US3888596A

US3888596A - Jacking anchor for post-tensioning concrete

Info

Publication number: US3888596A
Application number: US362908A
Authority: US
Inventors: William F Kelly
Original assignee: Individual
Current assignee: Individual
Priority date: 1973-05-23
Filing date: 1973-05-23
Publication date: 1975-06-10
Anticipated expiration: 1992-06-10

Abstract

A jacking anchor for use in the in-line post-tensioning of concrete. A concrete structure is provided with tendons fixed to opposed sides of the concrete structure and extending inwardly into a jacking pocket for engagement with the anchor. The anchor comprises a housing having means for receiving the ends of the tendons within the pocket. Jaws are provided within the housing for holding the ends of the tendons. A portion of the housing extends upwardly at an angle to the longitudinal axis of the housing, through which portion one of the tendons extends to permit operative engagement with a power jack before tensioning the tendons.

Description

United States Patent 1191 Kelly JACKING ANCHOR FOR POST-TENSIONING CONCRETE [76] lnventor: William F. Kelly, 100 Bellaire Dr.,

New Orleans, La. 70124 [22] Filed: May 23, 1973 [2]] Appl. No.: 362,908

[52] US. Cl. 403/314; 24/115 M; 52/223 L;

254/29 A', 339/255 1.. [51] Int. Cl. Fl6g 11/04 [58] Field of Search 24/115 R, 81 PE, 25;

403/275, 374, 211, 409, 314', 339/255 L, 273 S; 52/2232, 230; 254/29 A [56] References Cited UNITED STATES PATENTS 1,234,435 7/1917 Wood 403/374 June 10, 1975 3,698,749 10/1972 Yonkers 403/334 FOREIGN PATENTS OR APPLICATIONS 311,928 4/1919 Germany 403/211 679,221 9/1952 United Kingdom 339/273 S Primary ExaminerBernard A. Gelak Attorney, Agent, or FirmSchlesinger, Arkwright, Garvey & Dinsmore [57] ABSTRACT A jacking anchor for use in the in-line post-tensioning of concrete. A concrete structure is provided with tendons fixed to opposed sides of the concrete structure and extending inwardly into a jacking pocket for engagement with the anchor. The anchor comprises a housing having means for receiving the ends of the tendons within the pocket. Jaws are provided within the housing for holding the ends of the tendons. A

1,379,311 5/1921 Page 24/115 p n of e housing extends upwardly at an angle to 2,222,493 11/1940 Barlow 339/255 L the longitudinal axis of the housing, through which 2.834.081 5/ 95 Stumps" 24/263 DD portion one of the tendons extends to permit operative 9 Jllglem 339/273 5 engagement with a power jack before tensioning the 3,399,437 9/1968 Kelly 24 115 R tendons. 3,422,501 1/1969 Yoshimura 403/374 3,551,883 12/1970 Pasbrig 339/273 S 4 Claims, 5 Drawing Figures l/l/l/IM 44 55 ee 64 L 1 JACKING ANCHOR FOR POST-TENSIONING CONCRETE BACKGROUND AND OBJECTS In the stressing of concrete structures, it is standard practice to place cables or tendons between the forms prior to pouring concrete therein, and then elongating the tendons under tension in the concrete in order to induce a compression force in the concrete. Tensioning of the tendons is carried out by means of poweroperated jacks engaged with the tendons at one face of the concrete structure for pulling the tendon through an anchor fixed to the face of the structure.

In some installations, it is not possible to jack the tendon through the anchor at the face of the structure such as, for example, where the location of the face of the structure prevents engagement of the jack with the tendon. This necessitates the use of a pair of tendons which extend inwardly from opposite faces of the concrete structure to a pocket formed therein, where they are engaged with jacking apparatus which exerts inward tension on the tendon to produce the desired impression of the concrete structure.

Various means of effecting tensioning of tendons in this matter are illustrated in US. Pat. Nos. 2,696,040, 3,285,569, 3,405,409, 3,427,772, 3,371,909 and 3,701,509. The devices disclosed in these patents generally relate to specially designed equipment for this purpose which is unuscable for conventional jacking procedures, the apparatus further being of complex construction, thereby rendering the cost thereof excessive.

It is an object of this invention to provide a jacking anchor for use in the in-line post-tensioning concrete, the anchor engaging ends of opposed tendons in ajack' ing pocket intermediate the opposed faces of a concrete structure, and the anchor being so constructed to permit tensioning of the tendons with a conventional power jack.

Another object is to provide an anchor of the character described wherein the anchor floats within the jack ing pocket and tensioning is effected by jacking only one of the tendons through the anchor.

A further object is to provide a jacking anchor including a housing adapted to receive and grippingly engage the ends of tendons, a portion of the housing through which one of the tendons passes being angularly disposed to the longitudinal axis of the main por tion of the housing to direct one of the tendons up wardly out of the jacking pocket for engagement with a jack.

A further object is to provide an anchor of the char acter described, wherein the tendons are retained by the anchor in aligned relationship within the concrete structure, and wherein the power jack is readily engaged with the anchor for jacking the tendon.

A still further object is to provide an anchor comprising a few readily assembled parts of economic construction which may be readily inserted in place for operative engagement with the tendons.

Other objects will be apparent from the following description of the presently preferred form of the inver: tion taken in connection with the appended drawings.

SUMMARY OF THE INVENTION This invention pertains to ajacking anchor for use in the in-line post-tensioning of a concrete structure. The

anchor is lloatingly positioned in a pocket of the concrete structure intermediate the sides thereof. The anchor includes an elongated housing open at both ends to receive the ends of tendons extending into the pocket. The opposite ends of the tendons are anchored in opposed faces of the concrete structure.

A grippingjaw is positioned in one end of the housing to fixedly hold an end of one tendon. The opposite end of the housing is provided with an angular portion having a bore which communicates with an opening in the end of the housing for receiving the other tendon. The angular portion directs the tendon extending therethrough upwardly and longitudinally of the main portion of the anchor housing. A gripping member in the angular portion holds the tendon extending therethrough under tension, said tendon being readily engaged by a power jack for jacking the tendon through the anchor.

DESCRIPTION OF THE FIGURES OF THE DRAWINGS FIG, 1 is a top plan view of the anchor of the present invention illustrating its application;

FIG. 2 is a longitudinal sectional view taken along the line 22 of FIG. 1, looking in the direction of the arrows;

FIG. 3 is an enlarged side elcvational view of the present anchor per se;

FIG. 4 is a sectional view taken along the line 44 of FIG. 3, looking in the direction of the arrows, and

FIG. 5 is a sectional view taken along the line 55 of FIG. 3, looking in the direction of the arrows.

DESCRIPTION OF THE INVENTION In FIGS. 1 and 2, there is illustrated the application of the anchor of the present invention for use in connection with a concrete structure 10 having an elongated jacking pocket 12 between opposite faces thereof, which pocket is adapted to receive the ends of tendons l4 and 16. Tendons I4 and 16 extend to the opposed faces of concrete structure 10 where they are securely held by anchors l8 and 20. Anchors 18 and 20 may be of any conventional type such as illustrated in previously granted US. Pat. No. 3,524,228.

In accordance with the present invention, a jacking anchor 22 is constructed in accordance with this invention is adapted to be tloatingly positioned within jacking pocket 12 for the purpose of tensioning tendons I4 and 16 towards each other rather than the conventional means of tensioning from the face of the concrete structure.

As shown in FIG. 3, jacking anchor 22 includes an elongated housing 24 comprising a first or main portion and a second or angular portion, one end of which first portion is provided with a tendonreceiving bore 26 which extends axially of the first portion of the housing to a point approximately mid length thereof. The wall defining bore 26 is enlarged and tapered at 28, which taper is increased at 30. Taper 30 communicates with an enlarged bore 32 and the wall of housing 24 is provided with an opening 34 at this point to permit insertion of components interiorly of the housing. The interior wall of the housing adjacent enlarged bore 32 is sloped as indicated at 36 to facilitate insertion of the components to be inserted into the housing. Beyond slope wall 36, there is provided a bore 38 of uniform cross-section which is adapted to receive the terminal portion of tendon 14.

In accordance with the present invention, a chuck assembly 40 is inserted through opening 34 into the bore of the housing. As illustrated in FIGS. 3, 4 and 5, chuck assembly 40 includes a plurality of tapered jaw segments 42 which are held together by a retaining ring 44. The jaw segments are provided with teeth 46 for grippingly engaging the tendon in a well known manner. It will be noted from FIG. 3 that the outer periphcry of jaw segments 42 engage tapered portion 30 of the housing wall. A convolute spring 48 is placed within enlarged bore 32 and extends from the inner limit thereof into engagement with chuck assembly 40 for urging the leading portion of the jaw segment through wall taper 30 into engagement with tapered portion 28, thereby affording relief to the forward portion of the chuck assembly in a manner similar to that set out in my previously granted US. Pat. No. 3,524,228. By affording relief to one end of the chuck assembly, the force exerted by the chuck assembly on the tendon is distributed over a greater length of the tendon without severing any of the strands thereof.

The anchor of the present invention further includes an axial bore which extends into the housing in opposed relation to bore 26, and is adapted to receive tendon 16. By this arrangement, tendons l4 and 16 are aligned or in colinear relationshhip with each other as they enter the anchor from opposite ends. Axial bore 50 communicates with a curved bore section 52 for passage through the second portion of the housing which comprises an angular portion 54 having a bore 56 in communication with bore 52 for directing tendon l6 upwardly at an angle to the longitudinal axis of the main portion of the housing, as illustrated in FIGS. 1, 2 and 3.

Bore 56 includes a tapered wall portion 58, the angularity of which is decreased at 60.

A chuck assembly 62, similar to chuck assembly 40, is mounted within bore 56 and includes a plurality of jaw segments 64 held together by a retaining ring 66 and provided with tendonengaging teeth 68.

Angular portion 54 terminates in a jacking face 70 which is disposed at an angle to the longitudinal axis of the anchor, the angularity of the face being such that it permits facile engagement of standard jacking apparatus, such as illustrated in my previously granted US. Pat. No. 3,399,865 leaving sufficient clearance between concrete structure 10 and the jack to effect en gagement of the jack with jacking face 70.

OPERATION In use of the anchor of the present invention, after tendons l4 and 16 are suitably anchored at 18 and 20, they are drawn into jacking pocket 12. Tendon 14 is in serted into bore 26 of the anchor and tendon 16 is in serted into bore 50 at the opposite end thereof as illustrated to advantage in FIG. 3. As shown in FIG. 3, tendon i6 is drawn through angular portion 54 and beyond jacking face 70 thereof. A hydraulic jack is engaged with tendon 14 at the locus ofjacking face 70, a predetermined time after the pouring of the concrete. Upon exertion of tension on tendon 16 by the jack, chuck assembly 62 grippingly engages the tendon, thereby effecting movement of the anchor within the pocket to the right as viewed in FIG. 1, thereby equalizing the forces on tendons l4 and 16. As tendon 14 is placed under tension. teeth 46 ofjaw segments 42 grippingly engage the tendon and the jaw segments are subjected to forces tending to move the ame longitudinally of the tendon and outwardly of the housing, thereby increasing the force exerted by the teeth on the tendon. As the jaw segments move in ngagement with reduced wall taper 28, relief is thereby afforded to the forward edge of the jaw segments effecting a slight distortion of the jaw segments to distribute the forces exerted by the teeth over a larger section of the tendons length.

A similar effect is produced by chuck assembly 62 wherein the forward portions ofjaw segment 64 are afforded relief by reduced wall taper 60.

With the anchor of the present invention, therefore, posttensioning of the in-line tendons is effected by the tensioning of one of the tendons, the anchor effecting equalization of the tension of the tendons automatically. Also, by the arrangement of the parts of the present anchor, the two tendons to which the anchor is connected are maintained in aligned relationship between opposed faces of the concrete structure.

The present anchor affords a simple but effective means for jacking one tendon against the other and re quires only a few readily assembled parts which may be easily connected to the tendons by unskilled labor preparatory to the tensioning operation. A structural arrangement of the anchor additionally permits jacking to be carried out with standard jacking equipment conventionally employed for jacking at the face of the concrete structure.

The present anchor affords a means of tensioning the tendon anywhere along the span of the tendon and not necessarily near the center of the tendon span,

While there has been herein shown and described the presently preferred form of this invention, it is to be understood that such has been done for purposes of illustration only, and that various changes may be made therein within the scope of the appended claims.

What is claimed is: 1. An anchor for use in the in-line tensioning by a jack of tendons extending from the opposed faces of a concrete structure to a jacking pocket, the anchor being positioned in the jacket pocket and including:

a. an elongated housing having first and second portions, b. the opposite ends of said first portion of the housing being provided with first and second longitudinal bores along the common longitudinal axis of the first portion of the housing for receiving ends of the tendons extending from opposite faces of the concrete structure, c. said first bore terminating in the interior of the housing and said second bore having a generally unobstructed constant diameter throughout, a first movable gripping means in said first bore for holding an end of one tendon, the second portion of the housing being angularly disposed with respect to the said longitudinal axis of the first portion of the housing and extending outwardly at a predetermined angle from the outer surface of the first portion of the housing,

said angularly disposed second portion having a bore extending therethrough and in communication with said second longitudinal bore of the first portion of the housing, whereby the other of the tendons may be passed through the second longitudinal bore and the bore of the angularly disposed second portion, said second longitudinal bore communicating solely with said bore in said second portion.

g. the angularly disposed second portion terminating in a face generally transverse to said bore in said second portion and disposed at a predetermined angle to the longitudinal axis of the first portion of the housing to facilitate operative engagement with the jack, and

h. a second movable gripping means in the bore of said angularly disposed second portion for holding the other tendon extending therethrough.

2. The anchor of claim 1. wherein:

a. said first movable gripping means comprises a chuck assembly through which the one tendon passes.

b. said chuck assembly including jaw segments having tendon-engaging teeth. and

c. spring means within said first bore for urging said tendon-engaging teeth into gripping relation with the tendon.

3. The anchor of claim 2, wherein:

a. said second movable gripping means comprises a chuck assembly through which the other tendon passes,

LII

b. said chuck assembly including jaw segments having tendonengaging teeth in gripping relation with the other tendon.

4. The anchor of claim 3. wherein:

a. the walls defining said first bore of said first portion and the bore of said second portion are tapered between the limits thereof,

b. the angle of each of the tapered walls being altered intermediate their length thereby providing a first and second working wall taper c. the angularity of the second wall taper with respect to the longitudinal axis of each of said first bore of said first portion and the bore of said second portion being less than the first wall taper,

d the outer surface of the jaw segments of said first and second gripping means being tapered in the direction of the walls defining the first bore of said first portion and the bore of said second portion,

e. said jaw segments being urged under tension ex erted on the tendons into the area of the second working wall taper whereby relief is offered to the forward portion of the jaw segments, thereby distributing the forces exerted on the tendons by the gripping teeth of the jaw segments over a substan-

Claims

1. An anchor for use in the in-line tensioning by a jack of tendons extending from the opposed faces of a concrete structure to a jacking pocket, the anchor being positioned in the jacket pocket and including: a. an elongated housing having first and second portions, b. the opposite ends of said first portion of the housing being provided with first and second longitudinal bores along the common longitudinal axis of the first portion of the housing for receiving ends of the tendons extending from opposite faces of the concrete structure, c. said first bore terminating in the interior of the housing and said second bore having a generally unobstructed constant diameter throughout, d. a first movable gripping means in said first bore for holding an end of one tendon, e. the second portion of the housing being angularly disposed with respect to the said longitudinal axis of the first portion of the housing and extending outwardly at a predetermined angle from the outer surface of the first portion of the housing, f. said angularly disposed second portion having a bore extending therethrough and in communication with said second longitudinal bore of the first portion of the housing, whereby the other of the tendons may be passed through the second longitudinal bore and the bore of the angularly disposed second portion, said second longitudinal bore communicating solely with said bore in said second portion, g. the angularly disposed second portion terminating in a face generally transverse to said bore in said second portion and disposed at a predetermined angle to the longitudinal axis of the first portion of the housing to facilitate operative engagement with the jack, and h. a second movable gripping means in the bore of said angularly disposed second portion for holding the other tendon extending therethrough.

2. The anchor of claim 1, wherein: a. said first movable gripping means comprises a chuck assembly through which the one tendon passes, b. said chuck assembly including jaw segments having tendon-engaging teeth, and c. spring means within said first bore for urging said tendon-engaging teeth into gripping relation with the tendon.

3. The anchor of claim 2, wherein: a. said second movable gripping means comprises a chuck assembly through which the other tendon passes, b. said chuck assembly including jaw segments having tendon-engaging teeth in gripping relation with the other tendon.

4. The anchor of claim 3, wherein: a. the walls defining said first bore of said first portion and the bore of said second portion are tapered between the limits thereof, b. the angle of each of the tapered walls being altered intermediate their length thereby providing a first and sEcond working wall taper, c. the angularity of the second wall taper with respect to the longitudinal axis of each of said first bore of said first portion and the bore of said second portion being less than the first wall taper, d. the outer surface of the jaw segments of said first and second gripping means being tapered in the direction of the walls defining the first bore of said first portion and the bore of said second portion, e. said jaw segments being urged under tension exerted on the tendons into the area of the second working wall taper whereby relief is offered to the forward portion of the jaw segments, thereby distributing the forces exerted on the tendons by the gripping teeth of the jaw segments over a substantial length thereof.