A Creep Non-Linear FEM Analysis of Glulam Timber

This work is focused on a creep formulation in bending for timber beams, of glue laminated (glulam) type, which is suited to be implemented in both geometrical and material non-linear finite element method (FEM) models. It studies the performance of timber beams by accounting the deformation under increments of time and stress in the long term. The proposed creep formulation uses a power-law function expressing the creep strain by means of one coefficient and two exponents. This function needs a fewer number of material coefficients than a classical mathematical analysis of non-linear viscoelasticity, so design applications, such as FEM codes, may more simply describe the deformations in the long term. The formulation has been developed for cantilever beams made of glulam timber using experimental tests in bending and accounting the relations between strains, and both time and tension progresses. Also, the timber creep law has been numerically tested by FEM code runs, with large displacements and large strains assumptions, and further compared with a Navier analytical model. The scatters between experimental and analytical values, and FEM numerical values have reached a standard deviation of 4.06 and of 7.66%, respectively. The acceptable agreement in the comparison between experimental, analytical, and FEM numerical results have demonstrated the capability of the creep formulation to model the behavior in bending of a glulam timber. Also, the proposed creep model has shown an interesting ability to be employed in a FEM code to analyze a timber beam in bending, along time and load evolutions.