Study On The Seismic Behavior Of Exposed CFT Pile To Concrete Cap Edge Connections Subjected To Scouring

The concrete filled steel tube(CFT) pile is popular in recent years due to its many advantages such as large vertical bearing capacity, convenient construction. However, present researches mainly focus on the CFT piles or caps respectively. Research on connection joint between CFT piles and caps are relatively less, especially on the seismic performance of exposed CFT pile to concrete cap edge connections subjected to scouring. Research and earthquake disaster survey showed that scoure could cause more serious damage of the connection joint under earthquake. So this paper took the edge connections of the CFT pile to caps as the research object, and completed the following research work:(1) Six large scale exposed CFT pile to concrete cap edge connecctions were tested under low frequency cycling loads to study the influence of embeded depth CFT pile in the cap, reinforcement effect of U-shaped anchor reinforcement, the high-strength concrete filled steel tube, the hingle joint and oblique pile to cap connection joint on the seismic behavior of specimens. And the seismic performance indexes such as hysteretic curve, skeleton curve, energy dissipation capacity, ductility, bearing capacity, stiffness degradation and moment-curvature curve of section were obtained.(2) The rigid connection joint’ positive bearing capacity had slight difference, the cap had good interlocking to steel pile under positive loading and the CFT pile all failed with bending, the connection joint’s bearing capacity was determined by the CFT pile’s bending failure. Negative bearing capacity increased with the increasement of embedded depth and concrete strength, and due to the edge concrete had bad interlocking to steel pile, the bearing capacity was determined by the edge concrete. Compared to rigid connection joint, the hinge joint’s bearing capacity decreased about 50%, and its hysteresis curve was not full, having poor energy dissipation, but its ductility coefficient had a certain degree of improvement. The paper also studied the seismic behavior of the CFT pile to cap edge joint with changing embeded angle of pile under the same depth and structure condition.The failure phenomena of oblique pile to cap connection was similar to straight pile-cap joint on same condition besides individual corners were easy stress concentration, which could cause the whole structural faliure of concrete cap.But the capacity of oblique pile to cap connection show better performance than straight pile on bearing capacity and energy consumption.(3) Discussing the possible failure modes of the CFT pile to cap edge connections based on the experimental result, and infering the bearing capacity of connection joint under different failure modes accoding relevant research literature at home and abroad. The calculation results show that the connection joint of 275mm(1.0D) embedment depth failed with the formation of plastic hinges, and with the embeded depth increasing, the connection joint tend to the bending failure. This paper also proposed new faomula to calculate the failure modes of the CFT pile to concrete cap edge connections under negative loading, and the calculation result match well with the experimeantal result.(4) Pushover analysis was carried out on four specimens(CFTP-C1~CFTP-C4) using ABAQUS software. The result indicated that the simulation results were similar to those of specimens with 1.0D embeded depth, and the accuracy of positive simulation wad less than negative simulation. Stress cloud could simulate the development of two oblique cracks effectively. In general, the simulation had a certain reference function but the accuracy shuould be improved.