A046 code of practice for the design of steel bridges

Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI A single copy of this Steel Construction Institute publication is licensed to fm03 on 15/08/2007 This is an uncontrolled copy Faber Maunsell This is an uncontrolled copy Ensure use of the most current version of this document by searching the Construction Information Service at www.tionestop.com tailieuxdcd@gmail.com Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI SCI PUBLICATION P295 Commentary on BS 5400-3: 2000 Code of practice for the design of steel bridges Editors: C W BROWN MA FICE D C ILES MSc ACGI DIC CEng MICE Published by: The Steel Construction Institute Silwood Park Ascot Berkshire SL5 7QN To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges Tel: 01344 623345 Fax: 01344 622944 tailieuxdcd@gmail.com © The Steel Construction Institute, 1991, 2000 Apart from any fair dealing for the purposes of research or private study or criticism or review, as permitted under the Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the UK Copyright Licensing Agency, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organisation outside the UK Enquiries concerning reproduction outside the terms stated here should be sent to the publishers, The Steel Construction Institute, at the address given on the title page Although care has been taken to ensure, to the best of our knowledge, that all data and information contained herein are accurate to the extent that they relate to either matters of fact or accepted practice or matters of opinion at the time of publication, The Steel Construction Institute, the authors and the reviewers assume no responsibility for any errors in or misinterpretations of such data and/or information or any loss or damage arising from or related to their use Publications supplied to the Members of the Institute at a discount are not for resale by them Publication Number: SCI P295 ISBN 85942 112 British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges ii tailieuxdcd@gmail.com To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI Order before 31st August 2005 to receive 15% discount off any SCI publication in the 2004/05 Edition of the SCI Publication Catalogue FREE postage & packing within the UK Commentaries to Standards Connections Fire Design Architectural Design Portal Frame Design tailieuxdcd@gmail.com SUMMER SPECIAL 15% Off any SCI publication 0rder up to 10 PUBLICATIONS with 15% off the total price (Minimum Order Publications) Offer open to Members & Non Members Free p & p within the UK Discount applies to this form only This offer is not available in the e-shop Offer ends 31st August 2005 (All orders received after this date will not be processed with discount) Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI Pub Ref Title Qty Non Member Price Member Price Total no of copies Total £ Sub-Total Less 15% P & P Rates* st Europe £12 for the Item.Additional items +£2 per item st Rest of World £15 for the Item Additional Items +£5 per item Membership No U.K Free *Postage & Packing Grand Total £ Customer Order ref: Name Company _ Delivery address _ _ Postcode Telephone _ Fax E-mail Please tick as appropriate Please Note: We not accept American Express I enclose a Cheque/Postal Order made payable to The SCI I wish to pay by Credit/Debit Card: VISA SWITCH (Issue no. _) MASTERCARD Card number Expiry date _ Name on card _ Registration address for card if different from delivery address: _ Postcode FAX BACK (01344 622944) The Steel Construction Institute Silwood Park, Ascot Berkshire SL5 7QN Publication Sales: Telephone: (01344) 872775 Fax: (01344) 622944 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges tailieuxdcd@gmail.com FOREWORD Foreword to Commentary on BS 5400-3: 1982 Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI This publication is one of a range of publications produced by The Steel Construction Institute which relate specifically to the design of steel and composite bridge structures and the use and interpretation of the various clauses within BS 5400: Part 3: 1982 It has been edited by Dr D M Martin (The Steel Construction Institute) and Dr J Tubman (Scott Wilson Kirkpatrick) The following Engineers contributed to the commentary on the various clauses: Dr M J Baker Mr A Bannister Mr C W Brown Mr B D Cheal Dr P Davidson Mr K Goodearl Mr D C Iles Dr W Manners Dr D M Martin Dr R Narayanan Dr G W Owens Dr J Spindel Dr J Tubman Imperial College of Science and Technology British Steel Swinden Laboratories The Steel Construction Institute Consultant Imperial College of Science and Technology Consultant The Steel Construction Institute University of Leicester The Steel Construction Institute The Steel Construction Institute The Steel Construction Institute Consultant Scott Wilson Kirkpatrick Our particular thanks are due to Mr S Chakrabarti of the Department of Transport for his valuable advice and comments on the text During the preparation of the Commentary many points of interpretation were resolved by discussion The document, therefore, represents a consensus of opinion on the various clauses within the Code and it should act as both an authoritative guide and a reference document for practising Bridge Engineers The work leading to this publication was funded by British Steel General Steels and the project was managed by Dr D M Martin (The Steel Construction Institute) Foreword to Commentary on BS 5400-3: 2000 The publication of a revised version of BS 5400-3 in 2000 has necessitated an update of the Commentary The editors, Mr D C Iles and Mr C W Brown of The Steel Construction Institute, have endeavoured to retain as much as possible of the original text, but have brought it into line with the new clauses Major revisions have been necessary to Sections and 9, and the opportunity has been taken to add a commentary on Clauses 9.10 and 9.15, which were not covered in the commentary on BS 5400-3: 1982 A summary of the clauses that have been amended in the 2000 version of BS 5400-3 is given in an Appendix The type of amendment (e.g editorial, major technical change, etc.) is indicated in that Appendix Further guidance on the use of BS 5400-3: 2000 can be found in two other SCI publications, Design guide for composite highway bridges (P289) and Design guide for composite highway bridges: Worked Examples (P290) To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges iii tailieuxdcd@gmail.com Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges iv tailieuxdcd@gmail.com To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 CONTENTS Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI Page No FOREWORD iii INTRODUCTION HISTORICAL BACKGROUND 2.1 General 2.2 Scope of BS 5400 relating to steel bridge construction 2.3 Safety factors 2.4 Load factors 2.5 Combinations of loads 2.6 The limit state design process 2.7 References 2 5 6 PREAMBLE TO COMMENTARY DESIGN OBJECTIVES 4.1 General 4.2 Limit states 4.3 Partial safety factors to be used 4.4 Structural support 4.5 Corrosion resistance and protection 4.6 Clearance gauges 4.7 References 8 10 12 12 13 13 LIMITATIONS ON CONSTRUCTION AND WORKMANSHIP 5.1 Workmanship 5.2 Robustness 5.3 Handling and transport 5.4 Composite steel/concrete construction 5.5 Built-up members 5.6 Diaphragms and fixings required during construction 5.7 Camber 5.8 End connections of beams 5.9 Support cross beams 14 14 14 14 14 14 14 15 15 15 PROPERTIES OF MATERIALS 6.1 General 6.2 Nominal yield stress 6.3 Ultimate tensile stress 6.4 Ductility 6.5 Notch toughness 16 18 18 19 19 19 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges v tailieuxdcd@gmail.com Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI 6.6 6.7 6.8 Properties of steel Modular ratio References 23 23 23 GLOBAL ANALYSIS FOR LOAD EFFECTS 7.1 General 7.2 Sectional properties 7.3 Allowance for shear lag 25 25 25 25 STRESS ANALYSIS 8.1 Longitudinal stresses in beams 8.2 Allowance for shear lag 8.3 Distortion and warping stresses in box girders 8.4 Shear stresses 8.5 Imperfections 8.6 Residual stresses 8.7 References 26 26 26 29 29 29 29 31 DESIGN OF BEAMS 32 9.1 General 32 9.2 Limit states 32 9.3 Shape limitations 33 9.4 Effective section 39 9.5 Evaluation of stresses 44 9.6 Effective length for lateral torsional buckling 51 9.7 Slenderness 60 9.8 Limiting moment of resistance 69 9.9 Beams without longitudinal stiffeners 71 9.10 Flanges in longitudinally stiffened beams 79 9.11 Webs in longitudinally stiffened beams 84 9.12 Restraints to compression flanges 89 9.13 Transverse web stiffeners other than at supports 95 9.14 Load bearing support stiffeners 98 9.15 Cross beams and other transverse members in stiffened flanges 101 9.16 Intermediate internal cross frames in box girders 105 9.17 Diaphragms in box girders at supports 105 9.18 References 105 10 DESIGN OF COMPRESSION MEMBERS 10.1 General 10.2 Limit states 10.3 Limitations on shape 10.4 Effective lengths 108 108 108 108 109 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges vi tailieuxdcd@gmail.com Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI 10.5 10.6 10.7 10.8 10.9 10.10 10.11 Effective section Compression members without longitudinal stiffeners Compression members with longitudinal stiffeners Battened compression members Laced compression members Compression members connected by perforated plates Compression members with components back to back 110 110 113 115 118 119 120 11 DESIGN OF TENSION MEMBERS 11.1 General 11.2 Limit states 11.3 Effective section 11.4 Thickness at pin-holes 11.5 Strength 11.6 Battened tension members 11.7 Laced tension members 11.8 Tension members connected by perforated plates 11.9 Tension members with components back to back 122 122 122 122 124 124 125 126 126 127 12 DESIGN OF TRUSSES 12.1 General 12.2 Limit states 12.3 Analysis 12.4 Effective length of compression members 12.5 Unbraced compression chords 12.6 Lateral bracing 12.7 Curved members 12.8 Gusset plates 130 130 130 130 132 132 133 133 133 13 DESIGN OF BASE, CAP AND END PLATES 134 14 DESIGN OF CONNECTIONS 14.1 General 14.2 Limit states 14.3 Basis of design 14.4 Splices 14.5 Connections made with bolts, rivets or pins 14.6 Welded connections 14.7 Hybrid connections 14.8 Lug angles 14.9 Other attachments 14.10 References 135 135 135 136 142 145 150 153 153 153 153 APPENDIX A Summary of Changes to BS 5400-3 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 155 vii tailieuxdcd@gmail.com By enhancing the design force the Code does not make it clear that both bending strength and stiffness are required, and that, generally, continuity of stiffness and strength is required about both axes For example, for a splice at the mid-point of a UC section strut, the flange cover plates and bolts or welds must all have bending capacities similar to those of the column flanges about the YY axis of the column σa = σ y Stocky strut Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI Deformation under axial load Initial deformation σy σa Short strut σy σa Long strut Stress diagrams at mid-height Figure 14.4.1 Stresses in initially curved strut 14.4.2.2 Design stresses For compression members the effective areas of 10.5 may be used for design of the spliced parts and the cover material Where shear is present, the equivalent stress is used The general expression for the equivalent stress (Fe) is: Fe = (F12 + F22 - F1F2 + J2)½ where F1,F2 and J are the coexistent components of stress shown in Figure 20 (see 9.11.3) 14.4.2.3 Machined abutting ends of parts in compression This clause is written for a splice at or near the end of a simple compression member (i.e with an effective length of 1.0L) For splices at other positions in simple members and in members where continuity is assumed, a more careful approach is required A simple approach would be to design the cover material and its fastenings for the remaining 25% of the compressive load plus the moments due to the initial imperfections The lateral force, equal to 2.5% of the compression force in the member, is to ensure that the end of the member is properly restrained (see commentary on 14.3.5) The effects of any other external loads or moments on the member must also be allowed for To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 144 tailieuxdcd@gmail.com 14.4.3 Tension members 14.4.3.1 Loads to be transmitted No comment 14.4.3.2 Design stresses For tension members the effective areas of 11.3 may be used for design of the spliced parts and the cover material Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI Where shear is present, the equivalent stress is used (see commentary on 14.4.2.2) For outer plies in connections made with HSFG bolts acting in friction, the stress is based on 0.8 times the effective section The factor of 0.8 is introduced to limit the loss of bolt preload The loss of preload would be due to the lateral contraction of the plies that accompanies the longitudinal extension and to local yielding of the plies under the head of the bolt The local compressive stress in the cover plate under the head of the bolt, due to the preload, is already beyond or close to the yield stress of the plate material 14.4.4 Members in bending 14.4.4.1 General A splice in a member subjected to bending and axial load is required to comply both with the general requirements of compression members (14.4.2) and tension members (14.4.3) as appropriate, together with satisfying the specific requirements of 14.4.4.2 and 14.4.4.3 14.4.4.2 Compression flanges The method refers to 14.4.2, but gives specific definitions for the flange forces to be resisted, based on the flexural capacity (taking account of lateral torsional buckling) rather than the axial capacity as in 14.4.2 14.4.4.3 Tension flanges The clause refers back to 14.4.3 14.4.4.4 Parts subject to shear A splice in a web or other part subjected to shear must withstand not only the shear, but also any moment on the part The moment may comprise two components which must be added together as appropriate: (a) the proportion of the overall bending moment carried by the part, based on engineers’ theory of bending In calculating this proportion, any ‘shedding’ of moment assumed in the design of the part itself must be ignored, since it may not occur at the splice; (b) that resulting from eccentricity of the centroids of the fastener groups To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 145 tailieuxdcd@gmail.com 14.5 Connections made with bolts, rivets or pins Note that all aspects of this Clause must be read bearing in mind that black bolts are not permitted for permanent main structural connections in railway or highway bridges (14.5.3.1) 14.5.1 Spacing of bolts or rivets 14.5.1.1 Minimum pitch The minimum pitch requirements are intended to prevent the bearing resistance of a bolt being affected by the adjacent bolts and to ensure adequate space for tightening Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI 14.5.1.2 Maximum pitch The maximum pitch requirements (and the maximum edge distance requirements of 14.5.2) are intended to avoid corrosion by ensuring that the plates are kept sufficiently close together for the paint film to be able to seal any gaps between the plates Where the parts are in compression, the requirements also prevent local buckling of the plates 14.5.1.2.1 In any direction No comment 14.5.1.2.2 In the direction of stress No comment 14.5.1.2.3 Adjacent to an edge No comment 14.5.1.3 Staggered spacing In Figure 46(b) the maximum spacing (perpendicular to the direction of stress) of (150mm + 6t) or 300mm cannot apply because the gauge limit of 75mm, which allows the 50% increase, would be exceeded For a gauge of up to 75mm (Note 1) the lateral spacing is governed by the gauge 14.5.1.4 Spacing in stiffener attachment No comment 14.5.2 Edge and end distance Minimum edge distances are specified to control failure by edge or end splitting of the connected parts The minimum end distance does not ensure that the full bearing capacity of the connected part can be achieved and this should be checked in accordance with 14.5.3.6, for HSFG bolts acting in friction as well as for ordinary bolts To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 146 tailieuxdcd@gmail.com 14.5.3 Strength of fasteners other than HSFG bolts acting in friction 14.5.3.1 General Note that ‘precision bolts’ to BS 3692[14.7] when used in clearance holes are classified as black bolts as far as the design clauses are concerned 14.5.3.2 Bolts subjected to axial tension From consideration of the equilibrium of the forces on the connection, the bolt load is the sum of the externally applied load per bolt plus the prying force (see 14.3.6) Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI The tensile stress area is less than the nominal shank area due to the threading of the bolt The adoption of the lesser of 0.7 × minimum ultimate tensile stress and yield stress (or the stress at a permanent set of 0.2%) as the basic design stress for bolts is an established tradition and maintains a minimum additional margin against failure for the higher grades of bolt which have a yield close to the ultimate The use of higher grade (parallel shank) bolts to carry external tension is not specifically precluded in the Code; whereas in the specification for the use of HSFG bolts, BS 4604-2[14.8], their use is limited to joints subject only to shear The reason for this limitation is concern over the ductility of the bolts in tension In view of this, to ensure that there is adequate ductility, where higher grade parallel shank bolts are used in tension it should be specified that there must be a minimum of clear threads in the grip length between the nut and the thread run-off Note that (m = 1.20 (see Table 2) 14.5.3.3 Rivets subjected to axial tension Note that (m = 1.20 for fasteners in tension (see Table 2) 14.5.3.4 Fasteners subjected to shear only It is usually advisable to assume that the shear plane passes through the threaded part Otherwise, special control procedures during fabrication and erection are required to ensure that the shear plane always passes through the unthreaded part In effect, the allowable shear stress is taken as the yield stress divided by %2 For black bolts (and hand driven rivets) a factor of 0.85 is included to allow for the effect of the hole clearances on the shear resistance The 0.85 factor is not required for HSFG bolts acting in shear, even though they are installed in clearance holes Fasteners subjected to shear must also be checked for their bearing resistance (see 14.5.3.6) Note that (m = 1.10 for fasteners in shear (See Table 2) To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 147 tailieuxdcd@gmail.com 14.5.3.5 Fasteners subjected to tension and shear The equation to be satisfied is a standard elliptical relationship However, in effect (m is taken as 1.20 for both tension and shear 14.5.3.6 Bolts and rivets in bearing Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI Apart from countersunk bolts and rivets, for which there is a special rule, the bearing stress is based on the nominal projected area (i.e the product of the shank diameter and the thickness of the connected part) As stated in the definition of Aeb, no allowance need be made for any threads within the bearing area This is normal design practice and it follows that the requirement in Clause 4.4.6 of BS 5400-6[14.9] that “Where the full bearing area of the shank of the bolt is to be developed, the threaded portion of the bolts shall not extend within the thickness of the connected parts” is unnecessary Because of the constraint from the surrounding plate, the bearing stress to cause failure between a fastener and the connected parts is much higher than that for a simple tension or compression member However, the design bearing stress is limited in order to prevent extensive deformation The coefficients k1 to k4 allow for the various factors affecting the bearing resistance: k1 Allows for the effect of the hole clearance k2 Reduces when the edge distance is less than 3d to allow for the full bearing resistance not being achieved because of possible tearing out of the plate Note that it is only the edge distance (normally referred to as the end distance) where the fastener force is towards the edge of the part that has this effect If the direction of the forces in Figure 47 were reversed, tear out would not be a problem and k2 could be taken as 2.5 Also note that it is only the end fasteners that are affected k3 Allows a higher bearing resistance for enclosed parts k4 Increases the bearing resistance when the fasteners are HSFG bolts acting in friction The bearing resistance is governed by the yield stress of the fastener material or the connected part, whichever is the lesser Note that in this clause and in 14.5.2, d is the diameter of the hole whereas elsewhere in the Code d represents the diameter of an element (e.g in 14.5.5) For bearing (m has the ‘standard’ value of 1.05 14.5.3.7 Pins in bearing It is assumed that a solid round and not a hollow section is being used for the pin The allowable bending stress in the pin of 1.5Fy/(m(f3 indicates that the elastic modulus should be used for the calculations (although a solid round would be classified as a compact section and as a normal beam would be designed using the To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 148 tailieuxdcd@gmail.com plastic modulus) The enhancement factor of 1.5 is then plausible, bearing in mind that the plastic modulus of a solid round is 1.7 times the elastic modulus 14.5.3.8 Long grip rivets The resistance of long grip rivets is reduced to allow for the effect of bending 14.5.3.9 Securing nuts The high preload used for HSFG bolts, provided that it is maintained, prevents the nuts from working loose 14.5.3.10 Bolts and rivets through packings The resistance of bolts and rivets through packings is reduced to allow for the effects of bending Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI 14.5.3.11 Pin plates No comment 14.5.4 Strength of HSFG bolts acting in friction 14.5.4.1 General In a connection using high strength friction grip (HSFG) bolts, the bolts are preloaded to a specified minimum tension which presses the connected plies together Due to the pre-compression of the plies, ‘shear” loads can be carried by friction at the contact surface between the plies 14.5.4.1.1 Ultimate limit state The design ultimate capacity of HSFG bolts in normal clearance holes is the greater of: (a) the friction capacity and (b) the capacity in shear and bearing Generally, the capacity of a bolt acting in shear is greater than the friction capacity For bolts in oversize or slotted holes and for bolts with waisted shanks, the design ultimate capacity must be based on the friction capacity, since the movement that would occur before the bolts are in bearing is unacceptable 14.5.4.1.2 Serviceability limit state When the capacity in shear and bearing at the ultimate limit state governs the design, a friction capacity serviceability check is required (see Table 1) The serviceability check is to ensure that there is a small but reasonable margin against slip occurring at working load, the full safety margin for the ultimate limit state being achieved in shear and bearing 14.5.4.2 Friction capacity The definition of N as the number of friction interfaces is strictly speaking incorrect For example, on the left had side of the splice in Figure 14.5.1, there are four friction interfaces but the value of N should be two As a general concept, it is safer to consider the load paths through a joint and to calculate the load to be carried through each interface The friction capacity of each interface To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 149 tailieuxdcd@gmail.com can then be checked (taking N equal to one) Once the load paths through the connection have been properly considered, it is obviously acceptable to use the formula where it is applicable with the appropriate value of N Note that, for friction capacity, (m = 1.30 for the ultimate limit state and (m = 1.20 for the serviceability limit state (see Table 2) Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI Figure 14.5.1 Cover plate splice 14.5.4.3 Prestress F0 is the minimum specified preload (shank tension) for the bolt, which is the proof load for general grade bolts[14.10] and 0.85 times the proof load for parallel shank higher grade bolts[14.8] If there is an externally applied load, this is deducted from the preload to give the net preload (Fv) that is used for the design No deduction need normally be made for the prying forces that are developed between a bolt and the edge of the plate or flange This comment is based on the assumption that the reduction in friction capacity under the bolt as a result of the prying force is balanced by a corresponding increase at the edge of the plate or flange It follows that the contact surfaces in the area where the prying force is applied must have the same slip factor as the surface around the bolt If, however, the pre-erection painting is extended under the edge of the connection for a small distance (to improve the corrosion protection) it might have a lower slip factor; in that case it would be conservative to deduct the prying force as well as the applied load before calculating friction capacity 14.5.4.4 Slip factor The slip factor is, in simple terms, the static coefficient of friction for the contact surfaces as defined in BS 4604[14.8][14.10] The slip factors given in this clause are the minimum values of the range of slip factors obtained from the available test results and should be used wherever possible Where the friction surfaces not conform, the slip factor should be established by test However, it should be noted that if the rather simple test approach given in BS 4604 is adopted, the slip factor obtained may be much greater than that achieved on site This could be particularly critical where oversized or slotted holes are used As an example of the variations that occur, the test results for category (a) in 14.5.4.4 weathered surfaces clear of mill scale and loose rust, gave slip factors ranging from 0.45 to 0.8 A more realistic procedure for establishing the slip factor can be found in Clause A.2 of Annex A of DD ENV1090-1:1998[14.11] The increased bolt load applied by higher grade bolts tends to result in a decrease in the slip factor This is allowed for by using slip factors 10% lower than those specified for use with general grade bolts To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 150 tailieuxdcd@gmail.com 14.5.4.5 Over-sized and slotted holes The consequence of slip in a connection with over-sized or slotted holes would generally be more serious than with standard tolerance holes and this is allowed for by the coefficient kh which, in effect, increases the safety margin It is made clear that the recommendations of all parts of 14.5.4 only apply to bolts tightened in accordance with BS 4604 Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI 14.5.5 Long connections In long cover plate splices, there is a significant variation in the loads carried by the individual fasteners This is due to the difference in strain between the cover plates and the adjacent connected element In the upper sketch of Figure 49, the stress (and therefore the strain) in the top plate varies from a maximum at the left-hand end to zero at the right-hand end; whereas the stress in the bottom plate is zero at the left-hand end and a maximum at the right-hand end The reduction in strength is principally dependent on the length of the joint, although in this clause it is made dependent on the ratio of the length to bolt diameter Note that the length (L) of the connection is the length over which the load is transferred from the member to the splice plate, not the full length of the splice detail (see Figure 49) The clause also applies to splices in elements of members, such as plate girders, in tension or compression The requirement only applies to connections transferring direct load (i.e where the load in an element is progressively reduced from a maximum at one end of the connection to zero at the other) No reduction is necessary where the fasteners are transferring shear forces from one element to another within a built-up section (e.g fasteners connecting the web to the flange in a plate girder) 14.6 Welded connections 14.6.1 General No comment 14.6.2 Butt welds 14.6.2.1 Intermittent butt welds No comment 14.6.2.2 Partial penetration butt welds It is reasonable to assume that the first paragraph of this clause is meant to apply to partial penetration butt welds welded from one side of a joint Single sided partial penetration butt welds are not used where they would be subject to tensile stresses, since the severe stress concentrations at the root of the weld are unacceptable In contrast, where joints are welded from both sides, symmetry ensures that bending across the throat does not occur to the same extent See comments on detail Type 3.11 in Clause H.4.3 of BS 5400-10[14.1] To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 151 tailieuxdcd@gmail.com A welded tee detail with partial penetration welds (reinforced by superimposed fillet welds) is shown in Table 17(c) of BS 5400-10 In this type of detail, where the joint is symmetrically welded from both sides, the welds should be designed as deep penetration fillet welds (see 14.6.3.9) In-line joints using double sided partial penetration butt welds (e.g a joint in the flange of a plate girder) are not shown in BS 5400-10, and no specific guidance is given concerning their suitability or use Generally, they would not be used for important joints in bridges In assessing the throat thickness, allowance is made for the fact that with a V preparation, the weld may not penetrate fully to the root Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI When the weld is unsymmetrical relative to the parts joined, the resulting eccentricity should be allowed for in the design 14.6.2.3 Strength of butt welds No comment 14.6.3 Fillet welds 14.6.3.1 Intermittent fillet welds The spacing requirements for intermittent fillet welds are similar to the maximum pitch requirements for bolts or rivets (see commentary on 14.5.1.2) 14.6.3.2 End returns Generally fillet welds contain craters at the start and end of each run Therefore, these regions are likely to be undersized and are prone to weld defects If end returns are provided, they ensure that the correct length of sound weld is provided and that the defect prone regions are removed from the points of maximum stress 14.6.3.3 End connections by side fillets The requirement that the length of weld on each side of the part should be not less than the distance between the welds, ensures that there is adequate dispersion of the loads The requirement that the length of weld should not less than 4t is intended to prevent the development of high local stresses that would significantly reduce the strength of the fillet welds The requirement for plug or slot welds, where the distance between the welds exceeds 16t, is to control distortion and prevent local buckling of the plates 14.6.3.4 End connections by transverse welds See the second and third paragraphs of the commentary on 14.6.3.3 14.6.3.5 Welds with packings No comment To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 152 tailieuxdcd@gmail.com 14.6.3.6 Welds in holes and slots No comment 14.6.3.7 Longitudinal welds in members subject to bending No comment 14.6.3.8 Effective length of fillet welds Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI Appendix A of BS 5135[14.2] contains notes on the design of fillet welds, including the rule that “the effective length of an open ended fillet weld should be taken as the overall length less twice the leg length, thereby discounting the contribution of the stop and start positions which are generally of reduced profile” (see commentary on 14.6.3.2) Open ended welds are normally only used as intermittent welds The clause does not apply when the weld has been returned (the return is not included in the effective length) There is a significant variation in load distribution within the length of a long fillet weld and this is allowed for by the factor The variation is due to the difference in strain between the connected parts (see commentary on 14.5.5) Note that for > = 2, there is no reduction for welds less than 1.67 m in length 14.6.3.9 Effective throat of a fillet weld No comment 14.6.3.10 Effective area of a fillet weld No comment 14.6.3.11 Capacity of a fillet weld 14.6.3.11.1 Weld subject to longitudinal shear The strength of a fillet weld really depends on the ultimate tensile strength of the weaker part joined, and the formula is an approximation to allow for this 14.6.3.11.2 Weld subject to transverse force The formula for the factor K can become unconservative for values of approaching 90o and hence K is limited to a maximum value of 1.4 (the approximate ratio of the tension strength to the shear strength of a weld) It should also be noted that for an end fillet weld the deformation at rupture is very limited (about mm) and this should be kept in mind when detailing connections 14.6.3.11.3 Weld subject to forces in both transverse and longitudinal directions In this case, the rule is effectively a vectorial combination of the rules in the two previous clauses 14.6.4 Plug welds No comment To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 153 tailieuxdcd@gmail.com 14.6.5 Load transfer by parts in contact In Appendix A of BS 5135[14.2] it is stated that “In fillet welded joints carrying a compressive load, it should not be assumed that the parts joined are in contact under the joint For critical applications the use of a full penetration weld should be considered” This is particularly important when checking for fatigue endurance (see Clause 6.3 of BS 5400-10[14.1]) 14.7 Hybrid connections Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI Where there is a combination of welds and fasteners in a connection with different load/deformation characteristics, the load will tend to be carried by the stiffer parts of the connection For example, with a combination of fillet welds and bolts in tolerance holes, the welds would initially carry the load and may even fail, due to their limited ductility, before the tolerance in the bolt holes has been taken up 14.7.1 Allowable combinations No comment 14.7.2 Other combinations No comment 14.8 Lug angles No comment 14.9 Other attachments No comment 14.10 References 14.1 BRITISH STANDARDS INSTITUTION BS 5400-10: Steel, concrete and composite bridges - Code of practice for fatigue BSI, London, 1980 14.2 BRITISH STANDARDS INSTITUTION BS 5135: Specification for arc welding of carbon and carbon manganese steels BSI, London, 1984 14.3 KULAK, G.L., FISHER, J.W AND STRUIK, J.H.A Guide to design criteria for bolted and riveted joints 2nd edition J Wiley & Sons, New York, 1987 14.4 OWENS, G.W and CHEAL, B.D Structural steelwork connections Butterworths, London, 1989 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 154 tailieuxdcd@gmail.com 14.5 BRITISH STANDARDS INSTITUTION DD ENV1993-1-1:1992 Eurocode 3: Design of steel structures Part 1.1: General rules and rules for buildings BSI, London, 1992 14.6 THE STEEL CONSTRUCTION INSTITUTE Advisory desk AD004 Steel Construction Today, Vol 2(2), SCI, Ascot, April 1988 14.7 BRITISH STANDARDS INSTITUTION BS 3692: Specification for ISO metric precision hexagon bolts, screws and nuts BSI, London, 1967 14.8 BRITISH STANDARDS INSTITUTION BS 4604: Part 2: Specification for the use of high strength friction grip bolts in structural steelwork - metric series - higher grade (parallel shank) BSI, London, 1970 14.9 BRITISH STANDARDS INSTITUTION BS 5400-6: Steel, concrete and composite bridges - specification for materials and workmanship, steel BSI, London, 1999 14.10 BRITISH STANDARDS INSTITUTION BS 4604: Part 1: Specification for the use of high strength friction grip bolts in structural steelwork - metric series - general grade BSI, London, 1970 14.11 BRITISH STANDARDS INSTITUTION DD ENV 1090-1: Execution of steel structures Part General rules and rules for buildings (together with United Kingdom National Application Document) BSI, London, 1998 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 155 tailieuxdcd@gmail.com APPENDIX A Summary of Changes to BS 5400-3 Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI The following table summarises the types of changes made to the various clauses of BS 5400-3 by the 2000 revision of the Code The BSI documents should be consulted for the details of the texts Clause 4.1.1 4.1.2 4.2.2 4.3.3 4.5.6 5.2 6.1.1 6.1.2 6.2 6.3 6.4 6.5 7.2 7.3 8.2 8.3 8.6 9.2.1 9.2.3 9.3.1 9.3.2 9.3.6 9.3.7 9.4.2 9.5.1 9.5.4 9.5.5 9.5.6 9.6 9.7.1 9.7.2 9.7.3 9.7.4 9.7.5 9.8 9.9.1 9.9.2 9.9.3 9.9.4 9.9.5 9.9.6 9.9.7 9.10.1 9.10.2 9.10.3 9.10.5 9.11.3 9.11.4 9.11.5 9.11.6 Clause 9.12 9.13.3 9.13.5 9.13.6 9.14.1 9.14.3 9.14.5 9.15.4 9.16.1 9.16.2.4 9.16.3 9.16.4 9.17.2 9.17.4 9.17.5 9.17.6 9.17.7 10.3.1 10.3.2 10.3.3 10.5.2 10.6.1 10.6.2 10.6.3 10.9.1 10.9.3 11.3.2 11.5.1 11.5.2 12.5 12.6.1 12.6.2 12.8.1 12.8.2 13 14.4 14.5 14.6.3.11 14.9 B.1 B.2 B.3 B.4 D E Change Editorial New Significant technical Significant technical New Minor technical Significant technical New Minor technical Significant technical Significant technical Major technical Significant technical New Significant technical Editorial Minor technical Significant technical Significant technical Major technical Minor technical Significant technical Significant technical Significant technical Minor technical Significant technical Minor technical Minor technical Major technical Major technical Significant technical Significant technical Significant technical Significant technical Major technical Major technical Minor technical Significant technical Significant technical Major technical Minor technical Major technical Significant technical Significant technical Minor technical Significant technical Minor technical Minor technical Significant technical Significant technical Change Major technical Significant technical Significant technical Significant technical Minor technical Significant technical Editorial Editorial Minor technical New Minor technical Minor technical Minor technical Significant technical Minor technical Significant technical Minor technical Significant technical Editorial Significant technical Significant technical Minor technical Significant technical Significant technical Minor technical Editorial Significant technical Minor technical Significant technical Major technical Significant technical Significant technical Minor technical Minor technical Minor technical Minor technical Minor technical Major technical Minor technical Editorial Editorial Significant technical Significant technical Major technical Significant technical To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 156 tailieuxdcd@gmail.com Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges 157 tailieuxdcd@gmail.com To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005 Licensed copy:fm03, Faber Maunsell, 15/08/2007, Uncontrolled Copy, © SCI P295: Commentary on BS 5400-3: 2000, Code of practice for the design of steel bridges tailieuxdcd@gmail.com Typeset and make-up by The Steel Construction Institute, Ascot, Berks SL5 7QN Printed and bound by Alden Press, Osney Mead, Oxford, OX2 0EF 12000 - 10/00 (BCR714) 158 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ This material is copyright - all rights reserved Reproduced for IHS Technical Indexes Ltd under licence from The Steel Construction Institute on 15/8/2005