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BS 5950 MEMBER DESIGN

Friday 7 September 2012 15:51

BS 5950 Member Design Handbook page 2 CSCs Offices Worldwide

Friday 7 September 2012 15:51

CSC (UK) LtdYeadon House

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Leeds, UKLS28 8AQ

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Australia

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Email: [email protected]

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Disclaimer page 3Disclaimer 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.

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Fastrak documentation: Fastrak software: CSC (UK) Ltd 2012 CSC (UK) Ltd 2012All rights reserved. All rights reserved.

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DisclaimerMonday 10 September 2012 08:55

Table of Contents page 5BS5950 Member Design Handbook

Chapter 1 Introduction . . . . . . . . . . . . . . . 9

Chapter 2 Basic Principles . . . . . . . . . . . . . . . 10Definitions. . . . . . . . . . . . . . . . 10Design Method . . . . . . . . . . . . . . . 10Deflection checks . . . . . . . . . . . . . . 11Error messages . . . . . . . . . . . . . . . 11

Chapter 3 Simple Beam . . . . . . . . . . . . . . . 12Introduction . . . . . . . . . . . . . . . 12Scope . . . . . . . . . . . . . . . . 12

Beam . . . . . . . . . . . . . . . . 12Steel sections . . . . . . . . . . . . . . . 12Web openings. . . . . . . . . . . . . . . 12Restraint conditions . . . . . . . . . . . . . . 15Applied loading . . . . . . . . . . . . . . 15Design checks . . . . . . . . . . . . . . . 15

Theory and Assumptions . . . . . . . . . . . . . 16Analysis method . . . . . . . . . . . . . . 16Design method . . . . . . . . . . . . . . 16Section classification . . . . . . . . . . . . . 16Member strength checks . . . . . . . . . . . . . 16Lateral torsional buckling checks . . . . . . . . . . . 16Deflection checks . . . . . . . . . . . . . . 17Web Openings . . . . . . . . . . . . . . 18

Design Properties . . . . . . . . . . . . . . 19Size Constraints . . . . . . . . . . . . . . 19Sections for Study (in Fastrak Building Designer) . . . . . . . . . 19Sections for Study (in Simple Beam) . . . . . . . . . . . 20Deflection . . . . . . . . . . . . . . . 21

Worked Example . . . . . . . . . . . . . . 21Simple Beam Input (in Fastrak Building Designer) . . . . . . . . . 25Simple Beam Input (when run as a standalone program) . . . . . . . 26

Designing a beam . . . . . . . . . . . . . . 26Checking a beam . . . . . . . . . . . . . . 27

Further information . . . . . . . . . . . . . . 28Further information Westok Beams . . . . . . . . . . . 28

Chapter 4 Composite Beam . . . . . . . . . . . . . . 29Introduction . . . . . . . . . . . . . . . 29Scope . . . . . . . . . . . . . . . . 30

Beam . . . . . . . . . . . . . . . . 30Westok sections . . . . . . . . . . . . . . 30Westok Technical Support and Design Service . . . . . . . . . 31Steel sections . . . . . . . . . . . . . . . 32Web openings. . . . . . . . . . . . . . . 32Profiled metal decking . . . . . . . . . . . . . 35Precast concrete slabs . . . . . . . . . . . . . 37Concrete slab . . . . . . . . . . . . . . . 39Shear connectors . . . . . . . . . . . . . . 39Reinforcement . . . . . . . . . . . . . . 39

Table of ContentsFibre Reinforced Concrete . . . . . . . . . . . . . 40Construction stage restraint conditions . . . . . . . . . . . 41Construction stage loading . . . . . . . . . . . . . 41Composite stage loading . . . . . . . . . . . . . 42Construction stage design checks . . . . . . . . . . . . 42Composite stage design checks . . . . . . . . . . . . 43

Theory and Assumptions . . . . . . . . . . . . . 44Analysis method . . . . . . . . . . . . . . 44Design method . . . . . . . . . . . . . . . 44Construction stage . . . . . . . . . . . . . . 44Composite stage . . . . . . . . . . . . . . 46Web Openings . . . . . . . . . . . . . . . 50

Theory and Assumptions Westok beams . . . . . . . . . . 52Construction stage . . . . . . . . . . . . . . 52Composite Stage . . . . . . . . . . . . . . 56

Design Aspects . . . . . . . . . . . . . . . 60Use of Design Properties to Control Section Selection . . . . . . . . 60Checking the effective width used in the design . . . . . . . . . 64Layout of Studs . . . . . . . . . . . . . . . 65Non-composite design within Composite Beam . . . . . . . . . 72Automatic transverse shear reinforcement design . . . . . . . . . 73

Worked Example . . . . . . . . . . . . . . . 75Without transverse shear reinforcement. . . . . . . . . . . 75Design Pass 1 . . . . . . . . . . . . . . . 76Design Pass 2 . . . . . . . . . . . . . . . 78Design Pass 3 . . . . . . . . . . . . . . . 78

Composite Beam Input (in Fastrak Building Designer) . . . . . . . . 79Composite Beam Input (when run as a standalone program) . . . . . . . 81


Further Information . . . . . . . . . . . . . . 84Further information Bison precast concrete slabs . . . . . . . . . 84Further information Westok Beams . . . . . . . . . . . 84

Chapter 5 Simple Column . . . . . . . . . . . . . . . 85Introduction . . . . . . . . . . . . . . . . 85Scope . . . . . . . . . . . . . . . . . 85

Design Checks . . . . . . . . . . . . . . . 85Worked Example . . . . . . . . . . . . . . . 86

Design pass 1 . . . . . . . . . . . . . . . 86Design pass 2 . . . . . . . . . . . . . . . 87Design Pass 3 . . . . . . . . . . . . . . . 87

Design of concrete filled columns . . . . . . . . . . . . 88Proposed method . . . . . . . . . . . . . . 88Points to Note . . . . . . . . . . . . . . . 89

Simple Column Input (in Fastrak Building Designer) . . . . . . . . . 89.Simple Column Input (when run as a standalone program) . . . . . . . 90

Designing a column . . . . . . . . . . . . . . 90Checking a column . . . . . . . . . . . . . . 91

References and further information . . . . . . . . . . . 92

Chapter 6 General Beam . . . . . . . . . . . . . . . 93Introduction . . . . . . . . . . . . . . . . 93Scope . . . . . . . . . . . . . . . . . 93Limitations and Assumptions . . . . . . . . . . . . . 94Monday 10 September 2012 08:55

Table of Contents page 7Limitations . . . . . . . . . . . . . . . 94Assumptions . . . . . . . . . . . . . . . 95

Analysis . . . . . . . . . . . . . . . . 95Building Modeller object . . . . . . . . . . . . . 95General Beam . . . . . . . . . . . . . . . 95

Ultimate Limit State Strength . . . . . . . . . . . . 96Classification . . . . . . . . . . . . . . . 96Shear Capacity . . . . . . . . . . . . . . 96Moment Capacity . . . . . . . . . . . . . . 97Axial Capacity . . . . . . . . . . . . . . . 97Cross-section Capacity . . . . . . . . . . . . . 97

Ultimate Limit State Buckling . . . . . . . . . . . . 98Lateral Torsional Buckling Resistance, Clause 4.3 . . . . . . . . . 98Lateral Torsional Buckling Resistance, Annex G . . . . . . . . . 98Compression Resistance . . . . . . . . . . . . . 99Member Buckling Resistance, Clause 4.8.3.3.1 . . . . . . . . . 100Member Buckling Resistance, Clause 4.8.3.3.2 . . . . . . . . . 100Member Buckling Resistance, Clause 4.8.3.3.3 . . . . . . . . . 101

Serviceability Limit State . . . . . . . . . . . . . 101Member End Fixity and Supports . . . . . . . . . . . . 101

General Beam Stand-alone . . . . . . . . . . . . 102Building Designer . . . . . . . . . . . . . . 102

Design Procedure . . . . . . . . . . . . . . 103Lateral torsional buckling checks . . . . . . . . . . . 103Combined buckling checks . . . . . . . . . . . . 104

Worked Example . . . . . . . . . . . . . . 105Design pass 1 . . . . . . . . . . . . . . . 107Design pass 2 . . . . . . . . . . . . . . . 107Design Pass 3 . . . . . . . . . . . . . . . 109

General Beam Input (in Fastrak Building Designer) . . . . . . . . . 110General Beam Input (when run as a standalone program) . . . . . . . 110


Chapter 7 General Column . . . . . . . . . . . . . . 113Introduction . . . . . . . . . . . . . . . 113Scope . . . . . . . . . . . . . . . . 113Limitations and Assumptions . . . . . . . . . . . . 115

Limitations . . . . . . . . . . . . . . . 115Assumptions . . . . . . . . . . . . . . . 115

Analysis . . . . . . . . . . . . . . . . 116Building Modeller Object . . . . . . . . . . . . . 116

Ultimate Limit State Strength . . . . . . . . . . . . 116Classification . . . . . . . . . . . . . . . 116Shear Capacity . . . . . . . . . . . . . . 117Moment Capacity . . . . . . . . . . . . . . 117Axial Capacity . . . . . . . . . . . . . . . 118Cross-section Capacity . . . . . . . . . . . . . 118

Ultimate Limit State Buckling . . . . . . . . . . . . 118Lateral Torsional Buckling Resistance, Clause 4.3 . . . . . . . . . 118Lateral Torsional Buckling Resistance, Annex G . . . . . . . . . 119Compression Resistance . . . . . . . . . . . . . 120Member Buckling Resistance, Clause 4.8.3.3.2 . . . . . . . . . 121Member Buckling Resistance, Clause 4.8.3.3.3 . . . . . . . . . 121

Serviceability limit state . . . . . . . . . . . . . 122Worked Example . . . . . . . . . . . . . . 122

Table of ContentsDesign pass 1 . . . . . . . . . . . . . . .123Design pass 2 . . . . . . . . . . . . . . .124Design Pass 3 . . . . . . . . . . . . . . .124

General Column Input (in Fastrak Building Designer) . . . . . . . .125

Chapter 8 Braces . . . . . . . . . . . . . . . . .128Introduction . . . . . . . . . . . . . . . .128Scope . . . . . . . . . . . . . . . . .128

Steel sections . . . . . . . . . . . . . . .128End Connections . . . . . . . . . . . . . .128Applied loading . . . . . . . . . . . . . . .128Design Forces . . . . . . . . . . . . . . .129Design checks . . . . . . . . . . . . . . .129

Theory and Assumptions . . . . . . . . . . . . .129Analysis method . . . . . . . . . . . . . .129Design method . . . . . . . . . . . . . . .129Classification . . . . . . . . . . . . . . .129Axial Tension . . . . . . . . . . . . . . .129Axial Compression . . . . . . . . . . . . . .129Compression Buckling . . . . . . . . . . . . .129

Brace Input . . . . . . . . . . . . . . . .130

Chapter 9 Refining Member Designs . . . . . . . . . . . .131Introduction . . . . . . . . . . . . . . . .131

Why would you want to refine the original design? . . . . . . . . .131Interaction Effects . . . . . . . . . . . . . .131

How to Access Design Refinement . . . . . . . . . . . .132Simple Beam - Check Mode. . . . . . . . . . . . . .132Simple Beam - Design Mode. . . . . . . . . . . . .133Composite Beam - Check Mode . . . . . . . . . . . .134Composite Beam - Design Mode . . . . . . . . . . . .135General Beam - Check Mode . . . . . . . . . . . .136General Beam - Design Mode . . . . . . . . . . . .137General Column - Check Mode . . . . . . . . . . . .138General Column - Design Mode . . . . . . . . . . . .139

Effective Use of Order Files in Refined Design . . . . . . . . . .139

Chapter 10 References . . . . . . . . . . . . . . . .144Monday 10 September 2012 08:55

Chapter 1 : Introduction BS 5950 Member Design Handbook page 9BS5950 Member Design Handbook

Chapter 1 Introduction

Fastrak Building Designer designs steel members, composite members and connections to a range of international codes. This handbook specifically describes the design methods applied in the software when the BS 5950-1(Ref. 2) and BS 5950-3(Ref. 1) codes are selected.

A brief description of the contents follows:

Basic Principles (Chapter 2)terminology and basic principles common to each of the design applications.

Simple Beam (Chapter 3)non-composite steel beam with pinned ends designed for gravity loads acting through the web

Simple Column (Chapter 4)steel column in a simply designed structure

Composite Beam (Chapter 5)composite steel beam with pinned ends designed for gravity loads acting through the web

General Beam (Chapter 6)non-composite steel beam designed as a beam/column

General Column (Chapter 7)steel column designed as a beam/column

Braces (Chapter 8)steel members with pinned ends designed for axial loads only

Refining Member Designs (Chapter 9)advice to assist you in extracting individual members into each design application for more detailed assessment.

References (Chapter 10)references and further information.

BS 5950 Member Design Handbook page 10 Chapter 2 : Basic PrinciplesChapter 2 Basic Principles

Definitions

AttributesWhen a member is first created its properties (steel grade, maximum section depth etc.) are taken from the attribute set that is currently active. Once a member has been placed its properties can be edited as required. Ensuring the attribute set is correct before placement ensures the minimum amount of member editing.

Design Mode Within Building Designer you can access the member design routines automatically for every member in the building model to choose the smallest section from a list of sections (referred to in the program as an order file)

Check ModeAlternatively you can access the member design routines to check the section size already assigned by you to each member, to determine whether it is able to carry the applied loading.

Order FilesEach order file is a list of section sizes of a given type arranged in the sequence in which they will be tried during the design. Undesirable sections can be excluded if required.

Caution If you exclude sections from an order file they will remain excluded for all designs until you decide to include them again.

Interactive DesignWithin Building Designer you can also extract key members from the model into the appropriate design program for further investigation in either Design Mode or Check Mode, providing you with still greater control over the design:

to enable multiple order files to be considered at the same time to determine a list of alternative sections, all of which can withstand the applied loading.

to adjust the initial design manually without having to re-design the whole building. Any change to the section size or steel grade can then be passed back to the building model, but only affects the individual beam extracted. If the changes are to be applied to other beams also, you would need to update the building model separately and then re-design it.

For further details see Refining Member Designs

Design MethodUnless explicitly stated all calculations in Building Designer will be consistent with the design parameters as specified in BS 5950-1:2000(Ref. 1).

Chapter 2 : Basic Principles BS 5950 Member Design Handbook page 11Deflection checksBuilding Designer calculates both relative and absolute deflections. Relative deflections measure the internal displacement occurring within the length of the member and take no account of the support settlements or rotations, whereas absolute deflections are concerned with deflection of the structure as a whole. The absolute deflections are the ones displayed in the structure deflection graphics. The difference between relative and absolute deflections is illustrated in the cantilever beam example below.

Relative deflections are given in the member analysis results graphics and are the ones used in the member design.

Error messages As you define member data, Fastrak Building Designer continually checks to ensure that the data is valid. If a particular value is not valid, then it will be shown using a colour of your choice in the dialog (default red). If a value is not recommended, then a different colour will be used in the dialog, (default orange for warning). If you allow the cursor to rest over the error or warning field you will see a tip telling you the acceptable range of input. Until all the information within the dialog is valid (but not free of warnings) you will not be able to save the dialog since OK will be dimmed.

Although checking in this way prevents you from defining invalid data there are some cases where particular errors occur that cannot be trapped - for instance where an error occurs due to inconsistencies that have arisen between information covered on different dialogs. In these cases when you attempt to perform a design you will see an error message indicating that data is not suitable for the design to proceed. Each message is self-explanatory. You should take a careful note of the error message and then change the member data to correct the problem.

If there are other problems with the design, then you will see a series of warning messages in the results viewer. You should take note of any such warnings and take the action that you deem appropriate. Engineering tips are also available in the results viewer which may give you useful information about the assumptions or approach adopted for the particular calculation or about a particular recommendation of good practice with which we recommend that you comply.

Relative Deflection Absolute Deflection

BS 5950 Member Design Handbook page 12 Chapter 3 : Simple BeamChapter 3 Simple Beam

Introduction

The Simple Beam design application allows you to analyse and design a structural steel beam or cantilever which may have incoming beams providing restraint, and which may or may not be continuously restrained over any length between restraints.

Simple Beam can determine the sizes of member which can carry the forces and moments resulting from the applied loading.

Alternatively you may give the size of a beam and Simple Beam will then determine whether it is able to carry the previously mentioned forces and moments and satisfy the deflection requirements.

Unless explicitly stated all calculations in Simple Beam are in accordance with the relevant sections of BS 5950-1:2000(Ref. 2).

Scope The scope of the Simple Beam application is as follows:

BeamThe beam is designed for gravity loads acting through the web only. Minor axis bending and axial loads are not considered.

Note If either minor axis bending or axial loads exist which exceed the limit below which they can be ignored, a warning will be given in the beam design summary.

Steel sectionsSimple Beam can handle design for an international range of steel I-sections for many different countries. Plated sections can also be checked.

Web openingsIf you need to provide access for services, etc., then you can add openings to a designed beam and Simple Beam can then check these for you.

You can define rectangular or circular openings and these can be stiffened on one, or on both sides.

The checks that are performed are in accordance with the guidelines and design process given in the booklet Design for openings in the webs of simple beams.

SIMPLE BEAM - non-composite steel beam with pinned ends designed for gravity loads acting through the web

Chapter 3 : Simple Beam BS 5950 Member Design Handbook page 13We advise you to comply with the following positional recommendations for web openings: Web openings are designed using the bending moment and vertical shear values at the side

of the opening where the moment is lower, Openings should preferably be positioned at the mid-height of the section. If not, the

depth of the upper and lower sections of web should differ by not more than a factor of two,

Openings should not be located closer to the support than two times the beam depth or 10% of the span whichever is the greater,

The best location for any opening is between 1/5 and 1/3 of the span from a support in uniformly loaded beams, or in lower shear zone of beams subject to point loads,

Openings should be not less than the beam depth, D, apart, Unstiffened openings should not generally be deeper than 0.6D or longer than 1.5D, Stiffened openings should not generally be deeper than 0.7D or longer than 2D, Point loads should not be applied at less than D from the side of the adjacent opening.

You cannot currently automatically design sections with web openings, you must perform the design first to get a section size, and then add and check the openings. This gives you complete control of the design process, since you can add appropriate and cost effective levels of stiffening if required, or can choose a different beam with a stronger web in order to reduce or remove any stiffening requirement.

Web openings can be added to a beam by a 'Quick-layout' process or manually.

The 'Quick-layout' process, which is activated using the check box on the Web Openings dialog page, adds web openings which meet the geometric and proximity recommendations given above and in SCI Publication P068. The openings so created are the maximum depth spaced at the minimum centres recommended for the beam section size.

Web openings can be defined manually in two ways from the Web Openings dialog page. With the Quick-layout check box unchecked, the Add button adds a new line to the web openings grid to allow the geometric properties of the web opening to be defined, or alternatively, use of the Add... button opens the Web Opening Details dialog page which gives access to more help and guidance when defining the opening. Both methods make use of 'Warning' and 'Invalid' text for data entry checks [the default colours being orange and red respectively] to provide assistance as the opening parameters are defined.

On the Web Opening Details dialog page, the Centre button will position the opening on the beam centre whilst the Auto button will position the opening to meet the spacing recommendations given above and in P068. Also on this page tool tips give information on the recommended values for all the opening parameters.

As web openings are defined, they are immediately visible in the diagram on the Web Openings dialog page. This diagram displays the results of the geometric and proximity checks that are carried out on the opening parameters using 'Warning' and 'Invalid' display colours to highlight those areas that are outside the recommended limits.

BS 5950 Member Design Handbook page 14 Chapter 3 : Simple BeamA typical display is shown below:

The areas that are subjected to the checks are end posts, web posts, web opening dimensions and tee dimensions. Using the above example, it can be deduced that:

The left hand end post is less than the recommended limiting value WO #1 diameter is within the recommended limiting values Internal Web Post #2 is within the recommended limiting values WO #2 dimensions are outside the recommended limiting values Internal Web Post #3 is less than the recommended limiting value but quite close to the

limit. As the web post dimension reduces, the left and right triangles overlap to a greater degree at their apexes.

WO #3 dimensions are invalid and must be adjusted to progress the definition of the opening.

Internal Web Post #4 is within the recommended limiting values WO #4 dimensions are within the recommended limiting values Internal Web Post #5 is within the recommended limiting values WO #5 dimensions are within the recommended limiting values but the dimensions of the

tee(s) are not.

This display helps you to decide whether to make any adjustments to the opening parameters before their design is checked.

You should bear in mind that the checks carried out at this stage are geometric checks only and compliance with recommended limits is no guarantee that the opening will pass the subsequent engineering design checks.

Chapter 3 : Simple Beam BS 5950 Member Design Handbook page 15Note Adjustment to deflections. The calculated deflections are adjusted to allow for the web openings. See: Deflection checksin the Basic Principles section.

Note Dimensional checks. The program does not check that openings are positioned in the best position (between 1/5 and 1/3 length for udls and in a low shear zone for point loads). This is because for anything other than simple loading the best position becomes a question of engineering judgment.

Restraint conditionsIf you need to check the lateral torsional buckling of the beam you can:

define the degree of fixity that the end connections are able to provide and hence an effective length associated with the support,

position additional restraints at any point along the beam (Simple Beam automatically uses 1.0L and 1.2L as the factors for Normal and Destabilizing loads),

Help For a definition of Destabilizing Loads see BS 5950-1:2000 clause 4.3.4.

Simple Beam automatically takes the average of the effective length factors for differing supports, or between those for the support and the adjacent sub-beam.

alternatively you can specify the factors that you want to use for the lengths between restraints, or you can enter the effective length of the sub-beam directly by entering a value (in m).

specify that any length (or lengths) of the beam should be taken as being fully restrained against lateral torsional buckling, independent of the restraint conditions for the adjacent length(s).

Applied loading You can specify a wide range of applied loading for the simple condition:

uniform distributed loads (over the whole or part of the beam), point loads, varying distributed loads (over the whole or part of the beam), trapezoidal loads.

Design checksWhen you use Simple Beam to design or check a beam the following conditions are examined in accordance with BS 5950-1:2000:

section classification (Clause 3.5.2), shear capacity (Clause 4.2.3), moment capacity:

(Clause 4.2.5.2 for the low shear condition Clause 4.2.5.3 for the high shear condition),

lateral torsional buckling resistance (Clause 4.3.6) web openings, total load deflection check.

BS 5950 Member Design Handbook page 16 Chapter 3 : Simple BeamTheory and Assumptions This section describes the theory used in the development of Simple Beam and the major assumptions that have been made, particularly with respect to interpretation of BS 5950-1:2000.

Analysis methodSimple Beam uses a simple analysis of a statically determinate beam to determine the forces and moments to be resisted by the beam.

Design methodThe design methods employed to determine the adequacy of the section for each condition are those consistent with BS 5950-1:2000 unless specifically noted otherwise.

Section classificationCross-section classification is determined using Table 11 and Clause 3.5.

The classification of the section must be Plastic (Class 1), Compact (Class 2) or Semi-compact (Class 3).

Sections which are classified as Slender (Class 4) are beyond the scope of Simple Beam.

Note Asymmetric Slimflor beams (ASB) For all section types flange classification is only performed for the top flange, because for a simple beam this will be the flange in compression. However, in the case of a cantilever beam the bottom flange goes into compression. Hence for a cantilever beam, for the flange classification to be valid the section must be symmetric about the major axis. As a consequence ASB sections must NOT be specified for cantilever beams.

Member strength checksMember strength checks are performed at the point of maximum moment, the point of maximum shear, the position of application of each point load, and at each side of a web opening as well as all other points of interest along the beam.

Shear capacity is determined in accordance with Clause 4.2.3. Where the applied shear force exceeds 60% of the capacity of the section, the high shear condition applies to the bending moment capacity checks (see below).

Bending moment capacity is calculated to Clause 4.2.5.2 (low shear at point) or Clause 4.2.5.3 (high shear at point) for plastic, compact and semi-compact sections.

Lateral torsional buckling checksBS 5950-1:2000 states that lateral torsional buckling checks are required when any length is not continuously restrained.

Simple Beam allows you to switch off these checks by specifying that the entire length between the supports is continuously restrained against lateral torsional buckling.

Chapter 3 : Simple Beam BS 5950 Member Design Handbook page 17If you use this option you must be able to provide justification that the beam is adequately restrained against lateral torsional buckling.

When the checks are required you can position restraints at any point within the length of the main beam and can set the effective length of each sub-beam (the portion of the beam between one restraint and the next) either by giving factors to apply to the physical length of the beam, or by entering the effective length that you want to use. Each sub-beam which is not defined as being continuously restrained is checked in accordance with clause 4.3.6 and Annex B of BS 5950-1:2000.

Deflection checksSimple Beam calculates relative deflections. (see Deflection checksin the Theory and Assumptions section of this chapter.)

The Service Factor (default 1.0), specified against each load case in the combination is applied when calculating the deflections; the following deflections are available:

dead load deflections, imposed load deflections, total load deflection i.e. the sum of the previous items.

Deflection limits can be specified to each of the above, as a fraction of the span, or as an absolute limit, (or both).

Web OpeningsThe deflection of a beam with web openings will be greater than that of the same beam without openings. This is due to two effects,

the reduction in the beam inertia at the positions of openings due to primary bending of the beam,

the local deformations at the openings due to Vierendeel effects. This has two components - that due to shear deformation and that due to local bending of the upper and lower tee sections at the opening.

The primary bending deflection is established by 'discretising' the member and using a numerical integration technique based on 'Engineer's Bending Theory' - M/I = E/R = /y. In this way the discrete elements that incorporate all or part of an opening will contribute more to the total deflection.

The component of deflection due to the local deformations around the opening is established using a similar process to that used for cellular beams which is in turn based on the method for castellated beams given in the SCI publication, Design of castellated beams. For use with BS 5950 and BS 449".

The method works by applying a 'unit point load' at the position where the deflection is required and using a 'virtual work technique to estimate the deflection at that position.

For each opening, the deflection due to shear deformation, s, and that due to local bending, bt, is calculated for the upper and lower tee sections at the opening. These are summed for all openings and added to the result at the desired position from the numerical integration of primary bending deflection.

BS 5950 Member Design Handbook page 18 Chapter 3 : Simple BeamNote that in the original source document on castellated sections, there are two additional components to the deflection. These are due to bending and shear deformation of the web post. For castellated beams and cellular beams where the openings are very close together these effects are important and can be significant. For normal beams the openings are likely to be placed a reasonable distance apart. Thus in many cases these two effects will not be significant. They are not calculated for such beams but in the event that the openings are placed close together a warning is given. This will indicate that these effects on the deflection of the beam are not taken into account. This warning is issued when,

so < 2.5 * do for rectangular openings

so

Chapter 3 : Simple Beam BS 5950 Member Design Handbook page 19Design PropertiesThe Design Properties button provides a means by which you can both speed up the design process and control the design more precisely.

Note When you extract a beam from a Fastrak Building Designer model into Simple Beam for further investigation, Design Properties are accessed via the Design Wizard icon.

Size ConstraintsSize Constraints are only applicable when in Design Mode. They allow you to ensure that the sections that Simple Beam proposes match any particular size constraints you may have.

Sections for Study (in Fastrak Building Designer)This feature is only applicable when running the program in Design Mode. On the left of the page is a list of available order files, only one of which can be selected. The sections contained within the chosen order file appear in the Section Designation list on the right of the page. Only checked sections within this list are considered during the design process.

The design process commences by starting with the smallest section in the chosen order file. Any section that fails any of the design conditions is rejected and the design process is then repeated for the next available section in the list.

On completion of the design process, the first satisfactory section from the Section Designation list is assigned to the beam.

Caution Limiting the choice of sections by unchecking a section within an order file is a global change that affects ALL projects, (not just the currently open one). It is typically used therefore to eliminate unavailable or non-preferred sections from the design process. If design requirements for an individual beam require section sizes to be constrained, (due to, for example depth restrictions), then the choice of sections should be limited instead by using Size Constraints, (as these only affect the current beam).

BS 5950 Member Design Handbook page 20 Chapter 3 : Simple BeamNote It is possible to create additional order files using a text editor. If you require to do so, please contact your local CSC Technical Support Team for guidance.

Sections for Study (in Simple Beam)

When you extract a beam from a Fastrak Building Designer model into Simple Beam for further investigation, a benefit of doing so is that several order files can be considered at the same time. If a check is placed against an order file the sections contained within it appear in the Section Designation list on the right of the page. Only checked sections within this list are considered during the design process.

Typically, you would uncheck those order files that are unlikely to be appropriate for simple beam design, Doing so speeds up the solution.

The design process commences by starting with the smallest section in each order file. Any section that fails any of the design conditions is rejected and the design process is then repeated for the next available section in the list.

On completion of the design, all the satisfactory sections from the Section Designation list are displayed and the results for each of these can be examined before one of the sections is assigned to the beam.

Caution Limiting the choice of sections by either unchecking an order file or an individual section is a global change that affects ALL projects, (not just the currently open one). It is typically used therefore to eliminate unavailable or non-preferred sections from the design process. If design requirements for an individual beam require section sizes to be constrained, (due to, for example depth restrictions), then the choice of sections should be limited instead by using Size Constraints, (as these only affect the current beam).

Note It is possible to create additional order files using a text editor. If you require to do so, please contact your local CSC Technical Support Team for guidance.

Chapter 3 : Simple Beam BS 5950 Member Design Handbook page 21DeflectionThe Deflections page allows you to control the amount of deflection by applying either a relative or absolute limit to the deflection under different loading conditions.

A typical application of these settings might be: to apply the relative span/360 limit for imposed load deflection, to meet code

requirements, possibly, to apply an absolute limit to the total load deflection to ensure the overall

deflection is not too large.

Worked Example If you want to work through this example you will find the file Engineers Example in the \documents and settings \ All Users \Application

Data\CSC\Fastrak\ Examples folder. You can open and use this file, but you can not save it away unless you change its name, this is done to protect the original.

Lets take a simple example of a 9 m span spine beam with 6 m span secondary beams at third points.

The floor loading is:

Condition Value giving point load at 3 m and 6 m ofDry Slab 2.0 kN/m2 36kN

Services 1.0 kN/m2 18kN

Live load 5.0 kN/m2 90kN

BS 5950 Member Design Handbook page 22 Chapter 3 : Simple BeamDesign Pass 1If you run a design you will find that Simple Beam shows a dialog of acceptable sections. If no one has tailored the sections that Simple Beam investigates, then the list will appear as below.

If you move down the list of Available files, you will see all the Section Designations that can carry the applied loading. These are only the ones that pass the design, Simple Beam has tried all the sections in each of the Available files, to determine the acceptable ones. You may have noticed the different section designations in the progress bar as the design ran. However checking all these sections comes at a price, the more sections there are to investigate, the longer the design takes.

Simple Beam allows you to choose just the sections you want to include for the design through its Design Wizard.

Chapter 3 : Simple Beam BS 5950 Member Design Handbook page 23Design Pass 2Remove the tick against all the Available files whose section types you dont want to investigate, and Simple Beam wont look at any of these sections during the design process. If you remove the tick against all the Available files other than UBBeamOrder.Eur, and then re-perform the design you will find a significant increase in speed as Simple Beam only investigates the universal beams.

Furthermore Simple Beam investigates the sections in the order that they appear in the Section Designation list. If you scroll down many of the lists, you will find that there is a point at which larger sections give way to smaller ones again.

We have ordered the Section Designation list based on our many years experience of the industry, the sections at the top of the list are the ones we know you prefer to use, whilst those at the bottom are those which you use less frequently if at all. By default all the Section Designations are ticked, but you might want to remove the ticks against some or all of the non-preferred sections. Again this will speed the design process.

You may also have other requirements specific to your own company, for instance you may never want to use sections with flanges less than 150 mm wide for erection purposes. If you remove the tick against these section sizes, then Simple Beam will never include them when it is performing a design. Thus you are controlling the design, making Simple Beam look at just the section designations you are likely to accept, and in the process speeding up the design itself.

BS 5950 Member Design Handbook page 24 Chapter 3 : Simple BeamDesign Pass 3With the tick removed against all the non-preferred sections, and all sections with flanges less than 150 wide, Simple Beam only has to check around 20 sections and the design is instantaneous.

Simple Beam maintains the Sections for Study settings that you make, until you choose to change them again. It is therefore worthwhile taking the time to tailor the list so that Simple Beam picks sections of which you are likely to approve during its designs.

Chapter 3 : Simple Beam BS 5950 Member Design Handbook page 25Simple Beam Input (in Fastrak Building Designer) In order to create a simple beam within Fastrak Building Designer, you will first need to define an appropriate set of simple beam attributes.

Listed below is the typical procedure for defining these attributes. Items in brackets [] are optional.

*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 (e.g. notional loads and wind loads). Setting simple beams to be designed for gravity loads only can significantly reduce the design time.

Step Dialog Page Instructions 1 none none Create a new Beam Attribute Set.

2 Attribute Set General Give the Attribute Set a Title

3 Attribute Set Design Choose Simple construction type

4 Attribute Set DesignCheck the Automatic Design box if Design Beam Mode is required, else leave it unchecked to work in Check Beam Mode

5 Attribute Set Design [Check the Gravity Only Design box* if required]

6 Attribute Set Design Click the Design Properties button

7 Beam Design PropertiesSize Constraints

[Define the Beam Constraints: max and min beam size]

8 Beam Design PropertiesSections for Study If in Design Beam Mode choose the Order File

9 Beam Design Properties Deflection

Define and apply deflection limits [dead] imposed [total]

10 Attribute Set Alignment [No changes are applicable for simple beams]

11 Attribute Set Type [Check the Fully Restrained box if required]

12 Attribute Set Supports

For simple beams, simple connections are required at both ends.For cantilevers, one end must be fully fixed and the other must be free.

13 Attribute Set Size Choose the steel grade and,if in Check Beam Mode choose the section size

14 Attribute Set Restraints Define the restraint details. Note, this page is not visible if the beam is fully restrained.

BS 5950 Member Design Handbook page 26 Chapter 3 : Simple BeamSimple Beam Input (when run as a standalone program) The design and check mode input procedures are listed below. Items in brackets [] are optional

Designing a beam

Step Icon Instructions

15 Launch Simple Beam,

16 Create a new project giving the project name [and other project details],

17 Choose the type of beam as either a Simple Beam or a Cantilever Beam [and give the beam reference details],

18 Set Simple Beam into design beam mode,

19Define the properties for the beam:

grade; span.

20 Give the details of the beam restraints.

21 Define the loadcases that apply to the simple beam.

22 Incorporate the loadcases into a series of design combinations,

23 [Make any Design Wizard settings that you want to use to control the design.]

24 Perform the design

25 From the list of suitable sections preview the results for the more desirable sections and then choose the one that you would like to use,

26 Add in any web openings that you need to allow access for services etc.

27Check the beam with the web openings. [Stiffen the web openings if necessary, or increase the size of the beam until the beam with openings is satisfactory.]

28 Specify the content of the report [and print it].

29 Save the project to disk.

Chapter 3 : Simple Beam BS 5950 Member Design Handbook page 27Checking a beamIn the typical procedure below items in brackets [] are optional.

Step Icon Instructions

1 Launch Simple Beam,

2 Create a new project giving the project name [and other project details],

3 Choose the type of beam as either a Simple Beam or a Cantilever Beam [and give the beam reference details],

4 Set Simple Beam into check beam mode,

5

Define the properties for the beam: section size, grade, span,

6 Add in any web openings that you need to allow access for services etc.

7 Give the details of the beam restraints.

8 Define the loadcases that apply to the simple beam.

9 Incorporate the loadcases into a series of design combinations,

10 [Make any Design Wizard settings that you want to use to control the design.]

11 Perform the check, (including any web openings),

12 [Stiffen the web openings if necessary, or increase the size of the beam until the beam with openings is satisfactory.]

13 Specify the content of the report [and print it].

14 Save the project to disk.

BS 5950 Member Design Handbook page 28 Chapter 3 : Simple BeamFurther information

Further information Westok Beams

For further information or technical literature on Westok Beams please contact Westok Technical Support and Design Service.

Westok Structural Services Ltd.Horbury Junction Industrial EstateHorbury JunctionWakefieldWF4 5ERTel: 44-1924 264 121Fax: 44-1924 280 030email: [email protected].

You can also view this information while running the program by choosing Help / About Westok Structural Services Ltd which shows the About Westok Structural Services Ltd. dialog.

You can click on the email link on this dialog to create a new email message to Westok.

Chapter 4 : Composite Beam BS 5950 Member Design Handbook page 29Chapter 4 Composite Beam

Introduction

The Composite Beam design application allows you to analyse and design a structural steel beam acting compositely with a concrete slab. This slab may be created either by using profile steel decking or by using Bison precast concrete slabs.

Composite Beam can determine the size of member which: acting alone are able to carry the forces and moments resulting from the Construction

Stage, acting compositely with the slab using profile steel decking or with precast concrete slabs

(with full or partial interaction) are able to carry the forces and moments at the Ultimate Limit State,

acting compositely with the slab using profile steel decking or with precast concrete slabs (with full or partial interaction) are able to provide acceptable deflections, service stresses and natural frequency at the Serviceability Limit State.

A list of those sections meeting the above requirements is displayed from which you may prefer to choose a slightly heavier beam with less studs, or a simpler layout of studs, in order to provide a more economical solution, or one that is easier to construct.

Alternatively you may give the size of a beam and Composite Beam will then determine whether it is able to carry the previously mentioned forces and moments and satisfy the Serviceability Limit State.

Additionally you can also use Composite Beam to check any web openings that are necessary, stiffening them where needed to attain an acceptable result.

Unless explicitly stated all calculations in Composite Beam are in accordance with the relevant sections of BS 5950-3.1:1990+A1:2010(Ref. 1). You may find the handbook and commentary to the Code of Practice published by the Steel Construction Institute (Ref. 3 and 4) useful.

COMPOSITE BEAM - composite steel beam with pinned ends designed for gravity loads acting through the web

BS 5950 Member Design Handbook page 30 Chapter 4 : Composite BeamScopeThe scope of Composite Beam is described in this section:

BeamYou can specify and design any simply supported composite beam with the design span taken as that defined in BS 5950-1:2000.

Westok sections

You can either check or design Westok sections in Composite Beam. The top and bottom part of the section can be formed from different beam section sizes, although they must be of the same grade.

Help Westok provide a design service to assist you with designs. For further information see: .Westok Technical Support and Design Service

The following points are worthy of note: If the resistance of the web post is insufficient this will yield a Fail status. To overcome this

your best option is to manipulate the cell data, or to make a more effective choice of the parent sections.

Caution Although you can use stiffeners to overcome this we would encourage you not to use this option. Please refer to Westok literature which shows these requirements diagramatically. If you do choose to use stiffeners then you should be aware that there is no design, sizing or graphical representation of these.

If you define a point load within 0.45Ro of the centre-line of a cell, then the maximum shear at either side of the point load is checked against the shear resistance of the net section. If the shear resistance is inadequate you will be told that a filler plate is required. The filler plate is not checked since the adjacent web post resists the same (or similar) shear and the checks on this will confirm the adequacy of the full web.

Note The program does not check the shear resistance of the minimum upper tee section alone. If you are concerned about this you will need to produce additional hand calculations. Automated calculations for this condition could easily be produced in Tedds.

In this release of the program you cannot define Westok sections which have different steel grades for the top and bottom section.

When Composite Beam is calculating the properties of Westok sections the root radii are ignored.

Chapter 4 : Composite Beam BS 5950 Member Design Handbook page 31 The size and position of the cells that you define should comply with the following limits to ensure that the design model is valid and for practical reasons (see Westok literature). The limits are generally: 1.08 S / Do 1.5 and 1.25 D / Do 1.75. 1.5 < S / Do 1.8 is also allowed following the findings of the latest research program.

If you do not wish to use the Autospace facility, or accept the Composite Beam defaults you should ensure that your cells comply with the limit 0.7 Do / h 1.3. You should therefore set the value Do to be the depth of the shallower source beam, hmin, at a pitch of 1.5 Do.

The design model assumes that the beam spans from centre-line to centre-line (BS 5950-1:2000). However in order to check the web posts or cells Composite Beam needs to know how this relates to the physical length of the beam. You need to define this by giving offsets from the centre-line at each end of the beam to its physical end. These offsets are shown in the Analysis Results window. All shears, moments etc. can thus be taken directly from the analysis results for the span as a whole.

Note When you apply loading you need to position this based on the Design span and not on the Physical beam.

Westok Technical Support and Design ServiceCellular beams are not manufactured to standard sizes in the same way as castellated beams. All sections are manufactured to the details given by the specifier to meet the requirements of each particular project.

Design span c/c

ReactionEnd shear for physical beam

Shear force diagram

Beam on span

Beam setback

Physical beam

Note: the program graphics show the complete beam (design span) with the offset shown as solid.

BS 5950 Member Design Handbook page 32 Chapter 4 : Composite BeamTo help specifiers Westok provide a comprehensive design and advisory service completely free of charge or obligation. If you would like a Westok Engineer to provide a cellular beam design, or require technical support on any matter concerning cellular beams then please contact Westok.

Help For further details see: Further information Westok Beams.

Steel sectionsComposite Beam can handle design for an international range of steel I-sections for many different countries and also for many specific manufacturers. Plated sections can also be checked.

If required the section can be precambered to counteract the effects of dead load on the deflection of the beam.

Caution If you want to use Bison precast concrete slabs, then you should ensure that a minimum width of flange of 133 mm is achieved to allow sufficient bearing for the slabs (50 mm) whilst still allowing a reasonable gap for stud welding and concrete infilling.

Web openingsIf you need to provide access for services, etc., then you can add openings to a designed beam and Composite Beam can then check these for you.

You can define rectangular or circular openings and these can be stiffened on one, or on both sides.

The checks that are performed are in accordance with the guidelines and design process given in the publication Design for openings in the webs of composite beams(Ref. 5).

We advise you to comply with the following positional recommendations for web openings: Web openings are designed using the bending moment and vertical shear values at the side

of the opening where the moment is lower, Openings should preferably be positioned at the mid-height of the section. If not, the

depth of the upper and lower sections of web should differ by not more than a factor of two,

Openings should not be located closer to the support than two times the beam depth or 10% of the span whichever is the greater,

The best location for any opening is between 1/5 and 1/3 of the span from a support in uniformly loaded beams, or in the lower shear zone of beams subject to point loads,

Openings should be not less than the beam depth, D, apart, Unstiffened openings should not generally be deeper than 0.6D or longer than 1.5D, Stiffened openings should not generally be deeper than 0.7D or longer than 2D, Point loads should not be applied at less than D from the side of the adjacent opening.

Chapter 4 : Composite Beam BS 5950 Member Design Handbook page 33You cannot currently automatically design sections with web openings, you must perform the design first to get a section size, and then add and check the openings. This gives you complete control of the design process, since you can add appropriate and cost effective levels of stiffening if required, or can choose a different beam with a stronger web in order to reduce or remove any stiffening requirement.

Web openings can be added to a beam by a 'Quick-layout' process or manually.

The 'Quick-layout' process, which is activated using the check box on the Web Openings dialog page, adds web openings which meet the geometric and proximity recommendations given above and in SCI Publication P068. The openings so created are the maximum depth spaced at the minimum centres recommended for the beam section size.

Web openings can be defined manually in two ways from the Web Openings dialog page. With the Quick-layout check box unchecked, the Add button adds a new line to the web openings grid to allow the geometric properties of the web opening to be defined, or alternatively, use of the Add... button opens the Web Opening Details dialog page which gives access to more help and guidance when defining the opening. Both methods make use of 'Warning' and 'Invalid' text for data entry checks [the default colours being orange and red respectively] to provide assistance as the opening parameters are defined.

On the Web Opening Details dialog page, the Centre button will position the opening on the beam centre whilst the Auto button will position the opening to meet the spacing recommendations given above and in P068. Also on this page tool tips give information on the recommended values for all the opening parameters.

As web openings are defined, they are immediately visible in the diagram on the Web Openings dialog page. This diagram displays the results of the geometric and proximity checks that are carried out on the opening parameters using 'Warning' and 'Invalid' display colours to highlight those areas that are outside the recommended limits.

BS 5950 Member Design Handbook page 34 Chapter 4 : Composite BeamA typical display is shown below:

The areas that are subjected to the checks are end posts, web posts, web opening dimensions and tee dimensions. Using the above example, it can be deduced that:

The left hand end post is less than the recommended limiting value WO #1 diameter is within the recommended limiting values Internal Web Post #2 is within the recommended limiting values WO #2 dimensions are outside the recommended limiting values Internal Web Post #3 is less than the recommended limiting value but quite close to the

limit. As the web post dimension reduces, the left and right triangles overlap to a greater degree at their apexes.

WO #3 dimensions are invalid and must be adjusted to progress the definition of the opening.

Internal Web Post #4 is within the recommended limiting values WO #4 dimensions are within the recommended limiting values Internal Web Post #5 is within the recommended limiting values WO #5 dimensions are within the recommended limiting values but the dimensions of the

tee(s) are not.

This display helps you to decide whether to make any adjustments to the opening parameters before their design is checked.

You should bear in mind that the checks carried out at this stage are geometric checks only and compliance with recommended limits is no guarantee that the opening will pass the subsequent engineering design checks.

Chapter 4 : Composite Beam BS 5950 Member Design Handbook page 35Note Dimensional checks. The program does not check that openings are positioned in the best position (between 1/5 and 1/3 length for udls and in a low shear zone for point loads). This is because for anything other than simple loading the best position becomes a question of engineering judgment or is pre-defined by the service runs.

Note Adjustment to deflections. The calculated deflections at both construction stage and composite stage are adjusted to allow for the web openings. See: Web Openingsin the Theory and Assumptions section.

Note Westok beams. You cannot define other web openings when you are using Westok beams.

Profiled metal deckingA wide range of profiled steel decking from all current UK manufacturers and some international ones is included.

You may define the profiled metal decking to span at any angle between 0 (parallel) and 90 (perpendicular) to the direction of span of the steel beam. You can also specify the attachment of the decking for parallel, perpendicular and angled conditions giving edge distances for studs and the positions of any laps where these are known.

Where you specify that the direction of span of the profiled metal decking to that of the steel beam is >=45, then there is no need to check the beam for lateral torsional buckling during construction stage.

Where you specify that the direction of span of the profiled metal decking to that of the steel beam is 45, then you are given the opportunity to check the steel beam for lateral torsional buckling at the construction stage.

Note This check is not mandatory in all instances. For a particular profile, gauge and fixing conditions etc. you might be able to prove that the profiled metal decking is able to provide a sufficient restraining action to the steel beam until the concrete hardens. If this is so, then you can specify that the whole beam (or a part of it) is continuously restrained. If you do need to check the beam for lateral torsional buckling during construction then this is in accordance with the requirements of BS 5950-1:2000(Ref. 2).

Where you specify that the direction of span of the profiled metal decking and that of the steel beam are parallel, then you must check the steel beam for lateral torsional buckling at the construction stage.

Longitudinal shear and deckingThe factors that influence the Longitudinal Shear capacity of your composite beam are:

concrete strength, slab depth and slab width you can not change these independently for the longitudinal shear check, since they apply equally to the entire composite beam design,

the attachment (or lack of attachment) of the decking and the assumed position of the lap (which applies only to certain configurations),

the areas of Transverse and Other reinforcement which you provide in your beam.

BS 5950 Member Design Handbook page 36 Chapter 4 : Composite BeamAttachment of decking and lap positionThere are six separate cases which are detailed in the following table:

Reinforcement in slabThe defaults are:

Transverse T10 @ 200, Other A142 Mesh.

Beam Type Decking angle Default setting

Internal

Perpendicular Discontinuous but effectively attached, default edge distance 30 mm.

Comment Discontinuous and not effectively attached would be a more onerous condition than the default.

Parallel Not applicable.

Comment The worst lap position i.e. zero distance to lap is assumed and can not be changed.

Angled Discontinuous but effectively attached, default edge distance 30 mm.

Comment The comments for perpendicular and parallel decking angles above apply to the angled condition.

Edge

Perpendicular Discontinuous not effectively attached. If you

choose the effectively attached option the edge distance is set to 30 mm.

Comment Details in publications show the decking continuing at least to the edge of the beam. So although not the most conservative setting, effectively attached is the most practical and most likely.

Parallel Not effectively attached.

Angled Not effectively attached.

Chapter 4 : Composite Beam BS 5950 Member Design Handbook page 37Precast concrete slabs You may define floors which use Bison Solid and Hollow Core precast concrete slabs. You may also choose the depth of slab that you want to use. The advice that is given below refers equally to both types of Bison slab.

You can also access safe-load tables equivalent to those provided by Bison as you are defining the precast concrete slabs. This is an invaluable aid to determining the appropriate type and thickness of precast concrete slab. The self-weights are also included for the precast concrete unit itself these should be increased by 5% when specifying loading at construction or composite stage to allow for the infill concrete.

The design strength of the infill concrete will always be set to 30 N/mm2 when you are using precast concrete slabs, this is a minimum requirement, concrete of greater strength can not be used. The modular ratios are defaulted to values appropriate to grade 30 concrete. You may change these if you can justify any alternative values. The overall slab depth that you specify must also comply with the recommendations given by Bison. The depth of the slab with or without topping is limited to a minimum of 150 mm and a maximum of 250 mm to assure the validity of the design rules.

The effective width of the concrete flange must be limited to the minimum of span/4 and 1000 mm for internal beams and span/8 and 500 mm for edge beams. Ongoing research may enable wider widths to be used in the future and these will be included as and when appropriate.

Since the use of precast concrete slabs produces a continuous trough along the beam you will find that diagrams in Composite Beam show this trough as parallel to the beam. However the use of precast concrete slabs does not usually require the steel beam to be checked for lateral torsional buckling at the construction stage and this is automatically catered for. For beams with a span greater than 9 m you need to give careful consideration to the construction sequence.

Typical precast concrete slab details

BS 5950 Member Design Handbook page 38 Chapter 4 : Composite BeamNote See also Shear connectors and Reinforcement for special requirements when using Bison precast concrete slabs.

Tip In order to meet the detailing requirements for minimum bearing and a minimum gap of 65 mm when in design mode set the Beam Size Constraints Minimum width to 133 mm.

Caution It is advisable that the position of the plastic neutral axis is such that the majority of the stud is in compression. This is best achieved by investigating the results (Moment, Plastic moment capacity details) and ensuring that the plastic neutral axis is no higher than 50 mm above the top of the beam flange.

Typical precast concrete slab details (Continued)

Chapter 4 : Composite Beam BS 5950 Member Design Handbook page 39Concrete slab You can define concrete slabs in both normal and lightweight concrete provided that you comply with the following constraints:

the slab depth must be between 90 and 500 mm, the concrete cube strength must be between 25 N/mm2 and 100 N/mm2 for normal or

lightweight concrete.

If you are defining an edge beam you can specify the projected distance from the centre-line of the beam to the free edge of the slab up to a maximum of 300 mm. If you use this facility then your construction details will need to justify this.

Shear connectorsThe shear connection between the concrete slab and the steel beam may be achieved by using normal studs or Hilti connectors.

For Hilti connectors the ultimate strengths used in the design are taken from tables published by Hilti Corporation, FL-9494 Schaan, Principality of Liechtenstein, (Group Headquarters, R & D and Manufacturing).

Note To enable the full strength of a Hilti connector to be achieved the minimum distance to the edge of the sheet must be at least 15 mm (3 times the diameter of the shot fired pin). The program assumes that this dimensional constraint is met and uses the full design strength of the connector in the calculations.

For other studs you can choose whether the ultimate strengths used in the design are to be those taken from Table 5 of BS 5950-3.1:1990+A1:2010 or those taken from tables published by T.R.W Nelson. Alternatively, if you have another source for the appropriate ultimate strengths you can enter the information directly yourself.

If you have chosen to use a precast concrete slab construction, then a particular set of stud information must be used (Diameter = 19 mm, Height = 125 mm, Ultimate Strength = 70 kN). You will not be allowed to change these values. Hilti studs can not be used with Bison precast concrete slabs.

You should ensure that a minimum distance of 30 mm from the centre line of the stud to the edge of the precast concrete slab is achievable.

All types of stud may be positioned in a range of patterns. However, since the A1 amendment to the code, the maximum number of studs in a group is now 2 (see clause 5.4.7.1).

Note Seethe Caution for Shear connectors (ULS) in Theory and Assumptions for essential information about the layout of shear connectors.

ReinforcementSince the profile metal decking can be perpendicular, parallel or at any other angle to the supporting beam the following assumptions have been made:

Transverse reinforcement, if you use single bars they are always assumed to be at 90 to the span of the beam,

BS 5950 Member Design Handbook page 40 Chapter 4 : Composite Beam if you use mesh then it is assumed to be laid so that the main bars1 are at 90 to the span of the beam.

Other reinforcement if you use single bars they are always assumed to be laid in the direction that is parallel to

the trough of the profile metal decking. if you use mesh then it is assumed to be laid such that the main bars(1) are always parallel

to the trough.

When using Bison precast concrete slabs only Transverse reinforcement can be specified. The default values are the recommended sizes and their spacing is fixed at 300 mm cross centres to coincide with the voids in the precast concrete slab.

In all cases a suitable bond length should be provided to anchor the reinforcement beyond the position where it is fully utilised.

Help For further information see: Typical precast concrete slab details.

Fibre Reinforced ConcreteWhen using decks from certain manufacturers an option exists to use fibre reinforcement as summarised below:

Note Fibre reinforcement can not be used with any other decking manufacturer.

Note Fibre reinforcement can't be used for edge beams, as these need traditional hooped reinf bars.

Help For further information see the Fibre Reinforced Concrete Advisory Notes.

Footnotes1. These are the bars that are referred to as longitudinal wires in BS 4483: 1998 Table 1.

Slab depth Reinforcement 150 T8 @ 300 200 T10 @ 300 250 T12 @ 300

Deck Manufacturer Fibre ReinforcementCORUS FibreFlor

Kingspan Dramix

RLSD Strux

SCFD Metfloor

SMD TAB-Deck

Chapter 4 : Composite Beam BS 5950 Member Design Handbook page 41Construction stage restraint conditionsIf you do need to check the lateral torsional buckling of the beam during construction (in the case where the profiled metal decking is unable to provide an acceptable level of restraint) you can:

define the degree of fixity that the end connections are able to provide and hence an effective length associated with the support,

position additional restraints at any point along the beam (Composite Beam automatically uses 1.0L and 1.2L+2D as the factors for Normal and Destabilizing loads),

Help For a definition of Destabilizing Loads see BS 5950-1:2000 clause 4.3.4.

Composite Beam automatically takes the average of the effective length factors for differing supports, or between those for the support and the adjacent sub-beam.

alternatively you can specify the factors that you want to use for the lengths between restraints, or you can enter the effective length of the sub-beam directly by entering a value (in m).

specify that any length (or lengths) of the beam should be taken as being fully restrained against lateral torsional buckling, independent of the restraint conditions for the adjacent length(s).

Construction stage loading You may specify a wide range of applied loading at the construction stage including:


You define these loads into one or more loadcases as required.

The Slab wet loadcase is reserved for the self weight of the wet concrete in the slab. If working within a Fastrak Building Designer model, by clicking the Automatic Loading check box this is automatically calculated based on the wet density of concrete and the area of slab supported. An allowance for ponding can optionally be included.

If you uncheck Automatic Loading, or if you are using Composite Beam as a standalone application, the Slab wet loadcase is initially empty - it is therefore important that you edit this loadcase and define directly the load in the beam due to the self weight of the wet concrete. If you do not do this then you effectively would be designing the beam on the assumption that it is propped at construction stage.

Having created the loadcases to be used at construction stage, you then include them, together with the appropriate factors in the dedicated Construction stage design combination. You can include or exclude the self-weight of the beam from this combination and you can define the load factors that apply to the self weight and to each loadcase in the combination.

BS 5950 Member Design Handbook page 42 Chapter 4 : Composite BeamNote You should include the Slab wet loadcase in the Construction stage combination, it can not be placed in any other combination since its loads relate to the slab in its wet state. Conversely, you can not include the Slab dry loadcase in the Construction stage combination, since its loads relate to the slab in its dry state. The loads in the Construction stage combination should relate to the slab in its wet state and any other loads that may be imposed during construction.

Tip If you give any additional construction stage loadcases a suitable title you will be able to identify them easily when you are creating the Construction stage combination.

Composite stage loading You may specify a wide range of applied loading for the composite condition:


You define these loads into one or more loadcases which you then include, together with the appropriate factors in the design combinations you create. You can include or exclude the self-weight of the steel beam from any combination and you can define the load factors that apply to the beam self weight and to each loadcase in the combination.

The Slab dry loadcase is reserved for the self weight of the dry concrete in the slab. If working within a Fastrak Building Designer model, by clicking the Automatic Loading check box this is automatically calculated based on the dry density of concrete and the area of slab supported. An allowance for ponding can optionally be included.

If you uncheck Automatic Loading, or if you are using Composite Beam as a standalone application, the Slab dry loadcase is initially empty - it is therefore important that you edit this loadcase and define directly the load in the beam due to the self weight of the dry concrete. For each other loadcase you create you specify the type of loads it contains Dead, Imposed or Wind.

For each load that you add to an Imposed loadcase you can specify the percentage of the load which is to be considered as acting long-term (and by inference that which acts only on a short-term basis).

All loads in Dead loadcases are considered to be completely long-term while those in Wind loadcases are considered totally short-term.

Construction stage design checksWhen you use Composite Beam to design or check a beam for the construction stage (the beam is acting alone before composite action is achieved) the following conditions are examined in accordance with BS 5950-1:2000:

section classification (Clause 3.5.2), shear capacity (Clause 4.2.3),

Chapter 4 : Composite Beam BS 5950 Member Design Handbook page 43 moment capacity: Clause 4.2.5.2 for the low shear condition, Clause 4.2.5.3 for the high shear condition,

lateral torsional buckling resistance (Clause 4.3.6),

Note This condition is only checked in those cases where the profile decking or precast concrete slab (at your request) does not provide adequate restraint to the beam,

web openings, Westok checks,

Shear horizontal, Web post buckling, Vierendeel bending,

construction stage total load deflection check.

Composite stage design checksWhen you use Composite Beam to design or check a beam for the composite stage (the beam and concrete act together, with shear interaction being achieved by appropriate shear connectors) the following Ultimate Limit State and Serviceability Limit State conditions are examined in accordance with BS 5950 : Part 3 : Section 3.1 : 1990 (unless specifically noted otherwise).

Ultimate Limit State Checks section classification (Clause 4.5.2), depending on whether adequate connection is

achieved between the compression flange and the slab. The section classification allows for the improvement of the classification of the section if the appropriate conditions are met,

vertical shear capacity (BS 5950-1:2000 - Clause 4.2.3), longitudinal shear capacity (Clause 5.6) allowing for the profiled metal decking, transverse

reinforcement and other reinforcement which has been defined, number of shear connectors required (Clause 5.4.7) between the point of maximum

moment and the end of the beam, or from and between the positions of significant point loads,

moment capacity: Clause 4.4.2 for the low shear condition, Clause 5.3.4 for the high shear condition,

web openings.

Serviceability Limit State Checks service stresses (Clause 6.2),

concrete steel top flange and bottom flange

deflections (Clause 6.1.2) self-weight SLAB loadcase,

BS 5950 Member Design Handbook page 44 Chapter 4 : Composite Beam dead load, imposed load1, total deflections,

natural frequency check (Clause 6.4).

Theory and Assumptions This section describes the theory used in the development of Composite Beam and the major assumptions that have been made, particularly with respect to interpretation of BS 5950-3.1:1990+A1:2010(Ref. 1). A basic knowledge of the design methods for composite beams in accordance with BS 5950-3.1:1990+A1:2010 is assumed.

Analysis methodComposite Beam uses a simple analysis of a statically determinate beam to determine the forces, moments and so on, to be resisted by the beam under the Construction stage, at the Serviceability Limit State and at the Ultimate Limit State.

Design methodThe design methods employed to determine the adequacy of the section for each condition are those consistent with BS 5950-3.1:1990+A1:2010 unless specifically noted otherwise.

Construction stageComposite Beam performs all checks for this condition in accordance with BS 5950-1:2000(Ref. 2)

Section classificationCross-section classification is determined using Table 11 and Clause 3.5.

The classification of the section must be Plastic (Class 1), Compact (Class 2) or Semi-compact (Class 3).

Sections which are classified as Slender (Class 4) are beyond the scope of Composite Beam.

Member strength checksMember strength checks are performed at the point of maximum moment, the point of maximum shear, the position of application of each point load, and at each side of a web opening as well as all other points of interest along the beam.

Shear capacity is determined in accordance with Clause 4.2.3. Where the applied shear force exceeds 60% of the capacity of the section, the high shear condition applies to the bending moment capacity checks (see below).

Bending moment capacity is calculated to Clause 4.2.5.2 (low shear at point) or Clause 4.2.5.3 (high shear at point) for plastic, compact and semi-compact sections.

Footnotes1. This is the only limit given in BS 5950 : Part 3 : Section 3.1 : 1990.

Chapter 4 : Composite Beam BS 5950 Member Design Handbook page 45Lateral torsional buckling checksBS 5950 : Part 3 : Section 3.1 : 1990 states that lateral torsional buckling checks are not required when the angle between the direction of span of the beam and that of the profile decking is greater than or equal to 45.

When the angle is less than this, then lateral torsional buckling checks will normally be required. Composite Beam allows you to switch off these checks by specifying that the entire length between the supports is continuously restrained against lateral torsional buckling.

If you use this option you must be able to provide justification that the beam is adequately restrained against lateral torsional buckling during construction.

For Bison precast concrete slabs you can specify whether or not the slabs are able to provide restraint to the beam against lateral torsional buckling. For beams with a span greater than 9 m you need to give careful consideration to the construction sequence.

When the checks are required you can position restraints at any point within the length of the main beam and can set the effective length of each sub-beam (the portion of the beam between one restraint and the next) either by giving factors to apply to the physical length of the beam, or by entering the effective length that you want to use. Each sub-beam which is not defined as being continuously restrained is checked in accordance with clause 4.3.8 and Annex B of BS 5950-1:2000.

Deflection checksComposite Beam calculates relative deflections. (See Deflection checksin the Basic Principles chapter of this handbook.)

The following deflections are calculated for the loads specified in the construction stage load combination:

the dead load deflections i.e. those due to the beam self weight, the Slab Wet loads and any other included dead loads,

the imposed load deflections i.e. those due to construction live loads, the total load deflection i.e. the sum of the previous items.

The loads are taken as acting on the steel beam alone.

The Service Factor (default 1.0), specified against each load case in the construction combination is applied when calculating the above deflections.

If requested by the user, the total load deflection is compared with either a span-over limit or an absolute value The initial default limit is span/200.

Note Adjustment to deflections. If web openings have been defined, the calculated deflections are adjusted accordingly. See: Web Openings in the Theory and Assumptions section.

Torsion for ASB and SFB beamsIn the design of ASB/SFB beams, torsion resulting from out of balance construction stage loading is not considered. If this condition occurs, then you will need to produce independent calculations to check this.

BS 5950 Member Design Handbook page 46 Chapter 4 : Composite BeamComposite stageComposite Beam performs all checks for the composite stage condition in accordance with BS 5950-3.1:1990+A1:2010 unless specifically noted otherwise.

Equivalent steel section - Ultimate limit state (ULS)An equivalent steel section is determined for use in the composite stage calculations by removing the root radii whilst maintaining the full area of the section. This approach reduces the number of change points in the calculations while maintaining optimum section properties.

Section classification (ULS)For section classification purposes the true section is used. Composite Beam classifies the section in accordance with the requirements of BS 5950-1:2000 except where specifically modified by those of BS 5950-3.1:1990+A1:2010.

There are a small number of sections which fail to meet a classification of compact at the composite stage. Although BS 5950-3.1:1990+A1:2010 covers the design of such members they are not allowed in this release of Composite Beam.

Member strength checks (ULS)Member strength checks are performed at the point of maximum moment, the point of maximum shear, the position of application of each point load, and at each side of a web opening as well as all other points of interest along the beam.

Shear Capacity (Vertical) is determined in accordance with Clause 4.2.3 of BS 5950-1:2000. Where the applied shear force exceeds 50% of the capacity of the section, the high shear condition applies to the bending moment capacity checks (see below).

Shear Capacity (Longitudinal) the longitudinal shear resistance of a unit length of the beam is calculated in accordance wi

bs5950 - member design handbook

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