STRUCTURAL CONDITION ASSESSMENT OF DAMS BASED ON CONTINUOUS DYNAMIC MONITORING SÉRGIO BOUÇA PEREIRA A dissertation presented to the Faculty of Engineering of the University of Porto for the degree of Doctor in Civil Engineering. Supervisors: Filipe Magalhães (Assistant Professor); Álvaro Cunha (Full Professor). Structural Condition Assessment of Dams Based on Continuous Dynamic Monitoring To my parents Structural Condition Assessment of Dams Based on Continuous Dynamic Monitoring Structural Condition Assessment of Dams Based on Continuous Dynamic Monitoring ABSTRACT Dams play a fundamental role in human societies, providing water for population and irrigation and serving as well as an important instrument for energy production. However, the enormous amount of potential energy held by dams in their reservoirs becomes a tremendous threat to human lives and properties in case of a structural failure. Thus, the risks of a malfunction in the structure, caused by external actions or simply by ageing, must be minimized by continuous monitoring and maintenance procedures. Structural health monitoring based on operational modal analysis is an adequate methodology to continuously assess the condition of civil engineering structures and has already been successfully implemented in bridges, buildings, wind turbines, towers and stadia. This work focuses on the development of numerical and experimental tools to assess the dynamic behaviour of dams during reservoir filling and operational phases, and to evaluate their structural condition using vibration-based monitoring systems. With this purpose, the present work involves, on the one hand, the performance of ambient vibration tests in a group of dams with different characteristics, and on the other hand the exploration of continuous dynamic monitoring systems installed in two recently built concrete arch dams. To achieve the presented goals and verify the structural integrity of dams, algorithms for automatic and continuous identification of modal parameters are implemented and applied, as well as tools to minimize the effects of environmental and operational conditions on the referred modal estimates, allowing the detection of structural anomalies. Numerically simulated damages are used to test the ability of damage detection tools to find these anomalies. Additionally, results obtained from ambient vibration tests are used to analyse the suitability of operational modal analysis to concrete dams, and the level of accuracy achieved during these tests using different types of sensors is studied. Structural Condition Assessment of Dams Based on Continuous Dynamic Monitoring Structural Condition Assessment of Dams Based on Continuous Dynamic Monitoring RESUMO As barragens desempenham um papel fundamental nas sociedades humanas, fornecendo água às populações e para irrigação e servindo ainda como um instrumento para a produção de energia. No entanto, a enorme quantidade de energia potencial detida pelas barragens nos seus reservatórios torna-se uma tremenda ameaça à vida e propriedades humanas, em caso de falha estrutural. Assim, os riscos de um mau funcionamento da estrutura causados por ações externas, ou simplesmente pelo envelhecimento, devem ser minimizados por procedimentos de monitorização e manutenção contínuos. A monitorização da integridade estrutural baseada em análise modal operacional é uma metodologia adequada para avaliar a condição de estruturas de engenharia civil de forma contínua e já foi implementada com sucesso em pontes, edifícios, turbinas eólicas, torres e estádios. Este trabalho foca-se no desenvolvimento de ferramentas numéricas e experimentais para avaliar o comportamento dinâmico de barragens durante as fases de enchimento e de operação, e avaliar a sua condição estrutural utilizando sistemas de monitorização dinâmica. Desta forma, o presente trabalho envolve, por um lado, a realização de ensaios de vibração ambiental num conjunto de barragens com diferentes características e, por outro, a exploração de sistemas de monitorização dinâmica contínua instalados em duas barragens de betão construídas recentemente. Para atingir os objetivos apresentados e verificar a integridade estrutural de barragens, são implementados e aplicados algoritmos de identificação automática de parâmetros modais, além de ferramentas para minimizar os efeitos das condições ambientais e operacionais nas referidas estimativas modais, permitindo a deteção de anomalias estruturais. Danos numericamente simulados são usados para testar a capacidade das ferramentas de deteção de danos em encontrar essas anomalias. Além disso, os resultados obtidos a partir de ensaios de vibração ambiental são usados para analisar a aptidão da análise modal operacional em barragens de betão, e é estudado o nível de precisão alcançado durante esses testes usando diferentes tipos de sensores. Structural Condition Assessment of Dams Based on Continuous Dynamic Monitoring Structural Condition Assessment of Dams Based on Continuous Dynamic Monitoring RÉSUMÉ Les barrages jouent un rôle fondamental dans les sociétés humaines en fournissant de l'eau pour la population et l'irrigation et en servant également d'instrument important pour la production d'énergie. Toutefois, l'énorme quantité d'énergie potentielle des barrages dans leurs réservoirs représente une menace considérable pour les biens et vies humaines en cas de défaillance structurelle. Ainsi, les risques de dysfonctionnement de la structure, dus à des actions externes, ou simplement au vieillissement, doivent être minimisés par des procédures de surveillance et de maintenance continues. La surveillance de l'état des structures basée sur l'analyse modale opérationnelle est une méthodologie adéquate pour évaluer en permanence l'état des ouvrages de génie civil, qu’a déjà été mise en œuvre avec succès dans les ponts, les bâtiments, les éoliennes, les tours et les stades. Ce travail porte sur le développement d'outils numériques et expérimentaux pour évaluer le comportement dynamique des barrages pendant les phases de remplissage et d'exploitation, ainsi que pour évaluer leur état structurel à l'aide de systèmes de surveillance basés sur les vibrations. À cette fin, les travaux en cours portent, d’une part, sur la réalisation d’essais de vibrations ambiantes dans un groupe de barrages présentant des caractéristiques différentes, et, d’autre part, sur l’exploration de systèmes de surveillance dynamique en continu installés dans deux barrages en béton. Pour atteindre les objectifs présentés et vérifier l'intégrité structurelle des barrages, des algorithmes d'identification automatique des paramètres modaux sont mis en œuvre et appliqués, ainsi que des outils permettant de minimiser les effets des conditions environnementales et opérationnelles sur les estimations modales référées, permettant ainsi de détecter des anomalies structurelles. Des dommages simulés numériquement permettent de tester la capacité des outils de détection des dommages à détecter ces anomalies. En outre, les résultats des tests de vibrations ambiantes permettent d'analyser l'adéquation de l'analyse modale opérationnelle aux barrages en béton et d'étudier le niveau de précision obtenu lors de ces tests avec différents types de capteurs. Structural Condition Assessment of Dams Based on Continuous Dynamic Monitoring Structural Condition Assessment of Dams Based on Continuous Dynamic Monitoring ACKNOWLEDGMENTS To all my family, friends and colleagues, who through their friendship and support helped me prepare this thesis, here I present my sincere gratitude. Nevertheless, I want to express a special thanks: to Professor Filipe Magalhães, my advisor, for all the support, the commitment, the time, the sympathy, the precious pieces of advice and the enormous patience when my countless “what-ifs” and “something’s wrong” were followed by his demonstrations of knowledge and kind motivational words; to Professor Álvaro Cunha, my co-advisor, for challenging me with this adventure and always making sure I had the necessary resources to develop my work, for encouraging me to participate in so many international conferences, but mostly for the close, gentle and constant support, motivation and guidance; to Doctors Jorge Pereira Gomes and José Vieira de Lemos, from the National Laboratory for Civil Engineering (Portugal), for receiving me at the Concrete Dams Department during almost two months, for their hospitality and for the time so kindly spent giving me insights about the numerical modelling of dams. Additionally, for all the support related with the monitoring of Baixo Sabor and Foz Tua dams; to Professor Edwin Reynders, from Katholieke Universiteit Leuven (Belgium) for all the support validating the routines for uncertainty quantification and the generous and useful suggestions on the topic; to Professor Carlo Rainieri, from the University of Molise (Italy), for the insights on automatic operational modal analysis and the conversations about the specific case of Baixo Sabor dam, which helped improve this thesis; Structural Condition Assessment of Dams Based on Continuous Dynamic Monitoring to Doctor Gustavo Oliveira for the cared reading of my Research Thesis Project, and the interesting suggestions that followed; to Energias de Portugal (EDP), in particular to Engineers Domingos Silva Matos and Ilídio Ferreira, for the opportunity of testing Aguieira, Alto Lindoso, Bouçã, Caldeirão, Castelo do Bode and Santa Luzia dams, and for the access to data related with the monitoring of Baixo Sabor and