Effect of welding and heat treatment on strength of high-strength steel columns

Arc welding is frequently applied to form built-up high strength steel (HSS) box columns from flat plates. Due to the thermal gradients happened in the welding processes, welding residual stresses and geometric imperfections are normally introduced into the columns which can deteriorate the column strength. In the current study, an experimental and finite element analysis study on the strength of built-upHSS box columns under a compressive load was carried out. To evaluate the effect of welding technique and heating treatment on the strength of high strength box columns, two different welding techniques, Flux-Cored Arc Welding (FCAW) and Submerged Arc Welding (SAW), were used in this study. For each welding technique, three different heat treatments including As-Welded condition (AW) without any heat treatment, Preheating (pH) before welding and Post-Weld Heat Treatment (PWHT) were studied. Firstly, the welding residual stresses determined using the hole-drilling method and the initial geometrical imperfections of the columns were carefully measured. After that, the column strength was tested and analysed. Finally, numerical investigations regarding welding residual stress and column strength were conducted to study the effect of welding processes, heat treatment on the strength of built-up high strength steel box columns with different slenderness under compressive load. For both FCAW and SAW fabricated columns, experimental and numerical results show that heating treatment (Preheating and PWHT) could produce a 3%-7% strength improvement depended on the slenderness of the HSS columns. The design approach for HSS columns including the effect of welding technique and different heat treatment was discussed in comparison with existing standards.