EVALUATION OF CROSS-LAMINATED TIMBER PANELS PRODUCED WITH YELLOW-POPLAR (Liriodendron tulipifera)

Abstract

Cross-Laminated Timber (CLT) panels are engineered wood products breaking into the building sector. Currently, the range of raw materials used in CLT is still limited to softwoods, while some hardwood species such as yellow-poplar could potentially be used to produce this wood product. Therefore, the main goal of this research was to assess the feasibility of using Appalachian Hardwoods in the production of Cross-Laminated Timber panels. Specifically, the objectives of the research were to 1) Determine the amount of yellow-poplar structural lumber that can be obtained from a representative population of low-grade, yellow-poplar lumber graded for appearance; 2) Evaluate whether CLT panels produced using No. 2 and No. 3 structural grade yellow-poplar in parallel and perpendicular orientations, respectively, meet the bending and bond line requirements prescribed in ANSI/APA PRG 320-2019 (2020); 3) Determine if improvements in CLT panel properties can be achieved by laying up panels based on non-destructively assessed static bending modulus of elasticity (MOEs) instead of visual structural grades; and 4) Evaluate whether or not placing lumber with high bending MOEs and visual structural grades in outside layers improves CLT properties. The material selected for this research was low-grade yellow-poplar (Liriodendron tulipifera) that was selected for its availability. First, an initial assessment of yellow-poplar mechanical properties was required to determine feasibility. Therefore, 8,000 board feet (18.9 m3) of yellow-poplar lumber graded as No. 2 Common and No. 3 Common, according to National Hardwood Association of Lumber (NHLA) grading rules, were evaluated. The yellow-poplar lumber was regraded according to a structural visual grade outlined by the Northeastern Lumber Manufacturers Association (NELMA) rules and by non-destructive test to obtain the board’s static modulus of elasticity (MOEs) to determine their potential to meet grade requirements for CLT panels. The percentage of boards that achieved a minimum structural visual grade (No. 3 or better) was 54.6%, and 96.6% of the boards showed MOEs above the minimum 1.2 x106 psi (8,274 MPa) as specified in ANSI/APA PRG 320-2019 (2020). Once the structural grades of the yellow-poplar boards were assigned, the material was then used to produce different sets of CLT panels. In each case, 5-layer CLT panels with dimensions of 3.7 inches thick x 18 inches wide x 120 inches long (95 mm x 457 mm x 3,040 mm) were produced using an Emulsion Polymer Isocyanates (EPI) adhesive. Three different panel configurations were produced to assess the feasibility of different layups patterns of