Forced-Vibration Tests of the Daniel-Johnson Multiple-Arch Dam

Abstract

The Daniel-Johnson dam is a 1314-m long multiple-arch-buttress dam composed of 14 buttresses and 13 arches with a central arch of 214 m high. The upper part of the dam is composed of gravity dam supported by the arches. Its height, length and the 2 million cubic meters concrete used for its construction make it the largest dam of its type in the world. Hydro-Quebec and the University of Sherbrooke carried out forced-vibration tests on the Daniel-Johnson dam that are presented in this paper. The tests aimed to determine the dynamic properties of the dam-reservoir-foundation (DRF) system to be used as a basis for the update of a 3D finite element model of the system. The outstanding size and the complex geometry of the dam are of great interest in this study, because they involved challenges in the experimental work not usually found for smaller dam of simpler geometry. The forced-vibration tests involved the use of an eccentric mass shaker generating forces up to 89 kN. The accurate modal identification of the dam required four different locations of the shaker, 52 measurement stations distributed along the crest of the dam and in the inspection galleries, and overall 13 tests configurations. These tests showed that it is possible to measure useful signals along the whole crest of a very large and massive concrete dam and as far as in the very lower inspection galleries, even with a relatively small excitation force. The analysis procedure of the experimental data were however quite complicated due to the numerous close local and global modes of the multiple-arch dam and their coupling. Twenty-two vibration modes were clearly identified. A 3D finite element model of the DRF system is briefly presented, and was correlated with the measured vibration modes.