Shear strengthening of reinforced concrete T-beams with anchored fiber-reinforced polymer composites

Abstract

T-shaped beams are widely used in reinforced concrete (RC) structures, both buildings and bridges. Under-designed shear reinforcement and long-term aging make these structural elements susceptible to shear failure during earthquakes. The currenlty availalbe experimental work investigating the retrofit of these beams against shear failure is very limited. In this work, the external strengthening of RC T-beams with splay anchored strips of fiber reinforced polymer (FRP) composites under cyclic shear loading for the cases of normal and high strength concrete was studied. Six beams with 3.05 m length and 0.46 m that were conservatively reinforced against flexural failure were designed. The shear reinforcement of the beams was sufficiently high to ensure the dominance of shear failure. Three of the beams were built using a normal strength concrete and the other three were built using a high strength concrete with 28-day strengths of 30.5 MPa and 44.0 MPa, respectively. From each group of normal and high strength RC beams, one beam served as the reference. The other two beams were retrofitted with external strips of FRP composites that were bonded on the web and anchored under the flange of the beams. The beams were tested under cyclic four-point loading to evaluate the performance of the FRP retrofitting system against shear failure under simulated seismic loading. The deflection and the strain in the FRP composites were recorded while monitoring the strain of the longitudinal reinforcement to ensure an elastic response in flexure. The reference beams failed by shear cracking and the retrofitted beams failed by shear cracking and FRP delamination. The retrofitting technique increased the shear capacity of the beams by up to 37% and 20% for the normal and high strength beams, respectively, and promoted the beam ductility prior to failure.