Two models for evaluating the bond behavior in pre- and post-yield phases of reinforced concrete

- The mean bond stress model, associated with steel strain level, is developed to simply predict bond characteristics in pre- and post-yield phases.
- The bond-strain model is presented to describe the bond behavior in terms of reinforcement strain.
- The mean bond stresses representing bond behavior in several characteristic phases of reinforced concrete members are suggested.

The performance and behavior of reinforced concrete structures at serviceability limit state and at ultimate limit state highly rely on the bond interaction between reinforcement and surrounding concrete; therefore a proper evaluation regarding the bond behavior under corresponding state is particularly critical. However, it is not easy to implement the common bond models, characterized by nonlinearity and affiliated with the variable of slip, into practical design and analysis. In this paper, the mean bond stress model associated with steel strain (stress) level and the bond-strain model representing the relationship between bond stress and reinforcement strain are developed to simplify and improve the normal analysis on bond behavior in pre- and post-yield phases. Compared with the results of some well-known experimental campaigns, the proposed models indicate a good agreement with the bond behavior at pre- and post-yield stages. Finally, a thorough discussion about the values of mean bond stresses is carried out; the suggested values considering bond characteristics in several phases of reinforced concrete members are presented by a series of analytical parametric studies on test results in the literature.