Estimation of Web Distortion Effect on the Elastic and Plastic Limiting Lengths for Lateral Torsional Buckling through the Web Strain Results

Abstract

The present study is aimed to estimate the influence of the web distortion on the elastic (L-r) and plastic ( L-p) limiting lengths given in the American Institute of Steel Construction (AISC code) for the lateral torsional buckling behavior of steel beams. For this aim, the W44x335 beam is adopted in the buckling analyses carried out by the ABAQUS finite element (FE) program. The strain results at mid-height of the web at mid-span of the beam are taken into account as monitoring parameters. The web strain results are found highly greater than the yield strain value when L/L-r is equal to 1.0. Hence, the elastic limiting length (L-r) is required to be considered greater than the calculated length as per the code formulation. The section is obtained to reach the maximum strain value at the web before the unbraced length (L) is equal to the plastic limiting length (L-p). Therefore, the calculated L-p is estimated with the given analytical formulation to be highly shorter than the length through the FE analysis. These outcomes prove that the formulations of the limiting lengths proposed in the AISC code don't consider the influence of the web distortion that is predicted to lead to reducing the torsional and warping rigidity of the section. With the study, it is proposed to determine a reduction coefficient by performing more numerical analyzes for different cross sections and free openings in the regulation.