Effective ambient vibration testing for validating numerical models of concrete dams

Ambient vibration tests were conducted on a 56 metre high concrete gravity dam to measure its modal properties for validating a finite element model o f the dam-reservoir-foundation system. Excitation was provided by wind, by reservoir water cascading down the spillweir, and by the force of water rel eased through outlet-pipes. Vibrations of the dam were measured using accel erometers, and 3-hour data records were acquired from each location. Data w ere processed by testing for stationarity and rejecting non-stationary port ions before Fourier analysis. Power spectra with low variance were generate d from which natural frequencies of the dam were identified clearly and mod al damping factors estimated. Modal analysis of the frequency response spec tra yielded mode shapes for the six lowest lateral modes of vibration of th e dam. The finite element model for the dam was analysed using EACD-3D, and the computed mode shapes and natural frequencies compared well with the me asured results. The study demonstrates that ambient vibration testing can o ffer a viable alternative to forced vibration testing when only the modal p roperties of a dam are required. Copyright (C) 1999 John Wiley & Sons, Ltd.