Hygro-mechanical analysis of wood subjected to constant mechanical load and varying relative humidity

Abstract

A hygro-mechanical (H-M) analysis of a wooden specimen sustaining a mechanical load while subjected to varying relative humidity was performed to predict the long-term rheological behavior of wood. The numerical analysis was based on the experimental results of total strains, monitored in two orthotropic material directions on oak wood specimens under constant uniaxial compression and with moisture content (MC) variation. For the moisture analysis, a multi-Fickian moisture transport model (MFMTM) was used to obtain temporal and spatial MC fields, which were the input data in the mechanical analysis. The presented mechanical model assumed a decomposition of the total strains into the elastic, viscoelastic and mechanosorptive strains and the strains due to shrinkage and swelling. The moisture and mechanical analyses required material parameters, which were taken from the literature or were empirically obtained by a fitting procedure. The performed H-M analysis gave accurate numerical predictions of the experimentally obtained total strains in two orthotropic directions simultaneously. Thus, the analysis developed has a high potential for predicting the long-term rheological behavior of timber structures, assuming that the material parameters are determined previously, based on specific, extensive, multidimensional experimental analyses.

Evaluation of Moisture-Induced Stresses in Wood Cross-Sections Determined with a Time-Dependent, Plastic Material Model during Long-Time Exposure

“…This model was extended in [18] to 3D and updated to yield a symmetric creep compliance matrix. In [19,20], the capabilities of the model from [16] were investigated regarding mechanosorptive creep.…”

Health Monitoring of Stress-Laminated Timber Bridges Assisted by a Hygro-Thermal Model for Wood Material

“…The multi-Fickian theory below the FSP is based on the identification of three phenomena occurring in cellular wood during moisture transfer, i.e., the diffusion of water vapour in the lumens, the sorption of bound water and the diffusion of bound water in the cell walls. In the multi-phase models available in the current literature, the two water phases are separated and the coupling between them is defined through a sorption rate [10][11][12][17][18][19][20]. Recently, Autengruber et al [21], developed a whole multi-Fickian model including also the transport of free water in the lumens above the FSP.…”

Numerical analysis of moisture-induced strains and stresses in glued-laminated timber

“…The rheological behavior of timber was first modeled one-dimensionally, applying the theory of deformation kinetics (Caulfield 1985;Hanhijärvi 1995;Engelund and Svensson 2011) and assemblies of spring and dashpot elements in series (Leicester 1971;Ranta-Maunus 1975) or parallel (Hunt 1989;Salin 1992;Mårtensson and Svensson 1997a,b;Hanhijärvi 2000;Svensson and Mårtensson 2002;Svensson and Toratti 2002). Three-dimensional (3D) formulations for describing the rheological behavior of timber are presented in Fortino et al (2009), Fragiacomo et al (2011, Ormarsson (1999), Hanhijärvi and Mackenzie-Helnwein (2003), Hassani et al (2015), Reichel and Kaliske (2015b), Frandsen (2007) and Huč et al (2018). The rheological models usually include a number of unknown material parameters, which are normally calibrated against experimental data.…”