Residual stresses and buckling resistances of Q960 ultra high-strength steel welded I-section columns after exposure to fire

This paper extensively studies the residual stresses and buckling resistances of post-fire Q960 ultra-high strength steel (UHSS) welded I-section columns through the experimental and numerical modeling program. An experimental program, incorporating heating, soaking and cooling of specimens, post-fire tensile coupon tests, extensive measurements of membrane and bending residual stresses, initial geometric imperfection measurements and ten pin-ended column tests, was first conducted. A numerical modeling study, in which finite models were developed, validated and then used in parametric study, was parallelly performed. The experimental and numerical data were used for assessing the applicability of the ambient temperature design provisions, as aet out in the European, Australian and American specifications, to post-fire Q960 UHSS welded I-section columns. The evaluation results reveal that (i) Eurocode and Australian standard yield slightly conservative ultimate load predictions for Q960 UHSS welded I-section columns after exposure to temperatures up to 600 ℃, but lead to overall accurate and consistent ultimate load predictions for temperatures beyond 600 ℃, and (ii) American specification results in unsafe ultimate load predictions for temperatures beyond 600 ℃, but yields relatively accurate ultimate load predictions for temperatures lower than this temperature level. Finally, a revised design approach based on Eurocode was proposed, with enhanced design accuracy identified.