Probabilistic assessment of failure time in steel frame subjected to fire load under progressive collapses scenario

Abstract

Consecutive loads can pose a serious threat to the safety of structures. The sudden removal of load-bearing elements such as columns is one of the causes of the progressive collapse in the structures. The local collapse caused by the sudden removal of the column could affect the response of the structure in the consecutive loads. The fire load is one of the loads that threatens the safety of the structure over the lifetime of the structure. The time a structure can resist the fire load is one of the main factors in the safety of structures against thermal loads. The local damage involved in the structure, including the sudden removal of the load-bearing elements, can affect the stability of the structures against the fire load as two successive events. This research aims to calculate the stability time of the steel frame during the consecutive loading from the sudden removal of column and the subsequent fire. Once designed, the 7-story steel frame is mechanically-thermally modeled and is subjected to the sudden removal of columns in different positions. The static and dynamic pushdown analysis is used to evaluate the structure response in the scenarios of sudden removal of the column. Different modes of thermal load are defined and applied to the structure in the positions of the removed column. Finally, the probability of structural failure is calculated under the fire load after the sudden removal of the column and presented at different times. The results show that the sudden removal of the column will have a great effect on the failure time of the structure and will increase the failure probability of the structure and reduce the failure and collapse time of the structure. Finally, the robustness index is also presented based on the probability of collapse time.