Caracterização numérica e experimental de ligações aparafusadas em madeira
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2014
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A madeira é um dos materiais de utilização mais antiga nas construções, foi utilizada por todo o mundo, quer nas civilizações primitivas, quer nas desenvolvidas, no oriente e no ocidente. A utilização da madeira como material estrutural, não é posta em pé de igualdade com o betão ou com o aço. Contudo, tem-se mostrado vantajosa, principalmente devido a várias características que apresenta, tais como a resistência mecânica, a estética, e a sua durabilidade. No entanto, ainda subsiste um desconhecimento sobre alguns aspetos do seu comportamento mecânico, designadamente à fratura, que a impedem de atingir todo o seu potencial como material de construção. Associado a esse desconhecimento, está a sua estrutura heterogénea e a forte anisotropia que exibe. Outro aspeto que reduz o potencial da madeira como material de construção é a sua existência em elementos estruturais de dimensão limitada. A solução encontrada para este problema é a utilização de ligações, como por exemplo ligações do tipo cavilha, ou através de múltiplas colagens. As ligações são componentes críticos das estruturas de madeira que transmitem cargas estáticas e dinâmicas entre os membros estruturais constituintes. Por este motivo, o conhecimento do seu comportamento mecânico revela-se muito importante para o alcance do potencial que a madeira apresenta como material de construção.
O presente trabalho teve como objetivo central o estudo do comportamento frágil de ligações do tipo cavilha, com diferentes geometrias, em estruturas de madeira da espécie Pinus pinaster Ait.
Nesta dissertação estudaram-se quatro cenários alternativos de fixação de duas peças de madeira maciça, a uma chapa metálica, recorrendo a cavilhas metálicas, submetidas a um carregamento quase-estático, com transmissão de momento. Os referidos cenários distinguiram-se pelas distâncias entre os centros das cavilhas, e destas, aos bordos das peças de madeira. Procedeu-se a uma comparação das curvas força-deslocamento, características dos diferentes cenários de fixação, tendo-se constatado a existência de diferenças notórias, quer ao nível da resistência mecânica, quer ao nível da rigidez inicial. Complementarmente, utilizou-se a técnica de correlação digital de imagem (CDI), com o objetivo de obter o campo de deslocamentos registado na vizinhança das cavilhas. Elaborou-se um modelo de elementos finitos visando a simulação de cada cenário de fixação estudado, usando elementos coesivos e uma rotina de modo misto (I+II). Os referidos modelos numéricos revelaram-se capazes de reproduzir as curvas força-deslocamento obtidas nos ensaios mecânicos, assim como de produzir os campos de deslocamento na vizinhança das cavilhas, e nas regiões afetadas pelo dano, em total acordo com as observações realizadas no decorrer dos ensaios de fratura. As ferramentas numéricas assim desenvolvidas poderão ser usadas no sentido de estudar o desempenho deste tipo de ligação, em cenários alternativos aos que foram analisados neste trabalho.
Wood is one of the oldest materials used in construction. It has been used all over the world, whether in primitive civilizations or in developed civilizations, in eastern and western countries. The use of wood as a structural material cannot be positioned at an equal level as concrete or steel. However, it presents remarkable advantages, especially because it has various characteristics such as mechanical strength, aesthetics and durability. However, there is still a lack of knowledge concerning some aspects of the mechanical behavior and fracture of wood, hindering the attainment of its full potential as a building material. Associated with this lack, is its heterogeneous structure and the strong anisotropy. Another aspect which reduces the potential of wood as a building material, is the existence of structural elements with limited dimensions. The solution to this problem is the use of connections such as dowel type, or by multiple glued connections. The connections are critical components of timber structures which transmit static and dynamic loads between the constituent of structural members. For this reason, knowledge of the mechanical behavior proves to be very important to achieve the potential of wood as a building material. The main objective of the present work is the study of fragile behavior of dowel type connections with different geometries using wood of Pinus pinaster Ait. In this Thesis four alternative scenarios to fixe two pieces of solid wood with a metallic sheet have been studied, using metal dowels submitted to quasi-static loading conditions. The scenarios mentioned above were distinguished by the distances between the centers of the dowels and, of these to the edges of the wood pieces. A comparison of the obtained load-displacement curves has been made, characteristic of different fixing scenarios. It was found that there were marked differences, both in terms of mechanical strength and in terms of initial stiffness. Additionally, the digital image correlation (CDI) technique was used. The goal was to obtain the displacement field recorded in the proximity of the dowels. A finite element model was built to perform the simulation of this connections for each studied scenario, using a routine that mimics the mixed mode (I + II) loading. The numerical model proved to reproduce the load-displacement curves obtained in the mechanical tests, as well as the displacement fields in the vicinity of the dowels. Also, a remarkable agreement with the damaged areas was observed. The numerical tool carried thereby, may be used in order to study the performance of this type of connections, in alternative to those sets that have not been analyzed in this study.
Wood is one of the oldest materials used in construction. It has been used all over the world, whether in primitive civilizations or in developed civilizations, in eastern and western countries. The use of wood as a structural material cannot be positioned at an equal level as concrete or steel. However, it presents remarkable advantages, especially because it has various characteristics such as mechanical strength, aesthetics and durability. However, there is still a lack of knowledge concerning some aspects of the mechanical behavior and fracture of wood, hindering the attainment of its full potential as a building material. Associated with this lack, is its heterogeneous structure and the strong anisotropy. Another aspect which reduces the potential of wood as a building material, is the existence of structural elements with limited dimensions. The solution to this problem is the use of connections such as dowel type, or by multiple glued connections. The connections are critical components of timber structures which transmit static and dynamic loads between the constituent of structural members. For this reason, knowledge of the mechanical behavior proves to be very important to achieve the potential of wood as a building material. The main objective of the present work is the study of fragile behavior of dowel type connections with different geometries using wood of Pinus pinaster Ait. In this Thesis four alternative scenarios to fixe two pieces of solid wood with a metallic sheet have been studied, using metal dowels submitted to quasi-static loading conditions. The scenarios mentioned above were distinguished by the distances between the centers of the dowels and, of these to the edges of the wood pieces. A comparison of the obtained load-displacement curves has been made, characteristic of different fixing scenarios. It was found that there were marked differences, both in terms of mechanical strength and in terms of initial stiffness. Additionally, the digital image correlation (CDI) technique was used. The goal was to obtain the displacement field recorded in the proximity of the dowels. A finite element model was built to perform the simulation of this connections for each studied scenario, using a routine that mimics the mixed mode (I + II) loading. The numerical model proved to reproduce the load-displacement curves obtained in the mechanical tests, as well as the displacement fields in the vicinity of the dowels. Also, a remarkable agreement with the damaged areas was observed. The numerical tool carried thereby, may be used in order to study the performance of this type of connections, in alternative to those sets that have not been analyzed in this study.
Descrição
Dissertação de Mestrado em Engenharia Mecânica
Palavras-chave
Madeira , Resistência dos materiais , Cavilhas