MODAL TESTING OF A GRAVITY DAM - INFLUENCE OF THE EXCITER PLACEMENT ON THE QUALITY OF THE IDENTIFIED MODAL PARAMETERS

摘要

It is possible to test a mechanical system consisting of dam-foundation-sediment-water in situ as a black-box system by employing the measurement data of the acceleration response of the dam to some force excitation signal, with no assumption being made as to the form of the possible differential equations. When the goal of testing is the construction of a mathematical model (modal model) of the dynamics of the dam, then the residuals of the driving point (point of collocating excitation and response) frequency response function are necessary in scaling the entire modal model. The accuracy in establishing these residues determines the accuracy of the modal parameters. The quality of the driving point frequency response functions depends strongly on the estimate of frequency response function employed, excitation signal and above all on the suitable location of excitation. In this paper we concentrate on the choice of excitation point for the modal testing of a gravity dam. A comparison of two models of the Vieux Emosson Dam in Switzerland obtained by excitation at two different points is presented and discussed. Included is a discussion of how to select a suitable excitation point for the modal testing of a gravity dam.