  When assessing the strength of sawn lumber for use in engineering
applications, the sizes and locations of knots are an important consideration.
Knots are the most common visual characteristics of lumber, that result from
the growth of tree branches. Large individual knots, as well as clusters of
distinct knots, are known to have strength-reducing effects. However, industry
grading rules that govern knots are informed by subjective judgment to some
extent, particularly the spatial interaction of knots and their relationship
with lumber strength. This case study reports the results of an experiment that
investigated and modelled the strength-reducing effects of knots on a sample of
Douglas Fir lumber. Experimental data were obtained by taking scans of lumber
surfaces and applying tensile strength testing. The modelling approach
presented incorporates all relevant knot information in a Bayesian framework,
thereby contributing a more refined way of managing the quality of manufactured
lumber.
