Design rules for stainless steel welded I-columns based on experimental and numerical studies

Stainless steel is characterised by its nonlinear stress-strain behaviour with significant strain hardening, although current design codes treat it as an elastic, perfectly plastic material like carbon steel. The continuous strength method (CSM) is a newly developed strain based design approach which was proposed for nonlinear metallic materials. With recent developments, CSM can be used to predict the cross-section resistance for stocky and slender sections, and CSM design rules have recently been proposed for predicting the buckling resistance of cold-formed RHS and SHS columns. Welded sections, however, could behave differently from cold-formed sections due to the presence of residual stresses. Despite offering more economic options in many design cases, research on stainless steel welded sections is very limited to date. In this study, the behaviour of stainless steel welded I-sections was investigated through a test program, and the investigation was complemented by finite element (FE) modelling. The test program covered tensile coupon tests, residual stress and initial geometric imperfection measurements, stub column tests and flexural buckling tests of pin-ended long columns. FE models were developed for both major and minor axis buckling based on test results, and the verified FE modelling technique was used to investigate the effects of cross-section slenderness λp, section height-to-width ratio H/Band the ratio of flange thickness-to-web thickness tf/tw on column curves of welded I-sections. Buckling formulas for welded I-columns were eventually proposed following the same philosophy recently adopted by the authors for cold-formed hollow section columns. The imperfection parameter was recalibrated appropriately to incorporate special features of welded I-sections. Two sets of equations were proposed to tackle the observed variation in buckling behaviour against major and minor axis buckling. Buckling resistance predictions obtained from the proposed method were deemed reliable showing good accuracy and consistency with test and FE results.