WVFA Mountain State Forestry Fall 2021

F E A T U R E D N E W S www.wvfa.org Fall 2021 | West Virginia Forestry Association Mountain State Forestry 11 Elasticity of Low-Grade Yellow-Poplar While NELMA visual grading indicated that a large proportion of NHLA low-grade lumber met structural grades, nearly half of the lumber graded visually was Below Grade (45.4%). To determine if the Below Grade lumber would actually be unsuitable for CLT manufacturing, non-destructive proof loading was used in the study as an alternative grading approach. Table 3 summarizes the non-destructive test results for MOE b of the NHLA low-grade yellow- poplar lumber as a sample population (i.e. , no breakdown by NHLA grade). The MOE b design values of a population are usually calculated from their mean, which, for this distribution, was 1.66 x10 6 psi. The minimal MOE b value was 0.77 x10 6 psi and the 5th percentile was 1.25 x10 6 psi showing that a majority of boards (96.6%) presented an acceptable MOE b relative to the minimal requirement for CLTs as outlined in the American Panel Association (APA) CLT standards (ANSI/APA PRG 320) 3 of 1.2 x10 6 psi for boards qualifying for the parallel layer of a CLT panel. Only 39 boards (3.4%) did not meet the minimum MOE requirement specified in ANSI/APA PRG 320. Taking into account the average MOE b , lumber within any NELMA grade would meet the minimum requirements of 1.2e as set in the American Panel Association (APA) CLT standards. Conclusions This study focused on an evaluation of the structural characteristics of a large sample of low-grade yellow-poplar lumber for use in CLT panel production. The boards were evaluated before and after processing. The parameters used for board evaluation included NELMA visual structural grading and non-destructive testing to determine the MOE b value for each board. The sampled population of yellow-poplar lumber with NHLA grades 2A and below produced a total of 651 acceptable boards out of a sample population of 1,192 boards. In other words, 54.6% of the tested boards, met visual NELMA structural grades. These findings support the argument that low- grade yellow-poplar lumber can be used for structural purposes, and in particular, as a raw material for manufacturing CLT panels. Results from non-destructive proof loading tests indicated that 96.6% of the boards met the minimum MOE b (1.2 x10 6 psi) specified for the production of CLT panels under ANSI/APA PRG 320 (2018). Finally, in terms of grading, the non-destructive test results showed a higher yield than visual grading and should be further evaluated as a more efficient and economical means for structurally grading low grade hardwood lumber for CLT applications. This can easily be accomplished through the incorporation of machine stress rating (MSR) technology in production settings, a common feature in many larger softwood manufacturing facilities. Any large-scale change in grading methods by hardwood lumber manufacturers will depend on investment and a market able to justify the investment. Although, based on these results, re-grading low- grade hardwood lumber, currently used primarily in pallet manufacturing, would add considerable value to this lumber and allow it to be used in CLT panel manufacturing. Statistic NELMA Grade 1 SS No.1 No.2 No.3 BG Number of boards 137 80 221 207 490 Mean (106 psi) 1.74 1.70 1.68 1.66 1.61 Min (106 psi) 1.19 1.10 0.89 0.86 0.77 Max (106 psi) 2.35 2.37 2.43 2.34 2.47 Number of boards with MOEb <1.2x106 psi 1 1 4 4 29 Table 3. MOE b analysis of the boards grouped by NELMA grades. 1SS = Select Structural and BG = Below Grade. 3 American National Standards Institutes. (2018). ANSI/APA PRG 320-2018: Standard for Performance-Rated Cross-Laminated Timber (Vol. 320), Tacoma WA. 40pp. Percent (%) Knots 90 80 70 60 50 40 30 20 10 0 Splits Slope of Grain Decay Shake Wane Bow Other Defects Grade 1 Grade 2 Grade 3 Below Grade Figure 2: Defects present in studied YP boards by percent for grades 1, 2, 3, and below grade.