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Biblioteca Digital do IPB (53.442 recursos)

A Biblioteca Digital do IPB, tem por objectivo divulgar e permitir o livre acesso à produção científica produzida pela comunidade académica, promovendo a integração, partilha e a visibilidade da informação científica e garantindo a preservação da memória intelectual do Instituto Politécnico de Bragança.

DMA - Artigos em Revistas Indexadas ao ISI

Mostrando recursos 1 - 20 de 29

  1. Experimental investigation of the fire resistance of partially encased beams

    Piloto, P.A.G.; Ramos Gavilán, A.B.; Zipponi, Marco; Marini, Alberto; Mesquita, L.M.R.; Plizzari, Giovanni
    This research presents the fire resistance of Partially Encased Beams (PEB). Fire resistance was determined by means of twelve experimental tests, according to European standard EN1363-1, for different load levels and shear conditions between stirrups and web steel. Three tests were also performed at room temperature for load bearing resistance. The experimental setup was designed for this purpose, using a small fire resistance furnace and portal reaction frame. Details about the specimens tested, the instruments used and the characteristics of the materials, are also presented. Load-deflection and load-strain results were determined at room temperature. Deflection and temperature measurements were determined...

  2. Monitoring historical masonry structures with operational modal analysis: two case studies

    Ramos, Luis F.; Marques, Leandro; Lourenço, Paulo B.; Roeck, G.; Costa, Alfredo Campos; Roque, João C. Almendra
    The paper addresses two complex case studies of modal and structural identification of monuments in Portugal: the ClockTower of Mogadouro and the Church of Jerónimos Monastery, in Lisbon. These are being monitored by University of Minho with vibration, temperature and relative air humidity sensors. Operational modal analysis is being used to estimate the modal parameters, followed by statistical analysis to evaluate the environmental effects on the dynamic response .The aim is to explore damage assessment in masonry structures at a nearly stage by vibration signatures, as a part of a health monitoring process that helps in the preservation of historical...

  3. A numerical-experimental method for damage location based on rotation fields spatial differentiation

    Lopes, H.; Santos, J.V. Araújo dos; Soares, C.M. Mota; Guedes, R.M.; Vaz, M.A.P.
    This paper presents a structural damage location method that decreases the number of spatial differentiations needed to compute modal curvature fields. The method is numerically and experimentally applied to isotropic and laminated rectangular plates, respectively. A speckle shear interferometer is used to measure the rotation fields of the laminated plate, while the isotropic plate is analysed by finite elements. It was found that the Gaussian differentiation is the most suited technique to compute the curvature fields. It is also demonstrated the superior performance of the curvature method using measured rotation fields instead of measured displacement fields.

  4. Calibration of model parameters for the cyclic response of end-plate beam-to-column steel-concrete composite joints

    Nogueiro, Pedro; Silva, Luís Simões da; Bento, Rita; Simões, Rui
    Composite joints, considering the composite action of steel and concrete, exhibit, in general, high strength and high ductility. As a consequence, the use of this type of joint has been increasing in many countries, especially in those that are located in earthquake-prone regions. In this paper, a hysteretic model with pinching is presented that is able to reproduce the cyclic response of steel and composite joints. Secondly, the computer implementation and adaptation of the model in a spring element within the computer code Seismosoft is described. The model is subsequently calibrated using a series of experimental test results for composite joints subjected to cyclic loading. Finally,...

  5. Numerical implementation and calibration of a hysteretic model with pinching for the cycling response of steel joints

    Nogueiro, Pedro; Silva, Luís Simões da; Bento, Rita; Simões, Rui
    In this paper, a hysteretic model with pinching is presented that is able to reproduce realistically the cyclic response of generic steel joints. Secondly, the computer implementation and adaptation of the model in a spring element within the computer code SeismoStruct is described. The model is subsequently calibrated using a series of experimental test results for steel joints subjected to cyclic loading. Finally, typical parameters for the various joint configurations are proposed.

  6. Damage localization in laminated composite plates using mode shapes measured by pulsed TV holography

    Santos, J.V. Araújo dos; Lopes, H.; Vaz, M.A.P.; Soares, C.M. Mota; Freitas, M.J.M. de
    Three methods for the damage localization of impact damage in laminated composite plates, based on their vibrational characteristics, are presented in this paper. These methods use double pulse TV holography with acoustic excitation for mode shapes acquisition and the differences in translations, rotations and curvatures. The rotations and curvatures are obtained by numerical differentiation of mode shapes translations using a differentiation/smoothing technique. The methods are applied to a carbon fiber reinforced epoxy rectangular plate, free in space, subjected to two cases of impact damage. It is shown that the method based on curvatures allows the localization of both cases of...

  7. 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...

  8. Experimental and numerical research on the critical temperature of laterally unrestrained steel I beams

    Mesquita, L.M.R.; Piloto, P.A.G.; Vaz, M.A.P.; Vila Real, P.M.M.
    Lateral unrestrained steel beams when subjected to high temperatures may collapse in service by lateral torsional buckling. This instability state may be predicted in the resistance, temperature and time domain. In this work the beam strength is determined in the temperature domain from a batch of numerical and experimental tests, with a specified degree of utilisation and a typical accident temperature rise. The experimental set-up is a reaction portal frame especially designed for beam elements under elevated temperatures. The specimens were heated by means of electroceramic resistances and a fibre mat specimen cover is used to increase the thermal efficiency. The...

  9. 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...

  10. 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...

  11. 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...

  12. 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.

  13. Pressure drop coefficient of laminar Newtonian flow in axisymmetric diffusers

    Rosa, Sérgio; Pinho, Fernando T.
    The laminar flow of Newtonian fluids in axisymmetric diffusers has been numerically investigated to evaluate the pressure-loss coefficient as a function of Reynolds number, diffusion angle and expansion ratio. The numerical simulations were carried out with a finitevolume based code using non-orthogonal collocated grids and second order accurate differencing schemes to discretize all terms of the transport equations. The calculations were carried out for Reynolds numbers between 2 and 200, diffusion angles from 0 to 90 and expansion ratios of 1.5 and 2 and the data are presented in tabular form and as correlations. A simplified 1D theoretical analysis helped explain the various contributions to the...

  14. Asymmetry in transitional pipe flow of drag-reducing polymer solutions

    Escudier, Marcel; Rosa, Sérgio; Poole, Rob
    New experimental data are presented and discussed for fully developed pipe flow of shear-thinning, viscoelastic polymer solutions in the transitional regime between laminar and turbulent flow. The data confirm that such transitional flows exhibit significant departures from axisymmetry in contrast to the fully developed pipe flow of Newtonian fluids or both laminar and turbulent flows of such drag-reducing liquids. The azimuthal structure of the asymmetry is investigated together with its axial development and also the velocity fluctuation levels. These data do not lead to an explanation for the asymmetry but do suggest that the influence of the flow geometry both...

  15. 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.

  16. 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.

  17. 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.

  18. 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,...

  19. 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...

  20. 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.

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