Bond Strengthening of Steel Bars Using External FRP Confinement: Implications on the Static and Cyclic Response of R/C Members

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Title: Bond Strengthening of Steel Bars Using External FRP Confinement: Implications on the Static and Cyclic Response of R/C Members

Author(s): M.H. Harajli

Publication: Special Publication

Volume: 230

Issue:

Appears on pages(s): 579-596

Keywords: bond stress; cyclic loading; fiber-reinforced polymer;seismic strengthening; splitting strength

Date: 10/1/2005

Abstract:
The effect of external confinement using fiber reinforced polymer (FRP)laminates on the bond strength and bond stress-slip response of steel bars under staticand cyclic loading is experimentally investigated. Beam specimens with spliced bars atmidspan were tested. The test variables included the diameter of the steel bars, theratio of concrete cover to bar diameter and the area of FRP confinement. Withoutconfinement, the spliced reinforcement suffered significant deterioration of bondstrength, accompanied by considerable stiffness degradation of the beam specimensin the initial few load cycles following bond splitting. Confining the concrete with arelatively small area of carbon FRP sheets increased the bond strength of the steelbars, reduced the bond deterioration of the specimens under cyclic loading, andresulted in superior seismic performance. The characteristics of the bond stress-slipresponse of steel bars embedded in FRP confined concrete in comparison withunconfined concrete are discussed, and a general relationship for the local bondstress-slip response of reinforcing bars embedded in FRP confined concrete andsubjected to monotonically increasing load in tension is presented. Also, a rationaldesign expression is developed for estimating the area of external FRP confinementrequired for bond strengthening.