PEER has just published Report No. 2013/17 titled “Response Spectrum Analysis of Concrete Gravity Dams Including Dam-Water-Foundation Interaction” as a new addition to the PEER Report Series. It was authored by Arnkjell Løkke of the Department of Structural Engineering at the Norwegian University of Science and Technology (NTNU) and Anil K. Chopra of the Department of Civil and Environmental Engineering at the University of California, Berkeley.
A response spectrum analysis (RSA) procedure, which estimates the peak response directly from the earthquake design spectrum, was developed in 1986 for the preliminary phase of design and safety evaluation of concrete gravity dams. The analysis procedure includes the effects of dam-water-foundation interaction, known to be important in the earthquake response of dams.
This report presents a comprehensive evaluation of the accuracy of the RSA procedure by comparing its results with those obtained from response history analysis (RHA) of the dam modeled as a finite element system, including dam-water-foundation interaction. The earthquake response of an actual dam to an ensemble of 58 ground motions, selected and scaled to be consistent with a target spectrum determined from a probabilistic seismic hazard analysis for the dam site, was determined by the RHA procedure. The median of the peak responses of the dam to 58 ground motions provided the benchmark result. The peak response was also estimated by the RSA procedure directly from the median response spectrum. Comparison of the two sets of results demonstrated that the RSA procedure estimates stresses to a degree of accuracy that is satisfactory for the preliminary phase in the design of new dams and in the safety evaluation of existing dams. The accuracy achieved in the RSA procedure is noteworthy, especially considering the complicated effects of dam-water-foundation interaction and reservoir bottom absorption on the dynamics of the system, and the number of approximations necessary to develop the procedure.
Also developed in the report is a more complete set of data for the parameters that characterize dam-foundation interaction in the RSA procedure. Availability of these data should provide sufficient control over the overall damping in the dam-water-foundation system to ensure consistency with damping measured from motions of dams recorded during forced vibration tests and earthquakes.