Abstract
The paper describes a method for computational assessment of the long-term performance of timber beams in variable climates. The method is based on a cross-section analysis, in which the moisture content and longitudinal stress-strain distributions are calculated as function of time and ambient conditions assuming asymmetrical mechanical behaviour in the tension and compression sides of the beam. The method is implemented as a non-linear FE-program, which combines the moisture transport and structural analysis, which is based on a non-linear model of longitudinal creep in wood. The calculated stress-strain state is monitored against a failure criterion, which is based on a definition of a local damage variable and on its integration over the volume in the fashion of the Weibull theory of weakest link to give a global damage parameter. Computational results include long-term deformation (eflection) and time-to-failure (long-term capacity) predictions. Examples of time-to-failure calculation are given.
Résumé
Ce papier présente une méthode d'évaluation des calculs de la performance à long terme des poutres en bois dans des conditions climatiques variables. La méthode est basée sur une analyse transversale, selon laquelle la teneur et les données de distribution longitudinale contrainte-déformation sont calculées en fonction du temps et des conditions environmenantes, prenant pour hypothèses un comportement mécanique asymétrique sur les côtés en tension et compression de la poutre. La méthode est appliquée selon un programme nonlinéaire d'éléments finis, qui associe les données de transport d'humidité et l'analyse structurelle basée sur un modèle nonlinéaire de fluage longitudinal dans le bois. Le calcul de la contrainte-déformation est confronté à un critère de rupture basé sur une définition d'une variable d'endommagement local et sur son intégration sur le volume, conformément à la théorie de Weibull du line le plus faible pour foumir un paramètre d'endommagement. Les résultats des calculs comportent les prévisions de la déformation sur le long terme (flexion) et des délais de rupture (capacités sur le long terme). Des exemples de délais de rupture sont fournis.
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Dr Antti Hanhijärvi works at VTT, a RILEM Titular Member. He was the RILEM Robert L'Hermite Medallist in 1999.
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Hanhijärvi, A. Computational method for predicting the long-term performance of timber beams in variable climates. Mat. Struct. 33, 127–134 (2000). https://doi.org/10.1007/BF02484167
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DOI: https://doi.org/10.1007/BF02484167