RC beams strengthened in shear with FRP-Reinforced UHPC overlay: An experimental and numerical study

Abstract

In this study, a hybrid strengthening technique consisting of ultra-high performance concrete (UHPC) overlay reinforced by fiber reinforced polymer (FRP) bars is proposed to strengthen reinforced concrete (RC) beams in shear. Eleven beams, five of which are physical samples tested under static load, and the other six are virtual ones derived from a robust finite element (FE) analysis, are used to assess the effectiveness of this retrofitting technique. Several parameters are examined, namely overlay thickness, overlay configuration (continuous vs. discontinuous), FRP reinforcement ratio in the overlay, and type of FRP rebar (Glass-FRP vs. Carbon-FRP). Results showed that the system was very effective in increasing the beam capacity (Pu) and altering the failure mode from shear to flexure. Increasing the overlay thickness (toverlay) from 0 to 30 mm for plain and FRP-reinforced overlays results in a significant increase in Pu of 76–117%, compared to the control beam. Using discontinuous UHPC strips, although does not alter the shear failure, results in 89% increase in Pu. Reinforcing the overlay with GFRP and CFRP bars results in reducing the overlay thickness needed to shift the failure mode from shear to flexure. The energy absorption index, which is a measure of ductility, of the strengthened specimens was 4.0 to 6.9 times that of the control beam. FRP bars resulted in 11–25% increase in energy absorption compared to plain overlays, with GFRP showing more ductility than CFRP. An analytical procedure is also included and used to predict Pu from modifying existing code equations to include the contribution of UHPC overlay to shear.