Influence of moment modification factor in lateral torsional buckling of doubly and monosymmetric sections

Simply supported doubly symmetric prismatic beam subjected to uniform moment along the unsupported length is the simplest and basic case in the buckling analysis. The closed form solution for the elastic critical moment was derived based on the assumptions of perfect beam with standard restraint conditions at both ends of the beam. A perfect beam will be having linear-elastic behaviour without any type of geometrical or material imperfections. The standard conditions of restraint at each end of the beam in basic case are restrained against lateral movement, restrained against rotation about the longitudinal axis and free to rotate on plan. But in reality, loading conditions and conditions of restraint will vary widely from the basic case. An equivalent uniform moment factor is typically applied to elastic critical moment to account for the effects of variable moment and end restraints along an unbraced girder length. The values are derived numerically and varies with specifications. In this article equivalent uniform moment factor for IS 800-2007 and Eurocode 3 provisions are compared. The study is also extended to monosymmetric I sections.