An orthotropic incremental model for the hydromechanical behaviour of softwood
In the present work, a 3D orthotropic model is developed, aiming at precisely predicting the hydromechanical behavior of timber structures. Based on test results and on thermodynamical considerations, an evolution law is proposed for the hydro-lock strain. This phenomenon is assumed to occur in the longitudinal direction, but not in the tangential and radial directions. Beside, a 3D incremental formulation is developed to depict the viscoelastic strain at variable humidity, what allows overcoming the memory effect. Finally, the coupling of these two parts leads to a new 3D incremental model suitable to simulate the time dependent hydromechanical behavior of softwood. It should be noted that the time step to be used for numerical simulations must be finite, but not necessarily small. This important feature significantly reduces the computational effort while maintaining good accuracy. For the sake of illustration, the model is finally used to simulate the effect of varying humidity on the evolution of stress and strain states in a plain wood beam loaded in axial tension and in bending.