FRP and FRCM systems for structural retrofitting

Frp and frcm systems for structural retrofitting

Francesco Romeo, Università degli Studi di Roma “La Sapienza”

Fiber reinforced polymers (FRP) are gaining acceptance in the rehabilitation and/or strengthening of existent structures since they are good alternatives to traditional strengthening systems, due to their high stiffness and tensile strength, low weight, good fatigue behavior, immunity to corrosion, and geometric versatility. FRP systems for strengthening primarily employ two distinct approaches: the externally bonded reinforcement, EBR, and the near-surface mounted techniques, NSM. These systems harness the exceptional properties of carbon fiber reinforced polymer, or glass fiber reinforced polymer, reshaping the future of structural enhancement. The EBR technique has been used to increase the flexural and the shear resistance of reinforced concrete (RC) elements, as well as the concrete confinement, and to control the cracking process. Externally bonded reinforcement (EBR) method, which is the most common method for strengthening reinforced concrete structures, is based on application of fabrics (in situ cured systems) or laminates (pre-cured systems) glued externally on the surface of the element to strengthen. EBR can be applied using strips or continuous jacketing. Three main configurations of FRP strengthening may be used for externally bonded reinforcement: side bonding, U-wrapping, and complete wrapping.

The installation process of EBR includes:

• Surface Preparation: remove the coating of concrete surface, polishing the surface, cleaning, setting out and apply primer adhesive into the surface of the concrete,
• Fabric Cutting: cutting fiber reinforced fabrics or laminates into the size,
• Applying impregnation adhesive and then the fabrics or laminates, and finally levelling the surface from one end to the other.

Despite the advantages of this technique, the bond between FRP and concrete surface can be susceptible of degradation, particularly due to environmental conditions such as fire, high temperatures, UV radiation, humidity and even vandalism acts. The NSM technique was proposed as an alternative strengthening technique and, when compared to the EBR, several advantages can be pointed out, mainly: the amount of site installation work and the surface preparation may be reduced; the NSM technique is less prone to the debonding from the concrete substrate; the FRP reinforcements can be more easily anchored into adjacent members (preventing debonding failures); the FRP reinforcements are protected by the concrete cover and, consequently, less exposed to mechanical damage and impact loading, and less exposed to the fire and vandalism acts. Furthermore, the aesthetic of the strengthened structure is virtually unchanged (De Lorenzis and Teng 2007). Near-surface mounted fiber reinforced polymer method for structural strengthening is based on the insertion of laminates or rods into grooves opened on the concrete cover or slits, where the width is relatively small. Flexural and shear strengthening of reinforced concrete structural elements are two of the most prevalent applications of NSM FRP technique.

The installation process of NSM FRP is included of:

• Cutting the groove on the concrete surface;
• Then cleaning the groove and applying adhesive into the groove to around half of the groove height;
• And finally inserting the FRP strip/bar into the groove and fully filling the groove with adhesive.