Visual strength grading supported by mechanical grading

This article describes how to allocate structural timber (spruce from Central Europe) into strength class C35 according to EN 338 by means of combined visual and machine strength grading methods. Three different visual-machine strength grading combinations are developed and discussed. They are composed of visual grading in accordance with German standard DIN 4074-1 and of machine strength grading of green or dry sawn timber by measuring the apparent density or the dynamic MOE. For these combinations appropriate settings for the machine grading parameter are estimated. Combinations based on the dynamic MOE are suitable for strength grading of boards in general, glulam-lamellae and joists. The combination based on the apparent density is only suitable for strength grading of boards in general and glulam-lamellae.