Transverse shear behaviour of novel FRP-UHPC hybrid bars

Fibre-reinforced polymers (FRP)-ultra-high performance concrete (UHPC) hybrid bars are a new type of steel-free hybrid bars, which comprise an outer FRP tube, a central FRP bar and an annular layer of UHPC. Hybrid bars are proposed to fix the issue that the fibers in FRP bar are easily buckled under compression and are expected to have an excellent durability because all the components in hybrid bars are anti-corrosion materials. As it is expected that the hybrid bars have satisfactory shear behavior, this paper presents an experimental study on the transverse shear behaviour of hybrid bars. The key variable was the fibre winding angle of the outer FRP tube and the counterparts included the UHPC-filled FRP tubes and the bare FRP bars. It is demonstrated that the two peak loads of hybrid bars are at least 58% larger than the peak load of their counterparts under the transverse shear loading. The deformation capacities of hybrid bars are also found to be at least 220% larger than that of the UHPC-filled FRP tubes, and the UHPC-filled FRP tube and the central FRP bar in hybrid bars are in an optimal combination, leading to excellent shear behaviour of hybrid bars. An equation for calculating the shear strength of hybrid bars is proposed and verified by the test results.