Precast, Prestressed Concrete Pile to Cast-in-Place Pile Cap Connections

Piles, especially when they are embedded in soft soils, may be subjected to large lateral deflections during earthquakes. This lateral deflection will result in high local curvature and moment demands at various locations along the pile length. The behavior at the pile-to-pile cap interface is of particular importance. At this location, if the pile-to-pile cap connection is assumed to be rigid, very high moment demands will result. In order for this behavior to occur as assumed, the connection must be properly designed and detailed in order to transmit lateral forces to the pile and remain essentially rigid. Here, it is assumed that the pile cap may translate but not rotate. If rotation is permitted, the demands on the connection will be reduced.

Severe pile damage has been observed in several past earthquakes. Pile design for seismic loading generally assumes that the pile can develop and maintain its moment capacity through large deformation demands. Indeed, past research has shown that well-detailed precast, prestressed piles can?develop and maintain large moments.

Although a pile may be detailed to resist large forces, it is also necessary that the pile-to-pile cap connection be designed to transfer these forces. There are only a few published investigations on the behavior of the pile-to-pile cap connection. The objective of designing the pile-to-pile cap?connection is to provide a connection capable of developing the moment demands on the pile while remaining essentially rigid. Conservatively, this requires the connection to be able to develop the theoretical capacity of the pile while remaining elastic. Only precast, prestressed piles embedded in cast-in-place pile caps are considered here.

A variety of details, as sown in the figure, have been used in the embedment region of piles in cast-in-place pile caps (Harries and Petrou, 2001). These details are described as below:

A. The pile is simply embedded in the pile cap without any treatment.

B. The exterior of the pile is roughened (for example, by using a rotary or chipping hammer) to provide an additional mechanical bond between the pile and pile cap.

C. The pile surface is grooved (cut or cast in place) to provide an additional mechanical bond.

D. Vertical dowels may be embedded in the driving head of the pile (after driving).

E. Horizontal dowels are placed through the pile, by drilling holes.

F. The immediate embedment region is confined with a hoop or square spiral reinforcement.

G. The immediate embedded region is confined with a round spiral reinforcement.

H. The strands are exposed and are embedded in the cast-in-place concrete. Often, the wires are “broomed” (separated) or twisted open to form an annular space (a so-called “olive” anchorage) to improve their development length.

Typically, embedments may include a combination of these details. Each additional detail has an associated cost in terms of both money and time.

Harries and Petrou(2001) proposed that providing a minimum embedment length equal to the width of the pile will conservatively result in an embedment having sufficient capacity to develop the pile. Furthermore, such an embedment may reasonably be assumed to provide a rigid end?condition for the top of the pile. Certainly, the pile embedment requirement may be significantly reduced for piles having a long shear span.

References:

Harries, K. A., and M. F. Petrou (2001) “Behavior of precast, prestressed concrete pile to CIP pile cap connections.” PCI J. 46 (4): 82–93.? https://doi.org/10.15554/pcij.07012001.82.92.

Arockiasamy, M., and Arvan, P.A.(2022) Behavior, "Performance, and Evaluation of Prestressed Concrete/Steel Pipe/Steel H-pile to Pile Cap?Connections", Practice Periodical on Structural Design and Construction, ASCE, 27(2), 35 pp.