Pilot tests on reinforced concrete beams strengthened in flexure with FRP-enveloped steel plates

Fiber sheets and steel plates are laminate materials, which are usually bonded on the surface of reinforced concrete beams for structural strengthening. A new type of composite plate was proposed with the corresponding method of strengthening. It was made of FRP sheet enveloped steel plate, and the abbreviation was the FESP. Firstly, to improve the bonding effect between FESP and the beam, the concrete surface was grooved rather than roughened. The reinforced concrete beams were strengthened in flexure by using the basalt FRP-steel composite plate. Secondly, through the tests of seven RC beams, the operation process was clarified for bonding FESP on the grooved concrete surface. Finally, the influence of the thickness of the steel plate, length of FESP, and operation techniques on the performance of the strengthened beams was discussed. The results show that the ultimate behavior of the RC beams can be significantly improved after being strengthened by bonding FESP onto the beams with grooved surface. When the steel plate is thinner, with the lengthening of FESP, the position of debonding shifts from the end to the middle of FESP, the load-bearing capacity and the failure ductility are substantially promoted. In the specimens with the longer FESP, both ends of the composite plate keep well bonded to the beam. When intermediate debonding occurres, the load can be increased furtherly until the concrete is crushed and the theoretical upper limit approaches. When the thickness of the steel plate is doubled, the bending stiffness of the strengthened specimens increases, but end debonding failure prematurely happens, leading to the decrease in ultimate load and ductility instead. Though the laminates are identical, the end debonding of the specimen without repair adhesive surface occurs prematurely, and the steel plate has not yet yielded, which reflects the importance of fully coating the bottom surface of the beam. © 2023 Central South University of Technology. All rights reserved.