Sound Bridge Effects of Mechanical Connectors in Concrete Sandwich Panels: Numerical Modeling Approaches and Design Parameters —A Review

Abstract

The use of concrete sandwich panels consisting of two concrete wythes separated by an insulating core and connected by mechanical connectors has become a popular choice for modern building envelopes due to their high structural and thermal efficiency. The mechanical connectors that are required for the composite action of concrete sandwich panels inadvertently create a “sound bridge” that allows for a bypassing of the insulating core and causes a reduction in the sound insulation. The present paper provides a detailed state-of-the-art review of the overall sound bridge phenomena due to mechanical connectors used in concrete sandwich structures, with a focus on numerical modeling techniques and essential design parameters that affect the vibro-acoustic response. A detailed synthesis of the underlying mechanisms for the transmission of sound in sandwich structures is provided, which includes the fundamental principles of mass-spring-mass resonance, coincidence effects, and wave propagation mechanisms over a range of frequency-dependent mechanisms. Various mechanical connectors used in sandwich structures, including steel trusses, shear pins, Fiber Reinforced Polymer connectors, and hybrid connectors, are discussed in detail from the point of view of their dual functionality in ensuring structural integrity while resulting in acoustic compromise. The effects of essential design parameters on the transmission loss characteristics are discussed. The review additionally assesses the range of numerical modeling techniques used in the literature, from complex 3D finite element methods and coupled fluid-structure interaction techniques to more simplified forms of analysis, such as the Transfer Matrix Method and homogenization techniques. Critical analysis of the literature reveals that, despite the significant advances in the ability to numerically predict the behavior, the literature is characterized by a notable lack of experimental verification, the use of ideal boundary conditions, simplified forms of acoustic loading, and the lack of consideration of manufacturing defects and material damping. Notable research areas are identified, including the lack of experimental characterization of the acoustics of the FRP connector, the lack of consideration of low-frequency behavior, and the lack of integrated design consideration for the structural, thermal, and acoustic requirements. The review concludes by discussing the future research directions, which focus on the necessity for experimentally validated high-fidelity models, standardized testing methods that include diffuse fields, and the development of multifunctional connectors that are optimized for both composite action and acoustic insulation. This is necessary for advancing the rational design of concrete sandwich structures that are capable of satisfying the increasingly demanding acoustic requirements for modern building envelopes and transportation structures.