Stress-strain behavior of ECC-GFRP spiral confined concrete cylinders

This paper introduces a new confinement system that combines engineered cementitious com-posites (ECC) with glass fiber-reinforced polymer (GFRP) spiral as a protective cover to confine the concrete core. Meanwhile, the precast ECC-GFRP spiral cover also can serve as permanent formwork to improve construction efficiency and save construction costs. This study analyzed the confinement mechanism from the combination of ECC and GFRP spiral, and the effects of con-crete strength and confinement stiffness on the stress-strain behavior of the confined concrete were investigated. The stress-strain behavior analyses confirm that the residual confining stress from ECC could enhance the ductility of the composite cylinder after GFRP rupture. Test results also indicate that an ECC-GFRP spiral layer has excellent crack control capability before peak loads, guaranteeing concrete cylinder durability. In addition, the model evaluation indicates that ultimate condition models for FRP-confined concrete are also applicable to ECC-GFRP spiral -confined concrete as long as the confining pressure from both ECC and GFRP spiral can be accurately predicted. A modified stress-strain model is proposed for this confinement form and performs well against test stress-strain curves.