Jean-Louis Guyader

Energy transmission in finite coupled plates, part I: Theory

Abstract A theoretical method for studying vibrational energy transmission in coupled structures, which differs radically from the previous statistical energy analysis (S.E.A.) studies, is presented. This method is based on a modal description of the global structure. General expressions are obtained for energies of the coupled substructures, and three different mechanisms of coupling are shown: spectral, spatial and excitation coupling. The important practical case of coupled plates forming an L, T or cross junction, is then treated and analytical expressions of the global eigenmodes are given. This enables an application to be made, in the companion paper (Part II), to a problem relevant to energy vibration transmission between adjacent rooms in a building.

Energy transmission in finite coupled plates, part II: Application to an L shaped structure

Abstract The method presented in the first of these two companion papers is applied to the case of two thin plates coupled in an L shape. Numerical calculations yield values of the vibrational energies of each plate. The influences of damping, thickness and area of the plates and of the excitation type are presented and discussed. The theoretical results are compared with results from a computerized experiment, in which special attention was given to the number and position of point velocity measurements.

Reconstructing Interfacial Force Distribution for Identification of Multi-debonding in Steel-reinforced Concrete Structures Using Noncontact Laser Vibrometry

Interfacial debonding in multilayered engineering structures can jeopardize the structural integrity without timely awareness. By reconstructing the distribution of interfacial forces and canvassing local perturbance to the structural dynamic equilibrium, an identification approach for interfacial debonding between different structural components was developed. A “debonding index,” governed by the derivatives of reconstructed interfacial forces, was established, able to predict debonding in a quantitative manner including the coexistence of multi-debonding and their individual locations and sizes. The index offers the flexibility of detecting debonding between a beam-like component and its neighboring constituents of any type (beam, plate, shell, or even more complex components) with distinct material properties. To enhance the robustness of the approach under noisy measurement conditions, two denoising techniques (low-pass wavenumber filtering and adjustment of measurement density), together with a data fusion algorithm, were proposed. Using a noncontact laser vibrometry, the approach was validated experimentally by identifying multiple debonding zones in a steel-reinforced concrete slab dismantled from a bridge model. The approach has been demonstrated sensitive to debonding of small dimension owing to the use of high-order differential equation of motion. In addition, it does not require a global model of the entire system, prior information on structural boundaries, benchmark, baseline signals, and additional excitation sources as long as the structure undergoes steady vibration.

Sound transmission by coupled structures: Application to flanking transmission in buildings

Abstract In the paper a new formulation for sound transmission by coupled structures with special application to flanking transmission is presented. As distinct from other approaches in which the couplings are considered to be similar, this method treats each type of coupling specifically: the mechanical/mechanical coupling is rigorously treated; the mechanical/acoustic coupling is considered to be weak, this hypothesis being generally admissible when air is the acoustic medium fluid. The formulation proceeds from the general to the specific; in this way, it is easier to measure the effect of the hypothesis introduced. The theoretical procedure for defining the transmissions leads to an experimental method in which measured data of the energy and spectral densities of the forces is used. The application of this method to the case of sound transmission in buildings was carried out to serve as an example. The proportions of the energy transmitted by the dividing wall and the flanking walls were calculated to diagnose the situation and thereby to improve the insulation between the rooms. An interactive computer program is being proposed and will be available to users.

On a hybrid use of structural vibration signatures for damage identification: a virtual vibration deflection (VVD) method

A damage identification method named virtual vibration deflection (VVD) was developed, the principle of which was formulated based on the “weak” modality of the pseudo-excitation (PE) approach previously established. In essence, VVD is based on locating structural damage within a series of “sub-regions” divided from the entire structure under inspection, and each sub-region was considered as a “virtual” structure undergoing independent vibration. The corresponding vibration deflection of the “virtual” structure was then used to derive the damage index of VVD. Besides various advantages inheriting from the PE approach, for example, capability of detecting damage without baseline signals and pre-developed benchmark structures, VVD exhibits improved detection accuracy and particularly enhanced noise immunity compared with the PE approach, attributed to a hybrid use of multi-types of vibration signatures (MTVS). As a proof-of-concept investigation, a beam model was used in a numerical study to examine the philosophy of VVD. And the influences from different factors (i.e., level of measurement noise and measurement density) on the detection accuracy of VVD were discussed based on the numerical model. An experiment was carried out subsequently to identify the locations of multiple defects contained in an aluminum beam-like structure. Identification results constructed by the PE approach, VVD using single-type of vibration signatures, and VVD using MTVS, were presented, respectively, for the purpose of comparison.