Abstract:

The general aim of the USDA FS 2017 Wood Innovation program is to significantly increase or stimulate markets for wood products utilizing low‐value small‐diameter material generated in National Forest System restoration programs. We believe that low‐value Ponderosa pine lumber from logs harvested in SW Oregon and Northern California forest restoration programs could be successfully utilized in massive structural cross-laminated timber (CLT) panels in low-rise modular structures. The objective of this project is to assess the feasibility of low-value ponderosa pine CLT through a series of standard performance tests.

 

Project Duration: 2018-2021

Research Team: Dr. Lech Muszynski, Dr. Mariapaola Riggio, Dr. Rakesh Gupta, Dr. Jeff Morrell (USC, Australia)

Graduate Research Assistants: Sina Jahedi

Undergraduate Student: Luke Walter

International exchange students: Benjamin Blengino, ESB, Nantes, France; Benjamin Strasser, SFH Salzburg/Kuchl, Austria

Research Advisory Group: Collins Lumber Co., DR Johnson Wood Innovations, Katerra, Vaagen Timbers.

Facilities: A.A. "Red" Emmerson Advanced Wood Products Lab, Richardson Hall High-bay Lab

Standards: American Society for Testing and Materials (ASTM), American National Standards Institute (ANSI/APA PRG-320), National Design Specifications (NDS)

 

Introduction:

Restoration programs in the Western states of the US are aimed at wildfire mitigation by selective thinnings and removing small diameter trees from overcrowded forests. These programs are expensive and produce large volumes of low-value small diameter Ponderosa pine (PP) logs, some containing blue-stain. These logs have limited market in the US. The high costs of restoration programs could to some extent be offset by finding a high-end market for lumber produced from these logs. One of such potential uses may be cross-laminated timber (CLT). CLT is a massive engineered wood panel consisting of three or more orthogonally arranged plies of lumber bonded with an adhesive. One striking characteristic of the global CLT industry compared to other engineered wood composites is that 95% of the production is custom made for specific products. Close collaboration between the architects, engineers and manufacturers is commonplace and these functions are often integrated within one company, creating custom CLT layups matching specific requirements for the project. The North American CLT product standard (ANSI/APA PRG320) allows manufacturers to create custom CLT grades in which non‐typical layups can be used to achieve characteristics suited for specific projects. Specification of custom CLT grades optimized for designs to be executed in large numbers of units creates an opportunity to utilize substantial volumes of lumber that otherwise might not be accepted for standard CLT grades. Previous research showed that blue-stain in PP does not affect strength of PUR bonds, and that acceptable structural performance may be achieved in hybrid CLT layups including low-grade PP lumber in the cores.

Research Details:

An iterative procedure is used to optimize both, the CLT layup and the structural engineering design of the structure, for which the panels are produced. The material/element level analysis is aimed at determination of mechanical properties and design values of low-value PP CLT generated by the forest restoration programs, which are needed as input for the analytical prediction of the engineering characteristics of prototype CLT layups. Material level analysis is currently focused on bond integrity tests as well as long- and short beam bending tests. CLT panel prototypes for these tests are fabricated in OSU A.A. Emmerson pilot plant. Once a viable prototype is developed, the full-size test panels will be produced by CLT manufacturers in the Pacific Northwest region.

Results + Resources:

Delamination resistance tests showed encouraging results regarding compatibility of melamine formaldehyde adhesive with blue-stain ponderosa pine. Further investigation is ongoing with the aim of examining the block shear resistance of the ponderosa pine CLT.

Selected conference posters and proceedings:

Jahedi S., L. Muszynski, R. Gupta, M. Riggio (2019): “Evaluation of Bond Integrity on Low-value Blue-Stain Ponderosa Pine CLT”, 2019 International Convention of the Society of Wood Science and Technology, Yosemite, CA,USA.

Jahedi S., L. Muszynski, R. Gupta, M. Riggio (2019): “Fabricating CLT Using Low-grade/Low-value Lumber: Investigation of factors affecting product performance”, 2019 Mass Timber Conference, Portland, OR, USA

Future Work:

  • Determination of design characteristics of PP CLT panels.
  • Definition of a custom CLT grade(s) designed for a specific modular CLT system.
  • Pre-qualifying industrial custom grade low-value PP CLT panels.