0.2 in n -4- I 12 mm gusset / plate -+- 0.5 m L 1.2 m 0.2 m 100 430 100 0.Sm — I 828 kN 350 kN Ehk 1.5m Worked examples 839 Subject Chapter ref. Design code Sheet no. Made by Checked by 27 1 FOUNDATION EXAMPLE 1 HB BS5950: Part 1 GWO The Steel Construction Institute Silwood Park, Ascot, Berks SL5 7QN Subject Chapter ref. Design code Sheet no. Made by Checked by 27 1 FOUNDATION EXAMPLE 4 HB BS 5950: Part 1 GWO Problem Design a built-up base for the valley stanchion of a double bay crane shed that is shown belon. The stanchion comprises twin 406 ¥ 178 UB. Taking moments about the tensile bolt, with n, the trial neutral axis as 0.4m depth, and taking Loading f f N mm assu g f N mm ccu cu == = () 0 6 12 20 22 . / min / 828 ¥ 1.5 - 350 ¥ 0.3 = C (2.0 - 0.2) CkN= ¥- ¥ = 828 1 5 350 0 3 18 632 . 4.13.1 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/ 840 Worked examples Subject Chapter ref. Design code Sheet no. Made by Checked by 27 1 FOUNDATION EXAMPLE 1 HB BS5950: Part 1 GWO The Steel Construction Institute Silwood Park, Ascot, Berks SL5 7QN Subject Chapter ref. Design code Sheet no. Made by Checked by 27 2 FOUNDATION EXAMPLE 4 HB BS 5950: Part 1 GWO Taking n as 0.2m, C becomes 598kN and f c is 4.98N/mm 2 T is then: 598 + 350 - 828 = 120kN To check, take moments about C The relative stiffness of the base plate and channels will determine the point of application of the compressive force. As an alternative therefore assume the lever arm to be equal to the bolt centres and the centre of compression at the bolt line with appropriate stiffen- ing added at this point. This is the minimum value of n for concrete strength of 20 N/mm 2 . Design of channels & gusset M = 669 ¥ 300/10 3 = 200.7kNm Use 2/229 ¥ 89 ¥ 32.76 RSCs, M cx = 95kNm These are satisfactory by inspection since the gussets and base plate acting compositely would also make a contribution. The internal stiffener and base plate would similarly be designed as a composite member taking the maximum outstand given in Table 11 of BS 5950. CkN TkN n Nmm mm = ¥- ¥ = =+-= = ¥ ¥ = 828 1 5 350 0 3 17 669 669 350 828 191 669 10 630 12 88 3 2 . / 828 0 4 350 1 6 19 120 4 ¥- ¥ = . .kN fNmm c = ¥ ¥¥ = 632 10 04 06 10 263 3 6 2 ./ 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/ 3 B Worked examples 841 Subject Chapter ref. Design code Sheet no. Made by Checked by 27 1 FOUNDATION EXAMPLE 1 HB BS5950: Part 1 GWO The Steel Construction Institute Silwood Park, Ascot, Berks SL5 7QN Subject Chapter ref. Design code Sheet no. Made by Checked by 27 3 FOUNDATION EXAMPLE 4 HB BS 5950: Part 1 GWO The base plate panel between the stiffeners should be checked using the Pounder expressions given in Chapter 30 as follows – the panel is shown below. Base plate K me , the Pounder expression for moment, in the centre of the long edge, when all four edges are encastre, is given below: w me , the ultimate load intensity is given by: The plate thickness of 16mm is therefore satisfactory. f N mm cf f N mm for n m cc = ¥ ¥ === 669 10 600 200 558 498 02 3 22 ./,. ./ . W t K me me = ¥¥ ¥ ¥ [] 275 12 1 2 6 170 2 2 . KK k K me =+- () +- () È Î Í ˘ ˚ ˙ = 1 11 35 1 79 141 1 0 9796 2 . L B K == = + = 406 170 238 238 238 1 097 4 4 . . . . 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/ Chapter 28 Bearings and joints by STEPHEN MATTHEWS 842 28.1 Introduction 28.1.1 Movement All structures move to some extent. Movements may be permanent and irreversible or short-term and possibly reversible. The effects can be significant in terms of the behaviour of the structure, its performance during its lifetime, and the continued integrity of the materials from which it is built. Movements can arise from a variety of sources: (1) environmental: thermal, humidity, wind-induced. (2) material properties: creep, shrinkage. (3) loading: axial and flexural strains, impact, braking, traction, centrifugal forces. (4) external sources: tilt, settlement, subsidence, seismic loads. (5) use of the building: heating, cold storage. (6) others: requirements for moving or lifting bridges, allowances for jacking pro- cedures, during or after construction. In general it is necessary to consider the behaviour of the structure at each point in terms of its possible movement in each of three principal directions, together with any associated rotations. The movements of a structure are not in themselves detri- mental; the problems arise where movements are restrained, either by the way in which the structure is connected to the ground, or by surrounding elements such as claddings, adjacent buildings, or other fixed or more rigid items. If provision is not made for such movements and associated forces it is possible that they will lead to, or contribute towards, deterioration in one or more elements. Deterioration in this context can range from, for example, cracking or disturbance of the finishes on a building to buckling or failure of primary structural elements due to large forces developed through inadvertent restraint. Note that for bridges with total lengths of up to 60m, it is possible to dispense with bearings and expansion joints through use of abutments and piers which are designed to be integral with the bridge deck. Further guidance on this topic can be found in Reference 1. 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/ Bearings 843 28.1.2 Design philosophies In catering for movement of a structure, one of three methods can be adopted: (1) Design the structure to withstand all the forces developed by restraint of move- ment. This is possible with smaller structures (small-span bridges) or structures which are comparatively flexible (portal frames, in the plane of the frame). The method will avoid joints but may require the use of additional material in construction. (2) Subdivide the structure into smaller structurally stable units, each of which then becomes essentially a structure in its own right, able to move independently of the surrounding units. This principle is ideal for controlling those factors such as thermal movement which are related to the size of the overall structure. In many cases, the need for bearings as discrete elements can be eliminated. The disadvantage lies in the need to provide joints between the various units of the structure capable of accommodating all the anticipated relative movements between the units, while at the same time fulfilling all the other requirements, i.e. visual, practical, etc. It is, however, generally possible to achieve a balance by subdividing the structure so that the movements at the joints between units are kept relatively small, permitting the joints to be simple and economical (possibly at the expense of larger numbers of joints). (3) Subdivide the structure into fewer but larger sections, and make provision for a smaller number of joints, each with larger movement capacity, and thus pos- sibly more complex than those that would be used at (2). Examples are to be found in bridges where use of the least number of road deck joints is prefer- able both in terms of riding quality, and also in the minimization of long-term maintenance requirements. The need to restrict strains on elements and thus to protect finishes will lead to the adoption of the second of the above methods for design of building structures. Bridges, for reasons cited above, are more frequently designed adopting the third method. 28.2 Bearings 28.2.1 Criteria for design and selection 28.2.1.1 Form of the unit Choice of form depends on several criteria: (1) Physical size limitations. The space available in the structure for the bearing. As bearings are subject to more wear than other parts of the structure they 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/ 844 Bearings and joints may have a shorter life and consequently this space should include allowance for access, inspection, maintenance and possible replacement. (2) Bearing pressure. The allowable bearing pressure on the materials above and below the bearing will dictate the minimum size of the top and bottom faces of the bearing unit. (3) Loading. The magnitude of the design load to be withstood by the bearing in each of the three principal directions will govern the form and type of the bearing. For each direction the maximum and minimum load should be considered at ultimate limit state, serviceability limit state or working load depending on the requirements of the design. In each case co-existent load and movement effects should be considered, together with a check for the exis- tence of any load combinations which would act so as to separate the compo- nents of the bearing (e.g. uplift). For bearings carrying both horizontal and vertical loads it is common that the design of the bearing requires a minimum vertical load to be present to ensure satisfactory performance under horizon- tal loads. (4) Rotations. The magnitude of the maximum anticipated rotations in the three principal directions should be considered. For certain types of bearing (e.g. elastomeric bearings) there exists an interaction between maximum load- carrying capacity and rotation/translation capacity, so that it may be necessary to consider co-existent effects under loading (3) and movement (5). (5) Movements. Provision for maximum calculated movements can affect the size of the moving parts of the bearing and thus the overall size of the unit.As with rotations, the design of certain types of bearing is sensitive to the interaction of movement and loading requirements. (6) Stiffness (vertical, rotational or translational). Certain structures may be sensi- tive to the deformation which occurs within the bearing during its support of the loads. The various types of bearing have different stiffness characteristics so that an appropriate form can be selected. (7) Dynamic considerations. Any particularly onerous dynamic loadings on the structure will have to be considered. Certain types of bearings (e.g. elastomeric bearings) have damping characteristics which may be desirable in particular instances, such as vibration of footbridges or machine foundations. (8) Connections to structure. The form of connection of the bearing to the struc- ture requires careful consideration of the materials involved and the need for installation, maintenance and replacement of the bearing. In addition, bearings are frequently at a position in the structure where different forms of construction meet, perhaps constructed by different contractors. In this case, it is necessary to ensure that surrounding construction is properly detailed so that design requirements for load transfer are achieved. (9) Use of proprietary bearings. Many types of bearings are commercially avail- able. These range from items which are available ‘off the shelf’ to more spe- cialized units which may be designed and proven, but which are only produced to order. It is often appropriate for bearings to be individually designed to meet a particular need in situations where proprietary types may not be suit- 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/ Bearings 845 able. In these instances the engineer has the option of designing the units using available literature (see references to Chapter 28) and perhaps incorporating standard bearings from a manufacturer as components of a completed assem- bly or alternatively engaging a recognized manufacturer to design and produce the item as a special bearing. For straightforward applications such as may be required on a short single-span bridge, it may be worthwhile investigating the relative costs of a simple fabricated bearing compared with the equivalent pro- prietary unit. Bearings (particularly ‘special’ bearings) can prove to be a large item of expenditure in a structure and an estimate of the costs involved should be made early in the design stage. (10) Summary of design requirements. Before selecting a particular bearing it is suggested that a summary of all relevant parameters is prepared.This can then be used if necessary for submission to the bearing manufacturers for exami- nation and recommendations as to particular bearing types. A typical format for such a sheet is given in Table 9 of BS 5400: Section 9.1. 2 28.2.1.2 Materials Generally materials fall into three groups: (1) those able to withstand high localized contact pressures e.g. steel. (2) those able to withstand lower contact pressures but having a low coefficient of friction; these slide easily in a direction perpendicular to the direction of the pressure and thus accommodate translational movement, e.g. polytetrafluoro- ethylene (PTFE). (3) those able to withstand contact pressure and also to accommodate translational or rotational movements by deformation of the material (e.g. elastomers). Certain of these materials may be confined within a steel cylinder in order to increase their compressive resistance. (a) Mild or high-yield steel The coefficient of friction of steel on steel is of the order of 0.3 to 0.5, unless con- tinuously lubricated; in order to provide for movement alternative arrangements are usually necessary. Traditionally this has been through the use of single or multiple rollers or knuckles. Rollers will permit translation in one direction and, if a single roller is used, rotation about an axis perpendicular to that direction. Knuckles permit rotation about one axis only. Rotation in two directions may be achieved using spherical-shaped bearing surfaces. The allowable pressures between surfaces for steel on steel contact depend upon the radii of the two surfaces and the hardness and ultimate tensile strength of the material used. BS 5400: Section 9.1 2 gives expressions for design load effects in such 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/ note! (i) if pure ptfe used unlubricated, use 2 x coefficient of friction shown (ii) if filled ptfe used, use 4 x values I I I I I I 510 15 20 25 30 bearing stress (N/mm2) 0.08 coefficient 0.06 of friction 0.04 0.02 846 Bearings and joints cases. As load-carrying requirements increase, the use of steels with greater hard- ness is dictated. This can be achieved by use of high-grade alloy steels of various compositions. For design purposes, Table 2 of BS 5400: Section 9.1 2 gives indicative values of coefficients of friction of between 0.01 and 0.05 for steel roller bearings. (b) Stainless steel Stainless steel is frequently used in strip or plate form to provide a smooth path for sliding surfaces. It is important to utilize a material for the sliding surface which will not deteriorate and adversely affect the coefficient of friction assumed for design of the structure.A typical arrangement is a polished austenitic stainless steel surface sliding against dimpled PTFE. (c) Polytetrafluoroethylene (PTFE) PTFE has good chemical resistance and very low coefficients of static and dynamic friction. Unfortunately, pure PTFE has a low compressive strength, high thermal expansion and very low thermal conductivity.As a consequence it is frequently used in conjunction with ‘filler’ materials which improve these detrimental effects without significantly affecting the coefficient of friction. The coefficient of friction varies with the bearing stress acting upon it. BS 5400: Section 9.1 2 gives the relationship shown in Fig. 28.1 for continuously lubricated pure PTFE sliding on stainless steel. Lubrication of the pure PTFE is commonly achieved by means of silicone grease confined in dimples which are rolled on to the surface of the material. References 2 and 3 give further guidance on the restrictions on shape, thickness and contain- ment on the PTFE and stainless steel components. In preliminary design and assessment of forces on structures using PTFE sliding Fig. 28.1 Coefficient of friction for continuously lubricated pure PTFE 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/ D (a) (b) Bearings 847 bearings, a figure of 0.06 is usually assumed for the coefficient of friction, and the value is checked later when the bearing selection is complete. (d) Phosphor bronze For particular applications, such as bearing guides, phosphor bronze may be used, BS 5400: Section 9.1 suggests a coefficient of friction of 0.35 for phosphor bronze sliding on steel or cast iron. (e) Elastomers An elastomer is either a natural rubber or a man-made material which has rubber- like characteristics. Elastomers are used frequently in bearings; they either consti- tute the bulk of the bearing itself or act as a medium for permitting rotation to take place (see sections 28.2.2.2 and 28.2.2.3(7)). Elastomers are principally characterized by their hardness, which is measured in several ways, the most common of which is the international rubber hardness (IRHD). This ranges on a scale from very soft at 0 to very hard at 100. Those elas- tomers used in bearings which are to comply with BS 5400: Part 9 have hardnesses in the range 45 IRHD to 75 IRHD. The tensile capacity of most elastomers is considerable.As an illustration BS 5400: Part 9 specifies a minimum tensile elongation at failure of between 300% and 450% depending on IRHD. When considering the behaviour of a block of elastomer under vertical com- pression it is assumed that the material is securely bonded to top and bottom loading plates. In this case (which is representative of most bearing situations) the vertical behaviour is related to the material’s ability to bulge on the four non-loaded faces and is expressed in terms of the shape factor for the block, which is the ratio of the loaded area to the force free surface area (see Fig. 28.2). S LB tL B S D t = + () = 2 4 for a rectangle for a circle Fig. 28.2 Elastomeric bearing dimensions for (a) a rectangular block, (b) a circular block 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/ [...]... al.)) Steel Designers' Manual - 6th Edition (2003) Chapter 29 Steel piles by TONY BIDDLE and ED YANDZIO 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/ This chapter is intended to serve as an introduction to the subject of steel. .. analysed and reported to design engineers Steel Designers' Manual - 6th Edition (2003) 870 Steel piles 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/ 29.1.2.3 Box sheet piling Hot-rolled steel sheet piling is more extensively used... two particular cases relating to a bridge superstructure are considered (see Fig 28.15(a) and (b)) Steel Designers' Manual - 6th Edition (2003) Joints 863 sealant — — sealant (b) 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/... are formed of leaves of steel with a common pin They will carry large vertical loads and permit large rotations about the axis Steel Designers' Manual - 6th Edition (2003) 852 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/ (5) (6)... 28.11 Wedging action Steel Designers' Manual - 6th Edition (2003) 860 Bearings and joints 28.3 Joints 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/ 28.3.1 General The form of joints in a structure will vary to suit particular requirements... all elastomeric, (b) all mechanical (i), (c) all mechanical (ii) Steel Designers' Manual - 6th Edition (2003) 858 Bearings and joints 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/ bearings on piers 2 to 5 At each pier transversely... tangentially-guided Steel Designers' Manual - 6th Edition (2003) Bearings 859 racy of setting out of radially-guided structures, and the magnitude of the forces developed in tangentially-guided structures.7 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/... surfaces to maintain relative position Steel Designers' Manual - 6th Edition (2003) Bearings Jq a Fig 28.5 C) U)— C 3— 0 2 U) Pl - — 2 n CD C 0 C/, — U) 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/ 0 C s O() 0 851 Mechanical.. .Steel Designers' Manual - 6th Edition (2003) 848 Bearings and joints stress dissipated energy area of loop 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/ Fig 28.3 '• 9 _ strain... larger numbers of joints, each with a small movement The restricted Steel Designers' Manual - 6th Edition (2003) 864 Bearings and joints 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/ (a) (i) (ii) (b) Fig 28.15 Radial and rotational . 3 17 669 669 350 828 191 669 10 630 12 88 3 2 . / 828 0 4 350 1 6 19 120 4 ¥- ¥ = . .kN fNmm c = ¥ ¥¥ = 632 10 04 06 10 263 3 6 2 ./ Steel Designers' Manual - 6th Edition (2003) This. Reference 1. 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. wear than other parts of the structure they Steel Designers' Manual - 6th Edition (2003) This material is copyright - all rights reserved. Reproduced under licence from The Steel Construction