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Strength grading of construction timber with large cross sections

: Kessel, M.H.; Plinke, B.; Augustin, R.; Huse, M.

Natterer, J.; Sandoz, J.-L.:
World Conference on Timber Engineering 1998. Proceedings. Vol. 1
Montreux: Presses polytechniques et universitaires romandes, 1998
ISBN: 2-88074-380-X
World Conference on Timber Engineering <5, 1998, Montreux>
Conference Paper
Fraunhofer WKI ()

A non-destructive method of grading construction timber beams with cross sections between 10x12 cm2 and 12x24 cm2 and lengths from 2.3 m to 7.5 m was developed. By means of beam geometry, the propagation time of an ultrasound impulse along the beam, longitudinal vibrations and the beam's mass a prediction of its bending strength MOR and its modulus of elasticity MOE was calculated. The relationships were derived by multivariate regression analysis of data sets of a sample of 450 spruce beams. Since the minimum beam length for bending tests according to EN 408 is given by 19 h, all beams were shortened. During these trials, a dependency of impulse velocity of the beam's length was observed. Limiting values for strength classes were determined by comparing the predicted MOR and MOE to the measured values.