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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.
- 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.
- The effect of residual stresses in the lateral-torsional buckling of steel I-beams at elevated temperaturePublication . Vila Real, Paulo M.M.; Cazeli, Ronisi; Silva, Luís Simões; Piloto, P.A.G.When a beam is bent about its greatest flexural resistance axis it may twist and move laterally, before it reaches its strength limit in bending. Although this problem of lateral-torsional buckling of steel beams at room temperature has well established solution, the same problem at elevated temperature has not. The lateral-torsional buckling of steel I- beams have been numerically investigated from room temperature up to 700 °C, with the aim of assessing the effects of the residual stresses in this mechanism of failure. A geometrically and materially non-linear finite element program i.e., a general model, has been used to determine the lateral-torsional resistance of steel 1-beams at elevated temperatures, according to the same material properties of Eurocode 3, Pan 1-2. The numerical results have been compared to the results of the simple model presented in Eurocode 3, Part 1-2 (1995) and to a new proposal that is being considered for approval.
- Fire resistance of wooden cellular slabs with rectangular perforationsPublication . Meireles, J.M.; Fonseca, E.M.M.; Piloto, P.A.G.; Ferreira, DéboraThis paper presents a numerical approach with finite element method in order to predict both the behaviour and the performance of the wooden slabs with rectangular perforations under fire exposure. These typical constructions have good sound absorption, thermal insulation and relevant architectonic features, they are used in many civil engineering applications as: concert and conference halls, classrooms, nurseries, airports, hotels, shopping, universities, and many other private and public buildings. These slabs are normally installed at lower level in building constructions essentially due to an easy maintenance requisite. Depending on the installation requirement, the perforated wooden slabs could have an additional insulation material inside the cavities [1]. The proposed numerical model could be applied to different design constructive slab solutions. For this purpose a 3D numerical simulation was conducted with particular attention to the wood thermal properties variation with temperature [2]. The numerical results were compared with those obtained experimentally in laboratory, for two wooden slabs. The fire resistance (performance criteria related to the insulation (I) and integrity (E)) was evaluated, as well as the effect of rectangular perforations into the residual cross section of the slab. This study was conducted in accordance with European Standard EN 1365-2 [3] and using a fire resistance furnace which complies the requirements of EN 1363-1 [4] in the experimental test.
- 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.
- Non-linear buckling analysis of composite columns made from high and normal strength concrete under firePublication . Fellouh, Abdelkadir; Bougara, Abdelkader; Piloto, P.A.G.; Benlakehal, Nourredine O.Composite structures made from the combination of steel profile and concrete have significant loadbearing capacity which depends on the behaviour of the two material components and their interaction, particularly in fire conditions. It is not possible to assess the fire resistance of composite members only by considering the temperature of the steel, because the presence of the concrete may contribute greatly to increase the resistance, strength and thermal inertia of the member, which improves consequently the fire behaviour of the element. The aim of this work is to develop an efficient non-linear 3D finite element model to investigate the behaviour of pin-ended axially loaded composite column made from high strength concrete (HSC) and normal strength concrete (NSC) at different fire rating classes. Two types of column section were selected, notably HEB 160 profile totally encased with concrete and HEB220 partially encased with concrete. The fire behaviour of the columns was tested according to ISO834 standard fire. The results show that the use of HSC in composite columns reduces the level of fire protection with the regard to NSC. NSC in composite structures accommodates higher deflections than HSC, which is safer in case of fire accident. The mechanical resistance in composite columns at room temperature is reduced more than twice after 30 min of fire exposure.
- 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.
- Numerical investigation on the fire resistance of partially encased steel columnsPublication . Hoffstaeter, Ricardo Anderson; Piloto, P.A.G.; Martins, Carlos Humberto; Rigobello, RonaldoThis paper presented the results of numerical analyses on the fire resistance of composite columns with partially encased steel columns (PEC). This investigation used 2D and 3D finite element models and assessed for the design method of composite elements under compression according to the Annex G of Eurocode 4. New proposals were presented to determine the buckling resistance of PEC under standard fire. The 2D and 3D numerical models were based on American and European steel profiles. The 2D thermal model was used to improve the design method of the current version of the Eurocode 4, enhancing the balance summation model, which is currently used to determine the plastic resistance to axial compression and the effective flexural stiffness of the four components of the cross-section. The 3D thermomechanical model used the temperature field for each fire rating time (30, 60, 90, and 120 min) and applied the incremental load step solution method, based on the Newton–Raphson, to determine the buckling load of partially encased columns with 3 and 5 m, considering different supporting conditions. These results present a safer buckling curve when compared to curve ‘‘c’’.