This article presents a test method that was developed to screen adhesive formulations for finger-jointed lumber. The goal was to develop a small-scale test that could be used to predict whether an adhesive would pass a full-scale ASTM E119 wall assembly test. The method involved loading a 38-mm square finger-jointed sample in a four-point bending test inside of an oven with a target sample temperature of 204°C. The deformation (creep) was examined as a function of time. It was found that samples fingerjointed with melamine formaldehyde and phenol resorcinol formaldehyde adhesives had the same creep behavior as solid wood. One-component polyurethane and polyvinyl acetate adhesives could not maintain the load at the target temperature measured middepth of the sample, and several different types of creep behavior were observed before failure. This method showed that the creep performance of the onecomponent adhesives may be quite different than the performance from short-term load deformation curves collected at high temperatures. The importance of creep performance of adhesives in the fire resistance of engineered wood is discussed.
This study on Circular Economy & the Built Environment Sector in Canada was carried out by The Delphi Group in collaboration with Scius Advisory and completed in March 2021 on behalf of Forestry Innovation Investment Ltd. (FII) in British Columbia and Natural Resources Canada (NRCan) as the co-sponsors for the research. The work identifies a broad range of current efforts across Canada and undertakes a deeper dive on design for disassembly and adaptability (DfD/A) best practices, including an analysis of the ISO Standard 20887:2020 (i.e., design for disassembly and adaptability) in line with current Canadian industry practice and market readiness.
Comparison of Different Assembling Techniques Regarding Cost, Durability, and Ecology: A Survey of Multi-Layer Wooden Panel Assembly Load-Bearing Construction Elements
Wood is a pure, sustainable, renewable material. The increasing use of wood for construction can improve its sustainability. There are various techniques to assemble multi-layer wooden panels into prefabricated, load-bearing construction elements. However, comparative market and economy studies are still scarce. In this study, the following assembling techniques were compared: laminating, nailing, stapling, screwing, stress laminating, doweling, dovetailing, and wood welding. The production costs, durability, and ecological considerations were presented. This study was based on reviews of published works and information gathered from 27 leading wood product manufacturing companies in six European countries. The study shows that the various techniques of assembling multi-layer wooden construction panel elements are very different. Cross laminated timber (CLT) exhibited the best results in terms of cost and durability. With regard to ecological concerns, dovetailing is the best. Taking into account both durability and ecological considerations, wooden screw-doweling is the best. These alternatives give manufacturers some freedom of choice regarding the visibility of surfaces and the efficient use of lower-quality timber. CLT is the most cost-effective, is not patented, and is a well-established option on the market today.
Cross-laminated timber (CLT) manufactured in North America must meet stringent product standards and be certified to the ANSI/APA PRG 320 Standard for Performance-Rated Cross-Laminated Timber. This publication from APA - The Engineered Wood Association explains the key characteristics that are evaluated in certification process. When comparing North Amarican CLT to products manufactured elsewhere, it is important to recognize that products manufactured outside of North Amarica may not meet the performance expections defined in the ANSI standard.
This thesis examines the development of a superstructure for a slab-on-girder wood-concrete composite highway bridge. Wood-concrete composite bridges have existed since the 1930's. Historically, they have been limited to spans of less than 10 m. Renewed research interest over the past two decades has shown great potential for longer span capabilities. Through composite action and suitable detailing, improvements in strength, stiffness, and durability can be achieved versus conventional wood bridges. The bridge makes use of a slender ultra-high performance fibre-reinforced concrete (UHPFRC) deck made partially-composite in longitudinal bending with glued-laminated wood girders. Longitudinal external unbonded post-tensioning is utilized to increase span capabilities. Prefabrication using double-T modules minimizes the need for cast-in-place concrete on-site. Durability is realized through the highly impermeable deck slab that protects the girders from moisture. Results show that the system can span up to 30 m while achieving span-to-depth ratios equivalent or better than competing slab-on-girder bridges.
The fire resistance of cross-laminated timber (CLT) could be improved by treating the lamina with fire retardants. The major issues with this technology are the reduced bondability of the treated lamina with commercial adhesives. This study assessed several surface preparation methods that could improve the bondability and bond durability of fire-retardant treated wood with two commercial adhesives. Four surface preparation methods, including moisture/heat/pressure, surface planing, surface chemical treatment, and surface plasma treatment were assessed for their impact on the bondability and bond durability of lodgepole pine lamina. The block shear test results indicated that all surface preparation methods were somewhat effective in improving bond performance of fire-retardant treated wood compared to the untreated control wood samples, depending on the types of fire retardants and wood adhesives applied in the treatment process and bonding process. The selection of surface preparation, fire retardant, and wood adhesive should be considered interactively to obtain the best bond properties and fire performance. It may be possible to effectively bond the treated lamina with PUR adhesive without any additional surface preparation for the fire retardant used in the treatment at FPInnovations.
The North American product standard for performance-rated cross-laminated timber (CLT), ANSI/APA PRG 320, was published in 2012. The standard recognizes the use of all major Canadian and US softwood species groups for CLT manufacturing and provides design properties for specific CLT layups with visually graded and E-rated/MSR laminations. While design properties for CLT layups with Spruce-Pine-Fir and Douglas fir-Larch laminations are specified in the current standard, no design properties are indicated for CLT layups with Hem-Fir laminations.
Design properties for two proposed CLT grades manufactured with Hem-Fir lumber were developed. These include a CLT layup with visually graded laminations and another layup with E-rated/MSR laminations. Design properties for these two CLT layups were calculated separately for use in Canada and the US.
Supporting information for the addition of design properties for Hem-Fir grades to the CLT product standard was generated. Recommended amendments to the CLT product standard include durability and wood failure requirements of bondlines, and design properties for Hem-Fir layups.
Project contact is Hyungsuk Lim at Mississippi State University
Summary
This project aims to develop the preservative-treatment procedures for industrial cross-laminated timber (CLT) mats composed of southern yellow pine (SYP) lumber. The feasibility of pre- and post-treating CLT panels with an environment-friendly preservative system for ground-contact applications at an industrial scale will be evaluated from adhesion, mechanical, and durability performance aspects. As for the pre-treatment method, CLT panels will be consolidated with preservative-treated lumber adopting industrial CLT manufacturing parameters, including glue-type and clamping pressure. Alternatively, conventional CLT panels will be pressure treated with the same preservative system and dried afterward. As one of the primary focuses of the research, drying schedules which would not damage wood or adhesive layers will be determined. Also, penetration and retention of the preservatives throughout the post-treated panels will be analyzed. Adhesion and mechanical performance of the treated panels will be evaluated according to industry-accepted standards. Durability performance of the treated panels will be examined through laboratory weathering and on-site field tests.
Mass timber structures have the potential to change wooden construction on a global scale. Numerous mass timber high-rise buildings are in planning, under development or already built and their performance will alter how architects and engineers view wood as a material. To date, the discussion of material durability and biodegradation in these structures has been limited. While all materials can be degraded by wetting, the potential for biodegradation of wood in a mass timber building requires special consideration. Identifying and eliminating the conditions that might lead to this degradation will be critical for ensuring proper performance of wood in these structures. This article reviews and contrasts potential sources of biodegradation that exist for traditional wood construction with those in mass timber construction and identifies methods for limiting the degradation risk. Finally, future research needs are outlined.
