Post-fire behavior and resistances of S890 ultra-high strength steel circular hollow section beam–columns

An experimental and numerical modeling program was carried out to investigate the post-fire structural behavior and residual resistances of S890 ultra-high strength steel (UHSS) circular hollow section (CHS) beam–columns after exposure to elevated temperatures and presented in this paper. Eighteen CHS beam–column specimens were tested, with heating, soaking and cooling of specimens, post-fire tensile coupon tests as well as measurements of initial global geometric imperfections firstly performed. Finite element (FE) models were developed and validated against the available experimental results, and then adopted for generating further numerical data covering a wider spectrum of member lengths, cross-sectional dimensions and loading combinations to expand the data pool. Owing to the absence of design provisions for steel structures after exposure to elevated temperatures, the relevant ambient temperature design interaction curves outlined in the current European, American and Australian specifications are evaluated for their applicability to S890 UHSS CHS beam–columns after exposure to elevated temperatures, with post-fire material properties used. The assessment results revealed that the codified provisions in the European, American and Australian specifications can lead to safe but slightly conservative resistance predictions for S890 UHSS CHS beam–columns after exposure to elevated temperatures, except for a few unsafe data points (for the elevated temperature of 800 °C) predicted by the Australian standard.