By Qingle Cheng, Xiang Zeng, Zhen Xu, Zhebiao Yang and Xinzheng Lu More details of the simulation can be found in the book: Earthquake Disaster Simulation of Civil Infrastructures: From Tall Buildings to Urban Areas, Singapore: Springer, 2017 http://www.springer.com/us/book/9789811030864 1. Research background 40 years ago, on July 28th, 1976, the entire Tangshan City of China was ruined by an M7.8 earthquake. In that catastrophe, 240,000 people died, 2.85 million buildings collapsed, and 960 thousand buildings were severely damaged. Now 40 years have passed. If the same strong earthquake strikes Tangshan again, what will happen? In terms of this question, the Department of Civil Engineering of Tsinghua University, with the support of Tangshan local government and the Tsinghua Tongheng Urban Planning and Design Institute, performed a seismic damage simulation for 230,683 buildings in downtown Tangshan and analyzed the seismic resistances of today’s buildings in Tangshan. The urban seismic damage is predicted through the nonlinear time-history analysis of urban buildings. The buildings are simulated using multiple degree-of-freedom (MDOF) shear model and MDOF flexural-shear model. Details of the models can be referred to: [1] Parameter determination and damage assessment for THA-based regional seismic damage prediction of multi-story buildings, Journal of Earthquake Engineering, 2016. DOI: 10.1080/13632469.2016.1160009. [2] A nonlinear computational model for regional seismic simulation of tall buildings, Bulletin of Earthquake Engineering, 2016, 14(4): 1047-1069. 2. Simulation results and discussions Due to the fact that the near-field ground motion of the main shock was not recorded during the Tangshan earthquake, 4 typical near-field records recommended in FEMA P695 (FEMA, 2009) report were selected as input ground motions. These ground motions are recorded from the M7.6 Chi-Chi earthquake, M7.5 Kacaeli earthquake, and M7.9 Denali earthquake. The magnitude of these 3 earthquake events are close to that of Tangshan earthquake (M7.8). Using the attenuation relationship proposed by Prof. Yuxian Hu, the ground motions were inputted to each building, then the nonlinear time-history analysis of different buildings were implemented. The simulation results show that: (1) The building seismic resistance of Tangshan City has been remarkably improved over the past 4 decades, and the seismic resistance of engineered buildings is much better than that of non-engineered buildings. According to the actual statistics provided by Su et al., 80% of the buildings in the studied area collapsed under the 1976 Tangshan earthquake. By contrast, the simulation results show that the average collapse percentage subjected to the 4 selected ground motions was 29.76%, which indicates that the building seismic resistance of Tangshan City is remarkably improved, compared to the collapse percentage of 80% in 1976. Further analysis shows that most of the collapsed buildings were aged non-engineered buildings. The average collapse percentage of engineered buildings was 13.95%, while the collapse percentage increased to 95.03% for non-engineered buildings. As a result, seismic design is critical to the seismic safety of buildings. The aged buildings in the city should be upgraded or retrofitted as soon as possible, in order to mitigate the seismic damage in the city. (2) The cost of post-earthquake reconstruction of the city is extremely high. Therefore, improving the seismic resilience is very important Even for the engineered buildings, the percentage of buildings reaches extensive damage or collapse was 83.67%. These buildings are almost impossible to repair. Hence, if the 1976 Tangshan earthquake strikes again, even though the casualty can be effectively reduced, most of the buildings have to be demolished and reconstructed. The estimated reconstruction area should be greater than 100 million sq. meter, resulting in extreme economy, environment, and resource costs. As a consequence, improving the seismic resilience is very important.