Structural behavior of partially encased composite columns after exposure to full‐range fire

Abstract With the increasing use of partially encased composite (PEC) columns in construction, the risk of fire also rises. The post‐fire performance of PEC columns is crucial for their rehabilitation and reuse. A finite element analysis (FEA) model was developed in this study to investigate the behavior of PEC columns after exposure to combined loading and full‐range fire, including ambient temperature loading, heating and cooling with constant load, and post‐fire loading to failure. The load ratio, heating time ratio, cooling rate, sectional perimeter, slenderness ratio, steel ratio, reinforcement ratio, load eccentricity, cement mortar thickness, yield strength of steel section, and strength of concrete on the post‐fire performance were analyzed. A design equation for the residual load‐carrying capacity of PEC columns after a fire was developed. The results show that the load‐carrying capacity of a PEC column with a cross‐section of 400 × 400 decreased by 14.9%, while the vertical deformation increased by 82.4% after the fire compared to those at ambient temperature. After the fire, the proportion of the external load shared by the steel section in the PEC column decreased from 56% at ambient temperature to 32%. The heating time ratio, load ratio, slenderness ratio, and cube strength of concrete are the primary factors that have the most significant influence on the post‐fire load‐carrying capacity of PEC columns. Additionally, a slower cooling rate exacerbates thermal damage to the structure and further diminishes its residual load‐carrying capacity. The calculated results of the residual load‐carrying capacity agree well with the FEA results.