Abstract:The bonding slip behavior between the prestressed concrete pipe pile and pile cap belongs to interfacial bond properties of new and old concrete,which is related to the strength of the concrete of pipe pile and pile cap,surface roughness of pipe pile,interfacial agent and the stress state. According to results of the pull-out test of connections between the prestressed concrete pipe pile with 1 200 mm in diameters and pile cap,the bonding mechanism,influencing factors and failure form of connections are discussed. The bond stress sharply drops along the embedded length of the pipe pile as the axial load increases,the bond effect is weakened,and relative slip occurs,which will also lead to reduction of bond stress and ingression of the maximum point of bond stress. Based on the equilibrium of free body of the pipe pile,the bond stress distribution,the magnitude of stress in pipe pile and the relative slip deformation between the concrete of pipe pile and the pile cap are theoretically analyzed. It is inferred that the bond stress is of negative exponential distribution with the position function that reflect the bonding slip relationship between the pile and pile cap at different position. And when the position function is linear,the results are similar to Mindlin¢s elastic displacement solution of bolts in form. The calculation formula is proposed based on the results of bond strength of new and old concrete,which can estimate the ultimate capacity of connections between prestressed concrete pipe pile and pile cap. The results by this formula coincides with the test data. A reasonable connection type is finally suggested for practice.