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BUILDING DESIGNER
Building Designer Documentation page 2 CSC (UK) Ltd Yeadon House New Street Pudsey Leeds LS28 8AQ Tel: (44) 113 239 3000 Fax: (44) 113 236 0546 Email: [email protected] [email protected] Internet: www.cscworld.com CSC Inc
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Table of Contents Building Designer Documentation page 5
Engineer’s Handbooks
Building Designer Engineer’s Handbook
Chapter 1
Modelling and Analysis
. . . 17Chapter 2
Building Effective Models in Fastrak Building Designer
. . . 18Grid Lines . . . 18
Attributes . . . 18
Loading Self Weight of Concrete Slabs . . . 18
Loading applied to slabs . . . 19
Staged modelling and design . . . 19
Simple Construction is still the best method . . . 19
Use ‘Simple’ beams and columns where possible . . . 19
NOTE — Simple Columns and Sway Stability. . . 20
Design Simple Construction for Gravity Loads only . . . 20
Diaphragm Action . . . 20
Composite Beam Design . . . 21
Composite or simple beam . . . 21
Setting the appropriate level of deflection checks . . . 22
Building Size and Orientation . . . 22
Automatic NHF calculations . . . 22
Number of design runs . . . 23
Number of load combinations . . . 23
Stepped Design Process . . . 23
Results . . . 23
Chapter 3
Simple Wind Loading
. . . 25Chapter 4
Overview of Construction Types
. . . 26Member Beams and Member Columns. . . 26
Section/Material Properties . . . 27
Analytical Properties (End Releases) . . . 27
General Beams . . . 27
Creating General Beams . . . 27
Analytical Properties (End Releases) . . . 28
Design Properties . . . 28
General Columns . . . 28
Creating General Columns. . . 28
Analytical Properties (End Releases) . . . 29
Design Properties . . . 29
Shear Walls . . . 29
Creating Shear Walls. . . 29
Shear Wall Limitations . . . 30
Analytical Properties . . . 30
Transfer Shear Walls. . . 31
Getting the Analysis Model Right. . . 31
End Releases . . . 32
Axial Releases. . . 33
Building Designer Documentation page 6 Table of Contents
Supports and Base Fixity . . . 34
Reviewing the Analysis Results . . . 35
Practical considerations . . . 35
Chapter 5
Overview of Analysis And Design Procedures
. . . 36Controlling the design procedure . . . 36
Why is it an iterative procedure? . . . 37
Controlling the iterative procedure. . . 38
Speeding up iterative analysis and design . . . 39
Limiting the iterations. . . 39
Leaving the Start from beginning of order file on each pass option un-checked . . . . 39
Initial Review of Analysis Results . . . 40
Maximum Nodal Deflections . . . 41
Sway Sensitivity. . . 41
Loading Summary . . . 41
Review of Selected Sections. . . 41
Review Analysis Results . . . 42
3D Analysis Effects . . . 42
Continuous Beam Example . . . 42
Braces Carry Gravity Loads Example . . . 45
Interactive Design. . . . 48
Chapter 6
Construction Levels, Floors and Diaphragms
. . . 49Is it a Floor? . . . 49
Diaphragm Modelling . . . 49
Single diaphragm. . . 50
Slab items defined. . . 50
No diaphragm. . . 51
Taking slabs out of a diaphragm. . . 51
Chapter 7
Rigid Framing and Gravity Loads
. . . 53Backspan Beams . . . 53
General Points to Note . . . 53
Pattern Loading. . . 53
Transfer Beams / Levels . . . 54
Chapter 8
Sway Resistance
. . . 55Introduction. . . . 55
Using Bracing . . . 55
Using Steel Moment Resisting Frames . . . 56
Using Other Moment Resisting Frames . . . 56
Using Shear Walls. . . 56
Chapter 9
Connections Integration
. . . 59Introduction. . . . 59
Simple Connections . . . 60
General Limitations . . . 60
Table of Contents Building Designer Documentation page 7
Vertical cross bracing . . . 62
Foundation shear and vertical load . . . 62
Column axial load . . . 62
Notional Horizontal Force Load Calculations. . . 63
Gravity loads carried by braces not accounted for in NHF load calculations. . . 63
Axial load in discontinuous columns used twice in NHF load calculations . . . 63
Chapter 11
Sign Conventions
. . . 64General beam sign conventions . . . 64
Simple beam sign conventions . . . 65
General column foundation sign conventions . . . 66
Simple column foundation sign conventions. . . 68
Supplementary supports sign conventions . . . 69
Column orientation effects . . . 70
Building Designer Advisory Note – Designing for Second-order Effects
Chapter 12
Summary
. . . 71Chapter 13
Introduction
. . . 73Chapter 14
Basic concepts
. . . 74Chapter 15
Second-order options
. . . 76Analysis options. . . 76 Design combinations . . . 76
Chapter 16
Analysis
. . . 80 General . . . 80 Analysis model . . . 80 Analysis results . . . 81Chapter 17
Design
. . . 86 Member design . . . 86Connection design information . . . 86
Serviceability Limit State . . . 89
Chapter 18
Other issues
. . . 90Determination of λcr . . . 90
Connection stiffness . . . 91
Base stiffness . . . 91
Chapter 19
References
. . . 93Building Designer Advisory Note – Integrated connection design
Building Designer Documentation page 8 Table of Contents
Chapter 20
Introduction
. . . 95Chapter 21
Practical Applications
. . . 97Simple Connections . . . 97
Moment Connections . . . 97
Column Base Connections . . . 98
Chapter 22
Scope
. . . 99Simple Connections . . . 99
Moment Connections . . . .100
Column Base Connections . . . 102
Chapter 23
Limitations and Assumptions
. . . 103. . . . . . . . . . . . . . Simple Connections103 Limitations - . . . 103 Assumptions - . . . 104 Moment Connections . . . .105 Limitations - . . . 105 Assumptions - . . . 107
Column Base Connections . . . 108
Chapter 24
Analysis
. . . .109Global analysis - . . . 109
Connection analysis - . . . .109
Chapter 25
Ultimate Limit State
. . . .110Simple Connections . . . .110
. . . . . . . . . . . . . . Moment Connections111 Column Base Connections . . . 115
Chapter 26
Accidental Limit State
. . . 116Structural Integrity . . . .116
Fire Limit State . . . 117
Chapter 27
Serviceability Limit State
. . . 118Building Designer Advisory Note – Definition and Design of Trusses and
Truss Members
Chapter 28
Introduction
. . . 119Table of Contents Building Designer Documentation page 9
Chapter 31
Limitations and Assumptions
. . . 123Limitations . . . 123 Assumptions . . . 123 Supports – . . . 123 Restraints – . . . 124
Chapter 32
Analysis
. . . 125 Global analysis – . . . 125 Member analysis – . . . 125Chapter 33
Ultimate Limit State – Strength
. . . 126Classification – . . . 126
Shear Capacity – . . . 126
Moment Capacity – . . . 127
Axial Capacity –. . . 127
Cross-section Capacity – . . . 128
Chapter 34
Ultimate Limit State – Buckling
. . . 130Lateral Torsional Buckling Resistance, Clause 4.3 –. . . 130
Lateral Torsional Buckling Resistance, Annex G – . . . 130
Compression Resistance – . . . 131
Member Buckling Resistance, Clause 4.8.3.3.1 – . . . 132
Member Buckling Resistance, Clause 4.8.3.3.2 – . . . 132
Member Buckling Resistance, Clause 4.8.3.3.3 – . . . 133
Chapter 35
Serviceability Limit State
. . . 134Chapter 36
Member End Fixity and Supports
. . . 135Chapter 37
Miscellaneous
. . . 137Wind Modeller Engineer’s Handbook
Chapter 38
Introduction
. . . 139Chapter 39
Scope
. . . 140Chapter 40
Limitations
. . . 142Chapter 41
Applying Walls and Roofs
. . . 14641.1 Applying Walls . . . 146
41.2 Applying Roofs . . . 146
Building Designer Documentation page 10 Table of Contents
Chapter 43
Creating Wind Zones on the Building
. . . 14843.1 Basic Geometry . . . .148 43.2 Wall Zones . . . 149 43.2.1 Wall Type . . . .149 43.2.2 Windward Walls . . . 149 43.2.3 Leeward Walls. . . .149 43.2.4 Side Walls . . . .150 43.3 Roof Zones . . . 150 43.3.1 Direction . . . .150 43.3.2 Automatic Zoning . . . 151 43.3.3 Non-Automatic Zoning . . . 152
43.4 User Modification of Zones . . . 152
Chapter 44
Load Decomposition
. . . .15344.1 Roofs . . . .153
44.2 Walls . . . .153
Chapter 45
References
. . . .154Simple Beam Engineer’s Handbook
Chapter 1
Introduction and application
. . . 157Practical applications . . . .157 Designing a beam . . . .157 Checking a beam . . . .158 Worked Example . . . 159 Design Pass 1 . . . 160 Design Pass 2 . . . 161 Design Pass 3 . . . 162
Chapter 2
Scope
. . . .163Scope of simple beam . . . .163
Beam . . . .163 Steel sections . . . 163 Web openings . . . 163 Restraint conditions . . . .164 Applied loading. . . 165 Design checks . . . 165
Error messages and limitations . . . 165
Chapter 3
Theory and Assumptions
. . . 167Analysis method . . . 167
Design method . . . 167
Section classification . . . .167
Member strength checks . . . 167
Lateral torsional buckling checks . . . 167
Table of Contents Building Designer Documentation page 11
Further information – Westok Beams . . . 169
Composite Beam Engineer’s Handbook
Chapter 1
Introduction
. . . 173Practical applications. . . 173
Designing a beam . . . 173
Checking a beam . . . 175
Chapter 2
Scope
. . . 177Scope of composite beam . . . 177
Beam . . . 178
Westok sections . . . 178
Westok Technical Support and Design Service . . . 179
Steel sections . . . 180
Web openings. . . 180
Profiled metal decking . . . 181
Precast concrete slabs . . . 183
Concrete slab . . . 185
Shear connectors . . . 186
Reinforcement . . . 186
Fibre Reinforced Concrete. . . 187
Construction stage restraint conditions . . . 187
Construction stage loading . . . 188
Composite stage loading . . . 188
Construction stage design checks . . . 189
Composite stage design checks . . . 189
Error messages and limitations . . . 190
Chapter 3
Design Aspects
. . . 192Non-composite design within Composite Beam . . . 192
To invoke non-composite design in Building Designer . . . 192
To invoke non-composite design in Composite Beam . . . 193
Automatic transverse shear reinforcement design . . . 194
Bar spacing as a multiple of stud spacing. . . 195
Controlling the bar spacing directly. . . 195
Automatic transverse shear reinforcement design with Fibre Reinforced Concrete . . . 195
Specify the stud spacing at the start of automatic design . . . 196
Worked Example . . . 196
Without transverse shear reinforcement . . . 197
Design Pass 1 . . . 198
Design Pass 2 . . . 200
Design Pass 3 . . . 200
Chapter 4
Theory and Assumptions
. . . 201Analysis method. . . . 201
Design method . . . 201
Construction stage . . . 201
Section classification . . . 201
Member strength checks . . . 201
Lateral torsional buckling checks . . . 201
Deflection checks . . . 202
Building Designer Documentation page 12 Table of Contents
Composite stage . . . 202
Equivalent steel section - Ultimate limit state (ULS) . . . 202
Section classification (ULS) . . . 202
Member strength checks (ULS) . . . 203
Shear connectors (ULS) . . . 204
Section properties - serviceability limit state (SLS) . . . 205
Stress checks (SLS) . . . .206
Deflection checks (SLS) . . . 206
Natural frequency checks (SLS) . . . 206
Chapter 5
Theory and Assumptions – Westok beams
. . . 207Construction stage . . . .207
Classification . . . 207
Vertical shear . . . 207
Horizontal Shear . . . .208
Moment Capacity . . . .208
Lateral Torsional Buckling . . . 209
Deflection. . . .209
Web Post Flexure and Buckling . . . 210
Vierendeel Bending . . . .210 Composite Stage . . . 211 Classification . . . 211 Vertical shear . . . 211 Horizontal Shear . . . .212 Longitudinal shear . . . .212 Moment Capacity . . . .213
Web Post Flexure and Buckling . . . 213
Vierendeel Bending . . . .214
Deflections . . . 214
Service Stresses. . . 215
Natural frequency . . . .215
Chapter 6
References & Further Information
. . . .216References . . . .216
Further information – Bison precast concrete slabs . . . 216
Further information – Westok Beams . . . .217
General Beam Engineer’s Handbook
Chapter 1
Introduction and application
. . . 221Practical applications . . . .221 Designing a beam . . . .221 Checking a beam . . . .222 Worked Example . . . 223 Design pass 1 . . . 224 Design pass 2 . . . 224 Design Pass 3 . . . 226
Chapter 2
Scope
. . . .227Table of Contents Building Designer Documentation page 13
Assumptions . . . 229
Chapter 4
Analysis
. . . 230Building Modeller object . . . 230
General Beam . . . 230
Chapter 5
Ultimate Limit State – Strength
. . . 231Classification . . . 231 Important Note . . . 231 Shear Capacity . . . 231 Moment Capacity . . . 232 Note . . . 232 Axial Capacity . . . 232 Cross-section Capacity . . . 232
Chapter 6
Ultimate Limit State – Buckling
. . . 233Lateral Torsional Buckling Resistance, Clause 4.3 . . . 233
Lateral Torsional Buckling Resistance, Annex G . . . 233
Compression Resistance . . . 234
Member Buckling Resistance, Clause 4.8.3.3.1 . . . 235
Member Buckling Resistance, Clause 4.8.3.3.2 . . . 235
Important Note . . . 236
Member Buckling Resistance, Clause 4.8.3.3.3 . . . 236
Chapter 7
Serviceability Limit State
. . . 237Chapter 8
Member End Fixity and Supports
. . . 238General Beam Stand-alone. . . 238
Building Designer . . . 238
Chapter 9
Design Procedure
. . . 240Lateral torsional buckling checks. . . 240
Combined buckling checks . . . 241
Simple Column Engineer’s Handbook
Chapter 1
Introduction and application
. . . 245Practical applications. . . 245 Designing a column. . . 245 Checking a column . . . 246 Worked Example . . . 247 Design pass 1 . . . 248 Design pass 2 . . . 249 Design Pass 3 . . . 249
Chapter 2
Design of concrete filled columns
. . . 251Proposed method . . . 251
Building Designer Documentation page 14 Table of Contents
Chapter 3
References and further information
. . . 252References . . . .252
General Column Engineer’s Handbook
Chapter 1
Introduction and application
. . . 255Practical applications . . . .255 Designing a column . . . .255 Checking a column . . . .257 Worked Example . . . 258 Design pass 1 . . . 258 Design pass 2 . . . 260 Design Pass 3 . . . 260
Chapter 2
Scope
. . . .262Chapter 3
Limitations and Assumptions
. . . 264Limitations . . . .264
Assumptions . . . 264
Chapter 4
Analysis
. . . .266Building Modeller Object . . . 266
Chapter 5
Ultimate Limit State – Strength
. . . .267Classification . . . 267 Important Note. . . 267 Shear Capacity . . . 267 Moment Capacity. . . 268 Note . . . .268 Axial Capacity . . . 268 Cross-section Capacity . . . .269
Chapter 6
Ultimate Limit State – Buckling
. . . .270Lateral Torsional Buckling Resistance, Clause 4.3 . . . 270
Lateral Torsional Buckling Resistance, Annex G . . . 270
Compression Resistance . . . 271
Member Buckling Resistance, Clause 4.8.3.3.2 . . . 272
Important Notes . . . .272
Member Buckling Resistance, Clause 4.8.3.3.3 . . . 272
Chapter 7
Serviceability limit state
. . . 274Chapter 8
Design Procedure
. . . .275Chapter : Building Designer Documentation page 15
Engineer’s Handbooks
Introduction
This part of the documentation system contains essential engineering information relating to the individual design engines for each member type which is available in Building Designer. The following chapters deal with each object type in turn, and include essential tips on using the applications, as well as advanced engineering information pertaining to the applications, and references to the documentation on which the design requirements are based.
We recommend that all engineers using this software adopt the advice of SCOSS* and CROSS in their comments on the use of computer software - their advice is "to know the scope of the software, check results, ...., and check that the computer aided design is to the relevant codes of practice. Designers must remember that it is they, not software suppliers, who are responsible for design." (CROSS Newsletter No. 1 - Nov 2005)
Based on this advice, we strongly recommend that all users of the software familiarise themselves with all the relevant sections on Scope and Limitations and Assumptions to be found in the Engineer's Handbooks.
*UK Standing Committee On Structural Safety
The following Engineer’s Handbooks are available:
•
the Building Designer Engineer’s Handbook•
the Wind Modeller Engineer’s Handbook•
the Simple Beam Engineer’s Handbook•
the Composite Beam Engineer’s Handbook•
the General Beam Engineer’s Handbook•
the Simple Column Engineer’s Handbook•
the General Column Engineer’s HandbookIn addition the following Advisory Notes are also available:
•
Building Designer Advisory Note – Designing for Second-order Effects•
Building Designer Advisory Note – Integrated connection designChapter 1 : Modelling and Analysis Building Designer Documentation page 17
Building Designer Engineer’s Handbook
Chapter 1
Modelling and Analysis
Building Designer gives you complete flexibility to define any member with almost any properties between any two points in 3D space. While this is clearly flexible, and may sound simple, it requires you to consider the modelling of your structure in more detail than if it contained only simple (pin ended) beams and simple columns with no moment connections. This part of the documentation seeks to introduce some of the issues that you may wish to consider.
Building Designer Documentation page 18 Chapter 2 : Building Effective Models in Fastrak Building Designer
Chapter 2
Building Effective Models in Fastrak Building Designer
Fastrak Building Designer is a design based structural modeller.
Please remember that Fastrak Building Designer is a modelling package, which dictates the design model and which creates analysis models to accomplish this design. It is important that you recognise that you must take ownership of the creation of the model and the results that the software gives.
It is possible to create complete building designs quickly and easily with Fastrak Building
Designer, however as it is a design based modeller you should take account of the following issues1.
Grid Lines
You can define grid lines quickly and simply in Fastrak Building Designer. Alternatively you can import them into your model from a DXF file.
If you are importing grid lines from DXF files, please ensure:
•
that the grid lines you are using are accurate,•
that the DXF file you are importing only contains grid lines.If you are in doubt we advise you to use Building Designer’s ability to import a DXF file and create a ghost image of the structure. You can then add your Building Designer grid lines on top of the ghosted DXF image.
Attributes
It is important to realise that the attribute sets are used to set up defaults for the elements (beams, columns… …) in your model. The attribute sets are not linked to the elements once they are created.
You can quickly make major changes to your model, for example changing the grade of steel, quickly and easily, you need to change the appropriate attribute(s) and then apply these attribute(s) to the members.
IMPORTANT — when you create any member it takes the current default attributes. The default setting for a simple beam (unless you change it) is that it is fully restrained. Please take care if creating beams that are not fully restrained.
Loading Self Weight of Concrete Slabs
Building Designer automatically calculates the self weight of the structural beams/columns for you and provides automatic calculation of items like Notional Horizontal Forces (NHFs) and Wind Loads.
Chapter 2 : Building Effective Models in Fastrak Building Designer Building Designer Documentation page 19
Please note however that Building Designer DOES NOT automatically calculate the dry weight, or the wet weight of the concrete slab. When you calculate these values you should allow for two key issues:
•
the slab loads you calculate should make some assessment of, and allowance for, ponding that may occur,•
when your model contains composite beams you need to create your loadcases carefully to take account of the staged construction that will actually take place. To this end BuildingDesigner automatically creates the Slab wet and Slab Dry loadcases. It is important that you apply the relevant loads in the relevant loadcase correctly.
Loading applied to slabs
Building Designer applies floor loading, area loads, line loads and point loads to the slabs in your model and distributes them in the direction of span of the slab.
If you wish to apply loading directly to a beam, PARTICULARLY IF THAT BEAM SITS AT
THE EDGE OF THE SLAB, then you should use element loads which apply the load directly to the member without involving the slab.
To aid this Building Designer has a Create Perimeter Load facility. You can access this from the Loading menu.
Staged modelling and design
Our major piece of advice when you are modelling in Building Designer is:
DO NOT BUILD THE ENTIRE MODEL BEFORE YOU VALIDATE AND DESIGN IT. It is important that you build the model, validate and design it in a staged process, for example:
•
Validate and design ONE floor before copying it up the building,•
Resolve the gravity design before looking at the lateral design,•
Resolve the sway stability before applying the wind loading.There are often many nuances to creating your model, in particular with composite design, and it is much more effective to resolve any issues once (before you copy the floor to other levels in your model) than it is to copy the floor to (say) ten other floor levels, and then address the (usually simple) issues on each copied floor (in this case ten times the work!).
Simple Construction is still the best method
The most effective design for a multi storey structure is still likely to be simple beams and columns with bracing to resist the lateral forces. Simple construction in BS 5950 implies
certain types of modelling and certain specific design rules (both inclusions and exclusions). We assume your familiarity with these.
Use ‘Simple
1’ beams and columns where possible
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.
Building Designer Documentation page 20 Chapter 2 : Building Effective Models in Fastrak Building Designer
If 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.
NOTE — Simple Columns and Sway Stability
When you use simple columns they are pinned at every floor level (except where they are connected to a braced bay) to ensure that all lateral load is transferred to the braced bay. This modelling is in line with the SCI guidelines in the Steel Designers Handbook. You may pin or fix general columns at each floor level as you wish.
Design Simple Construction for Gravity Loads only
In order to speed the design process a distinction is made between those combinations consisting of gravity loads only and those which contain some components acting laterally (eg.. NHFs and wind loads). Setting simple beams, composite beams and simple columns to be designed for gravity loads only can significantly reduce the design time.
General beams, general columns, trusses and braces are always designed for both gravity and lateral combinations.
Engineering judgement will be required when flagging members as being ‘gravity load only’. For example:
•
a simple/composite beam with an inclined braced member connected to it should be designed for both gravity and lateral loads.•
potentially, simple beams in a sloping roof would need to be designed for both gravity and lateral loadNote If a simple, or composite beam is flagged to be designed for both gravity and lateral combinations, only the component of the lateral load that acts in the plane of the strong axis of the member is considered. Any axial loads, or loads in the weak axis are ignored. A validation warning is provided if the ignored loads exceed a preset limit.
From release 7. 0 of Building Designer onwards it is now important that simple columns only receive forces from horizontal members. To ensure this a new validation check has been added. If a simple column is placed in a braced bay, or if it supports a sloping general beam or truss member a validation error will be displayed. In such circumstances it will be necessary to change the simple column to a general column.
Diaphragm Action
You can switch diaphragm action on or off for a given floor as you decide. If you switch diaphragm action on, you must also then decide if this applies to the entire floor, or to part of the floor only.
Chapter 2 : Building Effective Models in Fastrak Building Designer Building Designer Documentation page 21
For futher information about the diaphragm options available refer to “Diaphragm Modelling”.
Composite Beam Design
Composite 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 Building Designer.
Building Designer’s composite design routines can automatically choose the optimum stud layout and automatically select an appropriate transverse shear reinforcing layout, as such 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 for Building Designer 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 leaving Building Designer 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 which 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 give the minimum amount of shear interaction then the selection of a suitable beam size is not possible.
You should exercise care in the use of composite beams, if in doubt design all beams as simple
beams first and then simply select those beams that you wish to be composite at a second pass.
Composite 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 such as the critical ‘e’ dimension.
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.Note Many engineers consider edge beams to be an ineffective use of composite beams and specify simple beams to avoid significant use of transverse shear reinforcing.
Building Designer Documentation page 22 Chapter 2 : Building Effective Models in Fastrak Building Designer
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.
Setting the appropriate level of deflection checks
Building Designer provides very comprehensive deflection checks on all beams. You can set limits on the deflections for a variety of conditions (dead load only, imposed load only and/or total load). At the same time in order to allow for deflections with beams with significant web penetrations Building Designer employs a sophisticated integration based deflection check. You should take care when setting the range of deflection checks. You may consider the default deflection limits conservative for some buildings.
Building Size and Orientation
The automatic calculation of NHF’s and sway checks are done on the basis that we are checking a single building as outlined in section 2 of BS 5950-1. This effectively says that each portion of the building between expansion joints should be looked at separately for sway stability.
When using Building Designer we assume that you are following this logical process.
Note NHF’s and sway stability are calculated in the global X and Y direction, you should take care to input the model with this in mind.
Automatic NHF calculations
If you switch the automatic calculation of NHFs on, then Building Designer follows the process below:
•
it automatically calculates all NHF’s based on 0.5% of the factored vertical load that passes through any beam/column intersection in the structure,Note The values of the NHFs may vary for each load combination.
•
automatically creates a sway analysis to calculation the drift in X and Y of the structure under NHF’s only,•
automatically calculates the floor to floor drift of every column in the structure and thereby establishes the worst lambda crit in both X and Y directions,•
reports this back for the critical sway stability values of lambda crit in X and Y,•
if the λcrit value falls between 4 and 10, Building Designer can (if the option is selected) automatically apply the pΔ effects,•
Building Designer can automatically include the relevant NHFs in vertical load only combinations to allow for lack of fit (if required).Chapter 2 : Building Effective Models in Fastrak Building Designer Building Designer Documentation page 23
On a typical model, this very valuable automated process will significantly extend the design time, therefore we recommend that you leave it switched off until you require it. For instance, there is no point in switching this option on if you have no lateral load resisting system in place or if you are making small alterations to your model and you are iterating the design process.
Number of design runs
The default setting for Building Designer is 3 design runs (passes) with NHFs on. This carries out:
•
initial load decomposition,•
initial design of all members,•
automatic recalculation of the self weight of the structure,•
automatic calculation of NHFs,•
redesign of the structure with NHFs and self weight,•
automatic recalculation of NHFs allowing for the revised self weight,•
a design check of the entire structure.As a default this is a reasonable process that works for the automatic design of moment frames as well as simple structures.
However if you are dealing with a large simple multi storey structure we would suggest that it would be appropriate to perform only two passes.
Number of load combinations
Where you are looking at design changes, for example to rationalise an area of floor, you can switch off all the irrelevant load combinations.
For example if you are looking to redesign a series of composite floor beams, then it is likely that only the construction case load case and the dead + super load case are relevant. This may allow the you to switch off all other load cases and concentrate on the gravity design issues.
Stepped Design Process
If you put some of these things together you will see that there is a logical stepped design process. For example pinned beams (such as the composite beams) will mostly be unaffected by any lateral load, and hence you may design the beams looking at gravity load only. Using this ‘stepped’ process to carry out the design you should find the software provides detailed design very effectively.
Results
Upon completion of the design process the Workspace presents:
Model deflection results — these are not a pass/fail for the details of the model but simply an indication of the total defection of the model under all the differing loads applied. If the model suffers from excessive deflections then a warning will be shown. In this case the
Building Designer Documentation page 24 Chapter 2 : Building Effective Models in Fastrak Building Designer
remaining results could be incorrect as the overall building analysis may be indicating that the building will collapse. This may be irrelevant if you are looking at a gravity design and are happy to ignore lateral load, but it may also mean that the basic moment for which the building is being designed could alter once the building is stabilised.
Sway Stability — if the NHFs option in the analysis options is on then Building Designer will carry out a full sway stability analysis. Significant failure, may mean the lack of overall stability such as the omission of diaphragm action or simply a loose piece of the structure not connected into the main bracing/diaphragm action. Use the deflection results to look at this.
Lambda crit less than 4 — BS 5950-1 says that if λcrit is less than 4 a full second order analysis should be used. Methods for rigorous second order analysis are incompatible with imposed load reduction and therefore within Building Designer a λcrit less than 4 indicates that your model does not have sufficient lateral stiffness.
Load in versus load out — All loads are checked in and out of the model it is essential that you check these results.
Chapter 3 : Simple Wind Loading Building Designer Documentation page 25
Chapter 3
Simple Wind Loading
Fastrak Building Designer v6.0 has a new fully functional Wind Wizard which assesses wind loading on your building structure to BS6399-2:1997.
For users who do not have access to the comprehensive Wind Wizard, there was and is the facility to load walls with a stepped horizontal pressure load - now called Simple Wind Loading.
The introduction of the Wind Wizard alters the way that the Simple Wind Loading works in two respects:
1. Walls now have an inner and an outer surface. If the pressure in the direction of the wind hits the outer surface of a wall then the structure is loaded by the wind. However, if the wind strikes the inner surface of a wall then it passes through the wall and does not load the structure. The simple way to verify which way round your wall surfaces are, is to look at Show/Alter State in the structure view.
2. The Simple Wind loading strikes all outward facing walls which can be seen in the wind direction defined. There is no longer any "sheltering" of one wall by another - which was in previous versions. For many structures, this will make no difference but in some, this may alter the structure loading.
Note Please note that for existing models built in Fastrak Building Designer prior to v6.0 then the above are only relevant if you re-generate the Simple Wind Loading.
Building Designer Documentation page 26 Chapter 4 : Overview of Construction Types
Chapter 4
Overview of Construction Types
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 Building Designer – refer to “Member Beams and Member Columns”.•
Member Columns – these can be any section in any material but cannot be checked ordesigned by Building Designer – refer to “Member Beams and Member Columns”.
•
General Beams – these are restricted to steel sections but such beams can then be designed by Building Designer – refer to “General Beams”.•
General Columns – these are restricted to steel sections but such columns can then be designed by Building Designer – refer to “General Columns”.In addition to the above, you can also define:
•
Shear Walls – these are restricted to concrete or “Other” materials but cannot be checked or designed by Building Designer –Member Beams and Member Columns
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” 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 issues to give some consideration to are:
Chapter 4 : Overview of Construction Types Building Designer Documentation page 27
Section/Material Properties
You can set up any member properties you want, for example the dialog above is what you will see if you elect to set up a new concrete section. When analysing a concrete structure in isolation BS8110 suggests that for the purposes of establishing design forces you need to use consistent properties for all members. The point of this is that 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. PropertiesBuilding Designer calculates the gross section properties of a simple rectangular section for you. You can make whatever adjustments you wish to the calculated values to allow for cracking and/or to allow for irregular shapes, etc.)
•
adjusting the value of E (Young’s 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 “Getting the Analysis Model Right”.
General Beams
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,•
The advantage is that Building Designer designs these steel sections automatically.Creating General Beams
You 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.
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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.
2. If you click on any simple beam and alter its state to make it rigid, Building Designer converts the beam to a General Beam with fixed ends.
Note Where the converted beam frames into simple columns, these columns will also automatically be converted to General Columns.
3. If you click on two simple beams with the Split/Join tool active Building Designer converts these to a continuous general beam.
4. 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 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 “Getting the Analysis Model Right”.
Design Properties
As with simple- and composite-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 Beam in the same way as you would for a Simple Beam.
General Columns
General 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 Building Designer designs these steel sections automatically.Chapter 4 : Overview of Construction Types Building Designer Documentation page 29
You can create General Columns in several other ways:
1. While working in the 3D structure view you can create columns by clicking on start and end points. While creating any column in this way (regardless of the current default attribute set), you can hold down the control key to indicate a series of points that define a continuous column. If these points are not co-linear the column cannot be a Simple Column. In this case Building Designer automatically be converts it to a continuous general column.
2. If you click on any simple column and alter its state to make it rigid, Building Designer converts the column to a General Column.
Note On it’s own this would be a fairly pointless action, unless you have other fixed ended members with which the column can interact.
3. If you insert points in simple columns by using the Modify tool and then move those points to create a non co-linear column, then Building Designer converts the column into a continuous General Column.
Analytical Properties (End Releases)
This is common to all Member Beams, Member Columns, General Beams, and General Columns, refer to “Getting the Analysis Model Right”.
Design Properties
As 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 in the same way as you would for a Simple Column.
Shear Walls
Shear Walls introduce structural strength and stiffness to your structure. They are typically used to provide lateral stability to the building. (Refer to “Sway Resistance” for more notes on the alternative methods of providing lateral stability).
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.
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.
Openings can also be placed within the wall in the form of doors or windows. These will reduce the strength, stiffness and self weight of the wall.
Creating Shear Walls
To create Shear Walls you should first create an appropriate Shear Wall attribute set. The attribute set consists of the wall’s material, thickness and analysis properties.
Building Designer Documentation page 30 Chapter 4 : Overview of Construction Types
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.
Shear Wall Limitations
The following limitations apply:
•
Vertical walls only•
Rectangular walls only•
Concrete or “Other” materials only•
The shear walls will not be designedAnalytical 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 ant intermediate construction level that is flagged 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 4 : Overview of Construction Types Building Designer Documentation page 31
The “mid-pier” analytical model 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.
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.
Note The alignment (Left,Centre, or Right) of the shear wall is for cosmetic purposes only and does not affect its analytical properties.
Transfer Shear Walls
A 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 it’s model type for shear wall modelling is set to Top Edge Beam.
Getting the Analysis Model Right
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.
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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.
End Releases
Member end moment releases are best reviewed graphically by showing the release state of the model (pick Select/Show/Alter State, and then pick Releases from the dialog). The releases for all supports, general beams, general columns, member beams and member columns are shown. (The releases for simple beams, composite beams and simple columns are not shown purely to limit screen clutter – they are always released for major and minor axis bending.) Moment releases are indicated by an arrow with a double arrowhead.
In 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 select node positions (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.
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 (Mx) and minor axis (My) bending.
Moment Connection — The connection is fixed for major axis (Mx) bending but remains
pinned for minor axis (My) bending.
Chapter 4 : Overview of Construction Types Building Designer Documentation page 33
Continuous — 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.
When setting/changing moment releases for Member Beams the options are slightly different as follows:
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 — For member beams the focus is on the analysis model and so the usual analytical sign conventions are applied. X is along the member, Y is the major cross section axis and Z is the minor cross section axis. Hence this setting creates a pinned connection for major axis bending but the connection remains fixed for minor axis bending. These conflicting sign conventions are a universal issue when moving between analysis and British design codes.
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. Due to the conflicting sign conventions noted above the minor axis is referred to as Z rather than Y.
Fully Fixed — This is the same as the Fixed Connection noted above, the connection is fixed for both major axis and minor axis bending.
Continuous — 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 General Columns.
Axial Releases
Member end axial releases are best reviewed graphically by showing the axial release state of the model (pick Select/Show/Alter State, and then pick Axial Releases from the dialog). The axial releases for all general beams, general columns, member beams and member columns are shown. (The axial releases for simple beams and composite beams are not shown purely to limit screen clutter – they are always released axially.)
In the view above the rafters have been created as General Beams and the verticals as General Columns to form a moment resisting frame. All the General Columns are fixed axially apart from two that are to act as gable posts which have been modelled with releases at the top end. While this view is active clicking on a node will toggle its state between Fixed and Released.
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General Beams and Member Beams can be released axially at either end, but not both. If the beam is continuous it can only be released axially at one or other of it’s extreme ends. General Columns and Member Columns can only be released axially at the top end.
Member Orientations
All member orientations are reflected in the graphical views as appropriate.
By default Building Designer places beams of all types with their major axis horizontal (in the global XY) plane. For the vast majority of beams this will be the required orientation.
By default Building Designer places vertical columns 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 General Columns – as you define these
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 column’s local axis system the automatic calculation of the member orientation for inclined general columns can initially be a little confusing.
Supports and Base Fixity
A few points are worth noting on this topic:
1. The view in “End Releases” also shows that you can view and edit support releases when viewing member releases graphically.
2. Building Designer automatically creates supports as you create any columns, by default these supports are always released (pinned).
3. You cannot adjust the base fixity for Simple Columns, this is always pinned.
4. For General and Member Columns you can select the support and adjust the base fixity between different fixity settings. The settings are all based on the guidance provided in BS5950-1:2000 cl 5.1.3 as follows:
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.
Chapter 4 : Overview of Construction Types Building Designer Documentation page 35
Note Nominally fixed is not the same as a fully fixed support that you might define in a typical analysis package, a nominally fixed support will rotate according to the spring stiffness and this will affect deflections. If you have a genuinely fixed support you need to use the last option above to define an increased spring stiffness.
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 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.
Reviewing the Analysis Results
As is noted in the above sections, once you start using general beams, general columns, member beams, member columns and shear walls it is important to review and check the analysis model you are creating. An important double check on all of this is to spend some time reviewing the analysis results. You may want to review “Initial Review of Analysis Results”
for some notes/tips on this.
Practical considerations
Up to this point in this chapter we have said a lot about creating members with moment connections and the care that you need to take to ensure the model you are creating is the one you intended.
The automated design capabilities introduced by Building Designer in conjunction with those in General Beam and General Column allow you to consider solutions involving rigid steel framing quickly and easily in a way that may not previously have been practical from a design effort point of view.
In essence you may find it more feasible and practical (within design fee limitations) to consider some new, more sophisticated, solutions. However, consider other practicalities before being tempted to venture into new styles of construction. Construction and maintenance costs will be affected, as illustrated in the two simple examples below:
Connections — Moment connections will introduce fabrication and construction costs and difficulties that may offset other savings or advantages.
In some cases the assumed connections/intersections may prove to be completely impractical to construct because of physical limitations.
Flexibility — Simple beams operate quite independently – you can often remove a simple beam without having to worry about adjacent members.
If you have continuous framing you are more likely to find that other beams need to be strengthened in order to allow one beam to be removed.
Building Designer Documentation page 36 Chapter 5 : Overview of Analysis And Design Procedures
Chapter 5
Overview of Analysis And Design Procedures
Controlling the design procedure
Under the Design menu there is a Design Options… setting which shows the dialog below.
The first page of the dialog provides an option to Start from beginning of order file on each pass, this is unchecked by default. For all or the vast majority of members in most models this setting will have no effect on the results, it simply serves to speed up the iterative design procedure. However in some models checking this option may achieve a lighter weight design result. This is discussed further in “Leaving the Start from beginning of order file on each pass option un-checked”.
The Perform check of fields provide a way to speed up the design process when you want to only tweak a particular part of the design of your structure. For instance if you have designed all the floors in your model, and are satisfied with the resulting beams, but you want to work with the columns, you can remove the check against the types of member with which you are satisfied, and Building Designer will ignore these during the design process. These options only affect the checking process. If a particular element needs to be designed, then this will happen irrespective of the settings you make here.
A full 3D analysis may expose small forces that are normally ignored in the design of
members. The options for ignore forces below on the second page of the dialog simply provide you with a way of setting negligible/nominal force levels with which you are comfortable.
Chapter 5 : Overview of Analysis And Design Procedures Building Designer Documentation page 37
When the small forces from the 3D analysis are below the specified threshold levels they are ignored so that design can proceed automatically. If the forces are above these limits, then you will be warned during the design process.
The last page of the dialog provides similar functionality for the connections in your model. If forces below the threshold do arise, then they are ignored during the design process. Forces higher than these generate warnings during the design.
Why is it an iterative procedure?
Basically the procedure is as follows:
1. For the first analysis run Building Designer assumes (guesses) section properties for the members that are to be designed (as opposed to checked).
2. Building Designer constructs and analyses this model. 3. Building Designer designs all members.
4. Building Designer compares the member sizes that result from the design (step 3) with the member sizes which were used to construct the latest analysis model (step 2) – if any of these are different then Building Designer goes back to step 2 and constructs a new analysis model based on the sections resulting from the latest design and then again proceeds to step 3.
5. If the comparison at stage 4 shows no differences then Building Designer performs a final check design on all the members in the structure.
Building Designer Documentation page 38 Chapter 5 : Overview of Analysis And Design Procedures
The need for iteration on steps 2 to 4 above occurs when structures include moment connections between members. In such circumstances no member can be operated on in isolation, as soon as the stiffness of one member is changed it can affect design forces (principally the design moments) in lots of members. Hence the analysis model must be synchronised with the latest design.
Controlling the iterative procedure
Under the Design menu there is an Analysis Options… setting which shows the dialog below.
Building Designer can either perform a first-order or second-order analysis of the frame. If the sway of the frame is such that the amplification factor method for catering for sway is
acceptable, then Building Designer can automatically handle this for you.
