Fire resistance of ultra-high performance concrete-filled steel tubes slender columns at different concrete ages: Experimental and theoretical investigation

Abstract

Fire-related accidents are more frequent during the construction phase, posing serious risks to building structures, which can result in material damage, construction delays, and significant safety hazards. This paper investigates the fire-resistance performance of ultra-high performance concrete-filled steel tube (UHPCFST) slender columns at different curing ages of UHPC to simulate the occurrence of fire scenarios during construction phase. The fire-resistance tests were conducted on 10 full-scale UHPCFST slender columns subjected to the ISO-834 standard fire to investigate the effect of UHPC age and load ratio on the thermal and mechanical response of the UHPCFST columns at different early ages. The results indicate that the fire-resistance time of UHPCFST slender columns decreases as UHPC age increases, particularly in specimens with a 0.3 load ratio, where the age at 56 days was 148 % lower than at 3 days. Furthermore, based on the average temperature method, a predictive model for determining the fire-resistance bearing capacity of early-age UHPCFST slender columns was proposed and validated. This research provides valuable insights for fire safety design and structural reliability assessment of UHPCFST structures during the construction phase.