Abstract: To clarify the effect of different incident angles on the performance-based seismic design of high dams, the endurance time analysis (ETA) method is used to evaluate the variation in the seismic performance of a dam while considering spatial oblique incidences. First, three endurance acceleration time curves are synthesized based on this method; then a three-dimensional finite element model is constructed for the Koyna gravity dam-foundation, and the time curves are taken as inputs for simulations of the foundation at different angles. Finally, the dam’s seismic performance is evaluated using four performance indicators－crack penetration time, dam foundation damage index DBI, structural damage energy dissipation, and dam crest relative downstream displacement. The results show that significant differences occur in the dam’s seismic dynamic response when different incidences are input through the time curves, and this suggests the ETA method should consider oblique incidences. Generally, a seismic input at 60° incidences gives the most severe damage, highest damage energy dissipation, and largest dam crest relative downstream displacement.

Key words: concrete gravity dam, endurance time analysis method, spatial oblique incidences, seismic performance assessment