Oregon and southwest Washington are poised as a manufacturing hub for the emerging Cross Laminated Timber (CLT) market in the United States. The region is bountiful with luscious forestland, a large percentage of which is designated as working forests. Thirty million acres of forest span across Oregon alone. As a value add product that has environmental and social co-benefits, CLT is economically competitive as a structural framing product for multi-story, even high-rise building construction: a market previously dominated by concrete and steel.
The research and outreach activities performed as part of this 2015-2017 study have played a vital role in continuing the advancement of the CLT market in Oregon & SW Washington. Eager regional stakeholders see CLT and other mass timber panel products as forest products capable of providing economic benefit to communities within our region that had grown around forest product industries.
Although not yet seen as common practice, building with cross laminated timber (CLT) is gaining momentum in North America. Behind the scenes of the widely publicized project initiatives such as the Wood Innovation Design Centre Building in Canada and the recent U.S. Tall Wood Building Competition, substantial research, engineering, and development has been completed or is underway to enable the adoption of this innovative building system. This paper presents a brief overview of the current status of CLT building development in North America, highlighting some recent U.S. and Canadian research efforts related to CLT system performance, and identifies future CLT research directions based on the needs of the North American market. The majority of the research summarized herein is from a recent CLT research workshop in Madison, Wisconsin, USA, organized by the USDA Forest Products Laboratory. The opportunity and need for coordination in CLT research and development among the global timber engineering community are also highlighted in the conclusions of this paper.
Mass timber products, wood-based engineered construction materials, are becoming widely prevalent in the design and construction sector. Being a cost-effective, carbon efficient, durable, and sustainable building option, mass timber construction has already had a profound impact in residential and non-residential applications in Europe, and it has been reaching new heights in Canada, and recently gaining momentum in the United States. All architects, builders, designers, and forestry communities including the forest product industry, landowners, rural communities, and environmentalists have reason to be excited about these promising new timber products. Mass timber products are envisioned as substitutes for traditional building materials like concrete, masonry, and steel. The most widespread mass timber product is cross-laminated timber (CLT), which was first introduced in the early 1990s in Austria and Germany. It is currently on a rapid upward trajectory in North America. The main purpose of this article is to provide a brief overview of CLT and its market status and future prospects in North America.
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.
Cross-laminated timber (CLT) is a building system based on the use of massive, multi-layered solid wood panels. Although CLT as a construction system has been successful in Europe, only a handful of CLT projects have been built in the U.S. This manuscript presents the results from qualitative research, carried out with the objective of assessing the market potential and barriers to the adoption of CLT in the U.S. Insights from national and international experts were collected using semi-structured interviews. Topics included perceived benefits and disadvantages of CLT as a construction system, major barriers to its adoption in the U.S., and level of awareness about CLT among the architecture community.
Cross-Laminated Timber (CLT), has increased the possibilities of building with wood. CLT consists of multi-layer panels, manufactured with lumber boards that are glued together, alternating the direction of their fibers for each layer. The successful introduction of CLT into the Canadian market indicates that there is potential for further market penetration in North America, and more specifically the United States. To increase the understanding of the market potential for CLT in the U.S., this dissertation aimed at identifying the critical factors influencing the willingness of U.S. construction professionals to adopt innovative wood-based construction materials, such as CLT. The overall objective was achieved by: (a) investigating the level of awareness, perceptions, and willingness to adopt CLT among structural engineers and construction firms; (b) developing a conceptual model including the most critical factors that influence the adoption of innovate wood-based construction materials among structural engineers and construction firms; and (c) identifying distinct market segments for CLT adoption in the U.S. The outcomes from this research help fill the gap in the knowledge about the market adoption process for innovative wood-based materials in the construction industry. This study also contributes to advance the development of the CLT industry in the U.S. by increasing the demand of wood-based construction materials and supporting the creation of employment in a sector of critical importance to the U.S. economy. Findings from this thesis provide useful information that will help these actors accelerate the adoption of CLT through well-designed educational programs, demonstration projects, marketing strategies, and policy incentives.
One of the recent additions to the panoply of engineered wood products is cross-laminated timber (CLT). CLT is a prefabricated, large-scale, solid wood panel that consists of multiple layers of lumbers stacked together, with each layer arranged perpendicular to the next layer, glued with structural grade adhesives, and pressed. The use of massive CLT panels in wood construction provides several advantages over the traditional wood frame systems, making it particularly attractive for tall wood building construction. These main advantages are satisfactory distribution of defects, adequate seismic performance, ability to carry large loads, improved strength and stiffness, adequate acceptable fire performance, acceptable acoustic performance, and improved pre-fabrication.It is expected that as the CLT market will continue to mature, more diversified grades and special CLT products will be introduced into the markets. One special CLT product developed in at Oregon State University has been designated as hybrid CLT. Hybrid CLT refers to CLT panels manufactured with layers of high- and low-grade and low-density species, which aims at improving the economic efficiency and sustainability of the CLT industry with focus on the North America market.
One of the potential issues with hybrid CLT panel application is related to the unknown performance of the connection systems which are highly dependent on the density of the wood in which the fasteners embed. Most of the existing models that have been developed for estimation of the fasteners capacities in withdrawal and lateral loading scenarios are developed based on the assumption of uniform density profile across the layers to which fasteners penetrate. In a hybrid CLT panel, there is a possibility of a variation in density profile along the panel thickness so that the fasteners can be driven into wood of different densities and driven in directions parallel and perpendicular to grain. Because of the potential variation in density profile in the hybrid CLT, the connection system performance cannot be predicted using design models used for uniform density profile applications similar to the models in National Design Specification (NDS). Therefore, there is a need for evaluation of connections performance in hybrid layup.
The main objective of this work is to characterize the performance of connection systems for hybrid CLT. This is achieved through testing and modeling of single fastener connections and then testing and modeling of the typical connection systems. So, the specific objectives are: (1) evaluate the single fasteners performance to account for density variation and compare the results to a proposed modified model, (2) perform an experimental program to test different connection systems with different hybrid CLT panel layups, (3) develop a numerical algorithm based on the use of meta-heuristics tools to fit the optimal parameters for constitutive models to match the experimental data for the connection systems, (4) obtain the optimal parameters for constitutive models of the connection systems tested.
Wood-frame is the most common construction type for residential buildings in North America. However, there is a limit to the height of the building using a traditional wood-frame structure. Cross-laminated timber (CLT) provides possible solutions to mid-rise and high-rise wood buildings. CLT offers many advantages such as improved dimensional stability, a quicker erection time and good performance in case of fire. In order to introduce the cross-laminated timber products to the North American market, it is important to gain a comprehensive understanding of its structural properties. This paper focuses on the seismic performance of CLT connections. Over the last few years FPInnovations of Canada has conducted a test program to determine the structural properties of CLT panels and its application in shear walls. The test program comprised of more than 100 connection tests which followed the loading procedures of CUREE and ISO test protocols as specified in ASTM Standards ASTM E 2126-09 (2009). These tests were performed parallel and perpendicular to the grain of the outer layer, respectively. The impact of different connections on the seismic performance of CLT walls was investigated in a second phase on full size shearwall. CLT panels are relatively stiff and thus energy dissipation must be accomplished through the ductile behaviour of connections between different shear wall elements and the connections to the story below. A literature review on previous research work related to damage prediction and assessment for wood frame structures was performed. Different approaches for damage indices were compared and discussed. This paper describes how the energy-based cumulative damage assessment model was calibrated to the CLT connection and shear wall test data in order to investigate the damage under monotonic and cyclic loading. Comparison of different wall setup provided a deeper insight into the damage estimation of CLT shear walls and determination of the key parameters in the damage formulation. This represents a first published attempt to apply the damage indices to estimate the seismic behaviour of CLT shear walls.
CLT is becoming global. New countries and regions increasingly realize the potential of what can be done with CLT. As a result, new markets are forming and new companies are entering the industry. Every new region or country that opens its doors to CLT has its own challenges and opportunities. However, there is the unique opportunity to learn from the existing Original Market in Europe and the companies that have been successful there for many years. Especially the German-speaking alpine region was, and still is, the cradle of CLT innovation. Therefore, this research,using qualitative methods, analyzed market characteristics and business models of this region. Lessons learned over the years were identified such as the importance of high-level timber education, the role of designing for building services, hype versus reality with respect to tall wood buildings and how careful design processes are key to competitiveness of CLT buildings. Threats and challenges in the North American CLT market were also identified there. The combined findings give an enhanced understanding of how the implementation of CLT in North America, as an example of a new global market, can be fostered.