Abstract
To clarify post-earthquake fire resistance of steel frames, this paper studies analytically the ultimate temperatures of seismically designed multi-story and multi-span steel frames which have suffered some or severe damages due to preceding earthquakes. Refined finite element analysis and simplified theoretical analysis have both been conducted assuming that the frames, which have undergone permanent relative story displacement and/or fracture of beam-end-connection due to earthquakes, are next subjected to whole floor fire at the first floor. It is found that the lowering in ultimate temperature of the damaged frames is caused by P-Δ effect depending on the amount of the residual relative story displacement of the floor in fire. Their ultimate temperatures are therefore affected solely by the amount of axial forces and slenderness ratios of columns, but they are almost independent of the number or length of spans or of the number of stories. Theoretical consideration aims to analyze simply the post-earthquake P-Δ effect of the heated columns and the resulting predicted ultimate temperatures are found in good agreement with finite element solutions for all cases.
