No abstract is provided for this article.
No abstract is provided for this article.
Most of the mode-based damage identification techniques have been well verified by numerical simulations. However, many of them still face problems when applied to real measurements where noise is present. In this paper, an experimental program of a reinforced concrete beam is aimed to establish the relation between damage and changes of the structural dynamic characteristics. A damage identification scheme is developed using the mode-based damage identification method described in an accompany paper. The proposed damage identification scheme is applied to the experimental data and the consequent results are compared. It is demonstrated that the proposal of a realistic damage pattern that can describe damage by few representative parameters is necessary to guarantee the localization of damage. An adaptation of the initial finite-element model is required to give the best agreement with the reference measurements. A possible advantage of the algorithm is that the modal forces can be directly extracted from any finite-element package and the mode shape expansion is involved in the damage identification scheme using a static recovery technique.
The transfer matrix method (TMM) is commonly employed for wave propagation analysis in layered media of fluid, elastic and porous nature. Up to now it has been used extensively to analyze airborne sound transmission and sound absorption. Its use for impact sound transmission has been investigated to a limited extent, i.e. for thick homogeneous elastic plates of infinite extent and for specific receiver points. This contribution aims to broaden the scope such that the global impact sound, radiated by finite floor structures containing elastic, fluid and/or porous layers, can be analyzed in a more robust way than previously available in literature. A disadvantage of the conventional TMM is that only floors of infinite extent can be implemented. It is possible to remove this drawback using a spatial windowing technique. Furthermore, the modal behavior of the floor is approximately taken into account by projecting the impact force onto the mode shapes and only allowing for the propagation of those waves, corresponding to modal wavenumbers, in the structure. Predictions of the radiated sound power are made for various bare floors and floating floor systems of both infinite and finite extent.
No abstract is provided for this article.
Vibration testing is a well-known practice for damage identification of civil engineering structures. The real modal parameters of a structure can be determined from the data obtained by tests using system identification methods. By comparing these measured modal parameters with the modal parameters of a numerical model of the same structure in undamaged condition, damage detection, localization, and quantification is possible. This paper presents a real-life application of this technique to assess the structural health of the 50-year old bridge of Tilff, a prestressed three-cell box-girder concrete bridge with variable height. A complete ambient vibration survey comprising both vertical accelerations and axial strains has been carried out. The in situ use of optical fiber strain sensors for the direct measurement of modal strains is an original contribution of this work. It is a big step forward in the exploration of modal curvatures for damage identification because the accuracy in calculating the modal curvatures is substantially improved by directly measuring modal strains rather than deriving the modal curvatures from acceleration measurements. From the ambient vibrations, natural frequencies, damping factors, modal displacements and modal curvatures are extracted by the stochastic subspace identification method. These modal param- eters are used for damage identification which is performed by the updating of a finite element model of the intact structure. The obtained results are then compared to the inspections performed on the bridge.
A framework for quantifying the combined effect of uncertain parameters in sound insulation assessment, such as test sample dimensions, damping loss factors, room properties, and loudspeaker positions, in a logically consistent way, has been recently developed [1]. In this contribution, the application of this framework towards virtual round robin testing - this means, computing the uncertainty of the sound insulation of a given building element that is inherent in a given standardized measurement procedure - is presented. Results are discussed for three walls for which the airborne sound insulation is determined in accordance with ISO 10140: a heavy calcium silicate block wall, a lightweight gypsum block wall, and a double glazing. The resulting uncertainty levels are very large, especially in the lowest frequency bands, and agree with experimental observations. A comparison is also made with the reproducibility values from ISO 140-2 and draft ISO 12999-1, which are based on a limited number of inter-laboratory experiments, and which should provide a rough indication of the uncertainty that can be expected.
An exact stiffness formalism is presented to study harmonic and transient wave propagation in multilayered dry, saturated and unsaturated isotropic poroelastic media. Smeulders’ extension of Biot’s poroelastic theory is used to incorporate unsaturated porous media with a small gas fraction. A wide range of problems in geophysical and civil engineering can be treated, ranging from amplification of plane harmonic waves, dispersion and attenuation of surface waves to transient wave propagation due to a forced excitation. The effect of full or partial saturation on wave propagation in a poroelastic layered halfspace is demonstrated in a numerical example, in which the layering is caused by a moving ground water table.
No abstract is provided for this article.
The sound transmission loss of a partitioning structure depends on the nature of the sound fields in the source and receiver spaces. In an indoor setting, both sound fields are often taken to be diffuse. A diffuse field may represent the sound field of a conceptual ensemble of rooms with the same volume and reverberation time, but otherwise any possible arrangement of boundaries and small objects that have a wave scattering effect. Uncertainty due to random wave scattering is therefore inherently present in the diffuse transmission loss values. In this paper, closed-form expressions are derived for quantifying this uncertainty, such that it becomes possible to estimate by how much the transmission loss of a particular room–wall–room system may deviate from the nominal, ensemble-averaged diffuse value which corresponds to omni-directional incidence and halfspace radiation. First, an exact expression is derived for the harmonic or band-averaged diffuse transmission loss variance, based on hybrid deterministic–statistical energy analysis theory. Its evaluation requires knowledge of the dynamic stiffness of the partitioning structure and of the radiation impedances of the surrounding fluids. Subsequently, an approximate expression is derived, which depends on energy-related quantities only, making it also applicable in an experimental setting. Furthermore, it is demonstrated that the diffuse transmission loss is approximately normally distributed, such that a complete uncertainty quantification is possible from the mean and variance values. The expressions are verified in a Monte-Carlo simulation study involving a single wall and then validated with experimental data of double-leaf plasterboard walls containing flexible steel studs.
No abstract is provided for this article.
Engineering offices and manufacturers of acoustic building systems or materials often rely on measurement data to determine the adequacy of solutions for specific situations. This typically involves numerous costly and time-consuming laboratory measurements, making it difficult to efficiently explore and optimize various design configurations. In this paper, a prediction method is presented to accurately and efficiently predict the sound insulation of multilayer structures. Accuracy ensures reliability, while efficiency is crucial for optimization, where numerous simulations are needed, for example to identify the ideal layering or material properties of a(n) (inter)layer. The prediction method accounts for arbitrary layering, finite dimensions, boundary conditions and resulting modal behavior, as well as frequency- and temperature-dependent material properties. Extensive validation has been conducted using numerous examples with a specific focus on floating floors, demonstrating the model's robustness and reliability. An accuracy of 3 dB in the single number ration is generally achieved using predefined values from a material database. The method achieves higher accuracy when material properties are determined from testing.
No abstract is provided for this article.
In vibration-based damage detection techniques, the change in modal data is used as an indicator to detect and to identify the damage in the structure. An inverse problem is solved that consists in predicting the location and severity of the damage, given the structural dynamic characteristics before and after the damage.
