Stress-strain modelling for FRP-confined engineered cementitious composites under cyclic axial compression

As a high-performance building material, engineered cementitious composites (ECC) presents good ductility and toughness with strain hardening behaviour, multiple cracking behaviour and large tensile strain capacity under tensile loading, compared with normal concrete. On the other hand, ECC also shows the similar brittle failure to normal concrete in terms of compressive behaviour. Adopting fibre-reinforced polymer (FRP) confinement is an effective approach to improve the compressive strength, strain and axial deformation ductility of ECC. The current investigations on FRP-confined ECC including experimental tests as well as analytical and design modelling are mainly focused on the monotonic loading, while cyclic model for FRP-confined ECC is not available in the literature. Understanding the behaviour of FRP-confined ECC under cyclic loading is also of vital importance, especially that FRP-confined ECC is usually used in seismic retrofitting. Therefore, this study focuses on the development of stress-strain model of FRP-confined ECC under cyclic compression. Test database for FRP-confined ECC was firstly collected, followed by the assessment of the existing cyclic models developed for FRP-confined normal concrete. New equations were also developed based on the test results of FRP-confined ECC. Different components in the cyclic model, including envelope curve, unloading/reloading curves, plastic strains and stress deterioration, were discussed in detail. Finally, two cyclic models, Model Ⅰ and Model Ⅱ, were proposed to predict the cyclic stress-strain behaviour of FRP-confined ECC. Close agreements between the predicted curves by Model Ⅰ and test curves can be obtained, indicating that Model Ⅰ has good prediction performance and can be adopted to provide design guidance for FRP-confined ECC under cyclic axial compression.