Numerical Assessment of LTB Resistance Equations of Aisc for Laterally Un-Restrained High Strength Steel I-Shaped Beams

Abstract

To date, numerous research studies have focused on examining the Lateral Torsional Buckling (LTB) behavior of Normal Strength Steel (NSS) beams. Consequently, the current design codes offer extensive guidance for calculating the LTB strength of NSS beams. With the rising popularity of High Strength Steel (HSS) (with a yield strength of fy ≥ 690 MPa or approximately 100 ksi), many design standards now permit the use of HSS up to grades of 690 MPa. However, the AISC 360-22 standard does not yet support the use of HSS, as there is a shortage of sufficient experimental and numerical studies needed to assess the LTB strength of HSS beams. This research aims to numerically investigate the LTB strength of HSS I-shaped beams under various moment gradients. A comprehensive three-dimensional finite element (FE) model of HSS I-beams was created using ABAQUS, incorporating both geometric and material nonlinearities. Since HSS has distinct material and residual stress characteristics compared to NSS, experimentally determined material properties and residual stress patterns unique to HSS were included in the model. The FE model was first validated against existing test results before being used to perform a parametric evaluation. The parametric study considered a wide range of factors, including steel grades, beam lengths, and both linear and non-linear moment gradients, to determine the LTB strength of HSS beams. Finally, the 6 numerical results obtained were compared with the LTB strength values derived from the existing equations in AISC 360-22