Prediction of residual stresses in high-strength S690 cold-formed square hollow sections using integrated numerical simulations

In general, residual stresses are induced in structural members during various fabrication processes, such as welding, bending, press-braking, folding, flame cutting and punching. The presence of those residual stresses in cold-formed square hollow sections (CFSHS) primarily caused by i) transverse bending (or cold-forming), and ii) longitudinal welding, is widely considered to have modified both initial stress and strain conditions of these steel members significantly. Hence, these residual stresses are widely considered to have significant adverse effects onto the structural performance of these CFSHS under various actions. In order to examine and quantify both magnitudes and distributions of these residual stresses in S690 CFSHS, an investigation is undertaken to measure residual stresses due to transverse bending and longitudinal welding. Moreover, an approach of integrated numerical simulations is adopted in which a total of three co-ordinated finite element models are established together with various element types and block data transfers to generate compatible meshes for the following three analyses: i) two-dimensional plane-strain bending analyses with large plastic deformations and springback, ii) three-dimensional heat transfer analyses for transient temperature distributions under a heat source, and iii) three-dimensional thermomechanical analyses for welding-induced residual stresses. The predicted results of these three analyses have been carefully calibrated against various experimental data, such as surface temperatures during welding, and residual stresses and strains after welding. Good comparisons between the measured and the predicted data of these S690 CFSHS are demonstrated. The complete residual stress distributions within typical S690 CFSHS due to transverse bending and longitudinal welding are illustrated in three-dimensional plots while simplified residual stress patterns of these sections with specific values and parameters are also provided for subsequent advanced structural analyses and design. The proposed modelling technique for transverse bending and longitudinal welding with compatible meshes of two-dimensional and three-dimensional models with various element types and block data transfers is demonstrated to be highly effective. The technique is readily applicable to simulate residual stresses of all fabricated sections manufactured with transverse bending and longitudinal welding, and, thus, the simulated residual stresses can be employed in subsequent structural analyses of all fabricated members.