The effect of CFRP-shear strengthening on existing circular RC columns under impact loads

In recent decades, accidents involving derailed train collisions have increased, owing to the rapid development of railway construction worldwide. Reinforced concrete (RC) columns in train stations are likely to be subjected to derailed train collisions, resulting in a brittle shear failure of the columns and catastrophic damage to the entire structure. In view of these problems, this study investigated the effectiveness of carbon fiber-reinforced polymer (CFRP) shear strengthening in improving the failure modes of circular RC columns. A drop hammer impact test was performed on a plain circular RC specimen and a CFRP-shear-strengthened circular RC specimen with fixed supports. The tested specimens were scaled from a regular train station column in China, and the impact height was selected as 2/9 of the effective span length, in accordance with the dimensions of a high-speed train locomotive. The test results revealed that wrapping a layer of CFRP sheets can effectively mitigate the shear damage of the concrete, and transform the failure mode of the column specimen from brittle-shear to ductile-flexural. In addition, finite element (FE) models were developed and verified based on the experimental results. Using the verified FE models, the structural design-related parameters (e.g., the longitudinal reinforcement ratio, transverse reinforcement ratio, impact location, concrete compressive strength, and axial load ratio) were extensively analyzed, aiming to further investigate the effectiveness of CFRP strengthening on RC columns. The results demonstrated that wrapping existing RC columns with CFRP can achieve a consistent good strengthening effect, despite variations in these basic design parameters.