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Advisor(s)
Abstract(s)
A utilização da madeira como material de construção em estruturas e edifícios representa, nos
dias de hoje, um aumento significativo. Esse crescente aumento deve-se, entre outros aspetos, à
preocupação ambiental (alterações climáticas) e ao facto deste material apresentar um
comportamento seguro e previsível aquando da ocorrência de um incêndio.
Com a presente dissertação, sobre ligações de madeira e aço em corte simples e submetidas ao
fogo, foi possível um melhor entendimento acerca do seu comportamento térmico e
termomecânico, para diferentes tipos de configurações (aço-madeira e madeira-madeira),
utilizando cavilhas em aço como elementos de ligação.
Inicialmente, efetuou-se uma revisão bibliográfica dos temas subjacentes à análise
termomecânica de três tipos de ligações aço-madeira com cavilhas metálicas, particularmente:
ligações inteiramente em madeira (MM), e ligações com madeira e uma chapa de aço fina (MAf)
ou uma chapa de aço espessa (MAe). Foram abordadas também as propriedades mecânicas e
térmicas da madeira e do aço; a análise do processo de carbonização na madeira e a sua
velocidade; a resistência das ligações à aplicação de cargas; uma abordagem ao processo de
transferência de calor aquando de um incêndio; as curvas nominais de incêndio e a análise ao
impacto que a utilização da madeira impõe em termos de sustentabilidade. Após essa revisão
bibliográfica, concluiu-se a inexistência de estudos na quantificação da resistência da madeira ao
fogo, comparativamente a outros materiais.
No que diz respeito ao desenvolvimento do tema de dissertação, desenvolveu-se uma análise
numérica termomecânica para diferentes tipos de ligações madeira-madeira e aço-madeira com
cavilhas em aço, submetidas à tração em corte simples e expostas à ação do fogo. Consideraram se, ainda, três tipos de madeira com massa volúmica distinta. Através destas simulações, foi
possível determinar o campo de tensões de origem térmica e mecânica, com base no método dos
elementos finitos. Numa primeira fase, calculou-se o campo de temperaturas nas ligações, através
de uma análise térmica em regime transiente. Com base no perfil de temperaturas calculado e na
aplicação de uma carga de tração incremental, determinou-se a capacidade resistente da ligação.
Nas diferentes análises, foram considerados os materiais com comportamento não linear
dependentes da temperatura. Os resultados permitiram, ainda, analisar a influência da massa
volúmica da madeira, quer na resistência térmica da ligação, como também na resistência
mecânica da ligação.
The use of wood as a construction material in structures and buildings represents, nowadays, a significant increase. This increase is due, among other aspects, to environmental concerns (climate change) and to the fact that this material presents a safe and predictable behavior in fire situation. With the present dissertation, on wood-steel connections in single shear and submitted to fire, it was possible to better understand their thermal and thermomechanical behavior, for different types of configurations (steel-wood and wood-wood), using dowels in steel as the connecting elements. First of all, a state of the art was carried out underlying the thermomechanical analysis of three types of steel-wood connections with metallic dowels, particularly: connections entirely in wood (MM) and connections with wood and a thin steel plate (MAf) or a thick steel plate (MAe). The mechanical and thermal properties of wood and steel were also discussed; the analysis of the char layer evolution in wood and its charring ratio; the resistance of connections to the application of loads; an approach to the heat transfer process during a fire, the nominal fire curves, and the analysis of the impact that the use of wood imposes in terms of sustainability. After this bibliographical review, it was concluded that there are no studies on the quantification of fire resistance of wood, compared to other materials. With regard to the development of the dissertation subject, a numerical thermomechanical analysis was developed for different types of wood-wood and steel-wood connections with steel dowels, submitted to tensile in simple shear and exposed to the fire action. Three types of wood with different densities were also considered. Through these simulations, it was possible to determine the stress field of thermal and mechanical source, based on the finite element method. In a first step, the temperature field in the connections was calculated, through a transient thermal analysis. Based on the calculated temperature profile and the application of an incremental tensile load, the strength capacity of the connection was determined. In the different analyses, materials with temperature-dependent nonlinear behavior were considered. The results also allowed analyzing the influence of wood density, both on the thermal resistance of the connection, as well as on the mechanical resistance of the connection.
The use of wood as a construction material in structures and buildings represents, nowadays, a significant increase. This increase is due, among other aspects, to environmental concerns (climate change) and to the fact that this material presents a safe and predictable behavior in fire situation. With the present dissertation, on wood-steel connections in single shear and submitted to fire, it was possible to better understand their thermal and thermomechanical behavior, for different types of configurations (steel-wood and wood-wood), using dowels in steel as the connecting elements. First of all, a state of the art was carried out underlying the thermomechanical analysis of three types of steel-wood connections with metallic dowels, particularly: connections entirely in wood (MM) and connections with wood and a thin steel plate (MAf) or a thick steel plate (MAe). The mechanical and thermal properties of wood and steel were also discussed; the analysis of the char layer evolution in wood and its charring ratio; the resistance of connections to the application of loads; an approach to the heat transfer process during a fire, the nominal fire curves, and the analysis of the impact that the use of wood imposes in terms of sustainability. After this bibliographical review, it was concluded that there are no studies on the quantification of fire resistance of wood, compared to other materials. With regard to the development of the dissertation subject, a numerical thermomechanical analysis was developed for different types of wood-wood and steel-wood connections with steel dowels, submitted to tensile in simple shear and exposed to the fire action. Three types of wood with different densities were also considered. Through these simulations, it was possible to determine the stress field of thermal and mechanical source, based on the finite element method. In a first step, the temperature field in the connections was calculated, through a transient thermal analysis. Based on the calculated temperature profile and the application of an incremental tensile load, the strength capacity of the connection was determined. In the different analyses, materials with temperature-dependent nonlinear behavior were considered. The results also allowed analyzing the influence of wood density, both on the thermal resistance of the connection, as well as on the mechanical resistance of the connection.
Description
Keywords
Eurocodes Fire Steel Wood Thermomechanical behavior Connections in single shear