Le faible poids des produits en bois lamellé-croisé (CLT) combiné à leur degré élevé de préfabrication, ajoutés à la nécessité de fournir des produits de substitution à base de bois à l’acier et au béton, ont sensiblement contribué au développement des produits et des systèmes de CLT, tout particulièrement en ce qui a trait aux bâtiments de moyenne hauteur (5 à 9 étages). Tandis que ce produit est bien établi en Europe, la mise en place des produits et des systèmes de CLT en est à ses débuts au Canada et aux États-Unis. L’efficacité structurale du système de plancher agissant comme diaphragme et celle des murs en matière de résistance aux charges latérales dépend de l’efficacité des systèmes de fixation et des détails de connexion employés pour relier différents panneaux et assemblages. De longues vis autotaraudeuses sont généralement recommandées par les fabricants de CLT et sont utilisées pour relier les panneaux entre eux dans la construction de planchers ainsi que pour les assemblages plancher/mur. Cependant, il existe d’autres éléments et systèmes de fixation traditionnels et innovateurs qui peuvent être employés dans les assemblages de CLT.
Ce chapitre met l’accent sur quelques systèmes de connexion qui reflètent les pratiques actuelles, certains étant conventionnels, d’autres étant brevetés. En raison de l’introduction récente du CLT sur le marché de la construction, on s’attend à ce que de nouveaux types de connexion soient développés au fil du temps. Une variété de questions liées à la conception des connexions spécifiques aux assemblages de CLT y sont présentées. L’approche de conception européenne est présentée et l’applicabilité des dispositions de conception de la norme CSA O86-09 pour les fixations traditionnelles du CLT telles que les boulons, les goujons, les clous et les vis à bois sont passées en revue et des lignes directrices sont également fournies.
L’information fournie dans ce chapitre est dédiée aux concepteurs canadiens, un groupe ayant exprimé un vif intérêt pour la spécification des produits de CLT dans les applications non résidentielles et multi-étagées. Cependant, d’autres études seront nécessaires pour aider les concepteurs dans le développement de normes de conception et de procédures conformes aux normes canadiennes de conception des matériaux et au code national du bâtiment du Canada (CNBC). L’information technique sera également employée pour faciliter l’acceptation des produits de CLT en Amérique du Nord
In this study market opportunities for treated glue-laminated (glulam) products were investigated in the industrial wood sector. The main benefits of treated glulam are through-product treatment and the ability to manufacture treated products in shapes and sizes that do not fit into common treating chambers. These attributes provide for very durable and large glulam structures that are appropriate for outdoor use. For these reasons bridges, power poles, and sound abatement barriers were investigated. These are markets where wood has lost market share to or is being challenged by concrete and steel substitutes.
The vehicular bridge market was once heavy to the use of wood. Today wood accounts for only 7% of the number bridges in the US and less than 0.9% of the actual surface area of bridges in place. In interviewing municipalities in Canada it is clear that wood is not the preferred material with many wood bridges being replaced by concrete. Further, none of the municipalities contacted were planning wood bridges. However, wood bridges are still being installed. In the US 0.9% of the bridges installed by area in 2007 were wood. This is good news as wood is holding its market share. Steering clear of high volume or large bridges, local bridges are well suited for wood as they are plentiful, small in scale, and many are in disrepair. If 20% of local bridges were built with wood in Canada this would have equalled approximately $51 million in wood bridge construction in 2007.
Municipalities are much more open to the use of wood for pedestrian bridges and overpasses. Their quick construction and aesthetics are positive attributes in this application. One municipality contacted is planning multiple wood pedestrian bridges in the next five years. However, for the purpose of this market review there is little published information on pedestrian bridges.
Noise abatement barriers are a good high-volume technical fit for treated glulam. Increases in traffic and current road infrastructure improvements will lead to more demand for sound abatement in the future. This market is dominated by concrete, but at a very high price. If treated glulam can give adequate durability and sound performance properties it would be approximately 20% cheaper than concrete. The market for sound barriers in Canada could utilize up to 10 mmbf of wood per year to construct 80 km of barrier. This product can also be marketed as a high-performance acoustic fence for residential markets.
Treated glulam was also considered for utility poles. It is transmission grade poles where glulam would best fit the market as the demand is for longer poles which are more difficult to get in solid wood. This type of pole is where wood is currently being displaced by tubular steel. If glulam poles were used in 25% of the replacement transmission poles per year this could equal 8 mmbf. Light poles or standards are another market to consider. While this is a relatively low volume market glulam light standards are a premium product in European markets.
The B.C. Wood Specialties Group (BCWSG) laminating mission to Japan took place May 14-22, 1994 and involved visits to Japanese companies and industry associations in Nagoya, Osaka, and Nara. The mission was led by Mr. Peter Fisher, Director, Resource Industries Branch, B.C. Ministry of Employment and Investment. The purpose of the mission was to make contacts and to gather information so that the B.C. wood remanufacturing industry could capture further market opportunities during the trip and identify possible future markets for B.C. wood products.
The purpose of this small study was to examine the effect of various test methods upon the bending moduli of elasticity and to determine the bending strength of selected Douglas-fir and spruce laminated veneer lumber specimens.
A study was conducted with the primary objective of examining the efficacy of a standard block shear test method to assess the bond quality of cross-laminated timber (CLT) products. The secondary objective was to examine the effect of pressure and adhesive type on the block shear properties of CLT panels. The wood material used for the CLT samples was Select grade nominal 25 x 152-mm (1 x 6-inch) Hem-Fir. Three adhesive types were evaluated under two test conditions: dry and vacuum-pressure-dry (VPD), the latter as described in CSA standard O112.10. Shear strength and wood failure were evaluated for each test condition.
Among the four properties evaluated (dry and VPD shear strength, and dry and VPD wood failure), only the VPD wood failure showed consistency in assessing the bond quality of the CLT panels in terms of the factors (pressure and adhesive type) evaluated. Adhesive type had a strong effect on VPD wood failure. The different performance levels of the three adhesives were useful in providing insights into how the VPD block shear wood failure test responds to significant changes in CLT manufacturing parameters. The pressure used in fabricating the CLT panels showed a strong effect on VPD wood failure as demonstrated for one of the adhesives. VPD wood failure decreased with decreasing pressure. Although dry shear wood failure was able to detect the effect of pressure, it failed to detect the effect of adhesive type on the bond quality of the CLT panels.
These results provide support as to the effectiveness of the VPD block shear wood failure test in assessing the bond quality of CLT panels. The VPD conditioning treatment was able to identify poor bondline manufacturing conditions by observed changes in the mode of failure, which is also considered an indication of wood-adhesive bond durability. These results corroborate those obtained from the delamination test conducted in a previous study (Casilla et al. 2011).
Along with the delamination test proposed in an earlier report, the VPD block shear wood failure can be used to assess the CLT bond quality. Although promising, more testing is needed to assess whether the VPD block shear wood failure can be used in lieu of the delamination test. The other properties studied (shear strength and dry wood failure), however, were not found to be useful in consistently assessing bond line manufacturing quality.
Cross-laminated timber (CLT) has become popular in Europe for the prefabricated construction of wall, roof and flooring elements. The use of CLT in North America is gaining interest in both the construction and wood industries. Several North American manufacturers are in the process of product and manufacturing assessment or have already started pilot production.
For general principles of durability by design, the Best Practice Guide for Wood-Frame Envelopes (CMHC, 1999) and the Building Enclosure Design Guide – Wood-Frame Multi-Unit Residential Buildings (HPO, 2010) should be referred to for the design and construction of CLT buildings. The use of prefabricated CLT panels does not change the basic heat, air and moisture control design criteria for an exterior wall or roof assembly. However, different from conventional stick-built wood-frame buildings, the design of CLT building enclosures requires additional attention due to the unique characteristics of the product. CLT panels are massive solid wood elements and therefore have low vapour permeability and may provide a considerable level of insulation. They have a certain level of inherent air tightness but usually require an additional air barrier. The panels may absorb a large amount of moisture when exposed to excessive wetting and the consequent drying may be slow due to the mass of wood in such panels.
This chapter focuses on best practice heat, air and moisture control strategies for wall assemblies that utilize CLT panels in North American climate zones. The overlying strategies are to place insulation in such a way that the panels are kept warm and dry, to prevent moisture from being trapped or accumulating within the panel, and to control airflow through the panels, and at the joints and interfaces between them.
It is intended that these guidelines should assist practitioners in adapting CLT construction to North American conditions and ensuring a long life for their buildings. However, these guidelines are not intended to substitute for the input of a professional building scientist. This may be required in some jurisdictions, such as Vancouver BC, and is recommended in all areas at least until such time as CLT construction becomes common practice.
1re partie Empreinte environnementale du CLT – résultats préliminaires
Dans la présente partie, nous déterminons expérimentalement certaines caractéristiques environnementales quantifiées du CLT en tant que matériau de construction, sans toutefois effectuer une analyse du cycle de vie (ACV) exhaustive. Puisqu’il n’existe aucune documentation comparative sur le CLT, nous utiliserons plusieurs approches pour estimer son empreinte environnementale et pour le comparer au béton. À l’aide des données d’ACV existantes du bois lamellé-collé canadien en tant que valeurs de remplacement, nous examinerons l’empreinte du matériau en soi comparé aux matériaux du béton armé ainsi que des matériaux utilisés dans les bâtiments de moyenne hauteur comparativement au béton. Nous ajusterons ensuite les données de l’ACV du bois lamellé-collé pour qu’elles se rapprochent de celles d’une section de plancher de CLT aux fins de comparaison à une section de plancher en béton équivalente sur le plan fonctionnel. Dans chacun des cas, nous estimons que le CLT surpassera considérablement le béton dans chaque mesure environnementale abordée selon l’ACV.
2e partie Effets potentiels sur la qualité de l’air intérieur de l’utilisation du CLT dans les bâtiments – résultats préliminaires
Cinq produits de bois lamellé-croisé de différentes épaisseurs et lignes de collage ont été testés aux fins d’analyse de leurs composés organiques volatils (COV) comprenant les émissions de formaldéhyde et d’acétaldéhyde afin d’aider les ingénieurs et les constructeurs à mieux choisir les matériaux de construction ayant le moins d’incidence sur la qualité de l’air intérieur. Les émissions ont été évaluées selon la norme ASTM D 5116 et ont été recueillies après que les échantillons aient été exposés dans la chambre d’essais pendant 24 heures.
Aucune corrélation n’a pu être établie entre l’épaisseur du bois lamellé-croisé, les lignes de collage ou la quantité de COV individuels (COVi) émis, comprenant le formaldéhyde et l’acétaldéhyde, ou les COV totaux (COVt). Les cinq produits de CLT ont démontré de très faibles taux d’émissions de COVi et de COVt. La plupart des COV détectés provenaient de composés de terpène de bois résineux utilisés dans la fabrication de bois de construction laminé. Ainsi, lorsque le CLT est employé dans la construction d’un bâtiment, l’effet des COV sur la qualité de l’air intérieur est mineur, voire inexistant.
Lorsqu’on évalue les effets du produit sur la qualité de l’air intérieur, on peut facilement conclure qu’il serait négligeable, sinon nul. Les résultats relatifs aux COVt et aux émissions de formaldéhyde des cinq produits de bois lamellé-croisé après une exposition de 24 heures étaient généralement inférieurs à ceux indiqués dans les systèmes européens de marquage des émissions. En outre, le niveau européen E1 pour les émissions de formaldéhyde des produits de bois, qui est établi à 0,1 partie par million (ppm) ou à 100 parties par milliard (ppb), est de 6 à 20 fois supérieur aux niveaux mesurés pour les produits de bois lamellé-croisé.
D’ici juillet 2012, l’application de la phase 2 des normes du CARB (organisme de réglementation de l’État de Californie) relative à tous les produits composites sera complétée et les limitations d’émissions de formaldéhyde seront établies à des valeurs variant entre 0,13 ppm (130 ppb) pour les panneaux de MDF (panneaux de fibres de densité moyenne) minces et 0,05 ppm (50 ppb) pour le contreplaqué de feuillus avec noyau de composite (HWPW-CC). En comparant ces limitations à celles des produits de bois lamellé-croisé, on peut conclure que ces produits respectent amplement les limitations les plus rigoureuses du CARB, qui sont de 50 ppb.
The major defining characteristic of lumber cut from trees that have been infected with the mountain pine beetle is the extent of fungal bluestain in the sapwood. It is reported that bluestained wood has shown increased permeability, and questions arose as to whether the application of an adhesive or a finish coating may be adversely affected. Laminating of wood is a key value-added process and one that is very dependent on the quality of the bond between two or more components. Bluestain is a common phenomenon in the secondary wood processing industry where finishing is part of the value-adding process. The finishing evaluations made in this study were intended to benefit these processors.
Pieces of bluestained and non-stained 2 x 4 in. lodgepole pine lumber were dried to a moisture content typically targeted by the furniture sector — i.e., much drier than lumber used for structural purposes. From this lumber, specially constructed edge-glued panels were made which exhibited bluestained to bluestained joints and non-stained to non-stained joints. This construction method provides bluestained and non-stained joints for the laminating tests, as well as providing a good representation of what will really happen in an industrial setting where bluestain most likely will not be separated from non-stain. Each panel was cut in half, with one half being used for the laminating tests and the other half for the finishing evaluations. The strength and durability of the glue lines were measured. Various finish coatings either used alone or in combinations with others were subjectively evaluated.
The laminating tests show that gluelines in lodgepole pine that contains beetle-transmitted bluestain were not significantly different in strength from gluelines in unstained wood when PVA and PRF adhesives are used. The durability of the bluestained beetle-killed wood gluelines easily met the requirements specified by the ASTM D1101 standard.
Where desired, the appearance of bluestained wood can be enhanced or highlighted by a simple standard clear furniture finish. Bluestain in parts of edge-glued panels can be masked if certain types of finishes are employed. The finishes that gave more consistently good masking results were those containing blue, red, and charcoal tints in the stain, toner, or glaze coatings. Increased permeability of the bluestain did not affect the adherence of any of the finishes.
While the finishing evaluations indicate the possibilities for finishing pine, whether it has bluestain or not, market research is recommended, using the best performing finishes on full-scale furniture pieces, to test consumer acceptance.
