The effect of vertical motions on damage accumulation on concrete gravity dams

Abstract

The effect of vertical ground motions on the seismic response of dams has long been a concern in the seismic design and evaluation of concrete gravity dams. The guidelines regarding the use of vertical motions in time history analysis (THA) are not clear due to the complexity of the effect as well as the large uncertainty in the motion selection process. The goal of this study is to assess the significance of vertical motions' effects on concrete gravity dams considering the relevant variability due to ground motion, system frequency response as well as the shaking level. To this end, a carefully selected ground motion set providing realistic vertical(V)/horizontal(H) loading was used in nonlinear THAs of three different systems with different modal properties. In order to evaluate the intensity of shaking on the vertical motions' effect, the responses were calculated at different seismic levels corresponding to operation, design, and maximum shaking levels. Along with traditional demand parameters commonly employed in assessing seismic response, cracking on the base and at the upstream face of the monolith was adopted as demand measures using a model capable of yielding discrete cracking on the system. The effect of vertical motions was quantified by comparing the response of H + V to H only shaking. The results show the vertical shaking can significantly affect upstream cracking for the operation or design level earthquakes, the effect increasing for larger dams.