Reprint of: Effective bond length of FRP stiffeners

• Strengthening concrete or masonry with Fiber-Reinforced-Polymer (FRP) stiffeners is a promising technique.
• Traditional modeling neglects the deformation of the substrate and uses elaborated shear-stress vs. slip constitutive laws.
• Here we consider the elastic deformation of the substrate and a very simple cohesive law for the interface.
• The model, despite its simplicity, can capture the strength and the effective bond length of the reinforcement.
• Theoretical results are in excellent agreement with experimental evidence.

The problem of an elastic bar bonded to an elastic half space and pulled at one end is considered to model the performance of FRP strips glued to concrete or masonry substrates. If the bond is perfect, stress singularities at both bar-extremities do appear. These can be removed by assuming cohesive contact forces à là Baranblatt that annihilate the stress intensity factor. We show that the presence of such cohesive zones is crucial to predict the experimentally measured Effective Bond Length (EBL), i.e., the bond length beyond which no apparent increase of strength is attained. In particular, it is the cohesive zone at the loaded end of the stiffener, rather than that at the free end, that governs the phenomenon because the EBL coincides with the maximal length of such a zone. The proposed approach provides better estimates than formulas proposed in technical standards.