Cross Laminated Timber (CLT) is an innovative engineered wood product being acknowledged and utilized around the world and is pushing the height limitations of mass timber constructions. Shear walls built with cross-laminated timber (CLT) panels are an attractive system to resist seismic load in tall buildings due to their low weight. Given that the seismic performance of these CLT shear walls is largely governed by the connection behaviour, in this report, a critical review of past studies on CLT shear wall systems and the behaviour of their connections, including hold-down, angle brackets and panel joints, is presented.
Project contacts are Grant Kirker (Forest Products Laboratory), Katie Ohno (Forest Products Laboratory) and C. Elizabeth Stokes (Mississippi State University)
Mass timber, as a renewable prefabricated structural panel material, is seen as highly desirable in the “green” building movement and has excellent thermal insulation, sound insulation, and fire restriction qualities. CLT is one of the more recent additions to the mass timber market worldwide, and although the product has undergone structural property testing in several laboratories, degradation testing of this non-preservative-treated product has only recently been initiated (Singh and Page 2016). Preliminary testing with exposure to Oligoporus placenta and Antrodia xantha indicated that untreated CLT is susceptible to the spread of mold and decay fungi, while treatment with boron somewhat reduced the extent of the decay fungus spread (Singh and Page 2016). These panels are easily handled on-site and have a much higher strength-to-weight ratio than their precast concrete competitors, which make them ideal for rapid construction of modular buildings, including apartment/condominium structures (Van de Kuilen et al. 2011). However, installations using CLT as a primary structural component in humid/damp climates, such as the southeastern United States, may be heavily affected by molds and decay fungi, and effects on CLT strength should be determined prior to widespread use of the product in these areas.
Newly constructed wood buildings are visually appealing but can eventually lose their beauty without proper protection. To preserve the natural beauty of wood products exposed to outdoor conditions, protective coatings should be applied to reduce the effect of weathering degradation of wood. Currently, no published work defines criteria for choosing the best coatings for mass timber products. It is vital to provide comprehensive guidelines for protecting and maintaining the appearance and increasing the durability of mass timber products.
The objective of this research is to promote the application of mass timber products, especially CLT, by identifying a range of suitable coatings that can prolong performance and the natural appearance of these products used in the construction of tall buildings.
Project contacts are Gerald Presley, Oregon State University, and Scott Noble, Kaiser+Path
The primary goal of this project is to enhance the durability of mass timber assemblies in high-moisture, high-termite risk regions. Only a few U.S. jurisdictions allow mass timber use by code adoption. Hawaii requires that all structural wood be treated to resist insects. Current topical or pressure treatments are allowed, but it is unclear how these treatments will perform in mass timber elements. Assembled cross-laminated timber (CLT) panels are too large to fit in pressure vessels. We will test the performance of individually treated wood members (lamella), assembled into CLT panels for compliance to structural requirements as well as resistance to termite attack in field trials. The resulting data will identify the most effective treatment options to protect CLT and other mass timber assemblies for use in Hawaii and similar regions with high termite exposure. The research implications will contribute to educating architects, engineers, builders and developers on modern timber construction in new regions.
Project contacts are Shiling Pei (Colorado School of Mines) and Samuel L. Zelinka (Forest Products Laboratory)
This project will generate three benchmark data sets for multistory CLT building moisture performance in different climate zones. Data will include moisture contents at key wood components and high moisture risk locations throughout the buildings. A relatively simple, but fully validated, numerical model for analyzing similar building moisture performance will be recommended. These results will be useful for structural engineers and architects to accurately consider moisture in their design of mass timber buildings.
A key question about new generation taller wood buildings is how they will perform over time in terms of durability and livability. This project will determine how best to measure these qualities by selecting sensors, determining testing and measurement protocols, and implementing testing assemblies in selected CLT buildings in Oregon. Future research will use the knowledge developed through this project to carry out post-occupancy monitoring, generating valuable new insights into building performance.
The research conducted will provide new climatic data which takes into account certain extreme weather events being attributed to climate change to minimize and/or prevent the risk of failure of tall wood buildings and mass timber structures. The project will offer guidance on the design for durability of tall wood building enclosures and fill existing gaps in knowledge about the extent of the effects of the future climate conditions and extreme weather events (e.g. heat waves, rainfalls, wind storms, etc.) on the resistances to deterioration of building materials, air leakage, vapour diffusion, and water ingress.
Project contact is Mariapaola Riggio at Oregon State University
Earthquake engineers are focusing on performance-based design solutions that minimize damage, downtime, and dollars spent on repairs by designing buildings that have no residual drift or “leaning” after an event. The development of timber post-tensioned (PT), self-centering rocking shear walls addresses this high-performance demand. The system works by inserting unbonded steel rods or tendons into timber elements that are prestressed to provide a compressive force on the timber, which will pull the structure back into place after a strong horizontal action. But, because these systems are less than fifteen years old with just four real-world applications, little information is known regarding best practices and optimal methods for engineering design, construction and/or tensioning procedures, and long-term maintenance considerations. This project intends to contribute knowledge by testing both cross-laminated timber (CLT) and mass plywood panel (MPP) walls through testing of anchorage detailing, investigating tensioning procedures for construction, determining the contributions of creep on prestress loss over time, and comparing all laboratory test data to monitoring data from three of the four buildings in which this technology has been implemented, one of which is George W. Peavy Hall at Oregon State University. This will be accomplished by testing small- and full-scale specimens in the A.A. “Red” Emmerson Advanced Wood Products Laboratory, and small-scale specimens in an environmental chamber.
Project contact is Henry Quesada at Virginia Polytechnic Institute and State University
This project is a multistate industry-university collaboration between SmartLam, the Northeastern Lumber Manufacturers Association (NELMA), the American Plywood Association (APA), IKD Architectures, Virginia Tech, and Purdue University to advance the utilization of hardwood lumber for the fabrication of Cross- Laminated Timber (CLT). This new proposal builds upon a previous Wood Innovation project. The collaboration among the organizations proposes to: 1) apply the shear analogy method to hardwood species listed in the National Design Standards (NDS) supplement to assure these species are feasible for the construction of structural CLT panels, 2) create a custom grade CLT layup made of yellow poplar (Liriodendron tulipifera) lumber and get its approval by the Engineered Wood Association (APA), 3) train the hardwood industry in the Midwest and in the Southeast on the application of hardwood structural lumber grading rules, and 4) perform mechanical testing on the hardwood CLT panels used in the Conversation Plinth project by IKD Architectures in Columbus, IN. In 2012 Virginia Tech conducted the first experimental tests on hardwood CLT panels. Results indicated that bonding, strength, and stiffness of yellow poplar CLT panels matched or were superior to some of the softwood CLT layups in the APA standard. Similar results were also obtained by independent testing conducted by the American Hardwood Export Council (AHEC) in 2018. However, further investigation by Virginia Tech found that the main limitations for the use of yellow poplar and other low value hardwood species in CTL panels are 1) lack of experimental data on other hardwood species used in CLT panels, 2) lack of supply of structurally graded hardwood lumber, and 3) acceptance and validation of hardwood CLT panels by the APA standard. Overcoming these limitations is critical for the hardwood lumber industry in order to gain access to the CLT market. Currently, the annual production of CLT panels in the US is about 35,000 m3 but it is expected that in 10 years production will be close to 2 million m3 per year. The outcomes of this project are to increase the utilization of low-value hardwood species from national and private forests and to increase economic development in rural areas in the hardwood regions of the US.
Project contact is Junwon Seo at South Dakota State University
Cross-Laminated Timber (CLT) has great potential to promote wood products markets in appropriate transportation structures, particularly bridges on low-volume roads such as rural or forest roads. The project’s goals are to perform field load testing and evaluation of a demonstration CLT bridge on the nation’s low-volume roads and evaluate its long-term performance under in-service loads and environmental exposure. The team will pursue these goals through the following research objectives: 1) Design the demonstration CLT bridge system with design details; 2) Fabricate the designed CLT bridge; 3) Install the fabricated CLT bridge on a roadway in Grand Portage National Monument with Western Wood Structures, Wheeler, Cook County in Minnesota and the National Park Service; and 4) Perform load testing to assess performance of the implemented bridge and monitor its moisture content and field performance through visual inspection for its long-term behavior evaluation.