Performance of Steel Pipe Pile-to-Concrete Cap Connections Subject to Seismic or High Transverse Loading: Phase III Confirmation of Connection Performance

The efficacy of a new procedure developed by the Montana Department of Transportation (MDT) to design concrete filled steel tube (CFT) pile to concrete pile cap connections was investigated in this project. A series of CFT piles embedded in a concrete pile cap is a desirable system to support small to mid-span bridges. Traditional methods for designing the connection between the CFT piles and pile cap often lead to congested and complex reinforcing schemes, and this complexity can limit the use of this support system. MDT has developed a simple design method for this connection utilizing a new reinforcing scheme that greatly simplifies the design and construction of this connection. The new reinforcing scheme includes U-shaped reinforcing bars that encircle the embedded CFT piles within the cap that counteract the moment related demands introduced by the embedded pile under lateral load events. The efficacy of the MDT design method implementing the new reinforcing scheme, which was developed from previous research and testing completed by Montana State University, is evaluated in this research. In particular, this report presents the details and results of tests on six half-size connections designed to exercise various design parameters in the MDT design guide. In these tests four primary limit states were observed: (1) formation of a plastic hinge in the concrete-filled steel tube, (2) crushing of the concrete surrounding the embedded pile, (3) yielding of the longitudinal reinforcement, and (4) splitting failure of the concrete cap. The MDT design methodology addresses all of these limit states fairly accurately. Some possible improvements to MDT’s methodology suggested by the test results are presented and discussed.