This new study aims to generate hygrothermal, particularly moisture-related performance data for light wood-frame walls meeting the R22 effective (RSI 3.85) requirement for buildings up to six storeys in the City of Vancouver. The overarching goal is to identify and develop durable exterior wood-frame walls to assist in the design and construction of energy efficient buildings across the country. Twelve test wall panels in six types of wall assemblies are assessed in this study. The wall panels, each measuring 4 ft. (1200 mm) wide and 8 ft. (2400 mm) tall, form portions of the exterior walls of a test hut located in the rear yard of FPInnovations’ Vancouver laboratory. This report, second in a series on this study, documents the performance of these wall assemblies based on the data collected over 19 months’ period from October 2018 to May 2020, covering two winter seasons and one summer.
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.
Advanced sustainable lateral load resisting systems that combine ductile and recyclable materials offer a viable solution to resist seismic load effects in environmentally responsible ways. This paper presents the seismic response of a post-tensioned timber-steel hybrid braced frame. This hybrid system combines glulam frame with steel braces to improve lateral stiffness while providing self-centreing capability under seismic loads. The proposed system is first presented. A detailed numerical model of the proposed system is then developed with emphasis on the connections and inelastic response of bracing members. Various types of braced frames including diagonal, cross and chevron configurations are numerically examined to assess the viability of the proposed concept and to confirm the efficiency of the system. A summary of initial findings is presented to demonstrate usefulness of the hybrid system. The results demonstrate that the proposed system increases overall lateral stiffness and ductility while still being able to achieve self-centring. Some additional information on connection details are provided for implementation in practical structures. The braced-frame solution is expected to widen options for lateral load resisting systems for mid-to-high-rise buildings.