FIRE-INDUCED PROGRESSIVE COLLAPSE OF BRACED STEEL STRUCTURES

摘要

This paper investigates progressive collapse mechanisms of braced steel frames subjected to ground floor fire scenarios using OpenSees, an open-source object-oriented software developed at UC Berkeley.The OpenSees framework has been recently extended to deal with structural behavior under fire conditions by authors.The study considers two types of bracing systems (vertical and hat bracing) The thermal expansion of heated beams at early heating stage and their catenary action at high temperature have great influences on the collapse mechanisms.The vertical bracing systems has positive effects on increasing the lateral restraint of the frame against local or global drift, while when arranged at Edge Bays of frames they negatively contributes to the spreading of a local damage to a global collapse in the form of sequential buckling of adjacent columns through load-transfer mechanisms.Instead, using hat bracing can effectively optimize the load-transfer path through a more uniform redistribution of loads in columns and enhance the resistance of structures against progressive collapse.The application of vertical bracing systems alone on the steel frames to resist progressive collapse is proved to be unsafe and a combined vertical and hat bracing system is recommended in the practical.