Strength and ductility of innovative hybrid NSM reinforced and FRP confined short RC columns under axial compression

Strengthening of concrete structures using Fiber Reinforced Polymer (FRP) composites has gained prominence in the recent years due to its various advantages. Reinforced Concrete (RC) columns are predominantly subjected to compression loading and often need strengthening to increase their strength and ductility. This paper explores an innovative hybrid strengthening technique where short RC square column elements are strengthened using both Near Surface Mounted (NSM) CFRP laminates and Externally Bonded (EB) CFRP fabrics for confinement. Ten square column elements of cross sectional dimension 230 mm and height of 450 mm were cast, strengthened and tested under pure axial compression to investigate the efficiency of different combinations of strengthening techniques. Existing constitutive models available from past literature were used to predict the behavior of FRP strengthened RC column elements. A close correlation was observed between the peak strength obtained from experimental and analytical values. Hybrid strengthening technique was found to be more efficient leading to higher increase in strength, stiffness and ductility as compared to only NSM strengthened or only CFRP confined RC columns.