Tensile strength prediction of Norway spruce boards processed from recovered wood: performance of visual and machine grading

Abstract Biotic and abiotic climate stressors jeopardize Norway spruce stands, necessitating the evaluation of alternative pathways for structural timber. One promising alternative is the utilization of recovered wood. Dimensional irregularities and design requirements often render reuse infeasible, underscoring the need for processing. Processing corrects dimensional discrepancies; however, prior grading becomes invalid due to cross-sectional changes. To date, there is no German standard for grading recovered wood. Due to additional features compared to new-sawn wood, the applicability of machine grading and the visual standard DIN 4074—1 requires an initial evaluation. This paper experimentally analyzes the general tensile strength of 146 boards (30 × 90 mm 2 ) processed from 22 salvaged rafters. The applicability of DIN 4074—1:2012 is evaluated by assessing visual features and correlating them with tensile properties. Machine grading is evaluated based on an automated scanning process. The findings highlight that visual and machine strength grading are both applicable to the processed recovered wood boards investigated. The graded boards exhibited tensile properties comparable to those of new-sawn wood. In the characterized extent, no impact from fastener holes was observed.