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Abstract(s)
Esta tese apresenta um trabalho de investigação sobre o comportamento de vigas de aço a temperaturas elevadas, usando simulações de elementos finitos com o software ANSYS. São analisadas vigas sólidos e alveolares, considerando a variação transiente da temperatura ao longo do tempo, o comportamento não linear material e geométrico, bem como o efeito das imperfeições geométricas iniciais e das tensões residuais. As análises numéricas térmicas e mecânicas utilizam os modelos do comportamento do material dependente da temperatura, segundo o Eurocódigo 3 parte 1-2.
Os modelos numéricos utilizados no software Ansys, utilizam elementos finitos de casca de 4 nós, para as simulações térmicas (SHELL131) e para as simulações estruturais e termomecânicas (SHELL181). O comportamento ao fogo das vigas sólidas e alveolares é analisado numericamente comparado os resultados da evolução da temperatura com os obtidos experimentalmente por Lamri B. em vigas de aço não protegidas expostas á curva de incêndio padrão ISO834 e adicionalmente segundo o método simplificado do Eurocódigo 3 parte 1-2.
O comportamento termomecânico e os respetivos mecanismos de colapso das vigas foi analisado considerando uma distribuição de temperatura uniforme e uma carga distribuída continuamente crescente, permitindo a determinação da carga de colapso para diferentes valores de temperaturas. É determinada a resistência de várias secções transversais, com diferentes valores dos diâmetros dos furos circulares, da distância entre furos e da largura da alma entre furações (web-post).
A resistência à encurvadura lateral torsional de vigas sólidas e alveolares é igualmente analisada através de simulações numéricas, considerando a influência das imperfeições geométricas iniciais, para diferentes valores de temperatura. Os resultados são comparados com os obtidos pelos métodos simplificados do Eurocódigo 3 parte 1.2. Os resultados das simulações térmicas realizadas no software ansys seguem a tendência obtida com os resultados dos testes experimentais. Os resultados da LTB mostram que a resistência é mais influenciada pelas imperfeições geométricas do que pelas tensões residuais. Adicionalmente, foi verificado que o efeito da temperatura, da secção transversal e das imperfeições geométricas é mais significativo nas vigas alveolares do que no caso das vigas solidas.
This thesis presents a research work on the behaviour of steel beams at high temperatures, using finite element simulations with ANSYS software. Solid and cellular beams are analysed, considering the transient temperature variation over time, nonlinear material and geometric behaviour, as well as the effect of initial geometric imperfections and residual stresses. The thermal and mechanical numerical analyses consider the material properties temperature variation according to the Eurocode 3 part 1-2. The numerical models implemented in Ansys software use shell finite elements of 4-nodes for thermal simulations (SHELL131) and for structural and thermomechanical simulations (SHELL181). The fire behaviour of the solid and cellular beams is numerically analysed comparing the results of the temperature evolution with those obtained experimentally by Lamri B in unprotected steel beams exposed to the standard fire curve ISO834 and additionally according to the simplified method of the Eurocode 3 part 1-2. The thermomechanical behaviour and the beams collapse mechanisms were analysed considering a uniform temperature distribution and a continuously increasing distributed load in the top flange, allowing the determination of the collapse load for different temperature values. The resistance of several cross-sections, with different values of the holes diameter, the distance between holes and the web-post width is determined. The lateral torsional buckling resistance of solid and cellular beams is also analysed by numerical simulations, considering the influence of the initial geometric imperfections, for different temperature values. The results are compared with those obtained by the simplified methods of Eurocode 3 part 1-2. The simulations with ANSYS thermal finite element models have produced good predictions for temperature evolution with small discrepancies acceptable for comparison with tests. The LTB resistance is more influenced by geometric imperfections than the residual stress. The effect of residual stress disappear in height temperature and also effect by the temperature and the length. For cellular beams the effect of temperature, cross section and geometry imperfection is higher than what is obtained in solid beams.
This thesis presents a research work on the behaviour of steel beams at high temperatures, using finite element simulations with ANSYS software. Solid and cellular beams are analysed, considering the transient temperature variation over time, nonlinear material and geometric behaviour, as well as the effect of initial geometric imperfections and residual stresses. The thermal and mechanical numerical analyses consider the material properties temperature variation according to the Eurocode 3 part 1-2. The numerical models implemented in Ansys software use shell finite elements of 4-nodes for thermal simulations (SHELL131) and for structural and thermomechanical simulations (SHELL181). The fire behaviour of the solid and cellular beams is numerically analysed comparing the results of the temperature evolution with those obtained experimentally by Lamri B in unprotected steel beams exposed to the standard fire curve ISO834 and additionally according to the simplified method of the Eurocode 3 part 1-2. The thermomechanical behaviour and the beams collapse mechanisms were analysed considering a uniform temperature distribution and a continuously increasing distributed load in the top flange, allowing the determination of the collapse load for different temperature values. The resistance of several cross-sections, with different values of the holes diameter, the distance between holes and the web-post width is determined. The lateral torsional buckling resistance of solid and cellular beams is also analysed by numerical simulations, considering the influence of the initial geometric imperfections, for different temperature values. The results are compared with those obtained by the simplified methods of Eurocode 3 part 1-2. The simulations with ANSYS thermal finite element models have produced good predictions for temperature evolution with small discrepancies acceptable for comparison with tests. The LTB resistance is more influenced by geometric imperfections than the residual stress. The effect of residual stress disappear in height temperature and also effect by the temperature and the length. For cellular beams the effect of temperature, cross section and geometry imperfection is higher than what is obtained in solid beams.
Description
Mestrado em cooperação com a Hassiba Benbouali University of Chlef
Keywords
Vigas alveolares Temperaturas elevadas Simulações numéricas Encurvadura Lateral Torsional