BS 5950-1:2000 Section 1. General 1,1 Scope ‘This part of BS 5950 gives recommendations for the design of structural steelwork using hot rolled steel sections, flats, plates, hot finished structural hollow sections and cold formed structural hollow sections, in buildings and allied structures not specifically covered by other standards, NOTE 1 These recommendations accume that the standards of materials and construction are a8 specified in BS 660-2 NOTE2 Design using cold formed structural hollow sections conforming to BS EN 10219 a covered by this part of BS 6950. Design ‘using other forms of cold formed sections is cavered ia BS $950-5. NOTE 8 Design for seismic resistance is not covered in BS 6960. NOTE.4 "The publications referred toin this standard are listed on page 215, Detailed recommendations for practical direct application of “second order” methods of global analysis (based on the final deformed geometry of the frame), including allowances for geometrical imperfections and residual stresses, strain hardening, the relationship between member stability and frame stability and appropriate failure criteria, are beyond the scope of this document. However, such use is not precluded provided that appropriate allowances are made for these considerations (see 5.1.1). ‘The test procedures of 7.1.2 are intended only for stee! structures within the scope of this part of BS 6850. Other cases are covered in Section 3.1 or Parts 4, 5, 6 and 9 of BS 5950 as appropriate, 1.2 Normative references ‘The following normative documents contain provisions which, through reference in this text, constitute provisions of this British Standard, For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. For undated referenece, the latest edition of the publication referred to applies. BS 2678-1, Rules for the design of cranes — Part 1: Specification for classification, stress calculations and design eriteria for structures. BS 2853, Specification for the design and testing of steel overhead runway beams. BS 3100, Specification for steel castings for general engineering purposes. BS 4896-1, Specification for high strength friction grip bolts and associated nuts and washers for structural engineering — Part 1: General grade. BS 4996-2, Specification for high strength friction grip boles and associated nuts and washers for structural engineering — Part 2: Higher grade bolts and nuts and general grade washers. BS 4449, Specification for carbon sive! bars for the reinforcement of concrete. BS 4482, Specification for cold reduced steel wire for the reinforcement of concrete. BS 4489, Steel fabric for the reinforcement of concrete. BS 4604-1, Specification for the use of high strength friction grip bolts in structural steelwork — ‘Metric series — Part 1: General grade, BS 4604-2, Specification for the use of high strength friction grip bolts in structural steelwork — Metric series — Part 2: Higher grade (parallel shank). BS 5400-8, Steel, concrete and composite bridges — Part 3: Code of practice for the design of steel bridges. BS 5950-2, Structural use of steelwork in building — Part 2: Specification for materials, fabrication and erection — Rolled and welded sections. ‘BS 5950-3, Structural use of steelwork in building — Part 3: Design in composite construction — ‘Section 8.1: Code of practice for design of simple and continuous composite beams. BS 5950-4, Structural use of steeltcork in building — Part 4: Code of practice for design of composite slabs with profiled steel sheeting. BS 5960-6, Siructurat use of steelwork in building — Part $: Code of practice for design of cold formed thin gauge sections. BS 5950-6, Structural use of steelwork in building — Part 6: Code of practice for design of light gauge profiled steel sheeting. BS 5950-9, Structural use of steelwork in building — Part 9: Code of practice far stressed skin design. © BSI 05-2001 aBS 5950-1:2000 Section 1 BS 6399-1, Loading for buildings — Part 1: Code of practice for dead. and imposed loads. BS 6399-2, Loading for buildings — Part 2: Code of practice for wind loads. BS 6399-3, Loading for buildings — Part 3: Code of practice far imposed roof loads. BS 7419, Specification for holding down bolts. BS 7608, Code of practice for fatigue design and assessment of steel structures, BS 7644-1, Direct tension indicators — Part 1: Specification for compressible washers. BS 7644.2, Direct tension indicators — Part 2: Specification for nut face and bolt face washers. BS 7668, Specification for weldable structural steels — Hot finished structural hollow sections in weather resistant steels. BS 8002, Code of practice for earth retaining structures. BS 8004, Code of practice for foundations. BS 8110-1, Structural use of concrete — Part 1: Code of practice for design and construction. BS 8110-2, Structural use of concrete — Part 2: Code of practice for apecial circumstances, ‘BS EN 10002-1, Tensile testing of metallic materials — Part 1: Method of test at ambient temperature, BS EN 10025, Hot rolled products of non-alloy structural steels — Technical delivery conditions. BS EN 1011-2, Hot-rolled products in weldable fine grain structural steels — Part 2: Delivery conditions for normalized /nor malized rolled steels, BS EN 10118.8, Hot-rolled products in weldable fine grain structural steels — Part 8: Delivery conditions for thermomechanical rolled ateels. BS EN 10137-2, Plates and wide flats made of high yield strength structural steels in the quenched and tempered or precipitation hardened conditions — Part 2: Delivery conditions for quenched and tempered steels. BS EN 10156, Structural steels with improved atmospheric corrosion resistance — Technical delivery conditions. BS EN 10210-1, Hot finished structural hollow sections of non-alloy and fine grain structural steels — Part 1: Technical delivery requirements. BS EN 10219-1, Cold formed welded structural hollow sections of non-alloy and fine grain steels — Part 1: Technical delivery requirements, BS EN 10250-2, Open die steel forgings for general engineering purposes — Part 2: Non-alloy quality and special steels. BS EN 22553, Welded, brazed and soldered joints — Symbolic representation on drawings CP2, Earth retaining structures. Civil Engineering Code of Practice No. 2. London: The Institution of Structural Engineers, 1951. CP8:Ch V:Part 2, Code of basic data for the design of buildings — Chapter V: Loading — Part 2: Wind loads. London: BSI, 1972. NOTE Publications to which informative reforence is made for information or guidance are listed inthe Bibliography. 1.3 Terms and definitions For the purposes of this part of BS 5950, the following terms and definitions apply. 184 beam a member predominantly eubject to bending 13.2 brittle fracture brittle failure of stool at low temperature 2 ‘© BST 06-2001Section 1 BS 5950-1:2000 138.8 buckling resistance limit of force or moment that a member can withstand without buckling 1.84 built-up ‘constructed by interconnecting more than one rolled section to form a single member 1.35 cantilever a beam that is fixed at one end and free to deflect at the other 1.36 capacity Kimit of force or moment that can be resisted without failure due to yielding or rupture 1.8.7 column a vertical member carrying axial force and possibly moments 1.8.8 compact cross-section a cross-section that can develop its plastic moment capacity, but in which local buckling prevents rotation ateonstant moment 189 compound section sections, or plates and sections, intereonnected to form a single member 1.8.10 connection Jocation where a member is fixed to a supporting member or other support, including the bolts, welds and other material used to transfer loads 1341 dead load 2 load of constant magnitude and position that acts permanently, including self-weight 13.12 design strength the notional yield strength of the material used in design, obtained by applying partial factors to the spetified minimum yield strength and tensile strength of the material 1.3.13 dynamic load part of an imposed load resulting from motion 1.3.14 edge distance distance from the centre of a bolt hole to the nearest edge of an element, measured perpendicular to the direction in which the bolt bears 1.8.15 effective length for a beam. Length betweon adjacent restraints against lateral-torsional buckling, multiplied by a factor that allows for the effect of the actual restraint conditions compared to a sizaple beam with torsional end restraint for a compression member. Length between adjacent lateral restraints against buckling about a given axis, multiplied by a factor that allows for the effect of the actual restraint conditions compared to pinned ends (© BSI 05-2001 aBS 5950-1:2000 Section 1 ——— eee 1.3.16 elastic analysis structural analysis that assumes no redistribution of moments in a continuous member or frame due to plastic hinge rotation 1.3.17 empirical method simplified method of design justified by experience or by tests 1.8.18 end distance distance from the centre of a bolt hole to the edge of an element, measured parallel to the direction in which ‘the bolt bears 1.3.19 factored load specified load multiplied by the relevant partial factor 1.3.20 fatigue damage to a structural member caused by repeated application of strosees that are ineulficient to cause failure by a single application 1.3.21 foundation part of a structure that distributes load directly to the ground 18.22 friction grip connection a bolted connection that relies on friction to transmit shear between components 1.8.28 H-section section with a central web and two flanges, thet has an overall depth not greater than 1.2 tim width, 1.8.24 hybrid section ‘Teection with a web of a lower strength grade than the flanges 1.3.25 Fsection section with a central web and two flanges, that has an overall depth greater than 1.2 times its overall width, 1.3.26 imposed load Joad on a structure or member, other than wind load, produced by the external environment or the intended occupancy or use 1.8.27 instability inability to carry further load due to vanishing stiffness 1.3.28 joint element of a structure that connects members together and enables forces and moments to be transmitted between them 1.8.29 lateral restraint for a beam, Restrsint that prevente lateral movement of the compression flange for a compression member. Restraint that prevents lateral movement of the member in a given plane its overall 4 © BSI 05-2001Section 1 BS 5950-1:2000 1.3.30 longitudinal along the length of the member 1.3.81 notched end connected end of « member with one or both flanges cut away locally for clearance 1.8.32, pattera loading loads arranged ta give the most severe effect on a particular element 1.8.83, pitch distance between centres of bolts lying in the direction of force transfer 1.8.84 plastic analysis structural analysis that allows for redistribution of moments in a continuous member or frame due to plastic hinge rotation 1.3.85 plastic cross-section cross-section that can develop a plastic hinge with sufficient rotation capacity to allow redistribution of bending moments within a continuous member or frame 1.5.86 plastic load factor the ratio by which each of the factored loads would have to be increased to produce a plastic hinge mechanism 1.8.87 plastic moment ‘moment capacity allowing for redistribution of stress within & cross-section, 1.3.88 portal frame a single storey frame with rigid moment-resisting joints 1.3.89 preloaded bolt bolt tightened to « specified initial tension 1.8.40 rotation capacity the angle through which a joint can rotate without failing 1.3.41 rotational stiffness the moment required to produce unit rotation in a joint 13.42 segment ‘a portion of the length of a member, between adjacent points that are laterally restrained 1.3.43 semi-compact cross-section a cross-section that can develop its elastic capacity in compression or bending, but in which local buckling prevents development of its plastic moment capacity (© BST 06-2001 5BS 5950-1:2000 Section 1 18.44 slender cross-section ‘cross-section in which focal buckling prevents development of its elastic capacity in compression and/or bending 1.3.45 slenderness the effective length divided by the radius of gyration 1.3.46 slip resistance limit of shear that can be applied before slip occurs in a friction grip connection 1.8.47 stability resistance to failure by buckling or loss of static equilibrium 1.3.48 strength resistance to failure by yielding or buckling 1.3.49 strut member carrying predominantly axial compressive force 1.8.50 subframe part of a larger frame 1.8.51 torsional restraint restraint that prevents rotation of a member about its longitudinal axis 1.8.52 transverse direction perpendicular to the stronger of the rectangular axes of the member 1.8.53 welded section cross-section fabricated from plates by welding 1.4 Major symbols A Area A, Effective net area Acq Effective cross-soctional area Ag Gros cross-sectional area 4, Net area A, Shear area of a bolt A, Tensile stress area of a bolt A, Shear area ofa membor @ Spacing of transverse stiffeners or Effective throat size of weld Bo Width b Outstand, 6 © BSI 06-2001Snort BS 5950-1:2000 bv by by PPP PIERERS Coe re eP Haas i fo Pps pes Poe or or or Depth of section Diameter of section Diameter of hole Depth of web Nominal diameter of bolt ‘Modulus of elasticity of steel Edge or end distance Compressive axial force Shear force in a bolt Tensile axial force Shear force ina member ‘Compressive stress due to axial force Shear stress Warping constant of section Storey height Second moment of area about the major axis Second moment of area about the minor axis Torsion constant of section Length Span Effective length Moment Buckling resistance moment (lateral-torsional buckling) ‘Moment capacity Reduced moment capacity in the presence of an axial force ‘Equivalent uniform moment factor Bearing capacity of a belt Friction grip bearing capacity Bearing capacity of connected parts Compression resistance Shear capacity of a bolt Slip resistance provided by a preloaded bolt ‘Tension capacity of a member or bolt Shear capacity of a member ‘Bonding strength (Lateral torsional buckling) Bearing strength of a bott ‘Bearing strength of connected parts Compressive strength Shear strength of a bolt ‘Tension strength of a bolt Design strength of a fillot weld Design strength of steel Shear buckling strength of a web Radius of gyration about the major axis © BST 05-2001, 7BS 5950-1:2000 Section 1 —————— Radius of gyration about the minor axis Effective plastic modulus Plastic modulus about the major axis Plastic modulus about the minor axis Leg length of a fillet weld Thickness of a flange ‘Thickness or Thickness of a web Thickness of a connected part Buckling parameter of a cross-section Shear buckling resistance of a web Critical shear buckling resistance of a web Slenderness factor for a beam ‘Torsional index of « cross-section Zaz Effective section modulus Z, Section modulus about the major axis (minimum value unless otherwise stated) 4, Section modulus about the minor axis (minimum value unless otherwise stated) Yr e a dee ca ep es x Snes Overall load factor Constant (275/p,)°* Slendemness, ic. the effective length divided by the radius of gyration Elastic critical load factor Ap _Lamiting equivalent slenderness (lateral-torsional buckling) Ayr Equivalent slenderness (lateral-torsional buckling) 4g Limiting slenderness (axial compression) 1.5 Other materials Where other structural roaterials are used in association with structural steelwork, they should conform to the appropriate British Standard. 1.6 Design documents ‘The design documents should contain sufficient information to enable the design to be detailed and the structure fabricated and erected. ‘The design documents should state the assumed behaviour of the structure, the design assumptions and whether any loads or reactions quoted aro factored or unfactored. Where weld symbols are used on drawings they should be in accordance with BS EN 22558, which should be referenced on the drawings concerned. 1.7 Reference to BS 5400-3 In BS 5400-3 the nominal values of material strengths and the method of applying partial safety factors are different, see Annex A. These differences should be taken into account when referring to BS 5400-3. 8 ‘© BSI 08-2001BS 5950-1:2000 Section 2. Limit states design 2.1 General principles and design methods 2.1.1 General principles 2.2.1.1 Aims of structural design ‘The aim of structural design should be to provide, with due regard to economy, a structure capable of fulfilling its intended function and sustaining the specified loads for its intended life, The design should facilitate safe fabrication, transport, handling and erection. Tt should also take account of the needs of future maintenance, final demolition, recycling and reuse of materials. ‘The structure should be designed to behave as a one three-dimensional entity. The layout of ita constituent parts, such as foundations, steelwork, joints and other structural components should constitute a robust and stable structure under normal loading to ensure that, in the event of misuse or accident, damage will not be disproportionate to the cause. ‘To achieve these aims the basic anatomy of the structure by which the loads are transmitted to the foundations should be clearly defined. Any features of the structure that have a critical influence on its overall stability should be identified and taken account of in the design. Bach part of the structure should be sufficiently robust and insensitive to the effects of minor incidental loads applied during service that the safoty of other parts is not prejudiced. Reference should be made to 2.4.5, Whilat the ultimate limit atate capacities and resistances given in this standard are to be rogarded as limiting values, the purpose in design should be to reach these limits in as many parts of the structure as possible, to adopt a layout such that maximum structural efficiency is attained and to rationalize the steel momber sizes and details in ordor to obtain the optimum combination of materials and workmanship, consistent with the overall requirements of the structure. 2.1.1.2 Overall stability ‘The designer who is responsible for the overall stability of the structure should be clearly identified. This designer should onsure the compatibility of the structural design and detailing between all those structural parts and components that are required for overall stability, even if some or all of the structural design and detailing of those structural parts and components is carried out by another designer. 2.1.8 Aceuracy of caleulation For the purpose of deciding whether a particular recommendation is satisfied, the final value, observed or calculated, expressing the result of a test or analysis should be rounded off. The number of significant places retained in the rounded off value should be the same as in the relevant value recommended in this standard, 2.1.2 Methods of design 2.1.2.1 Generat ‘Structures should be designed using the methods given in 2.1.2.2, 21.2.8, 2.1.24 and 2.1.2.5, Imeach case the details of the joints should be such as to fulfil the assumptions made in the relevant design method, without adversely affecting any other part of the structure. 2.1.2.2 Simple design ‘The joints should be assumed not to develop moments adversely affecting either the members or the structure as a whole, ‘The distribution of forces may connected. The necessary flexi materials, other than the bolts. ‘The structure should be laterally restreined, both in-plano and out-of-plane, to provide sway stability, see 2.4.2.5, and resist horizontal forces, see 2.4.2.8, determined assuming that members intersecting at a joint are pin ty in the connections may result in some non-elastie deformation of the © BSI 05-2001,BS 5950-1:2000 Section 2 2.1.2.8 Continuous design Either elastic or plastic analysis may be used. For clastic analysis the joints should have sufficient rotational stiffness to justify analysis based on full continuity. The joints should also be capable of resisting the moments and forces resulting from the analysis. For plastic analysis the joints should have sufficient momont capacity to justify analysis assuming plastic hinges in the members. Tho joints chould also have sufficiont rotational stiffness for in-plane stability. 2.1.2.4 Semi-continuous design ‘This method may be used where the joints have some degree of strength and stiffness, but insufficient to develop full continuity. Either elastic or plastic analysis may be used. ‘The moment capacity, rotational stiffness and rotation capacity of the joints should be based on experimental evidence. This may permit some limited plasticity, provided that the capacity of the bolts or welds is not the failure criterion. On this basis, the design should satisfy the strength, stif ness and in-plane stability requirements of all parts of the structure when partial continuity at the joints is taken {nto account in determining the moments and forces in the members. NOTE Detaia of desien procedures of this type are given in references [1] and (2, eee Bibliography. 2.1.2.5 Experimental verification ‘Where design of a structure or element by calculation in accordance with any of the preceding methods is, not practicable, or is inappropriate, the strength, stability, stifiness and deformation capacity may be confirmed by appropriate loading tests in accordance with Section 7. 2.1.8 Limit states concept Structures should be designed by considering the limit states beyond which they would become unfit for ‘their intended use. Appropriate partial factors should be applied to provide adequate degrees of reliability for ultimate limit states and serviceability limit states. Ultimate limit states concern the safety of the whole or part of the structure. Serviceability limit states correspond to limits beyond which specified service criteria are no longer met. ‘Examples of limit etates relevant to stec! structures are given in Table 1. In design, the limit states relevant to that structure or part should be considered. ‘The overall factor in any design has to cover variability of material strength: Ym — loading: Ye = structural performance: Yp In this code the materia! factor y,, is incorporated in the recommended design strengths. For structural stee] the material factor is taken as 1.0 applied to the yield strength Y, or 1.2 applied to the tensile strength U,. Different values are used for bolts and welds. ‘The values assigned for y; and y, depend on the type of load and the load combination. Their product is the factor y;by which the specified loads are to be multiplied in checking the strength and stability of a structure, cee 2.4. A detailed breakdown of y factors is given in Annox A. ‘Table 1 — Limit states ‘Ultimate limit states (ULS) Serviceability limit states (SL8) ‘Strength (including general yielding, rupture, [Deflection, seo 2.5.2. [buckling and forming a mechanism), see 2.4.1. ‘Stability against overturning and sway stability, _| Vibration, see 2.5.8. see 2.4.2, ‘Fracture due to fatigue, see 2.4.9. ‘Wind induced oscillation, see 2.5.8. [Brittle fracture, see 2.4.4. Durability, see 2.5.4. 10 ‘© BST 05.2001Section 2 BS 5950-1:2000 2.2 Loading 2.2.1 General All relevant loads should be considered separately and in such realistic combinations as to comprise the most critical effects on the elements and the structure as a whole. The magnitude und frequency of ‘fluctuating loads should also be considered. ‘Loading conditions during rection should receive particular attention. Settlement of supports should be ‘taken into account where necessary. 2.2.2 Dead, imposed and wind loading ‘The dead and imposed loads should be determined from BS 6599-1 and BS 6399-3; wind loads should be determined from BS 6399-2 or CP3:Ch V:Part 2. ‘NOTE. In countries other than the UK, londscan he determined in accordance with this clause, or in accordance with oeat or national provisions as appropriate, 2.2.8 Loads from overhead travelling cranes For overhead travelling cranes, the vertical and horizontal dynamic loads and impact effects should be determined in accordance with BS 2673-1, The values for cranes of loading class Q3 and Q4 as dofined in ‘BS 2573-1 should be established in consultation with the crane manufacturer. 2.2.4 Earth and ground-water loading ‘The earth and ground-water loading to which the partial factor ye of 1.2 given in Table 2 applies, should be taken as the worst credible earth and ground-water loads obtained in accordance with BS 8002, Where other earth and ground-water loads are used, such as nominal loads determined in accordance with CP2, the value of tho partial factor y, should be talon as 1. ‘When applying y;to earth and ground-water loads, no distinction should be made between adverse and beneficial loads. Moreover, the same value of yr should be applied in any load combination. 2.3 Temperature change ‘Where, in the design and erection of u structure, itis necessary to take account of changes in temperature, it may be assumed that in the UK the average temperature of internal steelwork varies from 5 °C to +35 °C. The actual range, however, depends on the location, type and purpose of the structure and special consideration may be necessary for structures in other conditions, and in locations abroad subjected to different temperature ranges. 2.4 Ultimate limit states 2.4.1 Limit state of strength 2.4.1.1 General In checking the strength of a structure, or of any part of it, the specified loads should be multiplied by the relevant partial factors ¥- given in Table 2, The factored loads should be applied in the most unfavourable realistic combination for the part or effect under consideration. ‘The load carrying capacity of each member and connection, as determined by the relevant provisions of this standard, should be such that the factored loads would not cause failure. Ineach load combination, a y; factor of 1.0 should be applied to dead load that counteracts the effects of other loads, including dead loads restraining sliding, overturning or uplift. 2.4.1.2 Buildings without cranes In the design of buildings not subject to loads from cranes, the following principal combinations of loads should be taken into account: — Load combination 1: ‘Dead load and imposed load (gravity loads); — Load combination 2: ‘Dead load and wind load; — Load combination 3: Dead load, imposed load and wind load. ‘OBST 05-2001 nBS 5950-1:2000 Section 2 ‘Table 2 — Partial factors for loads ¥¢ ‘Type of load and load combination Pector yp [Dead load, except as follows, ra Dead load acting together with wind load and imposed load combined. 2 [Dead load acting together with crane loads ond imposed load combined. 2 ‘Dead load acting together with crane loads and wind load combined. 1.2 Dead load whenever it counteracts the effects of other loads. 0 Dead load when restraining sliding, overturning or uplift. 1.0 [Tmposed load ne Hmposed load acting together with wind load. 2 |Wind load. 4 | Wind load acting together with imposed load. a 1.2 [Storage tanks, including contents, a \Storage tanks, empty, when restraining sliding, overturning or uplift. 1.0 [Rarth and ground-water load, worst credible values, see 2.2.4. 12 [Barth and ground-water load, nominal values, see 2.2.4 fey [Exceptional snow load (due to local drifting on roofs, see 7.4 in BS 6299-8:1988). {1.05 Hrorces due to temperature change. uz Vertical crane loads. 16 |Vertical crane loads acting together with horizontal crane loads. ae Horizontal crane loads (surge, see 2.2.3, or crabbing, see 4.11.2). 1.6 [Horizontal crane loads acting together with vertical crane loads. a [Vertical crane loads acting together with imposed load. ia Horizontal crane joads acting together with imposed load. 12 {tmposed load acting together with vertical erane loads. La Imposed load acting together with horizontal crane loads. 1.2 |Crane loads acting together with wind load. 12 |Wind load acting together with crane loads. 12 J ee y= 1.0 fr varia crane loads that counteract the effets of othr loads 12 © BSI 05-2001Section 2 BS 5950-1:2000 2.4.1.8 Overhead travelling cranes ‘The y¢ factors given in Table 2 for vertical loads from overhead travelling cranes should be applied to the dynamic vertical whee! loads, ie. the static vertical wheel loads increased by the appropriate allowance for dynamic effects, see 2.2.3. ‘Where a structure or member is aubject to loads from two or more cranes, the crane loads should be taken as the maximum vertical and horizontal loads acting simultaneously where this is reasonably possible. For overhead travelling cranes inside buildings, in the design of gantry girders and their supports the following principal combinations of loads should be taken into account: — Crane combination 1: Dead load, imposed load and vertical erane loads; — Grane combination 2: Dead load, imposed load and horizontal crane loads; — Crane combination 2; Dead load, imposed load, vertical crane loads and horizontal crane loads. Further load combinations should also be considered in the case of members that support overhead travelling cranes and are also subject to wind loads 2.4.1.4 Outdoor cranes ‘The wind loads on outdoor overhead travelling cranes should be obtained from: 8) BS 2573-1, for cranes under working conditions; +b) BS 6399-2, for cranes that are not in operation. 2.4.2 Stability limit states 2.4.2.1 General Static equilibrium, resistance to horizontal forces and sway stiffness should be checked. In checking the stability of a structure, or of any part of it, the loads should be increased by the relevant yr factors given in Table 2, The factored loads should be applied in the most unfavourable realistic combination for the part or effect undor consideration. 2.4.2.2 Static equilibrium ‘The factored loads, considered separately and in combination, should not cause the structure, or any part of it (including the foundations), to slide, overturn or liftoff its seating. The combination of dead, imposed and wind loads should bo such as to have the most severe effect on the stability limit state under consideration, see 2.2.1. Account should be taken of variations in dead load probable during construction or other temporary conditions. 2.4.2.8 Resistance to horizontal forces ‘To provide a practical level of robustness against the effects of incidental loading, all structures, including portions between expansion joints, should have adequate resistance to horizontal forces. In load combination 1 (gee 2.4.2.2) the notional horizontal forces given in 2.4.2.4 should be applied. In load ‘combinations 2 and 3 the horizontal component of the factored wind load should not be taken as less than 1.0 % of the factored dead load applied horizontally. Resistance to horizontal forces should be provided using one or more of the following systems: — triangulated bracing; — moment-resisting joints; —cantitever columns; ~ shear walls; — specially designed staircase enclosures, lift cores or similar construction. Whatever system of resisting horizontal forees is used, reversal of load direction should be accommodated. ‘The cladding, floors and roof should have adequate strength and be so secured to the structural framework as to transmit all horizontal forces to the points at which such resistance is provided. ‘Where resistance to horizontal forces is provided by construction other than the steel frame, the steelwork design should clearly indicate the need for such construction and state the forces acting on it, see 1.6. ‘© BSH 05-2001 33‘As the specified loads from overhead travelling cranes already include significant horizontal loads, itis not ‘necessary to include vertical crane loads when calculating the minimus wind load. 2.4.2.4 Notional horizontal forces ‘Toallow for the effects of practical imperfections such as lack of verticality, all structures should be capable of resisting notional horizontal forces, taken as a minimum of 0.6 % of the factored vertical dead and imposed loads applied at the same level. NOTE For certain structures, sch as internal platform floors or spectator grandstands, larger minimums horizontal forces are given in the relevant design documentation. ‘The notional horizontal forces should be assumed to act in any one direction at a time and should be appli at each roof and floor level or their equivalent. They should be taken as acting simultaneously with tl factored vertical dead and imposed loads (oad combination 1, see 2.4.1.2). Aa the specified loads from overhead travelling cranes already include significant horizontal loads, the vertical crane loads need not be included when calculating notional horizontal forces. ‘The notional horizontal forces appliod in load combination 1 should not: a) be applied when considering overturning; 1b) be applied when considering pattern loads; ©) be combined with applied horizontal loads; 4) be combined with temperature effects; ©) be taken to contribute to the net reactions at the foundations. NOTE. Thovo conditions donot apply tothe minimum wind led (1.0% of dead lad) in 2.42.8. 2.4.2.5 Sway stiffness All structures (including portions between expansion joints) should have sufficient sway stiffuess, so that the vertical loads acting with the lateral displacements of the structure do not induce excessive secondary forces or moments in the members or connections. Where such “second order’ ("P-A") effocts are significant, they should be allowed for in the design of those parts of the structure that contribute to its resistance to horizontal forces, see 2.4.2.6. ‘Sway stiffness should be provided by the system of resisting horizontal forces, se 2.4.2.8. Whatever system is used, sufficient stiffness should be provided to limit sway deformation in any horizontal direction and also to limit twisting of the structure on plan. ‘Where moment resisting joints are used to provide sway stiffness, unless they provide full continuity of member stiffness, their flexibility should be taken into account in the analysis. In the case of clad structures, the stiffening effect of masonry infill wall panels or diaphragms of profiled gigelsheting maybe explicitly taken into account by using the method of paral sway bracing given ie ‘Annex E. 2.4.2.6 “Non-sway” frames A structure or structural frame may be classed as “non-sway” if its sway deformation is sufficiently small. for the resulting secondary forces and moments to be negligible. For clad structures, provided that the stiffening effect of masonry infill wall panels or diaphragms of profiled steel sheeting is not explicitly taken into account (see 2.4.2.5), this may bo assumed to be satisfied if the sway mode elastic critical load factor Acq of the frame, under vertical load only, satisfies: dg 210 In all other cases the structure or frame should be classed as “sway-sensitive”, see 2.4.2.7. 4 ‘© BSI 05-2001Section 2 BS 5950-1:2000 Except for single-storey frames with moment-resisting joints, or other frames in which sloping members have moment-rsiating connections, Ay should bo takon as the smallest value, considering every storey, determi ym: where A is the storey height; 5 is the notional horizontal deflection of the top of the storey relative to the bottom of the storey, due to the notional horizontal forces from 2.4.2.4. For single-storey frames with rigid moment-resisting joints, reference should be made to 6.5. Other frames in which sloping members have moment-resisting connections may either be designed by obtaining A,, by second-order clastic analysis, or treated like portal frames, see 5.5. 2.42.7 “Sway-sensitive” frames ‘All structures that are not classed as “non-sway” (including those in which the stiffening effect of masonry infil wall panels or diphragms of profited steel sheeting is exlicily taken into acount, see 2 should be classed as “sway: xcopt where plastic anclysi in used, provided thu 2 is nat less than 40 the secondary forces and ‘momenta should be allowed for as follows: 4) ifthe resistance to horizontal forces is provided by moment resisting joints or by cantilever columns, either by using sway mode in-plane effective lengths for tho columns and designing the beams to remain clastic under the factored loads, or alternatively by using the method specified in b); by multiplying th sway effects (see 2.4.2.8) by the amplification factor kar, determined from the . 1I)for clad structures, provided that the stiffening effect of masonry infill wall panels cr diaphragms of profiled steel sheeting (see 2.4.2.8) is not explicitly taken into account: -— te ame = TERETE Bi Hamp? 10 2) for unclad frames, or for clad structures in which the stiffening effect of masonry infill wall panels or diaphragms of profiled steel sheeting (see 2.4.2,8) is explicitly taken into account: A k, famp = Fo If Ag is less than 4.0 second-order elastic analysis should be used. If plastic analysis is used, reference should be made to 6.5 for portal frames or 6.7 for multi-storey frames. 2.4.2.8 Sway effects In the case of a symmetrical frame, with symmetrical vertical loads, the sway effects should be taken as comprising the forces and moments in the frame due to the horizontal loads. © BSI 05.2001 5BS 5950-1:2000 Section 2 In any other case, the forces and moments at the ends of each member may conservatively be treated as sway effecte. Otherwise, the sway effects may be found by using one of the following alternatives. a) Deducting the non-sway effects, 1) Analyse the frame under the actual rostraint conditions. 2) Add horizontal restraints at each floor or roof level to prevent sway, then analyse the frame again. 8) Obtain the sway effects by deducting the second set of forces and moments from the first set. b) Direct calculation, 1) Analyse the frame with horizontal restraints added at each floor or roof level to prevent sway. 12) Reverse the directions of the horizontal reactions produced at the added horizontal restraints. 8) Apply them as loads to the otherwise unloaded frame under the actual restraint conditions, 4) Adopt the forces and moments from the second analysis as the sway effects. 2.4.2.9 Foundation design ‘The design of foundations should be in accordance with BS 8004 and should accommodate all the forces imposed on them. Attention should be given to the method of connecting the steel superstructure to the foundations and to the anchoring of holding-down bolts es recommended in 6.6. ‘Where it is necessary to quote the foundation reactions, it should be clearly stated whether the forces and ‘moments result from factored or unfactored loads. Where they result from factored loads, the relevant yr factors for each load in each combination should be stated. 2.4.8 Fatigue Fatigue need not be considered unless a structure or element is subjected to numerous significant fluctuations of stress. Stress changes due to normal fluctuations in wind loading need not be considered. However, where aerodynamic instability can occur, account should be taken of wind induced oscillations. Structural members that support heavy vibrating machinery or plant should be checked for fatigue resistance, In the design of crane supporting structures, only those members that support cranes of utilization claesos Ud to U9 as defined in BS 2573 need be checked. When designing for fatigue a ¥ factor of 1.0 should be used. Resistance to fatigue should be determined by reference 19 BS 7608, Where fatigue is critical, all design details should be. defined and the re id quality of wworkinansiip should he clearly specified. Presiooly quired quality NOTE 5 5060.2 does ot fly cover workmanship for cses whore otis s critial, ut rfrence can be md to 180 107212 2.4.4 Brittle fracture Brit entre shouldbe avoided by using ote quai with adoquate notch toughness, aking account — the minimum service temperature; — the thickness; the steel grade; — the type of detail; — the stress level; the strain level or strain rate. In addition, the welding electrodes or other welding consumables should have a specified Charpy impact value equivalent to, or better than, that specified for the parent metal, soe 6.8.5 and 6.8.1. In the UK the minimum service temperature Tria in the steel should normally be taken as ~5 °C for intornal stoelwork and ~15 °C for external steelwork. For cold stores, locations exposed to exceptionally low temperatures or structures to be constructed in other countries, Tiyi, should be taken as the minimum tomperature expected to occur in the steel within the intended design life of the structure. ‘The steel quality selected for each component should be such that the thickness t of each element satisfios: ts Kt 16 © BST 05-2001Section 2 BS 5950-1:2000 where K isa factor that depends on the type of detail, the general stress level, the stress concentration effects and the strain conditions, see Table 3; tis the limiting thickness at the appropriate minimum service temperature Tryin for a given steel grade and quality, when the factor K'= 1, from Table 4 or Table 5. In addition, the maximum thickness of the component should not exceed the maximum thickness fz at which the full Charpy impact value applies to the selected steel quality for that product type and steel grade, according to the relevant product standard, see Table 6. For rolled sections t and t should be related to the same element of the cross-section as the factor K, but tz should be related to the thickest element of the cross-section. Alternatively, the value of f; may be determined from the following: if Tans # Tin + 20°C: ua | 1,600.2)" o> if Tony > Trig + 20°C: 95+ Tin 4, $ 50(1.2)"| ——min 2 in which: Train Tons 10 Trin 8 the minimum service temperature (in °C) expected to occur in the steel within the intended design life of the part; Tyry is the test temperature (in °C) for which a minimum Charpy impact value C, of 27 J is specified in the product standard, or the equivalent value given in Table 7; Yoom is the nominal yield strength Gin N/mm?) [the specified minimum yield strength for thickness < 16 mm (or 12 mm for BS 7668), as in the steel grade designation]. ‘Table 3— Factor K for type of detail, stress level and strain conditions ‘Type of detail or location Components in tension due to | Components not factored loads subject to applied ‘tension Strona > O3%oq | Stren <0.8Tun (Plain steel iz 8 a | {Drilled holes or reamed holes 1s iz 3 ‘Flame cut edges 1 16 2 Punched holes (un-reamed) ir 16 iz |Welded, generally a ne lz [Welded across ends of cover plates Oa OTS o [Welded connections to unstiffened flanges, see 6.7.5 0.5 0.75 T INOTH1 Where parte are required to withstand sgnlfant plastic doformaton at the minimis eevicetemperatare (nich as lrauh bareers or crane stops) K should be halved. INOTE 2 Basoplates atached to eolunns by nominal welds only, forthe parposes of location in use and security i transit, should be classified as plain steel. NOTE 3 Welded atachmente not excuoding 150 rim in length should not by classified as cover plates, OBST 05.2001 uBS 5950-1:2000 Section 2 Table 4 — Thickness t, for plates, flats and rolled sectionst* Product standard, steel grade and| Maximum thickness +; (mm) when K= 1 according to minimum service quality temperature ‘Normal temperatures Lower temperatures Internal ‘External er a5°¢ 28°C 35°C —6C [BS EN 1002: iS 275 28 0 0 0 Is 2755R 30 ° 0 0 IS 275.50 65 bt 30 0 IS 275 32 94 8 65 54 30 IS 355 16 ° 0 0 I$ 355 JR 21 0 0 0 Is 355 J0 46 38 2 0 iS 355 J2 66 85 46 38 21 Is 355 Ke 9 66 85 46 38 [BS EN 10113: IS275M or S275N 113 4 8 65 54 IS275ML or S275NL — |162 135 413, joa 78 IS865M or S355N 9 66 65 46 38 IS865ML or S355NL |114 95 9 les 55 S460M or S460N 55 46 38 32 26 Is 460ML or $460NL p 66 85 46 138 BS EN 10137: Is 460 46 38 32 l26 15 Is 460 QL. 66 55 46 38 lz1 8 460 QL1 95 9 66 55, 46 BS EN 10156: 1S 365 JOW or S365 J0WP | 46 38 aL 0 0 ls 355 J2W or Sass J2wP | 66 55 46 38 21 Is 355 KOW 9 66 5B 46 38 | The values in tis table do not apply Ifthe thickness of tho part exconds the rclevant Limiting thickness for validity of the standard Charpy impact value for that product form, sco Table 6. }+ Tae inclusion ofa thickness in this able does not necessarily imply that steel ofthat thickness can be wupplied to that sade in all product forms. 18 ‘© BST 05-2001,Section 2 BS 5950-1:2000 ‘Table 5 — Thickness ¢, for structural hollow sections Product standard, steel grade and | Maximum thickness, (am) when K= | according to minimum service ‘quality temperature ‘Normal temperatures Lower temperatures Internal, External sc 5c 25°C 35°C °C BS EN 10210: 8275 JOH 85 ba 30 0 o S275 J2H 94 B 65 a4 30 IS 275 NH 13 94 8 65 Ba ls 275 NLH 62, 135 13 fod 78 |S 865 JOH 46 38 21 0 0 1S 865 J2H 66 55 46 38 21 Is 355 NH 9 66 55 46 38 IS 855 NLHL a4 95 8 66 55, Is 460 NH 55 6 38 32. 26 IS 460 NLH 9 66 55 se 38 IBSEN 10219: Is 275 JOH 65 5 30 0 0 Is 275 J2H of 8 65 54 30 IS275MH or S27BNH 113, 4 8 les 54 IS273MLH or S275NLH 162 136, 113, loa 78 |S 355 JOH 46 38 21 0 0 Is 955 J2H 68 55 46 38 21 S355MH or S855NH | 79 66 55 46 38 S308MLH or S355NLH [114 95 9 66 55 S460MH or S460NH | 55 46 38 32 la6 |S 460MLH or S460NLH | 79 66 55 46 a8 [BS 7688: |S $45 JOWH or $845 JOWPH | 48 40 2 0 0 IS 345 GWH 62 52, 43 36 10 19 ‘© BSI 05-2001BS 5950-1:2000 Section 2 ————————— ee ‘Table 6 — Maximum thickness é:* (mm) Product standard | Steel grade or quality Sections Plates and flats Hollow sections BS EN 10025 |S 275 or 8 855 [100 1150 — BS EN 1011-2 |8 275 or S355 150 150 — ls 460 100 100 IK [BS EN 1013-3 [8 275, $ 855 or S 460)160 63 I~ BS EN 101372 |S 460 — 150 = IBSEN 10155 |JOWP or J2WP 40 16 I JJow, J2W or K2W |100 100 | [BS EN 10210-1 [AD — [= [es [BS EN 10219-1 [AIL = = [40 [BS 7668 JOWPH = — iz |JOWH or GWH | I 140 + Maximum thickness at which the full Charpy impact value given in the product standard applios. Table 7— Charpy test temperature or equivalent test temperature Tos Steel quality Product standard [BS EN 10025] BS EN 10139 | BS EN 10137 |BSEN 10155|BS BN 10710[BS KN 10219] BS 7668 aR [20% J = — aos fe20°S = 0 oc fe I- orc oc orc arc ls L2orc J I- 20° f-2o°c tote |F Ka |-aorcs | I- -g0°ce | - - IM I— }so%ce J I— | sores |— ja I- |so°c | I- | sore | IN I sorte | I- -so°cs f-sorce | NL I a I sor soc | iQ | | aoece — |— I I- I- Qu I~ I orcs |— — I~ I- qua I I l-corcs |— |— | I a IK IE IE IK I I |-15°C }. Equivalent test tomparature far 27 J. Product standard specifies 40 J st 20°C. }+ Equivalent test temperature for 27 J. Product standard specifies 20 Jat the same temperature 20 ‘© BST 05-2001Section 2 BS 5950-1:2000 2.4.5 Structural integrity 2.4.5.1 General ‘The design of all structures should follow the principles given in 2.1.1.1. In addition, to reduce the risk of localized damage spreading, buildings should satisfy the further recommendations given in 2.4.8.2, 2.4.5.3, ‘and 2.4.5.4, For the purposes of 2.4.5.2, 2.4.5.3 and 2.4.5.4 it may be assumed that substantial permanent deformation of members and their connections is acceptable. 2.4.5.2 Tying of buildings All buildings should be effectively tiod together at each principal floor level. Each column should be ‘effectively held in position by means of horizontal ties in two directions, approximately at right angles, at ‘each principat floor level supported by that eolumn. Horizontal ties should similarly be provided at roof level, except where the steelwork only supports cladding that weighs not more than 0.7 KN/m? and that carries only imposed roof loads and wind loads. Continuous lines of ties should be arranged as close as practicable to the edges of the floor or roof and to each column line, see Figure 1. At re-entrant comers the tie members nearest to the edge should be anchored into the steel framework as indicated in Figure 1. All horizontal ties and their end connections should be of a standard of robustness commensurate with the structure of which they form a part. The horizontal ties may be: —steel members, including those also used for other purposes; -~ steel bar reinforcement that is anchored to the steel frame and embedded in concrete; — steel mesh reinforcement in a composite slab with profiled steel sheeting, see BS 5950-4, designed to ‘act compositely with steel beams, see BS 5950-3.1, the profiled steel sheets being directly connected to the beams by the shear connectors. All horizontal ties, and all other horizontal members, should be capable of resisting a factored tensile load, which should not be considered as additive to other loads, of not less than 76 KN. Each portion of a building between expansion joints should be treated as a separate building. Column ties Edge ties Re-entrant corner Tie anchor Tecentrant corner Edgeties HA Tae rt Edge ties Beams not used as ties Figure 1 — Example of tying the columns of a building ‘© BSL06-2001 aBS 5950-1:2000 Section 2 2.4.6.8 Avoidance of disproportionate collapse Where regulations stipulate that certain buildings should be specially designed to avoid disproportionate collapse, steel-framed buildings designed as recommended in this standard (including the recommendations of 2.1.1.1 and 2.4.5.2) may be assumed to moet this requirement provided that the following five conditions a) to e} are met. ) General tying. Horizontal ties generally similar to those doscribed in 2.4.6.2 should be arranged in continuous lines wherever practicable, distributed throughout each floor and roof level in two directions approximately at right angles, see Figure 2. Stect members acting as horizontal ties, and their end connections, should be capable of resisting the following factored tensile loads, which need not be considered as additive to other loads: — for internal ties: 0.(1.4g, + 1.6q,Je,L but not less than 75 KN; — for edge ties: 0.26(1.4g%, + 1.6q,)5:E. but not less than 75 KN. where Bx is the specified dead load per unit area of the floor or roaf; L is the span; qx is the specified imposed floor or roof load per unit area; s, is the mean transverse spacing of the ties adjacent to that being checked. ‘This may be assumed to be satisfied if, in the absence of other loading, the member and its end connections are capable of resisting a tensile force equal to its end reaction under factored loads, or the larger end reaction if they are unequal, but not less than 75 kN. Horizontal ties that consist of steel reinforcement should be designed as recommended in BS 8110. ) Tying of edge columns. The horizontal ties anchoring the columns nearest to the edges of a floor or roof should be capable of resisting a factored tensile load, acting perpendicular to the edge, equal to the greater of the load specified in a) or 1 % of the maximum factored vertical dead and imposed load in the column adjacent to that level. ©) Continuity of columns. Unless the steel frame is fully continuous in at least one direction, all columns should be carried through at each beam-to-column connection. All column splices should be capable of resisting a tensile force equal to the largest factored vertical dead and imposed load reaction applied to ‘the column at a single floor level located between that column aplice and the next column splice down. 4d) Resistance to horizontal forces. Braced bays or other systems for resisting horizontal forces a recommended in 2.4.2.3 should be distributed throughout the building such that, in each of two directions approximately at right angles, no substantial portion of the building is connected at only one Point to a aystem for resisting horizontal forces. ©) Heavy floor units. Where precast concrete or other heavy floor or roof units are used they should be effectively anchored in the direction of their span, either to each other over a support, or directly to their supports as recommended in BS 6110. Hf any of the first three conditions a) to c) are not met, the building should be checked, in each storey in ‘turn, to ensure that disproportionate collapse would not be precipitated by the notional removal, one at a ‘time, of each column. If condition d) is not met, a check should be made in each storey in turn to ensure that disproportionate collapse would not be precipitated by the notional removal, one at a time, of each element of the systems providing resistance to horizontal forces. ‘Tho portion of the building at risk of collapse should not exceed 15 % of the floor or roof area or 70 m= (whichever is less) at the relovant level and at one immediately adjoining floor or roof level, either above or below it. If the notional removal of a column, or of an element of a system providing resistance to horizontal forces, would risk the collapse of a greater area, that column or element should be designed as, a key element, as recommended in 2.4.5.4. In these checks for notional removal of members, only a third of the ordinary wind load and a third of the ordinary imposed load need he allowed for, together with the dead load, except that in the case of buildings ‘used predominantly for storage, or where the imposed load is of a permanent nature, the full imposed load. should be used. A partial factor ¥¢ of 1.05 should be applied, except that when considering overturning the dead load supplying the restoring moment should be multiplied by a partial factor yy of 0.9. 22 © BSI 05-2001Section 2 BS 5950-1:2000 | | Tie anchoring column A ~~ [_—_—- | HAA _———_I-_—1 {tI Figure 2— Example of general tying of a building 2.4.5.4 Key elements Ina multi-storey building that is required by regulations to be designed to avoid disproportionate collapse, a member that is recommended in 2.4.6.8 to be designed as a key clement should be designed for the accidental loading specified in BS 6399-1. Any other ateel member or other structural component that provides lateral restraint vital to the stability of a key clement should itself also be designed as a key element for the same accidental loading, ‘The accidental Joading should be applied to the member from all horizontal and vertical directions, in one direction at a time, together with the reactions from other building components attached to the member that are subject to the same accidental loading, but limited to the maximum reactions that could reasonably be transmitted, considering the breaking resistances of such components and their connections. In this check the effects of ordinary loads should also be considered, to the same extent and with the same partial factor y; as recommended in 2.4.5.3, 2.5 Serviceability limit states 2.5.1 Serviceability loads Generally the serviceability loads should be taken as the unfactored specified values. However, exceptional snow loed (due to local drifting on roofs, sce 7.4 in BS 6399-2:1988) should not be included in the imposed load when checking serviceability. In the case of combined imposed load and wind load, only 80 % of the full specified values need be ‘considered when checking serviceability. In the ease of combined horizontal crane loads and wind load, only the greater effect need be considered when checking serviceability. 2.5.2 Deflection ‘The deflections ofa building or part under serviceability loads should not impair the strength or efficiency of the structure or its components, nor eause damage to the finishings. ‘When checking for deflections the most adverse realistic combination and arrangement of serviceability Joads should be assumed, and the structure may be assumed to behave elastically. © BSI 05-2002 28BS 5950-1:2000 Section 2 ‘Table 8 gives suggested limits for the calculated deflections of cortain structural members. Circumstances ‘may aise where ‘greater or lessor values would be mare appropriate, Other members may also need ion limits. ‘On low pitched and flat roofs the possibility of ponding should be investigated. For deflection limits for runway beams reference should be made to BS 2863, 2.6.8 Vibration and oscillation ‘Vibration and oscillation of building structures should be limited to avoid discomfort to users and damage to contents. Reference to specialist literature should be made as appropriate. NOTE Guidance on lacr vibration is given in reference 3], se Bibliography. 2.5.4 Durability In order to ensure the durability of the structure under conditions relevant both to its intended use and to its intended life, the following factors should be taken into account in design: a) the environment of the structure and the degree of exposure; +b) the shape of the members and the structural detailing; ©) the protective measures, if any; 4) whether inspection and maintenance are possible. As an alternative to the use of protective coatings, weather resistant steels to BS EN 10156 may be used. Table 8— Suggested limits for calculated deflections a) Vertical deflection of beams due to imposed load [Cantilevers [Length/180 }Beams carrying plaster or other brittle finish |Span/360 [Other beams (except purlins and sheeting rails) [Span/200 [Purlins and sheeting rails [See 4.12.2 b) Horizontal deflection of columns due to imposed load and wind load Tops of columns in single-storey buildings, except portal frames |Height/300 [Columns in portal frame buildings, not supporting crano runways [To suit cladding [Columns supporting crane runways \To suit crane runway |In each storey of a building with more than one storey |Height of that storey/200 ld) Grane girders Vertical deflection due to static vertical wheel loads from overhead | Span/600 travelling cranes Horizontal deflection (calculated on the top flange properties alone) —_[Span/500 ‘due to horizontal crane loads 24 (© BST 06-2001BS 5950-1:2000 Section 3. Properties of materials and section properties 3.1 Structural steel 4.1.1 Design strength ‘This standard covers the design of structures fabricated from structural steels conforming to the grades and product standards specified in BS 5950-2. If other steels are used, due allowance should be made for variations in properties, including ductility and weldability. ‘The design strength p, should bo taken as 1.0¥, but not greater than U, /1.2 where Y, and U, are respectively the minicum yield strength Rg and the minimum tensile strength Ry, specified in the relevant product standard, For the more commonly used grades and thicknesses of steel from the product standards specified in BS 5950-2 the value of p, may he obtained from Table 9, Alternatively, the values of Raj and Re, may be obtained from the relevant product atandard. NOTE Additonal requirements apply where plastic analyis sured, se 8.2.8. ‘Table 9 — Design strength py Steel grade ‘Thicknesst leas than or equal ta Design strength p, Niomt 8275 16 276 40 265 6 285 80 245 100 1235 1150 225 3 355 16 355 40 345 63 335 80 }325 100 [ais 150 295 5 460 168 [460 40 l440 63 1430 80 430 100 |400 Js For rolled sections, use the specified thickness of the thickest element of the crots-section. 3.1.2 Notch toughness ‘The notch toughness of the steel, as quantified by the Charpy impact properties, should conform to that for the appropriate quality of steel for avoiding brittle fracture, see 24.4. ‘© BSI 05-2002BS 5950-1:2000 Section 3 4.1.8 Other properties For the elastic properties of steel, the following values should be used. —~Modulus of elasticity: E= 205 000 Nimm? —Shear modulus: Eva. + v9] — Poisson's ratio: 30 — Coefficient of linear thermal expansion (in the ambient temperature range): = 12. 10-8 per*C 3.2 Bolts and welds 3.2.1 Bolts, nuts and washers Assemblies of bolts, nuts and washers should correspond to one of the matching combinations specified in BS 5950-2. Holding-down bolt assemblies should conform to BS 7419. 43.2.2 Friction grip fasteners Friction grip fasteners should generally be preloaded HSFG bolts, with associated nuts and washers, conforming to BS 4395-1 or BS 4396-2. Direct tension indicators conforming to BS 7644 may be used. Other types of friction grip fasteners may also be used provided that they can be reliably tightened to at east the minimum shank tensions specified in BS 4604. 3.2.8 Welding consumables All welding consumables, including covered electrodes, wires, filler rods, flux and shielding gases, should conform to the relevant standard specified in BS 8950-2. ‘The yield strength ¥,, tensile strength U, and minimum elongation of a weld should be taken as equal to respectively the minimum yiold strength Rey, ot Ryo (depending on the relevant product standard), tensile strength Rj, and minimum percentage elongation on a five diameter gauge length according to the appropriate product standard, all as listed for standard classes 35, 42 and 50 in Table 10. ‘Table 10 ~ Strength and clongation of welds Clase ‘Yield strength Y, ‘Tensile strength U, ‘Minimum elongation Qvmm) (Wham?) to) [35 355 440 22 42, 420 500 20 150, 500 560 18 8.8 Steel castings and forgings Steel castings and forgings may be used for components in bearings, junctions and other similar parts. Castings should conform to BS 3100 and forgings should conform to BS EN 10250-2. Unless better information is available, design strengths corresponding to structural steel grade S 275 may be adopted. NOTE. Guidance on sacl caatings is given in reference (4, soo Bibliography. 26 © BSI05-2001,Section 3 BS 5950-1:2000 3.4 Section properties 8.4.1 Gross cross-section Gross cross-section properties should be determined from the specified shape and nominal dimensions of ‘the member or element. Holes for bolts should not be deducted, but due allowance should be mado for larger ‘openings. Material used solely in splices or as battens should not be inciuded. 3.4.2 Net area ‘The net area of a cross-section or an element of a cross-section should be taken as its gross area, less the deductions for bott holes given in 344. 3.4.8 Effective net area The effective net aren a, of each element of a cross-section with bolt holes should be determined from: ,=Kyay but a, 5 dy in which the effective net area coefficient K, is given by: —for grade 8 275: K=12 —for grade $ 255: R211 — for grade 8 460: K=10 —for other steel grades: K,=(Uy/L.2)py where Gg is the gross area of the eloment; a, is the net area of the element; Py is the dosign strength; U, i the specified minimum tensile strength. 3.4.4 Deductions for bolt holes 3.4.4.1 Hole rea In deducting for bott holes (including countersunk holes), the sectional area of the hole in the plane of its own axis should be deducted, not that of the bolt, 9.4.4.2 Holes not staggered Provided that the bolt holes are not staggered, the area to be deducted should be the sum of the sectional areas of the bolt holes in a cross-section perpendicular to the member axis or direction of direct stress. 3.4.4.8 Staggered holes Where the bolt holes are staggered, the area to be deducted should be the greater of: a) the deduction for non-staggered holes given in 8.4.4.2; +) the sum of the sectional areas of a chain of hotes lying on any diagonal or zig-zag line extending progressively across the member or element, see Figure 3, less an allowance of 0.25s%tig for each gauge space g that it traverses diagonally, where: is the gauge spacing perpendicular to the member axis or direction of direct stress, between the ‘centres of two consecutive holes in the chain, see Figure 8; 4 is the staggered pitch, i. the spacing parallel to the member axis or direction of direct stress, between the centres of the same two holes, see Figure 3; + isthe thickness of the holed material. For sections such as angles with holes in both legs, the gauge spacing g should be taken as the sum of the back marks to each hole, less the leg thickness, see Figure 4. © BSI 05-2001, a7BS 5950-1:2000 Section 3 ‘online A: Ag ib = 20} online B: ‘Ag =iIb- 8D +0.286/g) online C: 4 Aq =ilb~ 4D + 0.50y/g; + 0.2582%e,) 1 ‘where Dis the hole diamotor. Direction of 2) ———— direct stress. b ey Figure 3— Staggered holes Back mark Back mark. Figure 4 — Angle with holes in both legs ‘© BSI 05.2001,Section 3 BS 5950-1:2000 3.5 Classification of cross-sections 3.5.1 General Cross-sections should be classified to determine whether local buckling influences their capacity, without calculating their local buckling resistance. ‘The classification of each element of a cross-section subject to compression (due to a bending moment or an ‘axial force) should be hased on its width-to-thiekness ratio, The dimensions of these compression elements should be taken as shown in Figure 5. The elements of a cross-section are generally of constant thickness; for elements that taper in thickness the thickness specified in the relevant standard should be used. ‘A distinction should be made between the following types of element: 8) outstand elements attached to sn adjacent element at one edge only, the other edge being free; ) internal elements attached to other elements on both longitudinal edges and including: — webs comprising internal elements perpendicular to the axis of bending; — flanges comprising internal elements parellel to the axis of bending. All compression elements should be classified in accordance with 9.5.2. Generally, the complete erose-section shauld be classified according to the highest (least favourable) class of ite compression elements. Alternatively, a cross-section may be classified with its compression flange and its web in different classes. Cireular holiow sections should be classified separately for axial compression and for bending. bbe} bebe! Rolled channels Rust cus |v Foran RES or box section, Band b are flange dimensions and D and d are web dimensions. The diatinetian between webs and ‘anges depends upon whether the member is bont about ita major axis or ila minor axis, see 3.5.1. or en RHS, dimensions b end d are defined in fotnote +t0 Table 12. Figure § — Dimensions of compression elements (continued overleaf) © B61 05-2001 29BS 5950-1:2000 Section 3 iT ‘Welded box sections |: Foran RHS or box section, B and b are lange dimensions and D and d are web dimensions. The distinction between webs and ‘anges depends upon whether the member is bont about ite major exis or ite minor axa, ceo 85-1. For an RHS, dimensions 6 and d are defined in footnote *to Table 12 }> Foran angle, bis the width ofthe outstand leg and dis the width of the connected leg, Figure 5 — Dimensions of compression elements (continued) 3.5.2 Classification ‘The following classification should be applied = Class 1 plastic: Cross-sections with plastic hinge rotation capacity. Elements subject to compression that meet the limite for clase 1 given in Table 11 or Table 12 should be classified as class 1 plastic. — Class 2 compact: Cross-sections with plastic moment capacity. Elements subject to compression that meet the limits for class 2 given in Table 11 or Table 12 should be classified as class 2 compact. — Class 3 semi-compact: Cross-sections in which the stress at the extreme compression fibre can reach the design strength, but the plastic moment capacity cannot be developed. Elements subject to compression that meet the limits for class 3 given in Table 11 or Table 12 should be classified as class 3 semi-compact. — Clase 4 slender: Cross-sections in which it is necessary to make explicit allowance for the effects of local buckling. Elements subject to compression that do not meet the limits for claes 3 semi-compact given in Table 11 or Table 12 should be classified as class 4 slender. 30 © BST 05.2001,Section 3 BS 5950-1:2000 ————— 3.5.3 Flanges of compound I- or H-sections ‘The classification of the compression flange of a compound section, fabricated by welding a flange plate to a rolled I- or H-section should take account of the width-to-thickness ratios shown in Figure 6 as follows: a) the ratio of the outstand 6 of the compound flange, see Figure 6a), to the thickness T of the original flange should be classified under “ouisiand element of compression flange-rolled section”, see Table 11; b) the ratio of the internal width b, of the plate between the lines of welds or bolts connecting it to the original flange, eee Figure Gb), to the thickness t, ofthe plate should be classified under “internal element of compression flange’, see Table 11; ©) the ratio of the outstand 8, of the plate beyond the lines of welds or bolts connecting it to the original flange, see Figure 60), to the thickness t, of the plate should be classified under “outetand element of compression flange-welded section”, see Table 11. o. b T° Tt ©) Outstand of compound Nange b, 4 cy bette t bet be 4 1) Internal width of plate © Ouistand of plate Figure 6 — Dimensions of compound flanges 8.54 Longitudinally stiffened elements For the design of compression elements with longitudinal stiffeners, reference should be made to BS 5400-3. ‘© BST 05.2001 arBS 5950-1:2000 Table 11 — Limiting width-to-thickness ratios for sections other than CHS and RHS ‘Compression element Ratio®| Limiting value Giasst | Clase? | Clases plastic | compact |semi-compact lOutstand element of [Rolled section [BT se ide Tse [compression flange felded section _[6/T_ ae oe ise Internal element of [Compression due |b/T BE sae lcompression flange to bending 40e ‘compression |B/T [Not applic [Web of anI-, [Neutral axis at mid-depth ait BE fiooe [1206 |H. or box (Generally? |Ifr,is negative: |d/t 1006 Jsectione itr, [If ry is positive: dit 80e 1006 | 1206 Ter T+ Lor, |1 +20, lout 2 405 out = 408/but = 406 [Axial compression® aie [Not applicable [Web of'a channel — (aie 06 (die |ave (Angle, compression due to bending [ere Be TOE 156 |Both criteria should be satisfied) late ge 106 156 [Single angle, or double angles with the [bir 15e |components separated, axial compression \dft ‘Not applicable 15e |All three criteria should be satisfied) lo aye 24s |Gutstand Teg of an angle in contact ee lee fide hee lback-to-back in a double angle member (Outstand leg of an angle with its back in |continuous contact with another component (Stom of a T-section, rolled or cut fom arolled [Die Be pe ise 1 or H-section = Dimensions 6, D, d, T and tare defined in Figure 6 Pore box oction band Tare flange dimensions and d end fare web ‘and flanges depends upon whether the box section is bent about its major xia re ‘i Je For the web ofa hybrid section ¢ should he based on the design strength pyr of tho anges Jo The stress ration rand rare defined in 3.5.5. ‘© BSI 06-2001Section 3 BS 5950-1:2000 ‘Table 12 — Limiting width-to-thickness ratios for CHS and RHS Compression element Ratio® Limiting value? Clase 1 Clana 8 Clase 3 plastic compact sexal-compact [CHS |Compression due to bending | Dit l40e# 508 1408 [Acrial compression Dit Not applicable Eco [Fir [Flange [Compression due to [Blt Bae ade IRHS bending lout < 80s—dle |but = 62¢—0.5dit |aoe [Axial compression |b/t INot applicable Web Neutral axieat [dit ae 806 20s mid-depth [Generally [ale eae ‘806 1206 T+ 067, itn, T+2r, Ibut 2 405 but > 406 lout 2 408 [Axial compression? [dit (Not applicable [OF [Flange [Compression due to [6/t 265 28 RES bending lout <72¢-are |but < 54¢-o.5dit ane [Axial compression? [B/¢ Not applicable Neutral axis at [dle Bee rE 105e ‘mid-depth [Generally ait 106 1056 ier T+2ry but = 35¢ out = 36e [Axial compressioné [aft [Abbreviations CF Cold formed; |CHS Circular hollow section — including welded tube; IHF Hot finished; IRHS Rectangular hollow section — including square hollow seetion. Foran BS, ue deans ad dahl be tba ellos —for HF RHS t BS EN 10210: b= B~3k CErGrausteBeaNioaim $2B-30 d2b=00 land 8, Dand tare defined in Figure 5, For an RES auhjct to bending B and b are always Sango dimensions and D and dare always web dimension, but the definition of which side of the RHS are webe and which are Manges ebanges according tothe aris of bending, 00 3.51. > The parameter £ =(276p,)5, | For RHS subject to momenta about both exes see H.3 Je Theatres ration and rare defined in 2.6.5. © BST 05-2001 33BS 5950-1:2000 Section 3 3.5.5 Stress ratios for classification ‘The stress ratios r; and ry used in Table 11 and Table 12 should be determined from the following: 4) for I- or H-scotions with equal flanges: =e hw "1? apie batters ne 2 Aeon ) for I- or H-sections with unequal flanges: lens ©) for RHS or welded box sections with equal flanges: F ry = gyn but -1 0.6P,: — for class 1 plastic or class 2 compact cross-sections: M= py(S ~ PS) — for class 3 semi-compact cross-sections: M,=pj(Z-pS/L.6) or alternatively M,=p,(S.q-0S)) — for clase 4 slender cross-sections: M,= py(Gan~PS/I.8) in which S, is obtained from the following: —for sections with unequal flanges: S,=8-5; in which S; is the plastic modulus ofthe effective section excluding the shear area A, defined in 4.28; — otherwise: S, isthe plastic modulus of the shear area A, defined in 4.2.3; and pis given by: p=RUyA)—1F NOTE The redueton factor stars when F exceeds 0.57, bt the remiking eduction in moment apa mele unessF ‘Aernatively, for class 3 semi-compact cross-sections reference may be made to H.8, or for class 4 slender cross-sections reference may be made to 3.6 and H.3. If the ratio dit exceeds 706 for a rolled section, or 62¢ for a welded section, the moment capacity should be determined allowing for shear buckling in accordance with 4.4.4. © BSTOS-2001BS 5950-1:2000 Section 4 4.2.5.4 Notched ends Yor notched ends of l, H or channel section members the moment capacity M, should be taken as follows. a) Low shear: where F, < 0.75P,: — for singly notched ends: M.=PyZ — for doubly notched ends: M, = pytd'¥6 1) High shear: where F, > 0.75P,: — for singly notehed ends: M, = 1.5p,241-(/P,)° — for doubly notched ends: M, = (pytd?/4yfi-F/P where d__ is the residual depth of a doubly notched end; Z isthe relevant section modulus of the residual tee at a singly notched end. 4.2.5.5 Bolt holes No allowance need bé made for bolt holes in a compression flange (or leg). No allowance need be made for bolt holes in a tensios flange (or leg) if, for the tension element: net = OK, where a, isthe area of the tension element; ‘not is the net area of the tension element after deducting bolt holes; K, is the factor for effective net area given in 3.4.3. Noallowance need be made for bolt holes in the tension zone of a web unless there are also bolt holes in the tension flange at the same location. Furthermore, no allowance need be made for bolt holes in a web if the condition given above is satisfied when both a and a, ne, are based upon the complete tension zone, comprising the tension flange plus the tension zone af the web. Ti a4.not i less than aK, then an effective net area of Kc; not may be used. 4.3 Lateral-torsional buckling 43.1 General Unless a beam or cantilever has full lateral restraint to its compression flange as described in 4.2.2, thon in addition to satisfying 4.2 its resistance to lateral-torsional buckling should also be checked, Generally the resistance of a member to lateral-torsional buckling should be checked as detailed in 4.3.2, 4.3.8, 4.3.4, 4.3.5, 4.8.6, 4.3.7 and 4.8.8. However, for members that satisfy the conditions given in G.1, advantage may be taken of the methods for members with one flange restrained given in G.2. 4.8.2 Intermediate lateral restraints develop the required buckling resistance moment, these restraints should have sufficient stiffness and strength to inbibit lateral movement of the compression flange zelative to the supports. ery © BST 05-2001Section 4 BS 5950-1:2000 Intermediate lateral restraints should generally be connected to the member as close as practicable to the ‘compression flange and in any case closer to the level of the shear centre of the compression flange than to the level of the shear centre of the member. However, if an intermediate torsional restraint, see 4.3.8, also provided at the same cross-section, an intermediate lateral restraint may be connected at any level. 43.2.2 Restraint forces 4,3.2.2.1 Where intermediate lateral restraint is required at intervals within the length of a beam or cantilever, the intermediate lateral restraints should be capable of resisting a total force of not less than 2.5 % of the maximum value of the factored force in the compression flange within the relevant span, divided between the intermediate lateral restraints in proportion to their spacing, ‘The intermediate lateral restraints should either be connected to an appropriate system of bracing capable of transforring the restraint forces to the effective points of support of the member, or else connected to an independent robust part of the structure eapable of fulfilling a similar function, Where two or more parallel ‘members require intermediate lateral restraint, itis not adequate merely to connect the members together such that they become mutually dependent. 4,3.2,2.2 Whete three or more intermediate lateral restraints are provided, each intermediate lateral restraint should be capable of resisting a force of not less than 1% of the maximum value of the factored force in the compresoion flange within the relevant span. ‘The bracing system should be capable of resisting each of the following alternatives: 8) the 1 % restraint force considered as acting at only one point at a time; +) the 2.5 % restraint force from 4.3.2.2.1, divided between the intermediate lateral restraints in proportion to their spacing. 4,3,2.2.8 Bracing ystems that supply intermediate latoral restraint to more than one member should be designed to resist the sum of the lateral restraint forces from each member that they restrain, determined in gccordance with 4.8.2.2.1 and 4.3.2.2.2, reduced by the factor k, obtained from: = (0.2 + UNS in which N, is the number of parallel members restrained. 4,8.2.2.4 Purlins adequately restrained by sheeting need not normally be checked for forces eaused by restraining rafters of roof trusses or portal frames that carry predominantly roof loads, provided that either: a) there is bracing of adequate stiffness in the plane of the rafters; or bb) the roof sheeting is capable of acting as a strossed-skin diaphragm, see BS 5950-9. 4.8.8 Torsional restraints A member may be taken as torsionally restrained (against rotation about its longitudinal axis) at any point in ite length where hoth flanges are held in position relative to each other in the lateral direction, by external means not involving the lateral stiffness or resistance of the flanges themselves. Full torsional restraint at member supports (as distinet from nominal torsional restraint at member supports, see 4.2.2), should generally be provided in the form of lateral restraint to both flanges, or by similar means to intermediate torsional restraints. Alternatively, full torsional restraint at member supports may be provided by bearing stiffeners as recommended in 4.5.7. Intermediate torsional restraints within the length of the member may be provided by means of suitable diaphragms between two similar members, or olse by equivalent panels of triangulated bracing. Each torsional restraint should be capable of resisting a couple comprising two equal and opposite forces, acting at a lever arm equal to the depth betwoon the centroids of the flanges, each equal to the larger of: a) 1 % of the maximum value of the factored force in the compression flange within the relevant span; b) 2.5 % of the maximum value of the factored foree in the compression flange within the relevant span, divided between the intermediate lateral restraints in proportion to their spacing. ‘© BST 06-2001 6BS 5950-1:2000 Section 4 4.8.4 Destablizing load ‘The destabilizing loading condition should be taken where a load is applied to the top flange of a beam or a cantilever, and both the load and the flange are free to deflect laterally (and possibly rotationally alac) relative to the eentroid of the cross-section. Otherwise the normal leading condition should be assumed, 4.3.5 Effective length for lateral-torsional buckling 4.3.5.1 Simple beams without intermediate lateral restraints The effective length Lz for lateral-torsional buckling of a simple beam with restraints at the ends only, should be obtained from Table 13, taking the segment length Iy77 as equal to the span L of the beam. Ifthe restraint conditions at each end differ, the mean value of Ly should be taken, The conditions of restraint against rotation of flanges on plan at member supports should be assessed taking into account the stiffness of the connections as well as the stiffness of the supporting members or other construction supplying restraint at the supports. 4.3.5.2 Simple beams with intermediate lateral restraints The effective length Lg for lateral-torsional buckling of a simple beam with intermediate lateral restraints should be taken as 1.0L,7 for normal ioading conditions or 1.2Z;,y for the destabilizing loading condition (oe 4.8.4), where Lypis the length of the relevant segment between adjacent Interal restraints. For the segment between a support and the adjacent intermediate lateral restraint, account should be taken of the restraint conditions at the support. The effective length Lg should be taken as the mean of the value given above and the value given by Table 13 for the restraint conditions at the support, taking Li7 cas the length of the segment between the support and the lateral restraint in both cases. . 4.3.5.3 Beams with double curvature bending In the case of contimibus beams or other members subject to double curvature bending, consideration ‘should be given to the regions subject to sagging moments and hogging moments as follows. a) For a beam with intermediate lateral restraints to each flange, the segment length Zyy and the effective length Ly for lateral-torsional buckling should be determined as for a simple beam as given in 4.5.6.2 in hogging moment regions as well as in sagging moment regions, The lateral restraints to the compression flange of each region should extend up to or beyond the points of contraflexure. b) For a beam with intermediate lateral restraints to the compression flange in the sagging moment region only, for the sagging moment region the segment length Lyy and effective length Lg for late torsional buckling should be determined as for a simple beam as given in 4.8.5.2, lateral buckling resistance of the beam to the moments in the bogging moment regions should be determined ‘using G.2, ©) For a beam directly supporting a concrete or composite floor or roof slab that provides full Jatoral ‘restraint to the top flange, see 4.2.2, the lateral buckling resistance of the beam to the moments in the ‘hogging moment regions should be determined using G.2. @) For a beam directly supporting a concrete ar compasite floor or roof slab that provides both lateral and torsional restraint to the top flange, an allowance may be made for this torsional restraint by assuming virtual lateral reetraints to the bottom flange at the points of contraflexure when determining the segment length Lyr. In the absence of better information, torsional restraint of the top flange may be assumed if the depth of the beam is less than 550mm and tho slab is either: — a composite alab with profiled steel sheeting, see BS 5960-4, designed to act compositely with the steel beam, see BS 6950-3.1; or — a eolid in situ concrete slab with a depth of not less than 25 % of the beam depths, designed to be continuous over the beam. ‘These virtual restraints should not be assumed if another form of allowance is made for the torsional restraint of the top flange by the slab. Lateral restraint of the bottom flange should not be assumed at a point of contraflexure under other restraint conditions, unless a lateral restraint is actually provided at ‘that point. 46 ‘© BST 08-2001