FRP-confined concrete in square columns: an advanced stress-strain model based on a new approach

It is well-known that the strength and ductility of reinforced concrete (RC) columns can be significantly enhanced through lateral confinement with fiber reinforced polymer (FRP) jackets. As a result, extensive research has been conducted on the behavior of FRP-confined concrete in both circular and rectangular RC columns. For the former columns, the stress-strain behavior is now well understood and can be closely predicted by some of the existing models, but the same cannot be said about the latter columns. This paper presents a new attempt at understanding and modeling the confinement mechanism in square columns as a special case of rectangular columns, leading to a new stress-strain model. The salient features of the new model include a more rigorous definition of the effective confinement area and a corner hoop strain-axial strain relationship based on advanced finite element results as well as a more reliable definition of the ultimate condition based on experimental results. The proposed model is analogous in approach to analysis-oriented stress-strain models for FRP-confined concrete in circular columns, and represents a more advanced and robust method for modeling the stress-strain behavior of FRP-confined concrete in square columns than the existing stress-strain models for such columns which have normally been empirically based. The approach is believed to be easily extendable to FRPconfined concrete in rectangular columns.