CFRP-confined square RC columns. II: cyclic axial compression stress-strain model

For the seismic design of fiber reinforcement polymer (FRP) confined reinforced concrete (RC) columns, the development of an accurate axial stress-strain model that considers cyclic compression is necessary. In light of such a demand, this paper presents a cyclic axial stress-strain model for FRP-confined RC square columns. The model is informed from physical observations and test measurements obtained from an experimental investigation reported in the companion paper, in which FRP-confined square unreinforced and reinforced concrete columns of larger size under varying cyclic axial compression patterns were tested. In the current paper, the proposed stress-strain model is presented and it consists of three main components, namely (1) a monotonic stress-strain model to describe the envelope curve, (2) a polynomial expression for the unloading path, and (3) a straight line for the reloading path. The influence of internal longitudinal and hoop steel reinforcement is also considered in the proposed model, in addition to their influence on the ultimate stress and strain. The accuracy of the model is finally validated with an experimental database compiled of tests reported in the companion paper and other relevant tests extracted from the open literatureZhenyu Wang, Daiyu Wang, Scott T. Smith and Dagang L