Pre-Tensioned Centrifugal Concrete Pile Provided with Steel Strand and Manufacturing Method

A pre-tensioned centrifugal concrete pillar, comprising

• a hollow concrete body with two ends;
• a steel cage having an axis and disposed inside the concrete body, the steel cage comprises a plurality of pre-stressed rebars disposed parallel to the axis of the steel cage, a plurality of stirrups placed around the plurality of rebars;
• and
• two plates covering the two ends of the body, each plate has an inside facing the body and an outside facing away from the body;
• wherein, the pre-tensioned pre-stressed rebars are steel strands, and at least one plate is connected to an end of each steel strand through a second clip-type connecting mechanism;
• the second clip-type connecting mechanism comprises:
• a plurality of counter recesses provided on the plate;
• a transition element matched with the counter recesses in dimension is disposed inside each counter recess, the transition element has an annular stop shoulder resting on the counter recess and a conical transition through hole, the conical transition through hole has a diameter gradually increasing from the inside toward the outside of the plate and a position of each conical transition through hole corresponds to each steel strand;
• and
• multiple clips disposed inside each transition through hole, each clip having a toothed inner surface;
• the multiple clips are spliced together to form a chock assembly for clamping each steel strand, and a peripheral surface of the chock assembly has a conical surface matching with corresponding conical transition through hole;
• a clamping hole is formed in the center of the chock assembly with the toothed inner surface for receiving and clamping a steel strand, the steel strand passes through a corresponding clamping hole and is clamped tightly;
• an outer surface of the chock assembly is flush with or is slightly lower than an outer surface of the plate.

A method for manufacturing a pre-tensioned centrifugal concrete pillar, comprising the following steps:

• (1) cutting each steel strand into a predetermined length;
• (2) manufacturing a steel cage;
• (3) inserting each end of each steel strand into a clamping hole of a chock assembly inside a conical through hole on a plate, or inside a conical transition through hole of a transition element on a corresponding plate;
• (4) mounting an anchor plate on an outside of a first of two plates through bolts, and mounting a tension plate on an outside of a second of the two plate through bolts, then, putting the steel cage into a lower half-die with a tension plate located in a die cavity of the lower half-die and attaching the anchor plate to an outside surface of one end of the lower half-die;
• (5) pouring concrete into the lower half-die, and putting an upper half-die onto the lower half-die;
• (6) stretching the steel cage by pulling the tension plate at one end until the steel strand are tensioned to a prescribed numerical value;
• at the same time, retracting the chock assemblies towards a small diameter of the conical through holes or the conical transition through hole to make each chock assembly firmly positioned inside the corresponding conical through hole or the corresponding conical transition through hole, and clamping and locking the end of each steel strand inside the clamping hole;
• (7) shaping through rotating by means of centrifugal force;
• (8) curing through steaming;
• and
• (9) removing the dies, and disconnecting the tension plate and the anchor plate from the corresponding plate to release the tension.