Cyclic stress-strain behavior and model for FRP-confined engineered cementitious composite

A fiber-reinforced polymer (FRP) confined engineered cementitious composite (ECC) column as a new high-performance composite member achieves significant ductility. Understanding its cyclic behavior is necessary to guide seismic design. This paper presents an experimental study on the compressive behavior of large rupture strain (LRS) FRP and traditional glass FRP (GFRP) jacketed ECC cylinders subjected to full and partial cyclic loadings. Effects of FRP confinement level, FRP type, and loading scheme on the failure pattern, stress-strain relationship, ultimate condition, plastic strain, and stress deterioration ratio were examined. Existing equations for plastic strain and stress deterioration ratio of the envelope and internal cycles were evaluated. Based on the experimental results, new calculation formulas were derived for the plastic strain and stress deterioration ratio. A threshold involving partial unloading/reloading factors was determined to define the effective cycles. In addition, a cyclic model composed of a monotonic envelope model and an unloading/reloading model was developed for estimating the stress-strain hysteresis loops of both GFRP- and LRS FRP-confined ECC cylinders.