Elastic lateral-torsional buckling strength and torsional bracing stiffness requirement for monosymmetric I-beams

Abstract

Elastic lateral-torsional buckling (LTB) is a common failure mode of large span beams. In this phenomenon the beam becomes unstable along the unbraced length. This instability of beams can be identified by out-of-plane deflection and twisting. Using discrete torsional braces is one of the ways to prevent LTB. In this paper the LTB strength and bracing stiffness requirements of monosymmetric I-beams with discrete torsional braces, under pure bending condition is investigated. First, an analytical solution for an unlimited number of braces is presented by using an energy approach. Then the results of the proposed equations are compared with the results of a 1-D finite element analysis and the equivalent continuous brace stiffness concept. The comparison shows that the proposed equations are in good agreement with the finite element analysis. A parametric study is carried out for various dimensions and geometrical properties of cross sections. The results show that using the monosymmetric I-sections with larger compression flange is the more economical solution. Finally, the effects of linear moment gradient conditions and the cross sectional distortion on the LTB strength and bracing stiffness requirement are investigated.