American Wood Protection Association Annual Meeting
Cross laminated timber (CLT) is a relatively recent addition to the North American timber construction market. CLT has been successfully used for construction in Europe and, in the past few years, manufacturers have looked forward to expanding the use of this product into the North American market. However, no termite susceptibility experiments have been published for the product and no standards exist for testing of the CLT and other mass timber products against termites. It is extremely important to evaluate the resistance to degradation of CLT, especially if the manufacturers are trying to implement this product in areas where the occurrence of termite infestation is high...
The development of composite mass timber products in the late 20th century continues to generate new developments in the design and production of multi-layer wood products in a wide variety of orientations and for a wide variety of uses. In the US Congress’ Agricultural Act of 2014, provisions were specified in Section 7310 to establish a series of priorities for research into the needs of the forestry sector. Specifically, collaborative research efforts into the increased use of CLT in support of the expansion of this portion of the forest products industry were addressed. Cross laminated timber products have been included in updates to national and international building codes, and new production facilities continue to come online. WoodWorks (2019) reports that 105 CLT based construction projects are in construction or completed, and 200 are in the design process. These projects are scattered across the United States, including in the highest areas of decay potential (Figure 1). Mississippi State University Department of Sustainable Bioproducts has several ongoing projects to investigate the durability of CLT under various conditions. These are partnerships with other investigators, primarily with USDA Forest Products Lab personnel, and are housed at both MSU Department of Sustainable Bioproducts facilities in Starkville, MS as well as Forest Products Lab locations in Madison, WI, McNeill, MS, and Saucier, MS. CLT is being tested in several different formats and in test pieces of different sizes. In an ideal situation, CLT panels would be tested at their full size, however, the time it would take to do so, and the logistics of handling pieces of typical size is prohibitive for rapid assessment of the product. Assessments of CLT to date have focused on examining the durability of CLT when exposed to hazards that occur in the high hazard zones of deterioration, such as fungi, termites, and natural weathering. This report describes the collaborative testing of CLT against termite infestation and damage.
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.
This research was conducted to discover how the U.S. building construction and forest products sectors could benefit from the development of tall, cross-laminated (CLT) and mass timber buildings. Barriers that may restrict such development were also investigated. The primary benefits were discovered to be eco-performance and job creation. Code restrictions and material performance misconceptions were found to be the largest obstacles. Case studies of Treet, Tamedia, and the WIDC were conducted to demonstrate the benefits of tall wood buildings and the various paths around potential barriers. Opportunities for tall wood buildings in the U.S. are also discussed. This research discovered that a tall wood movement is gathering momentum in the U.S. To fully realize this potential, accurate information regarding the use of wood and the performance capacities of mass timber systems needs to be disseminated. Co-operation between academia and industry will also be necessary.
Project contact is Jianhui Zhou at the University of Northern British Columbia
Floor vibration performance could govern the allowable span of mass timber floors. The objectives of this project are:
1. to develop a mobile app to collect data from lab and field mass timber floors for acceleration-based performance criteria;
2. to investigate the dynamic properties of mass timber floors under different boundary conditions;
3. to adopt frequency equations to predict the fundamental frequencies of mass timber floors under different boundary conditions;
4. to develop numerical modeling strategies for predicting vibration response of mass timber floors under footfall excitations.
The development of this primer commenced shortly after the 2018 launch of the Mass Timber Institute (MTI) centered at the University of Toronto. Funding for this publication was generously provided by the Ontario Ministry of Natural Resources and Forestry. Although numerous jurisdictions have established design guides for tall mass timber buildings, architects and engineers often do not have access to the specialized building science knowledge required to deliver well performing mass timber buildings. MTI worked collaboratively with industry, design professionals, academia, researchers and code experts to develop the scope and content of this mass timber building science primer. Although provincially funded, the broader Canadian context underlying this publication was viewed as the most appropriate means of advancing Ontario’s nascent mass timber building industry. This publication also extends beyond Canada and is based on universally applicable principles of building science and how these principles may be used anywhere in all aspects of mass timber building technology. Specifically, these guidelines were developed to guide stakeholders in selecting and implementing appropriate building science practices and protocols to ensure the acceptable life cycle performance of mass timber buildings. It is essential that each representative stakeholder, developer/owner, architect/engineer, supplier, constructor, wood erector, building official, insurer, and facility manager, understand these principles and how to apply them during the design, procurement, construction and in-service phases before embarking on a mass timber building project.
When mass timber building technology has enjoyed the same degree of penetration as steel and concrete, this primer will be long outdated and its constituent concepts will have been baked into the training and education of design professionals and all those who fabricate, construct, maintain and manage mass timber buildings.
One of the most important reasons this publication was developed was to identify gaps in building science knowledge related to mass timber buildings and hopefully to address these gaps with appropriate research, development and demonstration programs. The mass timber building industry in Canada is still a collection of seedlings that continue to grow and as such they deserve the stewardship of the best available building science knowledge to sustain them until such time as they become a forest that can fend for itself.
Cross Laminated Timber (CLT) is gaining acceptance in tall building applications in the US. However, there are knowledge gaps concerning long-term performance, particularly effects due to moisture intrusion and biological decay in relation to connection systems. In a risk-averse industry, this knowledge gap impedes acceptance of CLT. The overall goal of the project is to characterize the effects of moisture accumulation in mass timber buildings on properties of building components and connections. The project will assess CLT connectors using small-scale assemblies, then use these data to develop predictive models that will be compared with full-scale tests. Connection assemblies will be constructed with two wood species and exposed to five moisture/biological regimes. Moisture behavior in the assemblies will be characterized using a combination of non-destructive tools, such as ultrasonic, wave propagation, CAT-Scan, and infrared imaging. The data generated from cyclic loading tests will be used to calibrate the SAWS connection model. This will provide a novel way to estimate the effects of moisture and biological degradation on connections. A deliverable for this project is a design guideline for engineers to account for the effects of moisture intrusion and subsequent fungal decay on panel and connection properties.
Structural Engineers Association of California Convention
September 9-12, 2015, Bellevue, Washington, USA
This study demonstrates a design of a code-compliant, highrise mass timber apartment tower in Los Angeles. Using the existing reinforced concrete Museum Tower Apartment building in downtown Los Angeles as a basis, the study demonstrates architectural, structural and fire performance improvements and tradeoffs of the mass timber design compared to the reinforced concrete design.
The existing, 20 story building is a reinforced concrete perimeter moment frame with a beamless interior utilizing post-tensioned slabs. Cladding is painted structural concrete and window wall glazing. No additional fireproofing is added to the concrete structure. The theoretical mass timber building is designed to match the existing building architectural massing, but uses wood-steel buckling-restrained brace frames, glulam columns and beamless composite concretecross laminated timber floor slabs. Cladding is weather-coated mass timber and window wall glazing. Fire protection is provided by oversized structural members with a sacrificial char layer as well as intumescent paint on exposed steel connections. The study demonstrates that mass timber provides a viable alternative to reinforced concrete construction in Los Angeles.