Determining the Base Shear Relationship of Moment Steel Frame to Ensure Life Safety Level in Post-Earthquake Fire

Post-Earthquake Fire (PEF) is an incident that can lead to a crisis and can be more critical than the earthquake itself due to the problems of passing vehicles and providing aid and assistance to the residents after the earthquake, and it can cause a lot of human and financial losses. Despite the large history of post-earthquake fires, the design regulations do not take into consideration the simultaneous effect of fire load and earthquake. On the other hand, in design based on the performance of structures, structural members should be designed for a specific level of performance that depends on the importance of the structure, which in the event of a post-earthquake fire, the performance level of the structure can change .Structures that are designed according to the regulations for the level of life safety performance may deviate from the desired level in the event of a fire after an earthquake. In this research, Post-Earthquake Fire was modeled in a moment steel frame. In this modeling, various levels of ground motion intensity and several time intervals were considered to extinguish the fire in the event of a post-earthquake fire. Three-story moment steel frame structures were modeled using OpenSEES software and studied to the performance level of life safety. Considering 44 different accelerograms, first, a scale of these accelerograms was applied to the structure. Then, assuming 60 seconds of free vibration to damping of the structure, the thermal load was applied to the members exposed to heat under the nine-point heat gradient, taking into account the ISO834 standard fire curve. Considering the maximum relative displacement between floors of 2.5% for the safety performance level, the quasi-acceleration spectrum component in the period of the first mode of the structure (Sa(T1)) was determined for this maximum relative displacement between floors under earthquake alone. Then, for different durations of post-earthquake fires, the maximum relative displacement between the floors under post-earthquake fires was determined and  Sa(T1) of a scale of the accelerogram applied was determined so that the structure under earthquake alone can have a maximum relative displacement between floors equal to the maximum displacement between floors under post-earthquake fire, and finally with this ratio Sa(T1) to Sa(T1) of the accelerogram scale, which had produced a maximum relative displacement of 2.5% between floors in the structure, a coefficient was obtained to modify the base shear to provide the performance level of life safety for various durations of post-earthquake fire.