Experimental and finite element studies on the flexural behavior of reinforced concrete elements strengthened with hybrid FRP technique

Abstract

The objective of this investigation is to assess the effectiveness of hybrid fiber reinforced polymer (FRP) strengthening on the overall behavioral improvement of reinforced concrete (RC) beams under flexure. Eight square RC beams were cast and strengthened using different FRP techniques including (i) near surface mounting (NSM), (ii) external bonding (EB) and (iii) hybrid strengthening using a combination of NSM carbon FRP laminates and EB CFRP fabric. Peak moment capacity was calculated analytically by enforcing the sectional equilibrium using the strain compatibility procedure. A micro plane based nonlinear three-dimensional finite element (FE) model was developed to simulate the behavior of the RC beams with and without FRP strengthening. Experimental results revealed that hybrid FRP strengthening could increase the strength by 160%. Moreover, the ultimate displacement of hybrid FRP strengthened beams improved significantly when compared to only the NSM technique. Only NSM strengthening improved the peak strength by 85% but had a brittle bond failure. Only EB strengthening improved the ductility of the flexural members due to confinement but did not significantly increase the strength. Predictions of the FE model correlated well with the experimental results and revealed that minimum edge distance for NSM laminates has to be ensured for preventing premature edge de-bonding failures.