Efficient near surface mounted CFRP shear strengthening of high strength prestressed concrete beams - An experimental study

Shear behavior of prestressed concrete members and its strengthening is complex due to its brittle nature of failure and a number of variables affecting its behavior. The main goal of this investigation is to assess the efficiency of different near surface mounted (NSM) strengthening configurations using CFRP (Carbon Fiber Reinforced Polymer) laminates on the shear behavior of prestressed concrete beams. The parameters considered in this study are (i) the presence of vertical stirrups and (ii) different NSM FRP shear strengthening configurations. Twelve prestressed concrete beams with and without vertical stirrups were cast and strengthened using different NSM CFRP configurations and tested under shear. All the beams were tested under three point bending at a shear span to depth (a/d) ratio of 2.5 to simulate the shear dominant behavior. Test results revealed that NSM strengthening of prestressed concrete beams using CFRP laminates at 45° was more efficient in improving the shear capacity of beams with and without vertical stirrups. It was also observed that the shear mode of failure could be converted to the flexural mode with improved ductility by designing a suitable NSM shear-strengthening scheme. Shear strength calculations of NSM strengthened beams were made using ACI codes and other analytical models. ACI calculations were found to be conservative in estimating the shear contribution of NSM laminates.