Hybrid system of longitudinal CFRP laminates and GFRP wraps for strengthening of existing circular concrete columns

This paper presents an investigation on the behavior of a strengthening system of longitudinal premanufactured carbon fiber-reinforced polymer (CFRP) laminates and transverse glass FRP (GFRP) wrapping for strengthening of concrete columns (here after is called a hybrid system). The idea behind using the longitudinal CFRP strips was to enhance the system by increasing the flexural stiffness of the column which is effective for the strengthening of slender columns and eccentrically loaded columns where additional flexural stiffness is required for buckling control. The study was conducted experimentally in two phases under monotonic loads. Phase I was conducted on small-scale concrete specimens to characterize the hybrid system and phase II was conducted to verify the effectiveness of the hybrid system for the strengthening of large-scale slender concrete columns. In phase I, it was observed that by applying GFRP wraps on longitudinal CFRPs, the failure mode of CFRP laminates changed from buckling/debonding to crushing to achieve the full capacity of the system. However, as expected, test results in phase I showed that the usage of wrapping without longitudinal CFRP laminates was more effective than the proposed hybrid system for the strengthening of small scale concrete columns subjected to pure axial loading. For slender columns in phase II, the hybrid system enhanced the wrapping system by adding 52%, 105%, and 94% gain for axial capacity, flexural capacity, and lateral displacement at peak load, respectively, by altering the load-deflection curve of the slender columns to achieve a higher performance level.