2024 Volume 10 Issue 31 Pages 1165-1170
Investigating the seismic response of earth dams is challenging but often controls decisions when evaluating existing dams. Dam fundamental frequency (f0) and second mode vibration, key parameters in the dynamic response of a dam, can be assessed using the horizontal-to-vertical spectral ratio (HVSR) and standard spectral ratio (SSR) methods. The HVSR is mostly assessed by performing microtremor measurements in the field. However, when earthquake records are available, HVSR can also be calculated using the recorded motions. Additionally, standard spectral ratio (SSR) is calculated to assess the vibration characteristics of the dam. The overarching goal of this research is to assess vibration characteristics for dam sites in California. This is achieved by using the ground motion data on the California Strong Ground Motion Instrumentation Program (CSMIP) database for dam sites with recordings at different locations (i.e., right crest, left crest, etc.) and to study the local and site-specific features. Signal-to-noise ratios (SNR) were calculated to determine the usable frequency range and assess the quality of the ground motions. Then the earthquake-based HVSRs are evaluated using the following different approaches; i) A Fourier amplitude spectra ratio of the horizontal to vertical components (FASH/FASV) of the ground motion records at the surface using the intense S-wave portion and using the entire motion. Standard spectral ratio (SSR) which is the ratio of the FASH of the crest records over the FASH of the abutment records are also calculated. The vibration characteristics are evaluated based on different methods and the resulting estimate of the fundamental frequency and second mode of vibration for Briones Dam are presented.
