Ambient Vibration Tests of Structures − a Review

A literature review on the subject of ambient vibration testing is presented, and a review of a recent study to illustrate state-of-the-art in the application of the ambient vibration method. Reports on testing of full-scale structures by the ambient vibration method began to appear regularly around 1970, with about 3/4 of all contributions devoted to the experiments in buildings, dams, chimneys and silos, and about 1/4 to bridges. Since 1985, there are only about 3 papers per year, world wide, dealing with this subject. The reviewed study is of a seven-story reinforced concrete building in Van Nuys, California, damaged by the 17 January 1994 Northridge earthquake and its early aftershocks. Two detailed ambient vibration surveys were conducted soon after the earthquake. The apparent frequencies and twoand three-dimensional mode shapes for longitudinal, transverse and vertical vibrations are presented in this paper. The attempts to detect the highly localized damage by simple spectral analyses of the ambient noise data were not successful. It is suggested that very high spatial resolution of recording is required to identify localized column and beam damage. The loss of axial capacity of the damaged columns could be seen in the vertical response of the columns, but similar moderate or weak damage typically would not be noticed in ambient vibration surveys. 1 Assistant Professor, Civil Eng. Dept., Univ. of Montenegro, Podgorica 81000, Montenegro, Yugoslavia. 2 Professor, Civil Eng. Dept., Univ. of Southern California, Los Angeles, CA 90089-2531. Corresponding author. 3 Research Associate Professor, Civil Eng. Dept., Univ. of Southern California, Los Angeles, CA 90089-2531