土木工程专业英语教学作者陈瑛53SteelBeams.ppt

单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,Chapter 5-3 Steel Beams,Characterisitics of Axially Loaded Members,Characteristics,Carry lateral loads,May be cantilevered,simply supported,fixed ended or continuous,Main uses,Support floors&columns,Carry roof sheeting as purlins,Side cladding as sheeting rails,Sections,I-and H-sections,most efficient section to resist uniaxial bending,Compound beam,-beam depth is limited;not strong enough to carry load,Crane beam,resist bending in both horizontal and vertical directions,Beam section may be uniform or non-uniform,Sections may be strengthened in regions of maximum moment by adding cover plates or haunches,Design criteria,Flexural strength criterion,Shear strength criterion,Criteria for concentrated loads,Deflection criterion,Strength in Bending(Flexure),Two types of beams,Laterally supported beam,Lateral buckling is prevented by adequately lateral support,Failure occurs by yielding,Plastic moment capacity can be reached,Laterally unsupported beam,Have greater strength and stiffness while bending about major axis,Without lateral bracing,failure occurs as lateral torsional buckling,Laterally supported beam,Compact sections,Width to thickness ratio is small,Beam can be fully plastified and reach plastic moment,Plastic sections,Section can sustain moment during additional plastic hinge rotation till failure mechanism is formed,Non-compact sections,Width to thickness ratio is larger,Compression flange may buckle locally before complete plastification occurs,Slender sections,Width to thickness ratio is sufficiently large,Local buckling of compression flange may occur even before extreme fibre yields,Design consideration,Using stiffeners to prevent web buckling,Transverse and longitudinal stiffeners are both used to stiffen the web,General considerations,Flanges are assumed to resist bending moment,Web provides resistance to shear force,For economic design,low flange size and deep webs are provided,Shear failure mode is buckling rather than yielding for web,Webs are vulnerable to buckling and hence stiffened if necessary,Design of beams and girders with solid webs,Flanges,Flange thickness not varied along beam span,Suitable breadth to thickness ratio of flange is chosen to make section be plastic or compact only(avoid local buckling),Flange plate may be curtailed at a distance from the maximum bending moment point,Connections,Flange joints should not be located at the points of main bending moment,Rivets/bolts or weld connecting the flanges and the web will be subjected to horizontal shear and sometimes vertical loads,Web splices are generally not used in buildings,they are mainly used in bridges,Splices in the web are designed to resist shear and moment at the spliced section,Stiffener Design,Stiffener classifications,Intermediate transverse web stiffeners,To prevent out of plane buckling of web,Must be sufficiently stiff not to deform appreciably as the web tends to buckle,Must be sufficiently strong to withstand the shear transmitted by web,Load carrying stiffeners,Bearing stiffeners,To resist concentrated loads which may cause vertical buckling of web,Must fit tightly against the loaded flange,Must be adequate against buckling,Connection to web must be sufficient to transmit the load,Torsion stiffeners,Tension stiffeners,Box Girder&Purlin,Box girders,Diaphragm used where external vertical as well as transverse forces are to be transmitted,Diaphragms and fastenings shall be proportioned to forces,Purlin,When attached to compression flange of a main member,it provides full torsional restraints,When attached to tension flange,it provides positional restraint but are unlikely to be capable of preventing twist and bending moment on the lateral instability of compression flange,Brief review for steel beams,Characteristics,Main uses,Support floors and columns,Carry roof sheetings,Sections,Open sections,Compound Sections,Built-up sections,Design criteria,Flextural strength criterion,Shear strength criterion,Criterion for concentrated load,Deflection criterion,Review,Flexural,Laterally supported beam,Laterally unsupported beam,Shear in Beam,Web buckling in diagonal direction,Occurs mainly in regions adjacent to supports or the vicinity of point loads,Web buckling can be avoided if stiffeners are placed correctly,Stiffener Design,Intermediate transverse web stiffener,Load carrying stiffener,Bearing stiffener,Torsion stiffener,Diagonal stiffener,Tension stiffener,