Cross laminated timber elements with functional grading and localised ballast to improve airborne and impact sound insulation

Abstract

All over the world, Cross-Laminated Timber (CLT) elements are commonly used in the construction of multistorey timber buildings due to their structural strength and relatively low weight. In some countries, to meet the stringent requirements for impact sound insulation at low frequencies, a common solution is to ballast the entire surface of the CLT floor with a gravel layer before a floating floor is installed on top. Hereby, the gravel doubles or even triples the mass of the bare CLT floor, reducing its benefits. In a recent research project, indentations were machined into the CLT floor to accommodate the gravel ballast. The depth profile of the indentations was functionally graded so that the localised gravel ballast inside attenuates structure-borne sound more efficiently and hence improves the sound insulation. The achieved performance and targeted frequency range crucially depend on the geometry (size, depth, and profile) and the location of the indentations. Laboratory experiments on a small-scale CLT plate with functional grading and localised gravel ballast demonstrated an excellent vibration reduction, while the total mass of the bare CLT floor was increased by only 50% to a reference CLT plate.