Engineered Properties and Structures
FS-FPL-4714

Mechanical Grading of Logs from Fire-Killed Trees for Use in Log Home Construction

Issue:
In the West, 80% to 90% of the logs used in log home manufacture come from standing dead trees, primarily trees killed during wildfires. If left in the woods, these dead trees contribute to fire risk and often have little value in other traditional markets. Log home manufacturing provides a high value use for such material and is an excellent source of employment in local communities. However, current structural grading methods for logs to be used in log homes is based solely on visual methods. Property assignments with this process are not very precise, and are probably overly conservative. Previous FPL research on structural timbers has demonstrated that a mechanical grading system based on a combination of visual grading and non-destructive testing is more precise and can lead to more efficient use of the available resource.

Objective:
The objective of this study is to develop the technical basis for a mechanical grading system for sawn round timbers for use in log buildings.

Cooperators:
This study is a cooperative effort between US Forest Service, Forest Products Laboratory, Madison, WI, U. of Idaho, Moscow, Rocky Mountain Log Homes, Victor, MT, and Timber Products Inspection Service, Conyers, GA.

Status:
Phase I of the two phase study is nearing completion. Phase I utilizes cut-logs having a uniform diameter of 9-inches produced from dead subalpine fire and lodgepole pine trees. In this phase, 60 logs will be tested at the U. of Montana in third-point bending to provide the MOR-MOE relationship needed to develop grade boundaries for mechanical sorting. An additional 60 logs will be tested at the Forest Products Laboratory as short columns to develop compression-bending relationships. Bending tests in Phase I are complete, and analysis is in progress. Compression testing is in progress. Phase II will demonstrate the potential of the grading system by sort logs into one or more mechanical grades and breaking these logs to access the accuracy of the property assignment.

Contact:
For additional information, contact Dr. David Green, Forest Products Laboratory, Madison, Wisc., at (608) 231-9261 or E-mail: dwgreen@fs.fed.us or Dr. Thomas Gorman, University of Idaho, Moscow, Idaho, at ( 208) 885-7402 or E-mail: tgorman@uidaho.edu.