Earthquake Response Records

This study was completed to examine typical acceleration responses at the top of concrete dams subjected to earthquake loadings. Comparisons were made between the input accelerations applied to finite element models and the accelerations generated at the dam crests during the dynamic analyses. This information will be instrumental in determining the number of cycles which would impact a spillway gate at the dam crest level during and immediately following an earthquake. The finite element analyses were continued for a long enough period of time after the ground motions had ceased for the response amplitude at the dam crest to decay to half its maximum response amplitude. Four arch and two gravity type dams were included in the study. In all cases, the input accelerations were significantly amplified at the dam crest. For the dams included in this study, the acceleration amplification ranged from 0.002 g per foot of dam height at Hoover Dam, to 0.043 g per foot of dam height at Deadwood Dam. Greater amplification occurred in the three thin arch dams than for either the gravity dams or the thick arch dam (Hoover). The crest and input acceleration curves generated for the gravity and thick arch dams tended to remain in phase, which was not the case for the thin arch dams. The crest accelerations generated for the two gravity dams and the thick arch dam also tended to decay very rapidly after the input motion ended. The crest accelerations generated for these dams decreased by half within 2 to 3 cycles after the input motion ended. The crest accelerations generated for the three thin arch dams decayed more slowly, requiring 5 to 25 cycles to reach half amplitude after the input motion ended.