Cracking and failure mode behavior of hybrid FRP strengthened RC column members under flexural loading

Abstract

Strengthening of reinforced concrete (RC) members in bridges and buildings is often required to improve flexural performance. Strengthening using fiber‐reinforced polymer (FRP) composites has become popular as FRPs offer multiple advantages compared with conventional strengthening practices like steel jacketing and concrete enlargement. External bonding (EB) using carbon FRP (CFRP) laminates/fabric has become a common strengthening practice. The effectiveness of the EB strengthened system is reduced due to possible debonding of FRP from concrete substrate. The near‐surface mounting (NSM) of FRP laminates is efficient in reducing the debonding failure, but it is not effective under dominant compression loading. Hybrid FRP (HYB) strengthening combines the advantages of both the NSM and EB techniques. HYB strengthening can enhance the performance of RC members under all loading combinations. The main objective of this study is to understand the flexural crack opening behavior of control and hybrid FRP strengthened RC column members under pure bending. The digital image correlation (DIC) analysis shows that the crack width and its propagation are significantly reduced due to hybrid FRP strengthening. The crack widths measured using the DIC are compared with the analytical predictions based on Eurocode 2 and fib bulletin 90. HYB FRP strengthening increased the strength and post‐cracking stiffness of RC elements under flexure without compromising the ductility. In addition, the HYB strengthening distributed the damage under flexural loading, unlike localized damage observed in control RC elements.