Collapse Probability of Immediate and Special Moment Frames in Tehran under MCE

Residential buildings in most cities, which make up the most significant percentage of buildings, generally contain the most financial and human losses in the face of strong earthquakes. The purpose of this study is to investigate the possibility of the collapse of intermediate and unique steel moment frames against maximum ground excitations. In this study, through the first two steps of PEER methodology, using four steel structural frames with intermediate and unique moment frames, after designing according to the codes of national building regulations of Iran and standard 2800, this probabilistic evaluation was used to ensure their safety against collapse. In the next step, to deepen the results, 7 other sites from Tehran were selected. Their hazard spectrum was used to calculate the probability of collapse. In the end, it was observed that, with the reduction of the number of structural floors, the IDA curves at the lower IM level become horizontal in this project. The results showed that some of the 5-story steel structures under study in some parts of Tehran have a higher probability of collapse than acceptable.

Seismic collapse performance of steel special moment frames designed using different analysis methods

Building structures designed according to current seismic design codes should satisfy the seismic performance objectives specified in codes during big earthquake events. ASCE 7-16 specifies that risk category I and II structures should have a probability of collapse less than 10% against the maximum considered earthquake (MCE) shaking hazard. ASCE 7-16 provides four analysis methods to calculate the seismic demands on structures. In this study, 4-, 8-, 12-, and 16-story steel special moment frames (SMFs) are designed using the two most popular elastic analysis methods: the equivalent lateral force (ELF) method and the modal response spectrum analysis (RSA) method. The collapse probabilities of these structures are estimated against MCE shaking hazards according to FEMA P695. It is observed that the collapse probabilities of these structures vary according to analysis methods used for design. To improve the seismic collapse performance of SMFs, a modified method is proposed.

Seismic characterization of steel special moment frames subjected to megathrust earthquakes

Current seismic design requirements were established considering mainly (almost exclusively) ground motions caused by shallow crustal earthquakes, hence they might lead to different-from-intended risk levels when applied at locations prone to large-magnitude subduction (i.e. megathrust) earthquakes. In this study, the seismic behavior of 40 modern steel special moment frames (SSMFs) subjected to both megathrust and crustal ground motions is evaluated. Three analyses are performed: (1) a hazard-consistent analysis; (2) a comparative collapse risk evaluation; and (3) a performance evaluation following the approach indicated in Federal Emergency Management Agency (FEMA) P695. Results indicate that the collapse probability of mid- and high-rise SSMFs subjected to megathrust ground motions is indeed larger than that under crustal ground motions. Modifications to the current design criteria are then suggested, intended not only for United States but also for countries, such as Ecuador, where the US seismic design requirements for steel structures were adopted and seismic ground motions are actually caused by megathrust earthquakes.