Modelling of uncertainties of timber structures due to growth inhomogeneities

A tree is exposed to varying environmental conditions during its growth which influence the mechanical and geometrical properties. Among others, branches affect the grain course and lead to knots in timber structures. This contribution is concerned with the modelling of these knots, referred to as growth inhomogeneities, and the resulting fibre orientation within the framework of a FE-analysis. The aim of the approach is an evaluation of the influence of the growth inhomogeneities on the load bearing capacity of timber structures. The geometrical parameters of the knots, like position, shape and size, can be considered as uncertain quantities due to the natural growth. Furthermore, material parameters are uncertain and cannot be described exactly. Hence, the uncertainty of these input quantities is taken into account within the numerical simulation as well. Due to the insufficient experimental data concerning wood, the uncertainty model fuzziness is applied.