Ce rapport décrit les résultats d’études en cours ou antérieures réalisées par Forintek sur les méthodes utilisées pour l’aboutage du bois et la qualité des produits. Il donne une description détaillée des différents paramètres susceptibles d’affecter le procédé d’aboutage et la qualité du produit fini. Il contient également une masse de renseignements publiés dans le cadre d’ateliers, de conférences ou de revues techniques. Cette information a été regroupée et intégrée dans un format simplifié de façon à être utilisable dans la fabrication des bois aboutés. L’un des chapitres porte sur le processus de qualification et de contrôle de la qualité des bois de charpente aboutés et décrit les normes canadiennes de produits spéciaux applicables. On trouvera à la fin de chaque section un paragraphe traitant d’idées de recherche novatrices, de questions importantes pour l’industrie canadienne du bois abouté et de lacunes dans les connaissances.
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
The light weight of cross-laminated timber (CLT) products combined with the high level of prefabrication involved, in addition to the need to provide wood-based alternative products and systems to steel and concrete, have significantly contributed to the development of CLT products and systems, especially in mid-rise buildings (5 to 9 storeys). While this product is well-established in Europe, work on the implementation of CLT products and systems has just begun in Canada and the USA. The structural efficiency of the floor system acting as a diaphragm and that of walls in resisting lateral loads depends on the efficiency of the fastening systems and connection details used to interconnect individual panels and assemblies. Long self-tapping screws are typically recommended by CLT manufacturers and are commonly used for connecting panels to panels in floors and floorto-wall assemblies. However, there are other types of traditional and innovative fasteners and fastening systems that can be used in CLT assemblies.
This chapter focuses on a few connector systems that reflect present-day practices, some being conventional, others being proprietary. Given the recent introduction of CLT into the construction market, it is expected that new connection types will be developed in time. Issues associated with connection design specific to CLT assemblies are presented. The European design approach is presented and the applicability of CSA O86-09 design provisions for traditional fasteners in CLT such as bolts, dowels, nails and wood screws are reviewed and design guidelines are provided.
The information given in this chapter is aimed at Canadian designers, a group which has expressed a strong interest in specifying CLT products for non-residential and multi-storey applications. However, further studies are needed to assist designers in the development of Canadian engineering design specifications and procedures consistent with Canadian material design standards and the National Building Code of Canada. The technical information will also be used to facilitate code acceptance of CLT products in North America.
Work reported in this study was carried out with the key objective of evaluating and providing recommendations on potential improvement of connection systems typically used in prefabricated wood wall panels. Several visits were made to major prefabricated wall panels and modular houses in Quebec to provide a better understanding of the typical connection systems being used in the prefabricated wall assemblies and to identify issues of concern.
Results of eighteen (18) racking tests and nine (9) bending tests on full-size 2.44 by 2.44 m walls composed of two segments (1.22 by 2.44 m) attached with three (3) different types of connection configurations are presented. Several wall-to-foundation attachments were also investigated; including bolted, nailed, and fully anchored walls. Monotonic and cyclic racking tests were performed according to relevant ASTM standards. Bending wall tests were carried out according to a proposed protocol based on the calculation of the wind pressure corresponding to five hurricane categories from 112 to 257 km/h. Bending wall tests were carried out using an airbag system to simulate the inward wind-pressure with three (3) types of attachments to the foundation.
Results reveal that the racking load carrying capacity of wall assemblies subjected to either monotonic or cyclic loading was not strongly affected by the type of central connection configuration used to joint the two wall segments. In addition, for all types of inter-segment connections tested under monotonic or cyclic loading, wall assemblies with hold-down anchors were nearly three times stronger than those nailed to the base. They showed 80% higher stiffness and dissipated five to seven times more energy before failure. Moreover, the type of loading seems to have some influence on the maximum load carrying capacity and to a less extent on stiffness of prefabricated wall assemblies, regardless of the type of inter-segment and wall-to-foundation attachments. As for out-of-plane loads, the tested wall assemblies resisted wind-pressure beyond 4.3 kPa corresponding to 232 km/h sustained wind speed equivalent to Category 4 hurricane. Their strength was controlled by the strength of the studs rather than the type of the connections used.
In addition, results on static and monotonic tests carried out on small size connections used in full-size racking and bending tests are also given. Such information is necessary for the finite element model being developed to predict the performance of prefabricated wall panels subjected to bending and racking forces, with special focus on the interface and anchorage behaviour for performance optimization.
Recommendations are given on how to improve the connection systems used in the assembly of wall panels. The information generated in this study provides data for comparative quantitative analysis of conventional and engineered wall assemblies and is expected to serve the development of design methodology for lateral load resisting systems of prefabricated houses.
Design for Deconstruction (DFD) is one of the most important strategies towards the reduction of the environmental burden of the construction environment. A better and deeper understanding of the DFD role and interrelationships involved in DFD should help this technique become an important consideration in any construction project. This is an exploratory study focused on review of current available state-of-the art information on design to dismantle concept and exploring potential applicability to wood-based assemblies and systems.
In Canada, few steps have been taken towards developing some guidelines and strategies for design for deconstruction and adaptability in buildings. However the process seems to have stopped after the publication of CSA guidelines in 2006 with no further activities planned. It has been demonstrated that DFD concepts could be applicable to most of the constructions methods where wood and wood-based products are used.
Aside from the analysis that needs to be done on accessibility, labelling, connections and layering, a special attention is required on the coordination to be created between the owners, architects, designers and builders. More work is needed to well-identify what are the specific problems/constraints related to each construction method (light wood-framed, post and beam, X-lam and any hybrid combination between them or even with concrete or steel).
Finally, it will be necessary to conduct a market study where it will be possible to quantify and identify professionals, developers and practisers that are most interested in adopting these concepts for the development of greener building designs.
Connections in timber structures play a key role in providing stability and stiffness to the structure. Timber joints may often become the weakest links of the structure and, therefore, require particular attention from the designers. Structural efficiency, simplicity of design, ease of fabrication and assembly in addition to cost effectiveness are some of the major parameters that need to be taken into account when specifying the appropriate connection system in timber projects.
The recent development of a new generation of structural composite wood-based products and assemblies (e.g. Cross Laminated Timber [CLT], parallel strand lumber, oriented strand lumber, etc.) and the recent interest in hybrid systems require the development of innovative connection systems as well as technical information on the design and performance of such connections. Moreover, the advancement in the Computer Numerical Control (CNC) systems which are being widely adopted in the manufacturing of timber and other wood-based products, is also contributing towards the development of such innovative connection systems as it facilitates the design and fabrication of such systems. Although some innovative timber connection systems have been developed (mainly in Europe and Japan) over the last 20 years or so, the lack of technical information and design guidelines is making it difficult for designers and engineers to adopt them in North America.
This report summarizes a series of activities focused on developing relevant technical information that would facilitate the design and construction of traditional and innovative connection systems for non-residential and mid-rise wood and hybrid construction using conventional and engineered wood products. The report also covers activities intended to support the design communities across the country which take the form of training courses and seminars organized to provide designers and engineers with the state-of-the-art technical information required to design their projects in accordance with the new design provisions in the Canadian timber design standard and using innovative connection systems from Europe and Japan. Since CLT is becoming one of the most promising alternative wood-based products to concrete in special applications, considerable work has been invested in developing appropriate connection systems to facilitate the use of this product for various applications.
One full chapter dedicated to the detailing and design issues of connection systems in CLT assemblies was drafted and compiled into a CLT handbook which was published recently by FPInnovations under the Transformative Technology Program under this project. In addition to that, results from an exploratory study focused on evaluating different CLT to CLT panel profiles typically used are presented in this report. Self-tapping screws are one type of fastening system that has been used extensively in Europe in CLT assemblies and one that has a great potential as it combines the ease of installation (i.e. requires no pre-drilling) with high efficiency. The report also describes some of the technical work conducted to support code change proposals in CSA O86 relating to improving current design procedure for ductile failure mode to account for additional capacity due to axial tensioning effect.
To be able to provide designers with a practical way of selecting the appropriate type of connection system for their specific application, detailed information on key performance attributes of traditional and innovative types of connection systems has been compiled in a table format. Such information will greatly assist design professionals who are pursuing the idea of using wood structural systems in non-residential buildings.
Work reported in this study was carried out with the key objective of evaluating fasteners holding capacity in commercial wood panels for the purpose of exploring potential markets or expanding existing ones for OSB and other panel products in the upholstered furniture industry.
In order to have a better understanding of the upholstery furniture industry, visits were made to major upholstered furniture manufacturers in the Montreal area in November and December of 2003. These visits provided the research group with a comprehensive knowledge on the various types of wood materials and processing technologies being used at these plants, including ways of connecting the various components of the frames. Interviews with the plants staff indicated that fasteners holding capacity in OSB and other panel products are some of the major issues that are currently limiting the increased use of wood-based panels in the upholstered furniture industry.
In order to better understand the relationship between the fasteners holding capacity and the density distribution in panels, a comprehensive testing program was established. A total of 20 panels of medium density fiberboard (MDF), 16-mm thick, particleboard (PB), 16 mm thick, and oriented strand board (OSB), 11 mm, 15 mm, and 18 mm thick, with 4 replications each, were scanned using a commercial X ray system to obtain in-plane (horizontal) density distribution of the full size panels. In addition, basic panel properties (i.e., bending strength (MOR) and stiffness (MOE), internal bond (IB) and density profile) were determined. Sampling of test specimens from mapped panels was carried out in such away to cover low and high horizontal density zones.
Fasteners holding capacity tests including; lateral resistance of screws, edge and face withdrawal and head pull-through resistance of screws and staples were carried out. Correlations between fasteners holding capacities and localized horizontal density distributions were established in order to investigate how density distribution within the plane of the panel could affect the fasteners holding capacity. Investigations on the fasteners holding capacity in panel specimens subjected to static and cyclic loadings were made as well for the purpose of examining the effect of repeated cycles of loading and unloading events (i.e., short-term fatigue).
Findings from this study indicated that poor fasteners holding capacity especially on the edge of the panel is one of the key panel attributes that is currently limiting the use of OSB and other wood panel products in the upholstered furniture. Fastener driven in low density points or zones may fail at much lower load level than that driven in high density points with failure initiating at those low density zones and progressing to other zones from there (i.e., loaded end or edge distance). For the type of cyclic loading regimes used in this study (90 cycles at different load levels), no significant differences were observed.
Recommendations are given on how to improve the panel attributes in order to increase the fasteners holding capacity and resolve some of the technical issues limiting the market access of wood panel products in the upholstered furniture industry.
This study was designed to evaluate the performance of a new wood-based portal frame system developed originally by APA with the purpose of providing alternative bracing systems to conventional prescribed details of small wood buildings. To achieve this objective, the study was divided into three components:
Study the performance of full-size portal frames with different configurations;
Evaluation of portal frame corners to optimize corner details and finally,
Develop a numerical model for portal frames to evaluate effect of the various parameters on performance and predict portal frame performance. Supplementary connections and material tests were conducted to generate input data for the finite element modelling of the portal frame.
Results from this preliminary test indicate that the lateral load carrying capacity of portal frames is approximately 75% the capacities of identical frames with hold-down. Those assemblies also had greater ultimate displacements than assemblies without hold-downs. Compared to portal frames without metal straps, the lateral load carrying capacity is slightly increased for with metal straps installed over sheathing. Same finding was observed in portal frame corner assembly tests. Full size portal frame and corner assemblies sheathed on one side without hold down had the lowest capacity among all assemblies tested. The addition of OSB sheathing to both sides of the portal frame corner has increased the moment resistance and rotational stiffness of the corner frame assembly.
Key findings from the FE modelling of portal frames with different types and locations of metal straps showed that the tensile strength of metal straps has the highest impact on the lateral load capacities and stiffness of portal frames assemblies. Portal frames assemblies with sheathings attached on both sides of the framing have approximately 30% higher lateral load capacities and stiffness than the walls with sheathings attached on one side of the framing. Moreover, it was found that it is more efficient to place metal straps directly on framing members. The efficiency is reduced if the metal straps are placed over the sheathing. The contribution of double bottom plates is insignificant. For portal frame assemblies with double bottom plates and two rows of nails fastened to the bottom plate, the stiffness and lateral load capacities are slightly increased compared to the walls with single bottom plate.
Results from current and previous studies on finger-jointing process and product quality carried out at Forintek are described in the report. A detailed description of the various parameters that can affect the finger-jointing process and the quality of the final product is given. The report also contains a good collection of information that has been published in various seminars, conferences and technical journals. Such information has been complied and integrated into a summarized format that manufacturers of finger-jointed lumber can use in their operations. One chapter is dedicated to qualification and quality control of finger-jointed structural lumber, where Canadian Special Products standards related to finger-jointed lumber are described. Special part that deals with new innovative research ideas, issues of concern and gaps of knowledge associated with the Canadian finger-jointing industry is presented at the end of each section.
In Eastern Canada, black spruce (Picea mariana (mill.)) lumber is often used by companies producing engineered wood products. Since it has only recently been utilized for finger-jointing, there is a need to examine this species with a view to optimizing the manufacturing parameters that influence the finger-jointing process. Key parameters influencing the finger-jointing process for softwoods such as black spruce were identified following visits to five finger-jointing plants in the Québec region.
The key parameters selected for study included: finger-joint geometry, curing time, pressure, machining parameters and moisture content and temperature of the jointed wood. Bending and tension tests were used to evaluate the finger-joints as per NLGA-SPS1-2000. Test results indicated a strong influence of finger-joint geometry on bending strength and, to a lesser extent, on tensile strength of finger-jointed black spruce. Optimum pressure was achieved at about 500 psi. Results on curing time of isocyanate adhesive indicated that mean tensile strength increased slightly with curing time until it stabilised at around 24 hours following joint assembly. More than 90% of finger-joint mean tensile strength was achieved after 5 hours of curing time at room temperature.
Results on the influence of machining parameters on the performance of finger-joints indicated no significant influence of cutting speed on tensile strength. Chip-load, however, was found to have some effect following a parabolic trend where the optimum value was achieved at 0.034 inch and at a feed speed of 60 feet/min. No clear trend on the influence of moisture content and temperature conditioning was observed for the combinations tested. However, the two combinations tested at -5oC exhibited the lowest mean tensile strength among all other combinations. There is a need to expand on this study to include more combinations of moisture content and temperature before concrete conclusions can be made.