Abstract:
"Validation Of Finite Element Analysis Techniques Using Loma Prieta Recordings At Lower Crystal Springs Dam"
This paper details the validation of finite element analysis techniques by comparing model calculations to physical recordings of the Lower Crystal Springs Dam's dynamic response during the 1989 Loma Prieta Earthquake. A three-dimensional finite element model of the dam, foundation, and reservoir was developed in LS-DYNA, comprising elastic solid and fluid elements with properties derived from extensive geological investigation. The core of the finite element methodology was a two-phase analysis to simulate the upward propagation of seismic waves, where an input motion was applied at depth and iteratively scaled using a transfer function to ensure the calculated accelerations at the dam's toe precisely matched the known earthquake recordings from that location. Once the model was calibrated to the toe measurements, the finite element analysis was used to predict the seismic response at other instrumented locations, including the dam crest and a free-field site. The finite element results for the dam crest showed very favorable agreement with the recorded data, demonstrating that the analysis can accurately capture structural response, wave propagation through the structure, and complex dam-foundation-reservoir interaction when foundation material properties are well-defined. In contrast, the finite element calculations for the free-field location did not align as closely with measurements, a discrepancy attributed to the high degree of uncertainty in the estimated geological profile in that area. To address this, further finite element simulations were performed as sensitivity studies to systematically vary the unknown foundation parameters, such as layer thickness, shear wave velocity, and damping, thereby illustrating how the finite element method can be employed to evaluate the impact of geotechnical uncertainties on site response.
