Analysis of CFRP-strengthened timber beams

International audienceThe aim of this study is to develop a numerical procedure to simulate the flexural behaviour of carbon fibre-reinforced plastic-strengthened timber beams. Since wood exhibits complex failure modes, its behaviour can only be captured through the use of multidimensional failure criteria, a local approach based on the coupling of orthotropic elasticity and anisotropic plasticity described with the quadratic criterion of Hill is presented to model this behaviour. The theoretical and numerical aspects of the constitutive equations are presented in detail. The resolution of the resulting system of equations is carried out via a VUMAT user material, using ABAQUS/Explicit finite element code. The obtained results show that the proposed formulation can efficiently capture the global response with acceptable accuracy

Numerical modelling of ductile damage evolution in tensile and bending tests of timber structures

International audienceThe characteristic values for strength and stiffness of all sorts of timber products are based on the assumption of a linear relation between stress and strain prior to failure and consequently verification of the load-bearing capacity of individual members in a construction is also based on a similar linear relation. Such an approach is very conservative and ill suited for performance-based design, which requires a full analysis of the structure with the possibility of moment and/or stress redistribution within parts of the structure. The development of material models that encompass the complex behaviour of wood is therefore necessary. The present work presents a model formulated within the frameworks of plasticity and continuum damage mechanics (CDM). It applies the classical flow theory of plasticity to formulate ductile failure of wood in compression and damage mechanics for the brittle failure modes. It takes into account the orthotropic elastic behaviour, the plastic anisotropic isotropic hardening, the isotropic ductile damage, and the large plastic deformations. The model was used to predict the initiation and growth of ductile damage in tensile and bending tests on different timbers types. Good agreement was found between the predictions of the model and the experimental results