102,208 research outputs found
Dataset for the figures in 'Reducing railway-induced ground-borne vibration by using open trenches and soft-filled barriers'
No full textData for the figures in the paper by Thompson, D., Jiang, J., Toward, M.G.R, Hussein, M.F.M., Ntotsios, E., Dickmans, A., Coulier, P., Lombaert, G. and Degrande, G. (2016) Reducing railway-induced ground-borne vibration by using open trenches and soft-filled barriers. Soil Dynamics and Earthquake Engineering</span
Ir. G. Lombaert
No full textIn Krylov's analytical prediction model, the free field response during the passage of a train is written as the superposition of the effect of all sleeper forces, using Lamb's approximate solution for the Green's function of a halfspace. When this formulation is extended with the Green's functions of a layered soil, a considerable computational effort is needed when these Green's functions are needed in a wide range of source-receiver distances and frequencies. It is demonstrated in this paper how the free field response can alternatively be computed, using the Betti-Rayleigh dynamic reciprocity theorem applied to moving loads. The formulation is based on the response of the soil due to the moving load distribution for a single axle load. The equations are written in the wavenumber-frequency domain, accounting for the invariance of the geometry in the direction of the track. The approach allows for avery efficient calculation of the free field response, distinguishing the quasi-static contribution from the effect of the sleeper passage frequency and its higher harmonics. The methodology is illustrated byanumerical example, where the passage of a tram vehicle is considered
Croissance aérienne et radiculaire de Lepidium Sativum (L.) en fonction des proportions alimentaires azote-phosphore et du mode d'application de Porthonil
No full textCette note étudie l'effet de la concentration et du mode d'application de l'orthonil sur le rendement en poids frais d'une part et, d'autre part, l'effet de celui-ci sur la proportion optimum de l'alimentation en azote et phosphore.
Cette expérience a mis en évidence une nouvelle relation liant le rendement des racines aux proportions alimentaires en azote et phosphore.Neumann G. L., Lombaert V. D. Croissance aérienne et radiculaire de Lepidium Sativum (L.) en fonction des proportions alimentaires azote-phosphore et du mode d'application de Porthonil. In: Bulletin de la Classe des sciences, tome 62, 1976. pp. 448-459
Automatic in-Operation Modal Analysis for the continuous monitoring of high-speed railway bridges
No full textSteel-concrete composite bridges have been widely utilising in high-speed railways due to the reduced time and overall cost of the designing and construction phases. Of course a continuous improvement of the design procedures is requested to enhance safety and durability of these civil structures. To achieve these goals, the main point is a correct description of the dynamic behaviour of the structure during operation and in particular during train passages. Experimental test campaigns on existing structures and long-term vibration-based structural health monitoring are hence needed to have a more detailed information on the actual loading and fatigue resistance of this bridge typology, to be utilised for the improvement of numerical structural models. In-Operation Modal Analysis (OMA) has been developed because aimed at the experimental identification of structural dynamics models (i) based on output-only data and (ii) in those that are the real operating conditions. In the area of civil engineering where the possibility of performing a classical modal test of a large structure is complicated by how to obtain and measure the needed excitation inputs, OMA becomes the natural answer. With regards to the employment of permanent monitoring systems in this field, one has to recall that structural identification becomes closely related to the detection of changes in some of the system dynamics parameters - e. g. the time evolution of the natural frequencies - to single out the presence or the growth of a structural damage. In this paper, the possibility of performing an automatic OMA, acting in real time on the data of such a monitoring system has been analysed. The results coming by manually and automatically performing the Operational Modal Analysis of the experimental data have been successfully compared. In particular, two fundamental cases have been considered for the identification of the modal parameters of the bridge, (i) the pure ambient excitation in absence of rail vehicles and (ii) the free vibration of the bridge structure following a train passage
Pedestrian-Induced Vibrations of Footbridges: An Extended Spectral Approach
No full textsponsorship: The first author is a postdoctoral fellow of the Research Foundation Flanders (FWO, 12E0816N). The research presented in this paper was performed within the framework of a research stay at the University of Genoa (FWO, Travel Grant V404918N). The financial support is gratefully acknowledged. (12E0816N, V404918N)status: Publishe
A two-step procedure for damage detection in beam structures with incomplete mode shapes
No full textIn this work, we present a two-step procedure for damage identification in beam structures exploiting modal curvature changes. The reconstruction of modal curvatures requires the knowledge of several mode shape components along the analyzed beam. This requirement is practically unachievable when mode shapes are identified via vibration-based monitoring using a limited number of accelerometers. To overcome this limitation, in the first step of the proposed procedure, we perform a mode shape expansion employing a reduced subset of measured modal components. The remaining measured components are used as control parameters to formulate a first hypothesis on damage location and extent. For this purpose, the expansion procedure is performed considering a number of possible damage scenarios, consisting of a location and a severity (loss of stiffness) of the damage. Using the Total modal assurance criterion (TMAC), we select the expanded modes with the highest degree of correspondence with the measured control components. These expanded modes are thus associated with a first guess of the damage location and severity. In the next step, this initial damage identification is verified through the computation of a modal curvature-based damage index. If the curvature-based damage identification confirms the previous identification, the damage location and extent are determined. The procedure can be easily extended to identify multiple simultaneously damaged elements. The approach is numerically validated using a benchmark beam modeled via finite elements, investigating the influence of different parameters such as noise, position of the control components and beam discretization on the identification success rate. Finally, the procedure is tested on two experimental specimens: a steel beam, with three different damage configurations and a concrete beam progressively damaged with multiple damage locations
Value of information of static and modal data for a concrete bridge exposed to reinforcement corrosion
No full textMeasurements performed on ageing bridges can provide information on the remaining capacity of these structures. Nevertheless, these measurements come at a cost, whereas the budgets for maintenance are limited. Based on pre-posterior analyses, the Value of Information (VoI) of these measurements can be determined on beforehand and the most optimal measuring strategy can be chosen. However, applying these VoI analyses to real-world structures, considering the time-dependent and spatial character of degradation, can be challenging. In this work, a case study is considered where the VoI analysis is applied to a reinforced concrete girder bridge subjected to corrosion, considering two situations: one with corrosion due to carbonation and one with corrosion due to chlorides. The influence of different assumptions in the VoI analysis is investigated
A 2.5D coupled FE-BE methodology for the prediction of railway induced vibrations
No full textGround vibrations induced by railway traffic are often studied by means of two-and-half dimensional (2.5D) models that are based on the longitudinal invariance of the track geometry. In this paper, a 2.5D methodology is used where the finite element method is combined with a boundary element method, based on a regularized boundary integral equation. In the formulation of the boundary integral equation, the Green's functions of a layered elastic halfspace are used, so that no discretization of the free surface or the layer interfaces is required. The methodology is applied to two cases. In the first case, two alternative models for a ballasted track on an embankment are compared. In the first model, the ballast and the embankment are modelled as a continuum using 2.5D solid elements, whereas a simplified beam representation is adopted in the second model. A very large difference is found for the free field mobility of both models, which demonstrates the need for detailed 2.5D modelling of the embankement. In the second case, the efficiency of a vibration isolating screen is studied. A vibration isolating screen is a soft or stiff wave barrier. Due to the impedance contrast between the isolating screen and the soil, incident waves are reflected. As a result, the vibration levels behind the screen are effectively reduced. Both examples demonstrate that the use of detailed 2.5D models result in a better insight in the mechanical behavior of the coupled soil-track system.status: Publishe
Dynamic testing and health monitoring via wireless sensor networks in the post-earthquake assessment of structural condition at L’Aquila
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