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Local and lateral-torsional buckling of wide-flange beams
Kwasniewski, Leslaw; Stojadinovic, Bozidar; Goel, Subhash C.
SAC/BD-99/20, [Sacramento, Calif.] : SAC Joint Venture, Report no. ;, 1999, 32p - PDF (610 S73BD 99/20)
A comprehensive investigation of a local and lateral-torsional buckling of wide-flange beams in moment-resisting frames was conducted using finite element models of fully restrained connections in full-span and half-span frame configurations. The scope of the investigation was limited to unreinforced connection designs where the beam flanges are not weakened or strengthened in any way. This study was focused on the effects of beam flange and web slenderness, number and location of lateral supports, and axial deformation restraint on the plastic rotation capacity of the connection. The results of parametric analyses on models with different slenderness characteristics show that beams compact according to the AISC Code criteria can develop 0.03 radian plastic rotation, i.e. sustain a total drift of 4%. Effect of beam web and flange slenderness on plastic rotation capacity is moderate, while the effect of number and location of lateral supports is very small. Axial restraint of beam deformation, provided by the full-span frame, has a small effect evident only at drifts larger than 5%. However, the rate of postpeak resistance degradation in half-span and full-span models is different, requiring the use of different resistance drop rules to evaluate their ultimate rotation capacity. Thus, if a 20% drop rule is used for half-span models, a 10% drop rule should be used for full span models. While the responses of unreduced and (reduced beam) RBS connections are different, the effects of beam slenderness parameters examined in this study are virtually identical. Therefore, the same slenderness code provisions should apply for both unreduced and RBS connections.
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