The bending strength of finger joints manufactured from beech wood (Fagus silvatica L.)

The bending strength of glulam depends on both board strength and finger joint strength. In the case of softwood glulam this fact is well known from experience. It was recently reported by the authors that visual strength grading of beech provides a characteristic glulam bending strength of 36 N/mm(2) and mechanical strength grading of 48 N/mm(2). Therefore, adequate values for the characteristic finger joint bending strength have to be met. At the time those values were unknown. It was the aim of the following project to study the influence of visual or mechanical strength grading techniques on the finger joint bending strength. Bending tests on finger joints were carried out. The specimens were manufactured from visually strength graded boards according to the German standard DIN 4074-5 and from mechanically strength graded boards according to the dynamic MOE. The test results confirm that visual strength grading provides strength class GL36 and mechanical grading provides GL48.