International audienc

Cracking initiation and propagation are frequently recognized as main causes leading to failure of timber structures. Since the kinematics of both processes is largely influenced by environmental conditions, a comprehensive reliability assessment of notched structures should take into account such environmental factors. The main purpose of this paper is to propose a methodology for reliability assessment and updating of notched timber components based on mechanical (A-integral formulation) and reliability (simulation and Bayesian networks) methods, and experimental data. The A-integral formulation is used to estimate energy release rates in modes I and II by taking into account thermal effects; but its numerical implementation is time-consuming for uncertainty propagation. In order to deal with this problem, Bayesian networks were used for reliability assessment and updating. The experimental data used for updating purposes were obtained from measurements of deflection, temperature and relative humidity on a notched beam (Douglas Fir specie) exposed to outdoor environment and constant loading. The whole proposed methodology was illustrated with the reliability assessment and updating of the studied notched beam. The results indicated that the proposed approach is able to integrate measurements of temperature and deflection for reliability updating.

The impact of variations of relative humidity, temperature and moisture content on the creep of notched beams of Douglas fir and white fir are investigated. Indoor static 4-points bending tests are followed by outdoor creep tests of notched beams designed to trigger the breakage mode associated with the use of notched ends. The dimensions of wood specimens follow Eurocode requirements. The maximum load applied to outdoor creep tests is derived from the failure load obtained during indoor instantaneous tests. The results show that the variations of the relative humidity and temperature, coupled with the loading, play a key role in the lifetime of timber, as they accelerate its aging. In addition, the link between the changes of climatic parameters and the damage of the beams and the limit of their lifetime as structure is shown.