Cross-laminated timber (CLT) is a prefabricated solid engineered wood product made of at least three orthogonally bonded layers of solid-sawn lumber or structural composite lumber that are laminated by gluing of longitudinal and transverse layers with structural adhesives to form a solid rectangular-shaped, straight, and plane timber intended for roof, floor, or wall applications. While this engineered wood product has been used in Europe for over 15 years, the production of CLT and design of CLT structural systems have just begun in North America. For the acceptance of new construction materials or systems in North America, such as CLT, a consensus-based product standard is essential to the designers and regulatory bodies. This paper describes and documents the background information and some key issues that were considered during the development of the ANSI/APA PRG 320 Standard for Performance-Rated Cross Laminated Timber. This standard was developed based on the consensus standard development process of APA-The Engineered Wood Association as a standards developer accredited by the American National Standards lnstitute (ANSI). The CLT stress classes incorporated in this product standard are also discussed. The ANSI/APA PRG 320 standard has been approved by the Structural Committee of the lnternational Code Council (lCC) for the 20'15 lnternational Building Code (lBC).
The superior fire performance of timber can be attributed to the charring effect of wood. As wood members are exposed to fire, an insulating char layer is formed that protects the core of the section. Thus, beams and columns can be designed so that a sufficient cross section of wood remains to sustain the design loads for the required duration of fire exposure. A standard fire exposure is used for design purposes. In North America, this exposure is described in the standard fire resistance test ASTM E 119 . Many other countries use a comparable test exposure found in ISO 834 . In spite of the difference between standard dire resistance tests, experimental charring rates measured in various parts of the world appear to be consistent. This justifies the use of such data for design, regardless of origin.
Cross Laminated Timber (CLT) technology has been growing in the EU and Canada since the early 1990's and utilizes the mechanical properties of structural grade lumber to create a strong panel product for use in floor, ceiling and wall systems. The hypothesis of this project was that CLT panels made from non-structural lumber from lightweight species could also meet the performance criteria of the CLT product Standard. The objective of this project was to compare bond integrity in an optimized hybrid poplar CLT panel with standard CLT performance criteria Standard bond integrity tests were performed on CLT samples constructed using two adhesive types and three clamping pressure levels in order to find combinations that may pass the CLT product standard requirements. A lightweight structural CLT product made from hybrid poplar could be used as a model for other low density CLT products made from other less utilized resources.
Cross laminated timber (CLT) is a new engineered wood product that has experienced rapid growth and market acceptance for residential and non-residential construction in western and central Europe. Potential exists for rapid market adoption in North America if manufacturing capacities are developed. Dissemination of information on CLT North America markets, manufacturing capabilities, and product standards are the next key steps for facilitating investment in CLT manufacturing capacities in North America. This paper compares standards for CLT between Europe and North America.
In the National Building Code of Canada (NBCC) and American Society of Civil Engineering (ASCE) standard (ASCE7) , different criteria for a two-step analysis procedure to design podium buildings are provided. However, nonlinear time-history dynamic analysis results show that such designed buildings may not meet the intended seismic performance. A new criterion has been developed at FPInnovations (Chen&Ni,2017&2020). Analysis results show that when the normalized stiffness ratio is at least 10 times greater than the normalized mass ratio, the buildings designed by the two-step analysis procedure can meet the performancere quirement. This InfoNote briefly reviews the two-step analysis procedure, demonstrates the shortcoming of the NBCC and ASCE criteria, and introduces the developed criterion.