Rebar-concrete bond behaviour in grouted sleeve connectors

Grouted sleeve connectors (GSCs) are commonly used in precast/prefabricated concrete structures. To ensure force transfer, connectors tend to be overdesigned, and this has a detrimental effect on the plastic deformation capacity of the connection region and the displacement ductility of the precast structure. To enable improvements in the design of precast RC connections involving GSCs, an accurate analysis of the bond behaviour of GSCs is required. This paper presents an analytical model for the local bond behaviour under the particular sleeve confinement. A representative cross-section of a GSC is treated as interconnected hollow circular tubes. Three stages are identified according to the state of the grout, namely elastic, partially cracked, and fully cracked. The confining pressure is formulated within the cross-section, and the bond stress is subsequently evaluated by a modified bond stress-slip law accounting explicitly for the confinement. Compared with traditional bond-slip laws, the model is capable of representing the evolution of confining stress in the loading process. Comparison with relevant experimental results show good agreement. A subsequent parametric study demonstrates the trends of influence of various parameters, and notably, within allowable limits, a reduction of the grout thickness tends to increase the bond strength in the connectors.