Reinforcement and Concrete Bond: State Determination along the Development Length

The distribution of bond on the lateral surface of steel reinforcement embedded in concrete is explored through systematic solution of the governing field equations of the associated mechanical problem. By separating the variables, the state of stress in the concrete surrounding the bar is represented by coupling two independent solutions, each describing attenuation of bond stresses either in the longitudinal direction or in the radial direction of the cover, respectively. Kinematic considerations are used to couple longitudinal slip with the radial translation of the cover, whereas the corresponding stress components developing along the lateral bar surface over the anchorage (radial pressure and bond stress) are related through a frictional relationship. Using the derived solution, various experimentally documented trends and phenomena pertaining to the study of bond, as represented by the international experimental databank, are reproduced analytically and interpreted. These include the processes of debonding and yield penetration and the sensitivity of the development capacity to important design variables such as the related rib area, cover to bar diameter ratio, concrete strength, bar yield strength, bar hardening characteristics, and confinement. A model representing the envelope curve of the local bond-slip relationship suitable for analysis and simulation is presented and calibrated in the paper.