Effect of design parameters on the fire resistance of multi-story steel moment resisting frames

Steel moment resisting frames (MRF) are one of the most widely used lateral load resisting systems for low- and medium-rise buildings. Depending on the existing design constraints and assumptions, different alternatives of this lateral load resisting system can be designed. Since one of the vulnerabilities of this structural system is its resistance to fire, this paper studies the effect of different design parameters on the fire resistance of designed alternatives. As steel MRFs may be designed with different ductility values, the main design parameter has been selected to be the ductility of frame in terms of being intermediate or special. In addition, the effect of the number of stories, the gravity load level, and the location of fire in the width and height of the structure have been studied. For this purpose, six intermediate and special MRFs with 3, 7, and 12 stories have been numerically modeled and analyzed under different levels of gravity load and fire scenarios. To compare the results, a comprehensive concept called "failure ratio" that shows the ratio of scenarios leading to failure to the total number of analyses at each fire temperature, is introduced and used. Based on the results, frames designed for regions with high seismic risk show an acceptable performance during the fire. In such regions, the use of both types of Intermediate Moment Frames (IMFs) and Special Moment Frames (SMFs) can be recommended. On the other hand, frames designed for low seismic risk, are vulnerable to fire and hence, it is crucial to check the fire resistance of MRFs in regions with a low seismic risk where the designed structures have lower reserve strength. In these regions, using IMF frames can be considered a competitive or even better option.