Percorrer por autor "Lopes, Nuno"
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- Accurate 3D numerical models for the fire performance on lsf partition walls under different fire scenariosPublication . Piloto, Paulo A.G.; Silva, Renata; Frizzera, Giovanna; Torres, Leonardo; Couto, Carlos; Vila Real, Paulo; Mesquita, Luís M.R.; Lopes, NunoThis study presents the development and validation of advanced 3D numerical models to analyse the fire performance of non-load-bearing Light Steel Frame (LSF) partition walls under different fire scenarios, specifically the standard ISO 834 and HYDROCARBON fire. Medium-scale experimental fire resistance tests from prior research were used for validation, focusing on LSF walls with and without cavity insulation (external composite insulation). Three computational solution methods were compared and used to predict the fire behaviour of LSF walls with a void cavity. The finite element method was employed for transient thermal analysis with temperature-dependent material properties, including adaptations to simulate material degradation such as gypsum board cracking and rock wool melting under HYDROCARBON fire conditions. Hydrocarbon fires reduced fire resistance by an average of 57% compared to ISO 834 fires for cavity-insulated walls, whereas external insulation configurations showed less reduction.
- Austenitic hollow stainless steel beams at elevated temperatures: experimental and numerical validationPublication . Piloto, Paulo A.G.; Mesquita, Luís M.R.; Cruz, Áureo; Lopes, Nuno; Arrais, Flávio; Vila Real, Paulo
- Bending resistance of austenitic stainless steel hollow sections at elevated temperaturesPublication . Piloto, P.A.G.; Mesquita, L.M.R.; Cruz, Áureo A.T.; Lopes, Nuno; Arrais, Flávio; Real, Paulo VilaThe present research aims to increase the knowledge of the structural behaviour of stainless steel members under fire. Eight experimental bending tests at elevated temperatures (500, 700 ºC) built with RHS 150×100×3 austenitic stainless-steel beams, using two different grades (1.4301, 1.4571) also known as 304 and 316Ti, are presented. Both grades 1.4301 (X5CrNi18–10) and 1.4571 (X6CrNiMo17–12–2) have almost the same core chemical composition but there are some differences, especially the grade 1.4571 has 2–2.5% molybdenum and a small amount of titanium (less than 0.7%). Grade 1.4301 presents good rust resistance, sufficient acid resistance and good weldability, while grade 1.4571 presents very good rust resistance, very good acid resistance and also good weldability. Both have almost the same strength, but grade 1.4571 has superior strength at elevated temperatures. Both material grades were experimentally characterised with coupon tensile tests at room temperature. The load-displacement behaviour is validated with 3D shell finite element models, assuming a true stress-strain material model, based on the two-stage Ramberg Osgood constitutive law. With the developed numerical model, a parametric analysis is presented to study the fire resistance of beams from both materials, using three different cross-sections and eleven different temperatures. The bending resistance obtained with the finite element model is in good agreement with the cross-sectional design moment resistance, when considering the effective area, confirming that the design rules from EN1993–1–2 are safe for less slender cross-sections and unsafe for the most slender cross-sections.
- Bending resistance of stainless steel beams at elevated temperaturesPublication . Alves, Matheus Henrique; Mesquita, L.M.R.; Piloto, P.A.G.; Lopes, Nuno; Arrais, Flávio; Vila Real, Paulo M.M.Structural stainless steel elements at elevated temperatures behave differently than structural carbon steels. To analyse this behaviour, a set of three-point bending tests on 150x100 RHS, Class 1 cross-section, stainless steel grade 1.4301 beams at elevated temperatures were conducted. Numerical modelling of these tests has been afterwards performed at the measured temperatures, achieving close approximation to observed experimental results.
- Bending resistance of stainless steel beams at elevated temperaturesPublication . Alves, Matheus Henrique; Mesquita, L.M.R.; Piloto, P.A.G.; Lopes, Nuno; Arrais, Flávio; Vila Real, Paulo M.M.; Pinho-da-Cruz, JoaquimTo analyse the structural behaviour of stainless steel members at elevated temperatures, a set of three-point bending tests on RHS 150x100x5 beams of the grade 1.4301 were conducted. Numerical modelling of these tests has been afterwards performed at the measured temperatures, achieving close approximation to observed experimental results. Analytical methods to predict the load-deflection behaviour are also analysed.
- Caracterização experimental da resistência ao fogo de vigas RHS em aço inoxidávelPublication . Lopes, Nuno; Arrais, Flávio; Vila Real, Paulo M.M.; Alves, Matheus Henrique; Mesquita, L.M.R.; Piloto, P.A.G.; Pinho-da-Cruz, JoaquimCom o objetivo de analisar experimentalmente o comportamento mecânico de elementos estruturais em aço inoxidável a temperaturas elevadas, foi realizado um conjunto de ensaios de resistência ao fogo, à flexão em três pontos, a perfis com secção transversal RHS150x100x5, em aço inoxidável 1.4301, aplicando a curva de aquecimento padrão ISO 834. Os resultados são analisados e comparados com os obtidos por modelação numérica, realizada com o programa de elementos finitos SAFIR, validando o modelo numérico construído e a aplicação da lei constitutiva para o aço inoxidável a temperaturas elevadas proposta na nova geração da Parte 1-2 do EC3.
- Comportamento ao fogo de vigas alveolares com aberturas circularesPublication . Silva, Luana Vidoti da; Mesquita, Luís M.R.; Piloto, Paulo A.G.; Ferreira, Débora; Barreira, Luísa; Lopes, Nuno; Couto, Carlos; Vila Real, PauloO comportamento de vigas alveolares de aço à flexão, especialmente em situação de incêndio, foi investigado através de uma campanha experimental e da validação de um modelo numérico. Os resultados demonstram que o modelo de elementos finitos prevê com boa precisão a capacidade de carga e os modos de falha observados nos ensaios. A análise evidencia que a geometria das aberturas condiciona o modo de colapso à temperatura ambiente, enquanto o aumento da temperatura pode alterar o mecanismo de falha para uma mesma geometria, promovendo o colapso por encurvadura do montante da alma ou pelo Mecanismo de Vierendeel. A investigação apresenta dados experimentais relevantes e um modelo numérico validado, essenciais para o desenvolvimento de futuras regras de dimensionamento.
- Comportamento de vigas - coluna em situação de incêndio: uma nova proposta de cálculo simples alternativa ao EC3Publication . Lopes, Nuno; Vila Real, Paulo M.M.; Silva, Luís Simões; Piloto, P.A.G.A parte 1-1 do Eurocódigo 3 foi recentemente alterada relativamente à verificação da segurança de vigas-coluna e de vigas sujeitas a encurvadura lateral. A fim de se estudar a possibilidade de se ter, na parte 1-1 e na parte 1-2 daquele Eurocódigo, a mesma abordagem para a verificação de vigas-coluna, foi realizado pelos autores, num artigo anterior, um estudo numérico, que concluiu que a nova abordagem (parte 1-1) pode ser usada em caso de incêndio. Foi também proposto, pelos autores noutro artigo recente, uma melhoria da análise da encurvadura lateral de vigas em situação de incêndio, usando uma abordagem similar à utilizada na parte 1-1 do Eurocódigo 3. No presente artigo foi usada a nova abordagem para a encurvadura lateral, com as fórmulas de verificação da segurança de vigas-coluna a temperaturas elevadas baseadas na prEN 1993-1-1 bem como com as fórmulas da prENl993-1-2. Em ambos os casos os resultados melhoraram significativamente relativamente aos resultados numéricos.
- Experimental investigation of cellular steel beams at ambient and elevated temperaturesPublication . Silva, Luana Vidoti da; Giacomitti, Nickolas; Ferreira, Débora; Lopes, Nuno; Mesquita, Luís M.R.Cellular steel beams, commonly used in modern construction, exhibit complex failure mechanisms that have not been thoroughly explored, especially under fire conditions. This research investigates the structural behaviour of cellular beams under both ambient and elevated temperatures, with a focus on load-bearing capacity and failure modes. Experimental tests were conducted on a solid beam and six cellular beams with varying hole spacings and diameters at different temperatures. All beams were tested under three-point bending, subjecting the openings and the web posts to different combinations of bending moments and shear forces. Experimental maximum loads and failure modes are compared with the design method of EN1993-1-13 and EN1993-1-2. At ambient temperature, failure modes varied with beam design: specimens with smaller opening spacings failed by web-post buckling, while larger openings resulted in a Vierendeel mechanism. While the Eurocode predictions for load capacity were conservative under ambient conditions, the design model did not accurately predict the correct failure mode. Elevated temperatures significantly reduced the load capacity and, in some cases, changed the collapse mechanism. These results highlight that current design rules are unreliable in predicting the failure mode and may not ensure safety at higher temperatures, stressing the need for specific design rules for cellular beams in fire conditions.
- Fire performance of light timber frame construction in Europe: a review on fire protection measures and fire safety designPublication . Alves, Matheus Henrique; Mesquita, Luís M.R.; Piloto, Paulo A.G.; Lopes, NunoTimber construction is becoming increasingly relevant for the climate and energy transition of the building sector. Notably, modern multilayered light frame elements are attractive due to their versatility and ease of prefabrication, and they are now used in a wide range of building heights and occupancies. However, wood and wood-based products are combustible, and verifying the fire resistance of timber frame elements and certification of innovative eco-materials require appropriate design and fire testing. This work contextualises the relevance of European timber structures towards the green transition. It further discusses the fire performance and fire safety design of light timber frame systems, emphasising passive fire protection measures. The paper also briefly addresses new developments in Eurocode 5 related to fire resistance verification of light timber frame elements. Additionally, as increasingly complex and innovative assemblies arise in construction practice, developing advanced models, such as finite element and comprehensive multiscale models, is required for performance-based fire engineering and product development. These models simulate the thermal and structural behaviour of timber at elevated temperatures, providing practical tools for assessing fire resistance. Therefore, an instructive background on comprehensive models for modelling the fire behaviour of timber is presented. This work is intended to be a one-stop reference for understanding the relevance of timber elements in Europe and the fire protection and fire safety design strategies for light timber frame construction within the framework of European guidelines.
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