Distortional lateral torsional buckling for simply supported beams with web cleats

摘要

Critical moment expressions for steel beams based on elastic lateral torsional buckling as given in classical solutions and present standard provisions are based on assumed fully restrained support conditions and simplifying kinematic assumptions that neglect distortional effects. The present study carefully examines the applicability of such assumptions in the case of simply supported beams with double angle cleat connections. A parametric study based on shell finite element analysis (FEA) is first conducted on steel beams and end connection details of common configurations. It is shown that, throughout buckling: (a) typical cleat angles provide only partial twist restraints to beam ends and (b) beams undergo some distortion not captured in the classical solution, both phenomena resulting in a reduced critical moment capacity. The associated critical moments are then quantified by applying three modifiers to existing design provisions: (1) a partial twist restraint factor based on a potential energy formulation, (2) a distortional coefficient based on regression analysis of FEA results, and (3) a standard dependent factor that ensures consistency in buckling predictions based on various design standards. The modified procedure is shown to yield critical moments that are consistent with those based on FEA buckling simulations. Comparative design examples are then provided to illustrate the merits and applicability of the proposed procedure in practical design situations.