Numerical study and design of thin walled cold formed steel built-up open and closed section columns

摘要

This paper, based on new proposed approaches, is a numerical investigation of the behavior of thin-walled cold-formed steel built-up columns under a uniform compression. Two types of cross sections have been studied, built-up closed and open sections formed by two channels connected by battens plates. First, a nonlinear finite element model has been developed and the results obtained show a good agreement against experimental results, such as the ultimate strength, the type of deformed shapes at failure and the lateral displacement. Second, a new proposed approach based on the DSM approach where the local, distortional or global buckling has been obtained numerically, using finite element method software, the thickness at the contact area in the web is taken as 1.0 times the thickness of the plate “t”, instead of 1.5 or 2.0 times “t”. In this case, the compound section is acting as one rigidly connected section. Comparisons with experimental data give a satisfactory degree of accuracy in the proposed design method (DSM-t) and the results are more conservative than those found by the DSM-1.5 and DSM-2. The results, for either closed or open sections, are also slightly conservative for columns failing in global modes than in local ones, if compared with the AISI and EC3 specifications. Some parameters, such as the spacing channels-web length ratio (B1/D) influence the stability and strength of the built-up columns.