Experimental and analytical studies on the flexural behavior of steel plate-UHPC composite strengthened RC beams

In view of the excellent mechanical property of Ultra-High Performance Concrete (UHPC), a new method of using steel plate and UHPC (SP-UHPC) composite to strengthen damaged reinforced concrete (RC) beams was proposed. Four-point bending tests were conducted to investigate the failure modes, deformation characteristics, crack resistance, and bearing capacity of five SP-UHPC strengthened beams (SPUB), one reinforced UHPC strengthened beam (RUB), and one reinforced concrete beam (RCB). Additionally, the impacts of different strengthening techniques, the thickness of steel plate and UHPC on the flexural performance of the strengthened beams were investigated and discussed. The effects of the shear strength of UHPC-RC interface on the bearing capacity of the strengthened beams were analyzed. The test results show that the failure mode of strengthened beams is interface peeling failure. Compared with RCB, the cracking moments of SPUBs and RUB increased by about 214.5%-271.5% and 43.7%, respectively. The bearing capacity of SPUBs and RUB increased by 53.1%-73.7% and 53.4%, respectively. The flexural stiffness of strengthened beams increased by nearly one time on average. Compared with RUB, the SPUBs showed a superior crack resistance and interface slip resistance. The increase in the thickness of the steel plate and UHPC can improve the flexural stiffness and the strain behavior of strengthened beams significantly. Based on the test results, the calculation formulae of UHPC cracking moments and bearing capacity of SP-UHPC strengthened beams were proposed considering the effective anchorage length of interface, the strain hardening behavior of UHPC, and the residual strain in RC beam. The calculation results of UHPC cracking moments and bearing capacity coincide with the test results, demonstrating the accuracy of proposed calculation formulae.