Method and apparatus for post-tensioning segmented concrete pilings

Information

  • Patent Grant
  • 6634830
  • Patent Number
    6,634,830
  • Date Filed
    Thursday, September 21, 2000
    24 years ago
  • Date Issued
    Tuesday, October 21, 2003
    21 years ago
  • Inventors
  • Examiners
    • Pezzuto; Robert E.
    • Mayo; Tara L.
    Agents
    • Bracewell & Patterson, L.L.P.
Abstract
A foundation repair piling made up of segments is post tensioned by a cable fed into the segments after the piling is installed. A cable anchor serves as a base segment of multiple concrete piling segments. After installing all the concrete segments on top of the base segment, a cable is inserted into passages in the segments. The cable is threaded through the completely installed piling segments and into the cable anchor. After the cable bottoms out in the cable anchor, upward tension is applied to the cable. As the cable is pulled, cable lock members in the cable anchor increase gripping pressure even as the cable tension increases, thereby solidly anchoring the end of the cable in the cable anchor. After the desired tension is reached, the cable is terminated at the top of the last segment. The tension is held by a termination lug at the top end of the cable.
Description




BACKGROUND OF THE INVENTION




1. Technical Field




The present invention generally relates to structure foundations and in particular to pilings that are utilized to support the foundations. Still more particularly, the present invention relates to segmented pilings.




2. Description of the Related Art




Many structures have been built on foundations or slabs made of concrete poured on top of soil. Constant changes in the weather and moisture levels in the soil frequently cause damage to such a foundation. In many instances, the foundation may buckle or even crack. This phenomenon occurs for a variety of reasons, including uneven changes in the water content of supporting soils, uneven compacting of soils, and uneven loads being placed on soils. Over time, uneven movement in the soils under a foundation can cause a foundation to bend or crack.




There are several methods used in repairing foundations. One of the most effective and widely used methods includes the use of one or more piles driven into the soil beneath a foundation to form one or more supports. Most of the supports are made primarily of concrete and have an overall cylindrical shape with length and diameter varying according to the soil type and the weight of the structure. For clarity, the words “piling section” and “section” signify a single cylindrical piece, and the words “pile” and “piling” signify a plurality of sequentially stacked pieces (sections) to form a single support column. A plurality of piles or pilings provide overall load support for a structure in the form of a piling system.




One of the most successful foundation repair procedures involves excavating, or partially excavating, underneath the grade beams that need to be supported or raised, placing a concrete or steel piling section in the excavated cavity underneath the grade beam, placing a construction jack between the grade beam and the piling section, and then operating the jack by hydraulic or pneumatic action to force the piling section downward into the ground while pushing against the bottom of the grade beam. Once the piling section is driven sufficiently into the ground so that its top is flush with the bottom of the excavated area, another piling section is put in place on top of the previous piling section and the jack is reactivated. Eventually, either the piling made up of the piling sections will hit a competent load bearing strata, or the combination of the skin friction between the piling and the ground and the resistance at the end of the piling will make it impossible to the piling any further.




Prior art utilizes piling systems, for foundation support, that are still in use today. For instance U.S. Pat. Nos. 2,645,090 and 3,899,891 describe inventions for assembling segmented pilings on site and then connecting the piling segments to each other with post tensioned cables. Both inventions contemplate tensioning the cable before the piling is driven. U.S. Pat. No. 5,399,055 describes a means for reinforcing a segmented piling, after the piling has been driven into the ground. U.S. Pat. No. 5,288,175 describes a system for driving segmented concrete pilings into the ground while concurrently threading the piling sections onto a cable. After the piling is driven, the cable can be tensioned.




The current art has problems. The sections are strung onto the cable above ground, generally next to the excavation. Threading each piling section onto the cable is labor intensive. Each piling section must be threaded onto the cable and moved along the length of the cable. Enough space must be available to perform the operation. Since cable lengths are typically a minimum of 25 feet, a considerable amount of working room is needed adjacent to the excavation. The ultimate length of the piling is not known before the piling is driven, and the length of precut cable sections will not match the length of the piling. If the cable is too long, material is wasted; if the cable is too short, the piling will not be properly reinforced or tensioned. Piling sections must be small enough for threading along the cable.




When driving a piling section, it is necessary to avoid placing pressure directly on the cable. This is accomplished by using a “bending template” as described by Knight, or by placing a driving ram (used to push a piling into the ground) in an off center position to avoid the cable. Using the “bending template” is labor intensive. Placing the driving ram in an off center position increases the failure rate of piling segments and can cause pilings to deviate from a vertical orientation as they are driven.




Therefore it would be desirable to provide a method and apparatus that would eliminate the specified pre-cut cable lengths for a piling with a plurality of sections. It would also be desirable to eliminate the need for a bending template. It would desirable to provide a cable anchor device that would eliminate the need to thread piling sections on the cable and still provide a positive lock on the end of the cable.




SUMMARY OF THE INVENTION




It is therefore one object of the present invention to provide a post-tensioned, segmented, concrete piling.




It is another object of the present invention to utilize a cable for post-tensioning a segmented piling system without the necessity for a bending template.




It is yet another object of the present invention to provide a cable anchor that will provide a positive lock on a cable that is utilized for post-tensioning a segmented piling system, where the cable is installed after the piling is driven.




The foregoing objects are achieved as is now described. The invention comprises a cable anchor as a base segment for multiple concrete piling segments. After installing all the concrete segments on top of the cable anchor, a cable is inserted into passages in the segments to provide post tensioning to the piling. The cable is threaded through the completely installed piling segments and into the cable anchor. After the cable bottoms out in the cable anchor, upward tension is applied to the cable. As the cable is pulled, cable locking members in the cable anchor increase gripping pressure even as the cable tension increases, thereby solidly anchoring the end of the cable in the cable anchor. After the desired tension is reached, the cable is terminated at the top of the last segment. The top end of the cable is then held in place by a termination lug.




The exterior of the cable anchor is a metal cylinder with an end plate on the bottom of the cylinder. Inside the cylinder is an insert that has a bore shaped like the interior of an hourglass with two truncated conical bore sections, wherein the smaller diameters are connected by a cylindrical bore section. The lower truncated conical section is shaped so that two half-conical cable lock members will fit tightly into said conical opening. The portion of the lower conical bore section that is not occupied by the cable lock members is filled with a conical resilient rubber pad.




In the present invention, each cable lock member consists of one half of a cone, where such cone has been split along the long axis of the cone that passes from the tip of the cone through the center of the bottom of the cone. A flat face is formed where the cone is split. A semi-cylindrical groove is cut into the flat face of each half cone such that the groove passes from the tip of the half cone down to the bottom of the half cone. The groove is cut parallel to the long axis of the half cone and passes from the tip of the half cone to the center of the bottom edge of the flat face of the half cone. Teeth are formed in the groove pointing inward to the center of the groove and downward away from the top of the cone.




When pressed together, the two lock members form a cone with a cylindrical opening that passes through the top of the cone, along the vertical axis of the cone, and out through the center of the bottom of the cone.




The upper conical opening in the insert, the cylindrical passage in the center of the insert, the lower conical opening in the insert, the cylindrical opening through the lock members, and a cylindrical opening in the resilient pad are all filled with oil, grease, or other agents designed to protect the end of the cable from corrosion. All the open space in the insert is filled with a rust inhibitor.




A cable is inserted through a channel, conduit, guide, or similar opening, that leads the end of the cable into the top opening of the cable anchor. The sloping sides of the top hollow truncated conical bore section in the insert guide the cable into the cylindrical passage, which connects the top conical bore section to the bottom conical bore section. The cable is then pushed into said cylindrical passage.




The cylindrical passage directs the end of the cable through the lock members into a cavity below the lock members. The two lock member are held in place by the resilient pad. The pad acts as a spring to hold the lock members in place and also allows the lock member to be pushed downward while a cable is being pushed through the cable lock members. The anchor is similar to a finger trap in that the harder the cable is pulled, the more firmly the anchor grips the cable.




The above as well as additional objectives, features, and advantages of the present invention will become apparent in the following detailed written description.











BRIEF DESCRIPTION OF THE DRAWINGS




The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein:





FIG. 1

is a schematic isometric view of a cable anchor in accordance with a preferred embodiment of the present invention;





FIG. 2

is a sectional view of the cable anchor of FIG.


1


.





FIG. 3

is schematic sectional view of the cable anchor of

FIG. 1

installed in is accordance with a preferred embodiment of the present invention; and





FIG. 4

is a high-level block diagram of a process for post-tensioning segmented pilings in accordance with a preferred embodiment of the present invention.











DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT




With reference now to the figures, and in particular with reference to

FIGS. 1 and 2

, a cable anchor in accordance with a preferred embodiment of the present invention, is depicted. Cable anchor assembly


100


comprises an exterior cylinder


102


having a cylindrical bore, an end plate


104


and an insert


106


. Cylinder


102


is preferably metal and is open on the top and enclosed on the bottom with end plate


104


. Insert


106


is located within the bore of cylinder


102


and comprises a cylindrical section containing two hollow truncated conical bore sections, an upper conical bore section


108


and a bottom conical bore section


110


. The larger diameter of upper conical bore section


108


is located on the top of insert


106


. The lower end of upper conical bore section


108


communicates with lower conical bore section


110


via a cylindrical passage


112


formed in insert


106


.




A pair of cable lock members


114


are installed at the lower opening of cylindrical passage


112


. Cable lock members


114


comprise two halves of a truncated cone. Each lock member


114


has an axial semi-cylindrical recess formed in a flat wall, resulting in a cylindrical passage


116


formed within cable lock members


114


when the flat walls of lock members


114


are abutted together as shown. The smaller diameter of lock members


114


is located on the upper end. The exterior of each lock member


114


slidingly mates with lower conical bore section


110


. The interior wall of cylindrical opening


116


has saw-tooth shaped teeth


118


extending inward and downward toward the axis of cylindrical opening


116


. When inserted into lower conical bore section


110


, cylindrical opening


116


aligns with cylindrical passage


112


along the vertical axis of anchor assembly


100


.




A truncated conical resilient pad


120


of neoprene or rubber is pressed between end plate


104


and the bottom of cable lock members


114


. Resilient pad


120


has a flat top that abuts the flat bottoms of lock members


114


, and a flat bottom that abuts end plate


104


. The conical side wall of resilient pad


120


mates with lower conical bore section


110


of insert


106


. Resilient pad


120


has an axial cylindrical passage


122


aligned with cylindrical passage


116


of lock members


114


. Oil, grease or any other rust inhibitor of choice fills both conical openings


108


and


110


, cylindrical passages


112


and


122


, and cylindrical passage


116


to prevent corrosion of an installed cable end.




Referring also to

FIG. 3

, cable anchor


100


is the first member installed in a piling installation. A first of several cylindrical piling segments


200


is then placed on top of cable anchor


100


. Each segment


200


has a cable passage


204


extending therethrough with a conical upper end


202


. Cable passage


204


is aligned with the hollow truncated conical bore section


108


of anchor assembly


100


. A second piling segment


200


is then installed, and cable passage


204


of the second segment is aligned with the conical upper end


202


of cable passage


204


of the first piling segment


200


. Piling segments


200


are added until the proper length is attained.




Cable


206


is then threaded downward through passage


204


in each segment until cable


206


reaches cable anchor


100


. Cable


206


is pushed through hollow truncated conical bore


108


, passage


116


of cable lock members


114


and into cylindrical hole


122


in resilient pad


120


. As cable


206


is forced through passage


116


of cable lock members


114


, downward pointing teeth


118


allow downward movement of cable


206


. Resilient pad


120


maintains an upward pressure on cable lock members


114


urging lock members


114


to move upward in conical bore section


110


. Resilient pad


120


also acts as a spring to allow lock members


114


to move downward slightly relative to insert


106


, allowing lock members


114


to separate and passage


16


to expand in diameter when cable


206


is pushed downward through the cylindrical opening


116


. When downward movement of cable


206


ceases by cable


206


contacting end plate


104


, tension will be applied. As cable


206


starts to move upward, teeth


118


and resilient pad


120


will prevent cable


206


from moving upward relative to lock members


114


. Cable lock members


114


will move upward with cable


206


, and lower conical bore section


110


causes lock member


114


to move together and forces teeth


118


into cable


206


. The diameter of passage


116


will decrease as teeth


118


embed further into cable


206


. When upward tension is applied to cable


206


, the downward pointing teeth


118


(

FIGS. 1 and 2

) grab the outer strands of cable


206


to prevent upward movement of cable


206


relative to lock members


114


. Increased tension in cable


206


produces increased pressure, by teeth


118


grabbing the cable strands and lock members


114


bearing against lower conical bore section


110


. Cable


206


is tightened to the desired tension level and then secured at the top piling segment


200


.




Referring also to

FIG. 4

, a high-level block diagram is shown of a process for post-tensioning segmented pilings in accordance with a preferred embodiment of the present invention. The process begins with step


300


, which depicts excavation of the earth below and around a foundation that is to be raised. The excavation is done to allow room for the workers to drive segments to construct the piling. The process passes to step


302


, which illustrates a cable anchor


100


, as described above, being driven into the excavated earth as a first segment. The process then passes to step


304


, which depicts adding a piling segment


200


onto the top of the previously installed cable anchor


100


. The preformed cable passages


204


in the piling segments


200


, as shown in

FIG. 3

, are aligned with each successive segment.




The process continues to step


306


, which illustrates a determination of whether there are enough segments


200


to complete the piling installation. If there are not enough segments


200


, the process returns to step


304


and repeats step


304


. If the determination is made that there are enough segments


200


installed to complete the piling installation, the process instead passes to step


308


, which depicts measuring and cutting the tensioning cable


206


for installation. The number and length of the piling segments


200


are known and the length of cable anchor


100


is known. Therefore the length of cable


206


necessary to complete the tensioning step is known.




The process then moves to step


310


, which illustrates the proper length of cable


206


being threaded through the aligned cable passages


204


in piling segments


200


and into cable anchor


100


. The process continues to step


312


, which depicts applying tension to the installed tensioning cable


206


as described above.




The process then passes to step


314


, which illustrates a termination lug (not shown) being applied to the top end of cable


206


to hold the desired tension. Any excess cable


206


is then trimmed and the process proceeds to step


316


, which depicts the step of lifting the foundation


210


, adding any shims necessary to keep the foundation at the desired level, and returning the excavated earth to the open area beneath the foundation.




Significant labor is saved since a tensioning cable is inserted into a piling in a single operation, after the segmented piling has been driven. The installer is able to cut the cable to the proper length. The excavation of the piling hole is minimized in that the only excavation necessary is that which is needed to receive the piling. The cable is threaded through the piling after the segments are completely installed, and the cable is then tensioned. Also, significantly less working room is required. The length of the piling is known before the cable is installed, allowing the cable to be cut to length on site, avoiding waste and the problems associated with cables that are too short. There is no need to slide piling sections along the cable allowing larger sizes of piling sections to be used.




Labor is also saved because it is not necessary to use a bending template while driving cylinders. There is no need to place the driving ram in an off center position to avoid a cable, which reduces the chance that a piling section will be damaged while being driven and reduces the chance that a piling will deviate from a vertical orientation while being driven.




While the invention has been particularly shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention.



Claims
  • 1. A cable anchor adapted to be located at the bottom of a foundation piling having a plurality of piling segments, each having an aligned hole for receiving a cable, comprising:a plurality of lock members, each having an outer wall and a partially cylindrical recess formed on an inner wall, the lock members being arranged around a longitudinal axis of the cable anchor so that the recesses combine to define an axially extending lock member passage for receiving an end of the cable; a cam surface that mates with the lock members so that axial movement of the lock members and the cam surface in a first direction causes the lock member passage to expand to receive an end of the cable, and axial movement of the lock members and the cam surface in a second direction causes the lock member passage to constrict to grip the end of the cable to post-tension the piling; and a resilient member that urges the lock members and the cam surface toward the second direction.
  • 2. The cable anchor of claim 1, further comprising:a plurality of teeth formed in the recesses to grip the cable.
  • 3. The cable anchor of claim 1, wherein the lock members move downward relative to the cam surface in the first direction and upward relative to the cam surface in the second direction.
  • 4. The cable anchor of claim 1, wherein the cam surface comprises a conical bore section, and the outer wall of each of the lock members slidingly mates with the conical bore section.
  • 5. The cable anchor of claim 1, wherein:the cam surface comprises a downward facing conical bore section; the outer wall of each of the lock members is partially conical; and wherein the resilient member is located below the lock members and urges the lock members upward relative to the cam surface.
  • 6. A cable anchor adapted to be located at the bottom of a foundation piling having a plurality of piling segments, each having an aligned hole for receiving a cable, comprising:a plurality of lock members, each having an outer wall and a partially cylindrical recess formed on an inner wall, the lock members being arranged around a longitudinal axis of the cable anchor so that the recesses combine to define an axially extending lock member passage for receiving an end of the cable; and a cam surface that mates with the lock members so that axial movement of the lock members and the cam surface in a first direction causes the lock member passage to expand to receive an end of the cable, and axial movement of the lock members and the cam surface in a second direction causes the lock member passage to constrict to grip the end of the cable to post-tension the piling; a cylinder having a bore; an insert located within the bore of the cylinder, the insert having an axially extending insert passage for receiving an end of the cable, the insert having a downward facing conical bore section that joins the insert passage and serves as the cam surface; wherein the outer walls of the lock members slidingly engage the conical bore section; and an elastomeric member located below the lock members and having an upper surface that urges the lock members upward in the second direction relative to the conical bore section.
  • 7. A cable anchor adapted to be located at the bottom of a foundation piling having a plurality of piling segments, each having an aligned hole for receiving a cable, comprising:a downward facing conical surface; a plurality of lock members, each having an outer wall slidingly mating with the conical surface and a partially cylindrical recess formed on an inner wall, the lock members being arranged around a longitudinal axis of the cable anchor so that the recesses combine to define an axially extending lock member passage for receiving an end of the cable; a plurality of teeth formed on the recesses for gripping the cable; and a resilient member engaging a lower side of the lock members for urging the lock members upward relative to the conical surface to reduce a diameter of the lock member passage for gripping the cable, the resilient member allowing downward movement of the lock members relative to the conical surface to expand the diameter of the lock member passage for receiving an end of the cable as it is lowered through the piling segments into the cable anchor.
  • 8. The cable anchor of claim 7, wherein the resilient member is elastomeric and has a partially conical side that mates with the conical surface.
  • 9. The cable anchor of claim 7, wherein resilient member is an elastomeric pad that bears against a lower plate, the elastomeric pad having an axially extending pad passage therethrough for receiving the end of the cable, and wherein the lower plate is adapted to be abutted by the end of the cable.
  • 10. The cable anchor of claim 7, further comprising an insert member, the conical surface being formed on a lower side of the insert member, the insert member having an axially extending insert passage that joins the conical surface for receiving an end of the cable.
  • 11. The cable anchor of claim 7, further comprising an insert member, the conical surface being formed on a lower side of the insert member, the insert member having an axially extending insert passage that joins the conical surface for receiving an end of the cable, the insert member having an upward facing conical guide surface extending upward from the insert passage.
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2646090 Kinneman et al. Jul 1953 A
3899891 Kelly et al. Aug 1975 A
4896470 Sorkin Jan 1990 A
5259703 Gillespie Nov 1993 A
5288175 Knight Feb 1994 A
5399055 Dutton, Jr. Mar 1995 A
5505561 Wilcox, III Apr 1996 A
5511909 Calandra, Jr. et al. Apr 1996 A
5802788 Ozawa et al. Sep 1998 A
6017165 Sorkin Jan 2000 A
6023894 Sorkin Feb 2000 A
6027278 Sorkin Feb 2000 A
6234709 Sorkin May 2001 B1