Probabilistic Assessment of Seismic Collapse Capacity of 3D Steel Moment-Resisting Frame Structures

Accurate determination of the collapse moment of structures by nonlinear analyses is one of the major challenges for engineers in the seismic design of buildings. Although, structural damage can be assessed at various levels, the collapse of buildings is one of the worst events in the construction industry where casualties reach their maximum. In this research, 3D steel moment-resisting frame structures with 4, 8 and 12 story with special ductility have been subjected to nonlinear analysis including nonlinear static analysis, incremental nonlinear dynamic analysis and finally to investigate their collapse capacity, the fragility curves were used and earthquakes were considered according to FEMA P695 instruction including a pair of 22 far fault records, 14 near fault records with pulse and 14 near fault records without pulse. The models are 3D structures designed in ETABS 2016 software. The design of the structures and their seismic criteria control are based on fully validated according to standard 2800 Fourth Edition. Nonlinear structural models are also created in 3D state in OpenSees2.5.0 software. The effect of stiffness and strength deterioration is considered based on the results of the experimental models and the collapse capacity of the three-dimensional structures of the special steel moment-resisting frame is investigated probabilistically. The results show that the collapse capacity of 4, 8 and 12-story structures is the highest under far fault earthquakes and the lowest under near fault earthquakes without pulse and among the low-rise structures, The 4-story has less collapse capacity. For example, in the 4-story structure, the structural collapse capacity at statistical level 84% under near fault with and without pulse and far fault ground motions is 3.21 g, 3.61 g and 4.14 g, respectively.