End plate for concrete piles

Abstract

A system for joining two separate spun piles by interlocking together a top end plate located at a bottom end of a first spun pile to a bottom end plate located at a top end of a second spun pile, wherein the end plates each have a plurality of segments comprising an equal number of segmental protrusions and segmental recesses.

Claims

1. An end plate system for joining spun piles together, comprising: a top end plate located at a bottom end of a first spun pile; a bottom end plate located at a top end of a second spun pile, wherein the end plates each have a plurality of segments comprising an equal number of segmental protrusions and segmental recesses; wherein each radial side of the segments is provided with tapered grooves; wherein the tapering of the tapered grooves increases as the tapered grooves extend horizontally towards a vertical center axis of either of the end plates; a plurality of tapered square pins; and a circular steel skirt; wherein mating together of the top end plate to the bottom end plate by mating one of the segmental protrusions of the top end plate to one of the segmental recesses of the bottom end plate and mating one of the segmental recesses of the top end plate to one of the segmental protrusions of the bottom end plate forms a plurality of square openings defined by outward ends of the tapered grooves so as to permit the plurality of tapered square pins to be jammed therethrough into a plurality of tapered square passageways defined by adjacent ones of the tapered grooves and in communication with the square openings so as to interlock the top end plate to the bottom end plate; wherein sloping edges are formed at radial edges of each of the top and bottom end plate segmental protrusions directly above or below the tapered square passageways so as to protect the tapered grooves from damage during impact driving; wherein outer side edges extend from an underside of each of the top and bottom end plate segmental protrusions such that a continuous circumference is formed on an outer side of the end plates and a rectangular groove traverses the circumference; wherein the rectangular groove receives a lip of the circular steel skirt.

2. The end plate system according to claim 1, wherein the top end plate is identical to the bottom end plate.

3. The end plate system according to claim 1, wherein the tapered grooves are rotated by 45 degrees relative to an axis perpendicular to a vertical axis of the spun piles.

4. The end plate system according to claim 3, wherein there is a gap of 0.5d to 0.15d between adjacent surfaces of the tapered grooves of the segmental protrusions and the segmental recesses, where d is a cross-sectional width of the square openings.

5. The end plate system according to claim 4, wherein a plane of the gap is rotated from 0-5 degrees from the vertical center axis in a direction that either decreases the gap between the adjacent surfaces of the segmental protrusions and the segmental recesses, or increases the gap between the adjacent surfaces of the segmental recesses and the segmental protrusions.

6. The end plate system according to claim 1, further comprising a plurality of prestressed steel tendon button heads, wherein the segmental protrusions and segmental recesses have indentations to accommodate the prestressed steel tendon button heads, such that the prestressed steel tendon button heads are positioned flush with or below a top surface of either of the end plates.

7. The end plate system according to claim 6, wherein the prestressed steel tendon button heads rest on tendon seats located at a distance of 2d-3d measured from a center of the tendon seats to an axis of the square pins along a perpendicular line to the axis of the square pins, where d is a cross-sectional width of the square openings.

8. The end plate system according to claim 1, wherein the sloping radial edges of the bottom end plate segmental protrusions include a declination of 20-45 degrees downwardly from a horizontal plane of a top flat surface of the bottom end plate in a direction towards the bottom end plate segmental recesses, and wherein the sloping radial edges of the top end plate segmental protrusions include an inclination of 20-45 degrees upwardly from a horizontal plane of a bottom flat surface of the top end plate in a direction towards the top end plate segmental recesses.

9. The end plate system according to claim 1, wherein either of the end plates is hot forged at about 1000° C. from carbon steel, stainless steel or any metallic material in a closed die to form the segmental protrusions and segmental recesses.

10. The end plate system according to claim 1, wherein the tapered square pins are jammed into the tapered square passageways.

11. A square end plate system for joining solid square concrete piles together, comprising: a top square end plate located at a bottom end of a first solid square concrete pile; a bottom square end plate located at a top end of a second solid square concrete pile; wherein each of the top and bottom square end plates have a plurality of segments comprising a number of segmental protrusions and segmental recesses provided with tapered grooves at internal edges of the segments; wherein the tapering of the tapered grooves increases as the tapered grooves extend horizontally towards a vertical center axis of either of the square end plates; and a plurality of tapered square pins; wherein mating together of the top square end plate to the bottom square end plate by mating one of the segmental protrusions of the top square end plate to one of the segmental recesses of the bottom square end plate and mating one of the segmental recesses of the top square end plate to one of the segmental protrusions of the bottom square end plate forms a plurality of square openings defined by outward ends of the tapered grooves so as to permit the plurality of tapered square pins to be jammed therethrough into a plurality of tapered square passageways defined by adjacent ones of the tapered grooves and in communication with the square openings so as to interlock the top square end plate to the bottom square end plate; wherein the top square end plate and bottom square end plate are not identical.

12. The square end plate system according to claim 11, wherein the top square end plate has steel bars welded to a surface thereof and the bottom square end plate has steel bars welded to a surface thereof.

13. The square end plate system according to claim 11, wherein the segment edges that form the segmental protrusions and segmental recesses are substantially straight.

14. The square end plate system according to claim 11, wherein the top end plate and the bottom end plate are cold formed.

15. The square end plate system according to claim 11, wherein the tapered square passageways are rotated by 45 degrees relative to an axis perpendicular to a vertical axis of the solid square concrete piles.

16. The square end plate system according to claim 11, wherein edges of the bottom square end plate segmental protrusions include a declination of 20-45 degrees downwardly from a horizontal plane of a top flat surface of bottom square end plate in a direction towards the bottom square end plate segmental recesses, and wherein edges of the top end plate segmental protrusions include an inclination of 20-45 degrees upwardly from a horizontal plane of a bottom flat surface of the top end plate in a direction towards the top square end plate segmental recesses.

17. The square end plate system according to claim 11, wherein there is a gap of 0.5d to 0.15d between adjacent surfaces of the tapered grooves of the segmental protrusions and the segmental recesses, where d is a cross-sectional width of the square openings.

18. The square end plate system according to claim 17, wherein a plane of the gap is rotated from 0-5 degrees from the vertical center axis in a direction that either decreases the gap between the adjacent surfaces of the segmental protrusions and the segmental recesses, or increases the gap between the adjacent surfaces of the segmental recesses and the segmental protrusions.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows the separated upper first spun pile and lower second spun pile with the attached top end plate attached to the base of the first spun pile and the bottom end plate attached to the top of the second spun pile.

(2) FIG. 2 shows the mated top and bottom spun piles with the tapered square pins inserted through the openings into the tapered square passageway.

(3) FIG. 3 shows the dissected components in the preferred embodiment of the present invention with the mated top and bottom end plates, top and bottom vertical steel tendons and top and bottom circular skirt exposed without the concrete.

(4) FIG. 4 shows the separated top and bottom end plates and top and bottom circular skirt exposed without the concrete and circular skirt.

(5) FIG. 5 shows the side view of the mated top and bottom end plates with the tapered square pins, the top and bottom indentations to the top and bottom end plates, and the top and bottom circumferential grooves to the top and bottom end plates respectively.

(6) FIG. 6 shows the detailed side view of the 45 degrees rotation of the square openings to the tapered square passageway of the mated top and bottom end plates.

(7) FIG. 7 shows the detailed side view of the square pin inserted to the opening of the square passageway created by mating of the top and bottom end plates.

(8) FIG. 8 shows the overall plan view the tapering alignment of the square passageway from 0-5 degrees towards the center of the annulus end plate

(9) FIG. 9 shows the detailed plan view the tapering alignment of the square passageway from 0-5 degrees towards the center of the annulus end plate

(10) FIG. 10 shows the detailed side view of the vertical alignment of the square passageway at 0-5 degrees to the axis of the pile with a parallel gap of 0.1d to 0.4d between the sides of top segmental protrusion and the bottom segmental recess.

(11) FIG. 11 shows the detailed side view of the gap tolerance opening of 0.5d to 1.5d between the sides of top segmental protrusion and the bottom segmental recess for ease of mating the end plates

(12) FIG. 12 shows the partial cut away 3D view of the mated the top and bottom indentations to the top and bottom end plates, the top and bottom steel tendons to the top and bottom end plates, and attachment of the top and bottom circular skirt to the top and bottom end plates respectively.

(13) FIG. 13 shows the position of section A-A and section B-B cut of the partial cut away plan view of the mated the top and bottom end plates.

(14) FIG. 14 shows the position of section A-A (FIG. 13) of the partial cut away plan view of the mated the top and bottom end plates with the inserted tapered square pins.

(15) FIG. 15 is a of section B-B (FIG. 13) showing partial cut away plan view of the mated end plates and the steel tendons with the top indentations to the top segmental recesses and protrusions, and the bottom indentations to the bottom segmental recesses and protrusions.

(16) FIG. 16 shows the finite element analysis of a mated top and bottom end plates with the inserted tapered square pins before subjecting to a tension force induced by resistance to the pile bending moment.

(17) FIG. 17 shows the finite element analysis of a mated top and bottom end plates that has opened up at the contact surface under ultimate failure due to a tension force induced by the steel tendons on to the end plates.

(18) FIG. 18 shows the compression forces derived from a horizontal square pin with a interlocking depth of 2d.

(19) FIG. 19 shows the compression forces derived from a rotated 45 degrees square pin with an interlocking depth of 1.4d, and the formula to compare the compression forces between the horizontal and rotated square pin.

(20) FIG. 20 shows the 3D view of the bottom end plates where there is a sloping edge above the tapered square pin to avoid contact with impact hammer during pile driving thus avoid compressing the dovetail groove.

(21) FIG. 21 shows the side view of the sloping edge above the tapered square pin varies from 20 to 45 degrees to the plane of the end plate.

(22) FIG. 22 shows the side view of the dimension of the dovetail groove opening in terms fraction of “d” which is the cross-section width of the square openings (4).

(23) FIG. 23 shows the top and bottom circular skirt and its embedment of one proximal end of the “L-shaped” lip into the circumferential groove in the top and bottom end plate respectively.

(24) FIG. 24 shows the mated top and bottom square end plates for a solid square piles with the tapered square pins inserted through the openings into the tapered square passageway.

(25) FIG. 25 shows the side view of the mated top and bottom square end plates with the tapered square pins, the top and bottom segmental recesses, the top and bottom segmental protrusions.

(26) FIG. 26 shows the separated top and bottom solid square piles with the tapered square pins located at the dovetail grooves of the segmental recess of the bottom end plate.

DETAILED DESCRIPTION OF THE INVENTION

(27) Referring to FIG. 1, the present invention discloses a pair of identical top end plate (1a) and bottom end plate (1b) for joining two separate spun piles by interlocking together at the top end plate (1a) located at the bottom end of the first spun pile (16a) to the bottom end plate (1b) located at the top end of the second spun pile (16b). The top annulus spun concrete (15a) and bottom annulus spun concrete (15b) is cast in place in a factory with the steel tendons (5a,5b) placed as a welded ribbed cage inside the mould, after which wet concrete poured into it and the mould is closed, following which the tendons are prestressed against the ends of the strong mould and spun to compact the concrete and allowed to cure before removing the spun pile from steel mould.

(28) As seen in FIG. 5, FIG. 12 and FIG. 23, there is a thickening at the outer segmental side edges (10a,10b) on the underside of the segmental protrusions (8a,8b) in order to create a continuous width all around the end plate whereby a deep rectangular groove (6a,6b) can traverses the circumference of the end plate (1a,1b) such that it can embed the proximal lipped edge of the circular steel skirt (11a,11b). Alternative it the edge of the circular skirt (11a,11b) must be corrugated and complex lipped edges must be formed to fit into the rectangular groove made into the sides of the end plate. Another method would be to cut the corrugated edges of the circular steel skirt (11a,11b) and fully weld to the outer side of the end plate (1a,1b) but this cumbersome and wasteful. The function of providing a circular skirt (11a,11b) around the perimeter of the end plate (1a,1b) is to prevent grout loss and acts as additional confining circumferential stress to prevent the concrete from spalling at the top of the spun pile under explosive impact of the drop hammer.

(29) In a competitive market, it will be necessary to reduce the weight of the end plates (1a,1b) as there are dead zones in the plates where it is lightly stressed, however the concentrated high prestress tendons (5a,5b) of 1100 MPa acting on the seat (9a,9b) causes high localised shear stress leading punching failure which the plate material is likely mild steel. However in this invention, the end plates (1a,1b) are hot forged in a closed die under high hydraulic force to create the segmental protrusion (8a,8b) and recesses (7a,7b) with indentations (2a,2b) that is drawn at about 30 degrees to 45 degrees to the horizontal plane whereby it create a localised deep profile to overcome the highly stressed zones in tendon seat (9a,9b) thus allowing weight savings as shown in FIG. 5 and FIG. 23.

(30) It is common that the contact surface of the hammer may not be completely flat and when pounding on the flat top surface of the end plate (1a,1b), certain asperities in the hammer surface can damage and compress the edges above the tapered square groove (14) thereby making the tapered square groove (14) to be irregular as seen in FIG. 1, FIG. 20 and FIG. 22. This problem is overcome by cutting a top sloping edge (12a,12b) on the exposed flat surface to avoid contact with the asperities at the underside of the drop hammer. In addition the angle of the top sloping edge (12a,12b) is generously angled at 20-45 degrees to the horizontal plane as seen in FIG. 22.

(31) It is normal in most of the mechanical joints in the prior art that the locking pin is likely to be a solid rod which may be tapered, some are solid tabular but placed squarely in a horizontal position into the passageway. From comparing FIG. 18 and FIG. 19, in the present invention differs in the rotating the square pin (3) by 45 degrees to the vertical axis, the edges of the segmental protrusion (8a,8b) and segmental recesses (7a,7b) have like dovetail grooves when viewed from the side elevation. This dovetail groove is formed from a concave 90 degrees edge that is rotated by 45 degrees to the axis of the spun pile (16a,16b) such that the enclosure formed by the two concave 90 degrees edge on one side by the segmental protrusion and the other side by the segmental recess, it results in a 45 degrees rotated square opening (4) on the side elevation of the end plate (1a,1b). This 45 degrees orientation gives twice the contact surface between the tapered square pin and tapered square passageway and that the critical shear cracking zone is longer and deeper into the endplate (1a,1b) therefore giving greater shear resistance to avoid the pin from dislodging from the square passageway as seen the FIG. 17. Further for a square opening (4) of width “d”, comparing FIG. 19 with the 45 degrees rotated square pin, it is noted that the depth for the segmental protrusion (8a,8b) and segmental recess (7a,7b) required is only 1.4d as compared to a minimum of 2d for the normal horizontal square pin in FIG. 18. In addition, the current invention has higher axial compression force of 283% as that for the square pin placed in the horizontal position due to the increase area of contacts between the square pin (3) and the dovetail groove (14). It is also noted that the tapering of the square pin should be about 0.5 to 2 degrees only and when the pin is jammed it, it will not be released as the friction has exceed the sliding of vertical pile under a axial load transmitted to the square pin (3). This jamming of the square pin (3) creates a large expansionary force due to the small taper angle into the tapered square passageway on the opposing contact surfaces along the dovetail grooves (14) of the top segmental protrusion (8a,8b) and the bottom segmental recess (7a,7b) which finally presses the mated flat surfaces of the end plates very tightly together hence giving a stiffer performance under a pile bending moment. This effect of this jamming force of the square pin creates a continuous prestressing across the mated end plates (1a,1b) thus preserving a continuous prestress force along the entire length of the spun pile such that the joint is invisible and can maintain bending moment and tension without initial large rotational displacements.

(32) Another key feature of the present invention is to enhanced shear transfer and reduced bending in the end plate (1a,2a) when mated and undergoing severe bending moments. The transfer of tension in the prestressed steel tendons across the connected piles is improved by placing the vertical prestressed tendons (5a,5b) in close proximity to horizontal interlocked tapered square pins (3) instead of being located at the centre of the segmental protrusions (8a,8b) or segmental recesses (7a,7b) as seen in FIG. 15 and unlike as in PI2012700742. As seen in the 5× deformed simulation of the end plate under ultimate bending stress in FIG. 17, the resulting additional tension in the vertical prestressed steel tendons will bends the end plate and open the contact between the end plates (1a,1b). In the present invention the vertical tendons (5a,5b) is placed as close to the edge of the dovetail groove (14) at about 2d-3d from the centreline of the vertical tendons (5a,5b) to the centreline of the square pins as seen in FIG. 15.

(33) Another important aspect of the invention is to make provision for sufficient tolerance during mating of the end plate (1a,1b) at the site, this is due to manufacturing inaccuracies and for ease of installation. As seen in FIG. 10, there is a large parallel gap width of about 0.1d to 0.4d on each side of the mated dovetail groove (14) when the segmental protrusion (8a) adjoins to the segmental recess (7b). In addition in FIG. 10, there is a flaring angle of about 0-5 degrees in the segmental recess (7b) to receive the segmental protrusion (8a). Thus when bringing the top end plate (1a) into the mating position with bottom end plate (1a) there is a tolerance of 0.5d to 1.5d which makes installation easy.

(34) In another adaptation of the present invention for use in a solid square concrete piles which is more common as compared to square hollow concrete piles. For a square pile without a hollow core, the dovetail groove (14) cannot be arranged to radiate out from a point as there would be congestion. In fact, the alignment of the dovetail groove (14) must avoid a sharp kink angle due to diameter of the dovetail side milling cutter otherwise a length of about half a diameter of the dovetail cutter to a sharp kink angle is obstructed.

(35) The square end plate (22a,22b) which is mounted at the ends of a solid square concrete pile (26a,26b) with steel bars (25a,25b) welded flush to the top of the square end plate (22a,22b) does not encounter the problem of the lowered tendon seat (9a,9b) in the end plate (1a,1b) for spun pile, moreover the yield stress in the reinforced concrete pile is about 355 MPa to 460 MPa which is less than half of the prestressed tendons, therefore less prone to local punching failure and there is no need for indentations in the square end plate (22a,22b). This simplifies the manufacturing of the square end plate in that it can be cold formed along straight lines. In FIG. 25 and FIG. 26, the fold lines that form the segmental protrusions (29a,29b) and segmental recesses (28a,28b) are nearly straight lines with a kink of not more than 5 degrees. The tapering of the dovetail groove (24) by 0-5 degrees is adopted similarly as illustrated in FIG. 9. One drawback is that the end plates (22a,22b) are not identical, therefore a male and female end plate must be attached to each ends of the RC pile, and it can only be mated in two orientation by rotating 180 degrees around the vertical axis. The top male square end plate (22a) of the top section concrete square pile (26a) is mated with the bottom female square end plate (22b) of the bottom section concrete square pile (26b), a tapered square passageway is formed in each side edge of the segments for insertion of the tapered square pin (23). The square skirt to surround the perimeter of the end cap can be formed from a thin plate and one proximal edge of the inner sides of the square skirt is welded to the outer side of the square end plate (22a,22b), in this way this welding it is more economical for square piles which is much smaller than spun piles.