The Vibration Reduction Index of Typical Canadian Cross-laminated Timber Junctions Jeffrey Mahn 1 National Research Council Canada 1200 Montreal Rd, Ottawa, Canada K1A 0R6 Markus Müller-Trapet National Research Council Canada 1200 Montreal Rd, Ottawa, Canada K1A 0R6 Iara B. Cunha National Research Council Canada 1200 Montreal Rd, Ottawa, Canada K1A 0R6

ABSTRACT In support of the National Building Code of Canada, The National Research Council Canada has published research report RR-335 which describes the results of measurements of the transmission of structure-borne noise through junctions between mass timber elements. The Code only allows for the use of measured data for the vibration reduction index from the NRC’s reports or reports from other research institutes. The Code does not currently allow for the use of empirical data for the calculation of the apparent sound transmission class of mass timber buildings. A lack of published data for typical mass timber junctions used in Canada can result in the overdesign of buildings or buildings which don’t meet the acoustic requirements of the Code. The NRC has embarked on a program to measure the vibration reduction index of a number of mock junctions of typical junctions used in Canada including junctions between cross-laminated timber floors and lightweight timber framed walls. The new data will aid in the development of empirical models of typical Canadian mass timber constructions. 1. INTRODUCTION

The acoustic requirements of the National Building Code of Canada describe the estimation of the apparent sound transmission class (ASTC) rating according to ISO 12354 [1], but modified to use ASTM metrics as outlined in the Guide RR-331 [2]. While the Code allows for the empirical data from Annex E of ISO 12354 to be used to estimate the vibration reduction index (𝐾 𝑖𝑗 ) for concrete and concrete masonry assemblies, the Code requires that the vibration reduction index for cross- laminated timber (CLT) assemblies must be measured. To this end, the National Research Council Canada (NRC) has published the Report RR-335 [3] which includes data for a number of different CLT junctions. However, not every possible combination of floor, wall and connectors has been evaluated in RR- 335 which limits the choices for designers and builders of CLT constructions.

1 jeffrey.mahn@nrc-cnrc.gc.ca

21-24 auGUST Scortsi event Cas La inter.noise | ee 2022

A new research project at the NRC has set out to measure data for floor / wall and wall / wall junctions using different connector types and spacing to fill in some of the gaps in the existing knowledge for the vibration reduction index of CLT junctions. The planned outcome will be curves based on the empirical data that can be used for the prediction of the 𝐾 𝑖𝑗 values, similar to what is presented in Annex E of ISO 12354. 2. JUNCTION DESIGN

The NRC has measured the 𝐾 𝑖𝑗 values for a number of junctions with similar mass rations such as a 3-ply wall connected to another 3-ply wall or a 5-ply wall. The CLT thicknesses for the wall / wall junctions of this study were chosen to measure the 𝐾 𝑖𝑗 values for more extreme mass ratios such as a 9-ply wall connected to a 3-ply wall. The new data points are intended to better define the curves shown in Report RR-335 such as that shown in Figure 1.

Figure 1: The mean 𝐾 𝑖𝑗 values and the best fit curves for cross-junctions using angle

brackets from RR-335 [3]. The 9-ply connected to the 3-ply will give mass ratios closer to 4 and .25. Other combinations of 3, 5 , 7 and 9 ply elements will fill in the empty spaces between the extremes. In addition to the cross-junctions to be evaluated, the 𝐾 𝑖𝑗 values for T-junctions will also be evaluated. 3. CONNECTORS

Research report RR-335 is currently restricted to data for brackets fastened at 600 mm on center. The new study will include data for brackets spaced at typical distances as well as resilient connections between the elements. For example, a 7-ply wall connected to a 3-ply wall in an X-junction with brackets spaced 600 mm on center is shown in Figure 2.

Wall-Wall Cross-Junction with Angle Brackets 11000 20000 ‘ass Ratio D/E (8 Pat and ot ====Trendforbicomtrous Path

Figure 2: A cross-junction between a 7-ply wall and 3-ply walls. The walls are

connected with brackets. The wall sizes are in full accordance with the requirements of ISO 10848 [4]. Each type of connector and spacing is anticipated to result in a different curve of 𝐾 𝑖𝑗 values. 3. RESULTS

All of the results of the study will be published in a new version of the Report RR-335 to be issued in 2023 to support the National Building Code of Canada. 4. CONCLUSIONS

The current lack of data and estimates for the 𝐾 𝑖𝑗 values for CLT junctions limits the use of CLT elements in building designs since it is difficult for designers and builders to demonstrate compliance with Code requirements without post-construction testing. The inclusion of new data in the development of empirical curves of the 𝐾 𝑖𝑗 values for typical Canadian CLTs will hasten the acceptance and use of CLT elements in building designs. 5. REFERENCES

[1] “ISO 12354-1:2017 Building acoustics. Estimation of acoustic performance in buildings from the

performance of elements - Part 1: Airborne sound insulation between rooms”, International Organization for Standardization, Geneva, Switzerland (2017). [2] Mahn, J., Quirt, D., Cunha, I., and Müller-Trapet, M., “RR-331: Guide to Calculating Airborne

Sound Transmission in Buildings: 6th Edition”, National Research Council Canada, Ottawa, Canada (2022).

[3] Mahn, J., Quirt, D., Mueller-Trapet, M., and Hoeller, C., “RR-335: Apparent Sound Insulation

in Mass Timber Buildings”, National Research Council Canada, Ottawa, Canada (2019). [4] “ISO 10848-1:2017 - Acoustics - Laboratory measurement of the flanking transmission of

airborne and impact sound between adjoining rooms - Part 1: Frame document”, International Standards Organization, Geneva, Switzerland (2017).