Project contact is Jianhui Zhou at the University of Northern British Columbia
Summary
Building acoustics has been identified as one of the key subjects for the success of mass timber in the multi-storey building markets. The project will investigate the acoustical performance of mass timber panels produced in British Columbia. The apparent sound transmission class (ASTC) and impact insulation class (AIIC) of bare mass timber elements as wall and/ or floor elements will be measured through a lab mock-up. It is expected that a database of the sound insulation performance of British Columbia mass timber products will be developed with guidance on optimal acoustical treatments to achieve different levels of performance.
FPInnovations initiated this project to demonstrate the ability of wood exit stairs in mid-rise buildings to perform adequately in a fire when NBCC requirements are followed, with the intent of changing perceptions of the fire safety of wood construction. The objective of this research is to investigate further the fire safety afforded by exit stair shafts of combustible construction, with the ultimate objective of better consistency between the provincial and national building codes with respect to fire requirements for exit stair shafts in mid-rise wood-frame construction.
This Report presents the results from experimental studies of the airborne sound transmission of mass timber assemblies, together with an explanation of the calculation procedures to predict the apparent sound transmission class (ASTC) rating between adjacent spaces in a building constructed of mass timber assemblies.
The experimental data which is the foundation for this Report includes the laboratory measured sound transmission loss of wall and floor assemblies constructed of Cross Laminated Timber (CLT), Nail-Laminated Timber (NLT) and Dowel-Laminated Timber (DLT), and the laboratory measured vibration reduction index between assemblies of junctions between CLT assemblies. The presentation of the measured data is combined with the presentation of the appropriate calculation procedures to determine the ASTC rating in buildings comprised of such assemblies along with numerous worked examples.
Several types of CLT constructions are commercially available in Canada, but this study focused on CLT assemblies with an adhesive applied between the faces of the timber elements in adjacent layers, but no adhesive bonding between the adjacent timber elements within a given layer. These CLT assemblies could be called “Face-Laminated CLT Assemblies” but are simply referred to as CLT assemblies in this Report. Another form of CLT assemblies does have adhesive applied between the faces of the timber elements in adjacent layers as well as adhesive to bond the adjacent timber elements within a given layer. These assemblies are referred to as “Fully-Bonded CLT Assemblies” in this Report. Because fully-bonded CLT assemblies have different properties than face-laminated CLT assemblies, the sound transmission data and predictions in this Report do not apply to fully-bonded CLT assemblies.
In many mass timber buildings, CLT or nail laminated timber (NLT) floors are designed with a concrete topping to improve acoustic separation, reduce vibration or act as a fire barrier. Little research has examined the fire behavior of these floor systems, but some preliminary tests involving LVL show that they may be able to meet three-hour fire resistance ratings, which could potentially open up the use of mass timber in Type I buildings, representing a large market opportunity. This project will test the behavior of composite floors under fire loading conditions considering the following parameters: shear connector type, mass timber panel types and thicknesses and concrete thicknesses. It will also test and validate an innovative fire research methodology using radiant panels.
This study illustrates the range of possible wood construction approaches for school buildings that are up to four storeys in height. As land values continue to rise, particularly in higher-density urban environments, schools with smaller footprints will become increasingly more necessary to satisfy enrollment demands. There are currently a number of planned new school projects throughout British Columbia that anticipate requiring either three-or four-storey buildings, and it is forecasted that the demand for school buildings of this size will continue to rise.
This study is closely related to the report Risk Analysis and Alternative Solution for Three- and Four-Storey Schools of Mass Timber and/or Wood-Frame Construction prepared by GHL Consultants, which explores the building code related considerations of wood construction for school buildings that are up to four storeys in height. Though wood construction offers a viable structural material option for these buildings, the British Columbia Building Code (BCBC 2018) currently limits schools comprised of wood construction to a maximum of two storeys, while also imposing limits on the overall floor area. As such, the reader is referred to the GHL report for further information regarding building code compliance (with a particular emphasis on fire protection) for wood school buildings.
This project studied the feasibility and performance of a mass timber wall system based on Nail Laminated Timber (NLT) for floor/wall applications, in order to quantify the effects of various design parameters. Thirteen 2.4 m × 2.4 m shear walls were manufactured and tested in this phase. Together with another five specimens tested before, a total eighteen shear wall specimens and ten configurations were investigated. The design variables included fastener type, sheathing thickness, number of sheathings, sheathing material, nailing pattern, wall opening, and lumber orientation. The NLT walls were made of SprucePine-Fir (SPF) No. 2 2×4 (38 mm × 89 mm) lumber and Oriented Strand Lumber (OSB) or plywood sheathing. They were tested under monotonic and reverse-cyclic loading protocols, in accordance with ASTM E564-06 (2018) and ASTM E2126-19, respectively.
Compared to traditional wood stud walls, the best performing NLT based shear wall had 2.5 times the peak load and 2 times the stiffness at 0.5-1.5% drift, while retaining high ductility. The advantage of these NLT-based wall was even greater under reverse-cyclic loading due to the internal energy dissipation of NLT.
The wall with ring nails had higher stiffness than the one with smooth nails. But the performance of ring nails deteriorated drastically under reverse-cyclic loading, leading to a considerably lower capacity. Changing the sheathing thickness from 11 mm to 15 mm improved the strength by 6% while having the same initial stiffness. Adding one more face of sheathing increased the peak load and stiffness by at least 50%. The wall was also very ductile as the load dropped less than 10% when the lateral displacement exceeded 150 mm. The difference created by sheathing material was not significant if they were of the same thickness. Reducing the nailing spacing by half led to a 40% increasing in the peak load and stiffness. Having an opening of 25% of the area at the center, the lateral capacity and stiffness reached 75% or more of the full wall.
A simplified method to estimate the lateral resistance of this mass timber wall system was proposed. The estimate was close to the tested capacity and was on the conservative side. Recommendations for design and manufacturing the system were also presented.
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