Numerical simulation of damage evolution of Daikai station during the 1995 Kobe earthquake

Three-dimensional (3D) finite element (FE) analyses are performed to identify the collapse mechanism of the Daikai station, which suffered major structural damage during the 1995 Kobe earthquake. To investigate the damage evolution in the reinforced concrete structure, concrete and steel rebars are modeled separately and assembled in a soil-tunnel model. Bilinear models are used for both the concrete and steel rebars, whereas a nonlinear hysteretic model is used for the soil. Simulation results illustrate that the 3D FE model is capable of accurately reproducing the structural collapse and surface settlement. The cracks are observed to form initially at the outer walls of the tunnels and subsequently in the center column. As the ground motion intensity increases, longitudinal and shear cracks form in the center column, inducing a significant loss of axial capacity and eventually leading to a structural collapse. Irrecoverable damage initiates in the center column under the combined shear force (V) and bending moment (M). Therefore, it is recommended to utilize the V-M failure surface to estimate the onset of structural damage. The damage evolution of the Daikai station is also correlated with the drift ratio of the center column. Additional analyses show that when the equivalent linear soil model is used, the calculated peak drift ratio is similar to that obtained using the nonlinear model. However, it results in unrealistic gapping at the tunnel-soil interface and lower surface settlement. The no-slip condition for the tunnel-soil contact interface produces a pronounced lower response of the tunnel and therefore should not be used in a damage analysis.