Structural Performance of Concrete Confined with Hybrid FRP Composites

ABSTRACT: External confinement of concrete by means of FRP external wrapping can significantly enhance its strength and ductility and result in a large energy absorption capacity. This paper studies the behavior of concrete cylinders confined with hybrid FRP composites. A total of 35 cylindrical specimens with dimensions of 150mm diameter by 300mm length were tested, which included three plain concrete cylinders as control specimens, 12 concrete cylinders confined with one kind of FRP sheet and 20 specimens confined with hybrid FRP sheets. The experimental parameters include the different types of FRP sheets, the number of layers of FRP sheets and the different kinds of hybridization with two or three types of FRP composites. First, the characteristics of the stress–strain curves of hybrid FRP-confined concrete are described based on previous studies. Then, in order to describe the main mechanical features of hybrid FRP-confined concrete cylinders including stress and strain behavior, some simple models are suggested based on a number of empirical equations determined from mechanical tests. Finally, a multi-linear model is proposed to predict the axial stress–strain model of concrete cylinders confined with hybrid FRP composite. The proposed model closely agrees with the experimental results of the present study. KEY WORDS: concrete cylinders, confinement, fiber reinforced polymer (FRP), hybrid composite, strain, stress