土木工程专业英语课件教学PPT作者陈瑛5.3SteelBeams课件.ppt

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 Laterally unsupported beam Assumptions Compression flange is restrained from moving laterally Any form of local buckling is prevented Failure modes Lateral buckling Distortional buckling Shear in Beams Characteristics shear failure occurs mostly at the webs Most severe condition in terms of web buckling is normally the pure shear case Shear failure occurs