS post is introduced to provide support to the
open face of this module (M. Lawson, 2007). ............................................. 55
Figure 2-26: An integral corridor is implemented in the longitudinal walls of
this module (Steelconstruction.info, n.d.). ................................................... 56
Figure 2-27: An open-sided bathroom module is installed on an existing
structure (M. Lawson, 2008). ....................................................................... 56
Figure 2-28: Floorplan of apartments incorporating the partially open-sided
module – alternate modules are shaded (M. Lawson, 2007). ...................... 57
Figure 2-29: The completed apartment building of Figure 2-28 – Barling Court,
Stockwell (M. Lawson, 2007). ..................................................................... 57
Figure 2-30: A steel corner-supported module (ArcelorMittal et al., 2008). ............. 58
Figure 2-31: Structural details of a corner-supported module, end view (M.
Lawson, 2007).............................................................................................. 58
Figure 2-32: Structural details of a corner-supported module, side view (M.
Lawson, 2007).............................................................................................. 59
Figure 2-33: An open-ended module with a welded end frame (M. Lawson et
al., 2014). ..................................................................................................... 59
Figure 2-34: citizenM Hotel of Glasgow (Cheshire, 2012). ...................................... 60
Figure 2-35: Basic components of load-bearing modules. Modified from Figure
2.3 of M. Lawson et al. (2014)..................................................................... 61
viii Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 2-36: Insulation profile of the ALHO Comfort Line by ALHO
Systembau GmbH (Rosenthal, Dörrhöfer, & Staib, 2008). ......................... 62
Figure 2-37: Conventional load-bearing side wall configuration. ............................. 63
Figure 2-38: The fin plate connection on a SHS (The Steel Construction
Institute, 2002). ............................................................................................ 65
Figure 2-39: Angle connections on the corner of steel modules (M. Lawson et
al., 2014). ..................................................................................................... 66
Figure 2-40: Workers assemble the floor base of MBSs (Vanguard Modular,
2014a). .......................................................................................................... 69
Figure 2-41: Completed metal flooring work on a MBS (Outdoor Aluminum,
n.d.). ............................................................................................................. 69
Figure 2-42: Workers assemble wall frameworks on a MBS (Outdoor
Aluminum, n.d.). .......................................................................................... 69
Figure 2-43: Workers completing the sheathing of walls on a MBS (Outdoor
Aluminum, n.d.). .......................................................................................... 69
Figure 2-44: Electrical wiring being completed on a MBS (Outdoor Aluminum,
n.d.). ............................................................................................................. 70
Figure 2-45: Inside a completed MBS (Outdoor Aluminum, n.d.). ........................... 70
Figure 2-46: MBS's wrapped, sealed and prepared for transportation to site
(Vanguard Modular, 2014b). ....................................................................... 70
Figure 2-47: Framed modular system with double skin steel wall panels (Hong
et al., 2011). .................................................................................................. 72
Figure 2-48: Double skin steel panel (Hong et al., 2011). ......................................... 72
Figure 2-49: Test arrangement used in Lawson’s and Richard’s study (R. M.
Lawson & Richards, 2009). ......................................................................... 74
Figure 2-50 General module to crane connection arrangements (M. Lawson et
al., 2014). ..................................................................................................... 77
Figure 2-51: Building joints influencing the appearance of a façade. ....................... 78
Figure 2-52: Effects due to misalignment (M. Lawson et al., 2014). ........................ 79
Figure 3-1: 461 Dean of the Pacific Park development project, New York
(Dezeen Magazine 2012). ............................................................................ 86
Figure 3-2: Structural scheme of the 461 Dean tower (Forest City Ratner
Companies, 2012). ....................................................................................... 87
Figure 3-3: Generic floorplan of 461 Dean Tower (FC Modular, n.d.). .................... 87
Figure 3-4: Structural scheme of base module chassis employed in the 461
Dean tower ................................................................................................... 88
Figure 3-5: Side view of completed a 461 Dean module chassis (Calcott, 2014). .... 89
Figure 3-6: End view of completed a 461 Dean module chassis (Calcott, 2014). ..... 89
Figure 3-7: Constructing the wall system of the modules of the 461 Dean tower
(FC Modular, 2015). .................................................................................... 89
Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations ix
Figure 3-8: The roof assembly of the base module of the 461 Dean Tower. ............. 90
Figure 3-9: The floor assembly of the base module employed in the 461 Dean
tower ............................................................................................................ 91
Figure 3-10: Misalignment of modules as seen on the 10th floor of the 461
Dean Tower (Oder, 2015). ........................................................................... 93
Figure 3-11: SOHO Apartments of Darwin, Australia. ............................................. 94
Figure 3-12: SOHO Apartments structural arrangement (Irwinconsult, 2014). ........ 95
Figure 3-13: Structural scheme of the base module chassis employed in the
SOHO Apartments structure (Irwinconsult, 2014). ..................................... 95
Figure 3-14: Side view of a completed SOHO Apartments module.
(Skyscrapercity.com, 2014). ........................................................................ 96
Figure 3-15: Module arrangement in SOHO Apartments, Darwin (Irwinconsult,
2014). ........................................................................................................... 97
Figure 3-16: Lifting of the modules forming the SOHO Apartments tower.............. 98
Figure 3-17: Octavio's and Pascual's modular tower structure (Octavio &
Pascual, 2009). ........................................................................................... 100
Figure 3-18: Octavio’s and Pascual’s Steel Module Design (Octavio & Pascual,
2009). ......................................................................................................... 101
Figure 3-19: Profiles of structural sections used in Octavio’s and Pascual’s
module design (Octavio & Pascual, 2009). ............................................... 103
Figure 3-20: Octavio's and Pascual's composite sandwich façade (Octavio &
Pascual, 2009). ........................................................................................... 104
Figure 3-21: Arrangement of concealed fasteners in Octavio's and Pascual's
composite sandwich façade (Octavio & Pascual, 2009). .......................... 104
Figure 3-22: Wall profiles of Octavio’s and Pascual’s module design (Octavio
& Pascual, 2009). ....................................................................................... 104
Figure 3-23: Roof profiles of Octavio’s and Pascual’s module design (Octavio
& Pascual, 2009). ....................................................................................... 106
Figure 3-24: Floor profiles of Octavio’s and Pascual’s module design (Octavio
& Pascual, 2009). ....................................................................................... 107
Figure 3-25: Angle connections employed in Octavio's and Pascual's module
(Octavio & Pascual, 2009). ........................................................................ 108
Figure 3-26: Overview of the module structural scheme of the Verbus System
(Verbus Systems, 2009). ............................................................................ 111
Figure 3-27: Example internal wall construction of the Verbus System
(Heather, Harding, Harding, MacDonald, & Ogden, 2007). ..................... 111
Figure 3-28: Example floor construction of the Verbus System (Heather et al.,
2007). ......................................................................................................... 113
Figure 3-29: Exploded view of corner castings (Heather et al., 2007). ................... 114
Figure 3-30: Assembled corner castings (Heather et al., 2007). .............................. 114
x Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 3-31: Hoisting process of the Verbus System (Heather et al., 2007). ........... 115
Figure 3-32: Double skin steel panels with insulation (specimen LSP-400S)
(Hong et al., 2011). .................................................................................... 118
Figure 3-33: Double panel configuration of the double skin steel panel
(specimen LSP-400D) (Hong et al., 2011). ............................................... 118
Figure 3-34: Framed modular system MF1 (Hong et al., 2011). ............................. 119
Figure 3-35: Profile of the MCO beam (Hong et al., 2011). .................................... 119
Figure 3-36: VectorBloc Connection Systems (Vector Praxis, 2016). .................... 121
Figure 3-37: Vector Praxis’s standard VectorBloc Systems (Vector Praxis,
2015). ......................................................................................................... 122
Figure 3-38: Assembly of the VectorBloc Connection System (Bowron,
Gulliford, Churchill, Cerone, & Mallie, 2014). ......................................... 123
Figure 3-39: Assembled improved connector system (Heather, 2012). ................... 125
Figure 3-40: Exploded view of the improved connector system (Heather,
2012). ......................................................................................................... 126
Figure 3-41: A horizontal ledge incorporated in the fixing plate (Heather,
2012). ......................................................................................................... 127
Figure 3-42: A vertical plate incorporated in the fixing plate (Heather, 2012). ...... 127
Figure 3-43: Extension of the fixing plate between connector blocks (Heather,
2012). ......................................................................................................... 128
Figure 3-44: Further extension of the fixing plate between connector blocks
(Heather, 2012). ......................................................................................... 128
Figure 3-45: Lateral extrusion of the fixing plate (Heather, 2012). ......................... 128
Figure 4-1: The Grenfell Tower fire incident of June, 2017 (Dame Judith,
2018). ......................................................................................................... 131
Figure 4-2: LSF Wall System (Vardakoulias, 2015). ............................................... 132
Figure 4-3: Thermal Properties of Gypsum Plasterboard (Keerthan and
Mahendran, 2012a). ................................................................................... 137
Figure 4-4: Thermal Conductivity of Rockwool Insulation (Keerthan and
Mahendran, 2012a). ................................................................................... 138
Figure 4-5: Specific Heat of Steel in the Eurocode 3 Part 1.2 (CEN, 2005). ........... 138
Figure 4-6: Finite Element Modelling of LSF Wall Panel. ...................................... 140
Figure 4-7: Hot - Flange Time - Temperature Profiles of Conventional and
Innovative LSF Wall System Configurations at Different Critical
Temperatures. ............................................................................................. 141
Figure 4-8: Temperature Contours across Configuration 1 at Different Critical
Temperatures. ............................................................................................. 143
Figure 4-9: Temperature Contours across Configuration 2 at Different Critical
Temperatures. ............................................................................................. 143
Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations xi
Figure 4-10: Temperature Contours across Configuration 3 at Different Critical
Temperatures.............................................................................................. 144
Figure 4-11: Temperature Contours across Configuration 4 at Different Critical
Temperatures.............................................................................................. 145
Figure 4-12: Temperature Contours across Configuration 5 at Different Critical
Temperatures.............................................................................................. 145
Figure 5-1: Overview of the proposed modular system. .......................................... 153
Figure 5-2: Isometric view of the internal skeleton arrangement of the modular
system. ....................................................................................................... 154
Figure 5-3: Isometric view of the arrangement of module chassis members. ......... 156
Figure 5-4: Section view of the roof system. ........................................................... 157
Figure 5-5: Internal section view of the roof system from the outside the
module........................................................................................................ 157
Figure 5-6: Internal section view of the roof system from the inside of the
module........................................................................................................ 158
Figure 5-7: Side view of the roof system. ................................................................ 158
Figure 5-8: Section viewof the floor system. ........................................................... 159
Figure 5-9: Internal section view of the floor system from the outisde of the
module........................................................................................................ 160
Figure 5-10: Internal section view of the floor system from the inside of the
module........................................................................................................ 160
Figure 5-11: Side view of the floor system. ............................................................. 160
Figure 5-12: Isometric view of the conventional wall system frame. ...................... 162
Figure 5-13: Section view of the conventional wall system connected to the
module chasiss. .......................................................................................... 162
Figure 5-14: Overview of Wall System 2. ............................................................... 163
Figure 5-15: Detailed view of Wall System2. .......................................................... 163
Figure 5-16: Section view of Wall System 2. .......................................................... 164
Figure 5-17: Overview of Wall System 3. ............................................................... 165
Figure 5-18: Detailed view of Wall System 3. ......................................................... 165
Figure 5-19: Section view of Wall System 3. .......................................................... 165
Figure 5-20: Overview of Wall System 4. ............................................................... 166
Figure 5-21: Section view of Wall System 4. .......................................................... 166
Figure 5-22: Isometric view of the double skin steel panels within the frame of
a module. .................................................................................................... 167
Figure 5-23: Floor joists to floor edge beam interface. ............................................ 168
Figure 5-24: Roof joists to roof edge beam interface. ............................................. 168
Figure 5-25: Isometric view of the roof edge beam to corner post interface. .......... 169
xii Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 5-26: Isometric view of the floor edge beam to corner post interface. ......... 169
Figure 5-27 Isometric view of the wall system illustrating Connection C. .............. 170
Figure 5-28: Side view of the Floor System illustrating Connection D. .................. 170
Figure 5-29: Cross bracing multi-storey configuration (left – side view, middle
– front view, right – isometric view). ......................................................... 172
Figure 5-30: Double skin steel panel multi-storey configuration (left – side
view, middle – front view, right – isometric view). ................................... 173
Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations xiii
List of Tables
Table 1-1: Yield Stress and Tensile Strength of the LiteSteel beam (OneSteel
Steel and Tube, 2010). ................................................................................. 24
Table 2-1: Various levels of building prefabrication (Smith, 2011). ......................... 45
Table 2-2: Rules of thumb for maximum dimensions of modules based on
transportation restrictions............................................................................. 60
Table 2-3: Rules of thumb for building heights of MBSs based on structural
material. ....................................................................................................... 61
Table 3-1: Summary project details of 461 Dean, New York City. ........................... 86
Table 3-2: Structural components of the base module employed the 461 Dean
tower. ........................................................................................................... 88
Table 3-3: Structural components in the wall assembly of the base module
employed in the 461 Dean tower. ................................................................ 90
Table 3-4: Structural components in the roof assembly of the base module
employed in the 461 Dean tower. ................................................................ 90
Table 3-5: Structural components in the floor assembly of the base module of
the 461 Dean tower. ..................................................................................... 91
Table 3-6: Project details of SOHO Apartments, Darwin.......................................... 94
Table 3-7: Structural components of the module chassis employed in the
SOHO Apartments structure. ....................................................................... 96
Table 3-8: Structural components of the wall system employed in SOHO
Apartments structure. ................................................................................... 97
Table 3-9: Structural components of the roof system employed in the SOHO
Apartments structure. ................................................................................... 98
Table 3-10: Structural components of the floor system employed in the SOHO
Apartments structure. ................................................................................... 98
Table 3-11: Octavio’s and Pascual’s Affordable Steel Concept – Project Details .. 101
Table 3-12: Structural details of Octavio’s and Pascual’s module design. .............. 102
Table 3-13: Structural sections used in Octavio’s and Pascual’s module design. ... 103
Table 3-14: Details of the interior wall profile of Octavio’s and Pascual’s
module design ............................................................................................ 105
Table 3-15: Details of the exterior wall profile of Octavio’s and Pascual’s
module design. ........................................................................................... 105
Table 3-16: Details of the interior roof profile of Octavio’s and Pascual’s
module design. ........................................................................................... 106
Table 3-17: Details of the exterior roof profile of Octavio’s and Pascual’s
module design. ........................................................................................... 106
xiv Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table 3-18: Details of the interior floor profile of Octavio’s and Pascual’s
module design. ........................................................................................... 107
Table 3-19: Details of the exterior floor profile of Octavio’s and Pascual’s
module design. ........................................................................................... 107
Table 3-20: Patent details of the Verbus System. .................................................... 110
Table 3-21: Details of the wall system profile of Verbus Systems’ module
design. ........................................................................................................ 112
Table 3-22: Details of the roof system profile of Verbus Systems’ module
design. ........................................................................................................ 112
Table 3-23: Details of the floor system profile of Verbus Systems’ module
design. ........................................................................................................ 113
Table 3-24: Material properties of the steel in the double skin steel panel (Hong
et al., 2011). ................................................................................................ 118
Table 3-25: Double skin steel panel test specimen configurations (Hong et al.,
2011). ......................................................................................................... 118
Table 3-26: Section details of the MCO beam (Hong et al., 2011). ......................... 119
Table 3-27: Patent details of the VectorBloc Connection System. .......................... 122
Table 3-28: Patent details of the Connector System for Building Modules............. 125
Table 4-1: Details of the test specimen configurations. ........................................... 134
Table 4-2: Comparison of FEA Predicted Fire Resistance Ratings of
Conventional and Innovative LSF Wall Systems. ..................................... 140
Table 5-1: Details of the internal skeleton members of the module. ....................... 156
Table 5-2: Details of the roof system profile. .......................................................... 158
Table 5-3: Details of the floor system profile. ......................................................... 161
Table 5-4: Details of Wall System 1. ....................................................................... 162
Table 5-5: Details of Wall System 2. ....................................................................... 163
Table 5-6: Details of Wall System 3. ....................................................................... 164
Table 5-7: Details of Wall System 4. ....................................................................... 166
Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations xv
List of Abbreviations
CFS – Cold-Formed Steel
DERW – Dual Electric Resistance Welding
ERW – Electric Resistance Welding
HFB – Hollow Flange Beam
HFS – Hollow Flange Section
HRS – Hot Rolled Steel
HSPR – Henrob Self-Pierce Riveting
LSB – LiteSteel Beam
LSF – Light Gauge Steel Frame
MBS – Modular Building System
MCM -Modular Construction Method
OSATM - OneSteel Australia Tube Mills
PFC – Parallel Flange Channel
RHFCB – Rectangular Hollow Flange Channel Beam
SHS – Square Hollow Section
QUT – Queensland University of Technology
QUT Verified Signature
Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations xvii
Acknowledgements
With great pleasure, I would like to acknowledge and thank my supervisors Dr.
Poologanathan Keerthan and Prof. Mahen Mahendran for their continual support and
instrumental guidance throughout my entire tertiary studies journey. Their wisdom and
knowledge have guided me through the ravines of higher education. Their passion for
teaching has excited my desire for lifelong continual learning. I, and many other
people, are in credit to these two remarkable leaders. I owe my deepest thanks to them.
I would also like to express my sincerest gratitude and appreciation to my fellow post-
graduate peer and dear friend, Edward (Edi). His tireless support, guidance and insight
has tremendously helped me to develop my goals and achieve them.
To my fellow peers and the Queensland University of Technology, thank you for
providing an amazing environment for my studies to thrive and grow in.
Finally, I would like to express my eternal gratitude to my family and friends for their
continual support throughout my life’s journey. There are too many to name, and I
hold them all close to my heart. I would not be who I am today if it weren’t for them;
I owe them everything.
Thank you.
19 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Chapter 1: Introduction
Modular construction is a developing construction technology that shows the potential
to deliver built environment structures at standards that far exceed traditional
construction methods. Possible improvements over traditional methods include: faster
construction, increased costs savings, greater sustainable capacities and further
benefits as discussed in later sections. Although modular construction technologies
have been around for a while, the advancements and developments of the technology
is relatively new and is still in its early stages. This is evident in the fact that there
cease to exist a recognised unified modular construction building code/standard.
This technology is currently developing though there are still many shortcomings that
need to be addressed before this technology can reach its full potential. This thesis will
examine these shortcomings and present innovative ideas to address them. The
innovative ideas largely stem from introducing improved cold-formed steel sections
and system configurations. Thus, this thesis will also examine the background of cold-
formed steel and improved system configurations.
This chapter introduces the research problem by presenting a background (Section 1.1)
of the relative topics introduced and then establishing the context of the research
(Section 1.2) as well as establishing the aim (Section 1.3). Succeeding this, the
significance and scope of the research (Section 1.4) is discussed followed by the
outline of the thesis layout (Section 1.5).
1.1 BACKGROUND
1.1.1 Modular Building Systems
Modular Buildings Systems (MBS) are a form of sectional structures characterized by
their segment-like construction and their unique manufacturing methods. Modular
buildings are manufactured using the Modular Construction Method (MCM). Modular
construction can be described as the prefabrication and off-site assembly of complete
volumetric, three dimensional, building units or essentially, ‘modules’. The MCM has
demonstrated capabilities to deliver construction results superior to those obtained
through traditional construction methods. The promising benefits include costs, time
and waste savings.
20 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
The benefits of MCM are attributed to its systematic and controlled process. Modular
construction differs from traditional prefabrication methods through several aspects.
One aspect is the fact that MBS arrive to site significantly more built, fabricated and
completed as three-dimensional building modules instead of bare minimal, relatively
two-dimensional structural frames and panels. Another aspect is the unique
manufacturing method that has been developed to efficiently produce MBS. Figure
1-1 shows a modular building unit being hoisted into place. Figure 1-2 shows a 2-
dimensional structural frame being erected.
Figure 1-1: A three-dimensional steel-framed modular building system being hoisted into place
(TLG Modular Building Solutions, n.d.).
Figure 1-2: A two-dimensional structural steel frame being erected (Reardon, David, &
Downton, 2013).
The manufacturing method of the MBS is similar to that of vehicle assembly line
manufacturing processes. Combined with the streamlined design of the modules, the
result is a faster delivered, more economical product with less waste and closer
tolerances. The controlled environment existing in the large manufacturing factories
also prevents undesirable defects occurring from prevalent weather conditions. These
processes along with advancing technologies have seen the MCM being implemented
into the design and construction of multi-storey, high-rise buildings, as well as plans
for towering superstructures. Figure 1-3 shows the Nicholson Social Housing Project
21 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
of Melbourne, Australia; a modular structure comprising of 197 apartments and
constructed from 341 individual modules (Hickory Group, n.d.).
Figure 1-3: The Nicholson of Melbourne, Australia (Archi Channel, n.d.).
1.1.2 Structural Steel
Structural steel represents a major market in the construction and built environment
sector. Engineers, designers and professionals alike often employ steel as structural
load-bearing members due to its high strength and predictable structural behaviour, its
adaptable form and shaping capabilities, its wide availability and economic advantages
as well as its aesthetic appeal. There are two distinct methods of producing structural
steel, each providing various advantages over the other. The methods are known as the
Hot-Rolled Method and Cold-Formed Method, and their resulting products are known
as Hot-Rolled Steel Sections (HRS Sections) and Cold-Formed Steel Sections (CFS
sections) respectively.
The hot-rolled method is the process of producing steel sections while at above the
steel’s recrystallization levels (room temperature), whereas the cold-formed method is
the process of producing steel sections while at below the steel’s recrystallization
levels. Dependent on method used, the end properties of the formed steel product can
greatly vary, offering advantages and disadvantages over one another in a given use.
HRS Sections are typical of higher strength capacities though are heavier in weight;
whereas CFS sections are relatively light weight but offer lower strength capacities.
Despite this, it is the far superior strength-to-weight ratio that distinguishes CFS
sections from their hot-rolled counterparts.
1.1.3 Cold-Formed Steel
In contrast to its heavier hot-rolled counterparts, CFS sections are recognized as a more
economical option. The light-weight of CFS sections allow it to be easily produced,
22 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
transported and installed. The relatively high-strength of the sections also provide
designers with an array of applications as structural load-bearing members. This
desirable combination of light-weight and high-strength could not have been achieved,
would it not have been for the unique manufacturing process of the steel sections.
CFS sections follow a relatively straightforward manufacturing process. At first steel
sheets are cut into predetermined widths and strips. The steel sheets are then passed
through a series of mechanical form rollers and press braking machines. These
machines apply strenuous forces to bend, shape and form desired profiles and sections
in a room temperature environment. The now formed sections are coated and painted
to specifications before being cut at required lengths. Lastly, the sections are bundled
and stored, ready for distribution.
CFS sections can be classified into two categories:
• Sheets and panels; and
• Structural members.
For an extended period, CFS structural members were only available in a small number
of standard designs, shapes and sections. This was partly due to the limiting mass-
manufacturing capabilities available. These standard structural member sections are
often simple and symmetrical designs; taking the form of a square, rectangle, circle or
C, L or Z like shape. Figure 1-4 shows several standard CFS structural sections.
Figure 1-4: Standard cold-formed steel sections and shapes.
In Australia there are three major companies who produce and supply CFS sections,
they are: Lysaght, OneSteel and Stramit. The applicable design standards for CFS
structures in the Australian and New Zealand industries are prescribed in the document
titled: “AS/NZS 4600:2018.” The document provides three established methods for
23 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
determining the structural capacities of CFS sections. These methods are: the Effective
Width Method, the Direct Strength Method and Formal Laboratory Testing.
The thin and slender geometrical profile of CFS sections is what keeps these sections
light-weight. Although, by being lean and slim these profiles are inherent of instable
structural behaviours. Thus, often it is the failure by buckling which governs the design
capacities of CFS sections.
Hollow Flange Sections
As manufacturing technologies advanced, researchers began exploring the possibility
of creating new and innovative shapes and sections with specific intentions to address
the flawed slender nature of CFS sections. Lately, a spur of innovative CFS sections
have appeared in the engineering design and research field including a series of Hollow
Flange Sections (HFS). These sections have the potential to exceed the current
capabilities of the standard CFS sections, thereby furthering the reaches of engineering
design.
HFS differ from traditional CFS sections through the inclusion of torsionally rigid
hollow flanges. The flanges are closed and sealed to the webs, establishing increased
rigidity at the extended regions of the section. Sealing the gaps between flange and
web required development of a new welding technology known as Electric Resistance
Welding (ERW). In addition, modifications to standard CFS sections producing mills
were made to accommodate the larger depth to width ratios of the HFS (Dempsey,
1990).
The first HFS to be produced were known as Hollow Flange Beams (HFB) and were
developed by Palmer Tube Mills Limited in the late 1980s (Dempsey, 1990). The HFB
consisted of a centred web met by closed triangular flanges at both ends as seen in
Figure 1-5.
Figure 1-5: Hollow Flange Beam Profile and Dimensions (Dempsey, 1990).
24 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
In comparison to standard CFS sections, the HFB was significantly stronger. However,
the awkward positioning of the flanges and their small enclosed spaces made it
difficult for member connections to be implemented and thus deemed the section
impractical. In addition, high manufacturing costs associated with the capital costs of
the new equipment, technology and the factory modifications needed to accommodate
the production of the new section, saw the discontinuance of the product in the late
1990s. As a response, several other HFS were later developed.
The LiteSteel Beam
The LiteSteel Beam (LSB) was developed to replace the HFB and was produced by
OneSteel Australian Tube Mills (OSATM) in the early 2000s (Siahaan, 2013).
OSATM developed the LSB with the intention to simplify the manufacturing
processes of the HFB and improve structural capacity. The LSB is made from
OSATM’s DuoSteel grade product. DuoSteel is a base steel with a minimum yield
stress of 𝑓𝑦 = 380𝑀𝑃𝑎 and a tensile strength of 𝑓𝑢 = 490𝑀𝑃𝑎. Cold-forming the base
steel into the LSB enhances the strength of the steel to give the following formed
properties.
Table 1-1: Yield Stress and Tensile Strength of the LiteSteel beam (OneSteel Steel and Tube,
2010).
Location Minimum Yield Stress,
𝑓𝑦 (MPa) Minimum Tensile Strength,
𝑓𝑢 (MPa)
Web 380 490
Flanges 480 500
Connection issues were prevalent in HFB due to its inclined flanges. The LSB
addresses this problem by adopting a flat web with straight flanges, allowing simple
connection in construction. Figure 1-6 shows the LSB and its profile.
Figure 1-6: Profile of the LiteSteel Beam (Steau, 2014).
25 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
The manufacturing process of LSB is similar to those of standard hollow sections, with
variation allowed for the unique geometric profile of the LSB. At first a coiled single
strip of steel is fed through a steel cutting machine; trimming and partitioning the large
sheet into specified strip widths. The steel strip is then passed through a series of
forming rolls; folding the strip into the form of a hollow flange section. The flanges
are welded to the web using a unique Dual Electric Resistance Welding (DERW)
process. To complete the production, scarfing and coating are applied followed by
sufficient cooling and drying. Figure 1-7 shows the manufacturing process of the
LiteSteel beam.
Figure 1-7: The manufacturing process of the LiteSteel beam (LiteSteel Technologies America
LLC, 2006).
Production of the LSB ceased in late 2012, when the section was recognised as
financially impractical. Siahaan (2013), associates the financial adversities of the LSB
to the higher manufacturing costs associated with the dual electric resistance welding
process, the high-priced Australian dollar and the declining Australian manufacturing
sector.
The LSB provided many applications in the Australian construction market,
particularly in residential, commercial and industrial buildings. The light weight and
strong performance of the LSB saw many applications as structural load-bearing
members. The LSB offered many advantages over other structural load-bearing
members in the application of basement beams, garage beams, ridge beams, long span
26 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
headers, floor and deck supports and mezzanine flooring (LiteSteel Technologies
America LLC, 2010). Figure 1-8 shows several example applications of the LSB.
Figure 1-8: Applications of LiteSteel Beams (LiteSteel Technologies America LLC, 2010) and
(Building Design & Construction, n.d.).
The Rivet-Fastened Rectangular Hollow Flange Channel Beam
The Rivet-Fastened Rectangular Hollow Flange Channel Beam (Rivet-Fastened
RHFCB) is the brainchild of the collaborative efforts of the researchers from the
Queensland University of Technology’s (QUT) research group; Wind and Fire
Engineering Lab. The innovation is made possible by the exclusive self-pierce riveting
technology patented by Henrob Self-Pierce Riveting (HSPR). At the time of this
proposal, the Rivet-Fastened RHFCB has yet to be patented and is only manufactured
in laboratories at the QUT and HSPR. Figure 1-9 and Figure 1-10 show the form and
profile of the Rivet-Fastened RHFCB.
Figure 1-9: Rendered images of the Rivet-Fastened RHFCB.
27 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 1-10: Profile of the Rivet-Fastened Rectangular Hollow Flange Channel Beam (Steau,
2014).
The Rivet-Fastened RHFCB was developed as an alternative to the LSB and unlike
the LSB, the Rivet-Fastened RHFCB is not formed from a single, continuous length
of uniformly thick steel sheeting. Instead, the Rivet-Fastened RHFCB comprises of
three individual and separate elements; the web and two hollow flanges. This design
feature allows the user to manipulate the combination of plate thicknesses used,
permitting optimization of behaviour and strength. For any given case, by increasing
the thickness of the web, a substantial increase in lateral distortional capacity is
achieved. In addition, the Rivet-Fastened RHFCB also has additional overlapping lip
area. This extra increase in cross-sectional area potentially provides additional strength
gains.
Several advantages are offered over the LSB using the Rivet-Fastened RHFCB. The
manufacturing process is simpler; resulting in lowered manufacturing costs. The
manufacturing process is also more flexible; allowing the ability to manipulate certain
elements of the design. In addition, the section provides sufficient room and straight
edges to allow for an array of possible connections and fixings.
Currently, ongoing work and studies are being performed to investigate the structural
behaviour of the Rivet-Fastened RHFCB under load-bearing conditions. Studies on
Rivet-Fastened RHFCB include the investigation of section moment capacity
(Siahaan, Poologanathan, & Mahendran, 2014) and web crippling capacity (Steau,
Poologanathan, & Mahendran, 2015). From what has been gathered, the section shows
promising results with expectations that it will significantly outperform traditional
CFS sections.
With the flexible design nature of modern CFS products and their inherent structural
properties, CFS products have recently gained significant popularity in the
28 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
construction industry. Engineers have begun trialling and applying the products to new
and different applications; of mention is the application of these steel sections in the
modular building industry.
1.2 CONTEXT
Although the MCM has existed for more than a century, it is still regarded as being in
its early stages of development with regards to the understanding, refinement and
progress of this construction technology. A testament to this, is the lack of a statutory
construction standard and guide to address the structural design of MBSs. The
possibilities and potential for modular construction are immense. This potential cannot
be fully realised until the shortcomings of this technology are addressed. Shortcomings
include:
• Limitations to capable efficiencies due to overbearingly heavy weight
systems of relatively low strength-to-weight ratios;
• Restrictions to achievable building heights due to insufficient lateral
strength capacities; and,
• Constraints to serviceability capacities (such as fire performance) inherent
in steel dominated systems.
This study seeks to address the shortcomings of MBSs by introducing recent
developments and advancements to incorporate in to MBSs. These advancements are
thoroughly discussed in later chapters and are summarised as follows:
• Introduction of light-weight, high-strength, innovative CFS sections;
• Inclusion of advanced, and fire rated wall systems; and,
• Incorporation of simple yet effective design arrangements.
1.3 AIM
The aim of this research is to develop an improved modular building system by
incorporating several design innovations such as:
• The Rivet-Fastened RHFCB;
• Stiffened Channel Sections
• Improved fire-rating wall systems;
29 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
• Simplified structural designs and arrangements.
This research will examine all these aspects and design innovations through a thorough
literature review. Case studies are conducted to summarise the current advances in
modular construction. Thermal finite element modelling is performed to showcase the
improved fire rating performance of several wall system configurations. The product
of this research will demonstrate the practicality of these design innovations in the
modular construction field. This thesis seeks to summarise the past, present and future
of MBSs.
1.4 SIGNIFICANCE, SCOPE AND DEFINITIONS
As examined earlier, CFS products have significant strength-to-weight ratios making
them desirable for several applications. One of such, is the application of these light-
weight sections in MBSs. In addition, the recent development of the Rivet-Fastened
RHFCB has shown promising results and improvements over traditional CFS as well
as older HFS such as:
• Expectations of greater stability and strength due to inclusion of torsionally
rigid flanges;
• Lowered manufacturing costs due to the simpler self-pierce riveting
technology patented by HSPR;
• Greater design flexibility due to the non-fixed preassembly of components;
and
• Capabilities of incorporating numerous connections due to the straight
flanges and sufficient room being provided in the web.
CFS sections have gained significant popularity in the past few years and are
continuing to do so. The market for CFS sections is large and potential exists to further
enlarge this and expand the uses of CFS sections in other markets. One of these
markets is the MBS market.
The MBS market has also seen recent and significant popularity gains, especially in
the high-rise building sector. Therefore, it is of interest that the applications of CFS
sections in MBS are explored, specifically the investigation of Rivet-Fastened
RHFCBs as load-bearing members in MBS.
30 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
This research study proposes the investigation of the application of Rivet-Fastened
Rectangular Hollow Flange Channel Beams in Modular Building Systems. It is
predicted that new MBSs with increased fire and lateral load resistance can be
developed using Rivet-Fastened RHFCB in comparison to other CFS sections. The
research seeks to further the understanding of structural and fire performances of steel
MBSs. In addition, the research will explore what structural design aspects need to be
considered to deliver a successful modular construction project.
1.5 THESIS OUTLINE
The outline and structure of this thesis follows:
Chapter 1 – Introduction: Introduce the concepts and topics of this thesis as
well as present the research problem;
Chapter 2 - Literature Review: Conduct a thorough literature review on CFS
sections including the recently developed Rivet-Fastened rectangular hollow
flange channel beam in addition to summarizing, past and present advances in
the field of MBSs;
Chapter 3 - Case Studies on Modular Building System: Investigate and
analyse existing MBSs including complete systems and individual components
(ceilings, floors, walls and connections) to establish winnings and
shortcomings;
Chapter 4 - Thermal Modelling of Innovative Modular LSF Wall System:
Investigate the fire performance of innovative modular light-gauge steel frame
wall systems using finite element modelling to recommend for incorporation
into MBSs;
Chapter 5 - Conceptual Modular Building Design: Develop and present an
improved modular building system made of Rivet-Fastened RHFCBs and
stiffened channel sections with considerably increased fire and lateral load
resistance at minimum cost using design innovations, the detailed case studies
review and thermal finite element model of the light-gauge steel frame wall.
Chapter 6 – Conclusion: Summarise the results of this thesis and make
recommendations for future works.
31 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Chapter 2: Literature Review
2.1 INTRODUCTION
The Rivet-Fastened RHFCB is a CFS section that was introduced as a replacement for
the now production-ceased LiteSteel Beam. The Rivet-Fastened RHFCB provides vast
improvements over the LiteSteel Beam which includes aspects such as cheaper
manufacturing costs, greater structural capacity and more flexible design options.
Without question, an array of superior applications can be developed using the Rivet-
Fastened RHFCB. A particular industry which can greatly benefit from application of
the Rivet-Fastened RHFCB is the Modular Building industry. The modular building
industry distinguishes itself from other traditional construction methods by the fast
tracked, efficient and resource saving benefits it offers. The Rivet-Fastened RHFCB
can contribute to improving more over these benefits and through design of a MBS
using the Rivet-Fastened RHFCB, this thesis seeks to examine the improvements that
can be attained.
In preparation of the design, a thorough literature review of these concepts has been
undertaken and is presented in this chapter. The two main topics explored in this
section are:
• Cold-Formed Steel; and,
• Modular Building Systems.
Concluding this chapter is a summary of the findings and implications of the current
advancements in these three fields.
2.2 COLD-FORMED STEEL
2.2.1 General
CFS members represent a significant market in the steel industry. The term is used to
refer to steel products manufactured at below their recrystallization levels (room
temperature). CFS products begin their journey as thin steel sheets formed from iron
materials. The steel sheets are passed through a combination of mechanical roll
formers and press braking machines that apply strenuous forces to the steel sheets to
bend and form the desired shapes of the CFS products. It is this unique manufacturing
32 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
process that gives CFS its favourable properties such as its high strength to weight
ratio and its ease of manufacturing.
In comparison to its heavier hot-rolled steel counterparts, CFS is recognized as the
more economical option. This largely due to its superior strength-to-weight ratio which
allows more products/assemblies to be produce for a given quantity of raw material in
contrast to hot-rolled sections. In addition, manufacturing processes are more efficient
with the simpler production processes involved and lower energy consumption of not
needing to operate at high/melting point temperatures. These distinct manufacturing
techniques and technology of CFS sections allow for shapes and designs that differ
significantly from standard hot-rolled sections.
CFS products seen in the construction industry often serve as structural bearing
members in buildings, dwellings and structures alike. CFS members can be employed
as wall studs, struts, chord members, open web steel joists, space-frames, arches and
storage racks (Yu & LaBoube, 2010) and even as roofing and cladding components.
CFS products are also used as the steel decking component of composite floor systems.
Figure 2-1 below, depicts a residential structure composed of several different types
of CFS sections. Figure 2-2 below, depicts the CFS decking present in composite floor
systems.
Figure 2-1: The structural frame of this residential structure consists of cold-formed steel
members (All Steel House Frames, n.d.).
Figure 2-2: Cold-formed steel decking overlayed by reinforced concrete in a composite floor
system (Luke Allen, 2014).
33 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
2.2.2 History of Cold-Formed Steel
CFS has commonly been mislabelled as being a recent development. This can be
attributed to the fact that CFS has gained most of its popularity over the last few
decades. Though the fact is, CFS first appeared over a century ago. The first emergence
of CFS for construction use is documented to be during the 1850’s. Pioneers in both
Europe and the United States of America began trialling the material in the
construction of residential homes.
Of notable mention is Peter Naylor. Naylor was a New York State based metal roofer
that advertised the sale of “Portable Iron Houses for California”. The text of the
advertisement can be seen in Figure 2-3. The advertisement states “a house 20 x 15
can be put up in less than a day” due to the ease of construction made possible by the
interlocking grooves. Allen (2006) concluded that the iron material used in Naylor’s
offer was indeed CFS. Naylor’s offer coincided with the housing demands that
occurred during the peak 1849 California Gold Rush. As a result of the demand, it is
estimated that Naylor sold between 500-600 units according to Adam Thomas (2003).
Figure 2-3: Peter Naylor's advertisement titled "Portable Iron Houses for California"
(Browning, 1995).
Contrary to Naylor’s success, popularity of CFS products remained dormant in the
early 20th century. This can be attributed to several facts such as:
• The shortage of research on the material properties and structural behaviour
of CFS;
• The lack of design codes and standards available; and
• The absence of technology to produce economical CFS products.
This issue was soon realised and in 1938 the American Iron and Steel Institute (AISI)
appointed a committee to develop the first set of design standards for the application
34 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
of CFS (American Iron and Steel Institute, 2010). Led by Professor George Winter,
research work was conducted at Cornell university and the first Specification for the
Design of Light Gage Steel Structural Members was published in 1946, followed by
the first Design Manual in 1949 (American Iron and Steel Institute, 2010). With further
refinement and reiterations of the design guidelines along with improved
manufacturing techniques, widespread acceptance of CFS as a suitable construction
material began growing with trend continuing into the 21st century.
2.2.3 Manufacturing Method of Cold-Formed Steel Members
There are two general manufacturing methods used to produce CFS sections, both
relatively simple though with the ability to complicatedly alter the behaviour of the
steel. These methods are known as cold roll-forming and press braking.
Cold-Roll Forming
Cold roll-forming is accomplished by feeding a steel strip through a series of
consecutive, opposing rollers which continuously bend and plastically deform the strip
in incremental steps until the desired shape is attained. This process is shown in Figure
2-4. Dependent on the complexity of the section, a section can be formed with very
few roller stations or the opposite. The process can become quite complex and thus
computer software is used to assist in the design the system of rollers. The cold roll-
forming process is advantageous in its ability to quickly mass produce formed steel
sections. Although, one severe drawback of the process is the time taken to adjust and
change rolls when a different size section is required to be produced.
Figure 2-4: The cold roll-forming process (Chicago Roll Company, n.d.).
35 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Press Braking
Press braking employs press brake machines to mimic a punch and die action, with the
punch action being the moving component and the die in the form of a fixed bed.
Figure 2-5 shows the working action of a press braking apparatus. The process begins
with the placement of a steel sheet between the punch and die. The punch is driven
down, and its resilient force bends the steel sheet to the fixed angle. This process is
repeated until the desired shape is acquired.
With the inherent stop and go nature of this process, press braking is usually employed
in situations where low volume of production is required and/or cannot be warranted
by the costs of cold roll-forming. The only major drawback of press braking is the
difficulty to produce sections exceeding 5 metres in length given the physical
constraints of the press braking machines.
Figure 2-5: The press braking method (ThomasNet.com, 2012).
2.2.4 Effects of Cold Forming
The abrupt and significant strength gains made by the steel, is specifically attributed
to the action of applying strenuous forces such as bending, rolling or punching to the
steel specimen while at room temperature. By executing the process as such, large
numbers of localised defects, cracks and fractures are created in the crystal structure
of the steel material as a result. Fundamentally, the grain sizes of the steel’s crystal
structure are reduced, and the number of grains is significantly increased, creating a
very dense, closely packed, localised environment. This change in micro-structure
prevents further slip and impedes traverse dislocations of grain boundaries thereby
effectively increasing the hardness and yield strength of the steel. This process is
known as Hall-Petch Strengthening or Grain Boundary Strengthening.
36 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
2.3 STRUCTURAL DESIGN OF COLD-FORMED STEEL STRUCTURES
2.3.1 General
CFS members are significantly thinner and lighter-weight in comparison to its hot-
rolled counterparts. Given this slender geometric profile of CFS members, a set of
different buckling modes and failures are encountered. Local buckling becomes a large
concern in with buckling stress levels at a point below the yield point. In addition, the
traditional cold-forming process often produces small geometric imperfections which
are exaggerated due to the relative thin sections that cold-formed members utilise. This
issue is not as commonly found in the traditional hot-rolled or welded members that
have larger, thicker sections. On the contrary, the local buckling of CFS also has the
potential to draw upon post-buckling reserve, providing additional strength.
Incorporating all these complex factors into simple design methods can prove quite
difficult.
2.3.2 Structural Behaviour of Cold-Formed Steel Sections
Local Buckling
Most structural steel sections can be regarded as an assembly and combination of
several individual plate elements connected to form the desired cross-sectional shape.
For example, the standard C-section, as shown in Figure 2-6, is composed of two
flange plate elements that sandwich together a single web plate element. The
compressive strength of these structural steel sections is dependent on the slenderness
ratio (width/thickness) of the individual plate elements.
Figure 2-6: The standard I-section is composed of two flange elements and a single web element.
When subjected to compressive stresses, the plate elements may buckle first before
overall buckling of the member or yielding has occurred. This event is denoted as local
37 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
buckling and the buckled plate element will display a ‘chequer board’ wave like
pattern as shown in Figure 2-7.
Figure 2-7: The ‘chequer board’ wave like pattern of local buckling deformation (Quimby,
2014).
From the onset of local buckling, the section will experience a reduction in stiffness
and hence, reduction in overall carrying capacity. Full yielding capacity will not be
achieved, and the efficiency of the section is reduced. Thus, it is desirable that local
buckling is avoided.
Hot-rolled steel sections generally consist of thick elements that provide a rigid
presence and thus carry a high local buckling capacity. CFS sections on the other hand,
are thin and slender in profile with local buckling having a greater influence on the
sections. Higher local buckling capacity can be achieved by:
• Reducing the slenderness of the plate element; in doing so, the moment of
inertia of the cross-section is increased; and/or,
• Introducing support to the longitudinal edge/s of the individual plate
elements; in doing so, the plate element will be restrained from out-of-plane
buckling. Essentially, an intersecting plate at a plate edge (the support) will
increase the relative moment of inertia of that plate element with deflection
restricted at that edge. Plate elements supported on one edge are termed as
unstiffened, whereas plate elements supported on both edges are termed as
stiffened.
Shear Buckling
Shear buckling is regarded as a form of local buckling. Keerthan (2010) regards the
occurrence of pure shear failure to be of greater chance when the member is shorter in
span. Hence, CFS sections are highly susceptible to shear buckling failure given their
slender webs and short spans. Figure 2-8 shows the stress distribution of a lipped
channel section undergoing shear buckling. As seen, the principal shear stress is
38 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
distributed in a diagonal direction. This compressive stress causes a destabilising effect
in the immediate surrounding area, resulting in buckling of the section.
Figure 2-8: Shear buckling of a lipped channel section (Hancock & Pham, 2013).
Distortional Buckling
Distortional buckling denotes the deformation of a section whereby rotation is
exhibited by the flange at the flange-web juncture, as depicted in Figure 2-9. The
distortional buckling capacity is relative to the rotational restraint at the flange-web
juncture. The onset of distortional buckling occurs when the elastic stiffness is
exceeded by geometric stiffness and flange-web juncture. Distortional buckling has
been observed to occur in both compression and flexural members although, flexural
members are more prone to distortional buckling with Schafer and Yu (2005)
attributing this to the presence of local web buckling in standard sections without web
stiffeners.
Figure 2-9: Distortional buckling of a channel section (Keerthan, 2010).
Lateral Distortional Buckling
Lateral distortional buckling denotes the deformation of a section where the web bends
transversely and the flanges exhibit zero or minimal rotation, as seen in Figure 2-10.
Figure 2-10: Lateral distortional buckling of a channel section (Keerthan, 2010).
39 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Lateral Torsional Buckling
Torsion is described as a twisting-like action that is attributed to applying a force at a
point located a distance away from the centroid of the element of question. Many CFS
sections are mono-symmetric and thus, their shear centres do not share the same
location as the centroid. Consequently, these sections are inherent to torsional effects,
as the eccentricity of the applied force at the shear centre causes the section to twist
and therefore, lead to deformation by lateral torsional buckling as depicted in Figure
2-11. In addition, the thin profiles of CFS sections are inherent of low torsional
stiffness and adopting an open cross-section design further lowers this value. The
lateral torsional buckling capacity of a beam can be increased by adding rotational
restrains at intervals or continuously along the span of the beam.
Figure 2-11: Lateral torsional buckling of a channel section (Keerthan, 2010).
2.3.3 Design Criteria
The first known research into the structural behaviour of CFS was undertaken by
Professor G. Winter in 1939 at Cornell University. Throughout the 1940’s – 1960’s
the first design clauses were established for the correct applied use of CFS in the
industry by the American Iron and Steel Institute (AISI).
From 1979 through to 1987, Rhodes and Walker presented notable discussions and
developments on the design concepts of applying thin-walled structures to building
systems. From Rhodes’s and Walker’s overview, an array of design practices and aids
have been released.
Currently, under Australian Law, engineers, designers and professionals utilize
AS/NZS 4600 for the provisions and standards of CFS structures. AS/NZS 4600 was
first published in 1974 as AS 1538. AS 1538 heavily relied on the specifications given
in the 1968 AISI edition. AS 1538 continued to be updated throughout the years,
relying on AISI specifications. Currently, AS/NZS 4600:2018 is the latest
specification that defines the legal requirements for the design and use of CFS
structures in Australia and New Zealand. AS/NZS 4600:2018 is only applicable to
40 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
cold-formed structural members of carbon or steel material. The structural members
must be no more than 25mm thick and used only for load-carrying purposes in
buildings. AS/NZS 4600:2018 is also applicable to structures other than buildings
provided that dynamic effects are accounted for.
2.4 THE RIVET-FASTENED RECTANGULAR HOLLOW FLANGE
CHANNEL BEAM
2.4.1 General
The Rivet-Fastened RHFCB is a newly developed CFS section, proposed as an
alternative to the advanced but discontinued LSB section. The LSB was a CFS section
that was considerably stronger and more efficient than conventional CFS sections.
These qualities were recognized by those in the building and construction market with
the LSB section being thoroughly used in many applications and holding a large share
in the market. However, due to the significant manufacturing costs associated with its
welding process and along with several other factors, the section was deemed
economically unviable and discontinued. In a response to the event, the Rivet-Fastened
RHFCB was developed to address the shortcomings of the LSB.
Unlike the LSB, the Rivet-Fastened RHFCB is composed of three separate steel
elements as opposed to the single steel sheet used to form the LSB. To join the three
elements, the Rivet-Fastened RHFCB employs a rivet-fastening process. Due to this
method of assembling the section, the thicknesses of the web and flange are not fixed
to a uniform value. The thicknesses can vary between the elements; allowing for
numerous web and flange thickness combinations to meet the designer’s needs.
A determinant in the local buckling capacity of a steel section is the longitudinal
support conditions of its plate elements. Plate elements supported on only one of its
longitudinal edges (unstiffened elements) are more prone to local buckling. Plate
elements with two supported longitudinal edges (stiffened elements) are more rigid
and hence possess higher capacity to resist local buckling. Most CFS sections compose
of stiffened web elements and a pair of unstiffened flange elements. The innovative
design of the Rivet-Fastened RHFCB has addressed this shortcoming of the flanges by
providing a stiffened flange design, whereby all plate elements in the flange are now
supported along both of their respective longitudinal edges as seen in Figure 2-12. In
41 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
addition, the hollow flanges have been strategically placed away from the neutral axis,
improving the section’s efficiency as a beam member.
Figure 2-12: The improved flange design of the Rivet-Fastened RHFCB.
Being a new and recent development, the Rivet-Fastened RHFCB has had limited
studies performed on its behaviour and capacity as a structural steel member. In
addition, the section is not ready for implementation into the market due to the lack,
more so, non-existent and absence of design provisions for the section. The current
CFS design provisions are unsuitable and not directly applicable to the Rivet-Fastened
RHFCB. This is attributed to the section’s unique profile and geometry. There are
currently, ongoing studies taking place at the Queensland University of Technology
(QUT) that are investigating this section’s structural behaviour. The following
examines the structural behaviour studies of the Rivet-Fastened RHFCB that are
currently taking place at the QUT.
2.4.2 Flexural Behaviour
Siahaan et al. (2014) recently investigated the appropriateness of current design codes
for use on the Rivet-Fastened RHFCB when determining bending strength. The
investigation was completed by comparing the experimental results of a Four Point
Bending Test to those obtained by applying the Australian design code AS/NZS 4600
Cold-Formed Steel Structures.
AS/NZS 4600 prescribes three methods to predict the flexural behaviour of CFS
sections. They are: the Effective Width Method (EWM), the Direct Strength Method
(DSM) and experimental laboratory testing. Upon application of the EWM, two
conditions of CL. 3.3.2.3 were not met by the Rivet-Fastened RHFCB. Applying the
EWM yields results that are reasonably accurate for rivet spacing arrangements up to
100mm. Exceeding this value, yields results unacceptable in accuracy. The DSM was
42 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
found to accurately predict the flexural capacity of the Rivet-Fastened RHFCB, as the
method can account for the effects of the rivet spacing. From the experimental test
results, Siahaan et al. (2014) observed that for sections of the same profile, when rivet
spacing increased, a corresponding increase was seen in the reduction of the section’s
moment capacity. In conclusion, for AS/NZS 4600 to be appropriately applied on the
Rivet-Fastened RHFCB when determining bending strength, provisions must be
incorporated to account for the effects of rivet spacing on the beam.
2.4.3 Shear Behaviour
Investigation of the shear capacity and shear behaviour of the Rivet-Fastened RHFCB
has been carried out with experimental studies to develop appropriate shear design
guidelines for the section conducted by Poologanathan and Mahendran (2014). Two
variations of the Rivet-Fastened RHFCB were investigated. The first being the
RHFCB1; a three-element Rivet-Fastened RHFCB as depicted in Figure 2-13(a), and
the second being the RHFCB2; a single element Rivet-Fastened RHFCB as depicted
in Figure 2-13(b). Both Rivet-Fastened RHFCBs investigated in this study, adopted
rivet spacing of 100mm.
Figure 2-13: RHFCB1 and RHFCB2 (Poologanathan & Mahendran, 2015).
Poologanathan and Mahendran (2014) conducted a series of 19 experimental shear
tests on the RHFCB1 and compared the results to those obtained from applying the
current relative design code AS/NZS 4600. The experimental tests were limited to the
RHFCB1, as the section was relatively easier to produce than the RHFCB2.
43 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Comparison of the experimental results and the results obtained through application of
AS/NZS 4600 found that the prescribed code was very conservative in predicting the
shear capacity of the beams. Poologanathan and Mahendran (2014) determined this
inaccuracy to be attributed to the code’s lack of provisions to account for the
significant post buckling reserves of the RHFCB1 and the effects of increased fixity at
the web-flange juncture
From the experimental tests conducted, Poologanathan and Mahendran (2014)
developed a set of shear design equations based on the Direct Strength Method’s
nominal shear capacity (𝑉𝑣). The equations are appropriately applicable to Rivet-
Fastened RHFCB with 100mm rivet spacing with current efforts currently being made
to thoroughly investigate the effects of other rivet spacing configurations.
2.4.4 Web Crippling Behaviour
A total of 52 experimental tests were recently conducted at the QUT by Steau et al.
(2015) to investigate the web crippling behaviour of the Rivet-Fastened RHFCB. Their
findings indicated that the web crippling behaviour of the Rivet-Fastened RHFCB is
slightly more complex than the traditional channel beam. This is partly due to the
advanced flange design of the Rivet-Fastened RHFCB, and the section’s design option
of allowing the designer to choose varying thicknesses and steel grades for the web
and flanges. The resultants of such factors are additional failure modes not normally
encountered in the common channel beam.
The types of failure mechanisms exhibited by the Rivet-Fastened RHFCB were either:
• Web Crippling Failure (36 tests) – the strength capacity of the web is lower
than the flanges and hence, the web reached failure first (Figure 2-14a);
• Flange Crushing Failure (4 tests) – the strength capacity of the flange is
lower than the web and hence, the flanges reach failure first (Figure 2-14b);
• Combined Web Crippling and Flange Crushing (11 tests) – the strength
capacity of the web and flanges are similar and hence both fail (Figure
2-14c); or
• Lip Failure (1 test) – absence of a rivet fastener at the absolute ends of the
member, leaves the lip more susceptible to deformation under applied loads
fail (Figure 2-14d).
44 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 2-14: Varying failure modes encountered by Steau et al. (2015). *Modified from Steau et
al. (2015).
Steau et al. (2015) compared the results of the experimental tests to those obtained
through application of the relative current design codes, AS/NZS 4600 and AISI S100.
They concluded that application of the codes on the Rivet-Fastened RHFCB resulted
in inaccurate results of varying degrees. The coefficient of variation (CV) between test
results and design code results was 0.175 and 0.315 for ETF and ITF load cases,
respectively. Steau et al. (2015) proposed two equations to address the unsuitability of
applying current design codes to the Rivet-Fastened RHFCB. The equations are only
applicable to Rivet-Fastened RHFCB with 100mm rivet spacing.
2.5 MODULAR BUILDING SYSTEMS
2.5.1 General
Several benefits are offered when using modular construction methods instead of
traditional methods to erect a building. Most of these benefits are due to manufacturing
or on-site construction improvements. The high-quality control environment of the
factories allows quick, efficient and systematic manufacturing of building components
(modules), while minimizing health and safety concerns. On site, construction and
installation are made easier with components specifically designed to be interlocking
45 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
and with less components to be installed, installation times are significantly reduced.
Furthermore, the unique process of modular construction projects allows simultaneous
construction phases to occur, reducing overall project delivery time. As explored in
this section, a thorough review of MBSs is presented along with an analysis of previous
studies performed on MBSs. This review will provide insight on how these benefits
are made possible in modular construction.
2.5.2 History of Modular Building System
The history of the modular building system follows the history of building
prefabrication, which is not straightforward and distinctly defined. This is partly due
to the unclear etymology and lack of a universally-agreed upon application of the
definition of the word “prefabrication”. Generally, a structure is considered
prefabricated when its components have been manufactured off-site and assembled on
site to form the structure. Though, through application of the definition, to what degree
of prefabrication must a structure be, to be considered prefabricated? Figure 2-15 best
illustrates this matter with Table 2-1 providing further details.
Figure 2-15: Degree of prefabrication (Smith, 2011).
Table 2-1: Various levels of building prefabrication (Smith, 2011).
Level Components Description of Technology
0 Materials Basic materials for site-intensive construction,
e.g. concrete, brickwork
1 Components Manufactured components that are used as part
of site-intensive building processes
2 Elements or planar
systems
Linear or 2D component in the form of
assemblies of structural frames and wall panels
3 Volumetric systems
3D components in the form of modules used to
create major parts of the buildings, which may
be combined with elemental systems
4 Complete Building
systems
Complete building systems, which comprise
modular components, and are essentially full
finished before delivery to the site
46 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
The author defines the modern definition of a modular system to be a structure
prefabricated off-site to the extent where a relatively volume-occupying structure
exists (Figure 2-15, far right). Modular systems are recognized as the greatest stage in
the degree of the prefabricated building spectrum. This section examines the history
of prefabricated buildings and its development to modern modular building systems.
The earliest documented record of complete prefabrication in the construction of
buildings is noted to have of occurred in the 16th century when Nonsuch House was
erected on the London Bridge. Figure 2-16 shows Nonsuch House (centre structure)
forming part of London Bridge.
Figure 2-16: Nonsuch House (centre structure) as seen on London Bridge (Landow, 2012).
Nonsuch House was a four-storey wooden structure, designed and wholly
manufactured in Holland (Picard, 2013). Nonsuch House was trial erected in Holland
in 1578 before being disassembled and shipped to London, England where it was
reassembled and completed in 1579 (Pepys, 2014). The assembly of the structure
employed a joiners’ technique, where no nails were used and only wooden pegs held
the structure together (Knight, 1841).
After the construction of Nonsuch House, more one-off prefabricated structures began
appearing. In the early 1830’s the world saw the introduction of the first mass-
produced prefabricated building system. The system was known as the Balloon Frame
system and is believed to have originated from Chicago, Illinois.
The Balloon Frame system composed of a series of long wooden studs (load-bearing
members) that ran from the sill plate to the top plate and was joined using metal nails.
Figure 2-17 shows the general layout of the Balloon Frame system.
47 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 2-17: The Balloon Frame system is composed of wooden members (Egonarts, 2014).
Marquit (2013), credits George Washington Snow as the developer of the balloon
frame system, though Bigott (2005), proposes that Snow was not the sole inventor and
that the system was not an idea but rather a build-up of “modest shifts in the practice
of many carpenters over time”. Marquit (2013) acknowledges that the first building to
be constructed using the balloon frame system was the St Mary’s Catholic Church on
Lake Street in 1833. However, Miller (1997), suggests the possibility that a Chicagoan
warehouse built in 1832 by Snow himself, was the first structure to employ the balloon
frame system. Though, circumstantial and insufficient evidence supports the rationale
that the structure was manufactured off-site and assembled on site by Snow. Figure
2-18 below, reproduces photographs taken of St Mary’s Catholic Church.
Figure 2-18: St Mary's Catholic Church (Goodman Theatre, n.d.).
Several years later on November 27, 1837, Australia saw its first instance of mass-
produced prefabricated buildings with an advertisement issued in the South Australian
Record by British carpenter Henry Manning (McDonald, n.d.). The advertisement was
titled “Manning Portable Cottage” and announced the availability for the purchase of
48 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
portable cottages built in London and shipped to Australia for erection. Figure 2-19
shows the images used in Manning’s 1837 advertisement.
Figure 2-19: Advertised image of Manning's Portable Cottages (McDonald, n.d.).
The idea and notion of the modular construction method began forming in the early
20th century when technological advances developed potential to address the demand
for quick housing production. Beginning mid-18th century, England’s industrial
revolution initiated quick spread of machined powered factory production. In 1906,
the world saw the first advertisement for the sale of mail-order, factory-made,
prefabricated structures produced by Aladdin Readi-Cut Houses (Marquit, 2013). A
better-known example, due to the company’s success and popularity, was Sears
Roebuck & Co., whom advertised their prefabricated building products throughout
1908–1940. During this period, Sears Roebuck & Co. is believed to have sold over
500,000 prefabricated homes (Sunbelt Modular INC., 2014).
When Henry Ford introduced the standardised assembly line, he sprouted an upheaval
of manufacturing technologies and capabilities. Dubbed Fordism, the notion is
recognised by economists to have revolutionised industrial mass production. Pioneers
recognised the possibilities of implementing assembly line production techniques in
the manufacturing of prefabricated structures and when transportation technology was
capable of transporting large volume-occupying goods, the modern modular building
industry was born.
The Modular Home Building Council, part of the National Association of Home
Builders (NAHB) of the United States, recognizes the formal birth year of the Modular
Construction Method to be 1958, when a home manufacturer produced a two-section
home conforming to applicable building codes (n.d.). Figure 2-20 reproduces the cover
of the Modular Quarterly, showing the first officially recognised modular assembly.
49 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 2-20: Autumn 1958 cover print of the Modular Quarterly, showing the first officially
recognised Modular Assembly (Wall, 2013).
Since the formal recognised birth year, modular buildings have slowly gained
popularity with introduction into other areas of building construction. Modular
systems are now incorporated in many multi-storey buildings and high-rise buildings.
In addition, there are developing plans for super structures utilising modular methods.
2.5.3 Materials Forming Modular Building Systems
The possible architectural arrangements of a MBS is governed by its structural form
and structural performance which is dependent on the materials selected for its load
bearing elements. The structural form of MBSs can be assembled from almost any
material and with modern technology it is not uncommon to find prefabricated
structures comprising of composites made of more than one material. Even with the
possibilities offered by modern technology, the wider construction industry has always
preferred traditional materials; namely concrete, steel and timber. These materials
offer an established and extensive history, with thorough research and information
detailing their behaviours. Skilled labour involving the use of these materials is widely
available and their manufacturing methods have been well refined to allow economical
production. The following section elaborates on the three most common construction
materials seen in MBSs.
Concrete
In the early modern era of the MBS, precast concrete systems were believed to be the
answer to fast construction needs, especially in the 1960s (Smith, 2011). However,
concrete systems are quite heavy and required the use of heavy-duty crane and
50 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
transport systems; resulting in high installation costs especially for smaller projects
such as residential and light commercial structures. Modular concrete construction is
preferred in larger projects, often in applications where high levels of security are
needed such as prisons, hotels, financial institutions and alike. Concrete performs very
well in mitigating vibrations and as such, they are often also employed in applications
where vibration sensitive equipment exists such as hospitals, laboratories and
factories.
Timber
Timber is a widely available material often employed in modular construction for its
natural aesthetic appeal and sustainable production. Timber modules are lightweight
and are easily manufactured. However, due to its lower structural performance
capabilities and inherently low fire rating, timber modular construction is best suited
to smaller applications such as residential buildings. Timber can competently perform
in structures up to three stories, any further and a robust, advanced, structural frame
must be implemented. In turn, this affects its price point and economy (Smith, 2011).
Steel
Currently, steel is the preferred material in modular construction for most building
heights and applications due to its all-round performance in both structural and
economical criterion. Mass-produced, thin-walled steel members provide sufficient
strength in low to medium height structures, whereas thicker steel members are
introduced in taller buildings when greater structural performance in load bearing and
seismic conditions are required. In comparison to concrete and wood, steel has greater
precision of manufacturing lending way to more accurate performance predictions.
Steel modular assemblies are relatively light weight and provide sufficient rigidity for
economical transport and placement without collapsing.
2.5.4 Types of Steel Modular Building Systems
According to ArcelorMittal et al. (2008), there are three generic structural forms of
MBS:
1. Fully modular construction using load-bearing modules;
2. Modules supported by a separate steel structure or bracing system; and
3. Non-load-bearing ‘pods’ for bathrooms etc.
51 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Non-load-bearing pods are not structural load-bearing systems and do not pertain to
the discussion of structural forms of MBS in this section and hence herein will not be
discussed. The floor layout of modular buildings often follows a ‘systematic style’
with little variation dependent on intended function and architectural needs.
Systematic layouts reduce the difficulty in design, construction and assembly co-
ordination.
Fully Modular Construction
In fully modular construction, the overall structural stability of the MBS is the
summation of the structural capacities of the individual modules, without structural
support from any other structural elements such as frames, core walls or podiums.
Simply, fully modular construction systems are stacked assemblies of individual
modules capable of supporting their own loads and of those above. Modules in this
system are joined together through a series of connections. Figure 2-21 shows a fully
modular building being constructed.
Figure 2-21: A full modular hospital being constructed (Steelconstruction.info, n.d.).
Fully modular construction is suitable for buildings of low-medium height. Their
construction speed is superior to other forms of modular construction given the need
to not assemble and construct other structural elements such as steel frames, podiums
or core walls while on site. However, open plan space is restricted to the dimensions
of the individual modules.
Steel Frames Modular Construction
Steel Frames Modular construction denotes modular buildings which consist of a
primary and central steel frame encompassing individual modules. This type of
modular construction is often selected when large open plan space is required. The
steel frame provides the structural support to incorporate large open spaces as well as
52 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
provide additional overall stability of the structure. ArcelorMittal et al. (2008),
describes three forms of Steel Framed Modular Construction systems:
1. Modules supported on a steel podium, in which the locations of the columns
in the podium are aligned with multiples of the module dimensions, Figure
2-22.
2. Modules with fully or partially open sides supported by a steel framework
at entry floor level.
3. Modules that are stabilised by a braced steel or concrete core.
Figure 2-22: A modular structure comprising of a primary steel frame and supported on a
podium (ArcelorMittal et al., 2008).
Modular systems falling under this category are unbounded in building height. The
supporting central frame or core wall allows designers to engineer very high structures.
Larger open plan spaces are also achievable and in addition, podiums may function as
commercial spaces or car parks.
2.5.5 Types of Steel Modules
The individual modules of a modular building system determine how the system
structurally behaves as a whole system. Through combination of various module
forms, the designer can create a multipurpose building with small enclosed spaces or
large open floor plans. Selection of modules can also affect which architectural
features, building skins and facades are possible. There are four basic forms of load-
supporting modules, they are:
1. Four-sided modules;
2. Partially open-sided modules;
3. Corner-supported modules; and
4. Open-ended modules.
53 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Four-Sided Modules
Four-sided modules, also known as continuously supported modules, are the most
common and most basic form of modules available. The four-sided module is a closed
volumetric unit composed of 2D panels. Beginning with a floor cassette, four walls are
erected, and the system is sealed with the addition of the ceiling assembly. Perforations
such as windows and doors can be incorporated, and the external dimensions of the
system are often dictated by transportation limits. Typically, four-sided modules are
4m wide with a length spanning 6-10m. Figure 2-23 shows a common four-sided
module design.
Figure 2-23: A four-sided steel module with load-bearing walls (ArcelorMittal et al., 2008).
Four-sided modules transfer their vertical loads directly through the continuous run of
walls encompassing the module. These load-bearing walls are assembled from a series
of intermediately spaced steel sections often in the form of 65-100mm deep channel
sections. The maximum height of the building is dependent on the compression
capacity of these sections and the bracing characteristics of the modules. For fully-
modular construction using four-sided modules, buildings can reach 6-10 stories
provided adequate bracing is achieved.
Corner columns, usually of larger profiles, form the end columns of the walls. In
addition to providing compression capacity, the larger corner columns often serve as
lifting points and attachments for other structural components such as balconies.
Additional steel angles can be introduced in the recessed corners of the modules for
improved stability as shown in Figure 2-24. Edge beams surround the ceiling assembly
and floor cassette of the module. Floor joists are usually 150-200mm deep channel
sections and the combined floor and ceiling depth is in the vicinity of 300-450mm
deep. Module-to-module connections are completed on site using plates and bolted
connections.
54 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 2-24: Design details of a typical four-sided steel module (M. Lawson, 2007).
Stability of the system can be established by implementing cross-bracing in the walls,
by diaphragm action of sheathing boards, by an entirely separate bracing system or by
a combination these systems. Suitability of the implemented stability measures is
dependent on the geometric form of the structure. For:
• Low rise buildings – sufficient bracing can be achieved with in-plane
bracing measures such as cross-bracing systems or diaphragm action of
board materials. Module-to-module connections will assure effective
transfer of wind action to the group of modules.
• Buildings of 6-10 stories – an access core can serve as the primary vertical
bracing system with horizontal bracing measures implemented or through
diaphragm action in the corridor floor between modules.
• Taller buildings – a podium constructed of concrete or steel is recommended
to provide a stable platform for the modules to be stacked on. In addition,
inclusion of concrete or steel cores are recommended.
As mentioned earlier, four-sided modules are the most basic form of modules available
and hence can serve in a variety of applications. It is common to implement this form
55 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
of module in buildings with cellular layouts such as hotels, student residences,
residential buildings, and key worker accommodation.
Partially Open-Sided Modules
For greater open space design capabilities, four-sided modules can be designed with
partially open sides. Structurally, the system is made possible through the introduction
of stiff, continuous, edge beams, corner posts and intermediate posts if necessary. The
partially open-sided module allows several design features to be implemented. The
manipulation of open space is more flexible and easier, with introduction of corridors,
balconies and future extensions possible. Combining the open faces of these modules
allow for wider, open, interior space to be created.
The maximum width of the opening is restricted by the structural performance of the
edge beam, namely stiffness and bending resistance. The edge beam encompasses the
floor cassette and can also be introduce in the ceiling assembly if required. The
maximum height of the building is controlled by the compression capacity of the
corner or internal posts. Structures of 6-8 stories are possible with partially open-sided
modules.
Smaller intermediate posts are introduced to provide support and additional stiffening
to the edge beams. These posts usually take the form of Square Hollow Sections (SHS).
Figure 2-25 illustrates the use of an intermediate post in a partially open-sided module.
Figure 2-25: An intermediate SHS post is introduced to provide support to the open face of this
module (M. Lawson, 2007).
The stability of these modules is dictated by their partially open sides. Often, additional
temporary stiffening is required during transport and installation of the partially open-
sided module. Insufficient shear resistance is also a common problem and can be
addressed through the introduction of a separate bracing system.
56 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Integral corridors can be incorporated by employing partially-opened faces and are
often seen in larger and longer modules, as shown in Figure 2-26. The built-in corridor
helps to avoid the weather tightness problems that occur in creating corridors by
extending the ceiling in a void of space, thereby speeding up construction rates.
Figure 2-26: An integral corridor is implemented in the longitudinal walls of this module
(Steelconstruction.info, n.d.).
Introduction of rigid corner posts and internal posts allow balconies and extending
structures to be implemented. Partially open-sided modules may also serve as a means
of renovation to existing structures. Additional building space can be achieved by
attaching partially open-sided modules to pre-existing structures. These additional
fixtures are often load bearing with stabilisation achieved by connection to the existing
structure. Figure 2-27 shows open-sided bathroom modules being attached to an
existing building.
Figure 2-27: An open-sided bathroom module is installed on an existing structure (M. Lawson,
2008).
Partially open-sided modules are usually integrated in apartments, hotels with
corridors, student residences, communal areas and worker accommodation. The floor
layout of an apartment building (called Barling Court, Stockwell) incorporating
partially open-sided modules is shown in Figure 2-28. The erection of the modules
took four days and the building was completed in two weeks (Mike Kirk Consulting
Ltd., n.d.). The constructed and completed apartment building is shown in Figure 2-29.
57 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 2-28: Floorplan of apartments incorporating the partially open-sided module – alternate
modules are shaded (M. Lawson, 2007).
Figure 2-29: The completed apartment building of Figure 2-28 – Barling Court, Stockwell (M.
Lawson, 2007).
Corner-Supported Modules
Corner-supported modules are essentially fully open-sided modules, in other words,
all four walls have been removed. Removing all walls allows for greater open space to
be achieved, though the downfall is the severe decrease in the overall stabilisation of
the module. The width of corner-supported modules is usually between 3-3.6m and
rooms of 6-12m width can be created by combining these modules together. These
large open spaces are often required in places of mass assembly such as schools and
hospitals. Figure 2-30 shows a steel corner-supported module.
58 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 2-30: A steel corner-supported module (ArcelorMittal et al., 2008).
Corner-supported modules direct all their vertical loads through the corner posts of the
module. Edge beams surround the floor cassette to stabilise the module. In turn, both
types of members are often larger and thicker in profile to provide sufficient capacity.
Sometimes, intermediate load supporting members are introduced between the corner
posts to reduce the span of the edge beams or for stable transportation requirements
(M. Lawson, Ogden, & Goodier, 2014).
The corner posts of this module are usually in the form of Square Hollow Sections
(SHS) in common profiles of 70x70 to 100x100. If bracing is adequate, these corner
post profiles can provide sufficient compression resistance for buildings up to 10
stories tall. The edge beams often take the form of heavy CFS sections or HRS sections
such as the Parallel Flange Channel (PFC) section. Dependent on the span of the
module (usually 5-8m), the edge beams are generally between 300-450mm deep. The
combined depth of the floor and ceiling edge beams can be as high as 600-800mm.
Figure 2-31 and Figure 2-32 shows typical structural details of a corner-supported
module.
Figure 2-31: Structural details of a corner-supported module, end view (M. Lawson, 2007).
59 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 2-32: Structural details of a corner-supported module, side view (M. Lawson, 2007).
Corner-supported modules are prone to stability issues when grouped together due to
their weak bending resistance at the beam to post connections. On their own, these
modules are only stable for 1-2 stories, thus additional bracing must be employed. To
effectively disperse in-plane forces to all modules, suitable connections are to be
adopted. These connections usually take the form of end plates and hollo-bolts at the
corners of the modules. Fin plate connections are used to provide the nominal bending
resistance. Though even with these measures, additional bracing is often still required
in the structure. Thus, core lifts, core stairs or core walls are usually implemented.
Open-Ended Modules
Open-ended modules are four-sided modules without the inclusion of end walls in their
structural frame. Instead, a strong, rigid and often welded, steel end frame is
incorporated at the ends of the module to provide the bracing, stabilisation and to
support the load that the end wall would have provided. Figure 2-33 shows an open-
ended module with a welded end frame . This configuration allows the designer to
combine modules along their length and allows for full-height glazed façades.
Figure 2-33: An open-ended module with a welded end frame (M. Lawson et al., 2014).
60 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
The end frame usually consists of Rectangular Hollow Sections (RHS) welded or
rigidly connected together. The rigidity of the end frame determines the overall
stability of open-ended modules. If insufficient, stability can be improved by
incorporating a steel “exo-skeleton” system in the building. This form of modular
construction is achievable up to six stories. The overall floor depth of open-ended
modules is generally 450mm. Module-to-module connections take the form of plates
and bolts. The end frame allows full width cantilever balconies or walkways to be
attached at the ends of the modules.
In Glasgow of Scotland, citizenM constructed a 198 room hotel in the form of modular
building system. The building incorporates open-ended modules with full-height
glazing that serves as architectural features and windows as seen in Figure 2-34.
Figure 2-34: citizenM Hotel of Glasgow (Cheshire, 2012).
Dimensions of Modular Building System Modules
The dimensions of modules are dictated by several factors encompassing the project.
Though usually, the dominating factor are the requirements determined by
transportation restrictions. Local authorities enforce restrictions on the maximum
allowable dimensions and weight of transported goods as to avoid damaging transport
infrastructure and prevent the occurrence of traffic-related accidents. Specific
restrictions vary with location. General rules of thumb, detailed by Smith (2011), are
presented in Table 2-2 and Table 2-3.
Table 2-2: Rules of thumb for maximum dimensions of modules based on transportation
restrictions.
Dimension Description Common Maximum (ft.) Oversize Maximum (ft.)
Module Width 13 16
Module Length 52 60
Module Height 12 12
61 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table 2-3: Rules of thumb for building heights of MBSs based on structural material.
Modular Material Building Height (stories)
Wood 1 to 3
Steel 5 to 12
Steel and Precast Specialized 12 to 20+
Structural Components of Modular Building Modules
The type, quantity and configuration of individual structural members used to form the
modules of MBS are dependent on the structural form of the building system. M.
Lawson et al. (2014) details load-bearing modules to be comprised of six basic
components, these components are:
1. Ceilings;
2. Corner posts;
3. Edge Beams;
4. Floors;
5. Load-bearing side walls; and
6. Non-load-bearing end walls (or side walls if edge beams are used).
Figure 2-35 shows the six basic components of load-bearing modules.
Figure 2-35: Basic components of load-bearing modules. Modified from Figure 2.3 of M.
Lawson et al. (2014).
Standard cladding is used to form the enclosing envelope, usually in the form of
galvanised steel sheets. Within the enclosed space, insulation is often installed to
provide fire protection, improve acoustic performance, and enhance thermal control.
The insulation profile of the ALHO Comfort Line, a modular building system
developed by ALHO Systembau GmbH, is shown in Figure 2-36.
62 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 2-36: Insulation profile of the ALHO Comfort Line by ALHO Systembau GmbH
(Rosenthal, Dörrhöfer, & Staib, 2008).
Structural Design of Modular Units
In Australia, steel MBS are classified as steel structures and their behaviour is that of
frame structures. Therefore, Australian MBS can be designed using the prescribed
standards AS 4600 (for hot-rolled steel components) or AS/NZS 4600 (for CFS
components). When designing the modules, M. Lawson et al. (2014), recommend that
the designer consider other issues of structural performance, such as:
• Diaphragm action for transfer of in-plane forces due to wind actions and
notional horizontal forces.
• Structural integrity or robustness to accidental actions, which are generally
resisted by tying forces developed at connections.
• Fire resistance, which required that the structural members are fire protected
and that fire does not spread from one module to another.
The type of connections used to join the components depend on the geometric profile
of the members, their positioning, nature and magnitude of the acting loads, available
equipment, fabrication and erection considerations, and costs involved. Common steel
connections include:
• Splices (cover plate connections);
• Gusset plate connections;
• Framed connections where only webs are connected; and
• Moment connections where both flange and webs are connected.
63 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Load-Bearing Walls
Load-bearing walls in steel modules are primarily subjected to vertical loading applied
from the weight of the modules above. Commonly, CFS sections are employed as the
vertical and horizontal structural members forming the load-bearing wall. In Australia
these sections frequently take the form of C sections that are 100mm deep and 1-3mm
thick with a steel strength of G300 (300MPa yield stress). Conventional design
configurations include spacing the vertical C sections at 400mm or 600mm centres and
in the case of heavier loadings, C sections can be paired together. Tracks (horizontal
members) encompass the vertical C sections at their ends, creating a load path for
vertical loads to be transferred between the modules above and below. Sheathing and
plasterboard are employed to enclose the structural frame of the wall. With effective
connection, the sheathing and plasterboards can prevent buckling in the plane of the
wall and lateral torsional buckling of the structural members. The void space between
structural member and sheathing is filled with insulating materials to improve fire
ratings, improve acoustic performance and mitigate vibration. Figure 2-37 presents the
conventional load-bearing side wall configuration.
Figure 2-37: Conventional load-bearing side wall configuration.
Floors
The structural role of the floor is to support the imposed dead and live loads applied
directly to them. The design of the floor is usually governed by the deflection and
vibration limits. Due consideration of the flexural behaviour of the floor is required
during phases where the floor is to be hoisted i.e. during manufacturing and installation
phases.
64 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Generally, C sections of 150 – 200mm depth and 1.2 – 1.5mm thickness are employed
at intervals of 400mm. The 400mm spacing interval is concurrent and compatible with
most floorboard profiles. Adding of floorboards can prevent lateral-torsional buckling
and should be considered.
Ceilings
Ceiling configurations compose of a set of ceiling joists that are sandwiched between
sheathing and ceiling plasterboards. The structural role of the ceiling is to support its
self-weight and loads applied during installation and construction including indirect
flexural response when hoisting the ceiling and trafficable loads. Lawson (2008),
proposes that this temporary construction load is taken as a minimum of 1kN/m2.
Generally, the governing design factors of ceilings are the deflection and vibration
limits. Designers should consider choosing similar joists depths and profiles for both
ceiling and floor joists; in doing so, the manufacturer will be able to use the same
production system when fabricating these elements.
Edge Beams
Spanning between corner posts, edge beams are provided at ceiling and floor heights.
Their structural role is to effectively transfer half the width loading of the floor or
ceiling to the load-bearing wall below. Similar to floor and ceiling designs, the design
of the edge beam is usually governed by deflection or vibration requirements. M.
Lawson et al. (2014) recommends that the deflection ratio (span:section) of the edge
beam should fall between 18 – 24 for acceptable serviceability performance. To meet
these performance criteria, PFCs are often selected for the edge beam.
Corner Posts
Corner posts are provided in modules to resist the vertical compressive loading. For
partially and fully open-sided modules (corner supported modules), the corner posts
act as the primary (and only) vertical load resisting element. For four-sided and open-
ended modules, the corner posts acts as the secondary vertical load resisting element
in which it assists the load bearing walls in withstanding the compressive loading.
Generally, SHS of 100 or 150mm width are adopted as the corner posts. The geometric
shape of the SHS is favourable in addition to its compressive strength. Connections
between modules are often located on the corner posts. Adjacent walls are understood
to provide lateral restraint for the corner posts, though this is dependent on the profile
and stiffness of the wall i.e. highly perforated walls may not provide sufficient lateral
65 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
restraint. Due consideration of the eccentricity effects is required when designing for
combined bending and axial loading in addition to biaxial bending effects. M. Lawson
et al. (2014) recommend the eccentricity of the moment is taken as 12 mm and thus,
the total eccentricity, e (in mm), is given by:
𝑒 = 12 +𝑏
𝑛
Where: 𝑏 = width of the corner posts and 𝑛 = the number of storeys. A minimum total
eccentricity of 𝑒 = 30mm is recommended by M. Lawson et al. (2014).
Connections
The overall structural stability of a modular structure is heavily influenced by the
behaviour of the individual module-to-module connections. In addition to providing
adequate structural performance, connections need to be easily accessible and
installed. This following will examine common connection systems.
There are two common connection systems employed in most modular buildings; they
are the Fin Plate Connection and the Angle Connection; both dependent on the section
employed as the corner posts.
Fin plate connections are protruding steel plates, welded to the face of the supporting
member and with holes for bolting connection to the supported member. They are often
reserved for when SHS are employed as the corner posts of a module. Figure 2-38
shows the fin plate connection employed on a SHS (supporting member) to connect
several I-beams (supported member). The fin plate connection is designed to resist
bending moments between edge beams and corner posts.
Figure 2-38: The fin plate connection on a SHS (The Steel Construction Institute, 2002).
66 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Angle connections are employed when angle sections are employed as the corner posts
of a module. Often, the angle section corner post will consist of welded nuts that allow
bolting to supported members. Bolting can be made directly onto the supported
member or by employing a connector plate. Figure 2-39 shows an angle connection
where a connector plate (steel framing angle) is employed to connect to supported
members.
Figure 2-39: Angle connections on the corner of steel modules (M. Lawson et al., 2014).
2.5.6 Manufacturing
Modular construction derives most of its benefits from its unique manufacturing
process and hence, the manufacturing details that follow are vital in the success of a
modular construction project. Manufacturing conditions vary and are dependent on
project needs, location and availability of resources. Most manufacturers produce
modules through one of two or a combination of factory production arrangements
called Static Production and Linear Production. These production methods and the
general manufacturing process of MBS are presented in this section.
Static Production
Static production describes the manufacturing process of assembling a module in a
fixed or stationary position from beginning to end i.e. a static position. For the duration
of the assembly, the module remains fixed in place while materials, equipment, tools
and personnel are brought to the module. In some cases, components such as wall
frames, ceiling and floor assemblies are often constructed elsewhere and brought to
the module.
67 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Multiple components of the module can be constructed simultaneously and the rate of
production using this manufacturing process is dependent on the availability of
personnel for specialist tasks. Hence, production may be slow but on the other hand
the critical path is not limited to the completion of any one task. Typically, a large
factory can have 30 modules being built simultaneously with a completion time of 3-
7 days per module (M. Lawson et al., 2014)
Linear Production
Linear production describes the manufacturing process of assembling modules through
utilisation of a series of assembly stations. The process is sequential and follows the
principles of vehicle assembly lines. In this manufacturing process, modules are either
built on fixed rails and conveyed between stations or built on trolleys and moved
between stations. Each station has a certain set of tasks to complete in the production
of the module. Stations consist of dedicated teams, tools and equipment, specifically
prescribed for the set of tasks that needs to be completed at that particular station.
The difference between linear and static production is that modules are moved between
dedicated stations rather than the production teams having to move from module-to-
module. The main advantage that linear production offers is the faster production rates;
made possible by employing automated machines to assist in the assembly of modules.
These machines can perform with great efficiency and high accuracy. Though there
are several downfalls to employing automated machines. Primarily, these are the
capital costs of purchasing these machines and the initial setup and start up times of
the machines.
It is critical that thorough consideration of time spent at each station is made when
planning and designing the production line. In doing so, a steady production pace can
be achieved with minimization of bottlenecks and production halts. The design of
modules should also consider the sequential nature of the line. Any design changes
made late in the project’s cycle can cause disruption to the manufacturing process, as
machines are updated to reflect the changes.
Manufacturing Process of Steel Modular Building System Modules
The manufacturing process of MBSs is similar to that of automobiles, that is to say,
they both are constructed on assembly lines. To achieve the potential economic
savings, some degree of standardised manufacturing must be completed. The advance
68 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
machinery of the factory will allow repetitive processes to be completed in efficient
manners, where the potential of manufacturing savings is greatest.
Factory productions of modular systems allow the modules to stay clear from
undesirable weather conditions and be contained in controlled environments. The
controlled environment minimizes exposure to safety hazards. These factories are
typically equipped with overhead cranes and rollers to assist with transporting modules
and bulk materials. Special machinery and equipment unsuitable for use on site are
present in the factory environment allowing the factory to yield better and more
accurate products. Established factories can construct and assembling all aspects of
MBSs including mechanical fittings, painting, finishes and plumbing. Most of the
manufacturing processes involved can be completed simultaneously while other work
occurs, further reducing manufacturing times.
The manufacturing process of MBSs all follow a similar process, though with minor
variations dependent on manufacturer capabilities and the details of the output product
such as geometry and finishes. The general manufacturing process follows:
1. Floor base structure assembled and sheathed.
2. Wall framework constructed and connected to floor base.
3. Flooring completed, including all tiling, carpeting and installation of other
floor elements.
4. Wall sheathing and vapour membranes installed.
5. Plumbing, electrical installation and other services are completed.
6. Roof frame built and attached to modular unit.
7. Roof insulation, cladding and roofing installed.
8. Windows fitted.
9. Interior and exterior finished installed.
10. Modules wrapped, sealed and prepared for transportation to site.
The following figures (Figure 2-40 - Figure 2-46) show the construction sequence of
a typical modular building system in order of occurrence.
69 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 2-40: Workers assemble the floor base of MBSs (Vanguard Modular, 2014a).
Figure 2-41: Completed metal flooring work on a MBS (Outdoor Aluminum, n.d.).
Figure 2-42: Workers assemble wall frameworks on a MBS (Outdoor Aluminum, n.d.).
Figure 2-43: Workers completing the sheathing of walls on a MBS (Outdoor Aluminum, n.d.).
70 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 2-44: Electrical wiring being completed on a MBS (Outdoor Aluminum, n.d.).
Figure 2-45: Inside a completed MBS (Outdoor Aluminum, n.d.).
Figure 2-46: MBS's wrapped, sealed and prepared for transportation to site (Vanguard
Modular, 2014b).
2.5.7 Modular Building Systems in Australia
The MBS industry in Australia is relatively small in comparison to other countries.
However, there has been recent and significant growth in the sector with several large
MBS projects having been completed recently or in the process of being completed. A
large majority of these MBS projects were completed to support the growth and need
for accommodation in rural and mining towns. In 2009, Ausco Modular was tasked to
deliver a 1200 bed village and facilities project at BHP’s Spinifex Village project in
Yandi of Western Australia (Ausco Modular, 2009). Melbourne has also seen several
71 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
large MBS projects been completed, with most cases to address housing needs in
heavily dense urban locations.
To date, there yet to exists a modular building system specific statutory publication or
standard document to address the structural design of MBSs in Australia. However,
there are current works to develop a code to be applicable in the next few years.
Leading the development of the code is the Australasian Modular Construction Codes
Board. The committee comprises of researchers from Monash and Swinburne
Universities, Engineering Innovations Group, Arup, Robert Bird Group, Felicetti,
Hickory Building Systems, ML Design, Australian Steel Institute, Master Builders
Association Building Services, Laing O’Rourke and others (PrefabAUS, 2014).
2.5.8 Previous Studies Performed on Modular Building Systems
Several studies have been performed on most aspects of MBSs including structural
behaviour, economics, application to various building types (high-rise, industrial etc.),
and manufacturing and construction co-ordination. However, investigations of the
structural performance and behaviour of complete MBSs as a whole tower structure
are limited. This section briefly presents several completed and notable studies in the
MBSs field.
Handbook for the Design of Modular Structures
Researchers at Monash University (2017) formed a collaborative group with industry
professionals to produce the “Handbook for the Design of Modular Structures”. The
very recent publication is a conglomerate of design principles for the design of MBSs
with guides specific to meeting Australian Standards. It is the closest resemblance of
a document pertaining to the structural design of MBSs in Australia. The authors have
expressed that the handbook is only meant to serve as a guide and not a standards
specification document. The authors also expressed that the handbook was created to
pave the way for a standards specification document specific to the design of MBSs in
Australia to be developed.
Behaviour of Framed Modular Building System with Double Skin Steel
Panels
Hong, Cho, Chung, and Moon (2011), performed a thorough investigation on the
adoption of double skin steel wall panels in MBSs. Their research was performed with
the intention to investigate the cyclic behaviour of the new type of lateral load resisting
72 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
systems and the effect of their applications to steel frames. The new type of lateral load
resisting system was proposed as an alternative to steel plate shear walls. Steel plate
shear walls are noted to be relatively expensive given the high number of welding
connections. In addition, creating wall openings in steel plate shear walls are
considerably difficult.
The proposed alternative is a steel framed modular system incorporating double skin
steel wall panels as shown in Figure 2-47. The panels consisted of a corrugated steel
core sandwiched by two steel sheets as shown in Figure 2-48. The steel corrugated
steel core was implemented to prevent premature local buckling of the steel sheets.
The steel sheets were soldered to the corrugated metal core to ensure that an even
surface was maintained on the thin base metal (steel sheets).
Figure 2-47: Framed modular system with double skin steel wall panels (Hong et al., 2011).
Figure 2-48: Double skin steel panel (Hong et al., 2011).
Both theoretical analysis and full-scale testing were performed. Dynamic analyses of
the hysteretic behaviour of the systems were derived using an earthquake engineering
simulation program. Experimental testing was performed on four steel panel
specimens and three modular system specimens.
73 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
The study found that incorporating the double skin, steel wall panels produced lateral
stiffness (4.00 kN/mm) four-times greater than the same steel frame without panels
(1.00 kN/mm). In addition, the steel wall panels yielded first before the steel columns
indicating a sense of control in preventing severe damage to the frame which is
employed as the primary structural system. Concluding, the lightweight, steel panels
demonstrated their capability to be an effective supplementary lateral force, resisting
systems with single-wall hysteresis capable of defining their behaviour.
Modular Design for High-Rise Buildings
Professor Robert Mark Lawson of the University of Surrey is renowned for his
extensive investigations, works and publications in the field of MBS. Recently,
Lawson co-authored a paper with Richards titled “Modular Design for High-Rise
Buildings”, (R. M. Lawson & Richards, 2009). The paper presented a discussion of
the application of modular design to high-rise buildings, and the results of
experimental tests and analysis of light-weight steel modular walls in compression.
Lawson and Richards present several examples of modular constructed high-rise
buildings and relative case studies. They advise that reinforced concrete or steel-plate
cores must be adopted to provide lateral stability for MBS of great height. Lawson and
Richards also discuss the complex structural behaviour of high-rise MBS. They
attribute this behaviour to the influence of the implicit construction tolerances during
the installation procedure, the multiple interconnections between the modules and the
process of transferring the forces to the stabilising elements such as the core walls.
Lawson and Richards prescribed the following design considerations:
• The influence of initial eccentricities and construction tolerances on the
additional forces and moments in the walls of the modules;
• Application of the design standard for steelwork, BS 5950-1 to modular
technology, using the notional horizontal load approach;
• Second-order effects due to sway stability of the group of modules,
especially in the corner columns;
• Mechanism of force transfer of horizontal loads to the stabilising system,
for example concrete cores; and
• Robustness to accidental actions (also known as structural integrity) for
modular systems.
74 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Experimental tests and analyses were conducted to investigate the structural action of
the load-bearing walls in a typical modular building system. Specifically, the
experiments sought to study the compressive resistance of C sections, spaced at
300mm intervals, taking into the account of the restraining and stiffening effects of
various types of boards. The experiments also investigated the sensitivities to
eccentricities up to 20mm; considered to surpass the maximum envisaged tolerable
amount. The wall panels were loaded using a spreader beam. Further details of the
configuration and arrangement used in the tests is seen in Figure 2-49.
Figure 2-49: Test arrangement used in Lawson’s and Richard’s study (R. M. Lawson &
Richards, 2009).
The results of the test indicated that plasterboards and external sheathing boards
effectively prevent minor axis buckling of the C sections and hence failure occurred
by either failure of the major axis or crushing of the section. In comparison to the
predicted strength given by application of BS 5850-5, it was found that all tests
involving the use of 75mm and 100mm deep sections of 1.6mm thickness exceeded
their predicted failures by 0 to 40%. When a 20mm load eccentricity was introduced,
a reduction in capacity of 8 to 36% was witnessed; attributed to the local crushing of
the C sections.
2.5.9 Transportation
Frequently overlooked but highly critical to the success of a modular construction
project is the transportation phase of module units from plant to site. Units should
75 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
arrive to site intact, on time and with minimal costs. In the UK, the National Audit
Office (2005), determined that Transport and equipment account for 7% of the overall
costs in modular construction of multistorey residential buildings. Coordination of this
process is crucial, and many factors need to be taken into consideration. This section
will present these factors.
When enroute to site, transported goods are exposed to changing environments leaving
them susceptible to a variety of events with detrimental effects. To mitigate these
issues, the goods should be properly secured and protected. A series of fasteners and
straps appropriately fixed will ensure the goods are secured to the transporting vehicle.
Weather seals, plastic wraps, cardboard or even wooden crates and shipping containers
can be used to protect the goods from the changing environments.
Both damage to the transported goods and transport infrastructure can occur when en
route to site. Local governing bodies have set regulations to minimise the occurrence
of these events. Often, the size of modular units is not restricted by engineering
capabilities but rather the conditions that govern the transportation process of the
modular units. Conditions which include dimensional limits, combined mass limits,
physical obstructions along the route and structural capacities of the transport
infrastructure.
The planning of the route and schedule of deliveries is a major factor in the success of
the transportation phase. Numerous variables must be accounted, with several
unpredictable in nature and constantly changing. Variables to consider include:
• Mode of transport – road, rail, sea or air;
• Selection of transport vehicle – form, capacity and operating requirements
(fuel consumption, required operators, drivers etc.);
• Selection of route – road topography, profile, gradients, climb, descent,
width and obstructions (sign posts heights, overpasses etc.);
• Supporting infrastructure – loading bays, shipping, rail yards, airports and
infrastructure along the route (bridges, crossings and culvert capacities);
• Imposed conditions of travel – speed limit, customs, checkpoints etc.;
• Time of travel – weather conditions, visibility and traffic conditions (critical
routes, peak traffic hours etc.);
76 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Generally, the local governing transport body will enforce conditions which consider
most of the above variables. In Australia the governing body that regulates the
conditions of heavy vehicle road transportation is the National Heavy Vehicle
Regulator (NHVR). The enforcing document is the Heavy Vehicle National Law Act
2012 – Heavy Vehicle (Mass, Dimension and Loading) National Regulation.
2.5.10 Assembly and Installation
Once module units have been manufactured and delivered to site, the assembly of the
building by installation of modules can take place. The assembly phase includes secure
hoisting and lifting of the units into position. Careful consideration of the method of
hoisting must be made, as forces exerted on the module can be greater during
installation than during its service life.
The assembly stage begins with the preparation of modules by removing weather
sealing and other protective measurements put in place for the transport of the modules
to site. Next, hooks, beams, load spreaders and other necessary attachment
mechanisms are set in place, ready to be hoisted by the crane. Unstable and fragile
units (often larger modules or weak open-sided modules) will require extra attention
and care which can be provided with the use of a supplementary bracing system. When
ready, several teams coordinate the hoisting and positioning of the module unit into
place. Once in place, the modules are connected to the other in-placed modules through
a method called jointing. To finish off the assembly phase, weatherproofing of the
modules and joints is completed.
Modular buildings are erected in a horizontal process and are organized floor by floor.
The time coordination of the assembly process is paramount to the project success.
Project planners must accurately estimate and coordinate the exact time to deliver,
prepare, hoist, position and connect a module. In doing so, congestion of deliveries at
site can be avoided.
Generally, modules are lifted at their corners using inclined cables or through the
assistance of a spreader beam or frame. In some cases, modules may be lifted from
their bases but often this is avoided to minimize potential damage to the base. Figure
2-50 presents several arrangements of module to crane connections.
77 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 2-50 General module to crane connection arrangements (M. Lawson et al., 2014).
In the arrangements where cables are inclined at the connections, additional horizontal
forces will be exerted throughout the modules. It is preferable that the additional forces
exerted on the modules are limited to only vertical forces and hence, lifting beams and
frames are incorporated to reduce the horizontal loading. The most preferred method
of arrangement is by using a two-dimensional frame (bottom right of Figure 2-50).
Jointing
In the construction of structures, jointing describes the process of how two or more
elements are connected and joined. In buildings, joints appear where building elements
meet, enclosing a void of space. The layout of joints is determined by the size, shape
and dimensions of the building elements and thus has a heavy influence on the
appearance of façade as shown in Figure 2-51. Often the voids at the joints are not
completely closed and moisture is capable of penetrating through, leaving the structure
exposed to several adverse effects. To combat this, the joint is protected against
moisture by use of a sealant in addition to other constructional solutions.
78 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 2-51: Building joints influencing the appearance of a façade.
Tolerances
Vital to the structural performance of a structure is the permitted tolerance. In this
regard, tolerance refers to the possible difference between the nominal and as-built
dimensions of the structure. The slightest deviation in placement or misalignment can
result in catastrophic consequences especially in large structures where loads are of a
very high magnitude. For this reason, the connection and jointing systems of the
structure should be designed to expect, allow and tolerate these deviations without
adverse effects to the structure’s performance.
Tolerance should be thoroughly planned and considered during the design and
planning phases especially in the case of modular systems, where modules are often
repetitive designs and the possibility to make changes to the structure on site is very
difficult. Several connection systems to allow for tolerances include implementation
of elastic joints and bearers, and oblong holes for screw fixings.
There are several sources throughout the life cycle of a modular structure that can
contribute to deviations of the dimensions. These deviations are most likely to occur
during the manufacturing and assembly phases with physical damage during transport
an unlikely event. M. Lawson et al. (2014), stated that for the case of light-weight,
steel frame modules, manufacturers can accurately, mass produce modules within an
error margin of +1 to -3mm. This margin appears very minute; however, a series of
modules with these deviations will accumulate to a very significant sum.
During the assembly phase, there are several events which may contribute to a change
in the dimensions of the modules. Given modules can amass to a self-weight of over
20 tonnes, flexing of components will occur during any lifting phase i.e. from factory
grounds to truck, truck to construction site and during installation on site. The degree
79 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
of flex and whether permanent or temporary damage occurs is dependent on the
material properties of the components and the arrangements used to lift the module.
Mitigation of flex during lifts can be completed by employing spreader beams,
temporary bracing measures and dedicated load-tie arrangements.
Another event during the assembly phase that can contribute to dimensional deviations
is the event of positioning and installing modules. The accuracy of placement and
positioning is controlled by the crane operators and dedicated installation labourers
any deviations from this event will be of human error. To minimize the degree of
human error in the placement of modules, high precision global positioning system
(GPS) devices can be employed to assist with the process.
The consequences of having dimensional deviations from designed specifications to
as-constructed specifications can be of very high calibre. The two most prevalent
consequences are structural performance and aesthetic appeal. The most critical
dimensions to be aware of are the plan (horizontal) dimensions, as shown in Figure
2-52(a). Variations in horizontal alignments will reduce space between modules, lifts
and other services which can lead to misalignment with foundations. Variations in
vertical alignments can cause modules to extrude outwards becoming wedge shaped,
as shown in Figure 2-52(b). Vertical alignment is critical for modular structures of 6
or more stories (M. Lawson et al., 2014).
Figure 2-52: Effects due to misalignment (M. Lawson et al., 2014).
2.6 FINDINGS, SUMMARY AND IMPLICATIONS
2.6.1 Cold-formed Steel
Researchers at the QUT have recently developed a new, innovative and improved CFS
section called the Rivet-Fastened Rectangular Hollow Flange Channel Beam. The
80 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Rivet-Fastened RHFCB was developed as an alternative to the LiteSteel Beam, a
discontinued CFS section superior to traditional CFS sections in terms of weight,
strength and design application. The creators of the Rivet-Fastened RHFCB believe
the section also shares similar, if not greater, strength reserves of the LiteSteel Beam
amongst other favourable properties. Current works are underway to further
investigate the structural behaviour of the Rivet-Fastened RHFCB, with completed
findings concluding:
• Preliminary evidence supporting AS/NZS 4600’s prescribed EWM is
suitable for calculating the section moment capacity of Rivet-Fastened
RHFCB with rivet spacing up to 100mm. Although, effects of intermittent
rivet fastening cannot be included in the EWM.
• Preliminary evidence supporting that the DSM can reasonably well predict
the section moment capacity of Rivet-Fastened RHFCB with provisions to
account for the effects of intermittent rivet fastening.
• Application of AS/NZS 4600 for determination of the shear capacity of
Rivet-Fastened RHFCB yields very conservative results. As such, suitable
equations based on the DSM have been proposed and are recommended for
use only for sections with 100mm rivet spacing pending further research.
• Application of AS/NZS 4600 for determination of the web crippling
capacity of Rivet-Fastened RHFCB yields inaccurate results of varying
degrees. As such, new equations have been proposed to determine the web
crippling capacity of Rivet-Fastened RHFCB with 100mm rivet spacing.
2.6.2 Modular Construction Technology
The modular construction method is gaining popularity as an alternative to traditional
construction methods. This popularity increase can be attributed to the numerous
benefits that the modular construction method offers over traditional methods. The
main benefits include:
• Faster project delivery times;
• Significant project costs reductions;
• Greater quality control and reduced waste; and
81 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
• Minimized health and safety concerns involved in construction of the
structure.
Although, for a modular building project to deliver such benefits, it is crucial
that extensive planning is executed in all phases of the project. The modular
construction project is very much an interconnected and integrated design process.
Changes in one phase of the project are highly likely to result in changes in one and
usually more other phases of the project. Hence, due consideration must be made to:
• Structural Design;
o Types of modular systems – there are three general types of modular
systems; fully modular construction, modules supported by a separate
bracing system and non-load bearing pods.
o Types of steel modules – there are four general types of modules; four-
sided modules, partially-open sided modules, corner supported modules
and open-ended modules. The type of module selected will usually be
influenced by architectural requirements and this choice will influence
the structural behaviour of the entire structure.
o Module materials – common materials chosen for the structural frame
of modules include wood, concrete and steel. Steel is the most common
choice, given its broad structural capabilities, predictable behaviour,
high strength-to-weight ratio and wide availability.
o Current design codes – presently in Australia, there does not exist a
solely dedicated design code for the modular structures. At best, a
designer wishing to design a modular structure should design the
structure using the most relevant and existing design, often dependent
on structural material chosen, and should consider the overall structural
behaviour of the modular system.
o Manufacturing considerations – the structural design of modules will
be heavily influenced by manufacturing factors. Factory capabilities are
to be considered and the system should be easy to mass produced within
a small period.
o Connections – connections are a key component to the success of a
modular construction project. Ease of connections heavily influence the
installation time and should be designed to provide minimal degree of
82 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
difficulty when installing, sufficient strength and be relatively easy to
mass-produce.
o Bracing – several bracing systems can be employed in modular
structures, dependent on the structure’s height, the type of modular
system chosen and its interaction with individual modules. Stability of
individual modules should also be considered when the module is
undergoing production and being hoisted into place.
o Tolerances – the difference in designed and as-built structural
dimensions (tolerance) is attributed to two events; manufacturing and
installation. Tight manufacturing controls can minimize tolerance
values. Employing advanced GPS technologies can minimize
installation tolerances. Though, complete elimination of tolerance is
highly unlikely and hence the structural designer must incorporate
measures to allow for tolerances. This usually details in the design of
connections. Exceeding tolerance values can result in disastrous effects,
both aesthetically and structurally.
• Manufacturing;
o Location - the factory should be within proximity to the project site to
minimize transportation costs. In some cases, it can be beneficial to
establish a field factory. The chosen factory location should also
provide sufficient room for manufacturing of modules as well as storage
and stockpiling of completed modules.
o Manufacturing process design - extensive planning is required in design
of the production process to produce modules quickly, efficiently and
economically. Two main processes currently exist, which are linear and
static production, as well as hybrid combinations of these processes.
Manufacturing process and structural design are interrelated,
influencing each other in all details.
o Factory layout – the factory layout will heavily depend on the details of
the production process. The layout of the factory should be systematic,
orderly and with sufficient room to allow storage and stockpiling of
materials and completed modules.
• Transport;
83 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
o Transport mode type - the selection of transport type will be influenced
by proximity of project site to manufacturing factory, topography,
existing infrastructure and economic circumstances.
o Local governing restrictions - road transport authorities have existing
restrictions on transporting large loads such as completed modules.
Often, the size of the module is restricted by transport restrictions as
opposed to structural capabilities. Restrictions may include size
limitations, time of delivery, restricted routes and safety measures such
as lighting and accompanying escorts.
• On site assembly and installation; and
o Site layout - the layout of the site should consider stockpiling of
modules, free flow delivery measures and crane and hoists spacing
requirements
o Modules should be able to be safely and quickly installed which is
heavily reliant on hoisting details and connection detailing.
• Project Delivery.
o BIM Software - Numerous benefits are offered by modular construction
but employing the method requires immense coordination between
planning, design, manufacturing, delivery and installation. To
maximize the benefits on offer, employing BIM software is a must and
will streamline the entire process. In a single package, BIM software
can coordinate planning, design, manufacturing and management.
2.6.3 Conclusion
As explored above, there exists an opportunity to advance the development and
address the shortcomings of modular construction technologies through implementing
recent innovative developments. This chapter has presented the potential benefits of
modular construction technologies and demonstrated the need to refine and realise this
technology. Realising these opportunities will result in increased savings, faster
construction times and greater sustainability of modular construction technologies.
85 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Chapter 3: Case Studies
3.1 INTRODUCTION
The 21st century has seen a rapid increase in the number of modular constructed
buildings, particularly in the market of high-rise structures. The increase is attributed
to many factors but generally, it is due to the advancing technologies that allow
modular structures to reach greater heights and address shortcomings. This section
presents and reviews several complete modular structures as well as individual system
components (connections, walls and floors) paying specific attention to the
technologies that allow modular construction to achieve such feats. Specifically, the
following case studies are examined:
• MBS: 461 Dean, New York City (Section 3.2);
• MBS: SOHO Apartments, Darwin (Section 3.3);
• MBS: Octavio’s and Pascual’s Affordable Steel Concept (Section 3.4);
• MBS: The Verbus System (Section 3.5);
• Component - Wall: Double Skin Steel Panel Wall System (Section 3.6);
• Component - Connection: VectorBloc Connection System (Section 3.7);
and,
• Component - Connection: Connector System for Building Modules by
Verbus Systems (Section 3.8).
All the case studies in this section are projects completed within the last 10 years. They
represent the epitome of the MBS field for which ideas and designs can be built upon
to continue achieving faster, stronger and better results.
3.2 461 DEAN, NEW YORK CITY.
3.2.1 General
Generating large interest in the multistorey and modular buildings sectors was the
delivery of 461 Dean (previously known as Tower B2) by developer Forest City Ratner
in partnership with construction company Skanska (former). The 32-storey modular
building is currently tallest modular constructed building in the world. 461 Dean is
86 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
located in Brooklyn, New York City as part of the Pacific Park development project
(previously known as Atlantic Yards). The building was constructed with intentions to
provide affordable housing to the growing New York City market and intentions to
demonstrate the capabilities and benefits of employing modular construction
techniques on high rise buildings. The building comprises of 930 modules forming 363
apartments. Summary project details of the building are presented in Table 3-1 with a
visual rendering presented in Figure 3-1.
Table 3-1: Summary project details of 461 Dean, New York City.
Project Name 461 Dean
Location New York, USA
Owner Forest City Ratner Companies, Greenland Holding’s and
Skanska (previous)
Architect SHoP Architects
Structural Engineer Arup
Construction
Company Forest City Ratner Companies and Skanska (previous)
Construction
Commencement 2012
Construction
Completion November, 2016
Project Value B2 BKLYN Tower (unknown)
Pacific Park Development ($4.9 billion)
Number of Floors 32
Number of Modules 930
Project Size 32144.5 m2 (346000 ft2)
Figure 3-1: 461 Dean of the Pacific Park development project, New York (Dezeen Magazine
2012).
87 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
3.2.2 Structural Review – Tower Structural Scheme
SHoP Architects led the architectural design of the building with Arup given the
responsibilities of structural and mechanical engineering design. The structure adopts
a steel-framed modular system design and comprises of a lower podium that supports
19 stories of modules above. The arrangement of these modules is essentially in the
form of 3 distinct building masses (left, centre and right) as seen in Figure 3-2.
Figure 3-2: Structural scheme of the 461 Dean tower (Forest City Ratner Companies, 2012).
The main bracing system occupies the centre building mass and consists of individual
braced frames joined together at the roof level with a hat truss. Sufficient module-to-
module (lateral and vertical) connections allow the modules to support their own
stability without the aid of the braced frames when subjected to service conditions.
The generic floorplan of B2 BKLYN Tower is presented in Figure 3-3. The largest
floorplan comprises of 36 modules in its floor.
Figure 3-3: Generic floorplan of 461 Dean Tower (FC Modular, n.d.).
88 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
3.2.3 Structural Review – Module Structural Scheme
Module Chassis
Given the various architectural features desired, a total of 225 unique modules were
designed for the B2 BKLYN Tower, ranging in weight from 7 tonnes to 24 tonnes.
The base chassis of the modules forming the B2 BKLYN Tower is presented in Figure
3-4 with further details about the structural components presented in Table 3-2.
Figure 3-4: Structural scheme of base module chassis employed in the 461 Dean tower
(Forest City Ratner Companies, 2012).
Table 3-2: Structural components of the base module employed the 461 Dean tower.
Chassis Structural
Component Section Profile
Size (Typical)
(inch) (mm)
Column (Corner) Square Hollow Section 6 x 6 150 x 150
Column (Intermediate) Rectangular Hollow
Section 3 x 2 75 x 50
Chord (Bottom) Rectangular Hollow
Section 8 x 4 200 x 100
Chord (Top) Square Hollow Section 4 x 4 100 x 100
Weatherproof Membrane Class A Building Wrap 2 layers of
5/8
2 layers of
16
Strap Bracing Flat Plate 10 250
The base chassis adopts a fully-welded, open-ended module design that consists of
thicker members located in the end frames and rigid connections to support the
redirected load. The base chassis assembly consists of large 150mm x 150mm SHS
that form the corner columns of the chassis with interconnecting links made by 100mm
x 100mm SHS (roof chords) and 200mm x 100mm RHS (floor chords). The closed
SHS of the roof chord members along with the decking form a lateral diaphragm that
89 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
carries lateral loads to the braced frames of the tower structure. Completed module
chassis are shown in Figure 3-5 and Figure 3-6.
Figure 3-5: Side view of completed a 461 Dean module chassis (Calcott, 2014).
Figure 3-6: End view of completed a 461 Dean module chassis (Calcott, 2014).
Wall System
The wall system of the base module used in the construction of the 461 Dean Tower
is presented in Figure 3-7 with further details on the structural components presented
in Table 3-3.
Figure 3-7: Constructing the wall system of the modules of the 461 Dean tower (FC Modular,
2015).
90 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table 3-3: Structural components in the wall assembly of the base module employed in the 461
Dean tower.
Wall Structural Component Section Profile
Wall Column CFS Stud
Wall Chord (Bottom) CFS Edge
Wall Chord (Top) CFS Edge
Wall Lining Gypsum Board 16mm
Weatherproofing Protection Ethylene Propylene Diene Monomer
Within the open-ended module design, the configuration of vertical members in the
side panels are laid out in the form of a Vierendeel Truss system. The intermediate
posts in the side panels are 75mm x 50mm RHS. Thin gauge steel in the form of
250mm flat plates are aligned diagonally in along the side panels to serve as strap
bracing elements.
Roof System
The roof system of the base module used in the construction of the 461 Dean Tower is
presented in Figure 3-8 with further details on the structural components presented in
Table 3-4.
Figure 3-8: The roof assembly of the base module of the 461 Dean Tower.
Table 3-4: Structural components in the roof assembly of the base module employed in the 461
Dean tower.
Roof Structural
Component Section Profile
Size (Typical)
(mm) (inch)
Weatherproof
Membrane
Ethylene Propylene Diene
Monomer (EPDM) 1 0.045
Outer Shell Ribbed Cladding 25 1
Purlin Square Hollow Section 75 x 75 3 x 3
Furring Furring Channel 22 7/8
Ceiling Board Gypsum Board (Type X) 2x layers of
16
2x layers of
5/8
91 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
The roof system consists of longitudinally directed 25mm ribbed decking supported
by 75mm x 75mm RHS purlins that are attached to the 100mm x 100mm RHS top
chords of the base module chassis via fillet welds. Fastened to the underside of the
purlins and running longitudinally are 22mm furring channels that support the 2 layers
of ceiling Type X1 Gypsum boards (16mm each). Completing the assembly is a 1mm
thick layer of ethylene propylene diene monomer (EPDM) weather proof membrane
placed atop of the ribbed decking.
Floor System
The floor system of the base module used in the construction of the 461 Dean Tower
is presented in Figure 3-9 with further details on the structural components presented
in Table 3-5.
.
Figure 3-9: The floor assembly of the base module employed in the 461 Dean tower
Table 3-5: Structural components in the floor assembly of the base module of the 461 Dean
tower.
Floor Structural Component Section Profile Size (Typical)
(mm) (inch)
Insulation Acoustic Padding 5 1/4
Floor Board Cementitious Particle Board 19 3/4
Decking Ribbed 50 2
Purlin Rectangular Hollow Section 150 x 75 6 x 3
The floor system consists of a 19mm layer of cementitious particle board fastened to
50mm ribbed decking running longitudinally. Supporting the decking are 150mm x
75mm RHS purlins which are attached to the 200mm x 100mm RHS bottom chords
1 Type X Gypsum Wall Board as per New York City Building Code 2008.
92 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
of the base module chassis via fillet welds. Completing the assembly is a 5mm layer
of acoustic padding atop of the floor board and sandwiched by the floor finish
(typically hardwood).
3.2.4 Performance Review
General
Intended to display the capbilities of modular construction, the delivery of the 461
Dean modular structure did not meet expectations. Forest City initially claimed to
deliver the tower in 18 months and at a considerably lower cost relative to traditional
construction methods but due to contractor disputes and other issues the construction
length of 461 Dean was almost doubled. Delivery and installation of the first module
occurred on December 12th, 2013 (one year after the intended start date) and the
structure was topped out in May, 2016 and fully completed almost 3 years later in
November, 2016.
Contract issues between Forest City and Skanska were the main factors contributing
to lengthy delays and disruption in the project. Forest City claims that Skanska had
failed in their execution of the contract and Skanska claims the design of the modules
from Forest City were faulty and had led to cost overuns on their behalf. Forest City
maintains that Skanska signed a fixed price contract and any cost overuns are the
responsibility of Skanska. Efforts to resolve the differences between the two
companies led to Forest city buying out Skanska’s stake in the project to continue
works.
The faulty module design claims from Skanska stem from the overly tight (often
exceeding standard industry practice) construction tolerances imposed by Forest City.
In addition, Skanska claims that Forest City’s design lacked adjustability with only a
single source of adjustability provided whereas in typical steel frame buildings, four
sources of adjustability would be provided.
Construction and Quality Performance
The construction of 461 Dean saw severe misalignment issues arise. The misalignment
of the modules is highly evident on the 10th floor and as depicted in Figure 3-10. As
a result of the misalignment, the building was left susceptible to weatherproof issues
during the installation of modules phase.
93 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 3-10: Misalignment of modules as seen on the 10th floor of the 461 Dean Tower (Oder,
2015).
During the court proceedings, it was observed that the match plates (3/8” thick) which
join the modules together were flawed in design. The engineering drawings produced
by the designer showed a 1/4” tolerance between columns in the modules was
permitted. Though, the bolt holes in the match plates only permitted a tolerance of
1/16” in horizontal movement. As a result of the error, the designer agreed to enlarge
the match plate hole diameter to 1 3/4".
In lieu of the misalignment issues, the simple steel structural design of the base chassis
forming the modules in 461 Dean has proven structurally adequate to support a high
rise structure. In addition, Farnsworthy (2014) notes that with the absence of concrete
in the structure of 461 Dean has resulted in the building weighing approximately 65%
of conventional reinforced concrete flat slab buildings.
3.2.5 Conclusion
The 461 Dean project is currently the world’s tallest modular building. The thick,
although heavy, steel members forming the module chasses provide sufficient capacity
to withstand the vertical loads. The effective, although complex, external, skeleton
bracing system ensured the building had sufficient lateral loading capcity.
Besides the hieight accomplishing feats, the 461 Dean project s has not been the best
example of modular construction use in multistorey buildings. Ineffective module
design has lead to severe misalignment of the modules and leading to further troubling
structural concerns such as weather-proofing issues during construction. Fortunately,
the designers were able to adjust the existing design to address the misalignment
issues.
94 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
3.3 SOHO APARTMENTS, DARWIN
3.3.1 General
In September of 2014, developer and builder - Gwelo Developments, completed
construction of a 29-storey modular structure in Darwin, Australia. Valued at $120
million, the project proposed to address the severe housing demand in Darwin during
the offshore gas boom. The building is currently owned by Minor Hotel Group and
through their subsidiary - Oaks Hotels and Resorts, a 4.5-star hotel is operated in the
building with commercial and retail tenants occupying the lower floors and apartments
forming the upper floors. Given the constrained labour market and the soft soil
conditions of the site, modular construction was utilised to address the shortcomings
of these conditions. Further details of the project are presented in Table 3-6 and a visual
rendering of the completed structure is shown in Figure 3-11.
Figure 3-11: SOHO Apartments of Darwin, Australia.
Table 3-6: Project details of SOHO Apartments, Darwin.
Project Name SOHO Apartments, Darwin
Location Darwin, Australia
Owner Gwelo Developments Pty. Ltd.
Architect DKJ Projects and Sidecart Studios
Structural Engineer Irwinconsult
Construction Company Gwelo Developments Pty. Ltd.
Construction Commencement March, 2012
Construction Completion September, 2014
Project Value $120 Million
Number of Floors 29 (21 Modular)
Number of Modules N/A
Project Size N/A
95 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
3.3.2 Structural Review – Tower Structural Scheme
Irwinconsult have utilised both steel and concrete elements in the design of this
modular tower (see Figure 3-12). The structure consists of 21 modular constructed
storeys supported on top of an 8-floor concrete podium. The modular structure utilises
a complex vertical loading system. During the transportation and installation phases,
vertical loading is supported by the steel columns alone. When installed on site, insitu
concrete is casted into these steel columns to form hybrid concrete-steel columns that
together act as the vertical load bearing members of the tower for its entire service life.
Lateral loading is addressed with a concrete core and individual module bracing.
Figure 3-12: SOHO Apartments structural arrangement (Irwinconsult, 2014).
3.3.3 Structural Review – Module Structural Scheme
Module Chassis
Built in Ningbo, China, the module chassis comprises of both concrete and steel
elements. The module chassis is presented in Figure 3-13 and further details of the
structural components presented in Table 3-7.
Figure 3-13: Structural scheme of the base module chassis employed in the SOHO Apartments
structure (Irwinconsult, 2014).
96 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table 3-7: Structural components of the module chassis employed in the SOHO Apartments
structure.
Chassis Structural Component Section Profile
Column (Corner) Combined Steel Flat Plate-Insitu Concrete
Column (Intermediate) Combined Steel Flat Plate-Insitu Concrete
Floor System Precast Concrete Floor Slab
Insulation Spray Polyurethane
Roof System Precast Concrete Ring Beam
Strap Bracing Steel Flat Plate
The layout of the elements resembles a portal frame structure, with intermediately
spaced frames and other similar traits. The module’s chassis is a hybrid partially open-
sided module with one end frame designed as an opened end. Irwinconsult have
utilised a truss system instead of employing thicker members for the opened end frame.
The vertical truss components adopt the Warren Truss form and the horizontal
components adopt the Double Warren Truss form.
Steel columns act as formwork for insitu concrete columns to be casted on site. The
steel columns have been designed with enough structural capacity to allow the modules
to be stacked four modules high during transport. A concrete ring beam encloses the
top of the module. A lightweight concrete slab forms the floor of the module. Steel flat
plate sections are utilised as strap bracing members along the walls to address the large
lateral loads during transportation. End bay bracing was also achieved with diagonally
aligned steel flat plates. Overall lateral stability of the structure is achieved through a
central concrete core. The concrete floor slabs of the modules transfer their loads to
the corridor slabs and onto the outrigger walls running from the central concrete core.
Wall System
Irwinconsult have developed a complex wall system to withstand the large vertical
loading of the tower structure. The wall system utilises the combination of steel and
concrete technologies as depicted in Figure 3-14 and detailed in Table 3-8.
Figure 3-14: Side view of a completed SOHO Apartments module. (Skyscrapercity.com, 2014).
97 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table 3-8: Structural components of the wall system employed in SOHO Apartments structure.
Wall Structural Component Section Profile
Column (Corner) Combined Steel Flat Plate-Insitu Concrete
Column (Intermediate) Combined Steel Flat Plate-Insitu Concrete
Wall Column CFS Stud
Wall Chord (Bottom) CFS Section
Wall Chord (Top) CFS Section
Strap Bracing Steel Flat Plates
Outer Shell Ribbed Steel Sheets
Heavy gauge steel sections form the columns of the wall system with placement in the
corners and at intermediate intervals along the wall. These steel columns act as the
main structural vertical load bearing members of the modules during the transportation
and installation of modules. The columns possess enough structural capacity to allow
the stacking of modules up to four modules high during transport and installation.
When the modules are placed next to each other, the steel columns create a void of
enclosed space and essentially form the formwork required for insitu concrete columns
to be cast on site. This now completed steel-concrete column acts as the main vertical
load bearing member of the tower structure.
Between the columns, wall frames are formed with the use of CFS sections as the top
chord, bottom chord and intermediate wall studs Diagonally aligned steel flat plates
are employed as strap bracing components providing lateral support. Ribbed steel
sheets are employed as the cladding components providing further structural capacity
as well as weather protection.
Roof System
The ceiling system, best depicted in Figure 3-15 and detailed in Table 3-9, comprises
of a concrete ring beam enclosing intermediately-spaced truss systems and CFS beams.
Figure 3-15: Module arrangement in SOHO Apartments, Darwin (Irwinconsult, 2014).
98 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table 3-9: Structural components of the roof system employed in the SOHO Apartments
structure.
Roof Structural Component Section Profile
Chord Precast Concrete Ring Beam
Roof Joist (Primary) CFS Section (Intermediate Placement Arrangement)
Roof Joist (Secondary) CFS Section (Truss Form Arrangement)
Ceiling Board Plasterboard
Outer Shell Thin Flat Steel Sheet
The concrete ring beam is cast during the fabrication of the module. Purlins are formed
with CFS sections placed at intermediate spacing. These are complimented with
another set of purlins in the arrangement of a truss system (Warren Truss form) and
are aligned with the insitu concrete columns. Bolted connections are used to join the
truss system to the heavy gauge steel formwork of the insitu columns.
Floor System
A 125mm thick concrete slab forms the floor of the modules as shown in Figure 3-16.
Figure 3-16: Lifting of the modules forming the SOHO Apartments tower.
Table 3-10: Structural components of the floor system employed in the SOHO Apartments
structure.
Floor Structural Component Section Profile
Floor Concrete Slab
Floor Finishing Tile/Polished Concrete Slab Floor
Irwinconsult designed the concrete slab with perimeter beams and cross beams which
align with the vertical load bearing position of the columns. This arrangement reduced
the overall thickness of the concrete slab resulting in weight reduction too. The
concrete slab is constructed off-site in alignment with the rest of the module.
99 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
The lightweight concrete mix design forming the floor slab targeted an initial density
of 1600 kg/m3 that could achieve a consistent specified strength. In practice, this target
was difficult to achieve and thus the design of the modules was modified. A specific
batching plant was set up for the lightweight concrete mix design to ensure strict
quality control.
3.3.4 Performance Review
General
SOHO Apartments, Darwin is currently Australia’s tallest modular structure.
Innovative structural designs and techniques made the feat possible in a remote and
cyclonic wind region designated site. The structure utilises a concrete podium and
concrete core stability system to stack 21 floors of concrete-steel modules. A prototype
all-steel module was proposed for the structure, however due to several requirements
concrete replaced several steel members and proved to be quite a beneficial decision.
Utilising concrete for the ring beam, columns and floors resulted in all the major
structural load bearing elements being concrete. As this was the case, Irwinconsult
were obliged to only provide fire protection for the concrete elements and not the steel
elements. This avoided difficulties in providing enough protection for the heat
vulnerable steel elements.
Construction and Quality Performance
The drawback of using this system is the additional time needed for preparing, pouring
and curing of the insitu concrete elements. Although, by designing the module’s
chassis to withstand the stacking load of four modules, simultaneous pouring of the
insitu concrete and installation of modules was possible. In addition, the concrete core
could also be constructed independently, behind the stacking of the modules.
The modules were manufactured to a tolerance of +/- 10mm. For a stacked system of
21 levels, cumulative tolerance would prove worrisome. However, given the insitu
placement of the concrete columns, the modules could be adjusted appropriately.
Adjustment and installation of modules was labour intensive and time consuming.
The modules were assembled and manufactured in Ningbo of China and transported
to Darwin by sea freight. During the transportation of some modules, typhoon
conditions occurred and resulted in damage to some modules
100 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
3.3.5 Conclusion
The SOHO Apartments project is Australia’s tallest modular constructed structure.
The innovative approach of combining both steel and concrete materials to form the
chassis of the modules delivered enough structural capacity to permit the structure to
be built to great heights. Although in doing so, the speed of construction was decreased
to allow the concrete sufficient curing time. To mitigate this issue the designers
developed each module to be capable of withstanding the load of three modules above
without the assistance of the insitu concrete members, which allowed construction to
take place on the above storeys while the insitu concrete elements set.
The presence of thick steel and concrete members in the modules resulted in a heavy
design. The volume of materials used is relatively large and hence, expensive. In
addition, the on-site efforts required to assemble the modular tower structure is greater
than most other modular system designs. With all being said, given the location of the
project, employing modular construction remained more economical than traditional
construction methods.
3.4 OCTAVIO’S AND PASCUAL’S AFFORDABLE STEEL CONCEPT
3.4.1 General
As part of their postgraduate studies, Octavio and Pascual (2009) of Luleå University
of Technology (LTU), Sweden, developed a steel modular building system to
investigate affordable building concepts and to push for further use of steel in a country
that largely employs other building materials. Their proposed module design is
duplicated 74 times to form a five-storey structure that will serve as a student
accommodation complex. A conceptual drawing of the structure is presented in Figure
3-17 with general details of their project are presented in Table 3-11.
Figure 3-17: Octavio's and Pascual's modular tower structure (Octavio & Pascual, 2009).
101 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table 3-11: Octavio’s and Pascual’s Affordable Steel Concept – Project Details
Project Name Affordable House with Intensive Use of Steel (thesis title)
Location Luleå, Sweden
Owner Luleå University of Technology (LTU)
Architect Architect
Structural Engineer Xavier Octavio and Marta Pascual
Number of Floors 5
Number of Modules 74
3.4.2 Structural Review – Tower Structural Scheme
Octavio’s and Pascual’s 5 storey tower structure adopts a fully modular concept, that
is to say, no podium, exoskeleton or additional bracing measures such as core walls
are employed in their tower structure. Modules are stacked upon each other with
module-to-module connections the only means of transferring horizontal forces.
3.4.3 Structural Review – Module Structural Scheme
Module Chassis
Octavio and Pascual adopted an open-ended module chassis design. The columns and
beams at the module ends are welded together. Figure 3-18 presents Octavio’s and
Pascual’s module design with Table 3-12 which details its structural members. Figure
3-19 presents the profiles of these sections with Table 3-13 presenting further details.
Figure 3-18: Octavio’s and Pascual’s Steel Module Design (Octavio & Pascual, 2009).
102 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table 3-12: Structural details of Octavio’s and Pascual’s module design.
No. Description Section Profile Quantity Location Orientation
(Direction) Notes
1 Primary Roof Beam UPE 220 2 Roof level. Lateral Welded to main column
2 Secondary Roof Beam UPE 160 2 Roof level, in longitudinal wall frame. Longitudinal
3 Supplementary Roof
Beam UPE 100 2 Roof level, borders. Lateral
Additional support
member
4 Primary Floor Beam UPE 220 2 Floor level, in longitudinal wall frame. Longitudinal Welded to main column
5 Secondary Floor Beam UPE 200 2 Floor level, borders. Lateral Additional support
member
6 Floor Joist C200x50x10x2 10 Floor level, in floor frame. Lateral 600mm spacing
7 Main Column UPE 220 4 In longitudinal wall frame, neighbouring the corner
members. Upright Welded to primary beam
8 Vertical Studs C70x34x1x0.7 21 Along both longitudinal walls and one lateral wall. Upright 600mm spacing
9 Rail Edge 70x43x0.7 4
Both ceiling and floor level, in longitudinal wall
frame, attached to primary floor beam (4) and
secondary ceiling beam (2).
Longitudinal Functions as guide for
vertical studs (8)
10 Corner Studs Angle 60x60x0.7 8 Corners. Upright Assembled in pairs
103 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table 3-13: Structural sections used in Octavio’s and Pascual’s module design.
Section Profile h (mm) b (mm) c (mm) t (mm) Weight per
metre (kg/m)
Angle 60x60x0.7 Angle 60 60 0 0.7 0.66
Edge 70x43x0.7 Edge 70 43 0 0.7 0.86
C70x34x1x0.7 Channel 70 34 1 0.7 0.77
C200x50x10x2 Channel 200 50 10 2 5.02
Section Profile h (mm) b (mm) tf (mm) tw (mm) Weight per
metre (kg/m)
UPE 100 UPE 100 55 7.5 4.5 9.82
UPE 160 UPE 160 70 9.5 5.5 17.00
UPE 220 UPE 220 85 12 6.5 26.60
UPE 200 UPE 200 80 11 6 22.80
Figure 3-19: Profiles of structural sections used in Octavio’s and Pascual’s module design
(Octavio & Pascual, 2009).
Octavio and Pascual have placed thicker steel members at the ends of the module
where the join between these members are a welded connection. Extending from the
end frame, CFS C-profile studs are grouped in pairs to provide adequate strength.
Between each end are thick UPE 220 beams that are welded to the end frames. CFS
vertical studs are placed at intermediate spacing between the end frames. Standard
module designs are typical in having intermediate spaced roof purlins. Though
interestingly, Octavio and Pascual have limited the number of roof beams to just being
the roof beams at the end frames of the module.
Composite Sandwich Façade
To address the severe cold-weather seen in Sweden, Octavio and Pascual have
designed a composite façade which is arranged in a sandwich profile. The arrangement
follows as two thin steel sheets sandwiching Polyurethane (PUR, 3% polyurethane +
104 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
97% gas) in between as depicted in Figure 3-20. Joining the sandwich panels together
is accomplished with concealed fasteners made possible with a clamp in the
longitudinal joint as depicted in Figure 3-21. The concealed fasteners arrangement is
depicted in Figure 3-21. Octavio and Pascual chose PUR as it exhibits the “lowest heat
transmission property of all commonly use thermal insulation materials” (Octavio &
Pascual, 2009).
Figure 3-20: Octavio's and Pascual's composite sandwich façade (Octavio & Pascual, 2009).
Figure 3-21: Arrangement of concealed fasteners in Octavio's and Pascual's composite sandwich
façade (Octavio & Pascual, 2009).
Wall System
Octavio’s and Pascual’s employed several wall profile designs. Though two general
wall profiles were adopted; interior walls and exterior walls. Figure 3-22 shows the
interior wall profile (a) and the exterior wall profile (b) and further details provided in
Table 3-14 and Table 3-15 respectively.
Figure 3-22: Wall profiles of Octavio’s and Pascual’s module design (Octavio & Pascual, 2009).
105 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table 3-14: Details of the interior wall profile of Octavio’s and Pascual’s module design
Interior Wall Structural Component Section Profile
Wall Column CFS Stud 70mm
Wall Chord (Bottom) CFS Edge 70x43x0.7
Wall Chord (Top) CFS Edge 70x43x0.7
Wall Lining Double Gypsum Board 13mm
Insulation Mineral Wool 70mm
Interior walls refer to walls which border against each other and are not exposed to
external environmental conditions. The interior walls, as depicted in Figure 3-22 (a)
and detailed in Table 3-14, consists of a double layer of gypsum board, followed by a
cavity of mineral wool surrounding the structural steel studs and then an empty void
of space separating the interior wall between another interior wall.
Table 3-15: Details of the exterior wall profile of Octavio’s and Pascual’s module design.
Exterior Wall Structural Component Section Profile
Wall Column CFS Stud 220mm
Wall Chord (Bottom) CFS Edge 220mm
Wall Chord (Top) CFS Edge 220mm
Wall Lining Gypsum Board 13mm
Insulation Mineral Wool 220mm
Weatherproofing Protection Plastic Film
Outer Shell Composite Profile
Exterior walls are referred to as walls which are exposed to external environment
conditions. Octavio and Pascual adopted an 80mm composite sandwich panel layout
for the façade which is attached to the exterior walls. Following the composite panel,
the exterior wall profile, depicted in Figure 3-22 (b) and detailed in Table 3-15,
consists of a gypsum board, a cavity consisting of the structural steel stud with infilled
mineral wool, plastic film and an enclosing gypsum board.
Roof System
Octavio and Pascual’s roof system are composed of six beams enclosed by several
panel elements. Similarly, like the wall systems, Octavio and Pascual have design two
roof systems; an interior system and exterior system. The interior roof profile is
106 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
presented in Figure 3-23 (a) with details given in Table 3-16. The exterior roof profile
is presented in Figure 3-23 (b) with details given in Table 3-17.
Figure 3-23: Roof profiles of Octavio’s and Pascual’s module design (Octavio & Pascual, 2009).
Table 3-16: Details of the interior roof profile of Octavio’s and Pascual’s module design.
Interior Roof Structural Component Section Profile
Roof Beam (Primary) UPE220
Roof Beam (Secondary) UPE 160
Roof Beam (Supplementary) UPE 100
Ceiling Board (Primary) Fire Resistant Gypsum Board 15mm
Ceiling Board (Secondary) Gypsum Board 13mm
Outer Shell Steel Sheet 45mm
Interior Roof Structural Component Section Profile
The interior roof system comprises of a sandwich arrangement of ceiling boards and
cladding. The ceiling boards are gypsum boards with the outer board being a normal
gypsum board and the inner board being a special fire-resistant type gypsum board.
Steel sheets of trapezoidal shape top the roof system as the cladding members.
Table 3-17: Details of the exterior roof profile of Octavio’s and Pascual’s module design.
Exterior Roof Structural Component Section Profile
Roof Beam (Primary) UPE220
Roof Beam (Secondary) UPE 160
Supplementary Roof Beam UPE 100
Ceiling Board (Primary) Fire Resistant Gypsum Board 15mm
Ceiling Board (Secondary) Gypsum Board 13mm
Outer Shell Composite 80mm
Weatherproofing Protection Plastic Film 2mm
Similarly, the exterior roof system comprises of a sandwich arrangement of ceiling
boards and cladding. The same gypsum boards arrangement is used, and the
107 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
trapezoidal steel sheet cladding is replaced with the composite board. Weatherproofing
protection is added in the form of a plastic film.
Floor System
Octavio and Pascual developed an interior and exterior floor system as shown in Figure
3-24 and detailed in Table 3-18 and Table 3-19 respectively.
Figure 3-24: Floor profiles of Octavio’s and Pascual’s module design (Octavio & Pascual, 2009).
Table 3-18: Details of the interior floor profile of Octavio’s and Pascual’s module design.
Interior Floor Structural Component Section Profile
Floor Beam (Primary) UPE 220
Floor Beam (Secondary) UPE 200
Floor Joist C Section 200x50x10x2
Floor Board Gypsum Board 2x layers of 13mm
Decking CFS Trapezoidal 45mm
Insulation Mineral Wool 20mm
The interior floor system comprises of two layers of gypsum boards on top of CFS
trapezoidal sheeting with mineral wool insulation all residing on the floor structural
chassis (primary floor beam, secondary floor beam and floor joists).
Table 3-19: Details of the exterior floor profile of Octavio’s and Pascual’s module design.
Exterior Floor Structural Component Section Profile
Floor Beam (Primary) UPE 220
Floor Beam (Secondary) UPE 200
Floor Joist C Section 200x50x10x2
Floor Board Gypsum Board 2 layers of 13mm
Decking CFS Trapezoidal 50mm
Insulation Mineral Wool 20mm
Outer Shell Composite 80mm
Weatherproofing Protection Plastic Film 2mm
108 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Similarly, the exterior floor system has the same configuration as the interior system
apart from cladding now being the sandwich composite and the addition of plastic film
for weatherproofing.
Connection Details
Two connection types are present in Octavio’s and Pascual’s design, they are welded
connections and angle connections. The angle connections have been incorporated on
the corners of the modules, connecting the rigid members together. The first angle
connection (Figure 3-25(a) is comprised of two holes and connects the rigid ceiling
members. The second angle connection (Figure 3-25 (b) is comprised of four holes
and connects the rigid floor members. Both angle connections employ M-20 Class 6.8
bolts. All other connections used to assemble the module are fillet weld connections.
Modules to module connections along the horizontal direction are completed via four
bolts in each main column. In the vertical direction, module-to-module connections
are also completed by bolting with details of the bolts unspecified.
Figure 3-25: Angle connections employed in Octavio's and Pascual's module (Octavio &
Pascual, 2009).
3.4.4 Performance Review
General
Octavio and Pascual have designed a simple yet effective modular system concept.
The concept has yet to be built and placed under real world tests. However, Octavio
and Pascual have completed extensive analysis of the entire concept from designing to
manufacturing and construction on site.
Construction and Quality Review
Overall, Octavio’s and Pascual’s modular system design is reasonably easy to
construct. The arrangement of the various sections, sheeting, boards, insulation and
109 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
weather proofing follow standard arrangements seen in traditional construction. The
simple bolt-on angle connections provide sufficient strength whilst keeping the
assembly of these members easy.
The greatest downfall in terms of constructability of the modules, is the inclusion of
welded connections. Welded connections have been employed in the joining of the
main beams to the main columns of the module chassis. The welded connections are
costly and significant time is required to assemble them.
Octavio and Pascual selected to utilise CFS for most structural members. The resulting
product is a lightweight and structurally adequate system. The selection of CFS
profiles is limited to C-profile, Edge profile and Angle profile sections. All three of
these sections are considered first generation CFS products. Newer generations of CFS
products provide more benefits including improved structural capacity, lower weight
and easy fabrication.
Octavio and Pascual have neglected to address and incorporate measures for probable
construction tolerance issues. The bolt connections between the main column, primary
roof beam, primary floor beam and module-to-module connections have not been
designed to permit any construction tolerances. Poor alignment of the complete
structure could result as seen in the 461 Dean project. Appropriately designed match
plates should be incorporated to address the construction tolerance issues.
3.4.5 Conclusion
Octavio and Pascual have developed a simple yet effective modular building design.
The structural scheme of Octavio’s and Pascual’s modules incorporated mostly steel
members with a majority being CFS. The few HRS were employed to form a rigid
module chassis as the main structural load members.
The minimal design of the angle connections is easy to install though an adjustment to
the design should be made to address alignment issues. The welded connections of the
module provided the strength necessary to facilitate the structural loading though the
downfall is the considerable time and costs to assemble the welds.
Overall, Octavio’s and Pascual’s modular building system design is suitable for low
load applications such as their intended low-rise student accommodation apartment.
To construct a taller system, Octavio and Pascual would need to incorporate more
bracing mechanisms such as a central structural core system.
110 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
3.5 THE VERBUS SYSTEM
3.5.1 General
The Verbus System, also known as V System, is a patented MBS consisting of a steel
monocoque shell and special column to column connections. The patent was
developed by Verbus Limited, whom is now owned by CIMC MBS (China
International Marine Containers Modular Building Systems). CIMC MBS is a major
provider of MBSs who are headquartered in Jiangmen, China with regional offices in
both Europe and Australia. Patent details of the Verbus System are presented in Table
3-20. The Verbus System is CIMC MBS’s flagship product and is has been attributed
to the completion of numerous modular building projects.
Table 3-20: Patent details of the Verbus System.
Patent Title: Building Modules
Patent No. (US): US 2007/0271857 A1
Date of Patent (US): Nov. 29, 2007
Patent No. (WIPO): WO 2005038155A1
Inventor:
David Heather, Buckinghamshire (GB); Collin Ewart Harding,
Bournemouth (GB); Rufus Harold Harding, Wiltshire (GB);
Roderick MacDonald, London (GB); Richard Clive Ogden,
Buckinghamshire (GB)
Assignee: Verbus Limited, Bournemouth (GB)
3.5.2 Structural Review – Module Structural Scheme
Module Chassis
The structural scheme of the Verbus System is essentially a monocoque shell, namely
structural loading is supported through the external skin; for the Verbus System this
means the loads are shared between the chassis as well as the are the wall, floor and
roof systems of the modules. The Verbus System and a complete overview of its design
features is depicted in Figure 3-26. The chassis of the Verbus System consists of four
horizontal side rails, four horizontal end rails and four vertical posts, all open steel
sections. Corrugated steel sheets are connected to these rails via welded connections.
The wall, floor and ceiling systems of the Verbus System prescribe two main
components; elongated members and metal panels. Together with the chassis, these
components bear the structural loading imposed on the module. The patent for the
Verbus System expresses that it is preferable that the elongated members are composed
of steel and take the form of open or hollow sections.
111 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 3-26: Overview of the module structural scheme of the Verbus System (Verbus Systems,
2009).
Wall System
The wall system configuration, presented in Figure 3-27, consists of five main
elements; steel panels, steel studding, insulation, plywood board and plasterboards.
Further details of the Verbus wall system is presented in Table 3-21.
Figure 3-27: Example internal wall construction of the Verbus System (Heather, Harding,
Harding, MacDonald, & Ogden, 2007).
112 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table 3-21: Details of the wall system profile of Verbus Systems’ module design.
Wall Structural Component Section Profile
Wall Column CFS L-Shape Studs
Wall Lining (Primary) Plywood 9mm
Wall Lining (Secondary) Plasterboard 12.5mm x 2
Insulation Insulation Boards 40mm
Outer Shell Corten Steel Sheet 1.6mm
Steel studding of L-shaped CFS sections form the main vertical members and are
connected to the interior of the steel panels via stitch welding. The L-shaped profile of
the steel studs allows for insulation boards to be slotted through and securely held in
placed. Plywood boards overlay the insulation boards and are attached to the steel
studding.
Roof System
The roof system configuration, best presented in Figure 3-26, consists of five main
elements; steel panels, steel studding, insulation, plywood board and plasterboards.
Further details of the Verbus roof system is presented in Table 3-22.
Table 3-22: Details of the roof system profile of Verbus Systems’ module design.
Roof Structural Component Section Profile
Roof Joist CFS C-Sections
Ceiling Board (Primary) Plywood 9mm
Ceiling Board (Secondary) Plasterboard 12.5mm x 2
Insulation Mineral Wool 100mm
Outer Shell Corten Steel Sheet 1.6mm
The arrangement of the roof system follows that roof joists in the form of C-sections
are attached to the Corten steel sheet that forms the outer shell. Slotted between the
roof joists are insulation boards. Attached to the lower face of the joists is plywood
followed two layers of plasterboard.
Floor System
The example floor construction from the patent is presented in Figure 3-28. It consists
of four main elements; steel panels, steel studding, insulation and plywood boards.
Further details of the Verbus floor system is presented in Table 3-23.
113 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 3-28: Example floor construction of the Verbus System (Heather et al., 2007).
Floor joists in the form of C-sections are attached to the corrugated steel panel. Within
the confined volume of adjacent floor joists, insulation boards are slotted through.
Overlying the floor joists and insulation boards is a plywood layer.
Table 3-23: Details of the floor system profile of Verbus Systems’ module design.
Floor Structural Component Section Profile
Floor Joist CFS C-Sections
Floor Board Plywood 28mm
Insulation Mineral Wool 100mm
Outer Shell Corten Steel Sheet 1.6mm
Connections - General
The connection elements in the Verbus System are a key component in the success of
Verbus System being a practical and effective modular building system. The
connection elements provided in the Verbus System have been designed generally in
accordance of ISO/TC-104-1161 (ISO/TC 104 Freight Containers), the same
connection elements found in the designs of conventional freight containers.
Connections - Corner Castings
Corner castings are the primary connection elements in the Verbus System. As the
name suggests, these elements are found in the corner of the modules. A spacing of
2259 mm centre-to-centre between the corner castings is adopted; in doing so, allows
the system to be hoisted and transported with conventional freight container load
handling equipment. Figure 3-29 shows an explode view of four corner castings and
the various elements forming them. Figure 3-30 shows the same four corner castings
in an assembled form.
114 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 3-29: Exploded view of corner castings (Heather et al., 2007).
Figure 3-30: Assembled corner castings (Heather et al., 2007).
As seen in Figure 3-29 and Figure 3-30, a simple position then lock mechanism is used
to join adjacent modules. Lugs (83) are guided into position to slot through the
apertures of the hollow constructed corner castings (21). Gaskets (85 and 87) form the
protective sealing between these elements, preventing exposure to the elements,
accommodating contraction and expansion of the modules, relieving stresses and
minimizing acoustic vibration. Once all in place, bolts (92) are fed through washers
(93), through the lock down plates (88) which pierce the corner castings and finally
fastened through the threaded holes (91) of their respective lugs. Essentially, the bolts
and lock down plates maintain the vertical connection and the lugs and plate part
maintain the horizontal connection.
115 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Connections - Intermediate Castings
Intermediate castings, like those of the corner castings, are placed at intermediate
intervals between the corner castings as seen in Figure 3-31. These extra castings are
positioned on opposite ends of the module, at a centre-to-centre spacing of 2259 mm
and at both top and bottoms railings. The role of these extra castings is to allow the
module to be fastened to standard fasteners on a heavy vehicle trailer whilst hoisted
by standard lifting equipment. Given their position (i.e. not at the corners), these extra
castings have less apertures than the corner castings.
Figure 3-31: Hoisting process of the Verbus System (Heather et al., 2007).
3.5.3 Performance Review
General
The steel monocoque shell adopted in the Verbus System is a structurally efficient
design. The system provides adequate structural capacity with minimal materials. CFS
sections provide the required strength to withstand the structural loading at minimal
weight. Utilising steel panels provide adequate lateral capacity without the need for
multiple connections and thus reducing fabrication efforts.
Construction and Quality Performance
Verbus System’s module is a simple to construct yet effective module design. The use
of CFS sections and other lightweight materials permits the modules to be reasonably
easy to assemble and transport. Incorporating an all-steel frame allows welding to be
116 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
utilised as the sole connection method within the modules. Although, by employing
welded connections the costs and manufacturing times are increased.
The Verbus System has chosen to make high use of the same ISO corner casting seen
on conventional freight containers. This design feature is very practical, as it reduces
the need to develop new technologies to hoist and transport the modules. Although, a
major downfall of the connection is that its assembly requires the workers to be outside
of the module and exposed to heights and the elements. In addition, the connection
lacks the necessary features to address tolerance issues and hence, must be perfectly
aligned for the connection to be assembled.
3.5.4 Conclusion
The Verbus System has managed to address many of the issues facing modular
construction. Employing a monocoque shell design has resulted in a light-weight as
well as structurally adequate modular building system. Utilizing CFS members in the
chassis and roof, floor and wall systems contributed largely to the low weight – high
strength design. By selecting L-shaped steel studding, insulation boards are simply
slotted between the closed cavities created.
The disadvantage exhibited in the monocoque shell design of the Verbus System is the
utilisation of welded connections for the join between the steel panels to steel rails and
steel panels to L-shaped steel studding. Employing welded connections results in
slower assembly times and increased associated costs.
The innovative implementation of the corner castings into the Verbus System has
provided a module-to-module connection that appropriately addresses alignment
issues and minimizes on site construction efforts such as on-site assembly time. The
corner castings adopt the form of a standard shipping container casting, permitting the
modules to be transported and hoisted by current technologies without the need for
any modifications or adjustments. The drawback of the corner casting is the
requirement to be outside of the module when assembling the connection; this draws
safety concerns for on-site installation.
The Verbus System by CIMC is a well-rounded module design. The system
incorporates elements that address many shortcomings seen in other systems such as
structural efficiency (weight-to-strength ratio), ease of construction and transportation.
The only notable fault is the concern for safety when installing the connections.
117 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
3.6 DOUBLE SKIN STEEL PANEL WALL SYSTEM
3.6.1 General
Full-scale experimental testing of framed MBSs with double skin steel panel wall
systems was performed by researchers in a cooperative study between the Seoul
National University, Ajou University, the Steel Structure Research Laboratory of the
Republic of Korea and the University of California. The study aimed to improve
modular construction quality by developing a lateral load resisting system alternative
to steel shear walls and insitu concrete walls. Steel shear walls are common and
effective lateral load resisting systems in modular systems. Although, they are
typically expensive due to the volume of material required, number of welding
connections needed and are not easily able to incorporate openings such as doors or
walkways. Similarly, insitu concrete walls are common and effect lateral load resisting
systems; however, due to the time required for concrete to cure and its weight, it is not
suitable for modular construction purposes.
The study proposed a steel panel wall system and investigated the structural behaviour
of the unique configuration, particularly its performance as a lateral resisting system.
A double (back-to-back) steel panel system is also investigated. The study then
investigated the application of these wall systems to framed modular steel systems.
3.6.2 Test Specimen Details
Double Skin Steel Panel Wall System
The double skin steel panel wall system consists of a 0.7 mm thick corrugated steel
panel sandwich on both sides by 2 mm thick flat steel panels. Further profile details of
the steel panel can be viewed in Figure 3-32. Material properties of the steel used in
the double skin steel panel can be viewed in Table 3-24. The corrugated steel panel is
attached to the flat steel panels by means of soldering, an uncommon method of
structural steel connection. Soldering was employed to ensure even surface contact of
the corrugated panel. Soldering was also considered a more economical alternative to
welding. Four double skin steel panel configurations were tested. Details of their
configurations are presented in Table 3-25. Three base configured specimens with
varying widths were tested. To investigate the behaviour between independent panels
a fourth specimen (LSP-400D), consisting of a double panel configuration and is
depicted in Figure 3-33, was tested.
118 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Double Steel Plates 0.7mm Corrugated Core
Soldering Connection
Figure 3-32: Double skin steel panels with insulation (specimen LSP-400S) (Hong et al., 2011).
Figure 3-33: Double panel configuration of the double skin steel panel (specimen LSP-400D)
(Hong et al., 2011).
Table 3-24: Material properties of the steel in the double skin steel panel (Hong et al., 2011).
Product Name,
Description
Modulus of
Elasticity, E
(GPa)
Yield
Strength σy
(MPa)
Tensile
Strength σu
(MPa)
Elongation at
Rupture ϵu
(%)
Material
Overstrength
Factor
SS400, t = 0.7
mm 210 259 432 39 1.10
SS400, t = 2 mm 213 258 412 37 1.10
SPH-A, t =
4.5mm 208 376 488 35 1.28
Table 3-25: Double skin steel panel test specimen configurations (Hong et al., 2011).
Specimen Double Skin Steel Panel
Wall Type Width of Steel Plate, b (mm) Slenderness Ratio
LSP-400S 400 6 Unit Panel
LSP-550S 550 4 Unit Panel
LSP-850S 850 3 Unit Panel
LSP-400D 400 6 Double Panel
Framed Modular System
The framed modular system followed a simple and standard design as depicted in
Figure 3-34. In each module unit, a floor system composed of MCO 330-12-7 beams
formed the foundation from which upon four columns of HSS 125-125-4.5 profile
supported a ceiling composed of four MCO 200-120-4.5 beams. Each unit module
measured 6 m long by 3 m wide by 3 m high. The profile of the MCO (Modular
Construction Optimized) beam is shown in Figure 3-35 with geometric details
presented in Table 3-26.
119 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Three variations of the framed modular system were tested; a one storey bare system
(M1F), a two-storey bare system (M2F) and a two-storey system incorporating the
double skin steel panel wall systems (M2F-SP). M1F was used determine the structural
performance of a single storey bare module unit. M2F was used to determine the
structural performance of a two-storey bare module system. M2F-SP was used to
determine the structural performance of a two-storey module system with additional
lateral reinforcement by inclusion of the double skin steel panel wall systems. The
double skin steel panel wall systems were placed in pairs in the longitudinal walls of
the two-storey modular system. This specimen arrangement was tested to investigate
the interaction behaviour between the steel panels and the modular frame.
Figure 3-34: Framed modular system MF1 (Hong et al., 2011).
Figure 3-35: Profile of the MCO beam (Hong et al., 2011).
Table 3-26: Section details of the MCO beam (Hong et al., 2011).
Section Height
(mm)
Flange Width
(mm)
Thickness of
Steel (mm)
Sectional
Area (cm2)
Second
Moment of
Area (cm4)
MCO 200-120-4.5 200 120 4.5 30.1 1529.66
MCO 330-120-7 300 120 7 55.64 8519.86
3.6.3 Test Details
Two types of experimental testing were executed; the first, to investigate the individual
capacities of the double skin steel panel wall systems and the other to investigate the
120 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
interaction behaviour of these panels when used in a modular frame system. The
testing apparatus was designed to allow longitudinal displacement and prevent
transverse displacement of the loading beam. Monotonic loading was applied with use
of an actuator, mimicking story drift conditions. Loading was applied three times at
each drift angle, R (1/500, 1/250, 1/100, 1/50). The resulting story drift and the external
steel plate strain were monitored using linear variable differential transformers.
3.6.4 Results and Review
The slender double skin steel panel wall systems were found to follow the theoretical
flexural behaviour of steel plates – single wall hysteresis. All specimens displayed
large initial stiffness. Connection failure between the internal corrugated sheet and the
external flat sheets initiated the onset of local buckling in the external sheets, resulting
in specific yield lines. Strength degradation would occur after initiation of transverse
deformations. Thus, the connection between the internal corrugate sheet and external
flat sheets by means of soldering was found to be effective in preventing early
unintended failure of the panels.
The study concludes that the proposed double skin steel panel wall system is an
effective supplementary lateral load resisting structure. Implementation of the panel
system in a modular frame system increased the lateral load resisting capacity by four
folds and also significantly increased the initial lateral stiffness of the system. Failure
occurred in the double skin steel panel wall systems before failure of the module’s
mainframe and hence, allows for control of severe damage to the chassis of the module.
3.6.5 Conclusion
The proposed double skin steel panel wall system has been proven to be an effective
supplementary lateral load resisting system for application in framed modular systems.
The double skin steel panel wall systems show moderate ductility with favourable
energy dissipation due to their post buckling strength. In comparison to steel shear
walls, these panel systems are cheaper, lighter and easier to manufacture. The steel
panels design also allows for openings and voids to be implemented and inclusion of
thermal insulation material, unlike steel shear walls. The greatest disadvantage shown
in these wall systems is the employment of soldered connections. Although soldering
is cheaper than welding, it is still time consuming to assemble.
121 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
3.7 VECTORBLOC CONNECTION SYSTEM
3.7.1 General
The VectorBloc Connection System is connection system specifically designed for
modular building applications. The VectorBloc Connection System itself is a part of a
larger collective of products, systems and concepts aimed at improving and
overcoming various drawbacks of modular construction including issues surrounding
accumulating tolerances, voids, difficult hoisting procedures and hazardous work
under suspended loads. This collective is called the VectorBloc Standardized Modular
Building System and was developed by Vector Praxis who is headed by Julian Bowron
of Toronto, Canada. Vector Praxis (2015), claims their VectorBloc:
• Allows for modules of any size;
• Provides sufficient scalable vertical tension and gravity capacity;
• Assembles safely from inside the module;
• Provides accessory connection points or connecting balconies, floors and
façade cassettes; and
• Does not rely on continuous walls for structural stability.
This review will examine both the corner and double connection (cruciform
connection for adjacent modules). Figure 3-36 shows the VectorBloc Corner
Connection System (a) and VectorBloc Double Connection System (b). Patent details
of the VectorBloc Connection System are presented in Table 3-27.
Figure 3-36: VectorBloc Connection Systems (Vector Praxis, 2016).
122 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table 3-27: Patent details of the VectorBloc Connection System.
Patent Title: Structural Modular Building Connector
Patent No. (US): US9845595B2
Date of Patent (US): 19/12/2017
Inventor: Julian Bowron
Assignee: Julian Bowron
3.7.2 Structural Details
The VectorBloc Connection System was inspired by the Malcom McLean’s ISO
Corner System, a design feature of modern freight and shipping containers. Building
upon McLean’s concept, Vector Praxis developed several features making the system
more suitable for application in modular buildings. Vector Praxis has introduced both
standard and customizable VectorBloc systems to suit the needs of the building
arrangement and other building design features. Only the standard design will be
discussed herein. Figure 3-37 shows exploded views of the standard VectorBloc
Corner Connection System (a) and the standard VectorBloc Double Connection
System (b).
Figure 3-37: Vector Praxis’s standard VectorBloc Systems (Vector Praxis, 2015).
The VectorBloc Connection system comprises of five key components, they are:
• Tension bolts, Figure 3-38(a);
• The lower VectorBloc connector, Figure 3-38(b);
• Gusset plate screws, Figure 3-38(c);
• The gusset plate, Figure 3-38(d); and,
• The upper VectorBloc connector, Figure 3-38(e).
123 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 3-38: Assembly of the VectorBloc Connection System (Bowron, Gulliford, Churchill,
Cerone, & Mallie, 2014).
As per Figure 3-38, the assembly of the VectorBloc Connection system is simply a
gusset plate sandwiched by upper and lower connector bodies via the fastening of bolts
and screws. Both upper and lower connectors are load bearing hollow bodied elements,
made from an unspecified weldable steel alloy. The connectors resemble a
quadrilateral (square-like) cross-section with extruding arms. Bevelled edges are
implemented in the design of the connectors to help guide the alignment of connecting
elements. For the lower connector, the top end receives the vertical corner member of
the module and the bottom end receives the gusset plate. For the upper connector, the
top end receives the gusset plate and the bottom end receives the vertical corner
member of the module. Joining of the connectors to their respective vertical and
horizontal module chassis members is completed by welding. Welding allows a
moment connection to be formed.
The extruding arms of the connection system provide a passage for the fastening of
bolts and contribute to compression and tension capacity of blocks. The holes in corner
blocks provide a means of connection to tie downs and hoisting devices for the
installation of the module.
The gusset plate forms the interposed element between the upper and lower connector
bodies serving mainly as a horizontal connection element for the corner connection
system. To facilitate the double connection system, the gusset plate is enlarged to
interpose between the upper and lower connectors as well as adjacent connectors. On
124 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
the top face of the gusset plate exist tapered pins extruding upwards. In combination
with the recesses on the underside of a connector block, an effective and simple means
of alignment is achieved for directing the descending modules in place.
Tension bolts are used to connect and fasten together the sandwiched assembly. The
bolts are accessible within the wall cavities. Passing the tension bolts through the upper
and lower blocks provides vertical structural continuity between the modules, forming
a robust vertical connection system. Passing the tension bolts through the gusset plate
provides horizontal structural continuity through the floors of the modules, forming a
robust horizontal connection system.
3.7.3 Review
The VectorBloc Connection System is an effective and appropriately design
connection system for use in MBSs. This connection system design ensures that
adequate structural capacities can be achieved. In addition, the design appropriately
addresses alignment issues by using extruding tapered pins. These tapered pins guide
the connector blocks and gusset plate into place. The design also allows the user to
assemble the connection from inside the module when connecting modules together
on site. This reduces the risks of on-site safety concerns. The drawback of the design
is the welding connections that are utilised. Although, through employing welded
connections, moment connections are effectively formed.
3.7.4 Conclusion
Vector Praxis has developed an innovative and highly effective connection system for
use in MBSs. Their intention is to introduce a standard connection design for the
assembly of module in modular buildings, analogous to that of the ISO Corner System
seen on all modern freight and shipping containers. The VectorBloc Connection
System has demonstrated to be cheap, safe and easy to install while providing adequate
structural performance. The system also provides accessory connection points to
accommodate architectural design options such as balconies, floors and façades.
The VectorBloc Connection System is a developing design with patents currently
being revised to incorporate amendments. Already, the VectorBloc Connection
System has been employed in real-life, multi-storey, modular building projects.
125 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
3.8 CONNECTOR SYSTEM FOR BUILDING MODULES BY VERBUS
SYSTEMS
3.8.1 General
An improved connector system for building modules has been developed and patented
by Verbus Systems Limited. Building upon their previous connector system, presented
in patent WO 2005038155A1, the connector system offers greater flexibility in design
and module arrangement as well as being more economical to produce and execute.
The updated connector system retains its ISO/TC 104 compatibility to continue
allowing conventional freight container handling equipment to interact with the
connection. Patent details of the new connector system are presented in Table 3-28.
Table 3-28: Patent details of the Connector System for Building Modules.
Patent Title: Connector System for Building Modules
Patent No. (US): US 8,549,796, B2
Date of Patent (US): Oct. 8, 2013
Patent No. (WIPO): WO 2008107693A1
Inventor: David Heather, High Wycombe (GB)
Assignee: Verbus International Limited, London (GB)
3.8.2 Structural Details
Verbus Systems’ connector system utilises a guided vertical system to initiate the
alignment and connection. The assembled connector system is shown in Figure 3-39.
The connector system comprises of numerous elements as shown Figure 3-40.
Essentially, the mechanism of the connection follows as spigots (61) preventing
horizontal movement and a fastening system preventing vertical translation. The
spigots (61) also facilitate the alignment with their tapering profiles.
Figure 3-39: Assembled improved connector system (Heather, 2012).
126 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 3-40: Exploded view of the improved connector system (Heather, 2012).
Establishing structural continuity in the connector system begins with laying the lower
modules alongside each other so that the position of their respective upper connector
blocks (51 and 52) is positioned as shown in Figure 3-40. Gaskets (64), which alleviate
stresses from contraction and expansion of the modules, are placed on the connector
blocks (51 and 52) in alignment with their respective connector block spigot openings
(58). The spigots (61) are inserted into the gasket (64) and spigot openings (58)
resulting in the first portions of the spigots (72) forming a tight fitting with the spigot
openings (58). A fixing plate (63) is installed over the top of the upper ends of the
spigot and rests on top of the gaskets (64). Additional gaskets (64) are then installed
over the top of the spigots (61) followed by lowering of the upper modules and their
lower connector blocks (53, 54) to fit on top of the spigots (61) and additional gaskets
(64), thus completing structural continuity of the connection.
Next, a vertical fastening set is employed to secure the connector blocks together. The
set consists of designations 65, 66, 67 and 68. The procedure begins with inserting the
bolt (66) and washer (68) into the slot (60) of the connector blocks (51, 52, 53 and 54).
A spacer plate (65) is fitted between the upper and lower connector blocks with its
cutaway encircling the bolt (66). A nut (67) is then used to fasten the system together,
thus completing the fastening and securing of the connector system.
127 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
The inclusion of the fixing plate has opened an array of design options for the
connection. The fixing plate can be altered in form, profile and dimensions as well as
incorporate attached elements, so as long as the openings in the fixing plate remain, a
secured connection is maintained. In the given example figures (Figure 3-41 - Figure
3-45), the fixing plate has been altered to present different design options.
From Figure 3-41, a horizontal ledge has been incorporated into the fixing plate. The
ledge could be used to provide an attachment point, for example brick cladding. From
Figure 3-42, a vertical plate with holes has been incorporated into the fixing plate. The
pate could be used to provide an attachment point, for example façade elements. From
Figure 3-43, the length of the fixing plate has been extended. This allows for spacing
to exist between connected modules. Further extending the fixing plate, as in Figure
3-44, provides significantly more spacing and by incorporating an I-beam design on
the fixing plate between the modules results in substantially more strength in the fixing
plate to allow another system to be supported, for example a corridor. Extrusion of the
fixing plate can occur in both longitudinal and lateral directions as seen in Figure 3-45.
Figure 3-41: A horizontal ledge incorporated in the fixing plate (Heather, 2012).
Figure 3-42: A vertical plate incorporated in the fixing plate (Heather, 2012).
128 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
e
Figure 3-43: Extension of the fixing plate between connector blocks (Heather, 2012).
Figure 3-44: Further extension of the fixing plate between connector blocks (Heather, 2012).
Figure 3-45: Lateral extrusion of the fixing plate (Heather, 2012).
3.8.3 Review
The updated connector system has had several changes made with significant
improvements seen in economy, ease of use and more design options; so significant,
that the Verbus System now adopts the updated connector system in favour of the
original design.
129 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Spigots (61) are introduced to the connection, essentially substituting to the lugs of the
older design. The major difference between the two, is that the spigots are separated
into two components allowing their location to vary. In addition, the increased tapering
in the ends of the spigot further eases the alignment procedure for the modules.
The updated connector system includes a new feature to allow for tolerance in the
alignment of modules. This feature is seen in the slot (60) and plate (65), where the
cutaway of these elements allows the bolt and nut to be fastened even if a minor
tolerance exists in the direction of the cutaways.
Attributing to the improvements is the inclusion of a fixing plate (63). The fixing plate
provides the needed horizontal structural continuity in the connection as well as
opening a wide range of design options. This is due to the adaptable and variable
design of the fixing plate; the fixing plate can be extruded, altered in form and can
accommodate additional elements. Although in manipulating the design of the fixing
plate, the resultant is a greater likelihood of increasing stress and altering its
distribution throughout the fixing plate and overall connector system.
With the addition of these new elements, it is evident that more material is needed to
manufacture the connector system and greater fabrication efforts are required. The
updated connector system still needs to be assembled from outside the modules,
introducing greater risk to the labourers who do so. The first set of lower modules will
also need to be placed with absolute precision to allow the spigot to pierce through the
fixing plate and aperture in the connector block.
3.8.4 Conclusion
The Connector System for Building Modules by Verbus Systems is an improved
connection system for application in MBSs. The system adequately provides sufficient
structural capacity to allow multi-storey modular buildings to be constructed. The
design features components that allows various architectural features to be connected
to the system such as brick cladding. The connection system also features improved
measures to address alignment issues. The downfall of the design is greater volume of
material and increased efforts to fabricate the various components of the connection
system. In addition, to minimize alignment issues, the first set of lower modules must
be placed with absolute precision to allow the connector system to be utilized
effectively.
130 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
3.9 CONCLUSION
This chapter has presented several case studies to highlight current advances in the
modular construction industry. The case studies have discussed the advantages and
drawbacks that each system has and their relevancy of application in MBSs. Four
complete MBSs were reviewed, these projects were: 461 Dean of New York City,
SOHO Apartments of Darwin, Octavio’s and Pascual’s Affordable Steel Concept and
the Verbus System.
461 Dean is currently the world’s tallest modular constructed building achieving
sufficient strength in its design to attain this title. The project was supposed to
demonstrate the capabilities of modular construction, though construction tolerance
issues were prevalent and caused the project to be severely delayed.
SOHO Apartments of Darwin is Australia’s tallest constructed modular building. The
structure sits upon a podium and employs integrated precast and insitu concrete
elements with steel elements to achieve the required structural strength. Using insitu
concrete elements delays the construction process (due to the required curing period),
but the designers were able to develop a construction process that minimized the delay.
Octavio and Pascual developed a modular building system concept for their
postgraduate studies. Their design kept costs to a minimum through simplifying their
design and adopting economical and sustainable measures. However, the simplified
design lacked measures for addressing construction tolerance issues and provisions for
multi-storey arrangements.
CIMC developed the patented Verbus System to address several shortcomings of
modular construction. Their design follows a monocoque shell incorporating
lightweight elements in structurally efficient configurations. Corner castings like those
seen in standard shipping containers were adopted for module-to-module connections.
This avoided the need to develop new technologies to lift, hoist and transport the
modules.
In addition to the case studies performed on complete MBSs, a further three case
studies were performed on the latest engineering developments in the modular
construction field. These case studies demonstrate the developments in progress to
address the shortcomings of MBSs. These case studies examined: two connections
systems and a wall system all specific to MBS.
131 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Chapter 4: Thermal Modelling of Light
Gauge Steel Framed Wall
Systems Proposed for Modular
Building Systems
4.1 INTRODUCTION
The tragic Grenfell Tower fire incident of June 2017 saw 20 out of 24 floors consumed
by fire within 30 minutes. Several design flaws and maintenance procedures
contributed to the rapid spread of fire, though the main contributing factor is said to be
the combustible exterior metal composite material (MCM) panels (Gaut, 2018). The
arrangement of an MCM panel follows a solid plastic core enclosed by an outer layer
of metal skin on each side. The Grenfell Tower fire incident sparked building and
construction statutory bodies to review their standards around the design of multi-
storey buildings and fire safety, specifically that of steel frame buildings and steel wall
panel systems.
Figure 4-1: The Grenfell Tower fire incident of June, 2017 (Dame Judith, 2018).
Cold-formed light-gauge steel frame (LSF) wall systems (see Figure 4-2) are
becoming increasing implemented into the structural designs of many MBSs. These
advanced steel wall panel systems are often incorporated in MBSs due to their
numerous benefits. The benefits include providing an efficient (weight-to-strength
ratio) load-bearing system, increased speed of construction, improved performance
characteristics and greater level of manufacturing control and geometric accuracy.
These wall systems can be used in both single or multi-storey structures. The standard
132 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
LSF wall system configuration comprises of a light-weight steel frame, wall lining that
encloses the wall and insulation within the cavities created by the wall lining.
Figure 4-2: LSF Wall System (Vardakoulias, 2015).
As highlighted previously, the fire performance of multi-storey buildings especially
those of steel frames and steel wall panel systems is a significant parameter to consider.
Most MBS are composed of steel frames with steel wall panel systems. In the case of
fire, the designer must devise measures to limit the passage of fire and delay its
movement and spread rates. If fire spreads to the steel frame elements, catastrophic
collapse of the entire building can occur by degradation of the steel frame.
For steel MBS, the passage of fire can be delayed with the incorporation of fire-
insulative materials in the wall systems. For standard LSF wall systems, single or
multiple layers of fire rated plasterboards (commonly gypsum plasterboard) are
attached to the steel studs and depending on the building requirements, cavity
insulation may be used to improve the thermal and acoustic performances of the
system.
Thermal insulation is an important design component of a building as it stipulates the
structural performance of the building as well as the comfort levels of the occupants
within the building. Thermal insulative materials such as rockwool are frequently used
to infill the cavities of LSF wall and MBSs. The implementation of the thermal
insulative materials results in lowering heat loss of and through the system.
Interestingly though, implementing thermal insulative materials (rockwool, cellulose
and glass fibre) in the cavities of LSF wall systems also have detrimental effects on
the structural performance of the systems (Gunalan et al., 2013). This is due to the
significantly lower thermal conductivity of the insulation material when compared to
133 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
the adjacent steel members in the cavities of the systems. They found that the cavity
insulating materials channels the heat along and through the steel studs resulting in a
non-uniform temperature distribution of the steel studs.
To thoroughly understand the fire performance and heat transfer behaviours of LSF
wall systems, full-scale fire tests should be undertaken. However, these tests are
extremely expensive, labour demanding and time consuming, and thus an alternative
method is needed. Thermal modelling offers an effective, inexpensive and timely
approach to understanding these behaviours.
Rusthi et al. (2017) performs thermal modelling of LSF wall systems by developing
three dimensional (3D) finite elements (FE) models using ABAQUS CAE to
investigate the fire performance and heat transfer of existing LSF wall system
configurations. They utilised eight node linear heat transfer brick elements (DC3D8)
with solid-solid heat transfer through elements in their model. Rusthi et al. (2017)
showed the developed FE models were able to accurately predict the heat transfer for
load-bearing LSF wall configurations.
The Grenfell Tower fire incident has incited building authorities to review their
understanding, standards and guidelines on the design of multistorey steel buildings
particularly those incorporating steel wall panel systems. This chapter introduces
improved LSF wall system configurations that have been developed for integration in
this study’s proposed MBS design that also includes innovative measures to improve
their fire performance. The thermal behaviour of the LSF wall system configurations
are modelled with FE software and a discussion on the results is presented.
4.2 INNOVATIVE LSF WALL SYSTEM CONFIGURATIONS
To improve the fire performance of LSF wall systems and to lessen the detrimental
effect that cavity insulation has on the CFS studs, three innovative LSF walls systems
are proposed. For comparative purposes, these three systems are evaluated against two
standard systems. Optimum non-load bearing LSF wall configurations have been
considered based on fire tests conducted by Dias et al. (2017) and Rusthi et al. (2017).
The configurations of the LSF wall systems proposed for analysis in this study are
discussed in this section. Table 4-1 presents details of the test specimen configurations.
134 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table 4-1: Details of the test specimen configurations.
Test
Specimen
No. Configuration Description
1
LSF wall system made with double layer
gypsum plasterboard on each side, SCS
studs and full cavity insulation.
2
LSF wall system made with double layer
gypsum plasterboard on each side, SCS
studs.
3
LSF wall system made with double layer
gypsum plasterboard on each side, SCS
studs and discontinuous cavity insulation.
4
LSF wall system made with double layer
gypsum plasterboard on each side, SCS
studs and back blocking gypsum
plasterboard on each side of the studs.
5
LSF wall system made with double layer
gypsum plasterboard on each side, SCS
studs, back blocking gypsum plasterboard
on each side of the studs and
discontinuous cavity insulation.
Configuration 1 – Standard LSF Wall System with Full Cavity Insulation
Configuration 1 is a standard LSF wall system with full cavity insulation. Stiffened
channel sections form the wall studs and the system is enclosed by a double layer of
gypsum plasterboard on each side of the wall system (internal and external walls). The
cavity of the wall system is completely occupied by insulation. This configuration shall
be referred to as the standard LSF wall system configuration and is shown as Test
Specimen 1 in Table 4-1.
Configuration 2 – Standard LSF Wall System with no Cavity Insulation
Configuration 2 is a standard LSF wall system with unoccupied cavities (no insulation
present). The wall studs consist of stiffened channel section members. A double layer
of gypsum plasterboard is attached to each flange of the wall stud members and thus
135 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
enclosing the wall system and creating cavities. No materials occupy the cavities. It is
predicted that the absence of cavity insulation will result in a more uniform
temperature distribution along the wall studs and thus increase the performance of the
wall system. Configuration 2 is presented as Test Specimen 2 in Table 4-1.
Configuration 3 – Innovative LSF Wall System with Discontinuous Cavity
Insulation
Configuration 3 is built upon Configuration 1 with a discontinuous arrangement of
cavity insulation is employed. The configuration follows the standard configuration of
stiffened channel sections as the wall studs and a double layer of gypsum plasterboard
on each flange of the wall studs to enclose the wall system. Within the cavities of the
wall system insulation is inserted, though a void of 100mm around the wall stud is left
and hence, a discontinuous path of insulation is formed. The break in insulation
material is expected to disrupt the flow of heat transfer and thus encourage uniform
temperature distribution along the wall stud. Configuration 3 is presented in Table 4-1
as Test Specimen 3.
Configuration 4 – Innovative LSF Wall System with Back-Blocking Board
Configuration 4 is built upon Configuration 2 with the addition of a layer of gypsum
plasterboard is incorporated in a back-blocking like arrangement. Rusthi et al. (2017)
showed that provision of an additional plasterboard strip, usually of 100mm width,
vertically along the stud surface was found to delay the stud temperature rise.
Configuration 4 is formed with stiffened channel sections as the wall studs and a
double layer of gypsum plasterboard on both sides of the wall system (internal and
external walls). No cavity insulation is incorporated. An additional layer of gypsum
plasterboard with a width slightly greater than the flanges of the stiffened channel
section is attached between the wall stud and the double layer of gypsum plasterboard
wall lining. Incorporating this extra layer of gypsum plasterboard effectively lengthens
the heat transfer travel path resulting in greater fire resistance performance.
Limiting the width of the new layer of gypsum plasterboard to not span the full width
of the wall, reduces the volume of material used whilst still providing the benefits from
increasing the length of the heat transfer travel path. Configuration 4 is seen as Test
Specimen 4 in Table 4-1.
136 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Configuration 5 – Innovative LSF Wall System with Discontinuous Cavity
Insulation and Back-Blocking Board
Configuration 5 is built upon the combination of Configurations 3 and 4. Like all
previously presented configurations, Configuration 5 consists of stiffened channel
sections as the wall studs and a double layer of gypsum plasterboard on each side of
the wall system (internal and external walls). The discontinuous cavity arrangement of
Configuration 3 is employed and incorporated with the back-blocking gypsum
plasterboard arrangement of Configuration 4. Configuration 5 is expected to exceed
the performance of all the other configurations as the configuration provides both
uniform temperature distribution along the wall studs and increase length of the heat
transfer travel path. Configuration 5 is presented in Table 4-1 as Test Specimen 5.
4.3 THERMAL PROPERTIES
To be able to numerically model LSF wall systems and simulate the heat transfer
through the configurations, the corresponding material thermal properties at elevated
temperatures are required. Theses thermal properties include specific heat, relative
density and thermal conductivity for temperatures up to 1200ºC and are used as inputs
within the finite element heat transfer models. This section summarises the applied
thermal properties for gypsum plasterboard, rockwool insulation and steel used in the
thermal analyses and ABAQUS CAE.
4.3.1 Gypsum Plasterboard
Gypsum plasterboard was chosen as the fire protective wall boards in all developed
FE models in this study. The thermal properties of gypsum plasterboard including
specific heat, relative density and thermal conductivity was derived from the data
presented by Keerthan and Mahendran (2012a) for temperatures up to 1200ºC. Figure
4-3 (a) (b) and (c) show the proposed values as a function of temperature.
The thermal conductivity for the gypsum plasterboards was modified to account for
the effect of ablation and moisture movement. Figure 4-3 (a) shows the modified
thermal conductivity of gypsum plasterboard to 0.80 W/m/K at 950ºC. Figure 4-3 (b)
shows the specific heat variation with temperature for gypsum plasterboard. The first
and second endothermic peak account for the first and second dehydrations that occur
at 100 to 150ºC and 150 to 200ºC, respectively (Keerthan and Mahendran, 2012a;
Thomas, 2010; Keerthan and Mahendran, 2012b). Figure 4-3 (c) shows the relative
137 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
density values that occur in gypsum plasterboards due to dehydration of the material
with a mass loss of 15%. The convective coefficient (h) were taken as 25 W/m2/K for
the exposed side and 10 W/m2/K for the unexposed side of the gypsum plasterboards
based on Keerthan and Mahendran (2012a). The surface emissivity of the gypsum
plasterboards was kept as 0.9 for all gypsum plasterboard surfaces.
(a) Thermal conductivity
(b) Specific heat at constant pressure
(c) Relative density
Figure 4-3: Thermal Properties of Gypsum Plasterboard (Keerthan and Mahendran, 2012a).
4.3.2 Insulation Material
LSF wall systems can be used with glass, rockwool or cellulose fibre insulation
material sandwiched between the plasterboard layers. Glass fibre is formed from
molten glass (silicate) fibres and is currently the most commonly used insulation in
Australia. Rockwool fibre is formed from basalt or iron ore blast furnace slag and
provides much higher levels of insulation and density.
138 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Rockwool insulation was inserted within the cavities of the several of the wall systems.
The thermal properties of rockwool insulation utilised in this study was based on
previous research (Keerthan and Mahendran, 2012a; Thomas, 2010; Keerthan and
Mahendran, 2012b). Figure 4-4 shows the thermal conductivity of rockwool insulation
as a function of temperature. The specific heat of rockwool was kept constant at 840
J/kg/°C for temperatures up to 1200°C (Keerthan and Mahendran, 2012a).
Figure 4-4: Thermal Conductivity of Rockwool Insulation (Keerthan and Mahendran, 2012a).
4.3.3 Steel
The temperature increase of steel members is a function of its thermal conductivity
and the specific heat of steel. The precision in the determination of thermal properties
of steel, such as specific heat and thermal conductivity, has little influence on the
thermal modelling of LSF walls under fire conditions since steel framing plays a minor
role in the overall heat transfer mechanism of the LSF wall assembly. The Eurocode 3
Part 1.2 (CEN, 2005) thermal properties of steel were used in the developed FE
models. Figure 4-5 shows the specific heat of steel and the endothermic peak of 5000
J/kg/°C at 735°C.
Figure 4-5: Specific Heat of Steel in the Eurocode 3 Part 1.2 (CEN, 2005).
4.4 METHOD OF NUMERICAL STUDIES
4.4.1 General
This section details the modelling technique of the developed FE heat transfer models
of LSF walls system configurations. ABAQUS CAE was used as the finite element
software for thermal analysis (Simulia, 2014).
139 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
4.4.2 Thermal Boundary Conditions and Material Properties
The heat flux at the boundary will be calculated from the temperature of the fire curve
Tg and the temperature on the surface Ts according to Equation (4-1).
𝑞 = ℎ(𝑇𝑔 − 𝑇𝑠) + 𝜎𝜀(𝑇𝑔4 − 𝑇𝑠
4) (4-1)
where
q is the total heat flux, ε is the relative emissivity, σ is the Stefan–Boltzmann constant (5.67x10−8
W/m2/C4), Tg and Ts are the gas and surface temperatures, respectively. For fire exposure to the standard
cellulosic curve, Tg = 345log (8t+1) + 20. Convective heat transfer coefficient (h) is approximately 25
W/m2K on the fire exposed side, and it is 10 W/m2K on the unexposed side. Emissivity of 0.9 was used
for both exposed and unexposed surfaces.
The LSF wall components were modelled using heat transfer solid elements (DC3D8)
and then connected using tie constraints to ensure solid-solid heat transfer between
them. The top, bottom and sides of the walls were assumed to be insulated, thus no
heat transfer occurs through them.
There are three major heat transfer modes in FEA, namely; conduction, convection
and radiation. The conduction effect was defined using appropriate conductivity values
as discussed in Section 4.2. The convection heat transfer was defined by assigning
convective film coefficients of 25 and 10 W/m2/ºC on the fire and ambient sides,
respectively. These values were selected based on those proposed in the past research
studies (Keerthan and Mahendran, 2012a). Finally, the radiation heat transfer was
defined by assigning an emissivity value of 0.9 on all the LSF wall surfaces.
The standard fire curve was defined as an amplitude curve following a time-
temperature profile based on ISO 834, where θ = 345log (8t + 1) + 20, θ is the
temperature and (t) is the time. This was assigned to the fire exposed side as a boundary
condition. The temperature on the fire exposed side was assigned to follow the fire
curve, whereas room temperature was assigned to the ambient side of gypsum
plasterboards.
The Stefan-Boltzmann constant (σ) of 5.67x10-8 W/m2/ºC4 was also assigned to the
model. In addition to the boundary conditions, the models without cavity insulation
materials were modelled in ABAQUS CAE using closed cavity radiation in the
enclosures. The cavity surfaces enclosed by the LSF wall components were selected
140 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
first and then a cavity radiation emissivity of 0.9 was assigned to those surfaces. These
boundary conditions are shown in Figure 4-6.
Figure 4-6: Finite Element Modelling of LSF Wall Panel.
4.5 RESULTS
The results of the FE modelling are presented and discussed in this section.
Table 4-2 summarises the results of modelling the developed LSF wall systems.
Table 4-2: Comparison of FEA Predicted Fire Resistance Ratings of Conventional and
Innovative LSF Wall Systems.
Test
Specimen
No. Configuration
Time at
500°C
(min)
Time at
600°C
(min)
Increment
at 500°C
(%)
Increment
at 600°C
(%)
1
82 90 - -
2
99 113 21 26
3
98 112 20 24
4
113 125 38 39
5
124 136 51 51
Note: Stud is 90x40x15x1.15mm SCS and 58x40x10x1.15 SCS (for Test 4 and 5) fy = 500 MPa; Board
material = Gypsum Plasterboard; Insulation material = Rockwool Insulation; Back Blocking Board
length = 100mm.
141 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Gunalan et al. (2013) determined the critical hot flange temperature of LSF wall
systems with 0.4 and 0.2 load ratios to be 500°C and 600°C respectively. Accordingly,
the comparisons of each configuration were completed by comparing the FE hot flange
time-temperature curves at 500°C and 600°C. Figure 4-7 (a) and (b) shows the FE hot
flange time-temperature profiles of the conventional and innovative LSF wall system
configurations at different critical temperatures.
(a) Hot - Flange comparison at critical temperature of 500°C (0.4 Load Ratio)
(b) Hot - Flange comparison at critical temperature of 600°C (0.2 Load Ratio)
Figure 4-7: Hot - Flange Time - Temperature Profiles of Conventional and Innovative
LSF Wall System Configurations at Different Critical Temperatures.
142 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Configuration 1 obtained 82 min and 90 min at the critical hot flange temperature of
500°C and 600°C respectively. Figure 4-8 (a) and (b) show the temperature contours
across configuration 1 at different critical temperatures.
Configuration 2 achieved 99 min and 113 min at critical temperature of 500°C and
600°C respectively. Figure 4-9 (a) and (b) shows the temperature contours across
configuration 2 at different critical temperatures.
Configuration 3 obtained 98 min and 112 min at critical temperature of 500°C and
600°C respectively. Figure 4-10 (a) and (b) shows the temperature contours across
configuration 3 at different critical temperatures.
Configuration 4 achieved 113 min and 125 min at critical temperature of 500°C and
600°C respectively. Figure 4-11 (a) and (b) shows the temperature contours across
configuration 4 at different critical temperatures.
Configuration 5 obtained 124 min and 136 min at the critical hot flange temperature
of 500°C and 600°C respectively. Figure 4-12 (a) and (b) shows the temperature
contours across configuration 5 at different critical temperatures.
Comparing the obtained hot flange FE results for Configurations 2, 3, 4 and 5 against
Configuration 1 (conventional cavity insulated LSF wall system), the improvement of
the fire resistance ratings was 21%, 20%, 38% and 51% for a critical hot flange
temperature of 500°C respectively. For a critical hot flange temperature of 600°C the
improvement was 26%, 24%, 39% and 51% respectively.
(a) Temperature Contours across Configuration 1 at 82 min or 500°C
143 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
(b) Temperature Contours across Configuration 1 at 90 min or 600°C
Figure 4-8: Temperature Contours across Configuration 1 at Different Critical Temperatures.
(a) Temperature Contours across Configuration 2 at 99 min or 500°C
(b) Temperature Contours across Configuration 2 at 113 min or 600°C
Figure 4-9: Temperature Contours across Configuration 2 at Different Critical Temperatures.
144 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
(a) Temperature Contours across Configuration 3 at 98 min or 500°C
(b) Temperature Contours across Configuration 3 at 112 min or 600°C
Figure 4-10: Temperature Contours across Configuration 3 at Different Critical Temperatures.
(a) Temperature Contours across Configuration 4 at 113 min or 500°C
145 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
(b) Temperature Contours across Configuration 4 at 125 min or 600°C
Figure 4-11: Temperature Contours across Configuration 4 at Different Critical Temperatures.
(a) Temperature Contours across Configuration 5 at 124 min or 500°C
(b) Temperature Contours across Configuration 5 at 136 min or 600°C
Figure 4-12: Temperature Contours across Configuration 5 at Different Critical Temperatures.
146 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
4.6 CONCLUSION
This chapter has presented the details of the developed 3D finite element heat transfer
models of conventional and innovative LSF wall systems proposed for use in MBSs.
It has been considered in order to improve the fire performance of LSF wall systems
and to lessen the detrimental effect that cavity insulation has on the CFS studs.
Gunalan et al. (2013) described the critical hot flange temperature of LSF wall systems
with 0.4 and 0.2 load ratios to be 500°C and 600°C, respectively. Hence, comparisons
were made for each configuration by comparing the FE hot flange time-temperature
curves at 500°C and 600°C, respectively. The study showed that when the obtained
hot flange FE results for Configurations 2, 3, 4 and 5 were compared against
Configuration 1, the improvement of the fire resistance rating were 21%, 20%, 38%
and 51% for critical hot flange temperature of 500°C while they were 26%, 24%, 39%
and 51% for critical hot flange temperature of 600°C, respectively. Thus, this study
has shown the expected increase fire resistance performance of the newly proposed
wall systems. The selection of which configuration of LSF wall system to adopt within
a modular building system will be dependent on the fire rating requirement of the
structure.
147 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Chapter 5: Conceptual Design of an
Improved Modular Building
System
5.1 INTRODUCTION
Modular construction offers an array of substantial benefits over traditional
construction methods. However, shortcomings in the development and practical
application of the technology has seen modular construction not fully attain these
ideals. Furthermore, the recent Grenfell Tower fire incident has criticised the safety of
steel frame structures and steel frame wall panel systems which are both often
employed in MBSs. This chapter proposes a conceptual design of an Improved
Modular Building System that addresses these concerns. This chapter begins with
discussing design considerations (Section 5.2) that re-examine and summarise the key
benefits and shortcomings derived from the case studies presented in Chapter 3. Next,
the design inputs that were taken into consideration for the design of the modular
building system are discussed (Section 5.3). Subsequent, the conceptual design of the
proposed modular building system is presented (Section 5.4) followed by the proposal
for multi-storey configurations (Section 5.5). Finally, a summary of the design is
presented and concluding remarks are made (Section 5.6).
5.2 DESIGN CONSIDERATIONS
Through the examination of several case studies of recent modular building designs
(Chapter 3), a concise summary of shortcomings and benefits is summarised as
follows. These shortcomings and benefits have contributed to developing this
improved modular building system.
5.2.1 On site Construction Efforts
From Chapter 3, several MBS projects required a fair degree of labouring on-site
resulting in longer construction times, increased safety concerns and greater financial
burden. The curing of concrete for the construction of SOHO Apartments engineered
by Irwinconsult resulted in lengthy construction times. The lengthy construction time
is due to waiting for the concrete to cure and amass the required strength before safe
148
construction of the upper levels could continue. However, Irwinconsult were able to
mitigate this issue by designing the steel chassis of the modules to withstand the load
of four modules. This allowed for construction and placement of the modules to run
simultaneously whilst preparing, pouring and curing of the concrete elements took
place.
5.2.2 Alignment Issues
Alignment issues were prevalent in several of the reviewed MBSs. Theoretically, it is
possible to design a construction process that sees minimal tolerance. Though, a real-
world environment exists, and unforeseen events and/or circumstances can occur that
can easily change a module and its properties. When addressing alignment issues, the
designer should develop several measures for adjustability when assembling the
modules together on site. The Verbus System addressed alignment issues by
developing a suitable connection, the corner casting connection. The lugs seen in the
corner castings have been shaped to guide themselves into the openings of the corner
castings and then are bolted in place.
5.2.3 Effectiveness of Connections
Several connections were impractical for on-site construction. Some were difficult to
install effectively and safely whilst there were others that were time consuming. When
designing the connections, the designer should develop connections that are simple,
structurally effective and practical in terms of on-site module-to-module assembly.
The compatibility of the connections with existing technologies including the
technologies to connect, disconnect, assemble, relocate and fix (tie down) should be
well considered. Vector Praxis and Verbus Systems designed connections based on
ISO corner castings seen in standard freight containers. The compatibility of their new
connections with existing technologies allowed their modular systems to be easily
assembled and transport with little to nil modifications of current technologies.
5.2.4 Weight of Modular Building Systems
The MBSs with the height accomplishing feats were also the heaviest systems
reviewed. The need for stronger building materials often results in heavier, denser-
grade materials. This dilemma cannot be avoided; however, it can be minimized
through the application of greater strength-to-weight ratio building materials.
149 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
The large hot-rolled sections in Arup’s 421 Dean structure and Irwinconsult’s SOHO
Apartments structure resulted in heavier module designs. Paradoxically, the heavier
gauge members also provided additional strength allowing both parties to construct a
tower to such heights.
The thinner CFS sections prevalent in Octavio’s and Pascual’s system and the Verbus
System resulted in modules that were light-weight and structurally sufficient to
withstand the loading of several stories. However, these systems were structurally
limited to several stories and the heights seen in Arup’s and Irwinconsult’s systems
cannot be reached without adjustment to the designs. Thus, it is here where the
introduction of strengthened CFS sections are prescribed such as the Rivet-Fastened
RHFCB.
5.3 DESIGN INPUTS
Designing a modular system encompasses a range of fields and aspects that the
designer must consider for the modular system to function effectively and maximise
the benefits that modular construction offers. The following sections describe several
aspects of the system’s design that have been taken into consideration. The Handbook
for the Design of Modular Structures by Monash University (2017) has been referred
to in developing the following section.
5.3.1 Overall Tower Stability
The overall stability and robustness of a modular tower structure is governed by the
loading interactions and tying actions that individual modules have on their
neighbouring modules. Overall stability can be provided by an external structure or by
individual modules acting together in unison. To maximise the benefits of modular
construction (quick construction, low costs) the designer should opt to address the
overall stability of a structure through the interactions and tying actions of the
individual modules.
The proposed modular system design suggests that the overall stability of the structure
is to be attained through the collective interactions of the modules via several proposed
bracing systems. The wall systems of the modules provide the bracing capacities of
the individual modules and through appropriate connection methods between modules
these forces can be dispersed across the entire structure.
150
5.3.2 Acoustic Performance
The acoustic properties of a structure are a significant aspect to consider when
addressing the comfort of the occupants. Sound is the term use to describe the
vibrations that travels through any medium. Sound is quantified through frequency and
amplitude. There are two types of sound classification; airborne sound and impact
sound. Airborne sound describes the sound that is transmitted through the air such as
speech or music. Impact sound describes the sound caused by impact and transmitted
through the structure such as footsteps or dropped objects.
The acoustic performance of a structure is regulated by the sound insulation present in
the structure. Sound plays a significant role in the overall sustainability structure and
thus, designers must consider the impacts that the acoustic performance has on the
sustainability of a structure. Acoustic performance can be controlled through adopting
several measures such as:
• Employing materials with poor stiffness properties;
• Incorporating damping materials in the structure;
• Increasing the depth of the wall cavities; and,
• Increasing the mass (especially thicknesses) of the incorporated materials.
The proposed modular system design has regulated the acoustic performance of the
system by incorporating a double ceiling and double wall partition configuration (2x
layers of gypsum plasterboard). The double layer provides a thicker depth of material
and a break in continuity of the material that sound must traverse through. Gypsum
plasterboard was chosen as it performs highly in reducing the transmission of sound
energy as well as being a high fire-resistant material. In addition to the gypsum
plasterboards, rockwool is housed within the cavities of the system as an insulating
material. This helps to further regulate acoustic transfer.
5.3.3 Thermal Performance
The thermal performance of a structure can be described as the capacity to regulate
and control the temperatures exposed to the structure. Thermal regulation is essential
in ensuring the comfort of the occupants and the protection of the structure from
exposure to unreasonable temperatures. Thermal performance is quantified by the heat
loss per m2 of the façade or roof (U-value). Selection of thermal regulation measures
151 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
is integral to contributing to the sustainability of a structure. Thermal regulation can
be provided by several means such as:
• Thermal insulation products (insulation batts);
• Heating and cooling appliances (air conditioners and heaters);
• Preventing air infiltration and leakage by sealing gaps; and,
• Ventilation and control of condensation.
The thermal regulation measures adopted in the proposed modular system design is
provide through introducing rockwool (an insulative material) into the cavities of the
wall, roof and floor systems. Rockwool was chosen as the insulating material based on
the multiple benefits that it provides over other insulating materials including:
• Great thermal insulating properties;
• Advanced acoustic insulating properties;
• Breathable structure; and,
• Capacity to withstand exposure to high temperatures before melting
(+1000℃).
5.3.4 Fire Resistance
The fire performance of buildings and structures is an essential element of the design
process. The designer must consider the possibility and effects that a fire would have
on the structure including the risk of spread to other parts of the structure and even
neighbouring structures. The designer should incorporate measures to prevent the
spread of a fire and measures to delay the onset of structural failure and collapse caused
by exposure to a fire.
The fire performance of a structure is governed by selection of materials, the
arrangement and profile of structural members and any firefighting systems in place.
In Australia the National Construction Code dictates the requirements for the fire
resistance of a structure.
In this proposed design several measures have been incorporated to ensure the system
best meets the fire performance requirements. The fire resistance measures proposed
include:
• Incorporating Rockwool in the cavities of the system;
152
• Proposing a discontinuous arrangement for the insulating materials;
• Employing double layer Gypsum Plasterboard arrangements; and,
• Integrating back blocking boards on the flanges of the internal frame
members (such as steel wall stud).
Contradictory of its intended purposes, employing insulation to completely fill the
cavities of a wall system has been previously shown to have a negative effect on the
fire resistance performance of the wall system. Adopting a discontinuous cavity
arrangement for the insulation material can simulate a uniform temperature
distribution on the steel members of the wall frame.
Gypsum plasterboard is chosen for its advanced fire resistance properties.
Incorporating a double layer configuration lengthens the heat transfer path to the
critical steel frame members and hence, increases the fire resistance performance.
Addition of another layer of gypsum plasterboard further increases the heat transfer
path and fire resistance performance but also introduces unnecessary and inefficient
use of materials. By limiting the width of the board to the width of the flange of the
steel frame member a back-blocking board is formed. The back-blocking board
reduces the quantity of material used and thus, saving costs and minimizing weight
while providing improved fire resistance performance.
5.3.5 Sustainability
With recent emphasis on developing sustainable structures, designers must consider
the entire lifecycle of a structure. Modular systems provide a great foundation for
sustainable practices as the systems inherently provide measures to systematically
disassemble the structure and salvage the constituent parts avoiding the need for
destructive demolition. Modular systems are also capable of being reused as an entire
system by dismantling and relocating the modules elsewhere. With these factors in
mind, the designer should consider the processes for dismantling the modular as
constituent parts and/or as entire modules for relocation.
The proposed modular system design utilizes simple connections that are reversible
and thus keeps the dismantling process easy. By using bolted connections, the system
can be easily undone using appropriate tools. The clutching hold of the wall studs by
the wall track is easily dismantled. The rivet connections of the Rivet-Fastened
RHFCBs can be removed allowing the flanges and web of the section to be recycled.
153 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
5.4 PROPOSED MODULAR BUILDING SYSTEM CONCEPTUAL
DESIGN
The modular building system conceptual design is proposed in this section. This
conceptual design encompasses a complete MBS module suitable for single storey
applications; multi-storey configurations are later discussed in Chapter 5.5 (i.e. top and
intermediate modules is discussed). The floor, roof and wall systems that form the
module are presented as well as the connections within the module. Note, the nominal
sizes presented in this section are general sizes for illustrative purposes. Specific sizes
have not been stated as they would vary with application, load and other project
specific requirements.
5.4.1 Module Structural Scheme Overview
The proposed design takes the form of a corner supported modular system with a wall
system that contributes to the cross bracing strength of the modules. Figure 5-1
presents an overview rendering of the proposed modular system.
Figure 5-1: Overview of the proposed modular system.
The system is designed to provide fully open sides by transfer of loads through the
longitudinal edge beams (Rivet-Fastened RHFCB) to the corner posts (SHS). This
allows designers to take advantage of the wider open spaces that the fully open-sided
modules provide. It is intended that the proposed modules will be be placed side by
154
side to create larger open plan spaces, as required in hospitals, schools, open settings
and alike. The internal skeleton arrangement of the proposed modular building system
is presented in Figure 5-2.
Figure 5-2: Isometric view of the internal skeleton arrangement of the modular system.
The corner posts provide the compression resistance and are typically 100 x 100 x 10
SHS members. The Rivet-Fastened RHFCB is employed as the edge beams which are
connected to the corner posts by fin plates that provide nominal bending resistance.
Shallower Rivet-Fastened RHFCB are employed as the joist members in the roof and
floor systems. The Rivet-Fastened RHFCB is employed widely throughout this system
and further discussion for this design selection is presented in Section 5.4.2.
The roof and floor system configurations are presented in Sections 5.4.4 and 5.4.5,
respectively. Their optimum designs are developed based on studies conducted by
Baleshan and Mahendran (2017).
Several wall system configurations are presented in Section 5.4.6. Selection of the final
wall system is dependent on the requirements of each specific module’s given location,
placement and loading conditions.
This conceptual design also presents several bracing systems. Details of these bracing
systems are presented in Section 5.5.
155 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
5.4.2 Application of the Rivet-Fastened RHFCB
The Rivet-Fastened RHFCB is used extensively throughout the system. The Rivet-
Fastened RHFCBs are not only cost effective, but also of comparable strength as
flexural members as Siahaan et al. (2017) found. Rivet-Fastened RHFCBs are on
average 40 to 50% lighter than traditional hot rolled structural steel beams of
equivalent structural performance. It is an ideal hollow flange flexural member that
can be used as the floor joist and bearer in LSF ceiling, floor and wall arrangements of
MBSs due to its significantly lighter weight. In addition, the Rivet-Fastened RHFCB
possesses a flexible design that allows the designer to select various combinations of
web and flange widths and thicknesses to suit the required applications.
Siahaan et al. (2017) recommended 100mm rivet spacing for Rivet-Fastened RHFCBs
based on their section moment capacity studies. They found a reduction of 10-15%
when using 100mm rivet spacing. The mono-symmetric section of the Rivet-Fastened
RHFCB is preferred by the industry as it can provide a greater number of connection
types. Rivet-Fastened RHFCBs can also be lifted and carried like structural timber
beam sections. Rivet-Fastened RHFCB can be cut, nailed, screwed and drilled on site
where necessary.
In various applications, connectivity between fire protective composite panels are
significantly improved when using Rivet-Fastened RHFCB instead of conventional
open CFS sections. This is due to the screws penetrating through both inner and outer
flanges of Rivet-Fastened RHFCBs. This stronger connection is expected to improve
the lateral stability of LSF floor systems and delay the fall-off time of plasterboards
under fire conditions consequently improving the fire rating of LSF floor systems.
Rivet-Fastened RHFCBs deliver a higher and more efficient structural performance in
terms of load bearing capacity, bending moment capacity and deflection from the
available steel. It is for this reason that they are incorporated into the following
proposed design.
5.4.3 Module Chassis
The module’s chassis bears the grunt of the loading. The proposed framework/chassis
of the module is formed from CFS members that include: Square Hollow Section
(SHS) columns and Rivet-Fastened RHFCBs edge beams that are bolted together
through welded fin plate connections stemming from the corner posts. The
156
arrangement of the module chassis members is shown in Figure 5-3. Details of the
structural components of the module chassis are presented in Table 5-1.
Figure 5-3: Isometric view of the arrangement of module chassis members.
Table 5-1: Details of the internal skeleton members of the module.
Module Chassis Structural
Component
Section Profile
Corner Post SHS 100x100x10
Edge Beam (Floor) Rivet-Fastened RHFCB 250x75x25x3x3
Edge Beam (Roof) Rivet-Fastened RHFCB 200x75x25x3x3
Connection 1 Connection B – Welded Fin Plate
5.4.4 Roof System
The roof system employs the Rivet-Fastened RHFCB in two applications; they are
employed as the joists and edge beam members. The roof joists are connected to the
larger roof edge beams via a single angle cleat connection (Connection A, see Section
5.4.7). The connection consists of an angle-shaped flat plate with a total of four bolt
holes to attach to the members (two bolts for each member).
On the top and bottom flanges of the edge beam, an inner and outer shell exists in the
form of a thin steel sheet (0.55mm). Attached to the inner shell are two layers of
gypsum plasterboard (16mm each) connected via roof screws and providing advanced
fire protective measures. Sitting on top of the outer shell is a layer of plywood (16 mm)
connected via roof screws as well.
157 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
A section view of the roof system is presented in Figure 5-4. Internal section views of
the roof system are presented in Figure 5-5 and Figure 5-6. The side view of the roof
system is presented in Figure 5-7 . Details of the roof system profile is presented in
Table 5-2.
Figure 5-4: Section view of the roof system.
Figure 5-5: Internal section view of the roof system from the outside the module.
158
Figure 5-6: Internal section view of the roof system from the inside of the module.
Figure 5-7: Side view of the roof system.
Table 5-2: Details of the roof system profile.
Roof Structural Component Section Profile
Edge Beam Rivet-Fastened RHFCB
200x75x25x3x3
Roof Joist Rivet-Fastened RHFCB
150x60x20x2x2
Internal Shell Steel sheet 0.55mm
Internal Roof Lining (Ceiling) 2x Layers of Gypsum Plasterboard 16mm (each)
External Shell Steel Sheet 0.55mm
External Roof Lining Plywood 16mm
Connection 1 Connection A – Single Angle Cleat
Connection 2 Connection B – Welded Fin Plate
Connection 3 Roof Screws
159 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
5.4.5 Floor System
Edge beams in the form of Rivet-Fastened RHFCB encircle the floor system. These
beams are connected to the corner posts via a welded fin plate connection (Connection
B, see Section 5.4.7). The edge beams act as the main floor load bearing members and
effectively transfer their loads to the corner posts.
Within the extents of the floor’s edge beams, floor joists are slotted in between and
provide the capacity to support the floor. These floor joists are smaller Rivet-Fastened
RHFCBs that are connected to the larger edge beams via a single angle cleat
connection (Connection A, see Section 5.4.7).
Upon the edge beams, a steel sheet underlies the plywood flooring as depicted in
Figure 5-11. The plywood flooring is connected to the floor joists by using nails.
Beneath the floor joists a second steel sheet followed by two layers of gypsum
plasterboards complete the floor system. The steel sheet and gypsum plasterboards are
connected to the floor joists using nails. Gypsum plasterboard is chosen as it provides
substantial fire performance ratings.
A section view of the floor system is presented in Figure 5-8. Internal section views of
the floor system are presented in Figure 5-9 and Figure 5-10. A side view of the floor
system is presented in Figure 5-11. Details of the floor system profile is presented in
Table 5-3.
Figure 5-8: Section viewof the floor system.
160
Figure 5-9: Internal section view of the floor system from the outisde of the module.
Figure 5-10: Internal section view of the floor system from the inside of the module.
Figure 5-11: Side view of the floor system.
161 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Table 5-3: Details of the floor system profile.
Floor Structural Component Section Profile
Edge Beam Rivet-Fastened RHFCB
250x75x25x3x3
Floor Joist Rivet-Fastened RHFCB
200x60x20x2x2
Internal Shell Steel sheet 0.55mm
Internal Floor Lining (Flooring) Plywood 16mm
External Shell Steel Sheet 0.55mm
External Floor Lining 2x Layers of Gypsum Plasterboard 16mm (each)
Connection 1 Connection A – Single Angle Cleat
Connection 2 Connection B – Welded Fin Plate
Connection 3 Floor Screws
5.4.6 Wall System
Several wall system designs are presented in this section. As this is only a conceptual
design, these wall systems have been selected to highlight the many benefits they have
over a standard wall system. It is recommended that these wall systems be further
studied to determine their complete behaviour characteristics.
Wall System 1: Stiffened Channel Section Double Board Wall System
Wall System 1 is the stiffened channel section double board wall system. This system
is based on the standard LSF wall system with the addition of innovative measures
including the stiffened channel section for the wall studs and a double layer of gypsum
plasterboard on each side of the frame. Dias et al. (2017) showed that the stiffened
channel section is as structurally efficient as the LSB but also a more economical
alternative due to eliminating the need for welding and thereby reducing fabrication
costs. In addition, Dias et al. (2017) also showed that the stiffened channel section is
equivalent to the LSB in terms of fire resistance performance.
Wall System 1 is a simple wall frame bounded by an internal and external shell as well
as lining. A top and bottom wall track with the profile of a standard channel section
holds together the wall studs with the profile of stiffened channel sections. Enclosing
this assembly are two layers of gypsum plasterboard on each side (internal and
external) of the wall frame.
Screw connections are used to fix the floor wall track to the wall studs, and to fix the
roof wall track with the wall studs. The screw connections are a simple and effective
connection that is also easy to assemble and disassemble. In addition, the screw
162
connections allow the wall studs to expand from thermal expansion without unduly
stress. Details of the conventional wall system frame is presented in Table 5-4. An
isometric and section view of the Wall System 1 is presented in Figure 5-12 and Figure
5-13 respectively.
Table 5-4: Details of Wall System 1.
Wall Structural Component Section Profile
Wall Stud Stiffened Channel Section
Wall Track (Top) CFS Channel Section
Wall Track (Bottom) CFS Channel Section
Wall Lining (Internal) 2x Layers of Gypsum Plasterboard 16mm (each)
Wall Lining (External) 2x Layers of Gypsum Plasterboard 16mm (each)
Connection Wall Screws
Figure 5-12: Isometric view of the conventional wall system frame.
Figure 5-13: Section view of the conventional wall system connected to the module chasiss.
163 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Wall System 2: Wall System with Discontinuous Cavity Insulation
Wall System 2 (initially presented in Chapter 4) employs a discontinuous cavity
insulation arrangement. Stiffened Channel Sections form the wall stud members and
standard Channel Sections form the wall track member. A double layer of gypsum
plasterboard is attached to each side of the frame via screw connections. Rockwool
(acting as the insulation material) is inserted in the internal cavities of the system in a
discontinuous configuration with voids left adjacent to both sides of the wall studs.
These voids aid to simulate uniform temperature distribution on the steel wall studs
that improve fire performance as discussed in Chapter 4.
Details of Wall System 2 are presented in Table 5-5, and overview, detailed view and
section view presented in Figure 5-14, Figure 5-15, Figure 5-16 respectively.
Table 5-5: Details of Wall System 2.
Wall Structural Component Section Profile
Wall Stud Stiffened Channel Section
Wall Track (Bottom) Channel Section
Wall Track (Top) Channel Section
Internal Wall Lining 2x Layers of Gypsum Plasterboard 16mm (each)
External Wall Lining 2x Layers of Gypsum Plasterboard 16mm (each)
Insulation Rockwool
Connection Wall Screws
Figure 5-14: Overview of Wall System 2.
Figure 5-15: Detailed view of Wall System2.
164
Figure 5-16: Section view of Wall System 2.
Wall System 3: Wall System with Discontinuous Cavity Insulation and Back-
Blocking Board
Wall System 3 (initially presented in Chapter 4) adopts a similar arrangement to Wall
System 2. Stiffened Channel Sections are used as the wall studs and standard Channel
Sections as the wall track members. Wall System 3 also adopts a discontinuous cavity
arrangement with rockwool similar to Wall System 2. The difference between the
systems is the implementation of a back-blocking board in Wall System 3. The back-
blocking board is attached to the flange of the Stiffened Channel Sections (wall studs)
succeeded by the double layer of Gypsum Plasterboard. All three layers of plasterboard
are attached to each flange (top and bottom) of the wall studs using screw connections.
Details of the components found in Wall System 3 are presented in Table 5-6. A
overview, detailed view and section view of Wall System 3 is presented in Figure 5-19,
Figure 5-17 and Figure 5-18 respectively.
Wall Structural Component Section Profile
Wall Stud Stiffened Channel Section
Wall Track (Bottom) Channel Section
Wall Track (Top) Channel Section
Internal Wall Lining 2x Layers of Gypsum Plasterboard 16mm (each)
External Wall Lining 2x Layers of Gypsum Plasterboard 16mm (each)
Back Blocking Board Gypsum Plasterboard 16mm
Insulation Rockwool
Connection Wall Screws
Table 5-6: Details of Wall System 3.
165 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 5-17: Overview of Wall System 3.
Figure 5-18: Detailed view of Wall System 3.
Figure 5-19: Section view of Wall System 3.
Wall System 4: Walls with Double Skin Steel Panels
Wall System 4 is an adaption of the Double Skin Steel Panel Wall System initially
presented in Chapter 3. Hong et al. (2011) showed that the lateral load capacity of a
bare frame module can be increased by up to four folds by implementing their panel
configuration. Their panel configuration has been built upon and improved here.
166
Wall System 4 consists of Stiffened Channel Sections as the wall studs effectively
replacing the corrugated steel sheet seen in the works of Hong et al. (2011). The
stiffened channel sections are bordered by thin steel sheets that are connected via
screws. By employing screw connections over soldered connections, the assembly
times of these steel panels are expected to shorten. These panels are slotted between
wall tracks that have been implemented into the chassis.
The steel panels are arranged in intermediate spacing intervals as shown in Figure
5-22. An overview and section view of Wall System 4 is presented in Figure 5-20 and
Figure 5-21 respectively. Details of the components found in Wall System 4 are
presented in Table 5-6.
Table 5-7: Details of Wall System 4.
Wall Structural Component Section Profile
Wall Stud Stiffened Channel Section
Wall Track (Bottom) Channel Section
Wall Track (Top) Channel Section
Internal Wall Lining Steel Sheet
External Wall Lining Steel Sheet
Connection Wall Screws
Figure 5-20: Overview of Wall System 4.
Figure 5-21: Section view of Wall System 4.
167 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Figure 5-22: Isometric view of the double skin steel panels within the frame of a module.
5.4.7 Connections
Connections are critical in the design of modular structures as they determine the load
paths that distribute the forces applied to the structure. The designer must consider
several aspects specific to MBSs when developing the connections of a modular
system. These are:
• Robustness of the structure, specifically discontinuities and load paths;
• Ease of assembly on site and in the manufacturing facility; and,
• Disassembly potential for reuse, recycle and sustainability opportunities.
The following sections present the connections chosen for employment in the proposed
modular building system. Note, Module-to-module connections are omitted from this
study as the interaction behaviour between modules become complex when modules
are arranged together to form a building.
Connection A: Single Angle Cleat Connection
Connection A is a single angle cleat that attaches the joists to the edge beams together
via two bolts. This simple connection has bolt holes that have been modified to
mitigate tolerance issues. Connection A is seen in Figure 5-23 and Figure 5-24.
Joist to Edge Beam Interface
The joists carry the loading from its application (floor or roof) and transfers them to
their respective edge beams. The Rivet-Fastened RHFCB is of advantage in this
168
application as it allows the floor and roof greater bearing capacity, bending moment
and deflection. It also provides a light-weight options which results in higher structural
efficiency. The joists are connected to the edge beams via a single angle cleat. The
floor joists to floor edge beam interface is presented in Figure 5-23, and the roof joists
to roof edge beam interface is presented in Figure 5-24.
Figure 5-23: Floor joists to floor edge beam interface.
Figure 5-24: Roof joists to roof edge beam interface.
Connection B: Welded Fin Plate Connection
Connection B is a welded fin plate connection that is assembled in the factory during
the assembly of the modules. The welded fin plate is welded to the corner posts and
connected to the edge beams via either two (roof) or three (floor) bolts. The bolt holes
have been modified to mitigate tolerance issues. The edge beams transfer their loads
to the corner posts which transfer the loads to the ground. Connection B is seen in
Figure 5-25 and Figure 5-26.
Edge Beam to Corner Post Interface
The edge beams transfer the loads on its application (floor or roof) to the corner posts
that effectively transfer these loads to the ground. The edge beams are attached to the
169 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
corner posts using a welded fin plate connection (Connection B). The welded fin plate
is welded to the corner posts and the edge beam is attached to the fin plate via two
bolts. The roof edge bam to corner post interface is seen in Figure 5-25.
Figure 5-25: Isometric view of the roof edge beam to corner post interface.
Figure 5-26: Isometric view of the floor edge beam to corner post interface.
Connection C: Screw Connection 1
Connection C (seen in Figure 5-27) is a simple screw connection seen in the connection
of the floor and roof level wall tracks to wall studs. Incorporating a secured screw
connection to the top and bottom of the wall studs fixes the members in place. The
screw penetrates through the flanges of the wall track and into the flange of the wall
stud. The simplicity of the screw connection allows the members to easily be
disassembled and reused improving the sustainability of the proposed modular
structure.
170
Figure 5-27 Isometric view of the wall system illustrating Connection C.
Connection D: Screw Connection 2
Connection D (seen in Figure 5-28) is also a simple screw connection, though it is seen
where linings (steel sheet, plywood and/or gypsum plasterboard) are attached to the
rivet-fastened RHFCB. This connection deviates from the Connection C: Screw
Connection 1, by which the screws penetrate both the inner and outer flanges of the
Rivet-Fastened RHFCB. In doing so, it is expected that the connectivity and lateral
stability of the roof, floor and roof sections are improved.
Figure 5-28: Side view of the Floor System illustrating Connection D.
5.5 MULTI-STOREY CONFIGURATIONS
Without an external lateral load resisting system, the proposed module presented
earlier in this chapter is only suitable for application in multi-storey structures up to
three stories. Inevitably, due to lateral loading conditions a dedicated lateral loading
system must be adopted to achieve greater heights. This section presents the system
171 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
configurations proposed for when constructing structures greater than three stories.
Note, only brief discussions about the proposed multi-storey configurations are
presented with further investigation of these systems recommended.
It is proposed that an integrated lateral load resisting system is adopted. The integrated
system is comprised of the combined actions of the individual module bracing systems
working together with a central/overall tower bracing system and the individual
actions of the module-to-modulae connections. The central tower bracing system may
be in the form of a concrete or steel core or exoskeleton bracing system. The combined
actions of the individual modual bracing systems have the potential to minimize the
effective lateral loading on the central tower bracing system. The following sections
briefly discuss two concepts for individual module bracing systems. Further
investigation should be undertaken to fully undertand the combined actions of
individual modules in a multi-storey arrangement; doing so will allow designers to
develop modular costructed buildings of great heights.
5.5.1 Intermediate Level Module Configuration
The type of module configuration presented in Chapter 5.4 is the module configuration
for single storey applications. For multi-storey applications, a slightly different module
configuration is introduced and placed beneath the single storey module to form the
multiple storeys of the building. This module is called an intermediate module and the
single storey module can be referred to as the roof module. The intermediate modules
are subjected to a slightly different set of loading that the roof module is subjected to
and thus will slightly differ in configuration.
The intermediate modules will no longer comprise of a roof system but instead of a
top-level system. By convention, the floor systems should also be called bottom-level
systems. The top-level systems of the intermediate modules adopt the same
configurations of the roof systems seen in the roof module with the exception of the
edge beam and joists sizes. The size of the edge beam and joists of the top-level system
are now identical to their bottom-level counterparts.
5.5.2 Module Cross-Bracing System
Cross-bracing systems are a well-developed lateral load resisting technology with
application seen abundantly in the building industry. The cross-bracing system in this
proposed design is composed of thin flat steel strips arranged in a X (cross) setting
172
(see Figure 5-29) that act only in tension. The steel strips are connected to the external
faces of the corner posts, edge beams and wall studs (at intermediate intervals) of the
modules. As the steel strips are thin, they do not interfere with the assembly of the
outer linings of the module. The long walls comprise of a pair of cross bracing systems
and the end walls comprise of a single cross bracing system. M. Lawson, Ogden, and
Bergin (2012) recommends that a modular structure of 4-6 stories can be achieved
when utilising cross-bracing systems and without a central tower bracing system. For
high loading, the width and grade of the steel strips can be increased.
Figure 5-29: Cross bracing multi-storey configuration (left – side view, middle – front view,
right – isometric view).
5.5.3 Double Skin Steel Panel System
The effectiveness of employing the double skin steel panel system for multi-storey
configurations was originally introduced in Chapter 3. A hypothesised improved
alternative to the original design was presented in Section 5.4.6 as Wall System 4. The
panel system comprises of wall studs in the form of stiffened channel sections bordered
by an internal and external layer of thin steel sheeting. The panels are inserted at
intermediate spacing intervals in the bare frame of a steel module. For the long walls
173 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
a pair of the panel systems is inserted and for the end walls a single panel system is
inserted. The arrangement of double skin steel panels is presented in Figure 5-30.
Figure 5-30: Double skin steel panel multi-storey configuration (left – side view, middle – front
view, right – isometric view).
5.5.4 Module-to-Module Connections
Module-to-module connections have been omitted from this study. Their behaviour
becomes complex as they must account for the interactions of module-to-modules and
the elements within the modules.
5.6 CONCLUSION
This section has presented the conceptual design of the proposed modular building
system. The complete framework of a module is presented and further dissected into
individual systems for discussion as the: chassis, floor system, roof system, wall
system and connections. Several designs of the wall system are presented. The
proposed design is suited to single storey configurations with multi-storey
configurations briefly discussed. Finalisation of the conceptual design would require
further analysis of the structural loading requirements.
174
Chapter 6: Conclusions
6.1 CONCLUSIONS
The modular construction method and modular building systems are construction
technologies capable of delivering results superior to traditional construction means.
The potential benefits of this technology over traditional means include time, costs and
waste savings. These benefits are made possible by the streamlined, systematic and
assembly line-like production of the modules used to form the buildings. In addition,
modular construction allows multiple construction phases to be completed
simultaneously and not be dependent on each other. These capabilities are yet to be
fully realised due to several shortcomings and drawbacks in the technology’s infant
development. Examination of real-life projects and case studies have revealed the
shortcomings to be: poor structural efficiency (strength-to-weight ratio) of the MBS
designs, lack of construction tolerance control, impractical to construct designs, and
lack of fire resisting measures. This thesis sought to address these shortcomings by
conducting series of studies to further the understanding of modular construction and
proposing solutions to the shortcomings. A brief summary of these studies are
presented below; further details of these works follow in later sub-sections.
A literature review was performed to establish the background and current
understanding of MBSs. Cold-formed steel and the Rivet-fastened Rectangular
Hollow Flange Channel Beam was also reviewed as it is later introduced as an
innovative solution to addressing the shortcomings of MBSs. It was found that the
Rivet-fastened RHFCB is superior in structural efficiency compared to conventional
CFS sections and other CFS sections. In addition, the section also considered easier to
produced, and thus lower in costs.
Case studies on recent modular construction projects were completed to pinpoint the
drawbacks and shortcomings of this technology and to establish the current advances
in the field. Case studies were also performed on current developing modular
technologies that seek to address the shortcomings. It was found that construction
tolerance is a major issue in some of the case studies. Most of the case studies also
lacked structurally efficient designs.
175 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
Several wall systems are developed and introduced as improved module components
that address the shortcomings of structural efficiency and fire-resisting performance.
These wall systems undergo thermal modelling to best understand their behaviour
under elevated temperatures. It was found that introduction of discontinuous cavity
insulation and backing boards contributed to improve the fire resistance rating by up
to 51%.
The innovative concepts presented throughout this study were then conglomerated and
used to develop an improved MBS module suitable for single-storey applications only.
Details of the structural components of the proposed design are presented. Finally, the
application of the module in multi-storey configurations is explored.
The study concludes with further recommendations for the proposed concepts to be
investigated before application into the real world. It is also recommended that
statutory standards specification document be developed immediately for the design
of MBSs.
6.2 LITERATURE REVIEW
This study presented a thorough literature review (Chapter 2) of cold-formed steel and
modular building systems. The following findings from the examination of cold-
formed steel are noted:
• CFS has many benefits over its HRS counterpart such as higher efficiency
in terms of strength-to-weight ratio and easier to manufacture and produce.
• Experimental studies of the Rivet-Fastened RHFCB show that the section is
structurally superior to conventional sections in respects to flexural, shear
and web crippling behaviour.
• A lack of specifications exist that appropriately address the design of
structures using the Rivet-Fastened RHFCB.
• The Rivet-Fastened RHFCB offers many benefits for utilisation in MBSs.
A thorough examination of MBSs was presented. The following findings are noted:
• The development of modular construction is still at its early stages and there
is yet to exist a statutory standards specification document for the design of
modular building systems.
176
• MBS modules can be categorised by their structural frame form. These
categories are:
o Four-sided modules;
o Partially open-sided modules;
o Corner-supported modules; and,
o Open-ended modules.
6.3 CASE STUDIES
Case studies of current industry developments including complete MBSs, wall systems
and connections specific to MBSs were presented in Chapter 3. The current advances
presently being implemented and/or studied in the modular construction field include:
• Arup’s complex steel bracing skeleton design of 461 Dean made the world
record breaking tallest modular constructed building possible.
• Irwinconsult’s hybrid use of concrete and steel materials in SOHO
Apartments to develop Australia’s tallest modular constructed building.
• Octavio and Pascual’s conceptual design kept the structural arrangement of
their MBS simple and economical for the building’s intended purpose as
student accommodation residences.
• CIMC’s patented Verbus System incorporated corner castings as
connections that had been designed based on the same corner castings seen
in ISO freight containers. This inclusion in their system maximised the
compatibility of their systems with current conventional transportation,
hoisting and lifting equipment.
The case studies were also able to pinpoint and define specific shortcomings of MBSs
in real world practice. The shortcomings include:
• 461 Dean’s design failed to appropriately address tolerance and positioning
concerns which led to extended project delivery delays.
• Although Irwinconsult developed effective techniques to minimize project
delivery time, the use of insitu concrete elements still demands a lengthy
curing time.
177 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
• Octavio and Pascual’s design incorporated welded connections which are
expensive and time costly to incorporate.
• Installation of CIMC’s Verbus System corner castings requires external
access when installing the modules on site which introduces a safety concern
for the installers.
6.4 THERMAL MODELLING OF LIGHT GAUGE STEEL FRAMED
WALL SYSTEMS PROPOSED FOR MODULAR BUILDING SYSTEMS
Chapter 4 presented a set of innovative LSF wall systems that had been developed with
advanced fire rating performances and with specific application to the later proposed
modular building system. The wall systems consisted of light-gauge steel frames
compounded by gypsum plasterboard layers in several compositions and with cavity
insulation in various arrangements. The LSF wall systems were built upon current
advances and their performance were analysed using 3D heat transfer finite element
modelling using ABAQUS.
To appropriately conduct the finite element modelling of innovative LSF walls
systems, the thermal properties of the materials in the wall systems were defined and
the method of analysis was established. The results of the analysis showed:
• Cavity insulation has a detrimental effect on the fire resistance performance
of the wall systems for a given arrangement due to the significantly lower
thermal conductivity of the insulation material.
• To improve this and to lessen the detrimental effect that cavity insulation
has on the CFS studs, innovative wall configurations were proposed using
discontinuous cavity insulation and 100 mm gypsum back-blocking boards.
• Gunalan et al. (2013) described the critical hot flange temperature of LSF
wall systems with 0.4 and 0.2 load ratios to be 500°C and 600°C,
respectively.
• Thus, hot flange FE results for Configurations 2, 3, 4 and 5 were compared
against Configuration 1 at critical hot flange temperatures. Improvement of
the fire resistance rating were 21%, 20%, 38% and 51% for critical hot
flange temperature of 500°C while they were 26%, 24%, 39% and 51% for
critical hot flange temperature of 600°C, respectively.
178
6.5 PROPOSED CONCEPTUAL DESIGN
Chapter 5 brought together the shortcomings of MBSs and relevant current
engineering advances to propose an improved and innovative modular building
system. The concept proposed is for single storey applications. The following design
details are noted:
• The proposed concept adopted a corner-supported module chassis where:
o horizontal loads are concentrated through the edge beams; and,
o vertical loads are concentrated through the columns.
• Light-weight and structurally efficient rivet-fastened RHFCBs formed the
edge beams of the module chassis while SHS formed the corner posts.
• Floor and roof system concepts were proposed employing the rivet-fastened
RHFCB as the joist members.
• Several wall system configurations were proposed for incorporation into the
conceptual module design.
• The wall systems act as the main lateral bracing elements.
• Simple connections were adopted throughout the module where the basis of
selection was to minimize the efforts and costs of assembly.
• The Rivet-Fastened RHFCB was used widely throughout the system for its
structurally efficient (weight-to-strength ratio) and ease of manufacturing
qualities.
• Gypsum plasterboard was used widely throughout the system for its
significant fire performance qualities.
• Bolted connections were used for all large (high load bearing) section-to-
section connections for its simple and ease of assembly qualities.
A brief proposal of design concepts to address multi-storey configurations followed.
Chapter 5 concluded with the need to further investigate the proposed conceptual
design before implementation into real world practice.
179 Development of Modular Building Systems Made of Innovative Steel Sections and Wall Configurations
6.6 RECOMMENDATIONS AND FUTURE RESEARCH
There is yet to exist a statutory standards specification document for the design of
MBSs. This lack of specifications is likely to leave designers weary of employing
modular construction methods in their projects and thus, is not favourable for
increasing the market share for modular construction. It is recommended that a
statutory standards specification document for MBSs is developed immediately to help
improve the popularity of the modular construction method.
Few studies on the structural behaviour of MBSs currently exist. The need to
understand the structural behaviours of MBSs is great, especially with regards to the
structural behaviours of individual modules and their interactions as a collective
assembly. It is recommended that further investigation of the following structural
aspects are investigated:
• Structural interaction and behaviour of multi-storey modular building
systems – minimal knowledge is understood about the complex behaviour
between the individual modules.
• Fire performance of modular building systems made of steel sections – as
highlighted in the Grenfell Tower Fire incident, fire safety of steel structures
is of utmost importance.
• Development of innovative connections for modular building systems – the
connections of modular building systems heavily influence the structural
behaviour and constructability of the systems.
• Development of advanced corner supported modular building systems –
there exists a great desire for corner supported modular building systems
because they make possible large open space configurations.
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