MOE Distribution in Visually graded Ponderosa Pine Lumber Harvested from Restoration Programs in Southern Oregon and Northern California

Abstract

Every year, restoration programs in Southern Oregon and Northern California produce large amounts of low-value ponderosa pine, Pinus ponderosa (PP) lumber. This material has a limited market in the United States. Engineered wood products, such as cross-laminated timber (CLT) and glulam, are expected to provide a value-added market to offset the high costs of restoration programs. However, restoration program lumber has larger amounts of juvenile wood and visual grades are reported to show lower mechanical properties compared with commercially harvested material, on which the National Design Specification (NDS) design values are based. This research addresses a knowledge gap on the impact of juvenile wood and visual strength-affecting characteristics on the mechanical performance of PP lumber generated in the region of interest. The purpose of this study was to assess this impact based on dynamically measured MOE of samples of visually graded and ungraded restoration program PP lumber. The material used in this study was intended for fabrication of CLT for another project, hence it could not be used for destructive tests to measure MOR. The results were compared with previous studies and published values for commercially harvested PP as reflected in the NDS Western Woods (WW) species group. The results show that characteristic MOE values of visual grade Nos. 1 and 2 of PP from restoration programs were lower than respective design values for NDS WW group. However, the mean MOE values of all groups considered individually as well as pooled together were higher than NDS WW grade No. 3. MOE

Bending Characteristics of Custom CLT Layups Laminated with Ponderosa Pine Harvested from Restoration Programs

“…However, defining such pooled grade for lumber generated from small logs harvested in restoration projects would require the determination of the statistical distribution of MOE in larger samples derived from a representative number of stands and One potential reason for the low-shear capacity may be the presence of interlaminar gaps detected in 80% of the specimens. These gaps led to delamination failures in standard bond integrity tests observed in a parallel study conducted within this project (Jahedi et al 2023). The interlaminar gaps may have resulted from a combination of high thickness variations along the laminations and uneven clamping pressure.…”

“…On average, interlaminar gaps covered 0.9% of the bond line perimeter of LP and 1.8% of the IP bending specimens. Bond integrity test samples are reported separately and showed that these gaps were the main cause for poor resistance to delamination (Jahedi et al 2023). In addition, that study isolated the impact of adhesive/species compatibilities and demonstrated that interlaminar gaps were caused by fabrication issues, which could include excessive thickness variations within laminations, uneven clamping pressure, or a combination of both.…”

“…The shear analogy method (Kreuzinger 1999) as formulated in PRG-320, Appendix X3 (ANSI/ APA 2019), was adopted in a computer application named Layup-App (Jahedi et al 2020), whose objective was to find a CLT layup with a minimum gross thickness that meets the structural requirements dictated by the modular building designed for this project. These requirements were the minimum allowable stress design (ASD) reference design values to satisfy the bending and shear criteria per NDS, short-term and long-term deflection criteria per IBC 2018 (ICC 2018), and vibration criteria per CLT Handbook for a 3.6 m (12 ft) span simply supported floor.…”

Utilizing Low-Value Wood Species From Forest Restoration Projects in Local CLT Manufacture and Design

“…White fir, for example, is a low-value species that only has preliminary structural data, but could potentially be used in a similar application to Ponderosa pine in CLT. There are several recently completed and planned low-value species testing projects undertaken at the TallWood Design Institute and Oregon State University on Oregon-harvested Ponderosa pine in collaboration with Vaagen Timbers, and, additionally, California white fir and Alaskan spruce using a more capital-intensive process with a large timber press; there is growing interest in the structural and commercial possibilities for these materials, along with the increasing local, less-capital intensive efforts as noted above [10][11][12]. Furthermore, continued development of construction details and the application of these panels to other building types, such as housing and multi-story structures, is a potential area of study.…”