Local and global bond characteristics of steel reinforcing bars

Abstract

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.