Parametric investigation of continuous beams strengthened with near surface mounted FRP bars

Abstract

This study evaluates the near surface mounted fiber-reinforced polymer (FRP) reinforcement technique for strengthening continuous reinforced concrete beams. A three-dimensional finite element model was developed and validated with a recent experimental study. The model incorporates robust features, including concrete nonlinear behavior, debonding and slipping of FRP bars, and various failures. It was able to capture the ultimate load (Pu) with maximum deviation of 7%, beam’s load–deflection curves, load–strain responses in rebar and concrete, and various failure modes. A parametric study was conducted and showed that failure mode changes from concrete shear to FRP bar debonding at concrete compressive strength fc’of 20–30 MPa, with a 26–52% increase in Pu relative to the un-strengthened beam. Varying the hogging/sagging FRP reinforcement ratio (ρh/ρs) from zero to 2.0 results in a 39% increase in Pu and a change of failure mode. A value of 1.5 is recommended for ρh/ρs. Also, the synergistic effects of NSM FRP and internal steel reinforcements were studied. An FRP bar length in the hogging and sagging zones of 80% the beam span was found to be sufficient to mitigate debonding and thus is recommended. Pu did not vary significantly with the span ratio for two-span continuous beams. A design expression for the debonding strain in FRP bars based on the American Concrete Institute design guide was assessed and a further refined model is developed.