Effects of Vertical Earthquake Ground Motion on the Seismic Response of Base-Isolated Reinforced Concrete Buildings

This study investigates the effects of vertical ground motion on the seismic design of base-isolated structures. Two soil classes were considered, and for each class, near-fault and far-fault ground motions were selected, resulting in four seismic scenarios. Earthquake acceleration records were identified for each scenario and scaled to the Maximum Considered Earthquake (MCE) and Design Basis Earthquake (DBE) hazard levels. A finite element model of a base-isolated building was developed, and nonlinear time-history analyses were performed to evaluate the influence of vertical ground motion on structural response. The results show that the vertical earthquake component significantly increases isolator forces, overturning moments, vertical displacements, and vertical accelerations. These effects are considerably more pronounced under near-fault ground motions than under far-fault conditions. In addition, differences in soil class further amplify the influence of vertical ground motion on the seismic response of base-isolated structures. The findings demonstrate that both fault distance and site conditions should be explicitly considered in the seismic design of base-isolated buildings. Furthermore, limiting the ratio of the shorter plan dimension to the building height, while accounting for fault distance and soil class, may contribute to safer and more reliable seismic design.