Post-earthquake damage assessment is an important topic of structural health monitoring, which offers suggestions for policymakers on building repairing and reinforcement. Smartphones, which integrates many sensors and is widely used, make crowd-sensing in SHM possible. This idea, however, is still hard to practice. Fortunately, game engines such as Unity and Unreal can carry out these kind of large scale experiments in virtual world. In this paper, a game engine Unity is utilized to simulate the whole crowd-sensing process when a city is struck by a main shock and a aftershock. The citizens driven by decision tree and the city brain work together to take refuge and install smartphones to get structural response for assessment. In order to cooperate with this smartphone-based SHM, a new type of sensor named MaxCpture, which can capture the maximum structural strain during earthquake, is also briefly introduced in this paper. The framework of using game engines to carry out virtual experiments can be further spread to other scenarios in structure health monitoring.