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Title: Comparison of vibration test results for a model and prototype arch dam
Authors: United States. Army. Office of the Chief of Engineers
Crowson, Roger D.
Norman, C. Dean
Keywords: Arch dam
Dynamic characteristics
Dynamic tests
Hydrodynamic pressures
North Fork Dam
Vibration tests
Publisher: Weapons Effects Laboratory (U.S.)
Engineer Research and Development Center (U.S.)
Description: Technical report
Abstract: Vibration tests were conducted on both the prototype and a 1:24-scale model of the North Fork Dam, a double curvature arch dam, to determine natural frequencies, mode shapes, damping ratios, and hydrodynamic pressures. Two vibrators mounted on the crest of the dam were used as input excitation sources for both series of tests. Electromagnetic shakers capable of a 40-lb output were used in the model tests, while counterrotating, eccentric mass exciters capable of a 5000-lb output were employed for the prototype. Velocities were measured along the crest and downstream face of the model, whereas accelerations were measured in the same locations on the prototype. Measurements in both curves were taken at the dam-reservoir interface while the structures were excited at resonant frequencies. Variations in the measured natural frequencies for the model and prototype ranged from approximately 3 percent for the third and fourth modes to approximately 25 percent in the second mode. Comparisons of corresponding mode shapes were quite good. A linear three-dimensional finite element code, SAP, was also used to compute mode shapes and natural frequencies for the dam. This analytical calculation was very accurate, as the variation in prototype and predicted natural frequencies ranged from less than 1 percent for modes 3 and 4 to 11.6 percent for mode 2. The finite element analysis also indicated the first natural frequency (compression mode) to be very close to the first bending model frequency. In both model and prototype tests these two modes could not be separated, and the compression mode was not excited. Damping in both model and prototype ranged from approximately 2 to 5 percent of critical. These values are consistent with structural damping values for these types of structures.
Rights: Approved for public release; distribution is unlimited.
Appears in Collections:Technical Report

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