Analytical model for concrete confined by steel stirrups and/or FRP jackets in rectangular sections

This paper illustrates the extension to the rectangular section of an analytical model for confined concrete proposed for square sections confined by steel stirrups and/or FRP jackets. The confined concrete model is developed starting from the elasticity theory and under the key assumption that the confinement acts under the plane-strain conditions. The confining pressure within the section core is obtained by an analogy formulated in polar coordinates regarding internal co-axial cylinders for obtaining the equivalent confining pressure within the section core. The model is suitable to be implemented by using any active confinement triaxial model and for describing the also the contribution offered by external FRP wraps and/or steel jackets. The paper concludes with some experimental results demonstrating the accuracy of the new analytical model proposed in predicting the confined concrete stress-strain relationship of rectangular section cores.