Flexural buckling and analysis of S690 high strength steel welded π-shaped section columns

High strength steel novel cross-section profiles are increasingly used in the construction industry to meet diverse structural demands. Among these profiles, the π-shaped section, composed of one horizontal flange and two vertical webs, is gaining growing attention in roof trusses and lateral bracing systems. This paper presents an experimental and numerical investigation into the flexural buckling behaviour and resistances of S690 high strength steel welded π-shaped section columns. Initial geometric imperfection measurements and ten pin-ended column tests were firstly conducted to establish a database. The key obtained test results, including the failure loads, load–deformation histories and failure modes with flexural buckling towards the web tips and towards the flange, were reported in detail and discussed. Following the laboratory testing, finite element models were developed and validated against the test results and parametric studies were then performed to expand the test database by generating additional numerical data over a wider range of cross-section dimensions and member effective lengths. Due to the absence of established design rules for steel welded π-shaped section members, the applicability of relevant codified design rules to S690 high strength steel welded π-shaped section columns failing by flexural buckling was evaluated, based on test and numerical data. The assessment results revealed that the buckling curves of the European code, American specification and Australian standard can be generally applied to the design of S690 high strength steel welded π-shaped section columns; however, the design flexural buckling resistances predicted by the European code and Australian standard were conservative for those columns with bucking towards the web tips, while the American specification led to many unsafe predictions. Finally, reliability analyses were conducted for each of the three codified buckling curves, revealing that the resistance factors specified in the American specification and Australian standard can be directly used for S690 high strength steel welded π-shaped section columns, while a higher partial safety factor equal to 1.1 was recommended for the European code.