Seismic and Structural Health Monitoring Systems For Large Dams: Theoretical, Computational and Practical Innovations

Abstract

Over the past decade, monitoring systems for Seismic and Structural Health Monitoring (SSHM) have been assuming a greater role in the safety control of large concrete dams. In this article, the dynamic behavior of two large arch dams equipped with SSHM systems is analyzed, in order to present some of the main theoretical, computational and practical innovations developed recently for the improvement of large dams’ continuous dynamic monitoring using SSHM systems. The case studies are two large arch dams that have been under continuous dynamic monitoring over the last ten years: Cabril dam (132 m high), the highest dam in Portugal, and Cahora Bassa dam (170 m high), located in Mozambique, one of the highest dams in Africa. The Seismic and Structural Health Monitoring (SSHM) systems installed in both dams have similar schemes and were designed to continuously record acceleration time series in several locations at the upper part of the dam body and near the dam-foundation interface, using uniaxial and triaxial accelerometers. Specific software was developed for monitoring data analysis, including automatic modal identification, to obtain natural frequencies and mode shapes, for automatic detection of vibrations induced by seismic events, to be distinguished by those caused by other operational sources, and for comparison between results retrieved from measured vibrations and numerical results obtained from computational 3DFE models. The numerical analyses are carried out using a 3DFE program for linear and non-linear dynamic analysis of concrete dams, based on a solid-fluid coupled formulation to simulate the dam-reservoir-foundation system, considering the dam-water dynamic interaction and the propagation of pressure waves throughout the reservoir. The most significant experimental results from continuous dynamic monitoring are presented for Cabril dam and Cahora Bassa dam and compared with numerical results, with emphasis on the evolution of natural frequencies over time, on vibration mode shapes for various water levels, and, finally, on the measured accelerations during seismic events. Furthermore, the main results of non-linear seismic response simulations, considering joint movements and concrete damage, are also presented for both dams in order to assess their seismic performance, using an intensifying seismic accelerogram prepared for Endurance Time Analysis.