Cross laminated timber geometry and joinery implications on low-frequency sound transmission: FEA and Laser Doppler Vibrometry studies

Abstract

Cross Laminated Timber (CLT) slabs are becoming more widespread in North American construction in large part because of the environmental advantage of lower embodied carbon when compared to concrete and steel slabs. This advantage is significantly reduced by the use of high embodied carbon layers in the mass timber floor assemblies, such as concrete or gypsum screeds, that are used to reduce the direct sound transmission. This paper presents a study on the potential to reduce low-frequency sound transmission in cross-laminated timber floors by means of geometric stiffness. A laser doppler vibrometry (LDV) experiment on two different geometries is presented. One sample has a flat geometry, the other has a folded plate design. The folded plate sample is built with the same CLT panels used on the flat one, but is made out of 12 custom parts assembled into a domical shape. Both samples were installed on a 6 × 7 foot glulam frame, subjected to shaker excitations in the low frequencies on their top side, and the vibration on their bottom sides measured with the LDV. The resulting data is used to calibrate an FEA model, and subsequently study the sound transmission implications of the sample’s boundary conditions and joinery.