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- Load bearing capacity of stainless steel beams at elevated temperaturesPublication . Alves, Matheus Henrique; Mesquita, L.M.M.; Piloto, P.A.G.; Lopes, Nuno; Arrais, Flávio; Vila Real, Paulo M.M.; Pinho-da-Cruz, JoaquimTo analyse the load bearing capacity of stainless steel (SS) members at elevated temperatures, a set of three-point bending tests was conducted on RHS 150x100x5 beams with SS grade 1.4301. The numerical modelling of these tests has been performed at elevated temperatures, achieving close approximation to observed experimental results. The load bearing capacity difference between the numerical results and the experimental results is smaller than 10%. Analytical methods were also used to predict the load-deflection behaviour.
- Comportamento de ligações autoperfurantes de perfis enformados a frio a temperaturas elevadasPublication . Parente, Armandino; Dias, Rui Paulo Silva; Mesquita, L.M.R.; Barreira, LuísaA aplicação de perfis estruturais de aço enformados a frio na construção metálica, nomeadamente construção de edifícios, tem um conjunto de vantagens das quais se destacam a elevada eficiência estrutural destes perfis, com uma elevada relação resistência estrutural/peso, a possibilidade de criação rápida de perfis de formas variadas e adaptadas às necessidades, assim como a economia no transporte e a elevada rapidez de execução da obra. Esta última está diretamente relacionada com os sistemas de ligação dos elementos estruturais utilizados, em que, por se tratarem de perfis de chapa fina, as ligações por parafusos autoroscantes e autoperfurantes são as mais utilizadas. O dimensionamento destes elementos estruturais e dos seus elementos de ligação devem ser dimensionados à temperatura ambiente e também numa situação acidental de incêndio, em que é necessário o valor de cálculo da resistência da ligação em função da temperatura de exposição. Este trabalho apresenta um conjunto de ensaios experimentais acerca do comportamento de ligações aparafusadas sujeitas ao corte simples de chapas de aço a temperaturas elevadas. As ligações são feitas com recurso a parafusos autoperfurantes e roscantes. É realizado um estudo paramétrico ao nível da espessura das chapas a ligar e a influência da posição da ligação para a temperaturas elevadas, representativas da situação de incêndio. Os resultados permitem verificar que a resistência da ligação é limitada pela resistência ao corte do parafuso ou pela resistência ao esmagamento da chapa de aço, dependendo da espessura das chapas a ligar, da distância da ligação à extremidade da placa e da temperatura de exposição.
- Instabilidade lateral de vigas a temperaturas elevadas: determinação da temperatura críticaPublication . Piloto, P.A.G.; Mesquita, L.M.R.; Vaz, M.A.P.; Vila Real, Paulo M.M.A resistência dos elementos de uma estrutura, quando submetidos a temperaturas elevadas, pode ser ver verificada no domínio da temperatura, definindo-se um valor crítico para a temperatura máxima quando o efeito das acções iguala o valor da resistência do elemento. Em elementos de viga não restringidos lateralmente, a temperatura crítica pode ser determinada em função do tipo de carregamento e grau de utilização, para uma situação de instabilidade por encurvadura lateral. Neste artigo serão apresentados resultados experimentais de ensaios realizados em perfis metálicos IPEJ 00, resultados de simulações numéricas efectuadas com o elemento SHELLJ8I do programa ANSYS e resultados propostos pelo Eurocódigo 3, parte 1.2.
- Determinação do factor concentração de tensões em placas utilizando a extensometria com validação numéricaPublication . Fonseca, E.M.M.; Caleiro, C.M.S.; Lopes, Hernani; Vaz, M.A.P.; Mesquita, L.M.R.É apresentada uma metodologia experimental para determinação do factor concentração de tensões, com base na técnica de extensometria, em placas com furos circulares. Pretende-se efectuar a comparação dos resultados experimentais com resultados numéricos obtidos em códigos comerciais: ANSYS e COSMOS/M. É ainda apresentada a mesma solução usando um programa de elementos finitos desenvolvido FEMSEF.
- Fire reaction of concrete with and without PP fibres: experimental analysis and numerical simulationPublication . Piloto, P.A.G.; Mesquita, L.M.R.; Balsa, CarlosStructural elements of reinforced concrete, in general, present good performance in case of fire. However, more recent structures have adapted new types of concrete (high strength, self-compacting, etc.) presenting different thermo mechanical behaviour, acquiring special importance the study of spalling. One of the most common procedures to minimize this events is the addition of polypropylene fibres (PP) to natural components, reducing the internal void pressure of the material through the channels created by the fusion of the fibres. The experimental study of concrete under fire conditions and the development of new numerical models has allowed the assessment of more or less complex phenomena to determine temperature evolution and other state variables, enabling different levels of approaches, using coupled or uncoupled field interaction (thermal, mechanical, hydrodynamic, chemical). This investigation studies the thermal performance of a two dimensional model, using nonlinear and transient finite element analysis.
- Valorization of lignin side-streams into polyols and rigid polyurethane foams—a contribution to the pulp and paper industry biorefineryPublication . Pinto, João A.; Fernandes, Isabel P.; Pinto, Virgínia; Gomes, Elson; Oliveira, Cátia F.; Pinto, Paula C.R.; Mesquita, L.M.R.; Piloto, P.A.G.; Rodrigues, Alírio; Barreiro, M.F.Valorization of industrial low-value side-streams are of great interest, contributing to boosts in the circular economy. In this context, lignin side-streams of the pulp and paper industry were oxypropylated to produce biobased polyols and tested in the synthesis of rigid polyurethane (RPU) foams. E. globulus lignins, namely a lignin isolated from an industrial Kraft black liquor and depolymerized lignins obtained as by-products of an oxidation process, were used. RPU foams, synthesized with 100% lignin-based polyols and using a 1.1 NCO/OH ratio, were characterized concerning apparent density, morphology, thermal conductivity, thermal stability, and heat release rate (HRR). Foams containing the lignin-based polyols presented densities varying from 44.7 to 112.2 kg/m3 and thermal conductivity in the range of 37.2–49.0 mW/mK. For the reference foam (sample produced with 100% wt. Daltofoam TP 32015 polyol), values of 70.9 kg/m3 and 41.1 mW/mK were obtained, respectively. The achieved results point out the viability of using the generated lignin-based polyols at 100% content in RPU foams, mainly when depolymerized lignins are used. Moreover, fire retardancy was favored when the lignin-based polyols were introduced. The proposed strategies can contribute to establishing the integrated pulp and paper biorefinery concept where material synthesis (polyols and RPU foams) can be combined with chemical production (vanillin and syringaldehyde).
- 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.
- Numerical analysis of instability failure modes of cellular steel beams in fire conditionsPublication . Mesquita, L.M.R.; Silva, Jaqueline; Dalcana, Paola ReginaBeams with long spans are increasingly used in the steel building constructions and usually are used with openings for technical equipment and ventilations systems cut in their web. These elements are structural steel beams that are deeper than normal rolled sections, with distributed circular openings, or other like squared or hexagonal, that are produced by cutting and welding hot rolled steel sections (Westok method). The split halves are then offset and welded together to form a deeper beam with full circular or hexagonal shaped web openings. This method reduces the floor height and therefore the overall height of building.
- Fire resistance of steel members protected with intumescent coatingsPublication . Mesquita, L.M.R.; Piloto, P.A.G.; Roque, Sérgio; Vaz, M.A.P.The required intumescent coating thicknesses needed for fire resistance are proposed by the paints manufactures based on the results of a limited number of standard fire resistance tests, considering different steel section factors and DFTs. This work presents a set of 50 experimental fire resistance tests made in a pilot gas furnace and considering: (i) different member cross-sections (IPE, SHS, CHS, LNP), (ii) analysis at ambient temperature and fire conditions, (iii) application of a mechanical loading in a tree-point bending setup, (iv) different utilization degree level (30%, 50%, 70%) and (v) different intumescent thicknesses. Results show that increasing intumescent fire protection thickness an increase in fire resistance time is achieved. For the same nominal protection thickness the critical temperature and fire resistance time decreases with increasing degree of utilisation. The results from the unprotected fire tests are compared with the ones obtained by the Eurocode 3 part 1.2 simplified calculation method.. Taking into account the nominal properties only the CHS section experimental results shows unsafe fire resistance times in comparison to the Eurocode values.
- Bending resistance of partially encased beams at elevated temperature: advanced calculation modelPublication . Piloto, P.A.G.; Almeida, David; Ramos Gavilán, Ana Belén; Mesquita, L.M.R.Partially Encased Beams (PEBs) are composite steel and concrete elements in which the web of the steel section is encased by reinforced concrete. The experimental investigation of the bending resistance was already verified in fire and under elevated temperature (Paulo A. G. Piloto el al., 2013a) (Paulo A. G. Piloto el al., 2013b). The three-dimensional finite element solution, with precise detail of each component (steel profile, reinforcement, stirrups and concrete) was used to determine the bending resistance under three point bending configuration. Four temperature levels were tested (20, 200, 400 and 600 degrees C) and three lengths were considered (2.5, 4.0 and 5.5 m), using three different cross section types, based on the dimensions of IPE100, IPE200 and IPE300 steel profiles. Two distinct types of welded stirrups were simulated (PEBA with "C" shape stirrups welded to the web and PEBB with "I" shape stirrups welded to the flange). The solution method is incremental and iterative (arc length), based on geometric and material non-linear analysis (ANSYS), using reduced integration method. Results are in accordance to the new formula presented (P. M. M Vila Real et al., 2004) and adapted to partially encased beams. The bending resistance was not significantly influenced by the type of welded stirrup