Hybrid confinement of concrete through use of low and high rupture strain FRP

This study investigates the behavior mechanisms and efficiency of concrete confinement formed with the hybridization of two different types of fiber reinforced polymer (FRP) sheets with the aim of utilizing superior features of these two FRP types. The originality of the study is to combine carbon or glass FRP sheets (CFRP or GFRP) with polyethylene terephthalate FRP sheets (PET-FRP), which have different mechanical features, particularly in terms of deformability. While CFRP and GFRP sheets have relatively high tensile strength and low rupture strain capacity, PET-FRP sheets have low tensile strength but remarkably high rupture strain capacity. Hybridization is performed through external wrapping of two different FRP sheets in a successive way. 24 standard cylinder concrete specimens are tested under compression loading. The test variables of the study are the types and number of layers of the inner and outer FRP constituents of hybrid jacket. Test results show that hybrid confinement of FRP sheets with low and high rupture strain capacities offers an enhanced ductility. Furthermore, it is seen that through the hybridization of FRP sheets with different mechanical properties, stress-strain relationship of FRP confined concrete can be tailored. Several available analytical models developed for stress-strain relationship of the concrete confined with a single type of FRP sheet and one model developed for the hybrid FRP confined concrete are used to predict key stress and strain values of the hybrid confined concrete. Considering the behavior mechanisms of the hybrid confined concrete specimens, several assumptions are made during the application of these models. It is shown that key stress and strain values of hybrid confined concrete can be reasonably predicted.