eurocode - building designer handbook

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EUROCODE BUILDING DESIGNER

Friday 5 August 2011 12:00

Building Designer - Eurocodes Handbook page 2 CSCs Offices Worldwide

Friday 5 August 2011 12:00

CSC (UK) LtdYeadon House

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Disclaimer page 3

Disclaimer CSC (UK) Ltd does not accept any liability whatsoever for loss or damage arising from any errors which might be contained in the documentation, text or operation of the programs supplied.

It shall be the responsibility of the customer (and not CSC)

to check the documentation, text and operation of the programs supplied,

to ensure that the person operating the programs or supervising their operation is suitably qualified and experienced,

to ensure that program operation is carried out in accordance with the user manuals,

at all times paying due regard to the specification and scope of the programs and to the CSC Software Licence Agreement.

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Fastrak documentation: Fastrak software: CSC (UK) Ltd 2011 CSC (UK) Ltd 2011All rights reserved. All rights reserved.

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Table of ContentsBuilding Designer Handbook - Eurocodes

Chapter 1 Introduction . . . . . . . . . . . . . . . 7

Chapter 2 Construction Methods and Member Types . . . . . . . . . 8Simple Construction . . . . . . . . . . . . . . 8

Composite or Simple Beam?. . . . . . . . . . . . . 10Composite Beam Design . . . . . . . . . . . . . 10

Continuous Construction . . . . . . . . . . . . . 11Member Beams and Member Columns . . . . . . . . . . . 11General Beams . . . . . . . . . . . . . . . 13General Columns . . . . . . . . . . . . . . 14

Moment Framing and Gravity Loads . . . . . . . . . . . 15Backspan Beams . . . . . . . . . . . . . . 15General Points to Note . . . . . . . . . . . . . 16

Additional Member Types . . . . . . . . . . . . . 17Trusses and Truss Members . . . . . . . . . . . . . 17Diaphragm Braces . . . . . . . . . . . . . . 17Shear Walls . . . . . . . . . . . . . . . 20Bearing Walls . . . . . . . . . . . . . . . 23

Chapter 3 Sway Resistance . . . . . . . . . . . . . . . 27Using Bracing . . . . . . . . . . . . . . . 27Using Steel Moment Frames . . . . . . . . . . . . . 28Using Other Moment Frames . . . . . . . . . . . . . 28Using Shear Walls . . . . . . . . . . . . . . . 28

Chapter 4 Diaphragm Modeling . . . . . . . . . . . . . 30Rigid Diaphragms. . . . . . . . . . . . . . . 30

.Single diaphragm . . . . . . . . . . . . . . 31Slab items defined . . . . . . . . . . . . . . 31No diaphragm . . . . . . . . . . . . . . . 32Taking slabs out of a diaphragm . . . . . . . . . . . . 32

Semi-Rigid Diaphragms . . . . . . . . . . . . . 34Flexible Diaphragms . . . . . . . . . . . . . . 34Storey Shears . . . . . . . . . . . . . . . 34

Chapter 5 Member End Releases and Member Orientation . . . . . . . . 35Moment Releases . . . . . . . . . . . . . . 35Axial Releases . . . . . . . . . . . . . . . 37Torsional Releases . . . . . . . . . . . . . . 38Release from a Diaphragm . . . . . . . . . . . . . 38Member Orientations . . . . . . . . . . . . . . 39Supports and Base Fixity . . . . . . . . . . . . . 40

Chapter 6 Load Cases and Load Combinations . . . . . . . . . . 41Nationally Determined Parameters (NDPs) . . . . . . . . . . 41

gamma factors . . . . . . . . . . . . . . . 41psi factors . . . . . . . . . . . . . . . . 42

Gravity Load Cases . . . . . . . . . . . . . . 43Friday 5 August 2011 12:01

Self Weight . . . . . . . . . . . . . . . 43

Table of Contents page 5Imposed and Roof Imposed Loads . . . . . . . . . . . 44Snow and Snow Drift Loads . . . . . . . . . . . . 44Perimeter Loads . . . . . . . . . . . . . . 45

Lateral Load Cases . . . . . . . . . . . . . . 45Wind Loads . . . . . . . . . . . . . . . 45

Combinations . . . . . . . . . . . . . . . 46The Construction Stage Combination . . . . . . . . . . . 46Manually Defined Combinations. . . . . . . . . . . . 46Equivalent Horizontal Forces (EHF) . . . . . . . . . . . 47Apply Imposed Load Reductions . . . . . . . . . . . 47The Combinations Wizard . . . . . . . . . . . . . 48

Classifying Combinations and Setting the Critical Combinations . . . . . . 50Gravity Combinations . . . . . . . . . . . . . 51Lateral Combinations . . . . . . . . . . . . . 51Seismic Combinations . . . . . . . . . . . . . 51Setting the Critical Combinations . . . . . . . . . . . 51

Chapter 7 Analysis And Design Procedures . . . . . . . . . . . 52Definitions. . . . . . . . . . . . . . . . 52Building Validation . . . . . . . . . . . . . . 53Overview of the Analysis and Design Process . . . . . . . . . . 53

Set Auto Design Mode . . . . . . . . . . . . . 55Analysis Options . . . . . . . . . . . . . . 55

First-order or Second-order Analysis? . . . . . . . . . . . 56Curved Beams . . . . . . . . . . . . . . . 57Torsion Factors . . . . . . . . . . . . . . 57Cracked Sections . . . . . . . . . . . . . . 57

Design Options . . . . . . . . . . . . . . . 58Design Codes . . . . . . . . . . . . . . . 58Design Control . . . . . . . . . . . . . . 58Force Limits - Members . . . . . . . . . . . . . 58Force Limits - Connections. . . . . . . . . . . . . 58Element Pre-sizing . . . . . . . . . . . . . . 59Portal Pre-sizing . . . . . . . . . . . . . . 59Composite . . . . . . . . . . . . . . . 59EHF Forces . . . . . . . . . . . . . . . 59

Initial Review of Analysis Results . . . . . . . . . . . . 60Maximum Nodal Deflections . . . . . . . . . . . . 60Sway Sensitivity . . . . . . . . . . . . . . 60Loading Summary . . . . . . . . . . . . . . 61Review of Selected Sections . . . . . . . . . . . . 62Review Analysis Results . . . . . . . . . . . . . 62Review Centre of Mass / Rigidity . . . . . . . . . . . . 62Reviewing Storey Shear . . . . . . . . . . . . . 63

3D Analysis Effects . . . . . . . . . . . . . . 63Continuous Beam Example . . . . . . . . . . . . 64Braces Carry Gravity Loads Example . . . . . . . . . . . 67

Refining Member Designs . . . . . . . . . . . . . 69

Chapter 8 Building Effective Models . . . . . . . . . . . . 70Place grid lines accurately . . . . . . . . . . . . . 70Save time by using Attributes effectively . . . . . . . . . . 70Use Simple beams and columns where possible . . . . . . . . . 71Use Perimeter Loading for edge beams where applicable . . . . . . . 71Is it a Floor? . . . . . . . . . . . . . . . 71

Table of ContentsSet the appropriate level of Diaphragm Action . . . . . . . . . . 72Set the appropriate level of deflection checks . . . . . . . . . . 72Building Size and Orientation. . . . . . . . . . . . . 72Switch off irrelevant load combinations . . . . . . . . . . . 73Design simple construction for gravity loads only . . . . . . . . . 73Staged modelling and design. . . . . . . . . . . . . 74Check the model analysis results . . . . . . . . . . . . 74

Chapter 9 Assumptions and Limitations . . . . . . . . . . . . 75Analysis Types . . . . . . . . . . . . . . . 75Analysis Results . . . . . . . . . . . . . . . 76Imperfections . . . . . . . . . . . . . . . 76

Imperfection for analysis of bracing systems - Clause 5.3.3 . . . . . . . . 76Imperfections for global analysis of frames - Clause 5.3.2 (6) . . . . . . . 76Torsional sway effects - Clause 5.3.2 (10) . . . . . . . . . . . 77

Deflection checks . . . . . . . . . . . . . . . 77Absolute and Relative Deflections . . . . . . . . . . . . 77Deflections in Composite Beams (and Beams with Web Openings) . . . . . . 77

Foundation loads . . . . . . . . . . . . . . . 78Vertical cross bracing . . . . . . . . . . . . . . 79

Foundation shear and vertical load . . . . . . . . . . . 79Column axial load . . . . . . . . . . . . . . 79

Imposed Load Reductions . . . . . . . . . . . . . 79Imposed Load Reductions applied to Brace Forces used in Column Design . . . . . 79

Equivalent Horizontal Force Load Calculations. . . . . . . . . . 80Loads used in EHF load calculations . . . . . . . . . . . 80Gravity loads carried by Braces not accounted for in EHF load calculations . . . . . 80Axial load in discontinuous columns used twice in EHF load calculations . . . . . 81

Consequences of changing Design Codes within an Existing Project . . . . . . 81BS models swapped to Eurocodes and designed . . . . . . . . . 81Eurocode models swapped to British Standards and designed . . . . . . . 82

Chapter 10 Sign Conventions . . . . . . . . . . . . . . 83Object Orientation . . . . . . . . . . . . . . 83Beams (Simple, Composite and General) and Truss member (chord) . . . . . . 84Braces and Truss member (internal) . . . . . . . . . . . 85Columns (Simple and General) . . . . . . . . . . . . 86Shear Walls . . . . . . . . . . . . . . . . 87Foundations/Bases - Foundation Forces . . . . . . . . . . . 88Foundations/Bases - Base Reactions . . . . . . . . . . . 90Nodal Deflections . . . . . . . . . . . . . . . 92Friday 5 August 2011 12:01

Chapter 1 : Introduction Building Designer - Eurocodes page 7Building Designer Handbook - Eurocodes

Chapter 1 Introduction

This handbook provides a general overview of Fastrak Building Designer in the context of design to Eurocodes. The applicable construction methods and member types are described, and the analysis/design procedures explained. In addition, guidance is provided on effective modelling with tips, and examples to help you to make the most of the software.

A brief description of the contents follows:

Construction Methods and Member Types (Chapter 2)discusses the use of simple and continuous construction and describes the various member types available.

Sway Resistance (Chapter 3)describes the various means of providing lateral resistance.

Diaphragm Modeling (Chapter 4)describes the different types of diaphragm modeling available for transferring horizontal loads to the lateral load resisting system.

Member End Releases and Member Orientation (Chapter 5)describes end releases, axial releases, member orientation, supports and practical considerations.

Load Cases and Load Combinations (Chapter 6)describes the different load case and load combinations types.

Note The Wind Wizard used for automatic loadcase generation is fully described in the EC1 1-4 Wind Modeller Handbook.

Analysis And Design Procedures (Chapter 7)provides an overview of the steps required to analyse and design your building and describes the various analysis and design options.

Note The member design procedures are fully described in the Eurocode Member Design Handbook

Building Effective Models (Chapter 8)hints and tips for creating a model that quickly and efficiently yields results.

Assumptions and Limitations (Chapter 9)these are fully described here.

Sign Conventions (Chapter 10)conventions used in reporting the results.

Building Designer - Eurocodes page 8 Chapter 2 : Construction Methods and Member TypesChapter 2 Construction Methods and Member Types

To maximise your construction options Fastrak Building Designer provides a range of member types.

Major topics Simple Construction Continuous Construction Composite Beam Design Member Beams and Member Columns General Beams Backspan Beams Trusses and Truss Members Diaphragm Braces Shear Walls Bearing Walls

Simple ConstructionFor simple construction The most effective design for a multi storey structure is still likely to be simple1 beams and

columns with bracing to resist the lateral forces.

Fastrak Building Designer will happily design moment frames or continuous beams automatically within a model, BUT, the design of these elements is much more comprehensive (and hence takes longer). For this reason you should only use such elements when your model specifically requires them.

Note If Fastrak Building Designer gives warnings about braces on Simple Beams, or intermediate floor levels on Simple Columns the answer is not necessarily to make the affected elements into General Beams/Columns. Look at the modelling and talk to CSC support if you are not sure of the route that you want to take.

Analytical Properties (simple construction)

BeamsBoth simple and composite beams are automatically configured with (and restricted to) pinned connections.

Footnotes

1. Pin type connections thus in this context a Composite Beam is simple.

Chapter 2 : Construction Methods and Member Types Building Designer - Eurocodes page 9ColumnsWhen considering stability you should be aware that:

columns set by you to be Simple - the program automatically inserts pins just above every floor level, apart from at the base level. The insertion of these pins ensures that all lateral load is transferred to the lateral load resisting system.

for columns set by you to be Gravity Only Design - the program also automatically inserts pins just above every floor level, apart from at the base level. Note however that pins do not get inserted where the columns are connected to a braced bay. The insertion of these pins ensures that all lateral load is transferred to the lateral load resisting system.

An example is shown in the figure below.

Note If a column is switched so that it is not Gravity Only Design, the program automatically removes any pins within it (unless it has been marked as a Simple column).

BracesBraces are automatically configured with (and restricted to) pinned connections. Torsional releases can be applied and the brace can have an axial end release at one end to prevent vertical load being carried by the brace.

Design Properties (simple construction)It is best to establish the default design properties (restraint assumptions, sections for study, and such like) by setting up appropriate default attributes. For information about working with attributes refer to - Fastrak Building Designer Help \ Working with Attributes

The Eurocode theory and assumptions applicable to Fastraks Simple Beam, Composite Beam, general column and brace design modules is given in the Eurocode Member Design Handbook.

Added release My and Mz

Building Designer - Eurocodes page 10 Chapter 2 : Construction Methods and Member TypesComposite or Simple Beam?Composite beam design is not a linear process, and some beams are simply not suitable for design as composite beams. You should take care when selecting beams for composite design, and set appropriate design attributes.

The benefits of composite design are well known, however many beams are not suitable for composite design, including:

beams with no slab, very short beams, beams with significant eccentric load (for example a beam supporting a column close to

the support), beams with decking arrangements that will not allow effective composite action.

In short you should be diligent about the use of composite beams. Exercise care when determining which beams are appropriate for composite design, if in doubt design all beams as simple beams first and simply select those beams that you wish to be composite at a second pass.

Composite Beam DesignComposite design of beams is a complex procedure when done rigorously. We assume that you are familiar with the concepts of composite design before you use Fastrak Building Designer.

Fastrak Building Designers composite design routines can automatically choose the optimum stud layout and automatically select an appropriate layout of transverse reinforcement to resist longitudinal shear. Thus the design of any composite beam may have a range of possible solutions.

Example A typical 9 m composite spine beam can be shown to be acceptable: with studs at 190 mm cross-centres and a 457x191x67 UB, with studs at 200mm cross-centres and a 457x191x74 UB, which of these solutions is better is up to you.

While it can sometimes be useful to optimise a design, you might well take the view that you would prefer to control the stud spacing and other critical design issues rather than allow the software to choose a different layout for every beam.

Please consider the following when you set up the attributes for a Composite Beam.

It is important to realise that you can define attributes that may make the design of composite beams impossible for example if you set the stud spacing on a spine beam to 300 mm, but this does not provide the minimum amount of shear interaction then the selection of a suitable beam size is not possible.

For a description of the Eurocode design methods, theory and assumptions applied to Composite Beams in Fastrak refer to the Eurocode Member Design Handbook.

Chapter 2 : Construction Methods and Member Types Building Designer - Eurocodes page 11Continuous ConstructionFor continuous steel construction Fastrak Building Designer allows you to model members which are more complex than pin

ended beams and simple columns. There are currently four member construction types that you can use:

Member Beams these can be any section in any material but cannot be checked or designed by Fastrak Building Designer refer to Member Beams and Member Columns.

Member Columns these can be any section in any material but cannot be checked or designed by Fastrak Building Designer refer to Member Beams and Member Columns.

General Beams these are restricted to steel sections. In the first Eurocode version of Fastrak Building Designer these cannot yet be checked or designed refer to General Beams.

General Columns these are restricted to steel sections but such columns can then be designed by Fastrak Building Designer refer to General Columns.

Member Beams and Member ColumnsFor construction in other materials including concrete and timber

A member can be almost anything. The view above shows Member Beams and Member Columns being used to form concrete framing to support part of the steel structure. In addition concrete shear walls are shown which provide lateral stability and support various beams. (Refer to Sway Resistance on page 27 for more notes on the alternative methods of providing lateral stability).

The procedure for defining Member Beams and Member Columns is identical to the procedure for defining other beams and columns you set up the default attributes and then create members by clicking between any two points. The two main topics that require some thought are given below.

Building Designer - Eurocodes page 12 Chapter 2 : Construction Methods and Member TypesMaterial/Section Properties

Fastrak Building Designer has default values for various materials. To use a material that is not listed choose Other and you will then be able to enter the properties directly.

Section properties can be calculated automatically for rectangular sections by entering the breadth and depth and clicking Calc. Props. The example above shows the section properties calculated for a concrete beam section.

When analysing a concrete structure in isolation, for the purposes of establishing design forces you should use consistent properties for all members. So long as everything is proportionately correct, then the design forces will be correct.

However, for the purposes of deflection estimation and in any model that mixes steel/concrete/other materials, more attention needs to be paid to defining the correct properties.

For concrete elements this means considering: adjusting the gross section properties to allow for cracking,

Note In the above dialog, if you define b and d then click Calc. Properties Fastrak Building Designer calculates the gross section properties of a simple rectangular section for you. You can make adjustments to the calculated values to allow for

cracking and/or to allow for irregular shapes, etc.)

Chapter 2 : Construction Methods and Member Types Building Designer - Eurocodes page 13 adjusting the value of E (Youngs Modulus) to allow for load duration. Note When you select a concrete grade an average short term value of E is indicated for

guidance. You must always define the value of E to be used for analysis.

Analytical Properties (End Releases)This is common to Member Beams, Member Columns, General Beams, and General Columns, refer to Member End Releases and Member Orientation on page 35.

General BeamsNote In the first Eurocode release of Fastrak Building Designer, General Beams can be

modelled but can not yet be checked or designed.

General Beams are, in a sense, a more constrained subset of Member Beams: You still have all the geometrical freedom to define the member at almost any angle/

orientation, General Beams are constrained to be a steel section,

Creating General BeamsYou can create General Beams in the same way as any simple- or composite-beam. Simply create a new beam attribute set and set the Construction Type on the Design tab to General. Any new beam you create using this attribute set will be a General Beam.

Note You can set the end releases as part of the attribute set (the default setting is pinned).

You can create General Beams in several other ways:1. While creating any beam (regardless of the current default attribute set), you can hold

down the control key to indicate a series of points that define a continuous beam. Since Simple Beams and Composite Beams are never continuous this procedure will always convert the beam to make it a continuous General Beam.

Note Continuous General Beams do not need to be co-linear, provided the web remains in a common vertical plane.

2. If you click on two Simple Beams with the Split/Join tool active Fastrak Building Designer converts these to a continuous General Beam.

3. If you insert points in Simple Beams by using the Modify tool and then move those points to create a non co-linear beam, then Fastrak Building Designer converts the beam into a continuous General Beam.

Analytical Properties (End Releases)This is common to all Member Beams, Member Columns, General Beams, and General Columns, refer to Member End Releases and Member Orientation on page 35.

Design PropertiesAs with simple and composite beams it is best to establish the default design properties (lateral bracing assumptions, sections for study, etc.) by setting up appropriate default attributes.

If you have not set up the attributes you wanted you could of course edit the properties of any

General Beam.

Building Designer - Eurocodes page 14 Chapter 2 : Construction Methods and Member TypesGeneral ColumnsGeneral Columns are, in a sense, a more constrained subset of Member Columns:

You still have all the geometrical freedom to define the member at almost any angle/orientation,

General Columns are constrained to be a steel section, The advantage is that Fastrak Building Designer designs these steel sections automatically. They can be designed for gravity and lateral loads, but if they are set for Gravity Only

Design, they are designed for gravity combinations only. Note When using simple construction you should set the columns as Simple.

General Columns can be designated part of a Moment Frame. Since columns in a moment frame require a greater inertia than would otherwise be the case, General Columns use a different orderfile containing sections more suited to resist bending.

Creating General ColumnsSimply create a new column attribute set with the desired properties. Any new column you create using this attribute set will be a General Column.

While working in the 3D structure view you can also create columns by clicking on start and end points. While creating any column in this way you can hold down the control key to indicate a series of points that define a continuous column.

Analytical Properties (End Releases)This is common to all Member Beams, Member Columns, General Beams, and General Columns - refer to Member End Releases and Member Orientationon page 35.

General Columns not set to be either Gravity Only Design or Simple are initially fixed at each floor level. You are able to introduce pins at any floor level as you then require.

However if you set General Columns to be Gravity Only Design, they are treated similarly to General Columns set to be Simple, i.e. the program automatically inserts pins just above every floor level, apart from at the base level. Note however that pins do not get inserted where the columns are connected to a braced bay. Should a General Column be switched so that it is no longer Gravity Only Design, the program automatically removes any pins within it.

Design PropertiesAs with beams it is best to establish the default design properties (restraint assumptions, sections for study, and such like) by setting up appropriate default attributes.

If you have not set up the attributes you wanted you could of course edit the properties of any General Column on an individual basis.

For a description of the Eurocode design methods applied to General Columns in Fastrak refer to the Eurocode Member Design Handbook.

Chapter 2 : Construction Methods and Member Types Building Designer - Eurocodes page 15Moment Framing and Gravity Loads

Backspan BeamsWe expect that (generally) for gravity loads you will only introduce moment framing locally and selectively. We anticipate that one of the most common requirements for this usage will be to define Backspan Beams.

The above view shows several simple examples of backspan beams at the first floor level.Note This model is for illustration purposes only - building layout is at your discretion.

Consider the left-hand-side you will see a cantilever slab area. Some of the cantilevers are on column lines, however, others extend from the side of a supporting beam and so rely on a backspan beam to restrict rotation.

Along the front elevation the column line steps back between foundation and first floor levels and so the columns from first floor to roof are supported on the ends of cantilevers with backspans.

This can all be achieved very effectively by using General Beam design. However you may find that the general points noted below still apply.

Building Designer - Eurocodes page 16 Chapter 2 : Construction Methods and Member TypesGeneral Points to Note

Pattern LoadingIf you are creating continuous beams you should consider the possibility that pattern load cases could be critical.

Fastrak Building Designer will NOT automatically create pattern load cases for continuous beams. However, you can create more load cases containing the appropriate loads and then create more combinations to cover the pattern load cases.

Pattern loading is also applicable to the backspan beam, it will not affect the cantilever, but if the cantilever load is reduced/removed the sagging moments in the backspan will increase. Hence, if the cantilever moment is significant the pattern load cases are likely to be more important to fully investigate.

Continuity

Care is required where the beam depth varies to either side of a beam or column web and it is desired for the supported beams to be continuous through the support. If the difference in flange levels is significant the load path through the two moment connections may not be clear or feasible. Undesirable local forces may be set up in the supporting member.

Transfer Beams / LevelsLevels where the columns that support the floors above are discontinuous are known as transfer levels and the beams/cantilevers that support these discontinuous columns tend to be known as transfer beams.

The screen shot at the start of this chapter showed transfer backspan beams. You can design various transfer beam configurations within Fastrak Building Designer.

Fastrak Building Designer considers imposed load reductions during the design of columns. However, these reductions are applied during the member design phase, the building analysis is always based on all loads applied simultaneously. By default therefore transfer beams will always be designed for the full (un-reduced) loading in the supported columns. If you regard this as over-conservative, then you can optimise the design of the transfer beams interactively.

Chapter 2 : Construction Methods and Member Types Building Designer - Eurocodes page 17Additional Member TypesPlus the following additional member types Fastrak Building Designer allows you to easily modelthe following more complex systems

which might comprise multiple analysis members: Trusses Truss members can be formed in any material. They will attract loads and

participate in the 3D structural analysis, elements of the truss can be checked (but not designed) provided they are defined in steel. refer to Trusses and Truss Membersbelow.

Diaphragm Braces these are used to model flexible or semi-rigid diaphragms, serving to transfer lateral loads to the lateral load resisting systems in the 3D structural analysis. As they are not real members they are neither checked or designed refer to Diaphragm Braces.

Shear Walls these are restricted to concrete or Other materials but cannot be checked or designed by Fastrak Building Designer refer to Shear Walls on page 20.

Bearing Walls these are subjected to gravity (vertical) loads only. They are typically built from masonry or timber but cannot be checked or designed by the software refer to Bearing Walls.

Trusses and Truss MembersIn the current version of Fastrak Building Designer you can define truss members in your model and then check their adequacy. Truss members will attract loads and participate in the 3D structural analysis, but elements of the truss can only be checked (but not designed).

Fastrak Building Designer has a Truss Wizard to help you define many different types of truss.

Diaphragm BracesDiaphragm braces are not real members - they are used in order to model those floors or roofs which can not be considered to be rigid due to their type of construction - they are usually termed Flexible Diaphragms or Semi-Rigid Diaphragms.

Whether the resulting diaphragm is considered flexible or semi-rigid can be controlled by careful definition of the diaphragm brace propeties.

Building Designer - Eurocodes page 18 Chapter 2 : Construction Methods and Member TypesCreating Diaphragm BracesYou create diaphragm braces in a similar way to simple braces. In the Brace attribute set you should specify Diaphragm on the Design tab and then enter the required values for elastic modulus and area on the Size tab.

Whilst they are applied singly, you are advised to always create a pair of cross diaphragm braces within a panel. Mostly these should connect between columns such that each column is restrained by at least two diaphragm braces at each floor level as shown in the plan below. .

In pitched roofs it would be advisable to tie the apex of roof members back to the vertical columns supporting the roof. .

Chapter 2 : Construction Methods and Member Types Building Designer - Eurocodes page 19You have to decide the layout of braces around openings. For small openings, the braces could cross the opening and join the surrounding columns - as shown for the smaller (lower) of the two openings in the figure below. For larger openings, they could be laid out around the opening to provide a triangulated framework connecting the nodes of the trimming steel. Two ways in which you might want to do this are shown below. .

Analytical PropertiesDiaphragm braces are released at both ends in the rotational y- and z-directions and fixed at both ends in the rotational x-direction.

The only properties required are an area (A) and elastic modulus (E). Default properties are given in the attributes set, however as there is no 'correct' answer for how stiff a semi-rigid diaphragm should be, you are entirely responsible for determining appropriate values. Typically they need to be very slender members with low stiffness.

To assist in this determination consideration should be given to the proportion of the horizontal loading that is resisted by each of the frames in the lateral load resisting system. This is achieved after analysis by considering the Storey Shear results. See Reviewing Storey Shear for more details.

Diaphragm braces have zero self weight.

Since they are not real members they are: not designed, not listed, not exported to 3D cad programs e.g. Revit.

However they are exported to analysis programs eg S-Frame.

Building Designer - Eurocodes page 20 Chapter 2 : Construction Methods and Member TypesShear WallsShear walls are typically used to provide resistance to lateral loads and support other members. The following limitations apply to their use:

Vertical walls only Rectangular walls only Concrete or Other materials only The shear walls will not be designed

Creating Shear WallsTo create Shear Walls you should first create an appropriate Shear Wall attribute set. The attribute set consists of the walls material, thickness and analysis properties.

If the material is specified as concrete, you should select the concrete grade. The program will then display a typical short term E value for the grade chosen. You will then need to decide on an appropriate value of E to be used in the analysis, taking into account factors such as creep, cracking and shrinkage. If the material is specified as Other you will also be required to specify an appropriate E to be used in the analysis.

You can then create the wall itself from any of the 3D or 2D views:

1. While working in the 3D structure view or a frame view you can create a shear wall by clicking on start and end points at the base of the wall, followed by a third point which can be located anywhere in the floor at the top of the wall. The wall will extend vertically upwards between the start and end point. To the height defined by the third point.

2. While working in a 2D floor view you can create a shear wall by clicking on start and end points. You then select the construction levels at which the wall starts and ends.

Analytical Properties A mid-pier idealisation is used for Shear Walls, this consists of:

Two horizontal elements at the bottom of the wall running between the two set out points and the mid point.

Two horizontal elements at the top of the wall running between the two set out points and the mid point.

Further pairs of horizontal elements for any intermediate construction level that is designated as a floor.

Vertical elements joining the mid-points at the top and bottom of the wall and any intermediate floor levels.

A fully fixed support is added at the midpoint of the wall baseline, unless it is being supported by one or more columns, another shear wall, or a transfer beam.

Chapter 2 : Construction Methods and Member Types Building Designer - Eurocodes page 21Consider the core wall arrangement shown below:

The mid-pier analytical model for this can best be reviewed graphically by showing the release state of the model (pick Select/Show/Alter State, and then pick Releases from the dialog).

If openings have been added to the wall the mid pier model will be modified accordingly. Additional vertical elements are introduced to the sides of the opening and a coupling beam introduced above. Addition of openings will reduce the strength, stiffness and self weight of the wall.

Once a shear wall has been defined, extensions can be added to the wall ends. These do not increase its strength or stiffness, but the self weight would be increased.

The strength and stiffness introduced to your structure will depend on the wall thickness and also the E value used in the analysis. Care should be taken to ensure that the E value used is realistic.

Building Designer - Eurocodes page 22 Chapter 2 : Construction Methods and Member TypesNote The alignment (Left, Centre, or Right) of the shear wall is for cosmetic purposes only and does not affect its analytical properties.

Note Shear Walls do not act as a medium via which loads calculated by the Simple Wind Loading generator and Wind Wizard are applied to your structure. If this is required an additional Wind Wall panel would have to created in the same location as the shear wall.

Transfer Shear WallsA shear wall may be partially or fully supported by a beam or truss member, but only if the supporting member has concrete or Other material properties and its model type for shear wall modelling is set to Top Edge Beam.

Chapter 2 : Construction Methods and Member Types Building Designer - Eurocodes page 23Bearing WallsBearing walls are used to provide resistance to vertical loads but not lateral loads and to support certain other member types.

LimitationsThe following limitations apply to their use:

Vertical walls only Wall is rectangular with a horizontal top. Analysis model considers vertical (gravity) load only. Design is not included. Members can only be defined onto the top of a bearing wall at grid intersection points,

wall column positions and at a user defined distance along the wall. However, the following members can not be supported by bearing walls - columns,

beams with moment connections and braces. A shear wall cannot be supported on a bearing wall but a bearing wall can be supported on

a shear wall. Beam members cannot be continuous over a wall (in the first release).

Please note that the program will allow beams to connect to the top of the wall at any slope or diagonal angle except

Horizontal along the top and parallel with the length of the bearing wallThe supported end of a sloping beam will have reaction components in both vertical and horizontal planes, the horizontal component is ignored by the bearing wall.

Features A bearing wall item can be defined across vertical steel but the wall panel will 'split' at the

steel position - see figure below.

Building Designer - Eurocodes page 24 Chapter 2 : Construction Methods and Member Types A bearing wall item can be defined over the top of a beam but cannot have a beam within or on top of the definition extents - see figure below. This is because a beam cannot be supported in the plane of a bearing wall.

Bearing wall items must be rectangular with their vertices at grid intersection points but do not have to coincide with steel members - see figure below.

Bearing wall items can be defined across floor levels but will be split at each floor level. Bearing walls can be connected to other bearing walls at ends or anywhere in their length

and do not have to be orthogonal.

Creating Bearing WallsTo create Bearing Walls you should first create an appropriate Bearing Wall attribute set. The attribute set consists of the walls material, thickness and self weight. The wall material is simply an identifying name - e.g. concrete, block, masonry.

Chapter 2 : Construction Methods and Member Types Building Designer - Eurocodes page 25You can then create the wall itself from any of the 3D or 2D views:

1. While working in the 3D structure view or a frame view you can create a bearing wall by clicking on start and end points at the base of the wall, followed by a third point which can be located anywhere in the floor at the top of the wall. The wall will extend vertically upwards between the start and end point. To the height defined by the third point.

2. While working in a 2D floor view you can create a bearing wall by clicking on start and end points. You then select the construction levels at which the wall starts and ends.

Analytical Properties Bearing walls are modelled using a series of vertical column members, 'wall columns', and horizontal beam members, 'wall beams', as indicated in the diagram below. The beams have pinned ends and are placed at the top of the wall spanning between the columns. The next panel above is pinned to the one below and similarly the lower end of a column is pinned to a supporting beam. At the lowest level the column is 'fixed' to a pinned support.

Members supported by the wall either (fortuitously) bear directly on one of the wall columns or on one of the wall beams at the head of the wall. All wall columns and wall beams in an individual panel are given properties automatically by Fastrak, based on the width of the panel with which they are associated.

Building Designer - Eurocodes page 26 Chapter 2 : Construction Methods and Member TypesFor bearing walls that are defined between other vertical column members e.g. General Columns, the wall columns at the edge of the panel are omitted and the associated wall beam is connected to the General Column (for example) and the adjacent wall column - see figure below.

Irrespective of whether the wall spans between other vertical column members or not - any load applied to the wall beam at the edge of the panel is shared between the end column and the first internal column. This can result in some load being lost directly into the supports.

Load transfer in the bearing wall model is not the same as it would be in for example, a masonry wall. A point load applied at the top of a masonry wall would result in a distributed load on any beam supporting the masonry wall, whereas in a bearing wall the supporting beam would be subjected to a pair of point loads, (or possibly even a single point load if the applied load coincides exactly with a wall column location).

Self weight of the bearing wall is concentrated in the wall beams so seismic weight is concentrated at the top of the wall and not split between the floor above and below.

Chapter 3 : Sway Resistance Building Designer - Eurocodes page 27Chapter 3 Sway Resistance

A simple overview of some of the alternative ways in which you can provide sway resistance in Fastrak Building Designer.

Major topics Using Bracing Using Steel Moment Frames Using Other Moment Frames Using Shear Walls

Using BracingThis is the most traditional approach and well positioned and proportioned bracing is undoubtedly the best method of providing sway resistance.

Fastrak Building Designer allows all sorts of bracing configurations including:

tension only bracing, K bracing, and inverted V bracing (as shown in the screen shot above).

Note For V and inverted V bracing the analytical model may need to include sliding connections so that the beam is not supported by the bracing under gravity loads. For further information on how to do this see Add bracing in the Quick Start Guide.

Note Care must be taken if modelling vertical cross bracings, see Vertical cross bracing in the Assumptions and Limitations chapter for more details.

Building Designer - Eurocodes page 28 Chapter 3 : Sway ResistanceUsing Steel Moment FramesIf you have to provide stability using moment frames, then you can do so within the software using General Beams and General Columns. In such circumstances it is highly likely that you will want to consider the advantages and disadvantages of introducing some level of base fixity. The base fixity options are noted in Supports and Base FixitySupports and Base Fixityon page 40.

Where General Beams and General Columns are used in this way, you should designate them as being part of a moment resisting frame. This will ensure that the initial sizes assigned in the analysis/design process are reasonable. The designation can be carried out graphically by using the Moment Frames feature located on the Building tab in the Show/Alter State dialog. Alternatively the designation can be set by editing the properties of each member.

Using Other Moment FramesYou are able to create moment frames using any material and section by using Member Beams and Member Columns. It is not necessary to designate such members as being Moment Frames as they only participate in the analysis and are not designed.

If you attempt to provide stability using other materials and framing, then you need to pay particular attention to the definition of appropriate section and material properties. This was touched upon in Member Beams and Member Columns on page 11.

Using Shear Walls

Stability for the very simple frame shown above is provided by shear walls. In this view the walls are rendered as if they are large solid panels, however the modelling idealisation being used is actually a mid-pier vertical beam element with a fixed base, and rigid cantilever arms extended out at each floor level to support any attached beams or slabs.

Chapter 3 : Sway Resistance Building Designer - Eurocodes page 29Swapping to the axis stick view shown below and switching off the beams and columns the idealisation becomes more apparent.

For further information refer to the article Shear Wall Analysis - New Modelling, Same Answers - The Structural Engineer, 1st February 2005, Vol. 83 No.3, page 20 which is available on the CSC web site - select Services, Technical Papers.

This modelling idealisation of shear walls with beam elements is traditionally well accepted. The points made in Using Other Moment Frames on page 28 regarding section and material properties are of course important.

In recent years we have seen a trend towards Finite Element modelling of shear walls. This can be accomplished by exporting the Fastrak Building Designer model to general analysis software such as CSC S-Frame, editing it to remove the General Beams and then meshing up the wall panels. While this appears to be a more detailed approach that has advantages such as the ability to deal with irregular openings in wall panels, there are disadvantages. For instance, you do not escape from the need to consider making the appropriate adjustments to gross section and material properties as touched upon in Member Beams and Member Columns on page 11. But, it can be done...

Building Designer - Eurocodes page 30 Chapter 4 : Diaphragm ModelingChapter 4 Diaphragm Modeling

In a typical building lateral load resistance is provided at a few discrete points and it is assumed that applied lateral loads will be distributed to the lateral load resisting system (LLRS) either by floor diaphragm action or by a bracing system.

Thick concrete floors provide adequate diaphragm action to distribute these loads. These diaphragms are usually assumed to be 'rigid'. However, floors and roofs of different construction can also be used to transmit the horizontal loads to the LLRS but are considered not to be 'rigid', instead they are classed as either semi-rigid or flexible. All three types of diaphragm can be modelled in Fastrak Building Designer.

Major topics Rigid Diaphragms Semi-Rigid Diaphragms Flexible Diaphragms Storey Shears

Rigid DiaphragmsA rigid diaphragm will maintain exact relative positioning of all nodes that it constrains, i.e. the distance between any two nodes constrained by a diaphragm will never change, therefore no axial load will develop in any member that lies in the plane of a diaphragm between any two constrained nodes. You can however elect to remove General Beam, Member Beam and truss chord nodes from the diaphragm, allowing axial forces to develop within those members.

Any asymmetry in the stiffness of the LLRS can produce 'twist' in the diaphragm - also referred to as torsion effects. Out of plane effects are usually minimized or eliminated.

Note Nodes at support positions, (either column or supplementary), are automatically excluded from all diaphragms.

In Fastrak Building Designer, at each floor level there are 3 options for rigid diaphragm modeling:

Single diaphragm (Default Setting) Slab items defined No diaphragm

It is also possible to switch diaphragm action off for one or more individual slabs within a floor by Taking slabs out of a diaphragm.

General Beams, Member Beam and Truss Chords can be taken out of a diaphragm in order to allow axial forces to develop within those members - see Release from a Diaphragm

Chapter 4 : Diaphragm Modeling Building Designer - Eurocodes page 31.Single diaphragm

This option switches diaphragm action on for an entire floor. Note that completely isolated areas of the floor are constrained by the same diaphragm. Hence, in the example above, if lateral load is applied to the left hand block it will be resisted by the combined bending of both blocks. The blocks can not move independently at the level of the diaphragm. This would produce incorrect results.

Note The extents of a diaphragm are best reviewed graphically (pick Select/Show/Alter State, and then pick Show Diaphragm from the dialog). Each independent diaphragm is shown in a different colour.

Slab items defined

Using this option discrete diaphragms are created for each area of interconnected slabs.

If this option were applied to the example from the previous section a more realistic model would be created. Two separate diaphragms would exist at each floor level above the podium. As a consequence lateral load applied to the left hand block is not resisted by the right hand block. Each can move independently.

Building Designer - Eurocodes page 32 Chapter 4 : Diaphragm ModelingNo diaphragm

This option switches diaphragm action off for an entire floor.

Taking slabs out of a diaphragm

It is possible to switch diaphragm action off for one or more individual slabs within a floor. This is only possible if the diaphragm has been defined using the Slab items defined option.

To demonstrate this, the example from the previous section is modified to include a link bridge between the blocks. Initially, by using the Slab items defined option, a single diaphragm is created at the level of the bridge. This constrains all the floor nodes within both blocks at the level of the bridge, so that at this level the blocks can not move independently.

Providing the linking slab is substantial this may be considered to be appropriate. However, if the link becomes more slender, a point will be reached where this is no longer the case.

Chapter 4 : Diaphragm Modeling Building Designer - Eurocodes page 33By using the Alter Diaphragm function in the Show/Alter State dialog, diaphragm action can be switched off for the slab within the link bridge.

Because the remaining areas of slab at this level are no longer considered interconnected, two discrete diaphragms are formed and the blocks act independently.

Building Designer - Eurocodes page 34 Chapter 4 : Diaphragm ModelingSemi-Rigid DiaphragmsA semi-rigid diaphragm cannot be assumed to be rigid. It can deform in plane (beam bending) and is influenced by the distribution of the stiffness of the lateral load resisting system (LLRS). Consequently, there can be 'twist' and the distribution of the horizontal loads is a complex interaction of the stiffness of the diaphragm and the LLRS.

In Fastrak Building Designer, semi-rigid diaphragms are modelled by introducing Diaphragm Braces. within the plane of the floor.

Flexible DiaphragmsThe accepted definition of a flexible diaphragm refers to the behaviour that allows for some deformation in plane of the diaphragm (similar to beam bending) but without the 'twist' that can occur in rigid diaphragms. As such the distribution of the lateral loads is not influenced by the distribution of the stiffness of the LLRS.

A flexible diaphragm can be considered as a discrete form of semi-rigid diaphragm.

Floors constructed from timber decking or thin sheets of profiled steel which, importantly, deform at the joints between sheets might be considered as flexible diaphragms.

In Fastrak Building Designer, flexible diaphragms are modelled in the same way as semi-rigid diaphragms, by introducing Diaphragm Braces. within the plane of the floor.

Storey ShearsWhen modelling semi-rigid and flexible diaphragms, the designer cannot be sure of the 'correct' value to enter for the elastic modulus and area of the diaphragm braces. One way in which he can make this judgement is by consideration of the proportion of the horizontal loading that is resisted by each of the frames at each level in the lateral load resisting system, LLRS.

This is achieved after analysis by considering the Storey Shear results. See Reviewing Storey Shear for more details.

Chapter 5 : Member End Releases and Member Orientation Building Designer - Eurocodes page 35Chapter 5 Member End Releases and Member Orientation

Once you start using Member Beams, Member Columns, General Beams, General Columns and Shear Walls, you are no longer dealing with a simple model where all the beams have pinned ends and only resist major axis moments.

The design forces established in frames with moment connections are all distributed according to relative member stiffnesses. Therefore, in addition to ensuring that the member properties are correct, you need to review and take control over member end releases and member orientations.

Note An important double check on all of this is to spend some time reviewing the analysis results. You may want to read Initial Review of Analysis Results on page 60 for some notes/tips on this.

Major topics Moment Releases Axial Releases Torsional Releases Release from a Diaphragm Member Orientations Supports and Base Fixity

Moment Releases

Member end moment releases are best reviewed graphically by showing the release state of the model (pick Edit/Show/Alter State, and then pick Moment Releases from the Analysis tab of the dialog).

Moment releases are indicated by an arrow with a double arrowhead. The releases for all supports, General Beams, General Columns, Member Beams and

Member Columns are shown. The releases for Simple Beams and Composite Beams are not shown purely to limit screen

clutter they are always released for major and minor axis bending.

Building Designer - Eurocodes page 36 Chapter 5 : Member End Releases and Member OrientationIn the view above the front-left-elevation is created with General Beams and General Columns to form a moment resisting frame. The downward arrows at the nodes at the end of most of the beams therefore indicate that the beams are pinned in the minor axis moment direction.

While this view is active you can click on node positions to select them (one or several at a time) and edit the releases via the Properties pane.

Note You can only select end nodes for the currently active member type. Releases for inactive member types are shown in grey.

When setting/changing moment releases for General Beams the options available include:

Free Used to indicate the free end of a cantilever. (Not really needed analytically, but needed to set effective lengths more appropriately.)

Simple Connection The connection is pinned for both major axis (My) and minor axis (Mz) bending.

Moment Connection The connection is fixed for major axis (My) bending but remains pinned for minor axis (Mz) bending.

Fully Fixed The connection is fixed for both major axis (My) and minor axis (Mz) bending.

Continuous This setting is automatically applied when a continuous beam is created and effectively creates a non-editable fully fixed connection between the spans of the continuous member. The connection can only be edited by splitting the beam.

When setting/changing moment releases for Member Beams the options are slightly different:

Free Used to indicate the free end of a cantilever.

Pinned This is the same as the Simple Connection noted above, the connection is pinned for both major axis and minor axis bending.

Pinned About Local y This setting creates a pinned connection for major axis bending but the connection remains fixed for minor axis bending. (x is along the member, y is the major cross section axis and z is the minor cross section axis.)

Pinned About Local z This is the same as the Moment Connection noted above for General Beams, the connection is fixed for major axis bending but remains pinned for minor axis bending.

Fully Fixed This is the same as the Fixed Connection noted above, the connection is fixed for both major axis and minor axis bending.

Chapter 5 : Member End Releases and Member Orientation Building Designer - Eurocodes page 37Continuous This setting is automatically applied when a continuous beam is created and effectively creates an non-editable fully fixed connection between the spans of the continuous member. The connection can only be edited by splitting the beam.

Note If the sign conventions seem confusing the very best way to review what you are doing is to show the graphical representation of the member releases as discussed at the start of this section.

Note You can also edit the intermediate connections on columns.

Axial Releases

Pick Edit/Show/Alter State, and then pick Axial Releases from the Analysis tab to graphically review the axial release state of the model.

The axial releases for all General Beams, General Columns, Member Beams, Member Columns and truss chords are shown and can be edited.

The axial releases for V Braces are shown, but can not be edited. The axial releases for Simple Beams, Composite Beams, Braces, Truss internals and sides

are not shown purely to limit screen clutter they are always released axially. General Beams and Member Beams can be released axially at either end, but not both. If a beam is continuous it can only be released axially at one or other of its extreme ends. Columns and Member Columns can only be released axially at the top end.

While this view is active clicking on a node will toggle its state between Fixed and Released.

Note You can only select end nodes for the currently active member type.

Building Designer - Eurocodes page 38 Chapter 5 : Member End Releases and Member OrientationTorsional Releases

Pick Edit/Show/Alter State, and then pick Torsional Releases from the Analysis tab to graphically review the torsional release state of the model.

The default torsional release state is Fixed. You are prevented from releasing both ends of the same member in torsion. Clicking on a node will toggle its state between Fixed and Released.

Note You can only select end nodes for the currently active member type.

Release from a DiaphragmA diaphragm will maintain exact relative positioning of all nodes that it constrains, i.e. the distance between any two nodes constrained by a diaphragm will never change, therefore no axial load will develop in any member that lies in the plane of a diaphragm between any two constrained nodes. You can however elect to remove General Beam, Member Beam and Truss Chord nodes from the diaphragm, allowing axial forces to develop within those members.

For example, consider the braced tower shown below, in which a lateral load has been applied at first floor level:

Chapter 5 : Member End Releases and Member Orientation Building Designer - Eurocodes page 39If a diaphragm has been activated at that level, then by default none of the lateral load will be transferred into the General Beam. To generate axial force in the beam you are required to edit the beam properties and exclude one or both of the beam ends from the diaphragm.

Because in the above example the load is being applied to end 1 of the beam, this is the end that requires to be excluded. If only end 2 were excluded the load would remain in the diaphragm.

Note Nodes at support positions, (either column or supplementary), are automatically excluded from all diaphragms.

Member OrientationsAll member orientations are reflected in the graphical views as appropriate.

By default beams of all types are placed with their major axis horizontal (in the global XY plane). For the vast majority of beams this will be the required orientation.

By default vertical columns are placed with their major axis in the global XZ plane. Clearly, at best, these default column orientations are only likely to be correct around 50% of the time.

You can control the orientation of each newly inserted member by setting the appropriate member orientation (under the Alignment tab) of the current attribute set.

You can edit the orientation of one or more selected members simultaneously by adjusting the appropriate details in the Property pane.

An exception to the above is the case of inclined Columns as you define these Fastrak Building Designer calculates the orientation angle automatically so that the web is vertical. You can not edit this angle.

Caution Since foundation shears and moments are reported relative to each columns local axis system the automatic calculation of the member orientation for inclined

Columns can initially be a little confusing.

Building Designer - Eurocodes page 40 Chapter 5 : Member End Releases and Member OrientationSupports and Base FixityA few points are worth noting on this topic:1. The view in Moment Releases also shows that you can view and edit support releases

when viewing member releases graphically.

2. Supports are automatically created as you create any columns, by default these supports are always released (pinned).

3. For General and Member Columns you can select the support and adjust the base fixity between different fixity settings:a) Pinned the default setting. b) Nominally Pinned where a rotational spring stiffness (10 or 20% of column stiffness)

is automatically calculated and applied.c) Nominally Fixed where a rotational spring stiffness of 100% column stiffness is

automatically calculated and applied.d) Fixed a fully fixed support.e) In cases b and c above you can also specify a user-defined base fixity.

Note A nominally fixed support is not the same as a fully fixed support, a nominally fixed support will rotate according to the spring stiffness and this will affect deflections. If you have a genuinely fixed support you are indicating that no rotation will occur at the support.

The above options may be of particular interest where you want to achieve overall stability by frame action as opposed to diagonally braced panels.

Overall you should find that, by default, members tend to be pinned in Fastrak Building Designer, so if you are editing releases you will generally be adding fixity. This is the opposite of the way in which most analysis packages work (where everything is initially fixed and releases have to be added) but we consider this to be a more conservative and realistic approach.

Chapter 6 : Load Cases and Load Combinations Building Designer - Eurocodes page 41Chapter 6 Load Cases and Load Combinations

Loads are applied to the model in loadcases categorised by type, (Dead, Imposed, Wind, etc.) Once the loadcases have been created, combinations are then generated for design. Various Wizards are provided to assist in this process.

Major topics Nationally Determined Parameters (NDPs) Gravity Load Cases Lateral Load Cases Combinations Classifying Combinations and Setting the Critical Combinations

Nationally Determined Parameters (NDPs)The Eurocode has differing NDPs for the Eurocode (Base) and for each of Eurocode (UK), Eurocode (Irish) etc. These are defined in the relevant country's National Annex.

Gamma () factors and psi () factors for each National Annex are listed below:

gamma factors

Factor EC Base value UK Value Irish ValueEQU combs

Gj,sup 1.10 1.10 1.10Gj,inf 0.9 0.9 0.9Q (fav) 1.5 1.5 1.5STR combs

Gj,sup 1.35 1.35 1.35Gj,inf 1.0 1.0 1.0Q (fav) 1.5 1.5 1.5 0.85 0.925 0.85GEO combs

Gj,sup 1.0 1.0 1.0Gj,inf 1.0 1.0 1.0Q 1.3 1.3 1.3

Building Designer - Eurocodes page 42 Chapter 6 : Load Cases and Load Combinationspsi factors

Factor EC Base value UK Value Irish Value0 1 2 0 1 2 0 1 2

Category A - imposed domestic/residential

0.7 0.5 0.3 0.7 0.5 0.3 0.7 0.5 0.3

Category B - imposed office

0.7 0.5 0.3 0.7 0.5 0.3 0.7 0.5 0.3

Category C - imposed congregation

0.7 0.7 0.6 0.7 0.7 0.6 0.7 0.7 0.6

Category D- imposed shopping

0.7 0.7 0.6 0.7 0.7 0.6 0.7 0.7 0.6

Category E- imposed storage

1.0 0.9 0.8 1.0 0.9 0.8 1.0 0.9 0.8

Category H- imposed roofs

0 0 0 0.7 0 0 0.6 0 0

Snow Loads < 1000m 0.5 0.2 0 0.5 0.2 0 0.5 0.2 0

Wind Loads 0.6 0.2 0 0.5 0.2 0 0.6 0.2 0

Chapter 6 : Load Cases and Load Combinations Building Designer - Eurocodes page 43Gravity Load CasesGravity loadcases can be created for:

self weights, dead, snow, snow drift, imposed, and roof imposed loads

Self weight loads can all be determined automatically. However other gravity load cases have to be applied manually as you build the structure.

Self Weight

Self weight - excluding slabs loadcase Fastrak Building Designer automatically calculates the self weight of the structural beams/columns for you. The Self weight - excluding slabs loadcase is pre-defined for this purpose. It can not be edited and by default it is added to each new load combination.

Self weight of concrete slabsFastrak Building Designer expects the wet and dry weight of concrete slab to be defined in separate loadcases. This is required to ensure that members are designed for the correct loads at construction stage and post construction stage. These loadcases are not pre-defined. However, two loadcase types are reserved to assist in their creation:

Slab Wet select this loadcase type to define the wet weight of concrete at construction stage.

Slab Dry .select this loadcase type to define the dry weight of concrete, post construction stage.

Fastrak Building Designer can automatically calculate the above weights for you taking into account the slab thickness, the shape of the deck profile and wet/dry concrete densities. It does not explicitly take account of the weight of any reinforcement but will include the weight of decking. Simply click the Automatic Loading check box when you create each loadcase. When calculated in this way you cant add extra loads of your own into the loadcase.

If you normally make an allowance for ponding in your slab weight calculations, Fastrak Building Designer can also do this for you. When specifying the slab Attributes - you will find two ways to add an allowance for ponding (on the Floor Construction tab). These are:

as a value, by specifying the average increased thickness of slab or, as a percentage of total volume.

Using either of these methods the additional load is added as a uniform load over the whole area of slab.

Building Designer - Eurocodes page 44 Chapter 6 : Load Cases and Load CombinationsImposed and Roof Imposed Loads

Imposed Load ReductionsReductions can be applied to imposed loads to take account of the unlikelihood of the whole building being loaded with its full design imposed load. Reductions can not however be applied to roof imposed loads.

Note If the imposed load is considered as an accompanying action (i.e. a factor is applied to the imposed load case in a combination) then as stated in the Base Eurocode Cl3.3.2, the imposed load reduction can not be applied at the same time - see Apply Imposed Load Reductions.

Although the code allows for imposed load reductions to be applied to floors (beams), Fastrak Building Designer does not implement this. Only the imposed loads on columns are reduced.

If a level is not set to be a floor then no reductions are accounted for at that level and it will not be counted as a floor in determining the amount of reduction to make. (See Is it a Floor?on page 71).

Note A floor that has loads that do not qualify for imposed load reduction does not count in the storey count. (Unlike the approach for the BS 5950 design code.)

The method used for determining the reductions is dependant on the National Annex: In the Base Eurocode a formula is given in Clause 6.3.1.2(11), this is also used if the Irish

National Annex is selected. In the UK, the NA permits an alternative method of reduction using NA 2.6.

Definition of psi factors for imposed load casesImposed loads are categorised as follows:

Category A - domestic/residential Category B - office Category C - congregation Category D - shopping Category E - storage

The default values of 0, 1 and 2 vary depending on the category selected and also with the National Annex being worked to. The values can be edited if required.

Definition of psi factors for roof imposed load casesRoof imposed loads are not categorised so the default values of 0, 1 and 2 only vary depending on the National Annex being worked to. Again, the values can be edited if required.

Snow and Snow Drift Loads

Definition of psi factors for snow and snow drift load casesThe default values of 0, 1 and 2 can vary depending on the National Annex being worked to. The values can be edited if required.

Note Snow drift loads are considered to be accidental load cases and are combined in the Accidental combinations.

Chapter 6 : Load Cases and Load Combinations Building Designer - Eurocodes page 45Perimeter LoadsProvided you have a gravity loadcase selected, (other than one of the self weight cases mentioned above), you will be able to access the Create Perimeter Load... command from the Loading menu. This will generate a uniform load for you around the entire building perimeter.

Lateral Load CasesLateral loadcases can be created for Wind Loads as detailed below.Equivalent Horizontal Forces (EHF) are also lateral loadcases, however these are only accessible when creating load combinations.

Wind Loads

The EC1-4 Wind WizardThe Wind Wizard is run to create a series of static forces that are combined with other actions due to dead and imposed loads in accordance with BS EN 1990.

The following assumptions/limitations exist:- The shape of the building meets the limitations allowed for in the code. It must be a rigid structure. The structure must be either enclosed or partially enclosed. Parapets and roof overhangs are not explicitly dealt with.

For further information on the wind loading capabilities of Fastrak Building Designer refer to the EC1 1-4 Wind Modeller Handbook.

Simple Wind LoadingIf use of the Wind Wizard is not appropriate for your structure there is a facility to load walls with a stepped horizontal pressure load - this facility is referred to as Simple Wind Loading.

Simple wind loads are created in a similar way to other loadcases. Within the Loadcases dialog, provided the load type is set to Wind, an extra Wind loading tab becomes available. The Generate... button on this tab is then used to create the stepped pressure. Alternatively, provided a loadcase of type wind is currently selected, the same Simple Wind Loading... functionality can be accessed from the Loading menu. To apply the wind to the building you must create a series of walls.

The Simple Wind loading strikes all outward facing walls which can be seen in the wind direction defined. If the wind strikes an inward facing wall then it passes through the wall and does not load the structure. The simple way to verify in which direction your wall surface faces is to use Show/Alter State in the structure view.

Definition of psi factors for wind load casesThe default values of 0, 1 and 2 vary depending on the National Annex being worked to. The values can be edited if required. .

Building Designer - Eurocodes page 46 Chapter 6 : Load Cases and Load CombinationsCombinationsOnce your load cases have been generated as required, you then combine them into load combinations. If The Construction Stage Combination is required, click the Add Construct. button. Additional combinations can either be created manually, by clicking Add... - or with the assistance of The Combinations Wizard, by clicking Generate...

The Construction Stage CombinationIf you have created a Slab Wet loadcase you are required to generate a Construction Stage load combination so that it is considered in the design process. Other loadcases can be included in this combination, however loadcases of type: Slab Dry and Wind are specifically excluded.

If you add/remove a load case type from this combination - the factors are defaulted as follows: 'Self weight' - default Strength factor = 1.35, default Service factor = 1.0 'Slab Wet' - default Strength factor = 1.35, default Service factor = 1.0 'Dead' - default Strength factor = 1.35, default Service factor = 1.0 'Imposed'- default Strength factor = 1.5, default Service factor = 1.0

The Construction Stage load combination is then used specifically in the design of any composite beams within the model.

Note The Slab Wet loadcase can not be included in any other combination.

Manually Defined CombinationsAs you build up combinations manually, the combination factors are automatically adjusted as load cases are added and removed from the combination.

If you add/remove a load case type from a combination - the factors are defaulted as follows: 'Self weight' - default Strength factor = 1.35, default Service factor = 1.0 'Slab Dry' - default Strength factor = 1.35, default Service factor = 1.0 'Dead' - default Strength factor = 1.35, default Service factor = 1.0 'Imposed'- default Strength factor = 1.5, default Service factor = 1.0 'Roof Imposed'- default Strength factor = 1.05, default Service factor = 1.0 With an Imposed load case

'Wind' - default Strength factor = 0.75, default Service factor = 0.5 'Snow' - default Strength factor = 0.75, default Service factor = 0.5

With No Imposed load case 'Wind' - default Strength factor = 1.5, default Service factor = 1.0 With Wind load case

'Snow' - default Strength factor = 0.75, default Service factor = 0.5 With no Wind load case

'Snow' - default Strength factor = 1.5, default Service factor = 1.0

Chapter 6 : Load Cases and Load Combinations Building Designer - Eurocodes page 47Equivalent Horizontal Forces (EHF)EHFs are used to represent frame imperfections. The Eurocode requires they are applied to all combinations. (Lateral wind combinations therefore should also have EHFs applied).

Note Fastrak Building Designer allows you to set up combinations without EHFs to save time during the initial Gravity Sizing, however you should ensure that they are subsequently taken into account at the Full Design stage.

EHFs are automatically derived from the factored load cases within the current combination. They are applied in the analysis as a horizontal force at each beam column intersection with a magnitude of 0.5% of the vertical load in the column at the column/beam intersection.

They can be applied to your combinations in each of four directions as follows: EHF X+ EHF X- EHF Y+ EHF Y-

Note If required EHF's can be applied in both X and Y within a load combination and factored appropriately to represent an application at an angle to the X/Y axes,

Caution See Equivalent Horizontal Force Load CalculationsEquivalent Horizontal Force Load Calculations in the Assumptions and Limitations section of this document for important information about which loads are taken into account in the EHF calculations.

Apply Imposed Load ReductionsAll imposed load cases can be set to have imposed load reductions calculated. However, reductions can not be applied if the imposed load case is an accompanying action within the combination (i.e. if 0 has been applied).If you define load combinations manually it is therefore your responsibility to check the Apply Imp. Reductions box if required when the combination is defined.

If you use the combinations wizard to automatically generate your load combinations, the imposed load reductions will only be applied to those combinations where 0 is not used.

Building Designer - Eurocodes page 48 Chapter 6 : Load Cases and Load CombinationsThe Combinations WizardAccessed via the Generate... button, this automatically sets up combinations for both strength and serviceability.

Combination Wizard - Initial ParametersAt the start of the wizard, you need to define certain parameters so that the correct combinations are generated - these are described below:

Combination for design of structural members (STR)You can chose between:

Table A1.2(B) - Eq 6.10, or Table A1.2(B) - Eq 6.10,a&b

Eq 6.10 is always equal to or more conservative than either 6.10a or 6.10b. The most economic combination of 6.10a or b will depend on if permanent actions are greater than 4.5 times the variable actions (except for storage loads).

Include GEO combinations - Table A1.2(C) - Eq 6.10The Eurocode version of Fastrak Building Designer does not currently design foundations, however if you require the foundation design forces reporting you should check this option.

Include Accidental combinations - Table A2.5 Eq 6.11a&bIf you have defined an accidental load type such as Snow drift you should check this option for the correct load combinations to be generated.

Note The Combinations Wizard refers to the relevant National Annex when determining the factors to apply in the above combinations, as they may vary from the Base Eurocode values.

Type of Structure for Default Generated CombinationsYou can chose between:

Multi-storey building, or Portal frame building

The default generated combinations that result are likely to be the most onerous for a typical structure of that type.

Combination Wizard - CombinationsThe second page of the wizard lists the combinations applicable (with appropriate factors) for the selections made on the first page. Any factors in bold will be multiplied by the relevant psi factors for that load case.

The type of structure chosen on the previous page affects which combinations default to being generated.

Chapter 6 : Load Cases and Load Combinations Building Designer - Eurocodes page 49The combination names are automatically generated as per the table below:

No. BS EN 1990 State and Eqn Type Load Combination

1 Str 6.10 Gravity Str1 - Gj,supD+QI+ QRI2 Str2 - Gj,supD+Q0I+QS3 Lateral (EHF) Str3.n - Gj,supD+QI+QRI+EHF4 Str4.n - Gj,supD+QI+Q0S+EHF5 Str5.n - Gj,supD+Q0I+QS+EHF6 Lateral (Wind+EHF) Str6.n - Gj,supD+QI+Q0S+Q0W+EHF7 Str7.n - Gj,supD+Q0I+QS+Q0W+EHF8 Str8.n - Gj,supD+Q0I+Q0S+QW+EHF9 Uplift (Wind+EHF) Str9.n - Gj,infD+QW+EHF

1 Str 6.10a&b Gravity Str1 - Gj,supD+Q0I+ Q0RI2 Str2 - Gj,supD+Q0I+Q0S3 Str3 - Gj,supD+QI+QRI4 Str4 - Gj,supD+Q0I+QS5 Lateral (EHF) Str5.n - Gj,supD+Q0I+Q0RI+EHF6 Str6.n - Gj,supD+Q0I+Q0S+EHF7 Str7.n - Gj,supD+QI+QRI+EHF8 Str8.n - Gj,supD+QI+Q0S+EHF9 Str9.n - Gj,supD+Q0I+QS+EHF10 Lateral (Wind+EHF) Str10.n - Gj,supD+Q0I+Q0S+Q0W+EHF11 Str11.n - Gj,supD+QI+Q0S+Q0W+EHF12 Str12.n - Gj,supD+Q0I+QS+Q0W+EHF13 Str13.n - Gj,supD+Q0I+Q0S+QW+EHF14 Uplift Str14.n - Gj,infD+QW+EHF

1 Geo - 6.10 Lateral (EHF) Geo1.n - Gj,supD+QI+QRI+EHF2 Geo2.n - Gj,supD+QI+Q0S+EHF3 Geo3.n - Gj,supD+Q0I+QS+EHF

Building Designer - Eurocodes page 50 Chapter 6 : Load Cases and Load CombinationsCombination Wizard - Service FactorsThe next page of the wizard indicates which combinations are to be checked for serviceability and the factors applied.

Combination Wizard - NLsThe last page of the wizard is used to set up the NLs or notional loads (for example the equivalent horizontal forces). You can specify EHFs and factors in each of four directions. For each direction selected a separate EHF combination will be generated.

Click Finish to see the list of generated combinations.

Classifying Combinations and Setting the Critical CombinationsHaving created your combinations you classify them as either Gravity Combinations, Lateral Combinations, or Seismic Combinations and also indicate whether they are to be checked for strength or service conditions, or both.

Note If generated via the Combinations Wizard they are classified for you automatically.

You also have the option to make any of the combinations inactive.

At the same time you should nominate which are to be the critical combinations for the automatic sizing process. (Gravity Sizing and Lateral Sizing) - see Setting the Critical Combinations

Note For details of Gravity Sizing, Lateral Sizing and Full Design see Overview of the Analysis and Design Processin the next chapter.

4 Lateral (Wind+EHF) Geo4.n - Gj,supD+QI+Q0W+Q0S+EHF5 Geo5.n - Gj,supD+Q0I+QS+Q0W+EHF6 Geo6.n - Gj,supD+Q0I+Q0S+QW+EHF7 Uplift (Wind+EHF) Geo7.n - Gj,infD+Q,1W+EHF

1 Acc 6.11 Lateral (EHF) Acc1.n - G+Ad+1I+EHF2 Lateral (Wind+EHF) Acc2.n - G+Ad+2I+1W+EHF

No. BS EN 1990 State and Eqn Type Load Combination

Chapter 6 : Load Cases and Load Combinations Building Designer - Eurocodes page 51Gravity CombinationsThese combinations are used for Gravity Sizing. (They are not used for Lateral Sizing.)

All members in the structure are automatically sized (or checked) for the gravity combinations during the gravity sizing process.

In addition, all members in the structure are checked for the gravity combinations during the Full Design process.

Lateral CombinationsThese combinations are used for Lateral Sizing. (They are not used for Gravity Sizing.)

All members which have not been set as Gravity Only are sized (or checked) for the lateral combinations during the gravity sizing process.

In addition, all members which have not been set as Gravity Only are checked for the lateral combinations during the Full Design process.

Seismic CombinationsNote Although included in this documentation, these are only available for use in

regions where seismic design is required.

These combinations are not considered in either the Gravity Sizing or Lateral Sizing.

All members are checked for the seismic combinations during the Full Design process.

Setting the Critical CombinationsYou are required to identify at least one critical gravity combination and one lateral combination. The critical lateral combination could contain notional, or wind loads (not seismic). Up to four lateral combinations can be selected, typically one of each sign (i.e. +X,+Y,-X,-Y) in which case they will be acting at 90 degrees to each other.

The purpose of nominating critical combinations is to reduce the time taken to perform the Gravity Sizing and Lateral Sizing processes.

It is down to your judgement as the designer to identify the most critical combinations. Given that this choice may not be clear or may be made incorrectly, there is the potential for sections to fail under other design combinations. However, this situation will be detected because Fastrak Building Designer always requires you to perform a Full Design, (which is a full analysis/check design process for all active load combinations) before the building can be given a 'valid overall design' status.

Note For details of Gravity Sizing, Lateral Sizing and Full Design see Overview of the Analysis and Design Processin the next chapter.

Building Designer - Eurocodes page 52 Chapter 7 : Analysis And Design ProceduresChapter 7 Analysis And Design Procedures

This chapter provides an overview of the analysis and design process, and describes the various options involved. Suggested techniques for reviewing the answers are also given.

Major topics Definitions Building Validation Overview of the Analysis and Design Process Analysis Options Design Options Initial Review of Analysis Results 3D Analysis Effects Refining Member Designs

DefinitionsSome definitions of words and phrases used in the remainder of the chapter are given below:

Alpha-crit (cr )the factor by which the design loading would have to be increased to cause instability in a global mode. cr is determined from a sway stability analysis and used to determine the sway sensitivity of the structure.

First-order analysis linear elastic analysis that takes no account of the effect on the forces due to deformations of the structure.

Second-order (P-Delta) analysis analysis that takes into account the effect on the forces due to deformations of the structure. Either:

by using the Amplified Forces Method, or by a rigorous method using a two step iterative approach.

Amplified Forces Method using this method, second order sway effects due to vertical loads are calculated by amplifying horizontal loads as per Clause 5.2.2 (5)B.

Gravity members gravity members resist only vertical loading. They are designed for gravity combinations only. Simple Beams, Simple Columns and Composite Beams are typically gravity members. However other members can also be set to Gravity Only

Lateral members lateral members resist vertical (gravity) and horizontal (lateral) loading. General Beams, General Columns and Braces are lateral members. They are designed for gravity and lateral combinations.

Chapter 7 : Analysis And Design Procedures Building Designer - Eurocodes page 53Equivalent Horizontal Forcesthese are used for two purposes:

for the calculation of cr to represent frame imperfections

EHFs are calculated as 0.5% of vertical Dead and Imposed loads. These are sometimes referred to as Notional Loads.

Building ValidationValidation is a check on your structure which you must perform before you can analyse and design it. Validation checks all elements in your structure for a wide range of conditions. If

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