A three-dimensional numerical model was employed in simulating nonlinear transient moisture flow in wood and the wood’s hygro-mechanical and visco-elastic behaviour under such conditions. The model was developed using the finite element software Abaqus FEA^®, while taking account of the fibre orientation of the wood. The purpose of the study was to assess the ability of the model to simulate the response of wood beams to bending and to the climate of northern Europe. Four-point bending tests of small and clear wood specimens exposed to a constant temperature and to systematic changes in relative humidity were conducted to calibrate the numerical model. A validation of the model was then performed on the basis of a four-point bending test of solid timber beams subjected to natural climatic conditions but sheltered from the direct effects of rain, wind and sunlight. The three-dimensional character of the model enabled a full analysis of the effects of changes in moisture content and in fibre orientation on stress developments in the wood. The results obtained showed a clear distinction between the effects of moisture on the stress developments caused by mechanical loads and the stress developments caused solely by changes in climate. The changes in moisture that occurred were found to have the strongest effect on the stress state that developed in areas in which the tangential direction of the material was aligned with the exchange surface of the beams. Such areas were found to be exposed to high-tension stress during drying and to stress reversal brought about by the uneven drying and shrinkage differences that developed between the outer surface and the inner sections of the beams.

采用三维数值模型模拟木材中的非线性瞬态水分流动以及木材在这种条件下的湿机械和粘弹性行为。该模型是使用有限元软件 Abaqus FEA ^{® 开发的}，同时考虑到木材的纤维取向。该研究的目的是评估模型模拟木梁对弯曲和北欧气候的响应的能力。对暴露于恒定温度和相对湿度系统变化的小而清晰的木材样品进行四点弯曲试验，以校准数值模型。然后，在对处于自然气候条件但不受雨、风和阳光直接影响的实木梁进行四点弯曲试验的基础上，对该模型进行了验证。该模型的三维特性能够全面分析水分含量和纤维取向的变化对木材应力发展的影响。获得的结果表明，水分对机械载荷引起的应力发展的影响与仅由气候变化引起的应力发展之间存在明显区别。发现发生的水分变化对材料切线方向与梁的交换表面对齐的区域中产生的应力状态具有最强的影响。发现这些区域在干燥过程中会受到高压应力，并且会受到由于不均匀干燥和梁的外表面和内部部分之间产生的收缩差异而导致的应力反转。发现发生的水分变化对材料切线方向与梁的交换表面对齐的区域中产生的应力状态具有最强的影响。发现这些区域在干燥过程中会受到高压应力，并且会受到由于不均匀干燥和梁的外表面和内部部分之间产生的收缩差异而导致的应力反转。发现发生的水分变化对材料切线方向与梁的交换表面对齐的区域中产生的应力状态具有最强的影响。发现这些区域在干燥过程中会受到高压应力，并且会受到由于不均匀干燥和梁的外表面和内部部分之间产生的收缩差异而导致的应力反转。