Creep Effects in Plain and Fiber-Reinforced Polymer-Strengthened Reinforced Concrete Beams

This study considers the potential effects of creep on reinforced concrete (RC) beams strengthened with externally applied fiber reinforced polymer (FRP) strips. The significance of creep in the epoxy adhesive and whether such creep might allow the FRP strips to unload over time is assessed. The long-term deflection behavior of two RC beams with similar dimensions and material properties was monitored. One beam was externally strengthened with fiber-reinforced polymer (FRP) strips, while the other was used as a control specimen. Both beams have been subjected to sustained loading for over 6-1/2 years. Slip movements at the ends of the FRP strips were also monitored. The experimental deflections have been compared to deflection predictions using ACI 209R-92 and CEB-FIP MC 90. The creep deformations of the FRP-strengthened beam are not as predicted from the control beam. A step-by-step in-time analysis and finite element modeling are used in the analysis, and both showed good ability to simulate long-term effects in RC beams strengthened with FRP. Results from both techniques show that creep of the adhesive layer can account for the differences observed between the predicted and actual behaviors of the beam, and that this creep should be included when assessing the long-term effects of strengthening a beam with externally applied FRP.