Storey-based stability of steel frames subjected to post-earthquake fire

Abstract

Post-earthquake fires occur after earthquakes and have commonly been encountered throughout history. The fires are particularly deadly and threaten the stability of buildings as possible structural damages caused by seismic loading can be exacerbated by temperature loading. Moreover, damage to insulation during seismic events causes accelerated heating in portions of members experiencing large bending moments. A method is proposed for evaluating the stability and deflection of a semibraced structural steel frame subjected to post-earthquake fire conditions. The proposed method adopts the interstorey drift concept and assumes that each member in the frame has three segments of differing temperatures, modelling the damage to insulation near moment connections and/or midspans of flexural members. The method is presented in the form of a deflection equation, which indicates the instability of the frame when the lateral stiffness in the denominator reaches zero. The proposed method is demonstrated via a numerical example, and the duration of fire until the given frame becomes unstable is computed, with the results validated via finite element analysis. The degrees of structural and insulation damage are also varied in parametric analyses, showing that the lateral stiffness and critical temperatures of a frame subjected to post-earthquake conditions can be severely reduced.