US3701509A

US3701509A - Splicing system and jack for stressing concrete

Info

Publication number: US3701509A
Application number: US35168A
Authority: US
Inventors: Frederick M Stinton
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-05-06
Filing date: 1970-05-06
Publication date: 1972-10-31
Anticipated expiration: 1989-10-31
Also published as: FR2091230A5

Abstract

A system and hydraulic jack are disclosed for stressing concrete structures with stranded steel cable. In one embodiment, a pocket is formed in a concrete slab with two pairs of stranded cables extending in opposite directions in the slab. Each pair of cables defines a plane that is perpendicular to the plane formed by the other cable pair. One pair of cables is passed in a first direction through apertures in a splice block and secured to it with conical grips. The other pair of cables is passed through the splice block and held releasably by a removable fitting. A hydraulic jack having first and second cylinder and piston rod units is then placed over the overlapped free ends of the cable pairs to force the temporary fitting away from the splice block and thereby tension the cable pairs against each other when the cylinder and piston rod units are expanded. The jack straddles the tensioned cables and is supported solely by the cables once suitable tension is achieved to bear the weight of the jack. A second pair of conical grips is located adjacent the splice block on the pair of cables held by the temporary fitting so that when the pressure is released in the jack, the second pair of grips are seated into the splice block to secure that cable pair and complete the stressing splice. Additional tension may be achieved by contracting the jack and taking a new grip on the free ends of the second pair of cables. Since the jack straddles the tensioned cables it is easily removed or placed into operative engagement with the cable pairs by lifting.

Description

United States Patent Stinton [451 Oct. 31, 1972 SPLICING SYSTEM AND JACK FOR [72] Inventor: Frederick M. Stinton, R.R. No. 2,

Woodbridge, Ontario, Canada [22] Filed: May 6, 1970 [21] Appl. No.: 35,168

[52] US. Cl. ..254/29 A, 29/452, 52/223 L [51] int. Cl ..E04g.21/12 [58] Field 01 Search ..254/29 A; 29/452; 52/223 R, 52/223 L [56] References Cited UNITED STATES PATENTS 2,761,649 9/1956 Woolcock ..254/29 A 3,285,569 11/1966 Marr et a1. ..254/29 A 3,427,772 2/ 1969 Williams ..52/223 R 3,456,918 7/1969 Dabney et a1 ..254/29 A 3,491,431 1/1970 Pewitt ..29/452 FOREIGN PATENTS OR APPLICATIONS 78,490 1 1/1954 Denmark ..29/452 Primary Examiner-Theron E. Condon Attorney-Mann, Brown, McWilliams 8!. Bradway [5 1 7 AB TRA concrete structures with stranded steel cable. in one embodiment, a pocket is formed in a concrete slab with two pairs of stranded cables extending in opposite directions in the slab. Each pair of cables defines a plane that is perpendicular to the plane formed by the other cable pair. One pair of cables is ipassed in a first direction through apertures in a splice blocl: and secured to it with conical grips. The other ;pair of cables is passed through the splice block and held releasably by a removable fitting. A hydraulic jack having first and second cylinder and piston rod units is then placed over the overlapped free ends of the cable pairs to force the temporary fitting away from the splice block and thereby tension the cable pairs against each other when the cylinder and piston rod units are expanded. The jack straddles the tensioned cables and is supported solely by the cables once suitable tension is achieved to bear the weight of the jack. A second pair of conical grips is located adjacent the splice block on the pair of cables held by the temporary fitting so that when the pressure is released in the jack, the second pair of grips are seated into the spliceblock to secure that cable pair and complete the stressing splice. Additional tension may be achieved by contracting the jack and taking a new grip on the free ends of the second pair of cables. Since the jack straddles the tensioned cables it is easily removed or placed into operative engagement with the cable pairs by lifting.

llQliPEz 15 DQ1 1 18 Figures A system and hydraulic jack are disclosed forstressing PATENTED our 3 1 ma sum 1 0F 5 PATENTED I973 3,701,509

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SPLICING SYSTEM AND JACK FOR STRESSING CONCRETE BACKGROUND AND SUMMARY The present invention relates to the stressing of concrete structures; and more particularly it relates to the stressing of concrete slabs by applying tension to cables embedded in the structure and brought into a central pocket defined in the structure.

In the stressing (that is, the inducing of a compression stress prior to loading) of concrete structures, steel rods, individual strands or cables composed of a plurality of strands are placed in position prior to the pouring of the concrete. Protective sheaths surround the cables so that the cables may be elongated, under tension within the concrete. After the concrete is poured and set, but before its intended load is placed on it, a tension force is induced in the cables which are, anchored at each end to the concrete to induce a compression force in the concrete.

In one known system for stressing concrete slabs, individual wire rods are secured at one end in the concrete structure and brought out through an edge (usually vertical) of the slab or other structure. The ends are brought through an anchor plate; and a hydraulic jack pulls the individual rods against the edge of the concrete to tension the rods. The rods are then secured to the anchor plate by bolts or other suitable means. This method has the disadvantages of requiring workmen to work over the edge of the slab being tensioned.

Another system for stressing concrete brings a plurality of individual strands of steel into a central pocket. The strands are divided into opposing sets which extend in opposite directions in the concrete slab. Each set of strands is secured to an anchor plate after passing through apertures in the complementary anchor plate. A hydraulic jack supported by the surface of the slab then forces the two anchor plates apart to tension the opposing sets of strand; and when suitable tension is induced in the strands, a wedge is forced between the plates to hold them permanently apart. After the hydraulic jacking apparatus is contracted, the opposing sets of strand remain under tension. The jack is then removed and the pocket filled with concrete. This type of system is described in U.S. Pat. No. 3,285,569.

An improved system and apparatus for the central stressing of concrete is disclosed in my application Ser. No. 596,576 entitled A METHOD FOR CENTRAL PRESTRESSING OF CONCRETE, filed Nov. 23, 1966 now abandoned. An improved jack apparatus for use in the central stressing of concrete is disclosed in my U.S. Pat. No. 3,371,909 entitled HYDRAULIC AP PARATUS FOR APPLYING TENSION TO CABLES, issued Mar. 5, 1968.

Prior systems have been been costly in installation and difficult in assembly. For example, prior jacks used for central stressing of concrete were designed to rest on the upper surface of the concrete thus obstructing access to the assemblies for anchoring the cables to their associated anchor plates. Further, some systems employ tendons whichhave to be fabricated to the desired length at a shop that is, they were not amenable to cutting on the job.

The present system presents an improvement over prior stressing techniques in its low cost, reliability and in the facility with which it is assembled. Further, it is preferably used in combination with strand steel cable (that is, a cable comprising a plurality of individual strands twisted together into a unitary cable) which is more desirable than rigid steel rods or individual separate strands of cable.

In the present system a pocket is formed in a concrete slab with two pairs of cables extending in opposite directions within the slab. One end of each pair of cables is secured to the slab or to the other cable pair; and the free ends of each pair extend into the pocket and overlap each other. Preferably, one pair of cables is arranged to define a vertical plane; and the opposing pair of cables are arranged to project into the pocket to define a horizontal plane. The pair of cables which defines the horizontal plane (sometimes referred to as the horizontal cables) are passed in one direction through a first pair of conical apertures in a splice block and secured thereto by means of conical gripping members. The pair of cables that defines the vertical plane (the vertical cables) are passed in the opposite direction through a second pair of conical apertures in the splice block, through conical gripping members (but not at this time tightly secured thereby), and then secured at their free ends to temporary gripping members or fittings which are adapted to fit overall four cables but are secure to only the vertical cables. Thus, prior to tensioning there are afirst pair of conical grips securing the horizontal cables to the splice block, a second intermediate pair of conical grips adjacent the splice block, but not seated in it, and a pair of temporary fittings secured to the vertical cables.

An expandable hydraulic jack is then lowered into the pocket and adapted to fit over the arrangement of cables between the splice block and the temporary fittings. The jack comprises first and second doubleacting cylinder and piston rod units which straddle the cables. The cylinders are connected together by a first yoke frame which engages the splice block; and the cylinder jackets are connected together by a yoke frame which engages the temporary fittings. When the jack is expanded, the splice block and the temporary fittings are forced apart to tension the cables against each other; and when sufficient tensioning force is induced in the cables, the jack is supported solely by the cables.

A pair of fingers is arranged on the yoke frame connecting the piston rods of the jack; and it straddles the vertical cables to hold the second pair of conical gripping members near the splice block as the vertical cables are pulled through this second pair of conical grips.

Thus, as the pairs of cables are tensioned against each other, the intermediate pair of grips remains in proximity to their associated seating surfaces in the splice block by means of these fingers. When the jack has reached its full extension or when sufficient tension force has been induced in the cables, the jack may be retracted slightly so as to seat this intermediate pair of grips in the splice blocks so that the pairs of cables are spliced together through the agency of the splice block. If it is desired to further tension the cables, the jack may be completely retracted and the temporary fittings moved further along the free ends'of the vertical pair of cables. When the jack is then again expanded, the intermediate pair of grips will become slightly unseated to permit the vertical cables to pass further through the splice block; and the jack may be continued to be expanded while maintaining the intermediate pair of conical grips adjacent the splice block. The procedure may be repeated as often as is necessary to induce the proper tension in the cables; and once the jack is finally retracted, the splice becomes permanent and very reliable.. The pocket may be filled in with concrete to cover the splice after removing the jack and the temporary fittings and cutting the vertical cables, if necessary.

The present invention provides a convenient technique for stressing concrete which is easily assembled in the field. A single block is used to splice two pairs of cables together; and the arrangement of the jack with double-acting cylinder and piston rod units straddling the cables permits access to the splicing mechanism. By resting the jack solely on the tension cables, greater accuracy is achieved in effecting the desired induced tension.

Other features and advantages of the instant invention will be apparent to persons-skilled in the art from the following detailed description of a preferred embodiment accompanied by the attached drawing wherein identical reference numerals will refer to like parts in the various views.

THE DRAWING FIG. 1 is a schematic showing in plan view of a preferred layout of strand cable according to the present invention;

FIG. 2 is a perspective view of the components of the inventive system with the hydraulic jack out of the pocket;v

FIG. 3 is an exploded perspective view of the arrangement of permanent and temporary cable grips employed in the inventive system;

FIG. 4 is an exploded view of a preferred conical gripping member employed in the inventive system;

FIG. 5 is an end elevation view of a preferred splice block and the arrangement of cablesthcrein;

FIGS. 6-10 are diagrammatic illustrations of the successive steps for tensioning cables according to the invention;

FIG. 11 is a perspective view of the inventive jack taken from the underside;

FIG. 12 is a left side end view in elevation of the hydraulic jack illustrated in FIG. 11;

FIG. 13 is a vertical cross-section view of the piston rod framing member of the jack of FIG. 11 showing the retaining fingers; and

FIGS. 14-15 illustrate a use of the inventive jack for tensioning successively formed slabs with abutting edges.

' DETAILED DESCRIPTION Referring first to FIG. 1, a chain line defines the interior border of a pocket formed in a concrete slab the cable pair 12); and corresponding cables are preferably permanently secured together as at 15. The connection 15 may be performed prior to pouring the concrete slab or those ends of the cable pairs may also be formed into a pocket if the width of the U-shape is such as to cause substantial friction between the cables and concrete defining the channel in which the cables are laid. It has been found that by placing the straight portions of the cable pairs at a distance of about 2 feet, one end of each of the cables may be permanently secured so that only one splice connection need be made in a pocket for each set of four cables. When the radius of the U-shape is relatively small, a brace plate 16 may be employed to cushion the pressure of the cables against the concrete when tension force is induced in the cables. The cables are enclosed in protective sheaths (not shown) so that they may be elongated, by applied tension, within the concrete. In lieu of the looped cables as shown in full line in FIG. I, the pair of cables may be defined by a single cable looped around a plate 16' as shown in dotted lines in FIG. 1, in which case fitting '15 is omitted.

As shown in FIG. 1, the pair of cables 12 are placed directly above and beneath each other respectively so that their centers define a vertical plane; and these are the so-called vertical pair of cables. On the other hand, the centers of the cable pair 13 define a horizontal plane. It will be appreciated that, although in the preferred embodiment, the plane defined by the centers of the cable pair 12 is perpendicular to the plane defined by the centers of the cables of pair 13, other arrangements may be employed as to minimize any coupling moment induced on the final splicing block permanently fastening the two pairs together.

Turning now to FIG. 2, the pocket 10 has a rectilinear shape; and it includes first and second opposing

vertical side walls

10a and 10b out of which the free ends of the cable pairs 12 and 13 project respectively in overlapping relation. The pocket 10 may be formed by any of a number of known techniques.

The individual cables comprising the cable pair 12 are designated A and A; and the individual cables comprising the pair 13 are designated B and B respectively. Each of the cables A, A, B and B may comprise seven individual strands twisted into a unitary cable, each strand being a wire of hardened structural steel having a diameter of three thirty-seconds inch.

In FIG. 2, the cable pairs 12 and 13 are shown in a state wherein they have been tensioned to a predetermined level and permanently secured together by means of a splice block 20. This connection is referred to as a stressing splice. After the cable pairs have thus been permanently spliced together, the pocket 10 may be filled with concrete and the free ends of the cables as well as the splice block 20 permanently embedded in the concrete. In one embodiment, the splice block 20 is a disc of hardened, high-strength stainless steel having a diameter of 3% inch and a thickness of 1% inch. Splice block 20 is also shown in the lower right-hand corner of FIG. 2; and it is seen to include four separate apertures. designated respectively 22, 23, 24, and 25. Each of the apertures 22-25 is frusto-conical in shape to provide a bearing surface; and the axis of each aperture is parallel to the axis of the cylindrical side wall 21 of the splice block 20. The taper of two opposing apertures (for example, apertures 22-and 24) is opposite in direction to the taper of the other pair of apertures (23 and 25 in this example). The pairs of

cables

12 and 13 are received in opposite ones of the apertures 22-25 and pass through their respective aperture in the direction of increasing diameter of the seating aperture for reasons presently to be explained. The axes of the apertures 22-25, in transverse section, define a square centered on the axis of the cylindrical side wall 21.

A frusto-conical (or simply conical) gripping member, such as the one generally designated 26 in FIG. 2 and seen in exploded view in FIG. 4, receives each of the stranded cables and seats into one of the apertures 22-25 of the block 20 to permanently secure its associated cable to the splice block. Preferably, each gripping member includes three separate sections or wedges; and these are designated 27, 28 and 29 in FIG. 4. When placed together in abutting relation, the wedge sections 27-29 define a central cylindrical aperture of uniform diameter for receiving one of the stranded cables while at the same time providing a frusto-conical bearing surface for seating into one of the frusto-conical apertures in the splice block so as to fully engage the seating surface and thereby spread the force over an extended area. In some cases the central aperture may be frusto-conical rather than cylindrical. A split ring 30 is received in a peripheral groove generally designated 31 formed in the exterior conical seating surface of each of the wedge sections 27-29 at a location adjacent the widest exterior diameter of the grip. The ring 30 spring-biases all of the wedge sections into a closed or retracted state yet permits the expansion of the individual wedge sections to receive the stranded cable.

FIG. 5 is an end view of the splice block 20 showing the seating apertures 22 and 24 for receiving the vertical cables A and A' having an expanding diameter into the plane of the page and the

other apertures

23 and 25 having a reduced diameter into the plane of the page of the drawing. The axis of each aperture is equidistant from and parallel to the axis of the cylindrical side wall 21.

The interior cylindrical surfaces of the wedge sections may be grooved circumferentially to provide teeth for better gripping of the stranded cable.

Referring now to FIGS. 2, 11 and 12, a hydraulic jack for applying tension to the cable pairs is generally designated by reference numeral 33. The jack 33 includes first and second hydraulic cylinder and piston rod units generally designated 34 and 35. The cylinder and piston rod unit 34 includes a piston rod 36 and a cylinder jacket 37 which defines a cavity, as is well known in the art, for receiving fluid under pressure to bear against a piston head attached to the rod 36 to move the rod 36 to an expanded or extended state. Similarly, the unit 35 includes a piston rod 38 and a cylinder jacket 39; and an input conduit 40 feeds the cavities of each of the

units

33 and 34 to expand the

rods

36 and 38 in unison. The input conduit 40 is connected to a header 41; and conduits 42 and 43 feed respectively the cavities of the

units

33 and 34. A return conduit 45 is similarly connected to the rod side of the piston as a return conduit, as is also well known.

The butt ends of the

cylinder jackets

37 and 39 are rigidly connected together by a transverse frame member 46 which is integrally formed with side cylindrical rings 47 and 48 connected respectively to the butt ends of the

cylinder jackets

37 and 39. A second frame 50 similarly interconnects the neck ends of the

cylinder jackets

37 and 38 so that a solid, rigid unitary frame is formed by means of the

cylinder jackets

37 and 39 and the

frame members

46 and 50. A third frame member 51 (seen best in FIG. 11) in secured to the distal ends of the

rods

36 and 38 by means of

bolts

52 and 53 so that the rods are also rigidly connected together and move in unison when expanded and retracted. Still referring to FIG.-11, each of the

frame members

46, 50 and 51 is in the form of a yoke, defining a central aperture communicating with the exterior of the jack (designated respectively 46a, 50a, and 51a) so that the entire jack may be set upon the stranded cables and removed therefrom simply by lifting. The aperture 46a further includes a vertical groove 46b for receiving the uppermost cable A, and first and second horizontal shoulders 46c and 46d for resting respectively on the horizontal cables B and B. The aperture 500 in the framing member 50 may be identical to the aperture 46a as just described.

Referring now to FIG. 12, the aperture 51a in the yoke frame 51 for the piston rods is provided with a vertically-extending aperture for receiving the uppermost cable A, and with inclined surfaces 51b and 51c. A fork generally designated by reference numeral 56 in FIG. 13 is located inboard of the yoke-frame 51 and includes first and second vertically depending

fingers

57 and 58 spaced apart at a distance sufficient to receive both of the vertical pair of cables A and A, as seen in FIG. 12. When the jack is lowered onto the cables for tensioning, the horizontal pair of cables B and B are located within the aperture 51a but outside of the

fingers

57 and 58 thus, the

inclined surfaces

51b and 510 engage the cables B and B respectively for support when the cables are stressed.

Referring now to FIGS. 11 and 12, a brace bar 59 is secured to the outboard face of the yoke frame 51 for rigidity; and extending from its lower surface is a semicylindrical hub 60 for receiving the disc-shaped splice 20. The hub 60 is also provided with an inwardly-projecting curved lip 61 which is spaced from the surface of the splice block 20. Thus, when the jack 33 is lowered onto the cables, the splice 20 is received in a vertical direction within a cavity defined by the hub 60, lip 61, and frame 51. The hub 60 is located relative to the face of the frame 51 such that when the splice 20 is thus received, the cables A, A, B and B are located as illustrated by dashed line in FIG. 12. When the jack is thus placed on the splice block, and the splice is secured to the cables, the frame member is constrained against longitudinal movement of the cables B and B.

As seen in FIGS. 2 and 13, an aperture 65 is formed vertically in the yoke frame 51 between the fork 56 and the brace bar 59 for receiving a tool 66 (FIG. 2) having two prongs 67 and 68 spaced apart to define an aper ture 69 for permitting the tool to be placed over the cables A and A when the tool 66 is lowered into the aperture 65. The prongs 67 and 68 are tapered to form a decreasing width or wedge for reasons presently to be made clear.

Still referring to FIG. 2, two temporary seating blocks are designated 70 and 71 in the right side of the drawing; and since they may be identical, only the seating block 70 will be described in greater detail. The seating block 70'includes a base 72 defining first and second

semi-cylindrical grooves

73 and 74 for fitting over (or under as in the case of the temporary seating block 71) the pair of horizontal cables B and B. Integral with the base 72 is a cylindrical extension 75 defining a frusto-conical seating surface 76 for receiving a temporary grip which may be identical to the previously-describedv conical grip 26. The aperture defined by the cylindrical seating surface 76 commu nicates with a cylindrical aperture in the base 72 for receiving one of the pair of cables A, A. The other temporary seating block 71 is intended to be similarly fit over the other of the cable pair A, A, so that the semi-cylindrical grooves on each block cooperate to receive the horizontal cable pair B, B.

Referring now to FIG. 3, there is shown in exploded view, an assemblage of the splice block 20, the first and second pairs of permanent grip members, and the temporary seating blocks 70 and 71. As will be recalled from the description accompanying FIG. 2, the cable pair A, A define a vertical plane; and they are passed through the splice block 20 and through their associated conical seating apertures designated respectively by reference numerals 22 and 24. It will be noted that the cables are all passed through the seating apertures in the splice block in the direction of expanding diameter. Next, first and second conical gripping

members

82 and 83 of the same type as member 26 are placed over the stranded cables A and A respectively and adjacentthe seating apertures 22 and 24 respectively. The

grips

82 and 83 are the ones that will ultimately be permanently secured to the splice block; but until the desired tension is induced in the cables, these grips are not seated unless it is required to take a new hold with the temporary grips, as presently to be described.

The horizontal cables B and B are then passed respectively through their associated conical seating apertures 23 and 25 (again, the cables are passed in the direction of expanding aperture diameter). A second pair of conical grips 87 and 88 (of the same type as grip 26) are then placed over the free ends of the cables B and B respectively and into the

conical seating apertures

23 and 25 of the splice block 20. The

grips

82 and 83, together with the previously mentioned

grips

87 and 88, are the permanent grips which will remain in contact with the splice block 20 after the splice is completed.

Next, the free end of cable A is passed through the cylindrical aperture in the block 71 and the conical aperture in its associated seating member 71a. The cable A passes through the aperture of the seating member 71a in the direction of expanding diameter so that a temporary gripping member 90 may then be placed over the cables A and fitted into the seating member 71a. Similarly, the block 70 is passed over the cable A, and a temporary conical grip 91 is fitted into the aperture 76 of the seating'block 70. Grips 90 and 91 are of the same type as grip 26. The

semi-cylindrical grooves

73 and 74 cooperate with similar grooves on the temporary block 71 to receive the cables B and B respectively. Thus, prior to stressing there are a first pair of permanent grips (87 and 88) securing the ends of the horizontal cables B and B to the splicing block 20, a second or intermediate pair of permanent grips (82 and 82) received on the vertical cables A and A but not secured thereto at this time, and a pair of temporary fittings (90 and 91) secured to the vertical cables but removable. After all of the elements shown in FIG. 3 are placed on the two cable pairs as just described, the jacking apparatus 33 is lowered into the pocket 10 with the semicylindrical cavity defined by the hub 60 and lip 61 (FIG. 11) fitting over the splice block 20 and the temporary blocks and 71 engaging the vertical surface of the yoke frame 50 which faces the yoke frame 46 of the cylinder jackets.

The sequence of steps for inducing a predetermined stress in the opposing pairs of cable is illustrated in FIGS. 6-10; however, for clarity, only one of each opposing pair of cables is illustrated; and it will be understood that what is disclosed in connection with upper cable A is also true for cable A, and whatever is disclosed in connection with cable B is true for cable B, the section shown being taken through the sight line 6-6 of FIG. 5 so that the cable B is rotated to a lower position to view the sequence in one plane.

In FIG. 6, the splice block 20 is seen to receive cables A and B in overlapping relation within the pocket 10. The cables extend in opposite directions within the slab and are secured to the slab in some suitable manner (as by the U-shape in FIG. 1 or by end anchorages for four separate cables which define the cables A A and B B. The temporary seating member 70 and its associated temporary fitting 91 are shown in chain line.

Turning now to FIG. 7, the jack 33 is lowered into the position withthe yoke frame 51 (which interconnects the piston rods 36 and 38) fitting over the splice block 20.

It will be observed that all of the four cables A, A, B and B extend through the

yoke frame members

46, 50 and 51 of the jacking apparatus; and the jack may easily be removed by simply lifting it off the cables. After thejack 33 is lowered to the position shown in FIG. 7, pressurized fluid is forced into the input conduit 40 on the jack to expand it by extending the

piston rods

36 and 38 to force the temporary seating block 70 to the right in FIG. 7 and the splice block 20 to the left. This initial motion seats the permanent conical grip 87 into its associated seating aperture in the splice block 20 to secure the cable B tightly to the splice 20 and to stress the cable B. Similarly, the temporary seating block 70, upon being forced to the right, engages the conical bearing surface of the temporary fitting 91 which, in turn, bites the cable A and forces it to the right to induce a stress in it. At this time the permanent conical grip 82 is unseated because cable A is being forced in a direction toward the right and pulls the grip 82 away from its associated conical seating surface within the splice block 20.. However, the

fingers

57 and 58 of the fork 56 which is secured to the frame 51 of the jack, limits the rightward motion of the intermediate grip 82 so that it remains in proximity to its associated conical bearing surface but is permitted to slide along the extending cable A. This motion is illustrated in FIG. 8 wherein the pressurized fluid forces an expansion between the piston rod and the cylinder jackets thereby inducing equal and opposite stress in the cables A and B.

After a predetermined stress has been induced in the cables A and B (as may be determined by monitoring the pressure of the fluid in the cylinder), or the jack has reached its full extension, or the jack has expanded to a state in which it begins to interfere with the end walls of the pocket, the tool 66 (FIG. 9) is placed into the aperture 65 formed in the frame member 51; and the inclined surface 66a of the tool 66 engages the permanent (intermediate) grip 82 and forces it away from the

teeth

57 and 58 of the fork 56 and into seating engagement with its associated conical bearing surface in the splice block 20. Next, the pressure in the cylinders of the jack 33 is reduced so that the jack contracts; and as it does so, the seating member 82 becomes permanently seated in the splice block 20 to securely grip the cable A. The jack may then be removed (if proper stressing force has been induced in it) or it may be forced to a fully contracted state to take a new bite and induce further stress in the cables. If the jack is fully contracted, the lip 61 which engages the outer vertical surface of the splice block 20 will hold the piston rods so that the cylinders of the jack 33 will move to the left in.FIG. 9. The temporary gripping blocks may then be moved into contact with the frame member 50 of the jack 33; and the steps of FIGS. 7-9 repeated. That is to say, when the temporary fitting 91 is again placed into engagement with its associated conical bearing surface on the temporary seating block 70 and the jack expanded, the intermediate grip 82 holding the cable A will become unseated (and held in proximity to the splice block by means of the teeth 57 and 58) so that additional stress may be induced in the cables if desired. A number of such passes may be taken. If the temporary fitting 71 becomes secured tightly to the cable A, a tap with a hammer will loosen it. Finally, after the desired stress has been induced in the cables A and B, the jack may be removed; and the permanent splice is formed as illustrated in FIG. 10. (Again, only for one each of the two opposing sets of cables). By the time the final stress is induced, the splice block 20 usually is well toward the left of the pocket, as seen in FIG. 2.

Turning now to FIGS. 14 and 15, there is shown a modification of the inventive system wherein a number of slabs of concrete may be laid side-by-sidc in succession with adjacent edges abutting so as to form a continuation surface for use, for example, as an air strip. In FIGS. 14 and 15 elements similar to those in FIGS. 1-13 are employed but the jack is not supported on the cables solely. In FIG. 14, the splice block is designated 120; and is similar to the previously described splice block 20, having two pairs of conical bearing surfaces, each pair tapering in different directions axially of the cylindrical side wall of the splice block. Again, the one pair of cables is designated A and A, and the opposing pair of cables is designated B and B.

In FIG. 15, a concrete slab is designated by reference numeral 121. The slab may be of any predetermined length or width; and there may be as many cable pairs as are required extending through it. The cables B and B are set in position before the concrete 121 is poured and extended through first and second end bearing plates 122 and 122' which are located in opposite vertical edges of the slab 121. The cables B and B' are brought out through suitable apertures in the

plates

122 and 122. A left-side splice or anchor block similar to block 20 may be used to secure the horizontal cables B and B to the plate 122' by means of

conical grips

123 and 124 which are similar to grips 26. The splice block 120 is placed over the cables B and B with

conical grips

125 and 126 then placed over the cables. A jack 133 is placed over the cables after a temporary block 127 is attached to the free end of cables B and B by means of

temporary fittings

130 and 131. Jack 133 is similar to jack 33. It may have a rod connecting yoke frame similar to frame 51 for reacting against block 120 and a cylinder connecting frame similar to frame 50 for reacting against temporary fitting 127.

The jack 133 stresses the cables B and B by pushing against the splice block 120 which bears against the plate 122, and pushing against temporary fitting 127. When the jack is expanded, the permanent

gripping members

125 and 126 will be unseated so that the

temporary fittings

130 and 131 pull the cables. After suitable tension has been induced in the cables or it is desired to take a second pull, the hydraulic jack 133 may be retracted so that the permanent

gripping members

125 and 126 become seated in the block 120 and holds the cable under tension against the plate 122. Vertical cables A and A (for the subsequently-laid concrete slab) then may be secured to the splice block 120 by means of permanent conical grip extending in an opposite direction to the

grips

125 and 126. After the cables B and B have been tensioned, the jack is removed, the cables A and A are anchored in block 120, and a second slab is laid to the right of the slab 121 and contiguous with it. The cables A and A extend through the subsequently-laid slab and may be tensioned as described above with the jack and other components remaining identical.

Having thus disclosed in detail a preferred embodiment of the present invention, it will be apparent to persons skilled in the art that certain modifications may be made to the inventive system without departing from the principles thereof and that substitutions may be made for the structure shown while continuing to practice the invention; and it is, therefore, intended that all such modifications and substitutions be covered as they are embraced within the spirit and scope of the appended claims.

I claim:

1. A system for tensioning concrete structures comprising first and second sets of cables extending respectively in opposite directions within said structure and each cable having one end secured relative to said structure and a free end extending into a pocket in said structure, the free ends of each set overlapping in said pocket; a splice block defining a first set of apertures, each for receiving one of said first set of cables and a second set of apertures each having an expanding diameter and defining a tapered seating surface for receiving one of said second set of cables in its direction of expanding diameter; gripping means securing respectively the'free ends of said first set of cables to said splice block; a set of tapered gripping means received on said second set of cables adjacent said splice block and adapted to be seated in an associated one of said tapered apertures therein; temporary fitting means for releasably holding the free ends of said second set of cables after passing through said splice block; and expandable hydraulic means for engaging said splice block and said temporary fitting means for urging the same apart to tension said sets of cables against each other whereby when said hydraulic means is contracted to release the tension on said temporary fitting means said tapered gripping means will be seated in said tapered apertures of splice block to secure said sets of cable together, and said hydraulic means and said temporary fitting means may be removed.

2. The system of claim 1 wherein said first and second sets of cables each comprise a pair of stranded steel cables and wherein the tapered seating surfaces of said second set of apertures of said splice block and said tapered gripping members are frusto-conical in shape.

3. The system of claim 1 wherein said first-named gripping means comprises a plurality of frusto-conical grip members, one for each of said first set of cables, and wherein said first set of apertures of said splice block comprises a plurality of frusto-conical seating surfaces each receiving one of said first set of cables in the direction of expanding diameter and adapted to receive one of saidfrusto-conical grip members for permanently securing said first set of cables to said splice block.

4. The system of claim 1 wherein said hydraulic means comprises first and second cylinder and piston rod units adapted to straddle said first and second sets of cables and to extend in the direction of elongation of said cables, first yoke frame means interconnecting the rods of said units and defining a throughway for fitting over and engaging at least one of said sets of cables, said first yoke frame means adapted to engage said splice block, second yoke frame means interconnecting said cylinders of said units and defining an aperture for receiving said sets of wires and engaging at least some of said second set, and bearing surface means for engaging said temporary fitting means, whereby when said units are expanded, said first yoke means will force said splice block relative to said temporary fitting.

means to tension all of said cables and at least some of said cables will engage their associated yoke means to lift said hydraulic means when said cables are under tension.

5 Apparatus for applying tension to first and second sets of spaced cables extending in opposite directions relative to each other with free ends overlapping, the free ends of one set of cables secured to a splice block, comprising: first and second cylinder and piston rod units adapted to straddle said sets of cables, first frame means fastened to the piston rods of said units to secure the same together, second frame means fastened to the cylinders of said units to secure the same together whereby said rods move in unison relative to said cylinders when said units are expanded, seating means connected to one of said frame means, said seating means having a surface formed and adapted for receiving said splice block in seating engagement, the other frame bles whereby said jack rests on and is supported by said cables when tensioned and it may be removed after said cables have been permanently fastened together by contracting and lifting the same transverse of th direction of elongation of said cables. 4

6. The apparatus of claim 5 wherein said one of said frame means includes means for engaging said splice block to limit motion of said one frame means relative to said splicing block along the direction of elongation of said cable.

7. The apparatus of claim 6 wherein said one of said frame means engaging said splice block further includes a vertical aperture communicating the upper side of said jack with said splice block for receiving an inclined tool to tap permanent gripping means into corresponding seating apertures of said splice block.

8. The apparatus of claim 5 wherein said sets of cables comprise a first pair of cables having centers defining a vertical plane and a second pair of cables having centers defining a horizontal plane, and wherein each of said throughways of said yoke frame means comprises a gen-erally vertical groove for receiving the uppermost of said pair of cables defining said vertical plane.

9. Apparatus for applying tension to first and second sets of cables extending in opposite. directions in a concrete structure and secured at their respective remote ends to said structure and including free ends extending into a pocket in said structure in overlapping relation, the cables of each set being spaced from one another and the cables of each set defining a plane with the planes so defined intersecting one another, comprising:

first and second cylinder and piston rod units extending in a direction of elongation of said cables when placed in operative relation relative to said cables and lying on either side of said cables when in said operative position; first yoke frame means interconnecting the rods of said units and adapted to fit over the tops of said cables and including an element formed and adapted to receive a splice block secured to one of said sets of cables; said element including a flange extending transversely to the axes of said cylinders, said flange being spaced from said first frame means to provide an abutment for the side of said splice block,and second yoke frame means interconnecting the cylinders of said units and adapted to receive all of said cables in a direction perpendicular to the direction of elongation of said cables, said second frame means providing a bearing surface for engaging a temporary fitting releasably secured to the other of said sets of cables and remotely located from said element.

10. A method of tensioning a concrete structure comprising forming said slab with an open pocket and first and second sets of cables extending into said pocket out of opposing surfaces of said pocket respectively, passing said first set of cables in a first direction through a first set of apertures in a splice block, passing said second set of cables in a direction opposite to said first direction through a second set of tapered apertures in said splice block in the direction of expanding diameter of said apertures, securing said first set of cables to said splice block, passing a tapered grip on each n,

of said second set of cables adapted to be received in an associated one of said tapered apertures in said spice block, then forcing said second set of cables against said splice block by hydraulic means to pull said second pair of cables through said splice block thereby to tension all of said cables, then urging said tapered grips into contact with the seating surface of said second set of apertures, and then releasing the force exerted by said hydraulic means on said cables to thereby seat said tapered grips in their associated apertures and to connect all of said cables directly to said splice block.

11. A fluid pressure operated jack assembly for applying tension to cables embedded in concrete including a pair of fluid cylinders, a first yoke spanning said cylinders and fixed thereto, a second yoke fixed to the piston rods of said cylinders, said yokes being formed and adapted to hold said cylinders in spaced, generally parallel relation, said first and second yokes having recesses formed therein to permit passage of cables through said yokes, the recess in each yoke providing spaced abutment surfaces extending generally parallel to the axes of said cylinders, and a cable receiving groove between said abutment surfaces, said abutment surfaces being spaced from said groove by additional surfaces extending between said abutment surfaces and said groove.

12. The structure of claim 11 wherein one of said yoke includes spaced fingers in the recess therein, the space between said fingers communicating with said groove, said fingers being spaced from said abutment surfaces to allow reception of cables between said fingers and said abutment surfaces.

Claims

1. A system for tensioning concrete structures comprising first and second sets of cables extending respectively in opposite directions within said structure and each cable having one end secured relative to said structure and a free end extending into a pocket in said structure, the free ends of each set overlapping in said pocket; a splice block defining a first set of apertures, each for receiving one of said first set of cables and a second set of apertures each having an expanding diameter and defining a tapered seating surface For receiving one of said second set of cables in its direction of expanding diameter; gripping means securing respectively the free ends of said first set of cables to said splice block; a set of tapered gripping means received on said second set of cables adjacent said splice block and adapted to be seated in an associated one of said tapered apertures therein; temporary fitting means for releasably holding the free ends of said second set of cables after passing through said splice block; and expandable hydraulic means for engaging said splice block and said temporary fitting means for urging the same apart to tension said sets of cables against each other whereby when said hydraulic means is contracted to release the tension on said temporary fitting means said tapered gripping means will be seated in said tapered apertures of splice block to secure said sets of cable together, and said hydraulic means and said temporary fitting means may be removed.

3. The system of claim 1 wherein said first-named gripping means comprises a plurality of frusto-conical grip members, one for each of said first set of cables, and wherein said first set of apertures of said splice block comprises a plurality of frusto-conical seating surfaces each receiving one of said first set of cables in the direction of expanding diameter and adapted to receive one of said frusto-conical grip members for permanently securing said first set of cables to said splice block.

4. The system of claim 1 wherein said hydraulic means comprises first and second cylinder and piston rod units adapted to straddle said first and second sets of cables and to extend in the direction of elongation of said cables, first yoke frame means interconnecting the rods of said units and defining a throughway for fitting over and engaging at least one of said sets of cables, said first yoke frame means adapted to engage said splice block, second yoke frame means interconnecting said cylinders of said units and defining an aperture for receiving said sets of wires and engaging at least some of said second set, and bearing surface means for engaging said temporary fitting means, whereby when said units are expanded, said first yoke means will force said splice block relative to said temporary fitting means to tension all of said cables and at least some of said cables will engage their associated yoke means to lift said hydraulic means when said cables are under tension.

5. Apparatus for applying tension to first and second sets of spaced cables extending in opposite directions relative to each other with free ends overlapping, the free ends of one set of cables secured to a splice block, comprising: first and second cylinder and piston rod units adapted to straddle said sets of cables, first frame means fastened to the piston rods of said units to secure the same together, second frame means fastened to the cylinders of said units to secure the same together whereby said rods move in unison relative to said cylinders when said units are expanded, seating means connected to one of said frame means, said seating means having a surface formed and adapted for receiving said splice block in seating engagement, the other frame means providing a surface for engaging gripping means temporarily secured to said second set of cables, said first and second frame means being yokes defining throughways for said cables between said units, said throughways communicating with the exterior of the jack, said throughways defining spaced surfaces adapted to engage and rest upon at least two of said cables whereby said jack rests on and is supported by said cables when tensioned and it may be removed after said cables have been permanently fastened together by contracting and liFting the same transverse of the direction of elongation of said cables.

8. The apparatus of claim 5 wherein said sets of cables comprise a first pair of cables having centers de-fining a vertical plane and a second pair of cables having centers defining a horizontal plane, and wherein each of said throughways of said yoke frame means comprises a gen-erally vertical groove for receiving the uppermost of said pair of cables defining said vertical plane.

9. Apparatus for applying tension to first and second sets of cables extending in opposite directions in a concrete structure and secured at their respective remote ends to said structure and including free ends extending into a pocket in said structure in overlapping relation, the cables of each set being spaced from one another and the cables of each set defining a plane with the planes so defined intersecting one another, comprising: first and second cylinder and piston rod units extending in a direction of elongation of said cables when placed in operative relation relative to said cables and lying on either side of said cables when in said operative position; first yoke frame means interconnecting the rods of said units and adapted to fit over the tops of said cables and including an element formed and adapted to receive a splice block secured to one of said sets of cables; said element including a flange extending transversely to the axes of said cylinders, said flange being spaced from said first frame means to provide an abutment for the side of said splice block,and second yoke frame means interconnecting the cylinders of said units and adapted to receive all of said cables in a direction perpendicular to the direction of elongation of said cables, said second frame means providing a bearing surface for engaging a temporary fitting releasably secured to the other of said sets of cables and remotely located from said element.

10. A method of tensioning a concrete structure comprising forming said slab with an open pocket and first and second sets of cables extending into said pocket out of opposing surfaces of said pocket respectively, passing said first set of cables in a first direction through a first set of apertures in a splice block, passing said second set of cables in a direction opposite to said first direction through a second set of tapered apertures in said splice block in the direction of expanding diameter of said apertures, securing said first set of cables to said splice block, passing a tapered grip on each of said second set of cables adapted to be received in an associated one of said tapered apertures in said spice block, then forcing said second set of cables against said splice block by hydraulic means to pull said second pair of cables through said splice block thereby to tension all of said cables, then urging said tapered grips into contact with the seating surface of said second set of apertures, and then releasing the force exerted by said hydraulic means on said cables to thereby seat said tapered grips in their associated apertures and to connect all of said cables directly to said splice block.

12. The structure of claim 11 wherein one of said yokes includes spaced fingers in the recess therein, the space between said fingers communicating with said groove, said fingers being spaced from said abutment surfaces to allow reception of cables between said fingers and said abutment surfaces.