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Advisor(s)
Abstract(s)
A maioria das grandes barragens atualmente em exploração, em construção ou na fase de
projeto, estão localizadas em zonas sísmicas e, muitas delas, em áreas de elevada sismicidade.
Um aspeto fundamental a ter em conta no controlo da segurança de barragens é a necessidade
de avaliar seu comportamento sob ações sísmicas. Com este propósito, é necessário desenvolver
modelos numéricos para simular a resposta sísmica dos sistemas barragem-fundação-albufeira,
que devem ser testados através da comparação entre resultados numéricos e experimentais
obtidos através da monitorização da resposta sísmica em barragens existentes (sistemas de
monitorização sísmica foram recentemente instalados em várias grandes barragens).
Para a simulação numérica da resposta sísmica medida, deve ser considerado o valor real
do nível da água do reservatório durante um sismo, bem como o acelerograma sísmico registado
na base da barragem (ao nível da inserção do maciço rochoso) e caracterizado pela sua duração,
amplitude e conteúdo em frequência. Ao realizar as comparações para vários eventos sísmicos
observados in situ, é possível calibrar e aumentar a fiabilidade dos modelos numéricos utilizados
para simular a resposta sísmica de grandes barragens.
O objetivo principal desta dissertação é contribuir para os estudos da simulação numérica
sobre a análise sísmica barragens abóbada, realçando a influência da cota da água do
reservatório na resposta estrutural da barragem, para um determinado acelerograma sísmico. A
modelação numérica da resposta sísmica é realizada no domínio do tempo, com base num modelo
clássico, utilizando elementos finitos 3D (com 20 nós) para discretizar a barragem e a fundação,
adotando a hipótese de massas de água associadas propostas por Westergaard para simular as
pressões hidrodinâmicas.
São apresentados os resultados da análise sísmica da barragem do Cabril (132 m de altura),
utilizando vários acelerogramas sísmicos, com diferentes conteúdos em frequência, que são
escalados para uma aceleração de pico de 0,2 g. Foram considerados três tipos de acelerogramas
sísmicos: i) gerados com modelos de rotura de falha desenvolvido no LNEC; ii) gerados através
do programa SIMQKE, diretamente a partir de espetros de resposta; e iii) acelerogramas sísmicos
correspondentes a sismos reais medidos.
Most of the large dams currently in operation, under construction or in the design phase, are located in seismic zones, and many of them in areas of high seismicity. A fundamental aspect to take into account in the dam safety control is the need to evaluate its behavior under seismic events. For this purpose, it is necessary to develop numerical models to simulate the seismic response of dam-foundation-reservoir systems, which must be tested through the comparison between numerical and experimental results obtained by monitoring the seismic response of the existing dams (seismic monitoring systems have been recently installed in several large dams). For the numerical simulation of the measured seismic response it must be considered the actual value of the reservoir water level during an earthquake, as well as the recorded seismic accelerogram at the dam base (at the level of the insertion in the rock foundation) and characterized by its duration, amplitude and frequency content. By performing such comparisons for several seismic events observed in situ, it is possible to calibrate and increase the reliability of the numerical models used to simulate the seismic response of large dams. The main goal of this work is to contribute for the numerical simulation studies regarding the seismic analysis of large arch dams, by focusing on the influence of the reservoir water level in the structural response of the dam, for a given seismic accelerogram. The numerical modeling of the seismic response is performed in the time domain, based on a classic model, using 3D finite elements (with 20 nodes) to discretize the dam and the foundation, while adopting the added water mass hypothesis of Westergaard to simulate the hydrodynamic pressures. The results of the seismic analysis of Cabril dam (132 m high) are presented, considering the use of several seismic accelerograms, with varying frequency content, which are scaled to a peak acceleration of 0.2g. Namely, three types of acceleration histories were considered: i) generated with a tectonic fault rupture model developed in LNEC; ii) computed directly from response spectra, using the SIMQKE program; and iii) real seismic accelerograms recorded in situ during earthquakes.
Most of the large dams currently in operation, under construction or in the design phase, are located in seismic zones, and many of them in areas of high seismicity. A fundamental aspect to take into account in the dam safety control is the need to evaluate its behavior under seismic events. For this purpose, it is necessary to develop numerical models to simulate the seismic response of dam-foundation-reservoir systems, which must be tested through the comparison between numerical and experimental results obtained by monitoring the seismic response of the existing dams (seismic monitoring systems have been recently installed in several large dams). For the numerical simulation of the measured seismic response it must be considered the actual value of the reservoir water level during an earthquake, as well as the recorded seismic accelerogram at the dam base (at the level of the insertion in the rock foundation) and characterized by its duration, amplitude and frequency content. By performing such comparisons for several seismic events observed in situ, it is possible to calibrate and increase the reliability of the numerical models used to simulate the seismic response of large dams. The main goal of this work is to contribute for the numerical simulation studies regarding the seismic analysis of large arch dams, by focusing on the influence of the reservoir water level in the structural response of the dam, for a given seismic accelerogram. The numerical modeling of the seismic response is performed in the time domain, based on a classic model, using 3D finite elements (with 20 nodes) to discretize the dam and the foundation, while adopting the added water mass hypothesis of Westergaard to simulate the hydrodynamic pressures. The results of the seismic analysis of Cabril dam (132 m high) are presented, considering the use of several seismic accelerograms, with varying frequency content, which are scaled to a peak acceleration of 0.2g. Namely, three types of acceleration histories were considered: i) generated with a tectonic fault rupture model developed in LNEC; ii) computed directly from response spectra, using the SIMQKE program; and iii) real seismic accelerograms recorded in situ during earthquakes.
Description
Trabalho final de mestrado elaborado no Laboratório Nacional de Engenharia Civil (LNEC) para a obtenção do grau de mestre em Engenharia Civil pelo Instituto Superior de Engenharia de Lisboa no âmbito do protocolo de cooperação entre o ISEL e o LNEC
Keywords
Barragens de betão Concrete dams Barragens abóbada Arch dams Sistema barragem-fundação-albufeira Dam-reservoir-foundation system Modelos numéricos EF3D 3D finite elements models Cota de água Reservoir water level Análise sísmica Seismic analysis Análise dinâmica Dynamic analysis Abordagem de estado State space approach Comportamento estrutural Structural behaviour MATLAB
Citation
RAMOS, Rafael Manuel da Silva - Modelação do comportamento sísmico de barragens abóbada : estudo da influência da cota de água. Lisboa: Instituto Superior de Engenharia de Lisboa, 2017. Dissertação de mestrado.
Publisher
Instituto Superior de Engenharia de Lisboa