eurocode - member design handbook

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EUROCODE MEMBER DESIGN

Friday 7 September 2012 15:40

Eurocode Member Design Handbook page 2 CSCs Offices Worldwide

Friday 7 September 2012 15:40

CSC (UK) LtdYeadon House

New StreetPudsey

Leeds, UKLS28 8AQ

Tel: (44) 113 239 3000Fax: (44) 113 236 0546

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Milton QLD 4064

Australia

Tel: 1300 882 393

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Email: [email protected]

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Disclaimer page 3

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

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

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

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

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

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

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CSC (UK) Ltd, hereinafter referred to as the OWNER, retains all proprietary rights with respect to this program package, consisting of all handbooks, drills, programs recorded on CD and all related materials. This program package has been provided pursuant to an agreement containing restrictions on its use.

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This confidentiality of the proprietary information and trade secrets of the OWNER shall be construed in accordance with and enforced under the laws of the United Kingdom.

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

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Table of ContentsEurocode Member Design Handbook

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

Chapter 2 Basic Principles . . . . . . . . . . . . . . . 8Definitions . . . . . . . . . . . . . . . . 8Convention for member axes . . . . . . . . . . . . . 10Deflection checks . . . . . . . . . . . . . . . 10Error messages . . . . . . . . . . . . . . . 11

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

Beam . . . . . . . . . . . . . . . . 12Steel sections . . . . . . . . . . . . . . . 12Web openings . . . . . . . . . . . . . . . 13Restraint conditions . . . . . . . . . . . . . . 17Applied loading . . . . . . . . . . . . . . . 17Design checks . . . . . . . . . . . . . . . 17

Theory and Assumptions . . . . . . . . . . . . . 18Analysis method . . . . . . . . . . . . . . 18Design method . . . . . . . . . . . . . . . 18Section classification . . . . . . . . . . . . . . 18Shear checks . . . . . . . . . . . . . . . 18Bending checks . . . . . . . . . . . . . . . 19Lateral torsional buckling checks . . . . . . . . . . . . 19Deflection checks . . . . . . . . . . . . . . 19Web Openings . . . . . . . . . . . . . . . 21

Design Properties . . . . . . . . . . . . . . . 21Size Constraints . . . . . . . . . . . . . . . 21Sections for Study (in Fastrak Building Designer) . . . . . . . . . 22Sections for Study (in Simple Beam) . . . . . . . . . . . 23Deflection. . . . . . . . . . . . . . . . 24

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

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

Chapter 4 Composite Beam . . . . . . . . . . . . . . 28Introduction . . . . . . . . . . . . . . . . 28Scope . . . . . . . . . . . . . . . . . 28

Beam . . . . . . . . . . . . . . . . 28Steel sections . . . . . . . . . . . . . . . 29Web openings . . . . . . . . . . . . . . . 29Profiled metal decking . . . . . . . . . . . . . 33Concrete slab . . . . . . . . . . . . . . . 34Shear connectors . . . . . . . . . . . . . . 35Reinforcement . . . . . . . . . . . . . . . 35Fibre Reinforced Concrete . . . . . . . . . . . . . 36Construction stage restraint conditions . . . . . . . . . . . 36Loading . . . . . . . . . . . . . . . . 36Construction stage design checks . . . . . . . . . . . . 38Composite stage design checks . . . . . . . . . . . . 38Friday 7 September 2012 15:40

Table of Contents page 5Theory and Assumptions . . . . . . . . . . . . . 39Analysis method . . . . . . . . . . . . . . 39Design method . . . . . . . . . . . . . . 39Construction stage . . . . . . . . . . . . . . 39Composite stage . . . . . . . . . . . . . . 40Web Openings . . . . . . . . . . . . . . 47

Design Aspects . . . . . . . . . . . . . . . 50Use of Design Properties to Control Section Selection . . . . . . . . 50Effective width calculations . . . . . . . . . . . . 54Application of NCCI PN002 to Partial Shear Connection . . . . . . . . 55Layout of Studs . . . . . . . . . . . . . . 56Non-composite design within Composite Beam . . . . . . . . . 63Automatic transverse shear reinforcement design . . . . . . . . . 64

Composite Beam Input (in Fastrak Building Designer) . . . . . . . . 66Composite Beam Input (when run as a standalone program) . . . . . . . 68


Chapter 5 General Beam . . . . . . . . . . . . . . . 71Introduction . . . . . . . . . . . . . . . 71Scope . . . . . . . . . . . . . . . . 71Limitations and Assumptions . . . . . . . . . . . . 73

Limitations . . . . . . . . . . . . . . . 73Assumptions . . . . . . . . . . . . . . . 73

Analysis . . . . . . . . . . . . . . . . 74Building Modeller object . . . . . . . . . . . . . 74General Beam . . . . . . . . . . . . . . . 74

Ultimate Limit State Strength . . . . . . . . . . . . 74Classification . . . . . . . . . . . . . . . 74Shear Capacity . . . . . . . . . . . . . . 75Moment Capacity . . . . . . . . . . . . . . 75Axial Capacity . . . . . . . . . . . . . . . 75Cross-section Capacity . . . . . . . . . . . . . 75

Ultimate Limit State Buckling . . . . . . . . . . . . 76Compression buckling . . . . . . . . . . . . . 76Lateral Torsional Buckling . . . . . . . . . . . . . 77Combined buckling . . . . . . . . . . . . . . 77Design Control . . . . . . . . . . . . . . 78

Member End Fixity and Supports . . . . . . . . . . . . 80General Beam Stand-alone . . . . . . . . . . . . 80Fastrak Building Designer . . . . . . . . . . . . . 80

General Beam Input (in Fastrak Building Designer) . . . . . . . . . 81General Beam Input (when run as a standalone program) . . . . . . . 82


Chapter 6 General Column . . . . . . . . . . . . . . 84Introduction . . . . . . . . . . . . . . . 84Scope . . . . . . . . . . . . . . . . 84

General Limitations . . . . . . . . . . . . . . 84Steel sections . . . . . . . . . . . . . . . 85Simple Columns . . . . . . . . . . . . . . 85End Releases . . . . . . . . . . . . . . . 85Imposed Load Reductions . . . . . . . . . . . . . 85Splices . . . . . . . . . . . . . . . . 85Design Forces . . . . . . . . . . . . . . . 86

Table of ContentsDesign Checks . . . . . . . . . . . . . . . 86Analysis . . . . . . . . . . . . . . . . 86

Building Modeller Object . . . . . . . . . . . . . 86Ultimate Limit State Strength . . . . . . . . . . . . 86

Classification . . . . . . . . . . . . . . . 87Axial Capacity . . . . . . . . . . . . . . . 87Shear Capacity . . . . . . . . . . . . . . . 87Moment Capacity . . . . . . . . . . . . . . 88Combined Bending and Axial Capacity . . . . . . . . . . . 88

Ultimate Limit State Buckling . . . . . . . . . . . . 89Compression buckling . . . . . . . . . . . . . 89Lateral Torsional Buckling . . . . . . . . . . . . . 91Combined Buckling . . . . . . . . . . . . . . 92

Serviceability limit state. . . . . . . . . . . . . . 92General Column Input (in Fastrak Building Designer) . . . . . . . . 93

Chapter 7 Braces . . . . . . . . . . . . . . . . . 94Introduction . . . . . . . . . . . . . . . . 94Scope . . . . . . . . . . . . . . . . . 94

Steel sections . . . . . . . . . . . . . . . 94End Connections . . . . . . . . . . . . . . 94Applied loading . . . . . . . . . . . . . . . 94Design Forces . . . . . . . . . . . . . . . 95Design checks . . . . . . . . . . . . . . . 95

Theory and Assumptions . . . . . . . . . . . . . 95Analysis method . . . . . . . . . . . . . . 95Design method . . . . . . . . . . . . . . . 95Classification . . . . . . . . . . . . . . . 95Axial Tension . . . . . . . . . . . . . . . 95Axial Compression . . . . . . . . . . . . . . 95Compression Buckling . . . . . . . . . . . . . 96

Brace Input . . . . . . . . . . . . . . . . 96

Chapter 8 Refining Member Designs . . . . . . . . . . . . 97Introduction . . . . . . . . . . . . . . . . 97

Why would you want to refine the original design? . . . . . . . . . 97Interaction Effects . . . . . . . . . . . . . . 97

How to Access Design Refinement . . . . . . . . . . . . 98Simple Beam - Check Mode. . . . . . . . . . . . . . 98Simple Beam - Design Mode. . . . . . . . . . . . . 99Composite Beam - Check Mode . . . . . . . . . . . .100Composite Beam - Design Mode . . . . . . . . . . . .101General Column - Check Mode . . . . . . . . . . . .102General Column - Design Mode . . . . . . . . . . . .103

Effective Use of Order Files in Refined Design . . . . . . . . . .103Design Pass 1 . . . . . . . . . . . . . . .104Design Pass 2 . . . . . . . . . . . . . . .105Design Pass 3 . . . . . . . . . . . . . . .106

Chapter 9 References . . . . . . . . . . . . . . . .108Friday 7 September 2012 15:40

Chapter 1 : Introduction Eurocode Member Design Handbook page 7Eurocode 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 EN 1993-1-1:2005(Ref. 1) and BS EN 1994-1-1:2004(Ref. 4) codes are selected.

Within the remainder of this handbook BS EN 1993-1-1:2005 and BS EN 1994-1-1:2004 are referred to as EC3 and EC4 respectively.

Unless explicitly noted otherwise, all clauses, figures and tables referred to are from EC3; apart from the Composite Beam section, within which references are to EC4 unless stated.

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

Composite Beam (Chapter 4)composite steel beam with pinned ends designed for gravity loads acting through the web

General Beam (Chapter 5)non-composite steel beam designed as a beam/column

General Column (Chapter 6)steel column designed as a beam/column

Braces (Chapter 7)steel members with pinned ends designed for axial loads only

Refining Member Designs (Chapter 8)advice to assist you in extracting individual members into each design application for more detailed assessment.

References (Chapter 9)

Eurocode Member Design Handbook page 8 Chapter 2 : Basic PrinciplesChapter 2 Basic Principles

DefinitionsCommonly applied Fastrak terms are defined below:

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 Fastrak 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 they are able to carry the applied loading.

Interactive DesignWithin Fastrak 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

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.

The following terms are relevant when using Fastrak to design to the Eurocodes.

Chapter 2 : Basic Principles Eurocode Member Design Handbook page 9National Annex (NA)Safety factors in the Eurocodes are recommended values and may be altered by the national annex of each member state.

Fastrak Building Designer currently has following EC3 national annex options are available: EC3 (base) EC3 UK NA EC3 Irish NA

You can select the desired National Annex as appropriate, in which case the nationally determined parameters are automatically applied, or if you choose EC3 (base), the Eurocode recommended values are applied.

Nationally Determined Parameters (NDPs)NDPs are choices of values, classes or alternative methods contained in a National Annex that can be applied in place of the base Eurocode.

Partial Factors for BuildingsThe partial factors M for buildings as described in Clause 6.1(1) should be applied to the various characteristic values of resistance as follows:

resistance of cross-sections irrespective of class: M1resistance of members to instability assessed by member checks: M1resistance of cross-sections in tension to fracture: M2

Depending on your choice of National Annex the above partial factors for buildings are set as follows:

NOTE - for connection design BS EN1991-1-8 - M2 = 1.25

Factor EC Base value UK Value Irish ValueM0 1.00 1.00 1.00M1 1.00 1.00 1.00M2 1.25 1.10* 1.25

Eurocode Member Design Handbook page 10 Chapter 2 : Basic PrinciplesConvention for member axesThe sign convention for member axes when designing to Eurocodes is as shown below.

Deflection checksFastrak Building 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.

Section axes - (x is into the page along the centroidal axis of the member).

Relative Deflection Absolute Deflection

Chapter 2 : Basic Principles Eurocode Member Design Handbook page 11Error 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.

Eurocode 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 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 size of member which can carry the forces and moments resulting from the applied loading.

Alternatively you can specify the member size 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 EC3(Ref. 1) and the associated UK(Ref. 2) or Irish(Ref. 3) National Annex.

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

BeamThe beam is designed for gravity loads acting through the shear centre in the plane of the web. Minor axis bending, uplift loads and axial loads are not considered.

Note If either minor axis bending, uplift loads, point moments or axial loads exist which exceed a 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 sections for many different countries. Plated sections can also be checked.

The following section types are available:

I (including rolled, ASB, SFB, plated), C, RHS, SHS

Where:I rolled = UKB, UKC, UB, UC, RSJ, IPE, HE, HD, IPNC = RSC, PFC, UAP, UPNRHS = RHS, Euro RHSSHS = SHS, Euro SHS

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

Chapter 3 : Simple Beam Eurocode Member Design Handbook page 13Web 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.

General guidance on size and positioning of openings is given in Table 2.1 of the SCI Publication P355(Ref. 8) and repeated below:

* A high shear region is where the design shear force is greater than half the maximum value of design shear force acting on the beam.

ParameterLimit

Circular Opening Rectangular OpeningMax. depth of opening: = 0.1h

Min. depth of Top Tee: As aboveAs above and >= 0.1lo

if unstiffened

Max. ratio of depth of Tees: hb/hthb/ht

= 0.5

= 1

Max. unstiffened opening length, lo

Max. stiffened opening length, lo

----

= lo

Corner radius of rectangular openings: -

ro >= 2twbut ro >= 15 mm

Min. width of end post, se: >= 0.5ho>= lo

and >= h

Min. horizontal distance to point load:

- no stiffeners- with stiffeners

>= 0.5h>= 0.25ho

>= h>= 0.5ho

Eurocode Member Design Handbook page 14 Chapter 3 : Simple BeamSymbols used in the above table:

h = overall depth of steel section

ho = depth of opening [diameter for circular openings]

ht = overall depth of upper Tee [including flange]

hb = overall depth of lower Tee [including flange]

lo =(clear) length of opening [diameter for circular openings]

se = width of end post [minimum clear distance between opening and support]

tf = thickness of flange

tw = thickness of web

ro = corner radius of opening

In addition, the following fundamental geometric requirements must be satisfied.

do

Chapter 3 : Simple Beam Eurocode Member Design Handbook page 15tb = the thickness of the bottom flange of the steel section

rt = root radius at the top of the steel section

rb = root radius at the bottom of the steel section

Lc = the distance to the centre line of the opening from the left hand support

L = the span of the beam

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 in Table 2.1 of SCI Publication P355. 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 in P355. 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.

Eurocode Member Design Handbook page 16 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 Eurocode Member Design Handbook page 17Note 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 are adjusted to allow for the web openings. See: Web Openingsin the Theory and Assumptions section. .

Restraint conditionsIf you need to check the lateral torsional buckling of the beam you can define the effective length by:

specifying 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),

You can position additional restraints at any point along the beam as required. You can also 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.

All loads must be positive since the beam is considered as simply supported and no negative moment effects are accommodated.

Design checksWhen you use Simple Beam to design or check a beam the following conditions are examined in accordance with EC3:

section classification (Table 5.2), shear capacity (Clause 6.2.6 (1)), web shear buckling (Clause 6.2.6 (6)), moment capacity:

Equation 6.13 for the low shear condition, Equation 6.29 for the high shear condition,

lateral torsional buckling resistance (Clause 6.3.2.3), web openings, dead, imposed and total load deflection check.

Eurocode Member Design Handbook page 18 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 EC3.

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 EC3 unless specifically noted otherwise.

Section classificationCross-section classification for flexure is determined using Table 5.2.

The classification of the section must be Class 1, Class 2 or Class 3. Sections which are classified as Class 4 are beyond the scope of Simple Beam.

Implementation of the below clauses is as follows: Classification is determined using 5.5.2 (6) and not 5.5.2 (7). 5.5.2 (9) is not implemented as clause (10) asks for the full classification to be used for

buckling resistance. 5.5.2 (11) is not implemented. 5.5.2 (12) is not implemented. A brief study of UK rolled UBs and UCs showed that flange

induced buckling in normal rolled sections is not a concern.

Shear checksMajor axis shear checks are performed at the point of maximum moment, the point of maximum shear, the position of application of each point load, and at all other points of interest along the beam.

Major axis shear is determined in accordance with clause 6.2.6 (1). 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).

Web Shear buckling the 6.2.6 (6) limit is checked and if exceeded a warning is given. The warning indicates that additional calculations to EN 1993-1-5 are not carried out.

The following points should be noted: No account is taken of fastener holes in the flange or web - see 6.2.6 (7) Shear is not combined with torsion and thus the resistance is not reduced as per 6.2.6 (8)

Chapter 3 : Simple Beam Eurocode Member Design Handbook page 19Bending checksMajor axis bending checks are performed at the point of maximum moment, the point of maximum shear, the position of application of each point load, as well as all other points of interest along the beam.

Bending moment capacity for low shear this is calculated to equation 6.13 for class 1 and 2 cross sections and equation 6.14 for class 3 cross sections. In the high shear case equation 6.29 is used for class 1 and 2 cross sections and equation 6.14 for class 3 cross sections. Where the high shear condition applies, the moment capacity calculation is made less complicated by conservatively adopting a simplified shear area.

Lateral torsional buckling checksLateral 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.

If 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. Any individual segment can be continuously restrained in which case no LTB check will be carried out over that segment. Each sub-beam which is not defined as being continuously restrained is checked in accordance with clause 6.3.2.3.

Effective lengthsThe value of effective length factor is entirely the choice of the engineer. The default value is 1.0. There is no specific factor for destabilizing loads - so you will have to adjust the 'normal' effective length factor to allow for such effects.

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

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).

Eurocode Member Design Handbook page 20 Chapter 3 : Simple BeamWeb 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.

Note 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 Eurocode Member Design Handbook page 21Web Openings

Circular Openings as an Equivalent RectangleEach circular opening is replaced by equivalent rectangular opening, the dimensions of this equivalent rectangle for use in all subsequent calculations are:

do'= 0.9*opening diameter

lo = 0.45*opening diameter

Properties of Tee SectionsWhen web openings have been added, the properties of the tee sections above and below each opening are calculated in accordance with Section 3.3.1 of SCI P355(Ref. 8) and Appendix B of the joint CIRIA/SCI Publication P068(Ref. 9). The bending moment resistance is calculated separately for each of the four corners of each opening.

Design ChecksThe following calculations are performed where required for web openings:

Axial resistance of tee sections Classification of section at opening Vertical shear resistance Vierendeel bending resistance Web post horizontal shear resistance Web post bending resistance Web post buckling resistance Lateral torsional buckling Deflections

Design 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.

Eurocode Member Design Handbook page 22 Chapter 3 : Simple BeamSections 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).

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 Eurocode Member Design Handbook page 23Sections 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.

Eurocode Member Design Handbook page 24 Chapter 3 : Simple BeamDeflectionThe 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.

Chapter 3 : Simple Beam Eurocode 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 Instructions1 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 SizeChoose 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.

Eurocode Member Design Handbook page 26 Chapter 3 : Simple BeamSimple Beam Input (when run as a standalone program) 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 Eurocode 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.

Eurocode Member Design Handbook page 28 Chapter 4 : Composite BeamChapter 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 created using profile steel decking.

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

Stage, acting compositely with the slab using profile steel decking (with full or partial

interaction) is able to carry the forces and moments at the Ultimate Limit State, acting compositely with the slab using profile steel decking (with full or partial

interaction) is able to provide acceptable deflections, service stresses and natural frequency at the Serviceability Limit State.

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.

An auto-layout feature can be used for stud placement which caters for both uniform and non-uniform layouts.

The construction stage calculations are performed in accordance with the relevant sections of EC3(Ref. 1) and the associated UK(Ref. 2) or Irish(Ref. 3) National Annex.

The composite stage design adopts a limit state approach consistent with the design parameters for simple and continuous composite beams as specified in EC4(Ref. 4) and the associated UK(Ref. 5) or Irish National Annex.

Unless explicitly noted otherwise, all clauses, figures and tables referred to are from EC4.

ScopeThe scope of Composite Beam is described in this section:

BeamThe beam must be a simply supported, single span unpropped structural steel beam.

The following are beyond scope: continuous or fixed ended composite beams, composite sections formed from hollow rolled sections, composite sections where the concrete slab bears on the bottom flange.

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

Chapter 4 : Composite Beam Eurocode Member Design Handbook page 29The 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 a limit below which they can be ignored, a warning is given in the beam design summary.

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

The following rolled section types are available:

UKB, UKC, UB, UC, RSJ, IPE, HE, HD, IPN

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

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.

General guidance on size and positioning of openings is given in Table 2.1 of the SCI Publication P355(Ref. 8) and repeated below:

ParameterLimit

Circular Opening Rectangular OpeningMax. depth of opening: = 0.1h

Min. depth of Top Tee: As aboveAs above and >= 0.1lo

if unstiffened

Max. ratio of depth of Tees: hb/hthb/ht

= 0.5

= 1

Max. unstiffened opening length, lo

Max. stiffened opening length, lo

----

Eurocode Member Design Handbook page 30 Chapter 4 : Composite Beam* A high shear region is where the design shear force is greater than half the maximum value of design shear force acting on the beam.

Symbols used in the above table:

h = overall depth of steel section

ho = depth of opening [diameter for circular openings]

ht = overall depth of upper Tee [including flange]

hb = overall depth of lower Tee [including flange]

lo =(clear) length of opening [diameter for circular openings]

se = width of end post [minimum clear distance between opening and support]

tf = thickness of flange

tw = thickness of web

ro = corner radius of opening

In addition, the following fundamental geometric requirements must be satisfied.

do = 0.4ho

>= 0.5lo>= lo

Corner radius of rectangular openings: -

ro >= 2twbut ro >= 15 mm

Min. width of end post, se: >= 0.5ho>= lo

and >= h

Min. horizontal distance to point load:

- no stiffeners- with stiffeners

>= 0.5h>= 0.25ho

>= h>= 0.5ho

ParameterLimit

Circular Opening Rectangular Opening

Chapter 4 : Composite Beam Eurocode Member Design Handbook page 31d2 < doc - do/2 - tt- ts/2

d2 < h - tb- doc - do - ts/2

lo < 2 * Lc

lo < 2 * (L - Lc)

Ls < 2 * Lc

Ls < 2 * (L - Lc)

where

dt=the depth of the web of the upper tee section measured from the underside of the top flange

doc = the distance to the centre line of the opening from the top of the steel section

d2 = the distance from the edge of the opening to the centre line of the stiffener

ts = thickness of stiffener [constrained to be the same top and bottom]

tt = the thickness of the top flange of the steel section

tb = the thickness of the bottom flange of the steel section

rt = root radius at the top of the steel section

rb = root radius at the bottom of the steel section

Lc = the distance to the centre line of the opening from the left hand support

L = the span of the beam

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 in Table 2.1 of SCI Publication P355. 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

Eurocode Member Design Handbook page 32 Chapter 4 : Composite Beamand 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 in P355. 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.

A 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

Chapter 4 : Composite Beam Eurocode Member Design Handbook page 33 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.

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 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.

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.

Where you specify that the direction of span of the profiled metal decking to that of the steel beam is >=45, then Composite Beam assumes it is not necessary 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 condition 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. Where you request to check the beam for lateral torsional buckling during construction then this is carried out in accordance with the requirements of EC3.

Where you specify that the direction of span of the profiled metal decking and that of the steel beam are parallel, you again have the same opportunity to either check the steel beam for lateral torsional buckling at the construction stage, or to set it as continuously restrained.

Eurocode Member Design Handbook page 34 Chapter 4 : Composite BeamLongitudinal 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 - not applicable for parallel decks, the areas of Transverse and Other reinforcement which you provide in your beam.

Attachment of decking There are six separate cases which are detailed in the following table:

Concrete 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, Normal concrete range C20/25 - C60/75 - See Clause 3.1(2), Lightweight concrete range LC20/22 - LC60/66 - See Clause 3.1(2), Minimum density for lightweight concrete 1750 kg/m3 - see Clause 6.6.3.1(1).

Concrete properties are obtained by reference to EN 1992-1-1, 3.1 for normal concrete and EN 1992-1-1, 11.3 for lightweight concrete. If normal concrete is specified, you are required to specify the type of aggregate used as this influences the value of Elastic Modulus.

Beam Type Decking angle Default setting

Internal

Perpendicular Discontinuous but effectively attached

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

Parallel not applicable.

Angled Discontinuous but effectively attached

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

Edge

Perpendicular Discontinuous not effectively attached.

Comment In this case you are expected to manually detail the provision of U-bars in accordance with SCI P333.

Parallel Not effectively attached.

Angled Not effectively attached.

Chapter 4 : Composite Beam Eurocode Member Design Handbook page 35The default concrete densities are as follows: normal concrete, wet - 2600 kg/m3, normal concrete, dry - 2500 kg/m3, lightweight concrete, wet - 2150 kg/m3, lightweight concrete, dry - 2050 kg/m3,

Note The default densities above allow for 0.5kN/m3 reinforcement; the wet densities also allow 1kN/m3 for water. The dry density of unreinforced concrete is taken from BS EN 1991-1-1 Annex A.

Shear connectorsIn the Eurocode version of Composite Beam, only 19 mm diameter studs with 100 and 125 nominal height (95 and 120 as welded height) are offered. These do not have a given capacity as their resistance is derived.

Studs may be positioned in a wide range of patterns.

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 is provided specifically for longitudinal shear, if you use single bars they are always assumed to be at 90 to the span of the 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 is provided for other reasons,

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.

The following reinforcement choices are available: high yield steel, H Mesh, A Mesh, B Mesh, C

The reinforcement you specify is assumed to be placed at a position in the depth of the slab where it is able to contribute to the longitudinal shear resistance.

Note The modulus of elasticity, Es is taken to be the same as for structural steel i.e. 210,000 N/mm2.

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

Eurocode Member Design Handbook page 36 Chapter 4 : Composite BeamFibre Reinforced ConcreteIn the Eurocode version of Composite Beam the option to use fibre reinforcement is not yet available.

Construction 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 effective length by:

specifying 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),

You can position additional restraints at any point along the beam as required. You can also 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).

LoadingYou may specify a wide range of applied loading including:

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.

All loads must be positive since the beam is considered as simply supported and no negative moment effects are accommodated.

Construction stage loading 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, clicking the Automatic Loading check box enables this to be automatically calculated based on the wet density of concrete1 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.

It is usual to define a loadcase for Imposed construction loads in order to account for heaping of the wet concrete etc.

Footnotes1. You will have defined this value on the Floor Construction page.

Chapter 4 : Composite Beam Eurocode Member Design Handbook page 37Having 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.

Note 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.

Note You are required to determine the effective lengths to be used in lateral torsional buckling (if such a check is appropriate). All loads within a Construction Stage combination are considered as 'non-destabilizing' - thus you must adjust the effective lengths if any of your loads are 'destabilizing'.

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 define the composite stage 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, clicking the Automatic Loading check box enables this to be automatically calculated based on the dry density of concrete1 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 entirely long-term while those in Wind loadcases are considered entirely short-term.

Footnotes1. You will have defined this value on the Floor Construction page

Eurocode Member Design Handbook page 38 Chapter 4 : Composite BeamConstruction 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 EC3:

section classification (EC3 Table 5.2), major axis shear capacity (EC3 Clause 6.2.6 (1)), web shear buckling (EC3 Clause 6.2.6 (6)), moment capacity:

EC3 Equation 6.13 for the low shear condition, EC3 Equation 6.29 for the high shear condition,

lateral torsional buckling resistance (EC3 Clause 6.3.2.3),Note This condition is only checked in those cases where the profile decking does not

provide adequate restraint to the beam,

web openings, 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 EC4, unless specifically noted otherwise.

Ultimate Limit State Checks section classification - the classification system defined in EC3 Clause 5.5.2 applies to

cross-sections of composite beams, vertical shear capacity in accordance with EC3 Clause 6.2.6, longitudinal shear capacity allowing for the profiled metal decking, transverse

reinforcement and other reinforcement which has been defined, number of shear connectors required (EC4 Clause 6.6.1.3 (5)) between the point of

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

moment capacity, web openings.

Serviceability Limit State Checks service stresses - although there is no requirement to check these in EC4 for buildings

(EC4 Clause 7.2.2), concrete and steel top/bottom flange stresses are calculated but only reported if the stress limit is exceeded.

deflections, self-weight, SLAB loadcase, dead load,

Chapter 4 : Composite Beam Eurocode Member Design Handbook page 39 imposed load, total deflections,

natural frequency check.

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 both EC3 and EC4. A basic knowledge of EC3 and the design methods for composite beams in EC4 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 EC4 unless specifically noted otherwise.

Construction stageComposite Beam performs all checks for this condition in accordance with EC3.

Section classificationCross-section classification is determined using EC3 Table 5.2.

At construction stage the classification of the section must be Class 1, Class 2 or Class 3.

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

Note Clause 5.5.2 (6) is implemented, not the alternative 5.5.2 (7).Clause 5.5.2 (11) is not implementedClause 5.5.2 (12) is not implemented

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 all other points of interest along the beam.

Shear capacity is determined in accordance with EC3 Clause 6.2.6 (1). 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).

The following points should be noted: No account is taken of fastener holes in the flange or web - see EC3 6.2.6 (7) Shear is not combined with torsion and thus the resistance is not reduced as per EC3

6.2.6(8)

Eurocode Member Design Handbook page 40 Chapter 4 : Composite BeamWeb Shear buckling the EC3 Clause 6.2.6 (6) limit is checked and if exceeded a warning is given. The warning indicates that additional calculations to EN 1993-1-5 are not carried out.

Bending moment capacity for low shear this is calculated to EC3 Equation 6.13. In the high shear case Equation 6.29 is used. Where the high shear condition applies, the moment capacity calculation is made less complicated by conservatively adopting a simplified shear area.

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

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

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 EC3 Clause 6.3.2.3.

Deflection checksComposite Beam calculates relative deflections. (see Deflection checks in 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.

Composite stageComposite Beam performs all checks for the composite stage condition in accordance with EC4 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.

Chapter 4 : Composite Beam Eurocode Member Design Handbook page 41Section classification (ULS)Composite Beam classifies the section in accordance with the requirements of EC3, 5.5.2 except where specifically modified by those of EC4.

A composite section is classified according to the highest (least favourable) class of its steel elements in compression. The compression flange and the web are therefore both classified and the least favourable is taken as that for the whole section.

Flanges of any class that are fully attached to a concrete flange are assumed to be Class 1. The requirements for maximum stud spacing according to Clause 6.6.5.5 (2) are checked and you are warned if these are not satisfied.

There are a small number of sections which fail to meet Class 2 at the composite stage. Although EC4 covers the design of such members they are not allowed in this release of Composite Beam.

Eurocode Member Design Handbook page 42 Chapter 4 : Composite BeamMember strength checks (ULS)It is assumed that there are no loads or support conditions that require the web to be checked for transverse force. (Clause 6.5)

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 all other points of interest along the beam.

Shear Capacity (Vertical) The resistance to vertical shear, VRd, is taken as the resistance of the structural steel section, Vpl,a,Rd. The contribution of the concrete slab is neglected in this calculation.

The shear check is performed in accordance with EC3, 6.2.6.

Moment Capacity for full shear connection the plastic resistance moment is determined in accordance with Clause 6.2.1.2. For the partial shear connection Clause 6.2.1.3 is adopted.

In these calculations the steel section is idealised to one without a root radius so that the position of the plastic neutral axis of the composite section can be determined correctly as it moves from the flange into the web.

Where the vertical shear force, VEd, exceeds half the shear resistance, VRd, a (1- ) factor is applied to reduce the design strength of the web - as per Clause 6.2.2.4.

Shear Capacity (Longitudinal) the design condition to be checked is: vEd vRdwhere

vEd = design longitudinal shear stress

vRd = design longitudinal shear strength (resistance)

vEd is evaluated at all relevant locations along the beam and the maximum value adopted.

vRd is evaluated taking account of the deck continuity, its orientation and the provided reinforcement.

This approach uses the truss analogy from EC2. (See Figure 6.7 of EC2).

In these calculations, two planes are assumed for an internal beam, and one for an edge beam. Only the concrete above the deck is used in the calculations.

The values of vRd based on the concrete strut and the reinforcement tie are calculated. The final value of vRd adopted is then taken as the minimum of these two values.

The angle of the strut is minimised to minimise the required amount of reinforcement - this angle must lie between 26.5 and 45 degrees.

Chapter 4 : Composite Beam Eurocode Member Design Handbook page 43In the calculations of vRd the areas used for the reinforcement are as shown in the following table.

If the decking spans at some intermediate angle (r) between these two extremes then the program calculates:

the longitudinal shear resistance as if the sheeting were perpendicular, vRd,perp, the longitudinal shear resistance as if the sheeting were parallel, vRd,par, then the modified longitudinal shear resistance is calculated from these using the

relationship, vRd,perpsin2(r) + vRd,parcos2(r).

Minimum area of transverse reinforcement

The minimum area of transverse reinforcement is checked in accordance with Clause 6.6.6.3.

Shear connectors (ULS)

Dimensional Requirements Various limitations on the use of studs are given in the code.

Decking angle Reinforcement type Area used

perpendicular

transversethat of the single bars defined or for mesh the area of the main wiresa

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

otherthat of the single bars defined or for mesh the area of the main wires(a)

parallel

transversethat of the single bars defined or for mesh the area of the main wires(a)

othersingle bars have no contribution, for mesh the area of the minor wiresb

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

Eurocode Member Design Handbook page 44 Chapter 4 : Composite BeamThe following conditions in particular are drawn to your attention:

The program does not check that the calculated stud layout can be fitted in the rib of the deck.

Design resistance of the shear connectors For ribs parallel to the beam the design resistance is determined in accordance with Clause 6.6.4.1. The reduction factor, kl is obtained from Equation 6.22.

For ribs perpendicular to the beam, Clause 6.6.4.2 is adopted. The reduction factor, kt is obtained from Equation 6.23.

The factor kt should not be taken greater than the appropriate value of kt,max from the following table;

Parameter Rule Clause/CommentSpacing Ductile connectors may be spaced uniformly

over length between critical cross-sections if:

- All critical cross-sections are Class 1 or 2

- The degree of shear connection, is within the range given by 6.6.1.2

and

- the plastic resistance moment of the composite section does not exceed 2.5 times the plastic resistance moment of the steel member alone.

6.6.1.3(3) - not checked

Edge Distance eD >= 20 mm 6.6.5.6(2) - not checked

eD 9*tf*sqrt(235/fy) 6.6.5.5(2) - applies if bare steel beam flange is Class 3 or 4 - not checked

Location If can't be located in centre of trough, place alternately either side of the trough throughout span


Cover The value from EC2 Table 4.4 less 5mm, or 20mm whichever is the greater.


No of Stud Connectors

per rib

Thickness of sheet,

t mm

Studs with d 20 mm and welded through profiled steel

sheeting, kt,max

Profiled sheeting with holes and studs with

d=19 or 22 mm, kt,maxnr = 1 1.0 0.85 0.75

> 1.0 1.00 0.75

nr = 2 1.0 0.70 0.60> 1.0 0.80 0.60

Chapter 4 : Composite Beam Eurocode Member Design Handbook page 45Note Only the first column of values of kt.max is used from the above table since the technique of leaving holes in the deck so that studs can be welded directly to the beam is not used.

For cases where the ribs run at an angle, r the reduction factor is calculated as: kt*sin

2r + kl*cos2rStud optimization is a useful facility since there is often some over conservatism in a design due to the discrete changes in the size of the section.

If you choose the option to optimise the shear studs, then Composite Beam will progressively reduce the number of studs either until the minimum number of studs to resist the applied moment is found, until the minimum allowable interaction ratio is reached or until the minimum spacing requirements are reached. This results in partial shear connection.

The program can also automatically layout groups of 1 or 2 studs with constraints that you specify. For details refer to Layout of Studs in the Design Aspects section of this chapter.

The degree of shear connection is checked at the point of maximum bending moment or the position of a point load if at that position the maximum utilisation ratio occurs.

Note During the selection process, in auto design mode point load positions are taken to be significant (i.e. considered as positions at which the maximum utilisation could occur) if they provide more than 10% of the total shear on the beam. For the final configuration and for check mode all point load positions are checked.

To determine if the degree of shear connection is acceptable Composite Beam applies the following rules:

If the degree of shear connection at the point of maximum moment is less than the minimum permissible shear connection, then this generates a FAIL status,

If the point of maximum utilisation ratio occurs at a point that is not the maximum moment position and the degree of shear connection is less than the minimum permissible shear connection, then this generates a WARNING status,

If the degree of shear connection at any other point load is less than the minimum permissible shear connection, then this does not affect the status in any way.

Lateral torsional buckling checks (ULS)The concrete slab is assumed to be laterally stable and hence there is no requirement to check lateral torsional buckling at the composite stage. (Clause 6.4.1).

Section properties - serviceability limit state (SLS)A value of the short term elastic (secant) modulus, Ecm is defaulted in Composite Beam for the selected grade of concrete. The long term elastic modulus is determined by dividing the short term value by a user defined factor - default 3.0. The elastic section properties of the composite section are then calculated using these values as appropriate (see the table below).

This approach is used as a substitute for the approach given in EC4 Equation 5.6 in which a knowledge of the creep coefficient, t, and the creep multiplier, L is required. It is envisaged that you will make use of EN 1992-1-1(Ref. 6) when establishing the appropriate value for the factor.

Eurocode Member Design Handbook page 46 Chapter 4 : Composite BeamEN 1994-1-1, Clause 7.3.1.(8) states that the effect on deflection due to curvature imposed by restrained drying shrinkage may be neglected when the ratio of the span to the overall beam depth is not greater than 20. This relates to normal weight concrete. Fastrak makes no specific allowance for shrinkage curvature but does provide you with a Warning when the span to overall depth exceeds 20 irrespective of whether the concrete is normal weight or lightweight. Where you consider allowance should be made, it is suggested that you include this as part of the 'factor' described above.

Composite Beam calculates the deflection for the beam based on the following properties:

Deflection checks (SLS)Composite Beam calculates relative deflections. (see Deflection checks in the Basic Principles chapter of this handbook.)

The composite stage deflections are calculated in one of two ways depending upon the previous and expected future load history:

the deflections due to all loads in the Slab Dry loadcase and the self-weight of the beam are calculated based on the inertia of the steel beam alone (these deflections are not modified for the effects of partial interaction).

Note It is the Slab Dry deflection alone which is compared with the limit, if any, specified for the Slab loadcase deflection.

the deflections for all loads in the other loadcases of the Design Combination will be based on the inertia of the composite section allowing for the proportions of the particular load that are long or short term (see above). When necessary these will be modified to include the effects of partial interaction.

Loadcase Type Properties usedself-weight bare beam

Slab Dry bare beam

Dead composite properties calculated using the long term elastic modulus

Live composite properties calculated using the effective elastic modulus appropriate to the long term load percentage for each load. The deflections for all loads in the loadcase are calculated using the principle of superposition.

Wind composite properties calculated using the short term elastic modulus

Total loads these are calculated from the individual loadcase loads as detailed above again using the principle of superposition

Chapter 4 : Composite Beam Eurocode Member Design Handbook page 47Note Composite Beam reports the deflection due to imposed loads alone (allowing for long and short term effects). It also reports the deflection for the SLAB loadcase, as this is useful for pre-cambering the beam. The beam Self-weight, Dead and Total deflections are also given to allow you to be sure that no component of the deflection is excessive.

Stress checks (SLS)There is no requirement to check service stresses in EC4 for buildings (Clause 7.2.2). However, since the deflection calculations are based on elastic analysis then at service loads it is logical to ensure that there is no plasticity at this load level.

Composite Beam calculates the worst stresses in the extreme fibres of the steel and the concrete at serviceability limit state for each load taking into account the proportion which is long term and that which is short term. These stresses are then summed algebraically. Factors of 1.00 are used on each loadcase in the design combination (you cannot amend these). The stress checks assume that full interaction exists between the steel and the concrete at serviceability state. The stresses are not reported unless the stress limit is exceeded, in which case a warning message is displayed.

Natural frequency checks (SLS) Composite Beam calculates the approximate natural frequency of the beam based on the simplified formula published in the Design Guide on the vibration of floors(Ref. 7) which states that

where is the maximum static instantaneous deflection that would occur under a load equivalent to the effects of self-weight, dead loading and 10% of the characteristic imposed loading, based upon the composite inertia (using the short term elastic modulus) but not modified for the effects of partial interaction.

Cracking of concrete (SLS)In Clause 7.4.1(4) simply supported beams in unpropped construction require a minimum amount of longitudinal reinforcement over an internal support. This is not checked by Composite Beam as it is considered a detailing requirement.

Web Openings

Circular Openings as an Equivalent RectangleEach circular opening is replaced by equivalent rectang

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