Modeling the bond-slip behavior of confined largediameter reinforcing bars

The performance of reinforced concrete structures depends on the bond strength and bond-slip behavior between the concrete and reinforcing steel. Although the bond behavior of deformed bars has been extensively studied, there is little data available for large-diameter reinforcing bars under cyclic load reversals. As a result, current code specifications for the development lengths of reinforcing bars are largely based on experimental data obtained for bars with diameters of 36 mm or smaller. This paper presents an analytical model to describe the bond-slip behavior of reinforcing bars in well-confined concrete under monotonic and low-cycle fatigue loads. The model has been validated and calibrated with recently obtained experimental data from pull-out tests conducted on reinforcing bars with diameters of 36, 43, and 57 mm. It is successful in predicting the bond-slip behavior including the degradation of the bond strength and stiffness under monotonic as well as different cyclic load histories. This model has been implemented in an interface element in a finite element program. Analyses have been conducted with finite element models to estimate the minimum development length required for these large-diameter bars under a well-confined situation.