The lateral torsional buckling (LTB) resistance equations for rolled and welded Ⅰ-sections differ considerably across the AASHTO/AISC, Eurocode, and other international design codes. These differences stem largely from residual stress and geometric imperfection sensitivity in the inelastic and elastic LTB regions of the curves. AISC/AASHTO employ a resistance calculation method by which the LTB resistance curve is clearly segmented into three distinct parts: the yield or plateau region, the inelastic buckling region and the elastic buckling region. This curve was established on the basis of experimental data, but tends to give larger strengths than common FEA test simulations in many situations. This paper evaluates the sensitivity of LTB resistances to imperfections and residual stresses on compact and on non-compact web sections. The paper then recommends nominal residual stresses and geometric imperfections to be used when conducting FEA simulations to study LTB, as well as modified LTB resistance equations based on evidence from experimental tests and test simulations.
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