Use of laser techniques for detecting modal shifts in damaged concrete intake tower models

摘要

In the event of an earthquake, it is vitally important that the catastrophic failure of a dam and subsequent sudden release of the reservoir be prevented. An important part of the prevention of such a failure is maintaining the ability to controlthe release of water after the earthquake. For most earthen dams, and some concrete dams, the release of water is controlled through a reinforced concrete intake tower. Most intake towers in the U.S. Army Corps of Engineers existing inventory are verylightly reinforced. The functional survival of such lightly reinforced towers was the main concern of a recent research effort conducted at the U.S. Army Engineer Waterways Experiment Station'. The ultimate objective of this research was the evaluationand/or development of approximate or simplified analysis procedures for the evaluation of the ductility of existing intake towers. As part of this research, a series of three experiments were conducted, each of which was composed of the static loading tofailure of 1/8th scale models of a typical intake tower configuration. Experimental results for two models (ITS-2 and ITS-3) are reported in this paper. Cyclic bending loads were applied to the models. Material properties and the percentage of steel werevaried to model extremes encountered in existing towers. Modal surveys of the experiment models before, during, and after experimentation were conducted using a Scanning Laser Doppler Vibrometer system. These surveys were used to quantify the changes inthe mode shapes and frequencies due to the damage accumulated during experimentation. The application of laser vibrometry and modal analysis to this problem is the main focus of this paper.