Confinement of concrete with hybrid FRP bistable structures

The ductility potential of concrete confined with fiber reinforced polymer (FRP) composites is limited by the low fracture strain and brittleness of the fiber and consequently poor energy dissipation in the system. To improve this aspect, a series of experiments were conducted to investigate the use of mechanism-based hybrid FRP bistable wraps, which consist of energy-absorbing “links” made of carbon and glass fabrics bonded together (with the main links designed as the primary load carrier and the waiting links as the secondary load carrier). The FRP bistable-confined concrete was found to have increased ductility and energy absorption with a controlled failure mode. The effect due to material type of the bistable links and core inserts was substantial in terms of load-carrying capacity and deformability. A two-step simulation method was developed for the FRP-confined concrete, where the FRP wrap was modeled with a material constitutive behavior obtained from a separate modeling step of the FRP bistable structure. A simplified bilinear model was also proposed for design purpose.