Institute for Transportation

The grading of structural timbers is currently based on
visual assessment of growth characteristics and defects,
with properties derived from tests of small clear
specimens. More efficient design of timber structures
and more efficient use of the nation‰Ûªs forest resource
demand more precise assignment of allowable
properties than is possible with the visual grading
system. In this paper, we summarize available data on
the mechanical properties of structural timbers and
evaluate an approach for mechanical grading based on
nondestructive testing. Potential mechanical grades
for timbers are discussed, and preliminary yield data are
presented for oak timbers.