Shaking table test of concrete columns hybrid reinforced by steel/FRP bars

Post-earthquake residual deformation can be decreased due to the designable post-yield stiffness of concrete column reinforced by steel bars/fiber reinforced polymer (FRP) bars. Shaking table tests of three concrete columns with similar initial stiffnesses were conducted, where the longitudinal reinforcement included ordinary steel bars, steel-FRP composite bars (SFCBs) and hybrid reinforcement (steel bars and FRP bars, C-H). The measurements included acceleration response and strain development. The test results showed that the absolute and relative peak ground acceleration (PGA) responses of different columns were similar to one another. The residual strain in the anchorage region was not consistent (tension or compression) and was affected by the longitudinal reinforcement type and the amplitude of the input PGA. For ordinary reinforced concrete (RC) columns, the plastic strain of steel bars developed rapidly after the input ground motion PGA reached 100 Gal, and the corresponding residual strain also developed dramatically. For the SFCB column, even after the peak strain reached 15,000 mu epsilon, the residual strain was still below 500 mu epsilon. For hybrid column C-H, the residual strain of the FRP bar was similar to that of the SFCB column. Even when the input wave PGA reached 560 Gal with concrete cover spalling and steel bar buckling, no damage was observed on the FRP bars. In general, compared to ordinary RC columns, concrete columns with hybrid steel and FRP bar reinforcement can achieve a smaller residual deformation, while SFCB reinforced columns can be constructed in severe environments due to a good anti-corrosion performance, such as in offshore structures.

Automated summary

Post-earthquake residual deformation of concrete columns can be reduced with the use of steel/FRP reinforcement designable for post-yield stiffness. The type of longitudinal reinforcement can affect the residual strain, where steel bars develop rapid plastic strain and corresponding residual strain in ordinary RC columns, while SFCB reinforced columns exhibit lower residual strain even at peak strain levels. Hybrid columns C-H show similar residual strain to SFCB columns. Additionally, FRP bars exhibit good performance in severe environments with high input wave PGAs.