Probabilistic characterisation of the length effect for parallel to the grain tensile strength of Central European spruce

The paper presents a probabilistic model characterising tensile strength parallel to grain of Central European spruce boards without longitudinal joints. The effect of length of members on strength is considered explicitly by considering a member by a serial arrangement of weak sections triggered by major knots of knot clusters. In order to demonstrate the applicability of the proposed model the model parameters are calibrated based on the analysis of three samples of spruce of Switzerland (Mischler-Schrepfer, 2000 [25]) and Austria (Schickhofer and Augustin, 2001 [28]), in total 460 boards tested in full size. This model might serve as basis for studies concerning the length effect of boards relevant for solid timber structures as well as basis for judging the length effect of finger jointed construction timber and glulam, and as starting point for modelling the process of proof loading.