Collapse modes and mechanisms of planar multi-story large-span steel frames under fire

Abstract

This paper investigates the collapse modes and mechanisms for planar multi-story large-span steel frames exposed to fire. Based on a systematic parametric analysis conducted with a wide range of parameters, including structural topological forms, fire scenarios, component sizes, load cases, fire protection levels, section temperature gradients, and wind loads. Eight potential collapse modes are identified: general inward collapse, rebalancing collapse, partial lateral collapse, heated large-span beam-induced inward collapse, restraint failure-induced collapse, overall downward collapse, unheated large-span beam-induced inward collapse, and overall lateral collapse. Simultaneously, by combining typical fire cases, corresponding structural collapse mechanisms are explored to reveal the differences in the failure sequence of locally heated components and the final structural collapse extent for different collapse modes. Furthermore, this study also analyzes the evolution laws of key horizontal and vertical displacements and velocities within the fire area for various modes, highlighting distinctions resulting from diverse collapse mechanisms. Finally, a detailed summary of various collapse modes is provided, involving reasons for inducing structural local collapse, the final extent of progressive collapse, possible areas of occurrence, and potential mode transitions as parameters change.