Influence of structural timber variability on reliability and damage tolerance of timber beams

Abstract: The thesis addresses two main problems: 1) Probablistic modelling of lengthwise variability in structural timber, 2) Reliability and damage tolerance analysis of beams made of structural timber. Timber is considered as an elastic-brittle material. Dependence of timber properties on time and environment conditions is neglected. The presented statistical analysis of MOE is based on experimental data. An original method for determination of the MOE function on the basis of a measured deflection curve has been developed. The Log-normal, Gumbel or Normal distributions can be recommended as the probability distribution model of the homogeneous random field of MOE with the scale of fluctuation equal to 1.5-2.5 m. The variability of bending strength of timber beams has been studied with help of a weak-zone model. Assuming a marked Poisson random field as a probabilistic model of bending strength, analytical solutions have been derived for a number of particular problems. The influence of the correlation between strengths of weak zones has been studied with help of the Monte Carlo simulation. Time invariant reliability indices and damage tolerance indices have been computed for the weak-zone model and the corresponding homogeneous modelof a timber beam. The difference in reliability indices between the homogeneous and weak-zone models depends more on the probability model of the weak-zone strength than on the mean distance between the weak zones. There is no significant difference in the damage tolerance indices computed for the two considered models of a timber beam.