Experimental testing and analytical modeling of CFRP-confined large circular RC columns subjected to cyclic axial compression

A physically informed analytical model which describes the cyclic axial stress–strain behavior of reinforced concrete (RC) columns confined with fiber-reinforced polymer (FRP) composite wraps is necessary for the non-linear analysis and seismic design of such columns. Although extensive studies have been conducted on the monotonic axial behavior of small sized FRP-confined unreinforced concrete columns, there is a lack of research on FRP-confined RC columns and also their cyclic axial response. As a consequence, there is a lack of cyclic axial stress–strain models which can enable seismic response to be reliably simulated by numerical means. Due to such knowledge gaps, this study reports the results of thirty CFRP-confined large-scale unreinforced and RC circular columns subjected to monotonic and cyclic axial compression loading. The test results indicate that the overall shape of the stress–strain curves, the peak compressive stress and strain at failure, the unloading/reloading paths, and also the plastic strain of CFRP-confined concrete are influenced by the CFRP wrap and internal hoop steel reinforcement. On the basis of the experimental results, a cyclic stress–strain model for CFRP-confined circular RC columns is then proposed. The proposed model consists of three main components, namely (i) a monotonically ascending portion to describe the envelope curve, (ii) a polynomial equation to describe unloading paths, and (iii) a straight line to describe reloading paths. The influence of internal hoop reinforcement on the monotonic model, as well as the unloading and reloading responses is also considered. The accuracy of the proposed model is validated with the test data reported in this paper as well as other test results of relevance extracted from the open literature.