Local and global bond characteristics of steel reinforcing bars

The development of an accurate local bond stress–slip ( τ – δ ) relationship for steel reinforcing bars has been hindered for two reasons: because steel reinforcing bars are internally encased, it is difficult to strain gauge the reinforcing bar to quantify the change in strain over a given length and, therefore, to directly measure the local τ – δ relationship; and because of the presence of yielding, which generally occurs before debonding and significantly influences the behaviour of the reinforcing bar. To overcome these difficulties associated with quantifying the local τ – δ relationship of steel reinforcing bars, theory developed to obtain the local τ – δ relationship from the global load slip ( P – Δ ) response of FRP plated reinforced concrete structures has been modified in this research to account for short embedment lengths. Furthermore, in this paper, a link between the global load–slip ( P – Δ ) response and the local τ – δ relationship of steel reinforcing bars, that is independent of embedment length, is presented for the first time. Additionally, the new theory is used to derive the local τ – δ relationship from test results and to illustrate the effect of corrosion on the local τ – δ relationship which quantifies the amount of corrosion to cause bar debonding in RC beams.