1 Glossary1 strengthThe capacity of resisting failure in member cross-section material or connection. Strength checking aims at preventing failure of structural members or connections from exceeding the material strength.2 load-carrying capacityThe largest internal force that a structure or member can bear without failure from strength, stability or fatigue, etc., or the largest internal force at the onset of failure mechanism in plastically analyzed structures; or the internal force generating a deformation that hinders further loading.3 brittle fractureIn general, the suddenly occurred brittle fracture of a steel structure subject to tensile stress without warning by plastic deformation.4 characteristic value of strength5 design value of strengthThe value obtained from division of the characteristic value of strength of steel or connection by corresponding partial factor of resistance.6 first order elastic analysisThe elastic analysis of structure internal forces and deformation, based on the equilibrium condition of undeformed structure, taking no account of the effect of the second order deformation on infernal forces.7 second order elastic analysisThe elastic analysis of structure internal forces and deformation, based on the equilibrium condition of deformed structure, taking account of the effect of the second order deformation on internal forces.8 bucklingAn abrupt large deformation, not conforming to the original configuration of members or plates subject to axial force, bending moment or shear force, and thereby causing loss of stability.9 post-buckling strength of web plateThe capacity of web plates to bear further loading after buckling.10 normalized web slendernessParameter, equal to the square root of the quotient of steel yield strength in flexion, shear or compression by corresponding elastic buckling stress of web plates in flexion, shear or local compression.11 overall stabilityAssessment of the possibility of buckling or loss of stability of structures or structural numbers as a whole under the action of external loading.12 effective widthThat part of plate width assumed effective in checking the section strength and the stability.13 effective width factorRatio of the effective width to the actual width of a plate element.14 effective lengthThe equivalent length of a member obtained by multiplying its geometrical length within adjacent effective restraining points by a coefficient taking account of end deformation condition and loading condition. The length of welds assumed in calculation of the strength of welded connections.15 slenderness ratioThe ratio of member effective length to the radius of gyration of its cross-section.6 equivalent slenderness ratioThe slenderness ratio transforming a laced or battened column into solid-web one according to the principle of equal critical force for checking the overall stability of axially compressed members. The slenderness ratio transforming a flexural-torsional buckling and torsional buckling into flexural buckling.17 nodal bracing forceForce to be applied at the location of lateral support installed for reducing the unsupported length of a compression member (or compression flange of a member).This force acts in the direction of member buckling at the shear center of the member section.18 unbraced frameFrames resisting lateral load by bending resistance of members and their connections.19 frame braced with strong bracing systemA frame braced with bracing system of large stiffness against lateral displacement (bracing truss, shear wall, elevator well, etc.), adequate to be regarded as frame without sidesway20 frame braced with weak bracing systemA frame braced with bracing system of weak stiffness against lateral displacement, inadequate to be regarded as frame without sidesway.21 leaning columnA column hinged at both ends and not capable of resisting lateral load in a framed structure.22 panel zone of column webThe zone of column web within the beam depth at a rigid joint of frame.23 spherical steel bearingA hinged or movable support transmitting force through a spheric surface allowing the structure to rotate in any direction at the support.24 composite rubber and steel supportA support transmitting end reaction through a composite product of rubber and thin steel plates satisfying the displacement requirement at the support.25 chord memberMembers continuous through panel points in tubular structures, similar to chord members in regular trusses.26 bracing memberMembers cut short and connected to the chord members at panel points in tubular structures, similar to web members in regular trusses.27 gap jointJoints of tubular structures where the toes of two bracing members are distant from each other by a gap.28 overlap jointJoints of tubular structures where the two bracing members are overlaping.29 uniplanar jointJoints where chord member is connected to bracing members in a same plane.30 multiplannar jointTubular joints where chord member is connected to bracing members in different planes.-31 built-up memberMembers fabricated by joining more than one plate members (or rolled shapes), such as built-up beams or columns of I- or box-section.-32 composite steel and concrete beamA beam composed of steel beam and concrete flange plate, acting as an integrated member by means of shear connectors.2 Strength1 The bending strength of solid web members bent in their principal planes shall be checked as follows:y x x nx y nyM M f W W γγ+≤ where M x , M y —bending moments about x - and y - axes at a common section (for I-section, x -axis is the strongaxis and y is the weak axis);W nx , W ny —net section moduli about x - and y -axis;γx , γy —plasticity adaptation factors, γx =1.05, γy =1.20 for I-section, γx , γy =1.05 for box section; f —design value of bending strength of steel.When the ratio of the free outstand of the compression flange to its thickness is larger than y 13235/f , but not exceeding y 15235/f , γx shall be taken as 1.0. f y is the yield strength of the material indicated by the steel grade.For beams requiring fatigue checking, γx =γy =1.0 should be used.2 The shear strength of solid web members bent in their principal plane shall be checked by the following formula (for members taking account of web post-buckling strength:v wVS f It τ=≤ where V —shear force in the calculated section along the plane of web;S —static moment about neutral axis of that part of the gross section above the location where shear stressis calculated;I —moment of inertia of gross section;t w —web thickness;f v —design value of shear strength of steel.3 When a concentrated load is acting along the web plane on the upper flange of the beam, and that no bearing stiffener is provided at the loading location, the local compressive stress of the web at the upper edge of its effective depth shall be computed as follows:c w zF f t l ψσ=≤ where F —concentrated load, taking into account the impact factor in case of dynamic loading;ψ—amplification coefficient of the concentrated load, ψ=1.35 for heavy duty crane girder; ψ=1.0 forother beams and girders;l z —assumed distribution length of the concentrated load on the upper edge of the effectiveweb depth taken as:z y R 52l a h h =++a —bearing length of the concentrated load along the beam span, taken as 50mm for wheelloading on rail;h y —distance from the top of girders or beams to the upper edge of the effective web depth;h R —depth of the rail, h R =0 for beams without rail on top;f —design value of compressive strength of steel.4 In case comparatively large normal stress σ, shear stress τ, and local compressive stress σc (or comparatively large σ and τ) exist simultaneously at the edge of the effective web depth of build –up girders, e. g. at the intermediate support of a continuous girder or at a section where the flange changes its dimensions, the reduced stress shall be checked by the following expression222c c 13f σσσστβ+-+≤where σ, τ, σc —normal stress, shear stress and local compressive stress occurring simultaneously at a same pointon the edge of effective web depth. while σ is determined as follows:1nM y I σ= σ and σc are taken as positive while being tensile and negative while compressive;I n —moment of inertia of the net beam section;y 1—distance from the calculated point to the neutral axis of the beam section;β1—amplification coefficient of design value of strength for reduced stress, β1=1.2 when σ and σc areof different signs, β1=1.1 when σ and σc are of the same sign or when σc =0.3 Overall stability1 Calculation of the overall stability of the beams may not be needed when one of the following situations takes place:A rigid decking (reinforced concrete slab or steel plate) is securely connected to the compression flange of the beam and capable of preventing its lateral deflection;2 Except for the situations specified in Clause 1, members bent in their principal plane of largest rigidity shall be checked for overall stability as follows:x b xM f W ϕ≤ where M x —maximum bending moment about the strong axis;W x —gross section modulus of the beam with respect to compression fibers;ϕb —overall stability factor determined according to Appendix B.3 Except for the situations specified in Clause 1, H- and I-section members bent in their two principal planes shall be checked for overall stability as follows:y x b x y yM M f W W ϕγ+≤ where W x , W y —gross section moduli about x- and y- axes with respect to compression fibers;ϕb —overall stability factor for members bent about the strong axis.4 Simply supported box section beams not conforming to the first situation specified in Clause 1 shall have their cross section dimension meeting the relationships h /b 0≤6 and 10y /95(235/)l b f ≤.Simply supported box section beams fulfilling the above requirement may not be checked for overall stability.5 Detailing measures shall be taken to prevent twisting of the section at beam end supports.6 Members subjected to combined axial load and bendingSolid web beam-columns bent in their plane of symmetric axis (about x -axis) shall have their stability checked as follows.（1） In-plane stability:mx x x x 1x Ex(10.8)M N f N A W N βϕγ+≤-' where N —axial compression in the calculated portion of the member;ExN '—parameter, 22Ex x /(1.1)N EA πλ'=; ϕx —stability factor of axially loaded compression members buckling in the plane of bending;M x —maximum moment in the calculated portion of the member;W 1x —gross section modulus referred to the more compressed fiber in the plane of bending;βmx —factor of equivalent moment , taken as follows:1) For columns of frames and for members supported at the two ends:(1) In the case of no transverse load: βmx =0.65+0.35M 2/M 1, where M 1 and M 2 are end moments taken asof same sign for members bent in single curvature (without inflexion point) and of different signs formembers bent in reverse curvatures (with inflexion point), |M 1|≥|M 2|;(2) In the case of having end moments combined with transverse load: βmx =1.0 for members bent insingle curvature and βmx = 0.85 for members bent in reverse curvatures;(3) In the case of having transverse loads and no end moments: βmx =1.0;2) For cantilevers, columns of pure frame not taking account of 2nd order effect in stress（2）Out-of-plane stability:tx x y b 1xM N f A W βηϕϕ+≤ where ϕy — stability factor of axially loaded compression members buckling out of the plane of M x ;ϕb — overall stability factor of beams under uniform bending;M x —maximum moment in the calculated member portion;η —factor of section effect, taken as η = 0.7 for box section and η = 1.0 for others;βtx — factor of equivalent moment, taken as follows:1) For members with lateral supports, βtx shall be determined according to loading and internal force situation in the member portion between two adjacent supporting points as follows:(1) In the case of no transverse load within the calculated portion: βtx = 0.65 + 0.35M 2/M 1 , where M 1 and M 2 are end moments in the plane of bending, taken as of same sign for member portions bentin a single curvature and of different signs for member portions bent in reverse curvatures;|M 1|≥|M 2|;(2) In the case of having end moments combined with transverse loads within the calculated portion:βtx =1.0 for member portions bent in single curvature, βtx =0.85 for those bent in reverse curvatures;(3) In the case of having transverse loads and no end moment within the calculated portion: βtx = 1.0.2) For members acting as cantilevers out of the plane of bending βtx =1.0.7 Laced or battened beam-columns bent about the open web axis (x -axis) shall be checked for in-plane stability by the following formula:mx x x 1x x Ex(1)M N f N A W N βϕϕ+≤-' where x 1x 0I W y =, I x being the moment of inertia of the gross area about the x -axis, y 0 being the distance from the x -axis to the axis of the more compressed component or to the outside face of web of this component, whicheveris larger; x ϕand ExN 'shall be determined using the equivalent slenderness ratio. The overall out-of-plane stability of the member may not be checked in this case, but the stability of components shall be checked. The axial force of these components shall be determined as in the chords of trusses. For battened columns, bending of the components due to shear force shall be taken into account.8 Laced or battened beam-columns bent about the solid web axis shall have their in-plane and out-of-plane stability checked in the same way as solid web members, but the equivalent slenderness ratios shall be used for out-of-plane overall stability calculation and ϕb taken as 1.0.9 Doubly symmetrical I- (H-) and box (closed) section beam-columns bent in two principal planes, shall be checked for stability by the following formulae:t y y m x x x b y y x x Ex(10.8)M M N f N A W W N ββηϕϕγ++≤-' my y tx x y bx x y y Ey(10.8)M M N f N A W W N ββηϕϕγ++≤-' Where ϕx , ϕy —stability factors of axially loaded compression members about the strong axis x -x and the weakaxis y -y ;ϕbx , ϕby —overall stability factors of beams under uniform bending;M x , M y —maximum bending moment about the strong and the weak axes in the calculated memberportion;ExN ', Ey N '—parameters, 22Ex x π/(1.1)N EA λ'=, 22Ey y π/(1.1)N EA λ'=; W x , W y —gross section moduli about the strong and the weak axes;βmx , βmy —factors of equivalent moment;βtx , βty —factors of equivalent moment;10 The stability of laced (or battened) beam-columns with two components bent in two principal planes shall be checked as follows:Overall stabilityty y mx x x 1y 1x x Ex(1)M M N f N A W W N ββϕϕ++≤-' Where W 1y —gross section modulus referred to the more compressed fiber under the action of M y .11 Axially loaded membersThe strength of members subject to axial tension or compression, except at high strength bolted friction-type connections, shall be checked as follows:n N f A σ=≤ where N — axial tension or compression;A n —net sectional area.The strength of member at a high-strength bolted friction-type connection shall be checked by the following formulae:1n(10.5)n N f n A σ=-≤ and N f Aσ=≤ where n — number of high-strength bolts of one end of the member at a joint or a splice;n 1— number of high-strength bolts on the calculated section (outermost line of bolts);A — gross sectional area of the member.The stability of axially loaded compression solid web members shall be checked as followsN f Aϕ≤ where ϕ —stability factor of axially loaded compression members.4 Local stability1 Stiffeners shall be provided for webs of built-up girders in accordance with the following provisions:(1). When 0w /h t ≤y 80235/f , transverse stiffeners shall be provided for girders with local compressivestress(σc ≠0) in accordance with detailing requirements, but may not be provided for girders without local compressive stress(σc =0).(2). Transverse stiffeners shall be provided in case 0w y /80235/h t f >, among which, when0w y /170235/h t f >(twisting of compression flange is restrained, such as connected with rigid slab, surge plateor welded-on rail) or 0w y /150235/h t f >(twisting of compression flange not restrained), or demanded bycalculation, longitudinal stiffeners shall be added in the compression zone of large flexural stress panels. For girders with considerable local compressive stress, additional short stiffeners should also be provided if necessary.h 0/t w shall in no case exceed 250.In the above, h 0 is the effective web depth (for monosymmetric girders, h 0 shall be taken as twice the height of compression zone h c in judging whether longitudinal stiffeners are necessary), t w is the web thickness.(3). Bearing stiffeners shall be provided at girder supports and anywhere a fixed and comparatively large concentrated load is applied on the upper flange.2 Panels of girder webs provided solely with transverse stiffeners shall be checked for local stability by thefollowing expression22c cr cr c, cr 1σστστσ⎛⎫⎛⎫++≤ ⎪ ⎪⎝⎭⎝⎭ where σ—bending compressive stress at the edge of effective depth of the web caused by the average bendingmoment in the calculated web panel;τ—mean shear stress of the web caused by the average shear force in the calculated web panel, ()w w V h t τ=, h w being the web depth.σc —local compressive stress at the edge of effective depth of the web, calculated with formula , buttaking ψ=1.0;σcr , τcr , σc, cr —critical value of bending-, shear- and local compressive stress.3 Local stability of compression membersThe ratio of free outstand, b , of a flange to its thickness, t , in compression members shall conform to the following requirements:（1） Axially loaded compression membersb t≤(10+0.1λ)y 235f where λ —the larger of the slenderness ratios of the member in two directions, taken as 30 when λ<30, and as100 when λ>100.（2） Beam-columnsb t≤13y 235f b /t may be enlarged to 15y 235/f in case γx =1.0 is used for strength and stability checking.Note: The free outstand b of the flange shall be taken as follows: the distance from the face of the web to the flange tip forwelded members; the distance from the toe of the fillet to the flange tip for rolled members.4 The ratio of effective web depth, h 0, to thickness, t w , in I-section compression members shall conform to the following requirements:（1） Axially loaded compression members0wh t ≤(25+0.25λ)y 235f where λ — the larger of the slenderness ratios of the member in two directions, taken as 30 when λ < 30, and as100 when λ > 100.（2） Beam-columns0wh t ≤(16α0+0.5λ+25)y 235f , when 0≤α0≤1.6 0wh t ≤(48α0+0.5λ–26.2)y 235f , when 1.6<α0≤2max min 0maxσσασ-=where max σ— maximum compressive stress on the edge of effective web depth, not taking account of thestability factor of the member, nor the plasticity adaptation factor of the section;min σ— corresponding stress on the other edge of effective web depth, taken as positive for compressionand negative for tension;λ — slenderness ratio in the plane of bending, taken as 30 when λ<30 and as 100 when λ>100. 5 whereas the ratio of the effective web depth, h 0, to thickness, t w , shall conform to the following requirements:（1） For axially loaded compression members, 0w h t ≤y23540f 6 The depth-to-thickness ratio of the web in T-section compression members shall not exceed the following values:(1) Axially loaded compression members and beam-columns in which bending moment causes tension on thefree edge of the web:For hot-rolled cut-T section (15 + 0.2 λ)y 235fFor welded T-section (13 + 0.17 λ)y 235f(2) Beam-columns, in which bending moment causes compression on the free edge of the web: 15y 235f , when α0≤1.0 18y 235f , when α0 > 1.07 The ratio of outside diameter to wall thickness of circular tubes subject to compression shall not exceed 100 (235/f y ).。