Progressive collapse mechanism of steel framed-structures subjected to a middle-column loss

Abstract

This paper analytically deals with the collapse resistance of steel framed-structures due to a middle column loss. The four-stage resistance-displacement relationships are proposed for both the bare steel frame and the braced steel frame. The reliability of the analytical method is verified against numerical analyses. Parametric studies are conducted to investigate the effects of frame height, span and stiffness ratio of beam to column on the collapse resistance of the frame. It is concluded that the yielding capacity, ultimate capacity, post-yielding stiffness and ultimate displacement of the steel frames can be reasonably predicted by the analytical method with acceptable errors. It is found that a greater number of storeys, shorter span of beams and larger beam to column stiffness ratio ensure better performances of the frame against collapse. Moreover, even though the bracing system can enhance the lateral stiffness of the main steel frame with certain extents, it reduces the collapse resistance and failure displacement of the frame because the column at the base-storey prematurely loses its stability.