Bond strengthening of lap spliced reinforcement using external FRP jackets: An effective technique for seismic retrofit of rectangular or circular RC columns

Confinement of concrete at the critical hinging regions is one of the most effective means for improving the seismic behavior of reinforced concrete (RC) members. Confinement reduces the bond degradation of the steel reinforcement and limits the concrete damage within the confined zone leading to increased energy absorption and dissipation capacity of the structure. Recent experimental and analytical studies undertaken on the use of FRP composites for seismic upgrading of RC members [FRPRCS08 Proceedings. In: Triantafillou TC, editor. 8th International symposium on fiber-reinforced polymer reinforcement for concrete structures. Patrace, Greece: University of Patrace; July 2007. p. 16–8] have clearly identified the advantages of this technology when compared to conventional strengthening methods. However, unfortunately, no guidelines have yet been developed by code committees for seismic retrofit using FRP composites. This paper provides a synthesis of the results of a series of experimental and analytical studies undertaken in the main part by the writer and in part by other investigators on the use of external FRP jackets for bond strengthening of developed/spliced steel bars in tension and its implications on the static and seismic response of concrete members. Results of the experimental programs are briefly discussed, and design expressions for evaluating the minimum thickness of FRP jacket required for seismic bond strengthening are presented and compared. The accuracy of the design expressions was verified against experimental data. In addition, a generalized model of the local bond stress–slip response of steel bars embedded in FRP confined concrete corresponding to splitting mode of bond failure is described. The model is composed of a monotonic envelope curve and bond degrading curve and can be used for evaluating the seismic behavior of the hinging zones in reinforced concrete members when confined externally with FRP jackets in comparison with the response of unconfined concrete.