Circulating structural timber and engineered wood products–challenges and potentials towards reliable evaluation of mechanical properties

Circulating structural timber and engineered wood products require reliable assessment of key mechanical properties. However, existing standards for strength grading sawn timber are not designed for the reuse and recycling of timber and are unsuitable for this in a number of ways. Furthermore, existing procedures for the re-assessment of structural components are mainly focused on the identification of in-use damage and assumptions about the original mechanical properties, and not on the quantitative re-evaluation of the current mechanical properties. In this paper, existing strength grading procedures in Europe are discussed according to their potential for the assessment of reused timber, with observations on shortcomings of the underlying basis when not applied to new, not previously graded timber. Since the situation for reused and recycled laminated components (glued laminated timber and cross-laminated timber) might be simpler, and perhaps more commercially relevant, a framework will be presented to estimate the mechanical properties of these structural components based on the load history and non-destructive assessment methods. The basis could be expanded by future work to allow the re-grading of sawn timber.