916 Floors and orthotropic decks 4. Pucher A. (1977) Influence Surfaces of Elastic Plates, 5th edn. Springer-Verlag, Wien. 5. Dowling P. & Bawa A.S. (1975) Influence surfaces for orthotropic decks. Proc. Instn Civ. Engrs, 59, Mar., 149–68. 6. Cuninghame J.R. (1982) Steel Bridge Decks, Fatigue Performance of Joints Between Longitudinal Stiffeners. LR 1066, Transport and Road Research Labo- ratory, Crowthorne, Bucks. Further reading for Chapter 30 Beales C. (1990) Assessment of Trough to Crossbeam Connections in Orthotropic Steel Bridge Decks. TRL Report RR 276. Transport Research Laboratory, Crowthorne, Bucks. Cuninghame J.R. (1990) Fatigue Classification of Welded Joints in Orthotropic Steel Bridge Decks. TRL Report RR 259.Transport Research Laboratory, Crowthorne, Bucks. Gurney T.R. (1992) Fatigue of Steel Bridge Decks. HMSO, London. Steel Designers' Manual - 6th Edition (2003) This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ F u ll P age A d, 3mm Bl ee d Chapter 31 Tolerances by COLIN TAYLOR 917 31.1 Introduction 31.1.1 Why set tolerances? Compared to other structural materials, steel (and aluminium) structures can be made economically to much closer tolerances. Compared to mechanical parts, however, it is neither economic nor necessary to achieve extreme accuracy. There are a number of distinct reasons why tolerances may need to be con- sidered. It is important to be quite clear which actually apply in any given case, par- ticularly when deciding the values to be specified, or when deciding the actions to be taken in cases of non-compliance. The various reasons for specifying tolerances are outlined in Table 31.1. In all cases no closer tolerances than are actually needed should normally be specified, because while additional accuracy may be achievable, it generally increases the costs disproportionately. 31.1.2 Terminology ‘Tolerance’ as a general term means a permitted range of values. Other terms which need definition are given in Table 31.2. 31.1.3 Classes of tolerance Table 31.3 defines the three classes of tolerances which are recognized in Euro- code 3. It is important to draw attention to any particular or special tolerances when calling for tenders, as they usually have cost implications. Where nothing is stated, fabricators will automatically assume that only normal tolerances are required. Steel Designers' Manual - 6th Edition (2003) This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ 918 Tolerances Table 31.1 Reasons for specifying tolerances Structural safety Dimensions (particularly of cross-sections, straightness, etc.) associated with structural resistance and safety of the structure. Assembly requirements Tolerances necessary to enable fabricated parts to be put together. Fit-up Requirements for fixing non-structural components, such as cladding panels, to the structure. Interference Tolerances to ensure that the structure does not foul with walls, door or window openings or service runs, etc. Clearances Clearances necessary between structures and moving parts, such as overhead travelling cranes, elevators, etc. or for rail tracks, and also between the structure and fixed or moving plant items. Site boundaries Boundaries of sites to be respected for legal reasons. Besides plan position, this can include limits on the inclination of outer faces of tall buildings. Serviceability Floors must be sufficiently flat and even, and crane gantry tracks etc. must be accurately aligned, to enable the structure to fulfil its function. Appearance The appearance of a building may impose limits on verticality, straightness, flatness and alignment, though generally the tolerance limits required for other reasons will already be sufficient. Table. 31.2 Definitions – deviations and tolerances Deviation The difference between a specified value and the actual measured value, expressed vectorially (i.e. as a positive or negative value). Permitted deviation The vectorial limit specified for a particular deviation. Tolerance range The sum of the absolute values of the permitted deviations each side of a specified value. Tolerance limits The permitted deviations each side of a specified value, e.g. ±3.5mm or +5mm -0mm. Table 31.3 Classes of tolerances Normal tolerances Those which are generally necessary for all buildings. They include those normally required for structural safety, together with normal structural assembly tolerances. Particular tolerances Tolerances which are closer than normal tolerances, but which apply only to certain components or only to certain dimensions. They may be necessary in specific cases for reasons of fit-up or interference or in order to respect clearances or boundaries. Special tolerances Tolerances which are closer than normal tolerances, and which apply to a complete structure or project. They may be necessary in specific cases for reasons of serviceability or appearance, or possibly for special structural reasons (such as dynamic or cyclic loading or critical design criteria), or for special assembly requirements (such as interchangeability or speed of assembly). Steel Designers' Manual - 6th Edition (2003) This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ 31.1.4 Types of tolerances For structural steel there are three types of dimensional tolerance: (1) Manufacturing tolerances, such as plate thickness and dimensions of sections. (2) Fabrication tolerances, applicable in the workshops. (3) Erection tolerances, relevant to work on site. Manufacturing tolerances are specified in standards such as BS 4, BS 4848, BS EN 10024, BS EN 10029, BS EN 10034 and BS EN 10210. Only fabrication and erec- tion tolerances will be covered here. 31.2 Standards 31.2.1 Relevant documents The standards covering tolerances applicable to building steelwork are: (1) BS 5950 Structural use of steelwork in building. Part 2: Specification for materials fabrication and erection: hot rolled sections. Part 7: Specification for materials and workmanship: cold formed sections and sheeting. (2) National structural steelwork specification for building construction NSSS, 4th edition. (3) ENV 1090-1 Execution of steel structures: Part 1: General rules and rules for buildings. (4) ISO 10721-2: 1999 Steel structures: Part 2: Fabrication and erection. (5) BS 5606 Guide to accuracy in building. 31.2.2 BS 5950 Structural use of steelwork in building The specification of tolerances for building steelwork was first introduced into British Standards in BS 5950: Part 2: 1985. The current edition was issued in 2001. This revision of the 1992 edition updates cross-references to other standards, many of which are now European Standards (BS EN standards). In addition the oppor- tunity was taken to align the code more closely with the industry standard docu- ment, the National structural steelwork specification for building construction. Standards 919 Steel Designers' Manual - 6th Edition (2003) This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ 31.2.3 National structural steelwork specification (NSSS) The limitations of the tolerances specified in earlier versions of BS 5950: Part 2 have been extended by an extensive coverage of tolerances in the National structural steelwork specification for building construction. This is an industry standard based on established sound practice. The widely accepted document, promoted by the British Constructional Steelwork Association (BCSA), is now in its 4th edition. 31.2.4 ENV 1090-1 Execution of steel structures As part of the harmonization of construction standards in Europe, CEN has issued ENV 1090: Part 1: General rules and rules for buildings, which is available through BSI as DD ENV 1090-1: 1998. This document includes comprehensive recommendations for both erection and manufacturing tolerances. To a large extent these recommendations are consistent with BS 5950: Part 2 and the NSSS. However, some of them are more detailed. 31.2.5 ISO 1071-2 Steel structures: Part 2: Fabrication and erection This is very similar to ENV 1090-1 and BS 5950: Part 2. It is unlikely to be issued as a BSI standard. 31.2.6 BS 5606 Guide to accuracy in building BS 5606 is concerned with buildings generally and is not specific to steelwork. The 1990 version has been rewritten as a guide, following difficulties due to incorrect application of the previous (1978) version, which was in the form of a code. BS 5606 is not intended as a document to be simply called up in a contract specification. It is primarily addressed to designers to explain the need for them to include means for adjustment, rather than to call for unattainable accuracy of con- struction. Provided that this advice is heeded, its tables of ‘normal’ accuracy can then be included in specifications, except where they conflict with overriding struc- tural requirements. This can in fact happen, so it is important to remember that the requirements of BS 5950 must take precedence over BS 5606. BS 5606 introduces the idea of characteristic accuracy, the concept that any con- struction process will inevitably lead to deviations from the target dimensions, and its objective is to advise designers on how to avoid resulting problems on site by appropriate detailing. The emphasis in BS 5606 is on the practical tolerances which will normally be achieved by good workmanship and proper site supervision. This can only be improved upon by adopting intrinsically more accurate techniques, 920 Tolerances Steel Designers' Manual - 6th Edition (2003) This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ which are likely to incur greater costs. These affect the fit-up, the boundary dimen- sions, the finishes and the interference problems. Data are given on the normal tol- erances (to be expected and catered for in detailed design) under two headings: (1) Site construction (table 1 of BS 5606). (2) Manufacture (table 2 of BS 5606). Unfortunately many of the values for site construction of steelwork are only esti- mated. No specific consideration is given in BS 5606 to dimensional tolerances nec- essary to comply with the assumptions inherent in structural design procedures, which may in fact be more stringent. It does however recognize that special accu- racy may be necessary for particular details, joints and interfaces. Another important point mentioned in BS 5606 is the need to specify methods of monitoring compliance, including methods of measurement. It has to be recog- nized that methods of measurement are also subject to deviations; for the methods necessary for monitoring site dimensions, these measurement deviations may in fact be quite significant compared to the permitted deviations of the structure itself. 31.3 Implications of tolerances 31.3.1 Member sizes 31.3.1.1 Encasement The tolerances on cross-sectional dimensions have to be allowed for when encasing steel columns or other members, whether for appearance, fire resistance or struc- tural reasons. It should not be forgotten that the permitted deviations represent a further variation over and above the difference between the serial size and the nominal size. For example, a 356 ¥ 406 ¥ 235 UC has a nominal size of 381mm deep by 395mm wide, but with tolerances to BS 4 may actually measure 401mm wide by 387mm deep one side, and have a depth of 381 mm the other side. The same is true of con- tinental sections. A 400 ¥ 400 ¥ 237 HD also has a nominal size of 381mm deep by 395mm wide, but with tolerances to Euronorm 34 may actually measure 398mm wide by 389mm deep one side, and have a depth of 380mm the other side. 31.3.1.2 Fabrication Variations of cross-sectional dimensions (with permitted deviations) may also need to be allowed for, either in detailing the workmanship drawings or in the fabrica- tion process itself, if problems are to be avoided during erection on site. Implications of tolerances 921 Steel Designers' Manual - 6th Edition (2003) This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ The most obvious case is a splice between two components of the same nominal size, where packs may be needed before the flange splice plates fit properly, unless the components are carefully matched. Similarly variations in the depths of adja- cent crane girders or runway beams may necessitate the provision of packs, unless the members are carefully matched. Less obviously, if the sizes of columns vary, the lengths of beams connected between them will need some form of adjustment, even if the columns are accu- rately located and the beams are exactly to length. 31.3.2 Attachment of non-structural components It is good practice to ensure that all other items attached to the steel frame have adequate provision for adjustment in their fixings to cater for the effects of all steel- work tolerances, plus an allowance for deviations in their own dimensions. Where necessary, further allowances may be needed to cater for structural movements under load and for differential expansion due to temperature changes. Where possible, the number of fixing points should be limited to three or four, only one of which should be positive with all the others having slotted holes or other means of adjustment. 31.3.3 Building envelope It must be appreciated that erection tolerances, including variation in the position of the site grid lines, will affect the exact location of the external building envelope relative to other buildings or to site boundaries, and there may be legal constraints to be respected which will have to be taken into account at the planning and pre- liminary stages of design. These effects also need to be taken into account where a building is intended to have provision for future extension or where the project is an extension of an exist- ing building, in which case deviations in the actual dimensions have to be catered for at the interface. In the case of tall multi-storey buildings, the building envelope deviates increas- ingly with height compared to the location at ground level, even though permitted deviations for column lean generally reduce with height. Unless there are step-backs or other features with a similar effect, it may be necessary to impose particular tol- erance limits on the outward deviations of the columns. 922 Tolerances Steel Designers' Manual - 6th Edition (2003) This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ 31.3.4 Lift shafts for elevators The deviations from verticality that can be tolerated in the construction of guides for ‘lifts’ or elevators are commonly more stringent than those for the construction of the building in which they operate. In low-rise buildings sufficient adjustment can be provided in association with the clearances, but in tall buildings it becomes nec- essary either to impose ‘special’ tolerances on column verticality or else to impose ‘particular’ tolerances on those columns bounding the lift shaft. In agreeing the limits to be observed with the lift supplier, it should not be over- looked that the horizontal deflections of the building due to wind load also have implications for the verticality of the lift shafts. 31.4 Fabrication tolerances 31.4.1 Scope of fabrication tolerances The description ‘fabrication tolerances’ is used here to include tolerances for all normal workshop operations except welding. It thus covers tolerances for: (1) cross sections, other than rolled sections, (2) member length, straightness and squareness, (3) webs, stiffened plates and stiffeners, (4) holes, edges and notches, (5) bolted joints and splices, (6) column baseplates and cap plates. However, tolerances for cross sections of rolled sections and for thicknesses of plates and flats are treated as manufacturing tolerances.Welding tolerances (includ- ing tolerances on weld preparations and fit-up and sizes of permitted weld defects) are treated elsewhere. 31.4.2 Relation to erection tolerances An overriding requirement for accuracy of fabrication must always be to ensure that it is possible to erect the steelwork within the specified erection tolerances. Due to the wide variety of steel structures and the even wider variety of their components, any recommended tolerances must always be specified in a very general way. Even if it were possible to specify fabrication tolerances in such a way that their cumulative effect would always permit the specified erection tolerances to be satisfied, the resulting permitted deviations would be so small as to be unrea- sonably expensive, if not impossible, to achieve. Fabrication tolerances 923 Steel Designers' Manual - 6th Edition (2003) This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ Fortunately in most cases it is possible to rely on the inherent improbability of all unfavourable extreme deviations occurring together. Also the usually accepted values for fabrication tolerances do make some limited allowances for the need to avoid cumulative effects developing on site. They are tolerances that have been shown by experience to be workable, provided that simple means of adjustment are incorporated where the effects of a number of deviations could otherwise become cumulative. For example, beams with bolted end cleats usually have sufficient adjustment available due to hole clearances, but where a line of beams all have end plate connections, provision for packing at intervals may be advisable, unless other measures are taken to ensure that the beams are not all systematically over-length or under-length by the normal permitted deviation. Other possible means for adjust- ment include threaded rods and slotted holes. Where it can be seen from the drawings that the fabrication tolerances could easily accumulate in such a way as to create a serious problem in erection, either closer tolerances or means of adjustment should be considered; however, the coin- cident occurrence of all extreme deviations is highly improbable, and judgement should be exercised both on the need for providing means of adjustment and on the range of adjustment to be incorporated. 31.4.3 Full contact bearing 31.4.3.1 Application The requirements for contact surfaces in joints which are required to transmit com- pression by ‘full contact bearing’ probably cause more trouble than any other item in a fabrication specification, largely due to misapprehension of what is actually intended to be achieved. First it is necessary to be clear about the kind of joint to which the requirements for full contact bearing should be applied. Figure 31.1(a) shows the normal case, where the profile of a member is required to be in full contact bearing on a base- plate or cap plate or division plate. The stress on the contact area equals the stress in the member: thus full contact is needed to transmit this stress from the member into the plate. Only that part of the plate in contact with the member need satisfy the full contact bearing criteria, though it may be easier to prepare the whole plate. Figure 31.1(b) shows two end plates in simple bearing.The potential contact area is substantially larger than the cross-sectional area of the member: thus full contact bearing is not necessary. All that is needed is for the end plates to be square to the axis of the member.Another common case of simple bearing is shown in Fig. 31.1(c). By contrast, the case shown in Fig. 31.1(d) is one where, if full contact bearing is needed, it is also necessary to take special measures to ensure that the profiles of the two members align accurately, otherwise the area in contact may be significantly less than the area required to transmit the load. Particular tolerances should be specified in such cases, based on the maximum local reduction of area that can be 924 Tolerances Steel Designers' Manual - 6th Edition (2003) This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 01344 872775 or go to http://shop.steelbiz.org/ [...]... from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 0134 4 872775 or go to http://shop.steelbiz.org/ Steel Designers' Manual - 6th Edition (2003) 930 Fig 31.4 Tolerances VA rI section B — B End plate with welding (exaggerated) detail a A Steel Designers' Manual - 6th Edition (2003) Erection tolerances Table 31.4 (Extract from National Structural Steelwork... steelwork specification, 4th edition, BCSA/SCI Acknowledgement Extracts from the National structural steelwork specification 4th Edition are reproduced with the kind permission of the British Constructional Steelwork Association Steel Designers' Manual - 6th Edition (2003) Chapter 32 Fabrication by DAVID DIBB-FULLER This material is copyright - all rights reserved Reproduced under licence from The Steel. .. bearing is required Steel Designers' Manual - 6th Edition (2003) Fabrication tolerances 927 slope = 1/250 parabolic curve — squareness of end (relative to over—all centreline) This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 0134 4 872775 or go to http://shop.steelbiz.org/ L/l000.. .Steel Designers' Manual - 6th Edition (2003) Fabrication tolerances (b) (a) This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 0134 4 872775 or go to http://shop.steelbiz.org/ 925 full contact bearing (location material not... 931 Steel Designers' Manual - 6th Edition (2003) 932 Tolerances Table 31.4 (contd ) 7.2.5 Length Length after cutting, measured un the centre line of the section or on the corner of angles This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 0134 4 872775 or go to http://shop.steelbiz.org/... edge shall not exceed A ©BCSA A=3mm A Th F N A= Steel Designers' Manual - 6th Edition (2003) Erection tolerances 933 Table 31.4 (contd ) 7.3.5 Flatness This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 0134 4 872775 or go to http://shop.steelbiz.org/ Where frill contact bearing is... whichever is the greater Steel Designers' Manual - 6th Edition (2003) Tolerances 936 Table 31.4 (contd ) 7.5.4 Web or Flange Straightness Straightness of individual web or flanges This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 0134 4 872775 or go to http://shop.steelbiz.org/ 7.5.5... site of a steel structure This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 0134 4 872775 or go to http://shop.steelbiz.org/ 31.5.2.2 Site practice Normal site practice is for the supporting concrete foundations, and other supporting structures, to be prepared in advance of steel erection,... members Steel Designers' Manual - 6th Edition (2003) 938 Tolerances Holding-down bolts and other fixing bolts are either: (1) fixed in position, or (2) adjustable, in sleeves or pockets This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 0134 4 872775 or go to http://shop.steelbiz.org/... considerations apply to the lengths of fixing bolts located horizontally Steel Designers' Manual - 6th Edition (2003) Erection tolerances 939 This material is copyright - all rights reserved Reproduced under licence from The Steel Construction Institute on 12/2/2007 To buy a hardcopy version of this document call 0134 4 872775 or go to http://shop.steelbiz.org/ 31.5.4 Erection – internal accuracy In terms of structural . Fatigue of Steel Bridge Decks. HMSO, London. Steel Designers' Manual - 6th Edition (2003) This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction. applicable to building steelwork are: (1) BS 5950 Structural use of steelwork in building. Part 2: Specification for materials fabrication and erection: hot rolled sections. Part 7: Specification. structural steelwork specification for building construction NSSS, 4th edition. (3) ENV 1090-1 Execution of steel structures: Part 1: General rules and rules for buildings. (4) ISO 10721-2: 1999 Steel