Cross-Laminated Timber Panels Produced by Low-Grade Yellow-Poplar Sorted by Nondestructive Evaluation

To manufacture and market a uniform and consistent product, the US lumber industry developed grading rules to classify their lumber. Visual grading is the most commonly applied grading system, although nondestructive evaluation (NDE) could be applied. Therefore, the objective of this research was to evaluate cross-laminated timber (CLT) panels produced from yellow-poplar (Liriodendron tulipifera) lumber sorted by NDE and compare their bending properties in the major direction to standard published panels by the American National Standards Institutes/The Engineered Wood Association (ANSI/APA) PRG 320-2019. Ten panels were produced with dimensions of 3.75 inches thick by 18 inches wide by 120 inches long. Flatwise bending, shear block, and cyclic delamination tests were performed following ANSI/APA PRG 320-2019. The results of the bending tests indicated that the calculated characteristic values using NDE-sorted lumber resulted in a 19 percent higher bending strength ([F.sub.b]) than published values in ANSI/APA PRG 320-2019 for stress-rated lumber (El and E4) and 35 percent higher than visually graded yellow-poplar CLT panels reported by Azambuja et al. However, the modulus of elasticity (MOE) values (1.56 by [10.sup.6] psi) were lower than those listed for El and E4 type panels. The adhesive evaluation showed delamination in some samples located in the outer areas of the panel, indicating that proper adhesion is possible with improvements in the panel production process used in the research. Overall, the results suggest potential opportunities to utilize yellow- poplar lumber that does not meet a visual structural grade category under Northeastern Lumber Association Manufacturers' rules by classifying and sorting the lumber according to static MOE ([MOE.sub.s]) values assessed using NDE.
Visual grading was developed to ensure the quality of commercialized lumber. The Northeastern Lumber Association Manufacturers (NELMA 2013) grading rules are the standard methods used for yellow-poplar (Liriodendron tulipifera) lumber [...]