Departamento De Engenharia Civil

Neste artigo, apresenta-se uma metodologia de análise da capacidade de uso urbano do solo, associada à identificação de áreas com adequabilidade preferencial a usos determinados. A análise baseia-se na aplicação de um modelo que permite definir classes de aptidão para diferentes tipos de uso, em função de critérios urbanísticos e limitações ao crescimento urbano, incluindo a possibilidade de manifestação de riscos naturais. A descrição das diferentes fases do modelo é apresentada em associação com um estudo de caso, numa área concreta da cidade de Coimbra.

The search for innovative mitigation solutions that can be adopted in urban areas to efficiently reduce the effects of induced vibrations by increasing numbers of vehicles has motivated a significant number of researchers from different fields. An interesting concept seems to be the use of buried elastic inclusions, periodically arranged parallel to the ground surface, applying sonic crystal inspired technologies and bandgap filtering on adequate frequency ranges. In previous works, preliminary numerical results have shown the influence of the presence of multiple elastic heterogeneities on the attenuation of the vibration fields in receivers located on the opposite side from the traffic vibration source. Following this concept, a 2.5D numerical model has been implemented, based on the Finite Element Method (FEM) and on the use of a numerical absorbing layer. The effects on the vibration levels provided by a set of periodic elastic inclusions inserted in the host propagation medium are parametrically analysed. In fact, frequency domain results, obtained when modelling different configurations of the periodic structure and host soil, are used to assess the efficiency of these arrays as a mitigation measure.

Phononic crystals have been extensively studied, and their capacity to attenuate the propagation of sound waves at specific frequency bands is well known and documented in the literature. However, few studies exist concerning the behaviour of such structures in the context of elastic media, with the purpose of attenuating the transmission of vibrations. Applying this concept can be quite interesting, and may allow new vibration control devices to be developed, tailored at specific applications. As an example, buried periodic structures may be used to control elastic wave propagation in the ground, and thus to help reducing the vibrations that can reach sensible structures. In this work, the authors make use of a 2.5D numerical model based on the Method of Fundamental Solutions (MFS) to analyse this complex problem, considering the case of arrays of elastic inclusions buried in a homogeneous medium, fully considering the complete elastodynamic interaction between the inclusions and the host medium. Due to the geometric periodicity of the analysed problem, the numerical formulation can be simplified, particularly in what concerns the calculation of the system matrix, and significant computational gains can be obtained. The results of a numerical study concerning the behaviour of a sequence of embedded inclusions within an elastic material, when subject to the incidence of waves with different frequencies, is here presented, and the interpretation of the involved phenomena is described in order to clarify the main wave propagation features in the presence of multiple elastic inclusions. The computed results are promising, clearly revealing the existence of band gaps where large attenuation occurs, although limitations related to the existence of guided waves traveling along the inclusions are also identified.

Buried structures may be used to control elastic wave propagation in soils and help to reduce vibrations in sensitive structures. The analysis of these structures using numerical tools is of high importance and is usually a demanding computational task. In the present work, the authors explore the possibility of using a meshless method for such simulations, namely the method of fundamental solutions (MFS). In many applications, the MFS has proved to be a worthy and more efficient alternative to classic methods, such as the FEM or even the BEM. Here, the authors present a study on the application of the MFS to simulate the propagation of elastic waves in a soil with multiple buried inclusions. Application examples are also presented, in which the vibration reduction provided by different sets of buried inclusions is analysed and discussed.

Digital image correlation (DIC) is an optical technique commonly used for measuring displacement fields by tracking artificially applied random speckle patterns, which can sometimes be a problem for tracking small-scale displacements. DIC is particularly useful for tracking the crack mouth opening displacement (CMOD) of a notched metallic specimen subjected to three-point bending for fracture toughness determination because the edges of the notch provide the required textural features for DIC without the need for speckle patterns. This simplifies the setup process as the specimen and stage geometries do not need to account for the placement of a strain gauge. To enhance the accuracy of DIC, this study then successfully downscaled a photogrammetry technique commonly used to track crack propagation in large scale concrete tests so that the pixel coordinates of the captured images can be automatically related to their real-world coordinates, allowing for small scale displacements to be accurately tracked.

Phononic crystals have been extensively studied, and their capacity to attenuate the propagation of sound waves at specific frequency bands is well known and documented in the literature. However, few studies exist concerning the behaviour of such structures in the context of elastic media, with the purpose of attenuating the transmission of vibrations. Applying this concept can be quite interesting, and may allow new vibration control devices to be developed, tailored at specific applications. As an example, buried periodic structures may be used to control elastic wave propagation in the ground, and thus to help reducing the vibrations that can reach sensible structures. In this work, the authors make use of a 2.5D numerical model based on the Method of Fundamental Solutions (MFS) to analyse this complex problem, considering the case of arrays of elastic inclusions buried in a homogeneous medium, fully considering the complete elastodynamic interaction between the inclusions and the host medium. Due to the geometric periodicity of the analysed problem, the numerical formulation can be simplified, particularly in what concerns the calculation of the system matrix, and significant computational gains can be obtained. The results of a numerical study concerning the behaviour of a sequence of embedded inclusions within an elastic material, when subject to the incidence of waves with different frequencies, is here presented, and the interpretation of the involved phenomena is described in order to clarify the main wave propagation features in the presence of multiple elastic inclusions. The computed results are promising, clearly revealing the existence of band gaps where large attenuation occurs, although limitations related to the existence of guided waves traveling along the inclusions are also identified.

Buried structures may be used to control elastic wave propagation in soils and help to reduce vibrations in sensitive structures. The analysis of these structures using numerical tools is of high importance and is usually a demanding computational task. In the present work, the authors explore the possibility of using a meshless method for such simulations, namely the method of fundamental solutions (MFS). In many applications, the MFS has proved to be a worthy and more efficient alternative to classic methods, such as the FEM or even the BEM. Here, the authors present a study on the application of the MFS to simulate the propagation of elastic waves in a soil with multiple buried inclusions. Application examples are also presented, in which the vibration reduction provided by different sets of buried inclusions is analysed and discussed.

A functionally graded NbChigh chromium white cast iron composite was successfully fabricated by centrifugal casting for high wear applications. The migration of primary NbC particles to the outer periphery, as predicted by Stokes' law, resulted in an extremely hard outer layer at the surface of a softer bulk material. Microstructural characterisation showed that both the volume fraction and the morphology of the carbides varies along the thickness of the specimen. At the outer surface, the NbC was present as primary carbides while Chinese-script NbC was found in the bulk of the material. Hardness, sliding wear and three-point bending tests confirmed that the outer layer was harder and more wear resistant than the rest of the material, which was correspondingly tougher. The study of the fracture surface of the specimens showed that there is a strong bond between NbC and the matrix such that delamination between the reinforcements and the matrix did not occur during fracture. If Chinese-script NbC can be reduced or prevented in the bulk material, further improvements to toughness could be achieved.

O presente trabalho incide na análise dos regimes transitórios induzidos pela paragem súbita de um grupo motobomba num sistema de adução. Foram realizados ensaios de campo, com medições de vazão e pressão durante os regimes transitórios no sistema adutor por bombeamento Prado-IPG, localizado na cidade da Guarda, Portugal, e explorado pela entidade gestora Águas do Zêzere e Côa. A estação elevatória do Prado é composta por cinco grupos motobomba em paralelo e a adutora principal é de ferro fundido dúctil com comprimento total de 2241 m. As medições de pressão durante os regimes transitórios foram comparados com os resultados obtidos por simulações hidráulicas. Foi observado um bom ajuste dos resultados numéricos aos dados coletados em termos do amortecimento e desfasamento das ondas de pressão apenas quando os efeitos devidos ao atrito em escoamento transitório foram levados em consideração no modelo matemático e a condição de contorno de jusante era corretamente definida. A última seção da adutora foi descrita numericamente por um pequeno tanque de nível variável e descarga livre para a atmosfera no reservatório. A presença de consideráveis variações nos níveis de água em tal condição de contorno de jusante produz alívio das pressões máximas ao longo da adutora e em particular imediatamente a jusante da válvula de retenção do grupo motobomba, além de mudanças na forma das ondas de pressão. Paragem de grupo motobomba, transitórios hidráulicos, sistema adutor, ensaios de campo.

The ordered probit model is used to examine the contribution of several factors to the injury severity faced by motor-vehicle occupants involved in road accidents. The estimated results suggest that motor-vehicle occupants travelling in light-vehicles, at two-way roads, and on dry road surfaces tend to suffer more severe injuries than those who travel in heavy-vehicles, at one-way roads, and on wet road surfaces. Additionally, the driver's seat is clearly the safest seating position, urban areas seem to originate less serious accidents than rural areas, and women tend to be more likely to suffer serious or fatal injuries than men.

A copper hexacyanoferrate film was obtained on a modified electrode prepared by self-assembly of 3-mercaptopropyltrimethoxysilane on a gold surface. The film thickness was controlled using a layer-by-layer technique to tune the electrocatalytic properties of the electrode. Two electrodes with different hexacyanoferrate film thicknesses were prepared via three immersions (AuS/CuHCF3) and six immersions (AuS/CuHCF6) of the film in the precursor solutions. Cyclic voltammetry data were obtained to determine the adequate film thickness. Scanning electron microscopy images showed a roughness increase due to the growth of the film thickness at the electrode surface. Electrochemical impedance spectroscopy showed distinct behavior for the two electrodes prepared; while diffusion and charge transfer processes can be observed in both electrodes, an additional capacitive process at intermediary frequencies was observed for the AuS/CuHCF6 electrode. The charge transfer resistance (R ct) for the AuS/CuHCF3 electrode (19.6 Ω cm2) was lower than for AuS/CuHCF6 (27.9 Ω cm2) due to the hexacyanoferrate film thickness, since the charge transfer process demands the simultaneous diffusion of K+ into the surface. Cyclic voltammetry was used to evaluate the application of the AuS/CuHCF3 electrode as an electrochemical sensor, revealing a linear correlation for hydrazine concentrations.

Timber-concrete composite floors can be seen as bi-dimensional elements constituted by repeatable longitudinal elements (timber beams) connected through an element capable to spread the load on the transverse direction (concrete slab). This is usually a fact to “take advantage of” in terms of design, in the light of current regulations, with the analysis of a “T-shape” beam. Nevertheless, when concerning the action of concentrated loads, considering them supported entirely by the beam to which they are applied can result in a disadvantage rather than an advantage. This study focus on the distribution of load in the transverse direction when composite floors are subjected to concentrated loads. There were analyzed not only timber-concrete composite floors, that already have proven their value, but also relatively new solutions as those using cross laminated timber (CLT) combined with steel beams. The results show that the load received by “the loaded beam” can be far from 100%.

1. Abstract This work presents a procedure for finding the discrete optimum design of cable-stayed bridges. The minimization problem is stated as the minimization of stresses and bridge cost. A finite-element approach is used for structural analysis. It includes a direct ...