Neither the National Building Code of Canada (NBCC) , nor any provincial code, such as the British Columbia Building Code (BCBC) , currently provide “acceptable solutions” to permit the construction of tall wood buildings, that is buildings of 7 stories and above. British Columbia, however, was the first province in Canada to allow mid-rise (5/6 storey) wood construction and other provinces have since followed. As more mid-rise wood buildings are erected, their benefits are becoming apparent to the industry, and therefore they are gaining popularity and becoming more desirable.
Forest product research has now begun to shift towards more substantial buildings, particularly in terms of height. High-rise buildings, typically taller than 6 storeys, are currently required to achieve 2 h fire resistance ratings (FRR) for floors and other structural elements, and need to be of non-combustible construction, as per the “acceptable solutions” of Division B of the NBCC . In order for a tall wood building to be approved, it must follow an “alternative solution” approach, which requires demonstrating that the design provides an equivalent or greater level of safety as compared to an accepted solution using non-combustible construction. One method to achieve this level of safety is by ‘encapsulating’ the assembly to provide additional protection before wood elements become involved in the fire, as intended by the Code objectives and functional statements (i.e., prolong the time before the wood elements potentially start to char and their structural capacity is affected). It is also necessary to demonstrate that the assembly, in particular the interior finishes, conform to any necessary flame spread requirements.
The Technical Guide for the Design and Construction of Tall Wood Buildings in Canada  recommends designing a tall wood building so that it is code-conforming in all respects, except that it employs mass timber construction. The guide presents various encapsulation methods, from full encapsulation of all wood elements to partial protection of select elements. National Research Council Canada (NRC), FPInnovations, and the Canadian Wood Council (CWC) began specifically investigating encapsulation techniques during their Mid-Rise Wood Buildings Consortium research project, and demonstrated that direct applied gypsum board, cement board and gypsum-concrete can delay the effects of fire on a wood substrate .
There is extensive data on the use of gypsum board as a means of encapsulation for wood-frame assemblies and cold-formed steel assemblies. However, tall wood buildings are more likely to employ mass timber elements due to higher load conditions, requirements for longer fire resistance ratings, as well as other factors. There is little knowledge currently available related to using gypsum board directly applied to mass timber, or in other configurations, for fire protection. Testing performed to date has been limited to direct applied Type X gypsum board using standard screw spacing, and showed promising results [5, 6, 7]. This represents an opportunity for other configurations that might provide enhanced protection of wood elements to be investigated.
Being able to provide equivalent fire performance of assemblies between non-combustible and combustible construction will thus improve the competiveness of tall timber buildings by providing additional options for designers.
Lack of research and design information for the seismic performance of balloon-type CLT shear walls prevents CLT from being used as an acceptable solution to resist seismic loads in balloon-type mass-timber buildings. To quantify the performance of balloon-type CLT structures subjected to lateral loads and create the research background for future code implementation of balloon-type CLT systems in CSA O86 and NBCC, FPInnovations initiated a project to determine the behaviour of balloon-type CLT construction. A series of tests on balloon-type CLT walls and connections used in these walls were conducted. Analytical models were developed based on engineering principles and basic mechanics to predict the deflection and resistance of the balloon-type CLT shear walls. This report covers the work related to development of the analytical models and the tests on balloon-type CLT walls that the models were verified against.
The latest developments in seismic design philosophy have been geared towards developing of so called "resilient" or "low damage" innovative structural systems that can reduce damage to the structure while offering the same or higher levels of safety to occupants. One such innovative structural system is the Pres-Lam system that is a wood-hybrid system that utilizes post-tensioned (PT) mass timber components in both rigid-frame and wall-based buildings along with various types of energy disspators. To help implement the Pres-Lam system in Canada and the US, information about the system performance made with North American engineered wood products is needed. That information can later be used to develop design guidelines for the designers for wider acceptance of the system by the design community. Several components influence the performance of the Pres-Lam systems: the load-deformation properties of the engineered wood products under compression, load-deformation and energy dissipation properties of the dissipators used, placement of the dissiaptors in the system, and the level of post-tensioning force. The influence of all these components on the performance of Pres-Lam wall systems under gravity and lateral loads was investigated in this research project. The research project consisted on two main parts: material tests and system tests.
In the material tests part of the program, a total of 110 compression tests were conducted to determine the load-deformation properties of four different engineered wood products (LVL, LSL, Glulam and CLT) in various directions. The LVL, LSL and Glulam specimens tested under compression parallel to grain had similar linear elastic behaviour with limited ductility. The CLT specimens tested under compression in the major-axis direction had linear elastic behaviour with moderate plasticity. Depending on the type of engineered wood product, typical failure modes included crushing, shear, wedge split and splitting. The compressive strength of the products tested ranged from 42.1 to 53.5 MPa, the global MOE (of the entire specimen under compression) varied between 6390 and 9554 MPa, the local (near the crushing surface) MOE parallel to grain was in the range of 2211 to 5090 MPa, while the local to global MOE ratio ranged from 29.2 to 58.0%, and was higher with the increase in the oven-dry density.
The specimens of the four different engineered wood products tested under compression perpendicular to grain or in the minor-axis direction had elastic-plastic behaviour with a clearly defined plastic plateau. Crushing (densification) of the fibres perpendicular to grain was the main failure mode for all specimens, and was in some cases followed by in-plane shear failure or cracking perpendicular to grain. Compression parallel to grain in the middle layer that was followed by its delamination and buckling was a unique failure mode for CLT specimens tested under compression in the minor strength direction. The compressive strength of the engineered wood products tested were in the range of 4.8 to 27.8 MPa, while the global and local MOE perpendicular to grain were in the range of 244 to 2555 MPa, and 320 to 1726 MPa, respectively. The compressive strength and global MOE perpendicular to grain increased with an increase in the oven-dry density. The results show no well-defined trend for the local MOE perpendicular to grain. The specimens loaded in the centre perpendicular to grain had higher strength, global and local MOE than those loaded at the end.
A convenient and timesaving design for the axial energy dissipators (fuses) was developed by replacing the epoxy in the original design with two half-tubes. Compared to the original design of fuses with epoxy, the new design with two half-tubes had similar necking failure mode and a longer failure displacment, thus providing user-friendly fuses that performed similar or even better than the original design.
In the system tests part of the program, a total of 17 different PT and Pres-Lam CLT walls with six different configurations were tested under monotonic and reversed cyclic loading. The studied parameters included the level of PT force, the position of the fuses, and the number of UFPs. CLT shear walls subjected only to post-tensioning, had non-linear elastic behaviour. The behaviour of the PT walls with and without energy dissipators was relatively similar under monotonic and cyclic loading. The strength degradation observed during the cyclic tests was low in all wall configurations suggesting that very little damage was inflicted upon the structure during the first cycles at any deformation level. Four major failure modes, including yielding and buckling of fuse, crushing and splitting of wood at the end of wall, and buckling of lumber in the exterior-layer of CLT wall, were observed in the tests. The yielding in fuses occurred at the early stage of loading as designed and the other failure modes happened when the lateral drift reached or beyond 2.5%.
The initial stiffness of the single-panel PT CLT walls tested ranged from 1.80 to 2.31 kN/mm, the load at the decompression point and 2.5% drift were in the range of 4.2 to 14.9 kN and 32.7 to 45.9 kN, respectively. The initial stiffness of the single-panel Pres-Lam CLT walls tested ranged from 1.69 to 2.44 kN/mm, the load at the decompression point and 2.5% drift were in the range of 21.0 to 30.2 kN and 59.6 to 69.8 kN, respectively. All the mechanical properties increased with an increase in the PT force. The average initial stiffness and the load at 2.5% drift of the coupled-panel Pres-Lam CLT walls tested were 4.59 kN/mm and 151.3 kN, respectively, while the load at the decompression point increased from 58.4 to 69.7 kN by increasing the number of UFP. The test results show that the behaviour of the Pre-Lam CLT shear walls can be de-coupled and a “superposition rule” can be applied to obtain the stiffness and resistance of such system.
The test results gave a valuable insight into the structural behaviour of the PT and Pres-Lam CLT shear wall under in-plane lateral loads. The data from the testing will be used in the future for development of numerical computer models. They will also be used for development of design guidelines for this system. All tests conducted in this study and the analyses in the future modelling research will form the basis for developing future design guidelines for PT and Pres-Lam mass timber systems.
A system which integrates architectural and structural design issues for timber connections will be developed for a limited number of connections and loading conditions which are dealt with in various national and international codes and standards. The scope of engineering issues relevant to connections will be expanded to include a wide range of timber connections and engineering solutions which are not covered by code procedures. This will include cases such as 3-dimensional loading configurations, dynamic analysis of connections and more rigorous analysis procedures. Progress on these objectives is described.
This literature review aims to provide a general picture of retrofit needs, markets, and commonly used strategies and measures to reduce building energy consumption, and is primarily focused on energy retrofit of the building envelope. Improving airtightness and thermal performance are the two key aspects for improving energy performance of the building envelope and subsequently reducing the energy required for space heating or cooling. This report focuses on the retrofit of single family houses and wood-frame buildings and covers potential use of wood-based systems in retrofitting the building envelope of concrete and steel buildings.
Air sealing is typically the first step and also one of the most cost-effective measures to improving energy performance of the building envelope. Airtightness can be achieved through sealing gaps in the existing air barrier, such as polyethylene or drywall, depending on the air barrier approach; or often more effectively, through installing a new air barrier, such as an airtight exterior sheathing membrane or continuous exterior insulation during retrofit. Interface detailing is always important to achieve continuity and effectiveness of an air barrier. For an airtight building, mechanical ventilation is needed to ensure good indoor air quality and heat recovery ventilators are typically required for an energy efficient building.
Improving thermal resistance of the building envelope is the other key strategy to improve building energy efficiency during retrofit. This can be achieved by: 1. blowing or injecting insulation into an existing wall or a roof; 2. building extra framing, for example, by creating double-stud exterior walls to accommodate more thermal insulation; or, 3. by installing continuous insulation, typically on the exterior. Adding exterior insulation is a major solution to improving thermal performance of the building envelope, particularly for large buildings. When highly insulated building envelope assemblies are built, more attention is required to ensure good moisture performance. An increased level of thermal insulation generally increases moisture risk due to increased vapour condensation potential but reduced drying ability. Adding exterior insulation can make exterior structural components warmer and consequently reduce vapour condensation risk in a heating climate. However, the vapour permeance of exterior insulation may also affect the drying ability and should be taken into account in design.
Overall energy retrofit remains a tremendous potential market since the majority of existing buildings were built prior to implementation of any energy requirement and have large room available for improving energy performance. However, significant barriers exist, mostly associated with retrofit cost. Improving energy performance of the building envelope typically has a long payback time depending on the building, climate, target performance, and measures taken. Use of wood-based products during energy retrofit also needs to be further identified and developed.
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 consolidation of the homebuilding industry is meant to continue and to have profound impacts on the forest products industry. It is changing the way houses are built as well as the relationships between building materials suppliers and home builders. Along the consolidation way, builders are also gaining more purchasing power as evidenced by the lumber consumption of the Top 100 builders, estimated to near 7 billion Board Feet.
More than ever before, large homebuilders are considering direct and longer term agreement with suppliers of lumber and OSB. It is expected that, due to the emergence of longer term and more direct purchasing agreement, collaborative practices become more developed. As far as building techniques go, we assume that the componentization of the housing industry will keep its advance, especially in the large builder segment. Componentization not only brings more off-site fabrication, but it also relies on a higher engineering content in the housing construction process.
Currently, purchasing agreements are short term based either for lumber, structural panels, engineered wood products, roof trusses and prefabricated walls. However, when questioned about the future of their purchasing agreements, respondents clearly showed a propensity to develop long term agreement. Indeed, every participant to this study pointed out to longer term agreements with suppliers and, in some cases, raised the possibility of more exclusive arrangements. This observation was further confirmed in site visits.
While centralization of the purchasing process is not the preferred choice of every large builder, we hypothesize that the specifiers will increasingly be centralized in the future in the wake of national purchasing agreements. Meanwhile, it is clear that regional offices will continue to have their word to say. Materials selection is not a one way process from top to bottom, but the head office is likely to be involved even when the process is regional.
As of now, most of the interactions between large builders and their suppliers may be summarized as information exchange. This indicates a fairly low level of inter-firm co-operation. However, the majority of participants expect either a shorter supply chain, more direct relationships or more partnering over the next five years. In turn, information and communication technologies, either for fund transfer of business planning, will spread out.