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

Abstract

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.

Probabilistic approach for modelling the load-bearing capacity of glued laminated timber

“…The underestimation of the stiffness properties was quantified in [20] with $3%, but the underestimation of the tensile strength was not quantified. For the presented example the underestimation of the tensile strength is assumed to be equal to the underestimation of the tensile stiffness.…”

“…To investigate the size effect, GLT beams with six different dimensions are simulated: h ¼ 320; 400; 480; 600; 800, and 1200 mm (8,10,12,15,20, and 30 lamellas, each 40 mm thick). To assure comparability with EN 408 [8], a constant ratio l ¼ 18 Á h is assumed.…”

“…The material model presented in [20] is developed based on the measured tensile stiffness of 864 knot clusters (b  t ¼ 126  44 mm), and the measured tensile capacity of 450 timber boards (b  t ¼ 90  45 mm, 110  45 mm, and 230  45 mm; each 150 timber boards) containing 2577 knot clusters. The stiffness properties of timber board sections were identified by using an optical camera device.…”

“…After the GLT fabrication, the material properties are allocated using the material models described in [20]. The strength and stiffness properties of each timber board section and FJ are calculated based on the associated indicators E dyn;F and tKAR-value (for FJ a specific tKAR-value has to be assumed) by using a linear regression model; Eq.…”

Inference on stiffness and strength of existing chestnut timber elements using Hierarchical Bayesian Probability Networks

“…In Fink et al [12] the interrelation between bending and/or tensile strength for different knot indicators have been discussed. Moreover, bending and tensile strength was also predicted regarding their morphological characteristics according to knot sections and clear wood sections [13].…”