Fire-induced Progressive Collapse of 3D Steel Frames with Concrete Floors

Abstract

This paper investigates the behavior of three-dimensional steel frames with reinforced concrete slabs exposed to localized fire against progressive collapse. The prototype of the model is based on the eight-story building in Cardington tests. The scenario of heating an individual column on the ground floor is adopted. The collapse modes and load redistribution scheme of the frame subjected to different load ratios of columns and fire locations are investigated. The results show that the frame does not collapse in the case of single column heated for a fire design load (load ratio of 0.25), due to the load redistribution to adjacent columns through floors. By increasing the load ratio to 0.5 as for the ambient design, progressive collapse occurs. The collapse modes are dominated by the uneven load redistribution in the two horizontal directions, which cannot be simulated by a 2D model. The loads previously sustained by the buckled heated column are transferred more along the short span than the long span, leading to the advanced buckling of columns along the short span. The critical temperature of a column in a frame is significantly lower (about 200oC) than that given in EC3, due to the fact that the translational and rotational restraints increase its load ratio and reduce its effective length, respectively.