SIMPLIFIED ENERGY-BASED METHOD FOR PROGRESSIVE COLLAPSE ANALYSIS OF STEEL STRUCTURES SUBJECTED TO LOCAL FIRE

To study the collapse mechanism and collapse resistance of steel structures subjected to local fire, a simplified collapse analysis model with single degree of freedom is established based on the initial collapse mechanism of steel structures under fire. In this model, the superstructure is modeled as a constraint spring with tri-linear elastic-plastic properties, and the heated column is simplified as a lumped plastic hinge model. Then the energy-based formula to calculate the structure response is deduced. Finally the rationality and feasibility of the proposed model and method are validated through a comparison with the numerical analysis results of the whole structure subjected to local fire.