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Análise do comportamento sísmico de pontes de alvenaria de pedra através do método dos blocos. Aplicação à ponte romana de Alcântara (Espanha)
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A presente dissertação tem como objetivo a utilização do método dos elementos discretos (também
conhecido por método dos blocos) na análise sísmica de pontes de alvenaria de pedra, usando como
caso de estudo a ponte romana de Alcântara, em Espanha. Trata-se de uma ponte em arco de alvenaria
de granito construída nos séculos I e II D.C.
O método dos elementos discretos é adequado para a análise de estruturas de alvenaria de pedra, já
que permite representar, com grande generalidade, o seu comportamento não linear, caracterizado pela
forte influência do comportamento das juntas entre os blocos de alvenaria. É muito útil na determinação
de cargas de colapso, na análise para grandes deslocamentos e em análises dinâmicas.
As análises através do método dos elementos discretos foram realizadas com o programa 3DEC, desen-
volvido pela empresa Itasca dos EUA. O programa tem uma interface gráfica que permite ao utilizador
visualizar o comportamento da estrutura e a evolução das principais variáveis.
Apresentam-se as características gerais da ponte de Alcântara e a sua história, fazendo-se referência,
em particular, à sua geometria e aos materiais que a constituem. Refere-se o desconhecimento de al-
guns processos construtivos da ponte e dos seus materiais. Apontam-se ainda as simplificações adota-
das, já que não existem nem foi possível fazer ensaios nos materiais e na própria estrutura.
Na ausência de ensaios “in situ” para obter as frequências próprias e os modos de vibração da estrutura,
o modelo de blocos rígidos da ponte foi calibrado com um modelo contínuo elástico desenvolvido há
cerca de uma década por Patrícia Gil (2012)[2]. As análises subsequentes foram realizadas com um mo-
delo de blocos rígidos, que é apropriado para representar o comportamento de estruturas de grandes
dimensões em que os deslocamentos se concentram nas juntas entre os blocos.
Foi realizada uma análise “pushover” da ponte, representando a ação sísmica como uma força estática
equivalente, que permitiu obter uma primeira estimativa da carga de colapso. De seguida foi realizada
uma análise dinâmica não linear no domínio do tempo sob a ação de um sismo regulamentar. Este sismo
foi escalado, de seguida, até se verificar o colapso da ponte. As análises sísmicas foram levadas a cabo
considerando dois modelos com propriedades mecânicas diferentes, com o objetivo de estudar o com-
portamento da ponte para diferentes estados de deterioração dos materiais.
This dissertation aims to use the Discrete Element Method (also known as Block Method) in the seismic analysis of stone masonry bridges, using the Alcântara roman bridge, located in Spain, as a case study. It is a masonry arch bridge, made of granite, dating back to the 1st and 2nd century, AD. The Discrete Element Method is suitable to analyze stone masonry structures, as it allows to represent their nonlinear behavior, which is characterized by the strong influence of the joints between the ma- sonry blocks. It’s very useful in the determination of collapse loads, in large displacement analysis and in seismic analysis. The analyses were performed using a program based on the Discrete Elements Method, 3DEC, devel- oped by Itasca, a USA company. The program has a graphical interface that allows the user to monitor the structure’s behavior, and the time evolution of the main variables. The bridge's general features, its history, the definition of its geometry and its materials are presented first. One of the barriers to overcome is the lack of knowledge about the constructive processes and the difficulty related to a precise materials description. Simplifications were made, since there are not, nor was it possible to do, tests on the materials and on the structure itself. In the absence of “in situ” measurements to obtain the structure’s natural frequencies and its corre- sponding vibration modes, the generated model was calibrated with an elastic continuous model cre- ated by Patrícia Gil (2012)[2]. A rigid block model was used as it is appropriate to represent a large-sized structure in which the large displacements are concentrated in the joints between the blocks. A pushover analysis was performed, with the goal of representing the seismic action by means of an equivalent static force, which allowed to obtain a first estimative of the bridge’s collapse load. Then it was performed a nonlinear dynamic analysis in the time domain under the action of a regulatory earth- quake. This earthquake was then scaled until the bridge’s collapse was verified. The seismic analyses were executed by means of two models with different mechanical properties, with the objective of providing information about the structure’s behavior with different materials and deterioration states.
This dissertation aims to use the Discrete Element Method (also known as Block Method) in the seismic analysis of stone masonry bridges, using the Alcântara roman bridge, located in Spain, as a case study. It is a masonry arch bridge, made of granite, dating back to the 1st and 2nd century, AD. The Discrete Element Method is suitable to analyze stone masonry structures, as it allows to represent their nonlinear behavior, which is characterized by the strong influence of the joints between the ma- sonry blocks. It’s very useful in the determination of collapse loads, in large displacement analysis and in seismic analysis. The analyses were performed using a program based on the Discrete Elements Method, 3DEC, devel- oped by Itasca, a USA company. The program has a graphical interface that allows the user to monitor the structure’s behavior, and the time evolution of the main variables. The bridge's general features, its history, the definition of its geometry and its materials are presented first. One of the barriers to overcome is the lack of knowledge about the constructive processes and the difficulty related to a precise materials description. Simplifications were made, since there are not, nor was it possible to do, tests on the materials and on the structure itself. In the absence of “in situ” measurements to obtain the structure’s natural frequencies and its corre- sponding vibration modes, the generated model was calibrated with an elastic continuous model cre- ated by Patrícia Gil (2012)[2]. A rigid block model was used as it is appropriate to represent a large-sized structure in which the large displacements are concentrated in the joints between the blocks. A pushover analysis was performed, with the goal of representing the seismic action by means of an equivalent static force, which allowed to obtain a first estimative of the bridge’s collapse load. Then it was performed a nonlinear dynamic analysis in the time domain under the action of a regulatory earth- quake. This earthquake was then scaled until the bridge’s collapse was verified. The seismic analyses were executed by means of two models with different mechanical properties, with the objective of providing information about the structure’s behavior with different materials and deterioration states.
Descrição
Palavras-chave
Ponte de Alcântara Alvenaria de pedra Comportamento não linear Método dos elementos discretos Grandes deslocamentos Cargas de colapso