FE simulation of repaired timber beams under tensile load using CFRP patches

Abstract

Timber is a highly orthotropic material with highest strength presented in tension along the grain direction. Repaired timber structural elements in pure tension using carbon fibre–epoxy patches provide new opportunities as it is well adapted to the nature of wood. Such repairing process is very interesting as it is easy to use for assembling two damaged parts of timber and has a low environmental impact. Before this process can become widespread in the industry, it is necessary to develop numerical tools for predicting the behaviour of such assemblies under tensile loads. Only a few experimental tests have been offered in the literature, and even fewer numerical studies have been carried out to analyse the complex mechanical behaviour of timber. The present paper describes the use of carbon fibre–epoxy patches for repairing timber beams under tensile stress along the grain direction. The repaired beams with CFRP patches using varying repair lengths were examined. The load-carrying capacity increased by about 47%, passing from a repair length of 5 mm (F = 3.8 kN) to a repair length of 10 mm (F = 6.6 kN) at a displacement u = 0.3 mm. A three-dimensional (3-D) numerical methodology for virtual loading process under pure tension, including the interaction between two adherent surfaces and taking the presence of an adhesive layer into account, is presented from both theoretical and numerical point of views. Predicted and measured load–displacement responses and failure modes are compared. The predicted results are in good agreement with the experimentally measured test data.

Keywords:

• reinforced timber beams
• CFRP
• FE analysis
• interface element
• tensile test
• elastoplastic behaviour

Acknowledgements

The authors gratefully acknowledge the financial support of the French National Research Agency (ANR) as part of the ‘Investissements d’Avenir’ programme (ANR-11-LABX-0002-01, Lab of Excellence ARBRE), as well as the financial support of the CPER 2007-2013 ‘Structuration du Pôle de Compétitivité Fibres Grand’Est’ (Competitiveness Fibre Cluster), through local (Conseil Général des Vosges), regional (Région Lorraine), national (DRRT and FNADT) and European (FEDER) funds.