Predictive stress–strain models of S890 ultra-high strength steel after exposure to fire: Laboratory testing and FE validation

This paper reports an experimental and numerical investigation into the residual material properties, local buckling behaviour and predictive stress–strain models of ultra-high strength steels (UHSSs) after exposure to fire. The experimental programme included heating, soaking and cooling of tensile coupons and stub column specimens, post-fire material tests, initial local geometric imperfection measurements and stub column tests on thirteen specimens. The post-fire material properties were obtained and carefully analysed, with a new set of retention factor curves proposed for key material parameters of S890 UHSS after exposure to fire, including Young's modulus, yield stress, ultimate stress and ultimate strain. On this basis, new stress–strain models with discontinuous and continuous yielding were proposed to predict the stress–strain curves of S890 UHSS after exposed to different elevated temperatures. Subsequently, a numerical modelling programme was carried out, where S890 UHSS circular hollow section stub column finite element models were developed based on the proposed stress–strain models and validated against the test results, demonstrating that the test load–end shortening curves can be precisely captured by the finite element models. It can be concluded that the proposed retention factor curves and predictive stress–strain models can be accurately used for S890 UHSS after exposure to fire up to 1050 °C, offering reliable predictive tools for post-fire structural analysis.