924 publications from this institution
While the low weight and high bending stiffness of cross-laminated timber (CLT) are key to its popularity, these properties also contribute to poor acoustic performance. Notably flanking sound transmission is a critical factor, driving the need for vibration reduction solutions such as resilient interlayers in the junction design. However, due to the complex material behavior of CLT and resilient interlayers, the improvement related to these solutions is difficult to predict. In this research, an analytical model with low computational cost is developed to evaluate the vibration reduction index K i j for CLT junctions with resilient interlayers. The CLT panels are considered as thin orthotropic plates with homogenized material properties. Three potential material models are proposed for the interlayer: it is considered as a thin plate, a thick flexible layer with out-of-plane motion governed by shear or distributed springs. The prediction model is experimentally validated for junctions consisting of CLT panels, with and without resilient interlayers. For junctions without interlayers, the predicted and experimentally determined vibration reduction index K i j correspond most closely when the junction is realized with stiff connectors. In this case, the predictions are moderately accurate with deviations below 5 dB in 1/3 octave bands up to approximately 2000 Hz for both corner and coplanar transmission paths. For junctions with resilient interlayers, the shear interlayer model exhibits the best performance with deviations of less than 5 dB in most 1/3 octave bands. For frequencies below 1000 Hz, the accuracy of the simplified spring model is comparable to that of the thick layer model. Simulations with equivalent isotropic material parameters yield slightly inferior predictions than for orthotropic parameters if the degree of orthotropy of the panels is high.
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This paper describes different dynamic tests carried out on three bridges, B14, B15, and B13, over highway E19, which connects Brussels and Antwerpen in Belgium. Different excitation types are considered: a drop weight, a heavy truck on the bridge, and ambient vibrations mainly due to the traffic under the bridge. Finite-element models are constructed to support and verify the dynamic measurements. The modal parameters are extracted from the response time series using the data dependent system approach. A vector autoregressive model is developed and successfully applied to the measured responses in time domain. Good correlation between the finite-element simulations and the experiments is obtained.
In the process of preservation of ancient masonry structures, damage evaluation and monitoring procedures are particularly attractive, due to the modern context of minimum re- pair and observational methods, with iterative and step-by-step approaches. High-priority re- search issues related to damage assessment and monitoring are global non-contact inspection techniques, sensor technology, data management, diagnostics (decision making and simulation), dynamic (modal) analysis, self-diagnosing / self-healing materials, and prediction of early deg- radation. On these concerns, the present paper aims to assess damage in masonry structures at an early stage. Replicates of historical constructions were built in virgin state. Afterwards, progres- sive damage was applied and modal identification analysis was performed at each damage stage, aiming at finding adequate correspondence between dynamic behavior and internal crack growth. Accelerations and dynamic strains were recorded in many points of the replicates. Comparisons between different techniques based on vibrations measurements are made to evaluate different damage identification methods.
One of the aims of the BRITE-EURAM project SIMCES is the comparison, adaptation and application of system identification methods to civil engineering structures. Special attention is paid to techniques making use of operational data. In this paper the peak-picking method, the polyreference LSCE and the stochastic subspace identification method are studied and compared. The basic principles of all three methods are briefly reviewed and the practical aspects of their application to bridge vibration data is discussed. The paper shows how the modal parameters can be extracted for increasing model orders and plotted in so-called stabilisation diagrams. These diagrams aid the engineer to find the correct model order and to distinguish the spurious modes from the true system modes, which is often a difficult task for the simple peak-picking method.
<p>Railway bridge KW51 in Leuven, Belgium, has been monitored since October 2018 with the aim of constructing a digital twin, i.e. a virtual representation that mimics the behaviour of the actual struc- ture. A linear finite element model of the bridge was updated using measurements carried out on the bridge. The pot bearings of the bridge, however, are found to behave in a non-linear way. This paper describes a methodology to account for this non-linear behaviour in the model, where friction in the bearings is accounted for by means of non-linear Bouc-Wen elements. The first results are presented, showing that the overall non-linear behaviour of the bearings during a train passage is well captured but that further research is needed to calibrate the model parameters.</p>
Predicting the sound insulation of an engineering system is a complex problem since not only the direct path through a separating element but also the flanking transmission paths can largely influence the sound insulation of the system. When conventionally analyzing flanking transmission, a diffuse field is assumed in the walls and floors, which are modelled as plates. The junction connecting the walls and floors is assumed to be of infinite extent and the transmission of vibration across the junction is calculated by integrating over all possible angles of incidence. Due to the limitations of the conventional approach, a new approach based on diffuse field reciprocity is proposed. The diffuse field reciprocity relationship relates the vibration transmission to the direct field of a diffuse subsystem to the direct field dynamic stiffness of the subsystem, i.e., the dynamic stiffness of the equivalent infinite subsystem as observed at the junction. The direct field dynamic stiffness matrices of thin, isotropic, elastic plates can be analytically derived. For more complex walls or floors a possible approach is to calculate the direct field dynamic stiffness using finite elements and perfectly matched layers. The perfectly matched layer surrounding the finite element model absorbs the wave propagating outwards from the bounded domain, thus simulating an infinite subsystem.
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In this contribution, the hybrid finite element-statistical energy analysis method is extended such that not only the mean and the ensemble variance of the harmonic system response can be computed, but also the ensemble variance of the frequency band-averaged system response. The computed variance represents the uncertainty that is due to the assumption of a diffuse field in components of the hybrid system. The developments start with a cross frequency generalization of the diffuse field reciprocity relationship between the total energy in a diffuse field and the cross spectrum of the external loading. By making extensive use of this generalization in a first-order perturbation analysis, explicit expressions are derived for the variance of the vibrational energies in the diffuse components and for the variance of the cross spectrum of the response of the deterministic components. These expressions are extensively validated against Monte Carlo analyses of systems consisting of connected plates, in which diffuse fields are simulated by randomly distributing small concentrated masses, acting as wave scatterers, across the diffuse components.
