Response Of The North Fork Of The American River California To Hydraulic Mining PDF Download

Vibration tests were conducted on a 1/24-scale model of the North Fork Dam, a double curvature arch dam, to determine natural frequencies, mode shapes, and damping ratios. The measured results were compared with results calculated using a linear elastic three-dimensional finite element method. The objective of the study was to evaluate the use of physical models and three-dimensional finite element methods for earthquake response predictions. Mode shapes, frequencies, and damping ratios were determined from vibration tests of the model using two vibrators mounted on the crest of the dam and from tests with a vibrator mounted at the base of the dam on the downstream foundation. The modal analysis of the dam was performed using a three-dimensional finite element computer program, the Structural Analysis Program. The dam was modeled with 110 solid elements and 278 nodes and with the boundary totally fixed at the canyon walls. The reservoir was assumed to exert a static water pressure on the dam. This load, the mass of the vibrators, and an apparent mass based on an approximation by Westergaard to account for the mobilized water were included in the analysis. The Rayleigh-Ritz technique was used to determine mode shapes and frequencies. (Modified author abstract).