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.