Local buckling behaviour and design of laser-welded stainless steel I-section stub columns after exposure to elevated temperatures

Abstract

Laser welding is a high precision joining technique that uses a focused laser beam to fuse metals with minimal heat input. Compared with conventional arc welding, it produces deep and narrow welds with limited thermal distortion and reduced residual stresses, thereby ensuring high fabrication accuracy and favourable mechanical performance. Recently, laser-welded stainless steel structural members have been gaining attraction in offshore and marine engineering applications, where durability and corrosion resistance are critical. Nevertheless, stainless steels exhibit pronounced degradation in mechanical properties when exposed to elevated temperatures, highlighting the necessity for reliable assessments of post-fire residual resistances to support cost-effective retrofitting and reuse. This paper presents experimental and numerical studies on the local buckling behaviour and residual cross-section compression resistances of laser-welded stainless steel I-section stub columns after exposure to elevated temperatures. An experimental study was firstly performed, which included heating and cooling of stub column specimens as well as post-fire initial local geometric imperfection measurements and 24 concentric compression tests, with the exposure temperatures ranging from 30 °C to 1000 °C and their influences on post-fire residual resistances discussed. A subsequent numerical study was conducted to repeat the test results and used to carry out parametric studies to generate additional numerical data. Due to the lack of specific design codes for stainless steel structures after exposure to elevated temperatures, the relevant design rules at ambient temperature, as given in the European code, American specification and continuous strength method, were evaluated, using post-fire material properties, for their applicability to laser-welded stainless steel I-section stub columns after exposure to elevated temperatures. The evaluation results revealed that (i) two sets of codified ambient temperature slenderness limits were accurate and safe when used for cross-section classification of laser-welded stainless steel I-section stub columns after exposure to elevated temperatures, (ii) both design codes led to slightly conservative post-fire residual resistance predictions, and (iii) the continuous strength method resulted in an improved level of design accuracy and consistency over the codified design rules, owing to the rational consideration of the favourable strain hardening of stainless steels and constituent plate element interactions within cross-sections.