Steel studs are used in double walls to provide structural stability. This creates a vibration transmission path between leaves that can often be more critical than the airborne path through the cavity. Some of the existing models for sound transmission consider the studs as elastic springs. The spring stiffness may be taken as the cross-section elastic stiffness of the stud, but this leads to an underestimation of the vibration transmission. A procedure to obtain more accurate parameters to be used in vibration and sound insulation models is presented. The results show that they must be obtained from dynamic models and/or experiments.
The vibration reduction index of heavy junctions is predicted by means of a model based on spectral finite elements. This is equivalent to a finite element method but faster and with smaller computational costs. This advantage is used in order to perform a parametric analysis of the vibration reduction index for several junction types: T-shaped, L-shaped and +-shaped. The influence of several parameters such as: damping, junction dimensions or the mass ratio on the vibration reduction index is observed. The study is focussed to provide data and guidelines oriented to the EN-12354 design method for flanking transmission in buildings.
Sound insulation prediction models in European and International standards use the vibration reduction index to calculate flanking transmission across junctions of walls and floors. These standards contain empirical relationships between the ratio of mass per unit areas for the walls/floors that form the junction and a frequency-independent vibration reduction index. Calculations using wave theory show that there is a stronger relationship between the ratio of characteristic moment impedances and the transmission loss from which the vibration reduction index can subsequently be calculated. In addition, the assumption of frequency-independent vibration reduction indices has been shown to be incorrect due to in-plane wave generation at the junction. Therefore numerical experiments with FEM, SFEM and wave theory have been used to develop new regression curves between these variables for the low-, mid- and high-frequency ranges. The junctions considered were L-, T- and X-junctions formed from heavyweight walls and floors. These new relationships have been implemented in the prediction models and they tend to improve the agreement between the measured and predicted airborne and impact sound insulation.Peer ReviewedPostprint (author's final draft
When building elements of wood-frame lightweight constructions are considered, laboratory acoustic measurement methods have to be rethought. Indeed, because lightweight elements are often highly damped, the vibrational fields are no longer reverberant and existing standards often lose relevance, particularly in the case of mechanical excitation (such as in impact noise measurements or in vibration reduction index measurements of junctions). In this paper, standardized methods are identified or new methods are proposed for characterizing lightweight elements in order to obtain input data for prediction models such as that adapted from the standards EN 12354-1 and-2 and described in a companion paper. Moreover, it is shown that a new parameter (the radiation efficiency) is required when predicting the performance of lightweight buildings. Measurement results are shown for both wall and floor elements and the results are discussed, particularly in comparison with heavy building elements.
When wood frame lightweight constructions are considered, both the standardized methods, EN 12354-1 and-2, for predicting building performances from the performances of building elements and the related standardized laboratory measurement methods for characterizing building elements and their junctions have to be reconsidered. In this paper, a prediction method based on Statistical Energy Analysis and adapted to lightweight constructions, is presented. It was applied to a two-storey four-room building where an analysis of the different transmission paths was required in order to understand and improve the acoustic performances of the building. Comparisons between results, expressed in terms of airborne and impact sound insulation between rooms, either directly measured or calculated using the prediction method, are given in the three cases of vertical, horizontal and diagonal transmission. A satisfactory agreement between calculated and measured results is obtained.
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