Progressive collapse resistance of RC frames subjected to localized fire

Abstract

Fire is one of the accidental loads that can cause progressive collapse of buildings. However, the behavior of fire-exposed reinforced concrete (RC) frames to resist progressive collapse are still unclear. Therefore, a numerical study on the RC assembly based on the sequential thermal-mechanical coupling method is conducted. Fire effects on the failure mode, load-resistant capacity, and the evolution of load-resistant mechanisms of the RC frame are captured. The numerical results show that compressive arch action (CAA) and catenary action (CA) can develop in sequence for the specimens exposed to fire within a short fire duration of 30 min. The failure of the specimen is controlled by the fracture of beam rebars near the removed column. However, when the fire duration exceeds 60 min, the specimen is difficult to develop effective CA due to a decrease of over 80% in the tensile strength of the bottom reinforcement. The failure of the specimen is dominated by the fracture of the rebar at the cut-off point of the beam top rebar. Fire lasting for 30 min, 60 min, 90 min and 120 min results in a decrease of 41%, 72%, 77% and 78% in ultimate load, respectively. Increasing the span-depth ratio can upgrade the deformation capacity of the specimen, but it is adverse to the development of CAA. The effects of the reinforcement ratio on the failure mode, the ultimate load and deformation capacity are mild as the fire exposure duration increases.