Vibration reduction index in Cross-Laminated Timber junctions: measurements, prediction curves, uncertainty, and critical issues

Cross Laminated Timber (CLT) is increasingly used in lightweight buildings. In these struc-tures, flanking transmission significantly affects acoustic comfort, making it necessary to study parameters describing junction performance, such as the vibration reduction index Kij. The measurement of Kij is described in ISO 10848-1. However, the literature provides limited information on the reliability and uncertainty of this method for CLT junctions. In addition, specific critical issues related to test conditions, fastening systems and resilient interlayers may reduce the comparability of results. Furthermore, the semi-empirical Kij curves currently available (ISO 12354-1 Annex F) do not always provide sufficient accuracy for predictive frequency calculations. The thesis aims to assess the applicability of the Kij measurement method to CLT junctions, identify the main critical issues, and propose predictive curves for their average behaviour. An extensive measurement campaign was carried out on two full-scale mock-ups located in Italy (University of Bologna) and Belgium (Buildwise). The reliability of ISO 10848-1 was assessed through a GUM-based uncertainty analysis. Critical issues such as parasitic airborne noise, fastening systems, and resilient interlayers were also investigated. The results show that the applicability of ISO 10848-1 to CLT structures requires ad hoc con-siderations. The low diffusivity of the vibration field in the panels proved to be the main source of uncertainty, leading to expanded uncertainty values typically ranging from 2 to 4 dB. Semi-empirical curves were proposed for the total loss factor of CLT panels and for Kij, dis-tinguishing between rigid junctions and junctions with resilient interlayers, and including the contribution of the resilient layer Δlayer. The results provide a basis for future standard updates (ISO 12354 and ISO 10848-1), with the aim of improving prediction accuracy and inter-laboratory comparability.