Timber is one of the most widely applied engineering materials due to its favorable physical and mechanical characteristics. Nevertheless, over the service life, the combination of mechanical load and varying environmental conditions can have a critical influence on the mechanical response of timber structures, considering especially the mechano-sorptive characteristics. In this work, the performance analysis of the existing time- and moisture-dependent models identifies the need of a more comprehensive 3D constitutive rheological model, which can take into account orthotropic, elastic-plastic, viscoelastic and mechano-sorptive aspects, including the complex mechano-sorptive recovery phases that may occur over the lifetime. Therefore, a comprehensive algorithm of such a model is developed here. An improvement is made for the mechano-sorptive component by introducing an ordinary and a transcending mechano-sorptive part, which are governed by the absolute change of moisture content and the change exceeding the historical highest moisture content at each loading phase, respectively. Simulations are run under cases with mechanical loading of tension and compression perpendicular and parallel to the direction of the fibers. Both medium-term (up to 2500 h) as well as short-term (up to 350 h) mechanical behavior of the material under constant temperature is analyzed and good agreements are achieved with literature results. Comparison with existing models indicates that the proposed model gives an improved prediction of the mechano-sorptive creep and recovery, which has a non-linear dependence on the moisture history. Furthermore, sensitivity analyses are performed and the applicability of the model to different species under different combinations of load and moisture variation is studied here.@en

Before timber boards can be used for engineering applications, they need to be strength graded. This step is currently done based on visual or machine grading methods. Each approach may face problems such as frequent measurement (human) errors or problems in dynamic measurements due to missing density values, respectively. To increase accuracy of the predictions, an advanced numerical method has been developed based on FE-analysis to predict tensile strength of the boards. By simulating the tensile test procedure virtually, stress developments around wood heterogeneities have been analysed, and identifying parameters (IPs) have been provided, representing the stress concentrations in 3D anisotropic space. Virtual dynamic-MoE has been derived after performing the stress-wave analysis, to be used as another IP for strength predictions. These parameters have been used in a non-linear multiple regression analysis with the tensile strength for the predictions. Similar approach has been performed, using the parameters of the visual and machine grading methods. The quality of strength prediction based on virtual method was in the same level/slightly higher than recently available methods, depending on the wood species. The model has been developed by considering a scatter for the quality range of 450 spruce, Douglas fir and beech boards. For the model verification, the approach has been used for strength prediction of a group of ash and maple boards, which provided satisfactory results.@en

Wood is one of the most widely applied engineering materials due to its favourable physical and mechanical characteristics. As an inhomogeneous biomaterial, wood exhibits complicated mechanical properties including anisotropy, elasto-plasticity, viscoelasticity, and hygroscopic characters. To analyse the time- and moisture-dependent behaviour of timber structures, both mechanical loading and moisture evolution has to be taken into account. This study analyzes the capability and limitations of different rheological models. A 3D-orthotropic viscoelastic, mechano-sorptive model for wood is presented here, which covers the timber behavior under varying moisture condition during loading and unloading phases.@en