Experimental study on T-shaped reinforced concrete beams with locally reduced cross-sections

The principle of strong column and weak beam (SCWB) is often adopted in the design of reinforced concrete (RC) frames to ensure their optimum seismic performance. However, insufficient consideration of the SCWB hierarchy has resulted in numerous existing RC frames violating such a hierarchy. Consequently, a novel seismic retrofitting technique (section reduction technique) was proposed for RC frames that violate the SCWB hierarchy. The section reduction (SR) technique involves creating a locally reduced cross-sections (i.e., a gap) in the bottom region of the beam (i.e., the compression region of the beam under negative bending) adjacent to the beam-to- column joint and applying a fiber-reinforced polymer (FRP) strengthening system, which reduces the negative bending capacity of the beam while improving the shear capacity of the gap region. Nine full-size RC beams were fabricated and three-point negative bending experiments were conducted to demonstrate the validity of the SR technique. Based on the test results, it was found that a gap of appropriate size can effectively reduce the negative bending capacity of a T-shaped RC beam. In addition, the ductility of the beams can be ensured if the occurrence of FRP U-jacket debonding can be effectively prevented when applying the FRP strengthening system.