Design-oriented stress-strain model for FRP-confined engineered cementitious composites

Engineered cementitious composites (ECC) is known for its enhanced tensile performance compared with normal concrete. Ductile strain hardening behavior, multiple cracking beahvior as well as large tensile strain capacity can be achieved for ECC under tensile loadings. For the compressive performance, using lateral fiber-reinforced polymer (FRP) confinement is an effective approach to improve the compressive strength and strain. However, the research work on design models of FRP-confined ECC, especially on the stress-strain relationship, is limited at the current stage. To address this aspect, this study focuses on developing the design-oriented stress-strain model for FRP-confined ECC under axial compression. A test database on FRP-confined ECC was firstly assembled. Existing design equations on FRP-confined concrete were evaluated and found not be able to provide satisfactory predictions for FRP-confined ECC. New design equations on ultimate conditions, including the ultimate compressive strength and ultimate axial strain, were then proposed and verified with the test results. Finally, the design-oriented stress-strain model for FRP-confined ECC was developed, which consists of the formulated form of a stress-strain model for FRP-confined normal concrete and the new design equations on ultimate conditions proposed for FRP-confined ECC. Predictions of stress-strain curve show close agreements with test results, indicating the good performance of the developed design-oriented stress-strain model.