Experimental study on bond and anchorage of steel bars in precast concrete structures with new-to-old concrete interface

Abstract

In monolithic precast concrete structures, the connection between precast components with extended reinforcing bars usually encounters problems regarding conflicts in reinforcement placement. In particular, the problem of reinforcement conflicts is more prominent for precast slabs in China. In order to solve reinforcement conflicts encountered during practical construction, a novel connecting approach for precast members is proposed. This new approach involves setting notches at the end of precast components and anchoring reinforcing bars at the specially designed notches. This new approach ensures that the structural performance of the joints for precast members is similar to that of cast-in-place structures while minimizing the protrusion of reinforcement at the end of the member. In order to investigate the force transfer mechanism of the proposed method and its applicability to precast slabs, a total of 54 specimens with and without notches are designed and tested using pull-out experiments. Based on the experimental analysis, it is found that the existence of the new-to-old concrete interface changes the anchorage strength of steel bars in the notches. The effect of new-to-old concrete interface on the bond strength of steel bars and the desirable anchorage length of steel bars at the concrete interface are analyzed. The influences of steel bar diameter, anchorage length, concrete strength and reinforcement ratio of the concrete cover on the structural performance are discussed and compared in depth. Through the experimental results, the main factors affecting the bond strength of steel bar anchorage in the notched connection are identified. The physical mechanism of force transfer of the proposed method is developed and described. Preliminary calculation and design methods are presented to guide the practical application of the proposed method and to further facilitate the construction process of the precast structures.