30 Novembre – Thesis defense - Édouard Sorin

10 h15 Amphi Sylvae - Bordeaux Sciences Agro (Gradignan)

Mixed-mode cracking in wood: diagnosis and evaluation of reinforcement methods.

The purpose of reinforcing assemblies and structural elements in wood is to overcome the resistance limits of the material, by transferring greater efforts in areas which can lead to premature cracking in structures. The reinforcements used can be made of steel, composite materials or even wood. They can be fastened by mechanical means (screwed bodies) or by adhesion (structural bonding such as glued-in rods for example).  In both cases, the transfer of stress remains poorly explored, and the effect of the beginning and the deflection of crack is not well understood. In engineering techniques, the wood resistance in the reinforced area remains neglected, which is in line with the precautionary principle. Currently, scientific investigations are focused on the resistance of those kind of techniques without considering the interactions between the quasi-brittle behavior of the wood and the reinforcements which govern the gain in mechanical performance.  However, these solutions can lead to a failure caused by the progressive splitting of the wood and loss of the reinforcement.  So it seems beneficial to propose predictions of the short-term strength for splitting of reinforced and unreinforced beams, which can be used for further exploration of the long-term failure mechanism. That is why, in this study, a global prediction model was developed of the ultimate strength of both reinforced and unreinforced structural components subjected to splitting. It considers the quasi-brittle behavior of the wood and crack propagation in mixed mode, using a mixing law established on the R-curves. The relevance of this modeling was then compared to the current dimensioning methods of the Eurocodes 5, for notched beams, by means of experimental campaigns conducted at different scales.

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