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.
The current interest and growth of cross laminated timber (CLT) products has spurred interest in the manufacture of CLTs in the United States. The purpose of this paper is to explore the development of CLT materials from southern pine lumber commonly available in Virginia. A 5-layer CLT panel has been constructed using No. 2 southern pine lumber. Evaluation of mechanical properties, fire performance and acoustical performance were conducted. Results of these evaluations can guide the development and acceptance of CLT products in the International Building Code.
Development of cross laminated timber (CLT) manufacturing facilities will require an optimization of manufacturing parameters to ensure efficient production. This study examined the effects of press pressure, press time and the addition of water to bond surfaces for a CLT panel composed of southern pine lumber and polyurethane adhesive. Evaluation of the CLT panels used the five-point bending test for bending stiffness, bending strength and shear stiffness in addition to measuring the resistance to shear by compression loading. The shear strength and percent wood failure values obtained from the resistance to shear by compression loading. The optimal combination of manufacturing parameters studied was 100% press pressure and a press time of 80% of the manufacturer recommendations. The addition of water to the bondline surfaces was deemed unnecessary for CLT materials conforming to the PRG-320 standard. Comparison of mechanical properties with Grade V3 showed higher bending strength and shear stiffness values.
Sustainable solutions to building construction can help improve material utilization efficiency while providing economic development. This paper focuses on the development of low-grade hardwood CLT made with Yellow-Poplar (Liriodendron tulipifera) as an exemplar species. Analysis programs developed at Virginia Tech (CLT-VT) investigate whether design methods developed for softwood species are suitable for use with the mechanical properties of hardwoods to predict structural behaviour of CLT panels. The CLT-VT programs will include the analytical design methods defined in the CLT Handbook for floor/roof and wall systems, and beams/lintels . The study will assist in further development of a sustainable building product while adding value to under-utilized low-grade hardwood lumber and creating a road map for the production of CLT materials from most every domestic wood species available in the United States.
This study examines if Cross-Laminated Timber (CLT) design methods approved for softwood species can be used with hardwood species, specifically low-grade hardwoods. Analytical predictions from researcher-generated computer programs will be compared to data from experimental evaluations of hardwood CLT. Successful completion will allow for an under-utilized timber resource to be incorporated into CLT production.
Cross laminated timber (CLT) connections in shearwalls require an understanding of the shear strength and stiffness of panel-to-panel connections within the wall. This research measures the strength and stiffness of three different panel-to-panel CLT connections considering both monotonic and cyclic loading. Connections included a laminated veneer lumber (LVL) spline, a half-lap connection and a butt joint with overlapping steel plate. All connections were ductile in nature. The butt joint with steel plate demonstrated the highest connection strength of the connections tested. The cyclic stiffness of the laminated veneer lumber spline was less than the monotonic stiffness, while the halflap joint experienced a sharp drop in load after ultimate load was achieved. Full details of the monotonic and cyclic behaviour will be discussed, including load, stiffness and ductility terms.
The purpose of this paper was to examine whether CLT made from fast growing hardwood species can provide sufficient mechanical performance need to be used in structural engineering applications. Yellow-poplar CLT was tested experimentally for stiffness and strength in five-point bending and four-point bending tests, respectively as well as resistance to shear by compression lading and resistance to delamination and the results were compared with American National Standard Institute/APA-The Engineered Wood Association (ANSI/APA) PRG 320-Standard for Performance Rated Cross-Laminated Timber and previous research. Bending stiffness, bending strength and resistance to delamination exceeded the required value in the standard, while wood failure in resistance to shear by compression loading was less than the required value. Shear strength of the yellow-poplar CLT was also greater than CLT produced from softwood species tested in previous research. Acceptable mechanical performance of yellow-poplar CLT confirmed in this research, could be a start point of using hardwood species in CLT structural design.
Cross-laminated timber (CLT) is a novel wood building material suitable for floor, roof, and wall assemblies in low and mid- rise construction as an alternative to concrete and steel. CLTs are considered to provide good seismic resistance, fast erection times, carbon sequestration, and a significant reduction in greenhouse gas emissions over other construction materials. Southern pine is an abundant forest resource, yet has not been commercially used for CLT manufacturing.
The purpose of this paper was to measure the bending and shear properties of CLT material fabricated using southern pine lumber compared to the ANSI/APA PRG-320 product standard. Bending strength, bending stiffness, shear strength, resistance to shear by compression loading strength, and resistance to delamination were measured according to ANSI/APA PRG-320, and test results were compared to the V3 grade values. Bending tests were conducted on jointed beams due to test length requirements. Bending strength, bending stiffness, and wood failure in resistance to shear by compression loading tests exceeded the published values for the V3 grade, while resistance to delamination did not meet the established criteria. The resistance to delamination results may have been effected by the uncontrolled moisture content of the lumber during fabrication of the CLTs. The application of glued laminated lumber standards to CLT products requires clarification in the orientation of loading directions for the resistance to shear by compression loading test and the measurement of all four sides of the resistance to delamination specimens. Increased scrutiny of moisture content quality control is highly encouraged for the production of CLTs.