Compression performance of ultra-high performance concrete filled steel tube(UHPCFST) columns exposed to elevated temperature during construction

To investigate the residual mechanical performance of ultra-high performance concrete filled steel tube (UHPCFST) columns exposed to high temperatures during construction, in this research, an experimental study on 27 UHPCFST columns is conducted to examine the impact of fire scenarios, age of the core UHPC exposed to elevated temperature, and volume ratio of coarse aggregates on the post fire behavior of the UHPCFST columns. Detailed analyses are carried out on the failure modes, the historical maximum temperatures in the cross-sections, the axial load-deformation curve, the residual compressive strengths, and the residual stiffness of the columns. The findings indicate that both the steel tubes and the bearing capacity UHPC cores show increases in the historical maximum temperatures with the increase in the aging of the core UHPC. For columns exposed to fire sources at greater distances, a significant enhancement in bearing capacity was observed following high-temperature exposure at varying ages. The bearing capacity demonstrated an increasing trend with the aging of the UHPC subjected to high temperatures. In contrast, when exposed to nearby fire sources, a decline in strength was noted, and the overall bearing capacity of the columns decreased as the age of UHPC exposed to elevated temperature increased. Furthermore, a predictive model for the residual bearing capacity of UHPCFST columns subjected to high temperatures during construction was developed and validated. This research is expected to provide valuable insights for the post-fire evaluation and reinforcement of UHPCFST structure in construction settings. • The axial compressive tests of UHPCFST short columns exposed to elevated temperature at different UHPC ages were carried out. • The influence of UHPC ages and fire scenarios on the residual performance of UHPCFST columns were investigated. • A formula for calculating the residual bearing capacity of UHPCFST columns exposed to high temperatures during construction is developed and validated.