924 publications from this institution
No abstract is provided for this article.
A sensitivity-based finite element (FE) model updating method using experimental modal data is presented. Such a procedure aims to adjust the uncertain properties of the FE model by minimising iteratively the differences between the measured modal parameters (natural frequencies and mode shapes) and the corresponding analytical predictions. In the paper the FE model updating method is applied to damage assessment (damage localisation and quantification) of structures whose damage pattern can be represented by a reduction factor of the element bending stiffness. But in order to reduce the number of unknown variables and to obtain a physically meaningful result, a limited set of damage functions is used to determine the bending stiffness distribution over the FE model. The updating parameters are the multiplication factors of the damage functions. The procedure is illustrated by a modal test before and after damage application, on a reinforced concrete beam.
The reproducibility of sound absorption testing with the reverberation room method is a long-standing concern. Absorptive samples induce directionality in the nearfield, while the farfield depends on the room geometry below the Schroeder frequency. Nevertheless, when properly accounting for nearfield effects, the theoretical diffuse absorption coefficient of a sample still represents its average performance across an ensemble of different rooms, even at very low frequencies. Recent research found that particular reverberation room designs allow for an accurate measurement of the diffuse sound absorption coefficient of highly absorptive samples at low frequencies. Pinpointing such designs hence opens up a possibility to sustainably improve the low-frequency reproducibility of sound absorption testing in reverberation rooms. The present paper introduces a numerical optimisation framework that serves this purpose. Specific room shapes are parametrised and the geometrical room parameters are optimised so as to minimise the difference between the measured and the diffuse absorption coefficient under appropriate constraints. The sound absorption testing of a sample in a particular reverberation room is numerically simulated using a method that is both accurate and computationally efficient at low frequencies. The diffuse absorption is computed with a hybrid deterministic-statistical energy analysis approach that accounts for the detailed absorber properties, geometry, and boundary conditions, as well as the nearfield effects. The methodology is applied to both cuboidal and hexahedral room shapes. Certain optimised designs are found not only to provide an excellent match for the absorber that was used during the optimisation, but they also maintain their performance across a range of absorptive samples. Additionally, potential geometrical deviations are found to be well tolerated by these reverberation room designs.
Many civil engineering structures have a repetitive or quasi-periodic geometry. Such structures have clustered modes with closely spaced natural frequencies corresponding to mode shapes with similar wavelengths. Such modes may be difficult to distinguish in modal tests and lead to difficulties when pairing calculated and experimentally determined modal characteristics in vibration-based model updating. For repetitive structures, the free wave characteristics, i.e. propagation constants and free waves, can be used alternatively to characterize their dynamic behaviour. The free wave characteristics can therefore be used instead of modal characteristics as data features in model updating of repetitive structures. This paper investigates the feasibility of model updating of repetitive structures based on free wave characteristics. First, the identification of the free wave characteristics from the measured vibration responses of a periodic structure is investigated. A stabilization diagram is constructed to pick up the stable free waves. Second, model updating of repetitive structures is performed through a match of the calculated and experimentally identified free wave characteristics. A least-squares cost function is formulated and minimized using a gradient-based optimization algorithm. This algorithm requires the sensitivity of the free wave characteristics to the model parameters that need to be updated. The analytical expressions for the free wave sensitivities are therefore derived. The proposed model updating procedure is demonstrated and validated by a numerical case study involving a repetitive frame structure and by an experiment on a four-storey steel frame structure. The results confirm the feasibility of model updating based on free wave characteristics for repetitive structures.
Cables offer interesting possibilities in bridge design, but are rather susceptible to damage. Since damage in a cable changes its natural vibration frequency, it can be assessed with a vibration-based finite element updating procedure. However, the natural frequency of a cable is also influenced by the temperature, and the measured frequencies are prone to measurement errors. Therefore, it is useful to check the sensitivity of the identified damage with respect to these factors. This paper presents a methodology based on fuzzy numbers to investigate the propagation of measurement errors and uncertainty on the structural temperature throughout the updating procedure.
No abstract is provided for this article.
The local response of built-up structural and acoustic systems, consisting of stiff components with low modal density and flexible components with high modal density, may be very sensitive to uncertainty in spatial variations in the geometry, material properties, and boundary conditions of the flexible components. In this work, this uncertainty is considered by modeling the low modal density master system as deterministic and the high modal density subsystems in a nonparametric stochastic way, and by subsequently computing the response probability density function. The probability distribution of the master system's displacement degrees of freedom and the total subsystem energies is numerically computed by assuming that the distribution of the eigenvalues and eigenvectors of a decoupled subsystem correspond to those of a Gaussian Orthogonal Ensemble matrix. This approach is extensively validated by application to structures, consisting of thin plates attached to stiff structural components. Good agreement between the predicted probability distributions and the results of detailed Monte Carlo simulations is found. The validation examples also illustrate that the numerical procedure agrees better with the Monte Carlo simulations than a closed-form evaluation of the response probability density, which requires additional assumptions. © (2012) by the Katholieke Universiteit Leuven Department of Mechanical Engineering All rights reserved.
No abstract is provided for this article.
In this paper, different dynamic tests carried out on bridge B15 over the highway E19 connecting Brussels and Antwerpen in Belgium are described. Two Different excitation types are considered: a drop weight and ambient vibrations due to the traffic under and over the bridge. Finite element model is constructed to support and verify the dynamic measurements. The current measurements are a part of a research project for diagnostic inspection and detection of damages for bridges. By repeating the dynamic test after a certain time of use, the bridge's dynamic parameters such as natural frequencies, mode shapes and modal damping ratios could be used to detect and quantify damages. The modal parameters are extracted from the response time series using the data dependent system (DDS) approach. Good correlation between the finite element simulation and the experiments is obtained.
No abstract is provided for this article.
{Fibre-optic Bragg Grating (FBG) strain sensors hold a great potential for vibration monitoring of civil structures because of their exceptional stability and accuracy; however, the accurate measurement of the very small strains levels occurring during ambient, or operational, excitation has been so far problematic. There are two ways to improve the measurement resolution: employing a strain-enhancing sensor package, and applying an improved wavelength detection algorithm. In this work, the potential of an improved wavelength detection algorithm for the identification of modal characteristics based on sub-microstrain data is investigated. The strategy is illustrated for a steel beam to which a chain of multiplexed FBG sensors has been attached at the top side of the beam. The raw FBG data are processed into strain values with an algorithm that is based on detecting the peak shifts in the wavelength spectrum by correlation analysis rather than by simply tracking the peak values. Subsequently, the strain sequences are used for identification of modal characteristics of the beam (natural frequencies and strain mode shapes) with ``Covariance driven Stochastic Subspace Identification (SSI/cov){''}. Computational results of a Finite Element Model are used to validate the experimental results.}
In this study, the effects of natural fire exposure on the post‐fire behavior of concrete beams are investigated. The study is based on laboratory tests where three reinforced concrete beams were subjected to fire exposure using an electric radiant panel. This panel enables a precise application of radiative heat exposure closely mimicking natural fire exposure in a safe manner. During the test, the deflections, deformations and temperature changes are measured for all three concrete beams. Additionally, finite element modeling (FEM) is applied to supplement these tests, demonstrating the performance of existing structural fire engineering calculation tools in evaluating the burnout performance of concrete beams. The results of the tests show that the electric radiant panel provide a novel approach for fire simulation which is effective in replicating natural fire conditions, by applying the heat flux as specified in the Eurocode Parametric Fire Curve in a highly controlled manner. The uniformity of the temperature field measured inside the beams and the consistent deformations observed during the heat exposure across all three tests underscores the accuracy of the fire simulation. Furthermore, post‐fire assessments reveal that while the exposed beams suffered some reduction in load‐bearing capacity, they retained a significant portion of their original strength that was consistent across all three beams. The numerical simulations conducted in this study demonstrate a high level of accuracy in predicting the behavior of the concrete beams during fire exposure. These simulations effectively mirrored the experimental results, validating that they are a valuable tool for assessing concrete structures' performance in fire scenarios.
