Site response analysis of vertical ground motion in consideration of soil nonlinearity

Vertical ground motion significantly affects the seismic response of engineering structures, particularly nuclear power plants and dams. However, most ground motion predictions or site response analyses focus on horizontal ground motion. As a result, knowledge of the characteristics of vertical ground motions is inadequate. In this study, a benchmark approach for equivalent linear vertical site response analyses is developed, with focus on the modeling of soil nonlinearity. The modeled soil exhibits different nonlinear behavior in the vertical direction depending on the saturation condition (i.e., above or below the groundwater table). Moreover, the vertical nonlinearity is different from that observed in the horizontal direction. The vertical ground responses predicted by the proposed approach are generally consistent with downhole measurements associated with different geological conditions, groundwater tables, and shaking intensities.