Shear strengthening effect by external post-tensioning steel rods in damaged reinforced concrete beams

Concrete structures typically degrade in performance because of the continuous resistance to loading and environmental factors, resulting in cracks or large deflections. Many repair and rehabilitation methods have been developed to restore the cracks and deflections, however, it is necessary to prove the reinforcement effect for practical application. This study evaluates the shear behavior of damaged reinforced concrete (RC) beams strengthened with external post-tensioning (EPT) steel rods. As for external strengthening with steel rods, a total of 19 tests were conducted to evaluate the strengthening effects of the strengthening amount of steel rod (A_ps) through the use of ϕ18, ϕ22, and ϕ28 mm steel rods, V-type and U-type deviator configurations, deviator location in the U-type configuration, and the effective depth (d_p) between the deviator center and the RC beam top. For the tests, the shear span-to-depth (a/d) ratios were classified based on three-point and four-point bending, and the specimens to be strengthened were post-tensioned after pre-loading them until two-thirds of the maximum strength in the control specimens. The EPT steel rod restored the deflection of RC beams by more than 3 mm, and it was found that the strengthening effect increased from approximately 19% to 128% compared with no strengthening, as the amount of strengthening rod (A_ps) and the effective depth (d_p) increased and the locations of the deviators were closer to the loading positions. The cost-effectiveness of EPT using 28 mm diameter steel rods was similar to that of carbon fiber-reinforced polymer (CFRP).