Probabilistic Output Control for Structural Timber - Modelling Approach

Authors

Markus K. Sandomeer, Jochen Köhler and Michael H. Faber

Abstract

Machine grading for quality control of structural timber in Europe presently takes basis in the so-called machine control method, rather than the output control method; the two alternative methods specified in the European Standard EN 14081 [14]. Despite its wide application it is, however, generally recognized that this method has potential for improvements. The issue is that the machine settings are fixed when the machine is taken into use and the present standard does not accommodate for adjustments of the machine settings based on the measured timber characteristics during the grading procedures. As a consequence in practice, the machine settings may be determined and fixed corresponding to a statistical population of timber material deviating from the populations subsequently being tested for quality control; as a result the quality control will be less efficient and/or even in extreme cases erroneous. The present paper proposes an alternative approach for the control of grading machine settings by which systematic quality variations of the timber material may easily be identified during grading by means of monitoring of the non-destructive measurements of the grading machine (indicating properties) which have a certain relationship to the grade determining properties of the tested timber material (e.g. strength, stiffness and density). Systematic shifts (or deviations) in the values of the indicating properties may reveal that the tested timber material origins from a population of timber different from the population(s) on the basis of which the machine settings were calibrated. Thus a recalibration is required or might be optimal. The recalibration may then be achieved through "updating" of the grading model and
a complete reassessment of the original grading machine settings based on destructive tests of specimens taken from the deviating population.

Published in/by

Proceedings of CIB-W18 - 41st meeting, St. Andrews, Canada, August 25-28, 2008.