Finite Element Analysis of Plastic Bending of Cold-Formed Rectangular Hollow Section Beams (No. R792)

Abstract

This report describes the finite element analysis of rectangular hollow section (RHS) beams, to simulate a series of bending tests. The finite element program ABAQUS was used for the analysis. The main aims of the analysis were to determine trends, to understand the occurrence of inelastic instability, and to attempt to predict the rotation capacity of cold-formed RHS beams. The maximum loads predicted were slightly lower than those observed experimentally, since the numerical model assumed only three distinct material properties in the RHS. In reality, the variation of material properties around the RHS cross-section is gradual. Introducing geometric imperfections into the model was essential to obtain results that were close to the experimental results. A perfect specimen without imperfections achieved rotation capacities much higher than those observed experimentally. Introducing a bow-out imperfection, constant along the length of the beam, as was measured (approximately) experimentally, did not affect the numerical results significantly. To simulate the effect of the imperfections induced by welding the loading plates to the beams in the experiments, the amplitude of the bow-out imperfection was varied sinusoidally along the length of the beam. The size of the imperfections had an unexpectedly large influence on the rotation capacity of the specimens. Larger imperfections were required on the more slender sections to simulate the experimental results. The sensitivity to imperfection size increased as the aspect ratio of the RHS decreased. The finite element analysis determined similar trends as observed experimentally, namely that the rotation capacity was a function of both the flange and web slenderness, and that for a given aspect ratio, the relationship between web slenderness and rotation capacity was non-linear, and the slope of the line describing the relationship increased as the web slenderness decreased.