Abstract:
This paper is focused on the study of the dynamic behaviour of two large arch dams, and
it presents some innovations for the improvement of Seismic and Structural Health Monitoring
(SSHM) systems for dams. The work describes a methodology based on the integrated
use of software for automatic monitoring data analysis and of computational 3D
finite element (3DFE) models for dam dynamic behaviour simulation. The monitoring data
analysis software was developed for automatic modal identification, in order to obtain natural
frequencies and mode shapes, for automatic detection of vibrations induced by seismic
events, to be distinguished from those caused by other operational sources, and for comparison
between results retrieved from measured vibrations and numerical results from 3DFE
modelling. The numerical simulations are carried out using a 3DFE program developed
for dynamic analysis of dam-reservoir-foundation systems, based on a solid–fluid coupled
formulation and considering the dam-water dynamic interaction, including calculation
modules for complex modal analysis and for linear and non-linear seismic analysis. 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), in Mozambique, one of the highest dams in Africa. The SSHM
systems installed in both dams have similar schemes and were designed to continuously
record accelerations in several locations at the upper part of the dam body and near the
dam-foundation interface, using uniaxial and triaxial accelerometers. The most significant
experimental results from continuous dynamic monitoring are presented and compared
with numerical results for both dams, with emphasis on the evolution of natural frequencies
over time, including the vibration mode shapes for various water levels, and on the
measured accelerations during low-intensity seismic events. Furthermore, the main results
of non-linear seismic response simulations are provided, considering the effects due to
joint movements and tensile and compressive concrete damage, aiming to assess the seismic
performance of both dams based on the Endurance Time Analysis method.