Investigation of the behavior of short moment-resisting steel frames with rigid connections during earthquake damage in two cases of post-earthquake fire and post-fire earthquake

The incidences of fire and earthquake are the two serious hazards to buildings that jeopardize the safety of occupants. Much research has been carried out on the effect of seismic loads on structures, but little is known on the concomitant impact of these threats, specifically fire before an earthquake. Besides, many buildings are currently in use after a fire event without any particular retrofitting, which are exposed to future earthquakes like undamaged structures. In this research, the behavior of a moment-resisting steel frame is studied in two cases of damage by fire before an earthquake as well as the post-fire earthquake damage. Accordingly, the structure under study was designed following the Iranian Standard for Seismic Resistant Design of Buildings (Code 2800, 3rd Ed.). A set of ten fire scenarios was considered for thermal analysis. The results indicate that the structure remains stable after seismic loading in the case of post-fire earthquake, given that a maximum temperature of 600-700 °C is experienced in different fire scenarios based on the Eurocode standard fire curve. However, in the case of post-earthquake fire, the maximum stability temperature after seismic loading lies in the range of 600-800 °C for different fire scenarios, according to the ISO 834 fire curve. In the former case, deflection of the beams increases downward rapidly upon reducing the stiffness and strength of steel as temperature exceeds 600 °C, while in the latter case, the beams deflection increases downward sharply in the temperature range of 650-800 °C.