Experimental and numerical investigation of cold-formed sigma sections subjected to bending and torsion moments

Abstract

Cold-Formed Steel (CFS) has gained prominence in the construction industry due to its sustainability and cost-effectiveness. This paper explores the behavior of CFS sigma beams, a monosymmetric profile that deviates from lipped C-sections by incorporating web stiffening to enhance structural efficiency in their applications as flexural members. The beams' behavior is experimentally investigated under eccentric loading, caused by load application offset from the cross-section shear center, combining bending and torsional moments. A total of 24 experimental tests were conducted on simply supported sigma beams with various profiles subjected to eccentric load at mid-span, varying both the thickness and the loading eccentricity. The test setup was designed to induce the required loading and end conditions. These tests were then utilized in the construction of numerical models using Abaqus non-linear finite element analysis (FEA). The numerical models were validated against the experimental test results, showing good agreement in terms of ultimate strength, lateral deformations, and failure modes. Finally, a comparative analysis was conducted comparing the experimental outcomes and the GB 50018-2002 for bending and torsion. The comparison showed that the current code underestimates the sectional capacity by 67 % on average. A modified design equation is proposed to predict the sigma sections subjected to both bending moment and torsion. The proposed equation improved the accuracy significantly, with only 13 % lower estimation on average.