924 publications from this institution
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No abstract is provided for this article.
No abstract is provided for this article.
No abstract is provided for this article.
For the purpose of damage evaluation, this paper studies the effect of temperature variations on modal parameters recorded at two different times in a prestressed concrete highway bridge. A drop weight and ambient vibration were used to excite the bridge. A finite element model was developed to support and verify the dynamic measurements. The effects of temperature change on the structure's natural frequencies are analyzed and interpreted.
Vibration monitoring is a well-known technique to determine wether a civil engineering structure is damaged or not. From the vibration tests, natural frequencies, modal displacements, damping ratios and modal curvatures can be determined using system identification methods. These modal parameters are subsequently used for damage identification. If a structure is damaged, the changes in modal curvatures tend to be more local than the changes in modal displacements, so modal curvatures are more useful for damage localization. The possibility of directly measuring modal curvatures using optical fibre strain sensors, instead of calculating them from modal displacements using a numerical integration procedure, is a big step forward in the exploitation of modal curvatures for damage identification. As a practical application, the damage identification at the Tilff bridge is discussed.
No abstract is provided for this article.
No abstract is provided for this article.
The Jubileumzaal is a large room at the KU Leuven University Hall which is used for social gatherings such as receptions and technical exhibitions.The room has a nominal capacity of 800 persons and it suffered from long-standing complaints about high noise levels and poor speech intelligibility.The main cause was the excessive reverberation time, which amounted to an average value of 5.1s across the 500, 1000 and 2000 Hz octave bands.However, due to the historical character of the room, the options for acoustic renovation were extremely limited.In the end, custom-made sound-absorbing chandeliers with integrated lighting were retained as an architecturally acceptable option.A total of 20 chandeliers were placed in the room, which reduced the reverberation time to 2.2 s, in close agreement with a theoretical assessment that accounts for the sound field directionality.In order to assess the effectiveness of the refurbishment, noise measurements were conducted during busy receptions before and after renovation.They are in good agreement with a prediction model that accounts for the Lombard effect, at least when the number of persons in the room is increasing.When it is decreasing, the measured noise levels are substantially higher, and an extension of the prediction model is offered to explain this result.
The construction industry uses cold-formed steel (CFS) sheets in the form of galvanised thin-walled profiles and corrugated sheets. In the past decade, CFS profiles have been competing with their hot-rolled counterparts as primary structural members of industrial halls, office buildings and residential housing of up to 3-4 storeys. The spans and column heights achieved with CFS profiles are ever larger. Due to the large slenderness of these members, adequate strength and stability are necessary, as well as reliability in design. Thin-walled members go through buckling during all stages of their working life. Local buckling appears at loads sometimes much lower than the design load. Distortional buckling seriously reduces the member resistance. It interacts with warping and lateral-torsional buckling, being significant for these asymmetric open sections. To restrict these effects, builders employ double sections - usually two standard cold-formed shapes bolted together to form a built-up section. These sections have the advantages of symmetry, higher stability and strength. The design of built-up members involves many uncertainties - although the European standard includes guidelines on the prediction of local, distortional and global buckling, the partial integrity and interaction between the parts of the composed members is still not studied. To study the actual behaviour, built-up members are tested in bending. An optical device for 3D motion analysis measures the displacement of points of interest on the specimen. Two interacting cameras use parallax to obtain the position of an arbitrary number of reflective markers glued to the specimen. The device tracks the movement of the markers in a 3D coordinate system without any contact with the specimen. Standard displacement transducers measure vertical displacements to validate the results. The paper gives an appraisal of the applicability of the method, a summary of the difficulties faced and the outcome of the test campaign.
If the acoustic wavelength is small compared to the characteristic size of an enclosed space, the sound field in that space is often modeled as diffuse. A diffuse sound field is conventionally defined as a zero-mean circularly-symmetric complex Gaussian random field. A more recent, generalized definition is that of a sound field having mode shapes that are diffuse in the conventional sense, and eigenfrequencies that conform to the Gaussian Orthogonal Ensemble. Such a generalized diffuse sound field can represent a random ensemble of sound fields that share gross features such as modal density and reverberation time, but otherwise have any possible arrangement of local wave scattering features. In this contribution, realizations of a conventional diffuse sound field or, equivalently, of the mode shapes of a generalized diffuse sound field, are generated in a Monte Carlo framework. As a discrete decomposition is numerically expensive when the sound pressures at many locations are of interest, a fast analytical decomposition based on prolate spheroidal wave functions is developed. The approach is numerically validated by comparison with a detailed room model, where random wave scatterers are explicitly modeled, and good correspondence is observed. Applications involving correlated sound sources and sound-structure interaction are presented.
