Effects of spiral confinement to the bond behavior of deformed reinforcement bars subjected to axial tension

• An alternative grouted connection using a spiral combined with splice bars improves the bond strength of connected main rebars significantly.
• The spiral acts as the shear key and confinement to the grout, which subsequently provides good interlocking mechanism and bond strength between the grout and connected main rebars.
• The influence of spiral diameter is more dominant than the spiral pitch distance, in providing more effective confinement and higher bond strength.

When grouted pipe splice connections are employed, the structural performance of the connected precast concrete components is significantly influenced by the bond behavior between the main reinforcing bars and the surrounding grout. Owing to this important characteristic, the bond behavior, in particular the local bond-stress slip relationship and the bond strength, of the main steel reinforcement bars embedded in grout needs to be investigated accordingly. This paper presents the bond behavior of main deformed steel reinforcement bars confined by a grouted spiral connection. A total of 36 pullout specimens were tested under increasing axial tensile load to investigate the effects of spiral confinement to the connected main steel bars. Parameters covered in this study were spiral diameter and spiral pitch distance. The experimental results showed that the spiral configurations influence the bond performance due to the effect of confinement generated by the spiral diameter and pitch distance. As compared to spiral pitch distance, the spiral diameter provides more dominant confinement effect which subsequently increases the bond strength significantly.