Lateral Strain-to-Axial Strain Relationship of Confined Concrete

The use of fiber-reinforced polymers (FRP) has become widely accepted engineering practice for strengthening reinforced concrete members. It is well established that lateral confinement of concrete with FRP composites can significantly enhance its strength and ductility. As the confinement pressure generated by FRP on the confined concrete depends on the lateral expansion of concrete, the mechanism of concrete expansion inside the FRP shell is of significant interest. A review of the existing stress-strain models of FRP-confined concrete revealed the need for a model that accurately predicts the dilation characteristic of confined concrete as it provides the essential link between the response of the concrete core and the passive confinement mechanism of the FRP shell. It is also understood that knowledge established from the research area of actively confined concrete can be employed in the development of a model applicable for both FRP-confined and actively confined concretes. Based on a large number of experimental test results of both FRP-confined and actively confined concretes, a generic model is proposed to describe the lateral strain-to-axial strain relationship of confined concrete. The instrumentation arrangements of the tested specimens have allowed for the lateral strain-axial strain relationships of confined concrete to be captured throughout the tests. The trend of the lateral strain-to-axial strain relationship of confined concrete is shown to be a function of the confining pressure, type of confining material and concrete strength. Assessment of models with the experimental databases showed that the predictions of the proposed model are well above existing models and in good agreement with the test results of both FRP-confined and actively confined concretes.