Model for the prediction of the tensile strength and tensile stiffness of knot clusters within structural timber

In the present paper, a model for the prediction of the local strength and stiffness properties is developed. Compared to existing models, here the local material properties are described according to their morphological characteristics; i.e. the timber boards are subdivided into sections containing knots (knot sections) and sections without knots (clear wood sections). The strains of the corresponding sections are measured during non-destructive tensile tests using an optical camera device. Based on these measurements the tensile stiffness of each particular section is estimated. For the estimation of the tensile strength, destructive tensile tests are performed. Herewith, the tensile strength of the entire timber board is measured. The strength of the other knot clusters are estimated using censored regression analysis. Taking into account the results of the experimental investigation, material models are developed to predict the tensile strength and the tensile stiffness of knot clusters.