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Biblioteca Digital do IPB (53.442 recursos)

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DMA - MSE - Artigos em Revistas Internacionais

Mostrando recursos 1 - 20 de 23

  1. A new proposal of a simple model for the lateral-torsional buckling of unrestrained steel I-beams in case of fire: Experimental and numerical validation

    Vila Real, P.M.M.; Piloto, P.A.G.; Franssen, J.-Marc
    The behaviour of Steel I-Beams exhibiting lateral-torsional buckling at elevated temperature has been studied by means of experimental and numerical analysis. The authors in an earlier paper have presented an analytical formula for the buckling resistance moment in the fire design situation. This new proposal, different from the actual proposal of the Eurocode 3 Part 1.2 has been validated in this work by comparison with the results from a set of 120 experimental and numerical tests performed on IPE 100 beams, submitted to temperatures varying from room temperature to 600 °C. The numerical simulations have been based on the measured...

  2. Numerical modelling of steel beam-columns in case of fire - Comparisons with Eurocode 3

    Vila Real, P.M.M.; Lopes, N.; Silva, L.S.; Piloto, P.A.G.
    This paper presents a numerical study of the behaviour of steel I-beams subjected to fire and a combination of axial force and bending moments. A geometrical and material non-linear finite element program, specially established in Liege for the analysis of structures submitted to fire, has been used to determine the resistance of a beam-column at elevated temperature, using the material properties of Eurocode 3, part 1–2. The numerical results have been compared with those obtained with the Eurocode 3, part 1–2 (1995) and the new version of the same Eurocode (2002). The results have confirmed that the new proposal for Eurocode...

  3. The effect of residual stresses in the lateral-torsional buckling of steel I-beams at elevated temperature

    Vila Real, P.M.M.; Cazeli, R.; Silva, L.S.; 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...

  4. Towards a consistent safety format of steel beam-columns: application of the new interaction formulae from ambient temperature to elevated temperatures

    Vila Real, P.M.M.; Lopes, N.; Silva, L.S.; Piloto, P.A.G.; Franssen, J.-Marc
    Two new formulae for the design of beam-columns at room temperature have been proposed into Eurocode 3, prEN 1993-1-1 (2002), and are the result of great efforts made by two working groups that followed different approaches, a French-Belgian team and an Austrian-German one. Under fire conditions the prEN 1993-1-2 (structural fire design) presents formulae, for the design of beam-columns based on the prENV 1993-1-1 (1992). In order to study the possibility of having, in part 1-1 and part 1-2 of the Eurocode 3, the same approach, a numerical research was made using the finite element program SAFIR, developed at the University of Liege for the...

  5. New proposals for the design of steel beam-columns in case of fire, including a new approach for the lateral-torsional buckling

    Lopes, N.; Silva, L.S.; Vila Real, P.M.M.; Piloto, P.A.G.
    The possibility of having, in parts 1-1 and 1-2 of Eurocode 3, the same approach for the design of beam-columns and for lateral–torsional buckling, was investigated by the authors in previous papers using a numerical approach, where it was concluded that those assumptions could be made. In the present paper, a new approach for lateral–torsional buckling has been used with the formulae for the design of beam-columns at elevated temperature based on prEN 1993-1-1 combined with the formulae from prEN 1993-1-2. In both cases the results obtained are much better than the current design expressions, when compared with those obtained in the numerical calculations.

  6. Proposal for underwater structural analysis using the techniques of ESPI and digital holography

    Valin Rivera, J.L.; Monteiro, J.M.; Lopes, H.; Vaz, M.A.P.; Palacios, Francisco; Gonçalves, Edison; Garcia del Pino, Gilberto; Pérez, Jorge Ricardo
    The purpose of this article is to study the application of the holographic interferometry techniques in the structural analysis of submarine environment. These techniques are widely used today, with applications in many areas. Nevertheless, its application in submarine environments presents some challenges. The application of two techniques, electronic speckle pattern interferometry (ESPI) and digital holography, comparison of advantages and disadvantages of each of them is presented. A brief study is done on the influence of water properties and the optical effects due to suspended particles as well as possible solutions to minimize these problems.

  7. An improved mixed numerical-experimental method for stress field calculation

    Lopes, H.; Guedes, R.M.; Vaz, M.A.P.
    In this work a numerical-experimental method is used to study the dynamic behavior of an aluminum plate subjected to a small mass impact.The out-of-plane displacements,due to transient bending wave propagation,were assessed for successive time instants,using double pulse TV-holography,also known as pulsed ESPI.

  8. Parameter estimation in active plate structures

    Araújo, A.L.; Lopes, H.; Vaz, M.A.P.; Soares, C.M. Mota; Herskovits, J.; Pedersen, P.
    In this paper two non-destructive methods for elastic and piezoelectric parameter estimation in active plate structures with surface bonded piezoelectric patches are presented. These methods rely on experimental undamped natural frequencies of free vibration. The first solves the inverse problem through gradient based optimization techniques, while the second is based on a metamodel of the inverse problem, using artificial neural networks. A numerical higher order finite element laminated plate model is used in both methods and results are compared and discussed through a simulated and an experimental test case.

  9. The modal analysis of a pipe elbow with realistic boundary conditions

    Carneiro, J.O.; Melo, F.J.M.Q. de; Rodrigues, J.F.D.; Lopes, H.; Teixeira, Viriato
    A vibration analysis for the determination of the natural frequencies and the associated eigenmodes of a pipe elbow with end-flanges or tangent terminations was performed. A numerical investigation of this problem was achieved with a semi-analytic definition finite ring element and a commercial finite element code. To assess the accuracy of the numerical solution for the elbow vibration, an experimental modal analysis was performed on a curved and on a straight pipe. The responses were processed by a data acquisition system which performs a fast Fourier transform on the time histories to convert them from a time to frequency domain,...

  10. Measurement of residual stresses with optical techniques

    Ribeiro, J.E.; Monteiro, Jaime; Vaz, M.A.P.; Lopes, H.; Piloto, P.A.G.
    The goal of this work was the development of other experimental techniques to measure residual stresses, as an alternative to the hole-drilling method with strain gauges. The proposed experimental techniques are based on the use of Moiré interferometry and in-plane electronic speckle pattern interferometry (ESPI). Both are field techniques allowing the assessment of in-plane displacements without contact and high resolution. Grating replication techniques were developed to record high-quality diffraction gratings onto the specimen's surfaces. An optical set-up of laser interferometry was developed to generate the master grating (virtual). An in-plane ESPI set-up was also designed and implemented to measure displacements...

  11. Decomposition of intumescent coatings: comparison between numerical method and experimental results

    Mesquita, L.M.R.; Piloto, P.A.G.; Vaz, M.A.P.; Pinto, T.
    An investigation of two different intumescent coatings used in steel fire protection has been performed to evaluate their efficiency. A set of experimental tests is presented. They were conducted in a cone calorimeter, considering different thicknesses and heat fluxes. Among other quantities, the steel temperature and the intumescence thickness variation were measured. A numerical model for the paint decomposition is also presented. Based on the intumescence experimental value, the model is able to provide a reasonably good prediction of the steel temperature evolution.

  12. Experimental modal analysis of a synthetic composite femur

    Rodrigues, J.F.D.; Lopes, H.; Melo, F.J.M.Q. de; Simões, J.A.
    In this paper we describe the experimental characterization of the modal parameters of asynthetic com- posite femur model widely used in biomechanical research studies.The objective of the experimental procedure was to identify the natural frequencies and modes hapes of anun- constrained (free–free) femur.

  13. The dynamic analysis of piping systems using pseudo-dynamic techniques

    Melo, F.J.M.Q. de; Carneiro, J.O.; Lopes, H.; Rodrigues, J.F.D.; Gomes, J.F.S.
    This paper describes an application of pseudo-dynamic techniques to the dynamic analysis of piping structures. Essentially it consists in coupling a direct time integration algorithm, such as the Newmark method, to an experimental step. At each time step the integration algorithm generates a displacement vector of the structure, which is prescribed for the test specimen. This is mounted in a rigid test rig fitted with a set of displacement actuators and load cells at the level of the structure degrees of freedom. The load cells allow the reading of the internal restoring force vector, which is fed back to the direct time integration algorithm in an...

  14. Simplified indexes for the seismic vulnerability of ancient masonry buildings

    Lourenço, Paulo B.; Roque, João C. Almendra
    This paper presents a contribution for the safety assessment of historical masonry buildings under seismic loading. Three different simplified safety indexes (in-plan area ratio, area to weight ratio and base shear ratio) are analyzed, taking into account a large sample of fifty-eight Portuguese churches. The sample of building has been organized according to the seismic zonation, from high to low seismicity. The results indicate that valuable information can be obtained from simplified methods, with respect to performing a first screening and to prioritizing further, deeper investigations. A new proposal is made regarding the combined usage of two of the indexes.

  15. Desenvolvimento de um elemento finito para análise de tensões em tubos curvos

    Fonseca, E.M.M.; Melo, F.J.M.Q. de; Oliveira, C.A.M de
    Apresenta-se uma formulação para a caracterização do estado de tensão e deformação de sistemas tubulares de parede fina usando o método dos elementos finitos. O elemento de tubo desenvolvido apresenta um campo de deslocamentos para uma casca com o modelo de deformação de semi-membrana. A solução para obter a distorção de qualquer secção do tubo necessita de condições de fronteira do tipo deslocamentos ou forças prescritas. É apresentado um estudo numérico para obtenção do campo de tensões longitudinais de membrana e posterior determinação do factor de flexibilidade em tubos curvos submetidos à flexão pura.

  16. The thermal and mechanical behaviour of structural steel piping systems

    Fonseca, E.M.M.; Melo, F.J.M.Q. de; Oliveira, C.A.M de
    The temperature, the deformation and the stress field in thermo-mechanical problems play a very important role in engineering applications. This paper presents a finite element algorithm developed to perform the thermal and mechanical analysis of structural steel piping systems subjected to elevated temperatures. The new pipe element with 22 degrees of freedom has a displacement field that results from the superposition of a beam displacement, with the displacement field associated with the section distortion. Having determined the temperature field, the consequent thermal displacement produced in the piping systems due to the thermal variation can be calculated. The temperature rise produces thermal expansion and a consequent...

  17. Trigonometric function used to formulate a multi-nodal finite tubular element

    Fonseca, E.M.M.; Melo, F.J.M.Q. de; Oliveira, C.A.M de
    It is presented an alternative formulation to solve the problem of the deformation analysis for tubular element under pinching loads. The solution is based on a new displacement field defined from a total set of trigonometric functions. The solution is developed in a multi-nodal finite tubular ring element with a total of eight degrees of freedom per section considered. The purpose of this paper is to provide an easy alternative formulation when compared with a complex finite shell element or beam element analysis for the same application. Several case studies presented have been compared and discussed with numerical analyses results...

  18. Numerical analysis of piping elbows for in-plane bending and internal pressure

    Fonseca, E.M.M.; Melo, F.J.M.Q. de; Oliveira, C.A.M de
    This work presents the development of two different finite piping elbow elements with two nodal tubular sections for mechanical analysis. The formulation is based on thin shell displacement theory, where the displacement is based on high-order polynomial or trigonometric functions for rigid-beam displacement, and uses Fourier series to model warping and ovalization phenomena of cross-tubular section. To model the internal pressure effect an additional formulation is used in the elementary stiffness matrix definition. Elbows attached to nozzle or straight pipes produce a stiffening effect due to the restraint of ovalization provided by the adjacent components. When submitted to any efforts,...

  19. Determination of flexibility factors in curved pipes with end restraints using a semi-analytic formulation

    Fonseca, E.M.M.; Melo, F.J.M.Q. de; Oliveira, C.A.M de
    Piping systems are structural sets used in the chemical industry, conventional or nuclear power plants and fluid transport in general-purpose process equipment. They include curved elements built as parts of toroidal thin-walled structures. The mechanical behaviour of such structural assemblies is of leading importance for satisfactory performance and safety standards of the installations. This paper presents a semi-analytic formulation based on Fourier trigonometric series for solving the pure bending problem in curved pipes. A pipe element is considered as a part of a toroidal shell. A displacement formulation pipe element was developed with Fourier series. The solution of this problem...

  20. Métodos avançados de cálculo de estruturas metálicas submetidas à acção do fogo

    Fonseca, E.M.M.; Oliveira, C.A.M de
    O cálculo de resistência ao fogo em estruturas metálicas, implica para além da caracterização da acção térmica, o conhecimento da variação com a temperatura das propriedades térmicas do material ou materiais que as constituem bem como a resolução de um problema de condução de calor num domínio com condições de fronteira conhecidas. Esta forma de proceder cai no domínio dos métodos avançados de cálculo proposto no Eurocódigo e pressupõem recurso a programas de cálculo automático adequados. Desenvolveu-se assim, um programa de elementos finitos para a análise de estruturas tridimensionais, bem como um elemento de interface bidimensional para aplicação das condições...

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