1

Light Steel Framing structures for buildings

Diogo José Martins Rego Instituto Superior Técnico, Technical University of Lisbon, Lisbon, Portugal

diogomrego@gmail.com

Abstract: The structures of buildings that use the Light Steel Framing (LSF) constructive method stand out as a possible

constructive system for the future, since it effectively addresses and resolves the ecological faults existent in other

methods. One of the objectives of this dissertation was to examine, study and evaluate several parameters related to

thermal performance, acoustics, fire resistance and sustainability, because these are decisive factors when selecting a

construction method. Comparing the construction method in study with the traditional masonry and reinforced concrete

solution, it was found that the LSF method presents (i) excellent thermal performance, (ii) good acoustical performance,

(iii) excellent durability, sustainability and eco-efficiency indicators. The main objective of this thesis consisted in the

development and analysis of a structural model of a LSF building, studying the behaviour of the structure in conjunction

with the OSB siding panels and the calculation techniques related with the system, prescribed in EN1993. Modelling the

structure in SAP2000 allowed the assessment of the best techniques for computational modelling of certain structural

elements and behaviours, predominantly the diagonal straps and the diaphragm effect of OSB. It was then concluded, that

this effect should be considered in the structural model due to its influence on the seismic behaviour. Subsequently, the

critical design values were analysed in the main structural elements, in order to proceed with its design. Given the

complexity of the design process of Class 4 steel sections, this was presented concisely through flowcharts that

summarize the requirements of EN1993. Because of the extension of the obtained results, charts which summarize the

design values were developed, depending on the type of structural element and section in analysis, so that they can be

used in the future for a more efficient pre-design.

Keywords: Light Steel Framing (LSF), Oriented Strand Board (OSB), EN1993, diaphragm effect, class 4 cross sections.

1. INTRODUCTION

Nowadays, more than ever, the search for

sustainability and eco-efficiency is present in all

types of industry, and construction is no exception.

From the energy consumed in every household to

the energy used in the production of the

construction materials, everything must be taken

into account. The true challenge consists in

analysing the costs from a life cycle perspective,

more than just thinking about the initial investment.

When one can save energy and water, expand the

durability and still increase the productivity, the

sustainability characteristics of the project and the

materials are very easy to justify (Pinheiro, 2003).

Light Steel Framing, commonly termed LSF,

stands out as a possible constructive system for

the future. It effectively addresses and resolves the

ecological faults in other construction methods.

The first objective of this dissertation was to study

and evaluate several parameters related to thermal

performance, acoustics, fire resistance and

sustainability, since these are decisive factors

when selecting a construction method.

1

Assessment of Bridge Behaviour Due to the Passage of High Speed Trains

André Filipe Biscaya Semedo Pereira da Graça Instituto Superior Técnico, Technical University of Lisbon, Lisbon, Portugal

andre.biscaya@gmail.com

Abstract: The railway bridges, due to the passage of high speed trains, can suffer high resonance phenomena that cause, for example, ballast instability, endangering the railway line. Therefore, the main goal of this paper

was to develop a simplified but efficient MATLAB model able to reproduce and analyze the dynamic response of

bridges to the passage of high speed trains, in order to obtain static (bending moments, shear forces and reactions) and cinematic (accelerations, displacements and rotations) envelopes along the bridge. This methodology offers the capacity, in a short period of time, of studying a large amount of different structural solutions. Implementation took place using a continuous beam model subjected to moving point loads, which was based on the determination of the free vibration modes, generated semi-analytically, considering simple supports model, or by finite elements, using spring supports model. Thereafter, the dynamic equilibrium equation was solved, using the Newmark-β method. For different tested solutions, the suitability of acceleration peak criterion, proposed in EN1991-2, was analyzed. Furthermore, extensive parametric studies were performed, which contributed to raise the sensibility to results, particularly for continuous bridges, the less studied type. With this purpose, the influence on the bridge response of the number of internal spans and the length relationship between the external span and the internal span was investigated, generating abacus and indications of conceiving. In this study, it was only used the box type prefabricated girders. Finally, studies were accomplished about the influence of foundation deformability on vertical acceleration of bridges, which allowed determining the minimum stiffness that obligates to consider foundation deformability in models and verifying the main response differences provoked by the stiffness relationship between piers and abutments.

Keywords: high speed railway bridges, dynamic analysis, moving loads, parametric analysis, acceleration, eurocode, foundation flexibility

1. INTRODUCTION In modern societies, transports play a crucial role in economic growth and globalization, by allowing people and goods traveling. Among the other transports, High speed trains can be more competitive for distances about 100/200km and 400/600km, comparing with terrestrial and aero transportation, respectively[1]. However, with the increase of high speed trains usage, some

resonance problems were identified (e.g. ballast liquefaction due to high accelerations produced by the passage of the trains[2]), being essential to evaluate the bridge response due to their passage. The bridges safety studies should be performed through dynamic analyses that allow the determination of accelerations and displacements (required to compute static parameters). Full dynamic analyses gives more accurate results, which are important if the designer intends

2

The main goal of this work, however, lies in the

analysis of the structural performance of such

method. In order to accomplish such objective, this

thesis studied the modelling, analysis and design

of a 4-storey building using the LSF structural

system. The modelling of the structure in SAP2000

allowed the assessment of the best techniques for

computational modelling of certain structural

elements and behaviours, predominantly the

diagonal straps and the diaphragm effect of OSB.

The design procedures of the class 4 steel

sections and the consideration of the multiple

types of buckling, although very extensive and

complex, was defined and implemented to all the

necessary sections.

2. LSF SYSTEM

2.1. Wall assemblies

In order to accurately analyse the performance of

the LSF wall assemblies, it was compared to the

masonry wall system. Figure 1 and 2 display the

schemes for each one of the considered external

walls.

Figure 1 - Masonry wall scheme: 1 - plastering mortar; 2 -

masonry; 3 - air; 4 - XPS board; 5 - masonry; 6 - plastering

mortar.

Figure 2 - LSF wall scheme: 1 - plastering mortar; 2 - ETICS; 3

- OSB board; 4 - C150 steel section; 5 - mineral wool; 6 - C150

steel section; 7 - OSB board; 8 - Gypsum board.

The first characteristic that differentiates the two

types is their weight, defining the LSF solution as a

lightweight wall and the masonry as a heavy wall.

Table 1 and 2 present the calculation and result of

the weight of the two wall classes.

Table 1 – Masonry wall mass calculation.

Material Thickness Density Mass/m2

(mm) (kg/m3) (kg/m2) Plastering

Mortar 20 500 10

Masonry 110 1400 154 Air 20 - -

XPS board 40 40 1,6 Masonry 150 1400 210

Plastering Mortar 20 500 10

Total 360 385,6

Table 2 – LSF wall mass calculation.

Material Thickness Density Mass/m2

(mm) (kg/m3) (kg/m2) Gypsum board 15 1000 15

OSB board 12 700 8,4 Air 15 - -

Mineral wool 120 135 16,2 Air 15 - -

OSB board 12 700 8,4 ETICS 60 35 2,1 Total 249 50,1

As shown in the previous tables, the weight of a

masonry wall is around 7,5 times greater than the

LSF, affecting significantly the total mass of the

structure.

3

2.1.1. Thermal performance

The main objective of the external walls, combined

with the roofing, is to establish a barrier between

the external and internal environments, in such

way that the internal environment can be

maintained within certain comfort conditions. Such

walls need to meet certain demands: be stable and

durable; establish an obstacle against wind, rain,

solar radiation, heat, noise, fire, insects and even

humans. The external walls compose most of the

exterior area of the building and it is there that the

majority of the thermal exchanges occur.

Subsequently, the meticulous study of thermal

performance is fundamental to reduce the energy

consumption, making the building more

sustainable and eco-efficient (Mateus, 2004). The

thermal conductivity (λ) of each material, in

conjunction with its thickness, allowed the

calculation of the total thermal resistance and thus

the thermal conductivity of both the studied walls,

as presented in Table 3 and 4. Table 3 - Thermal resistance for common masonry wall

Material Thermal

conductivity Thickness Thermal resistance

λ (W/m °C) t (mm) R (m2 °C/W) Plastering

Mortar 1,15 20 0,02

Masonry 0,36 150 0,42 XPS board 0,033 40 1,21 Masonry 0,38 110 0,29

Plastering Mortar 1,15 20 0,02

Total - 340 1,95

Table 4 - Thermal resistance for LSF wall.

Material Thermal

conductivity Thickness Thermal resistance

λ (W/m °C) t (mm) R (m2 °C/W) ETICS 0,034 50 1,47 OSB 0,12 12 0,10

Mineral wool 0,045 120 2,67 OSB 0,12 12 0,10

Gypsum board 0,19 15 0,08 Total - 209 4,42

Thus, it is possible to conclude that masonry walls

have a thermal conductivity coefficient λ=0,51

W/m2 °C and LSF walls λ=0,23 W/m2 °C. This

substantial difference results in significant thermal

efficiency, reducing the amount of energy required

to maintain a house within the comfort zone.

Moreover, this coefficient does not take into

account the thermal bridges, which are

significantly reduced in the LSF system due to the

usage of External thermal insulation composite

system (ETICS).

2.1.2. Durability

As denoted before, the durability of the materials

used in any given construction influence the

sustainability of the project. To achieve great

performance in this matter, hot-dip galvanising

process is used, which involves dipping steel in

almost pure molten zinc.

Zinc coatings provide a barrier that prevents

oxygen, moisture and other atmospheric pollutants

from reaching the steel. Furthermore, zinc is a

reactive metal and, on exposure to the

atmosphere, a complex mixture of zinc compounds

forms readily on a galvanised surface. As many of

the products formed are partially soluble in water,

the zinc is consumed over a period of time in any

damp location. Galvanising has the advantage

that, when the encapsulation is breached (for

example at cut edges or drilled holes, or when the

zinc has been eroded away locally) significant

corrosion of the steel substrate will not necessarily

occur. This is because zinc in close proximity to

the exposed steel will still corrode preferentially,

acting as a consumable anode in an electro-

chemical cell (i.e. it protects the steel cathodically)

(Lawson et al., 2010). The normal standard has

been 275 g/m2 (i.e. a surface thickness of about 20

4

mm) designated as G275. According to studies

performed in different environments, as long as the

galvanized steel is protected by the other wall

components, its loss rate does not exceed 0,3

g/m2 per year. For G275 galvanising, it follows that

the design life is at least 230 years (Lawson et al.,

2010).

2.1.3. Sustainability

In conclusion, the sustainability and eco-efficiency

of the LSF wall assemblies can be summarized by:

• Lightweight walls, which result in savings

in the foundations, transport to site and

handling in site;

• Reduced wall thickness, providing

maximized interior area and optimizing the

transport to site;

• Superior thermal performance, boosting

the reduction of energy consumption

required to maintain comfort;

• Durable and recyclable materials, which

guarantee a greater market value in the

end of its design life.

•

3. STRUCTURAL MODELING

In order to evaluate the structural performance of

the Light Steel Framing system, 3 computational

models were created and subjected to numerical

analysis within SAP2000. The models differ in

bracing system (considering, or not, the diaphragm

effect of the OSB boards) and beam support

condition (continuous or simply supported).

3.1. Architectural conception

The model was based in a 4-storey residential

building with an implementation area of 225 m2, as

shown in Figure 3.

Table 5 summarizes the characteristics of the

analysed models according to the aforementioned

objectives. Table 5 - Models characteristics.

Model Considering

OSB

Studs

spacing

Support

condition

#1 No 0,60 m Simply

supported

#2 No 0,60 m Continuous

#3 Yes 0,60 m Continuous

QUARTO QUARTOW.C.

SALA

COZINHA

SALASALA

SALA

QUARTO QUARTO

QUARTOQUARTOQUARTOQUARTO

W.C.

W.C.W.C.

COZINHA COZINHA

COZINHA

HALL

SOBE

JARDIMJARDIM

SOBE

A.S. A.S.

A.S. A.S.

9.4002.000

9.400

3.500

2.475

2.475

3.500 4.650

1.325

1.325

4.650

1.200

5.450 2.750 2.000 2.750 5.450

1.200

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Figure 3 - Architectural floor plans (dimensions in meters).

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3.2. Floors

Using the Releases option of SAP2000 the beams

where modelled to the abovementioned support

conditions. This allowed studying the bending

moment distribution that, depending on the length

limitation of the steel profiles, can help determine

the optimized and economic solution. Figure 1 and

2 show the floor model achieved in SAP2000, for

the simply supported beams and continuous

beams, respectively.

Figure 4 - Simply supported beams floor (left) and Continuously

supported beams floor (right)

3.3. Walls

3.3.1. Studs and diagonal straps

Both the studs and the diagonal straps were

considered simply supported elements, having no

moment restraint in both ends. Since the diagonal

straps are tension only members, but the Tension /

Compression limits defined in SAP2000 work

exclusively in non-linear analysis (implying

pushover analysis for seismic evaluation, which

was beyond this thesis scope), a different

approach was adopted. Only half the elements

were modelled (see Figure 5), that is, instead of

two diagonal straps for each braced frame, only

one diagonal strap was placed, because it works

equally in tension and compression, thus

reproducing its real rigidity.

Figure 5 - Modeling of X-bracing diagonals.

3.3.2. Diaphragm effect modelling

In order to correctly model the diaphragm effect of

the Oriented Strand Board (OSB) boards, two

different experimental tests were studied and used

to calibrate the design. Both studies used 12 mm

OSB panels and fasteners spaced 15 cm apart

along the board edge and 30 cm along the

intermediate studs. The first shear wall, tested by

AISI (AISI, 1997), was 2,44 x 12,2 m (as shown in

Figure 6) and was studied with different types of

openings, although the test used to calibrate the

model had no openings (Wall 1 in Figure 6).

Figure 6 - OSB panel test configuration (AISI, 1997)

The results, presented in Figure 7, display

pronounced rigidity and a linear behaviour in the

initial phase of the test.

Figure 7 - Force/displacement chart (AISI, 1997)

Similarly, the test performed by Tian (Tian et al.,

2004), which used a 2,45 x 1,25 m panel (as

INOVAÇÕES TECNOLÓGICAS 75

12,2m, com fechamento em placas de OSB de 12mm fixadas com parafusos espaçados a

cada 10 centímetros no perímetro externo das placas e a cada 20 centímetros nos apoios das

placas com os montantes intermediários em uma das faces e fechamento em gesso

acartonado na face oposta. A FIG. 3.10 apresenta as configurações geométricas dos painéis

ensaiados.

FIGURA 3.10 – Configurações dos painéis ensaiados AISI (1997)

Em tal trabalho são avaliadas diferentes configurações dos painéis, com diferentes relações

entre aberturas. A carga lateral foi aplicada aos painéis por meio de atuadores hidráulicos

posicionados no canto direito superior dos painéis. Os deslocamentos foram obtidos por

meio da instalação de três transdutores de deslocamento (DTs). Um para medir o

deslocamento do topo dos painéis, um segundo para medir o deslocamento no topo da guia

9

Three linear variable differential transformers (LVDT) were used to measure thedisplacement of the specimens during the test. LVDT #1 measured the horizontaldisplacement of the top of the wall. LVDT #2 measured the horizontal displacement, or slip,of the bottom track of the specimen. LVDT #3 was used to measure the uplift of the endstuds relative to the foundation.

All tests were one directional, displacing the top of the wall to a maximum of six inches over aten minute period. Data from the load cell and 3 LVDTs were collected 1 time per second.Each of the four wall configurations was tested once. Items of interest are ultimate shearload capacity, stiffness, and failure modes of the walls. Load-displacement curves wereplotted for each of the wall specimens to better understand and compare the behavior of thewalls during the test.

RESULTS

Force-Displacement Response

The response of all shear wall specimens to the monotonic loading history are shown in theforce-displacement curves of Figure 4. Initial response to load was linear and wascharacterized by large stiffness. The peak load, as well as the corresponding displacement,was gathered directly from the data. These loads and displacements are listed in Table 3.The equation developed by Sugiyama and Matsumoto conservatively predicts the ultimatecapacity of the steel-framed specimens (Figure 5). Figure 5 suggests the relation betweensheathing area ratio and peak load more closely follows the equation F = r/(2-r) for thesheathing area ratios tested. Additional testing should be conducted to confirm this finding.

FIGURE 4Force-Displacement Response

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

0.0 1.0 2.0 3.0 4.0 5.0 6.0Interstory Drift (in.)

Load

(lbs

)

WALL 1

WALL 2A

WALL 4WALL 2B

6

shown in Figure 8), generated a

force/displacement chart (shown in Figure 9). The

studied panel (A-2) corresponds to the OSB-3

steps curve.

Figure 8 - OSB panel test configuration (Tian et al., 2004)

Figure 9 - Force/displacement chart (Tian et al., 2004)

Because the studs have almost no influence in the

shear resistance of the walls, they were omitted

from the model. Based on a shell element with a

15 cm mesh (spacing of the fasteners), the effect

of the fasteners on the panel was simulated by

restraining the rotation around X and Z, and the

displacement in Y in every node that corresponded

to a fastener, as shown in Figure 10.

Figure 10 - Models for AISI test (left) and for Tian test (right)

Using the abovementioned charts and this two

SAP2000 models, it was concluded that the latter

represented the structural behaviour of the panels

in the linear phase. Therefore, all the OSB panels

with no openings considered in the building can be

regarded as shear walls and divided in 4

configurations, as presented in Figure 11.

Figure 11 - Panels considered in the structure.

Two similar methods were used to simulate the

panels’ rigidity, both leading to the same results.

The first method consisted of using an equivalent

diagonal of OSB (Smith, 1966), whereas the

second used steel (Inoue, 2004). Being R the

tension force of a given diagonal due to a

horizontal force on the top of the panel, d the

length of such diagonal, Ea the elasticity modulus

of steel and Δd the length variation of the diagonal,

the area of the equivalent steel rod (A) is given by:

𝐴 =  

𝑅.𝑑𝐸! .∆𝑑

(1)

Applying such logic to the 4 panels considered, the

equivalent diameter is as shown in Table 6. Table 6 - Equivalent diameter calculation summary.

Panel type

H L R d Δd D (m) (m) (kN) (mm) (mm) (mm)

1 2,8 1,2 2,54 3046,3 0,21 15,1 2 2,8 1,8 1,85 3328,7 0,15 15,9 3 2,8 2,4 1,54 3687,8 0,12 17,0 4 2,8 3,0 1,37 4103,7 0,10 18,4

+0,8

-1,2

-0,8

-0,5

-1,2

-0,8

Vento 90º

DA

B

A

B

E

Panel 1 - 1,2m x 2,8m

Panel 2 - 1,8m x 2,8m

Panel 3 - 2,4m x 2,8m

Panel 4 - 3,0m x 2,8m

Caption:

1

A

2

4

6

7

B C D E

3

5

Panel 1 - 1,2m x 2,8m

Panel 2 - 1,8m x 2,8m

Panel 3 - 2,4m x 2,8m

Panel 4 - 3,0m x 2,8m

Caption:

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3.4. Behaviour factor

This building was to be placed in Lisbon in a type

C soil. The definition of the behaviour factor for

LSF buildings is not clear in the EN1998. The

structure can be classified as a frame with

concentric diagonal bracings (dissipative zones in

tension diagonals only), when neglecting the OSB

panels, or as a frame with concentric V-bracings

(dissipative zones in tension and compression

diagonals) when considering the OSB panels’

rigidity, as show in Figure 12. In this dissertation,

since the OSB panels were to be considered, the

behavior factor prescribed in the EN1998 is q=2,0.

Figure 12 - Frames with: tension diagonals only (left) and

tension and compression diagonals (right)

4. STRUCTURAL ANALYSIS

4.1. Seismic analysis

The consideration of the OSB panels increases the

rigidity of the building thus reducing the

fundamental period the seismic and increasing the

design acceleration. For this reason, the

consideration of the diaphragm effect of the OSB

panels should not be ignored due to its influence

on the seismic performance of the building.

Moreover, if the OSB panels and the diagonal steel

straps are not coincident, the seismic behaviour of

the building can be even more influenced.

4.2. Design forces and displacements

The studs were analysed in two distinct parts, the

studs that only support the vertical loads (Stud

type 1) and the studs that constitute the bracing

system (Stud type 2). The most critical

combination to the latter was, as expected, the

fundamental combination with the imposed load as

leading variable. As the beam supporting

conditions were also analysed, it was also possible

to check how it influences the axial compression

force distribution. As expected, the axial

compression forces in the simply supported model

were more uniform, whereas the continuously

supported model presented higher values in the

interior supporting panels. On the other hand, the

continuously supported joists presented a more

even design moment, also as expected, as shown

in Table 7.

Table 7 - Joists design moments.

Support condition Alignment MEd+ MEd-

(kNm) (kNm)

Continuous A 1-2 and 6-7 5,0 - B 1-7 3,9 3,5 D 1-7 7,7 6,6

Simply supported

A 1-2 and 6-7 5,8 -

B 1-2 and 6-7 5,6 - 2-4 and 4-6 2,4 -

D 1-3 and 5-7 10,8 - 3-5 - -1,6

For the studs that comprised the shear wall

systems, the critical combination was the type 1

seismic action, which was predicted by the seismic

analysis of the fundamental period. The critical

design values for studs and the correspondent

storey drifts are presented in Table 8.

Table 8 - Critical design values for studs.

Stud type

OSB consideration

Axial dr,x dr,y Load combination (kN) (mm) (mm)

1 Yes 51,4 1,0 0,0 ULS -

imposed loading No 51,4 1,9 0,0

2 Yes 118,8 1,4 6,8 Type 1

seismic action No 115,1 7,7 2,9

,PSUHVVÔR�GH�

�,3

NP EN 1998-1 2010

p. 128 de 230

− contraventamentos diagonais nos quais a resistência às forças horizontais é exclusivamente assegurada pelas diagonais traccionadas, desprezando-se a contribuição das diagonais comprimidas;

− contraventamentos em V, nos quais a resistência às forças horizontais pode ser assegurada quer pelas diagonais traccionadas quer pelas comprimidas. O ponto de intersecção destas diagonais localiza-se num elemento horizontal que deve ser contínuo.

Não poderão ser utilizados contraventamentos em K, nos quais a intersecção das diagonais se localiza numa coluna (ver a Figura 6.9). (4) Para pórticos com contraventamentos excêntricos deverão utilizar-se configurações que garantem que todos os ligadores serão activos, como representado na Figura 6.4. (5) As estruturas em pêndulo invertido poderão considerar-se como sendo pórticos simples desde que a estrutura resistente aos sismos tenha mais do que uma coluna em cada plano resistente e que a condição de limitação do esforço normal: NEd < 0,3 Npl,Rd seja satisfeita em cada coluna.

a) b) c)

Figura 6.1 – Pórticos simples (zonas dissipativas nas vigas e na base das colunas). Valores por defeito para αu/α1 (ver 6.3.2(3) e o Quadro 6.2)

Figura 6.2 – Pórticos com contraventamentos diagonais centrados (zonas dissipativas unicamente nas diagonais traccionadas)

Figura 6.3 – Pórticos com contraventamentos em V centrados (zonas dissipativas nas diagonais traccionadas e comprimidas)

NP EN 1998-1 2010

p. 128 de 230

− contraventamentos diagonais nos quais a resistência às forças horizontais é exclusivamente assegurada pelas diagonais traccionadas, desprezando-se a contribuição das diagonais comprimidas;

− contraventamentos em V, nos quais a resistência às forças horizontais pode ser assegurada quer pelas diagonais traccionadas quer pelas comprimidas. O ponto de intersecção destas diagonais localiza-se num elemento horizontal que deve ser contínuo.

Não poderão ser utilizados contraventamentos em K, nos quais a intersecção das diagonais se localiza numa coluna (ver a Figura 6.9). (4) Para pórticos com contraventamentos excêntricos deverão utilizar-se configurações que garantem que todos os ligadores serão activos, como representado na Figura 6.4. (5) As estruturas em pêndulo invertido poderão considerar-se como sendo pórticos simples desde que a estrutura resistente aos sismos tenha mais do que uma coluna em cada plano resistente e que a condição de limitação do esforço normal: NEd < 0,3 Npl,Rd seja satisfeita em cada coluna.

a) b) c)

Figura 6.1 – Pórticos simples (zonas dissipativas nas vigas e na base das colunas). Valores por defeito para αu/α1 (ver 6.3.2(3) e o Quadro 6.2)

Figura 6.2 – Pórticos com contraventamentos diagonais centrados (zonas dissipativas unicamente nas diagonais traccionadas)

Figura 6.3 – Pórticos com contraventamentos em V centrados (zonas dissipativas nas diagonais traccionadas e comprimidas)

8

Since the OSB panels and the diagonal steel

straps are all part of the bracing system, the critical

combination for its design was also the type 1

seismic action, as presented in Table 9.

Table 9 - Critical design values for steel straps and OSB

equivalent diagonals

Panel type

OSB consideration

Steel strap OSB diagonal

(kN) (kN) 1

Yes

17,3 12,9 2 10,7 10,9 3 16,2 14,0 4 34,3 26,7 1

No

25,0 - 2 20,9 - 3 28,8 - 4 50,1 -

The two types of connections studied were the

steel - steel connection and the steel - OSB

connection. Fort the first one, one analysed the link

between the straps and the studs, given its

importance in the structural behaviour. However,

the design value for each fastener depends on its

quantity and spacing, consequently, the design

values can be obtained by the ones presented in

Table 9. Secondly, the link between the OSB

panels and the studs was studied. Similarly to the

previous elements, the critical combination was

seismic type 1 and, as the fastener spacing was

previously defined as 15 cm in the OSB board

edge, the critical design values are presented in

Table 10.

Table 10 - Fastener design value for steel - OSB connections.

Panel type FH Fv,Ed

(kN) (kN) 1 6,7 0,87 2 5,9 0,51 3 13,6 0,88 4 26,7 1,01

5. STRUCTURAL DESIGN

5.1. Instability phenomena

The ultimate resistance of open thin walled

sections is influenced by a diverse set of instability

phenomena. As Light steel framing typically

exploits class 4 cross sections (in which local

buckling will occur before the attainment of yield

stress in one or more parts of the cross-section),

the design of LSF sections is a complex process.

The members are also subjected to distortional

and global buckling, as show in Figure 13.

Figure 13 - Instability modes of a class 4 single open section

(Adaptaded from Pinto, 2010).

Figure 13 description: a) local mode in

compression b) local mode in bending c)

distortional mode in compression d) distortional

mode in bending e) global mode in compression f)

global mode in bending.

The local buckling is taken into account by the

effective section method and the distortional and

global buckling use reduction factors, calculated

using the gross cross section, to determine the

design buckling resistance of any given member.

5.2. Studs

In order to reduce the calculation volume involved

in the stud design, two summarizing charts were

developed, one of which is presented in Figure 14.

This chart condenses the design capacity of U153

and C150 single and built-up studs.

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Not only does this chart allow a simpler design, but

it also is a good pre-design tool.

5.3. Joists

Similarly to the studs, a chart that condenses the

joists’ design was developed. Since the joists are

limited not only by the ultimate limit state (ULS) but

also by the serviceability limit state (SLS), both this

conditions are presented in the graph, as shown in

Figure 15. The loads used in such graph were the

design loads employed in the studied building.

This way, the chart provides valuable design

information not only for this example, but also to

pre-design other simply supported spans.

Figure 14 - U153 and C150 single and built-up sections stud capacity.

Figure 15 - Joists capacity for simply supported spans.

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5.4. Connections

Different steel straps were adopted depending on

the design tension, which was then used to design

the stud-strap connections. The shear strength of

the analysed fasteners (along with the bearing

strength of 1,0 and 1,5 mm plates) is presented in

Table 11 and the number and type of fasteners

required by each strap shown in Table 12.

Table 11 - Shear and bearing strength of fasteners.

Gauge Diameter Fv,Rd Fb,Rd

1,5mm plate

Fb,Rd 1mm plate

(#) (mm) (kN) (kN) (kN) 6 3,56 1,91 3,84 2,56 8 4,06 2,49 4,38 2,92

10 4,83 3,52 5,22 3,48 12 5,33 4,28 5,76 3,84 14 6,35 6,08 6,86 4,57

Table 12 - Fastener design for each steel strap.

Width Thickness Area Nt,Rd Fasteners / connection

(mm) (mm) (mm2) (kN) Quantity Gauge 60 1,0 60 16,8 6 #10

100 1,0 100 28 10 #10 85 1,5 127,5 35,7 10 #12

120 1,5 180 50,4 10 #14

6. CONCLUSION

Focusing on the results about the non-structural

parameters, one concluded that the LSF method

presents (i) excellent thermal performance, (ii)

good acoustical performance, (iii) excellent

durability, sustainability and eco-efficiency

indicators.

Relatively to structural modeling, analysis and

design, one can prompt the following general

conclusions:

• LSF computational modeling is quite

complex, given the number of elements

involved, and presents many different

challenges, mainly related to the bracing

system and diaphragm effect;

• The OSB diaphragm effect should always

be considered, since it can significantly

influence the buildings’ structural behavior;

• The presented model satisfactorily

represented the structural behavior to all

the studied combinations and provided

reasonable results for each designed

member;

• The design of the class 4 sections was

successfully accomplished, providing

concrete designing values for the studs,

joists, straps and fasteners;

• The summarizing charts condense a great

deal of valuable information and can be

used for pre-design.

7. REFERENCES

AISI. (1997). Monotonic Tests of Cold-Formed Steel Shear Walls with Openings. National Association of Home Builders (NAHB) Research Center, Marlboro, MD.

Inoue, H. (2004). Sistemas diafragma com painéis de chapa fina aplicados a edificações estruturadas em aço (Tese de douturamento). Universidade Federal do Rio de Janeiro.

Lawson R. M., Popo-Ola S. O., Way A., Heatley T., Pedreschi R. (2010). Durability of light steel framing in residential applications. Proceedings of the Institution of Civil Engineers (ICE) - Construction Materials, 163(2):109–21.

Mateus, R. (2004). Novas tecnologias construtivas com vista à sustentabilidade da construção (Dissertação de Mestrado). Universidade do Minho.

Pinheiro, M. D. (2003). Construção Sustentável – Mito ou Realidade?. VII Congresso Nacional de Engenharia do Ambiente, Lisboa.

Pinto, A. R. (2010). Estabilidade local de perfis de aço enformados a frio (Dissertação de mestrado). Instituto Superior Técnico.

Smith, B. S. (1966). Behaviour of Square Infilled Frames. Journal of Structural Division – American Society of Civil Engineers (ASCE), 92(1):381-403.

Tian, Y. S., WANG, J., LU, T. J. (2004). Racking strength and stiffness of cold-formed steel wall frames. Journal of Constructional Steel Research, 60(7):1069-1093.