Lateral–torsional buckling of hollow tubular flange plate girders with slender stiffened webs

This paper is concerned with the assessment of the lateral–torsional buckling (LTB) of hollow tubular flange plate girders (HTFPGs) with slender stiffened webs. Using the general purpose finite element package ABAQUS, 3-D finite element (FE) models for simply supported HTFPGs subjected to uniform bending are built. First, a preliminary analysis is conducted to compare the HTFPGs with their equivalent I-section plate girders with flat flanges (IPGs). The results indicate that the HTFPGs display larger load-carrying capacities and stiffnesses compared to IPGs especially in the elastic LTB range. In addition, it is found that the inelastic LTB dominates the failure mode for higher spans of HTFPGs compared to equivalent IPGs. Consequently, a parametric study for the HTFPGs is carried out considering two key parameters; namely the radius of gyration of the compression–flange and the section modulus. The results showed that using HTFPGs with less slender webs (i.e. with shorter webs) for medium-to-long spans optimizes the girders by reducing their weight. Additionally, to save the fabrication costs via reducing the weld lengths, it is more significant to increase the hollow tubular flange depth. It is as well found that the AISC and EC3 provide highly conservative predictions for the HTFPGs under bending. A modified AISC design method is, therefore, suggested to predict the flexural strength of the HTFPGs. The results predicted by the proposed method show better agreement with the FE strengths than the values predicted by the AISC and EC3.