Comparison of different models of calculation to evaluate the resistance to compression of the concrete confined with carbon fiber tissues

Abstract

The resistance of concrete to compression can be increased very importantly by its confinement. The confinement of the concrete by means of the external gluing of high resistance fiber fabrics is a technique that has been known for decades and is increasingly used in reinforcement works of structural elements subjected to compression. Carbon fiber fabrics are commonly used, due to their high strength and high modulus of elasticity. The break of the elements occurs when the tensile fiber fails. There are different models to predict the compressive strength of concrete confined with this type of fabric. In America, the model proposed by the ACI is usually used, while in Europe, the one proposed by the FIB is used. In both models, the strength of the confined concrete is obtained from the geometry and strength of the unconfined concrete and the geometric and mechanical characteristics of the fabric that confines the concrete. However, the expressions used are conceptually different. First, for ACI the increased strength of the confined concrete is independent of the strength of the unconfined concrete. Secondly, ACI decreases the maximum deformation at which the fabric can work (and therefore its resistance) to a value close to half of the ultimate deformation of the fabric tested to pure traction, as a result of multiplying by the coefficients ?f y ke, while FIB does not specify this point clearly.