Assessing the impact of rockfall on a bridge by using hybrid DEM/FEM analysis: A case study in Central Taiwan

Two destructive rockfalls occurred in central Taiwan, wherein falling blocks severely damaged an essential bridge of a mountain expressway. A series of field investigations were conducted to recognize the trajectories of the rockfalls and gather information on the falling blocks and bridge damage. According to the obtained field data, a hybrid model of the discrete element method (DEM) and finite element method (FEM) was developed to assess the rockfall impact on the bridge. A DEM analysis was first performed to simulate the rockfall process, which agreed with the actual condition. A detailed FEM was developed with strain-rate-dependent material models to investigate the process, which caused severe damage to the bridge and protective structures under the rockfall impact based on the calculated velocity and kinetic energy of rock blocks obtained from the DEM analysis. The simulated damage mechanisms agreed well with the field observations. The simulated maximum impact force was 4.5 times higher than the original design load and caused severe damage to the bridge structure. The thorough and objective investigation results of this rockfall event and the rigorous hybrid DEM-FEM analysis framework can be essential guidelines for authorities to formulate future hazard mitigation strategies for similar infrastructures under the threats of rockfall impacts.