Abstract：The annex building of Chengdu urban planning exhibition hall has the characteristics of large cantilever, large span, vertical component transition, floor discontinuity and so on. As an important public building, it is necessary to evaluate the ability to resist progressive collapse under earthquakes. Firstly, the numerical model of the annex building structure was established by finite element software Midas Gen, and nonlinear behavior of the structure under earthquakes was simulated based on the modified IK skeleton model for beams. Secondly, 20 records of ground motion were selected according to the site class of the structure. Incremental dynamic analysis (IDA) method was used to conduct nonlinear analysis for the structure under three directional ground motion excitation. Moreover, the performance-based collapse criteria of structures were defined, in accordance with the maximum inter-story drift ratio and beam end rotation, and then the fragility analysis of structure collapse was carried out according to the IDA analysis results. Finally, the structural performance against collapse was evaluated using the collapse margin ratio (CMR) of the whole structure. Results show that under the rare earthquake of 7 degree, the probability of sway incremental collapse is 0.14%,and the maximum probability of vertical progressive collapse is 10.82%; under the design earthquake and frequent earthquake of 7 degree, the probability of sway incremental collapse and vertical progressive collapse is basically 0. At the same time, the CMR is 2.708 in accordance with column failure and the CMR is 1.469 in accordance with beam failure. The evaluation results suggest that the structure has good progressive collapse resistance against earthquakes.
