One of the most recent innovations in Engineered Wood Products is Cross-Laminated Timber (CLT). The system is based on the use of multi-layered panels made from solid wood boards glued together, with the grain direction of successive layers placed at 90° angles. The cross-laminated configuration improves rigidity, dimensional stability, and mechanical properties. Structurally, CLT offers performance comparable to concrete or steel, with panels suitable for use as walls, floors, roofs, and other applications. While CLT as a construction material has been successful in Europe for the past 20 years, and more recently has made inroads in the Australian and Canadian markets, it is not yet readily available in the United States. To better understand the market potential for CLT in the U.S., this study aims to assess the level of awareness, perceptions and willingness to adopt the system by U.S. professionals. To achieve these objectives, (a) a series of 10 interviews were conducted to gather insights from national and international CLT experts; (b) a web-based survey to U.S. architecture firms was conducted to gather information about familiarity, perceptions, performance and likelihood to adopt the system in the near future; and (c) a multi-family residential building project was designed to explore the architectural possibilities of the material.This study identified that the use of wood, a natural and renewable material, was the main advantage of CLT. Another important benefit of CLT over traditional construction systems is the dramatically shorter on-site construction time needed. CLT is a prefabricated system, thus reducing labor requirements, on-site waste, and accidents, all of which translates into significant cost reductions. The most commonly cited disadvantages of CLT were its acoustic and vibration performance. From the study it was found that the level of awareness about CLT is low among U.S. architects. Building Code compatibility, availability in the domestic market and cost were mentioned as the main barriers to the implementation of the system in the U.S. Cross-Laminated Timber appears to be a cost-competitive alternative to concrete structures, especially for buildings over six stories high. Architects seem to be willing to adopt CLT for their near-future projects, especially for multi-family, commercial, and recreational buildings. Importantly, this willingness to adopt CLT was found to be positively correlated to the level of awareness with the system. Results show that diffusion of knowledge about CLT and the role of early adopters will be essential for the successful introduction of this new building technology into the U.S. market. The preliminary design created as part of this study allowed demonstrating the structural capabilities of CLT, by maximizing the spans between structural elements achieving open and fluid living spaces. CLT also enabled the design of wide terraces and the inclusion of window openings on outside walls without compromising the structural integrity of the CLT elements.
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.
Many of the 1,400 timber bridges in Minnesota do not meet present day standards. Some of these bridges can be improved rather than replaced. When the desired service level can be attained by widening a bridge six feet or less, the bridge can be retrofitted by placing a second, wider, transverse deck onto the existing deck and substructure. Bridge components must be carefully inspected prior to a retrofit project. The retrofit of Bridge #6641 in Sibley County is a good example. First, the bituminous surface was removed. A longitudinal beam supported the extended deck. Grout was poured and leveled and then nail-laminated panels were laid transversely. A bituminous surface was laid over the full width of the new deck. The cost of the project was $51,632. (Replacing the bridge was estimated to take 2-3 years and cost $215,000.) The county quantified the strength change and load distribution characteristics by performing static and dynamic load tests before and after the retrofit. Adding a second deck effectively decreased the static deflections and improved the transverse load distribution. Nail-laminated timber bridge #2642, also in Sibley County, was retrofitted in 1992 and load-tested again in 1995. All dynamic deflections were lower than those of the post-retrofit tests in 1992. This improvement can be explained in part by the drying of the moisture that was introduced into the bridge deck during grouting. A retrofitted timber bridge is expected to last an additional 20-40 years.
Project contact is Jacob Mans at the University of Minnesota
As the acceptance of cross-laminated timber (CLT) grows among commercial and institutional clients, the hospitality industry, in general, has been hesitant to adopt CLT. This reluctance is linked to several real and perceived factors. One, the industry has fire safety and fire rating concerns with the construction system; these concerns have been largely addressed through independent research and building code updates. Two, the industry is concerned with the acoustic rating of standard CLT panels, which do not currently meet the elevated performance standards of the hospitality industry – specifically the sound transmission class (STC) rating -- and will require additional design research. Three, the industry is concerned with the aesthetics of the system and the dual challenges of exposing wood and simultaneously integrating Mechanical Electrical and Plumbing (MEP) systems. Image, brand identity, and indoor air quality are all key variables that factor into whether this rapidly-growing industry adopts CLT as a viable system for hotel construction. There is an opportunity to reframe these individual challenges as a collection of assets in order to provide a holistic solution that can will demonstrate the feasibility of CLT within the hospitality industry.
This grant will address these barriers and to facilitate the increased utilization of CLT within the hospitality industry. Such utilization has the potential to divert a substantial amount of fuel from federal forest and timber lands and to sequester its embedded carbon in buildings. Market analysis estimates that 715 hotels of 8 floors or lower (the target size for this project) will be built in the United States in 2020. If constructed out of CLT, this market represents approximately 94 million board feet of potential wood utilization through CLT per year (over 1 million metric tons of sequestered CO2). The opportunity to capture a fragment of this market warrants feasibility research to prove the viability of CLT for the hospitality industry.
The University of Minnesota and DLR Group will work with CLT manufactures and established hospitality partners to construct a modular hotel room prototype that can test acoustical and MEP systems integration strategies – as well as spark future research projects. This experimental apparatus will also double as a show unit to educate possible users and developers of the potential for a mass timber hotel. In addition to developing, constructing, and testing the prototype, the team will develop informational materials and a detailed cost analysis of the project that will encourage hospitality partners to implement these ideas with confidence.
CLT is an engineered wood product made from 3-7 layers of lumber assembled with alternating grains. Typically softwood lumber is used to manufacture CLT, but as Aspen (Populus tremuloides) lumber is highly available in Minnesota, this study was performed to investigate its feasibility for use in CLT panels. A CLT panel was manufactured using locally-acquired aspen lumber and tested for flatwise bending properties. A maximum load of 20.98 kN was found for the panel, which exceeds the standard . However, the values found for MOE and MOR of 8,068 MPa and 13.26 MPa, respectively, were below those of the standard. This research was supported by the Undergraduate Research Opportunities Program (UROP).