TEST STUDY ON REINFORCED CONCRETE BEAMS STRENGTHENED WITH PRESTRESSED NEAR SURFACE MOUNTED CFRP STRIPS

The techniques of strengthening RC structures with external-bonded (EB) prestressed FRP plates and near surface mounted (NSM) FRP strips are two promising methods used in structural engineering applications. Nevertheless, both the two have considerable limitations and disadvantages in some respects. The technique of strengthening structures with prestressed NSM FRP strips makes it possible to combine the advantages of the two and to achieve a higher utilization of FRP in retrofitting of concrete structures. This paper, making use of the anchors made by the author, conducts tests on a total of 7 RC beams to investigate the mechanical behavior and failure mode of each beam, especially those of the beam strengthened with NSM FRP strips, compares the load bearing capacity and deformability of the beam strengthened with EB FRP strips with those of the beam strengthened with NSM FRP strips, and analyzes the effects of various parameters on the beams strengthened with NSM FRP strips. Test results show that: the effect of NSM FRP strips on the improvement of the load bearing capacity of the beam is significant, similar to that of EB FRP strips; the bonding of FRP strips with epoxy adhesive makes the anchorage of prestressed FRP strips with mechanical anchorage devices unnecessary; still, the use of prestressing technique may lead to epoxy-concrete interfacial debonding at bond ends and the splitting of concrete cover; the increase in the bond length and the provision of U-shaped FRP strakes can prevent the above failure modes from happening. Two beams strengthened with the above methods make a higher utilization of the CFRP material, the failure mode of which is the rupture of the CFRP strip.