Abstract： In recent years, the collapse of steel structures under fire has frequently occurred, which not only caused property damage to residents, but also seriously threatened the lives of residents and firefighters. It has drawn great attention from the Fire Rescue Bureau of Emergency Management Department. Therefore, it is urgent to carry out the research on early-warning method for building collapse under fire. Based on full-scale fire test data and numerical simulation results, four typical collapse modes are summarized, and the change law of easy-measured key parameters of the structure under different collapse modes is specially studied. The early-warning indexes used for predicting the collapse probability of steel portal frames are determined, including horizontal and vertical deformation (displacement) and deformation rate at the location of two eaves and the apex, as well as maximum temperature of the structural steel elements during the fire, and then the early-warning methods applicable to different collapse modes of steel portal frames are proposed, providing an effective way for the establishment of structural collapse warning systems. The results show that the proposed early-warning method can easily predict the collapse of the steel portal frame under fire, and its accuracy and applicability have also been verified by experiments.
