Creep in Wood Under Variable Climate Conditions: Numerical Modeling and Experimental Validation

Abstract

Abstract. This paper deals with the modeling of linear viscoelastic behavior and strain accumulation (accelerated creep) during moisture content changes in timber. A generalized Kelvin-Voigt model is used and associated in series with a shrinkage-swelling element depending on the mechanical and moisture content states of materials. The hygrothermal aging due to climatic variations implies an evolution of rheological parameters depending upon moisture content and temperature. Two distinct viscoelastic laws, one for drying and the other for moistening, are coupled according to the thermodynamic principles when wood is subjected to nonmonotonous moisture variations. An incremental formulation of behavior is established in the finite element program CAST3M (Software developed by C.E.A. (Commissariatá l'Energi Atomique) and an experimental validation from tension creeprecovery tests is presented.

Moisture-dependent, viscoelastic creep of European beech wood in longitudinal direction

“…However, such a compliance function is thermodynamically admissible if thermodynamic laws are satisfied (Dubois et al 2005). Besides positive values of the compliance function J (ω, t) ≥ 0 as well as its derivative ∂J (ω, t)/∂t ≥ 0, every Kelvin-Voigt element has to fulfil specific thermodynamic restrictions.…”

Study for improvements in design codes of timber structures regarding developments in time

“…By many research works carried out on creep phenomenon it has been found that a number of factors influence the bending creep behaviour of timber beams, such as absolute load level and variation of one during service life, moisture content of wood and variation of one corresponding to relative humidity and temperature of air [2], [3], [4], microstructure and chemical composition of wood [5], [6], size effects of timber element [7], different response in compression and tension zones of the beam. It is described the correlation of rate of deformation increase that depends on the macrostructure of timber and stress directions regarding grains when behaves in bending.…”

Coupled two-dimensional modeling of viscoelastic creep of wood

“…Viscoelastic creep is a pure creep response solely inflicted by a load's magnitude and its duration. Even though pure creep for load-carrying wood in ordinary varying climate is small in magnitude when compared to, for example, mechano-sorptive creep (Toratti and Svensson 2000), its formulation is a fundamental basis for the description of wood behavior, impacted by all sorts of environment variation (Hanhijärvi 1995;Bonfield et al 1996;Hunt and Gril 1996;Hanhijärvi and Hunt 1998;Dubois et al 2005Dubois et al , 2012Colmars et al 2014;Reichel and Kaliske 2015b). Several series of experimental data on viscoelastic creep strains in different orthotropic directions of wood under constant tensile loading are reported in Schniewind and Barrett (1972), Hayashi et al (1993), Ando (2010), andO_ zyhar et al (2013).…”