Sound Bridging By Wall Ties in Cavity Brick Walls: Theory and Experiment

Abstract

In cavity brick wall construction, wall ties are frequently used to provide resistance to water penetration and to transfer lateral forces, thereby increasing the load-carrying capacity of the wall. The presence of such ties, however, introduces an additional path through which sound and vibration transmission can take place. As a consequence, the sound insulation performance of cavity walls with ties may be lower than those of identical walls with no ties. In this paper, sound transmission loss results obtained from laboratory measurements on a common cavity wall system with two different types of wall ties are reported. The statistical energy analysis (SEA) method is used to construct a model representing a cavity wall system with or without ties, and predicted airborne sound transmission loss values are compared with experimental results. By considering the wall ties as rigid point bridges that excite the second leaf, which in turn radiates the transmitted sound power, expressions are developed that allow the calculation of the reduction in transmission loss at different frequencies. Reasonable agreement between theory and experimental results has been found by using both methods.