New mechanics-based confinement model and stress-strain relationship for analysis and design of concrete columns wrapped with FRP composites

The analysis and design of concrete columns wrapped with fiber-reinforced polymer (FRP) composites require the mathematical equation of stress-strain relationship and the ultimate conditions (i.e., stress and strain) cor-responding to the failure of FRP-confined concrete. The ultimate conditions of FRP-confined concrete were mostly developed using empirical methods based on regression analysis of test data obtained from the literature. There is a lack of mechanics-based formulations of the ultimate condition. In addition, from a practical design perspective, despite new advancements in the field of FRP confinement and the availability of sophisticated analysis-oriented and data-driven models, design guidelines and practicing engineers mainly need a single equation for the stress-strain relationship of confined concrete. Thus, in this study, a five-parameter William-Warnke plasticity model was utilized to find a new mechanics-based prediction of the ultimate condition of FRP-confined concrete using an updated database of 788 test data. Moreover, a new optimized stress-strain rela-tionship based on the general expression of the Richard and Abbott equation was developed using 200 complete experimental stress-strain curves from 16 different independent studies. The proposed stress-strain relationship was presented in a single equation for the ease of application and its performance was verified against the experimental curves.