United States Patent Vanderhurst et al.

[151 3,647,184 [45] Mar. 7, 1972

[54] APPARATUS FOR TENSIONING TENDONS

[72] Inventors: William L. Vanderhurst, 20630 Carmel Road, Saratoga, Calif. 95070; Sidney D. Kemp, 339 Vassar Ave., Berkeley, Calif. 94708

[22] Filed: Nov. 25, 1969

[21] Appl.No.: 879,780

[52] U.S. Cl. ............................ ..254/29 A, 29/452, 52/223 R [51] lnt. Cl. ................ ..E2lb 19/00, B2ld 39/00, E040 3/20 [58] Field of Search ................ ..254/29 A; 29/452; 52/223 R,

52/223 L

[56] References Cited

UNITED STATES PATENTS

3,351,320 ll/ 1 967 Harvey ............................... ..254/29 A 3,491,431 1/1970 Pewitt ................................ ..254/29A

Primary Examiner—-Othell M. Simpson Atmmey—-Warren, Rubin, Bruker & Chickering

[5 7] ABSTRACT

Apparatus including a jacking device and a tendon aligning cartridge for use therewith, and a method of tensioning a plu rality of side-by-side tendons is disclosed. The jacking device is preferably formed as a ring-type or center hole ram having a central passageway formed of sufficient dimension to accept and receive a tendon gripping pulling head, as mounted on the ends of the tendons to be tensioned, and formed with pulling head engaging gates which allow the pulling head to be en gaged by the ram for tensioning of the tendons upon axial ad~ vancement of the ram. The jacking device is preferably addi tionally provided with a second ring-type ram which is used to insure uniform actuation of an anchorage having tendon gripping wedges therein after advancement of the tensioning ram to the desired position. A cartridgelike apparatus is also preferably used with the ram in order to align and separate the tendons between the tendon anchorage and the pulling head. The cartridge may also function to assist in properly actuating the tendon anchorage into gripping engagement of the ten dons. The method includes the mounting of a pulling head onto the plurality of tendons, and preferably a tendon aligning cartridge, prior to bringing the ram into position for engage ment of the pulling head and tensioning of the tendons.

8 Claims, 6 Drawing Figures

PAIENTEBMAR 7:912 3,647, 184

sum 3 or 3

INVENTORS William L. Vanderhurst

B Sidney D. Kemp

' _\ 7 _ Attorneys

3,647,184 I .

APPARATUS FOR TENSIONING TENDONS

BACKGROUND OF THE INVENTION

The construction of prestressed concrete members often requires the use a plurality of side-by-side adjacent tendon members in order to provide the necessary prestressing force. In many instances, these tendons are necessarily con?ned to a relatively small area, and they should be simultaneously ten sioned to substantially the same axial load. This type of a requirement exists when concrete members are prestressed by either pretensioning or posttensioning, although posttension ing systems may be most commonly employed. Similarly, the requirement of simultaneously tensioning a plurality of side by-side tendons may also be encountered in structures which are not concrete.

As will be readily appreciated, the dif?culties encountered in simultaneously tensioning a plurality of tendons dramati cally increases as the number, size and tensioning forces required increases. Thus, systems which are suitable for use in tensioning 10 or 20 wires one-fourth inch in diameter may be entirely unsuited for use in simultaneously tensioning 10 to as many as 50 or more one-half inch diameter cable strands. As

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used herein, the term “tendon” shall include wires as well as . strand (cablelike tensioning elements). A variety of previous tendon tensioning apparatus and

methods have been employed in order to simultaneously ten sion a plurality of tendons. These apparatus, however, have suffered from a number of defects. One approach has been used in the tensioning of a plurality of button-head wire ten dons. A plurality of wire tendons having upset ends forming a “button-head” are placed in a tendon anchorage which is comprised of a plate having a series of openings big enough to receive the body of the wire but small enough to prevent withdrawal of the button-head from the plate. The tendons are then tensioned by use of a jacking device which includes a drawbar. The drawbar reaches down the conduit and engages the plate, usually by threads. With a jack at each end, the anchore plates are then drawn out of the conduit until they are even with hearing plates disposed at the ends of the conduit, and suitable shims are inserted between the anchor plate and the bearing plates so as to hold the anchor plate in ?xed posi tion. This system has several disadvantages. First, the use of button-heads is limited to relatively small wires. Moreover, the use of a drawbar system when applied to tendons of large diameter would require a drawbar and jacking device of prohibitively large mass. This would in turn complicate the support structure for the jacking device and the anchorage en gaging structure, which could not be simply formed as a threaded connection in light of the tremendous axial forces generated. .

Accordingly, for larger tendons the approach generally em ployed is to use a tendon gripping anchorage mounted at each end of the concrete member with, in the case of posttension ing, a conduit extending between the anchorages. After the concrete member is cast, the tendons may be inserted into the conduit member and through both anchorages so as to have a portion thereof extend beyond the anchorages. The portion extending beyond the anchorages may then be gripped by a pulling head device in order to allow axial advancement for elongation of the tendons beyond the anchorages. Once the tendons are elongated to the proper axial load, the anchorages may be set or actuated to take the full axial load and the forces on the pulling heads released. The portion of the tendons ex tending beyond the anchorages may then be sheared off by a variety of techniques. At least two types of approaches have been taken to the problem of tensioning tendons which are secured by anchorages and gripped at a point beyond the anchorages to apply the tensioning forces. One such system is illustrated in US. Pat. No. 2,371,882, to Freyssinet. In the Freyssinet tensioning system the ram or jack is brought into jacking position adjacent to the tendon anchorage. While the jack is maintained in such position, the tendons are then one by one inserted into tendon receiving slots or holes in the

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2 jacking device. In Freyssinet the slots are on the exterior peripheral surface of the ram. After insertion into the slots a tendon gripping coupler, usually consisting of a plurality of wedges, is mounted on each of the tendons, with the slots being formed for engagement of the couplers upon axial ex tension of the tendons. As will be understood since the ten-' dons may be as large as one-half inch strand or one-fourth inch bar stock, the tendons are not easily manipulated, with the difficulty of manipulation of the tendons increasing with the number of tendons to be simultaneously tensioned. Ac cordingly, substantial difficulty often results in attempts to secure all of the tendons to the jacking device for tensioning. Moreover and very importantly, during the time when the dif ficulties are being encountered in securing the plurality of ten dons to the jacking device, the jacking device must be held in place adjacent to and in alignment with the anchorage. Jacking devices often weigh as much as 2,000 to 4,000'lbs. and require a crane or other heavy equipment to be held in position next to the anchorage. Accordingly, the difficulty in securing the plurality of tendons to the jacking device results in the tying up of a substantial amount of heavy equipment and skilled equipment operators. A second type of tendon tensioning device which has been

employed consists of a center hole type ram having a heavy plate or pulling head mounted on the far side of the ram. The portions of the tendons extending beyond the tendon anchorage are inserted into openings in the front of the ram and passed axially down the central bore of the ram to cor responding openings in the pulling head or plate member at the far end of the ram. The tendons are threaded through the second openings and wedge-type couplers are then mounted on the tendons to secure them against withdrawal from the pulling head. After all of the wedges are mounted on the ten dons, they may be simultaneously tensioned. In this system, however, the jacking device must again be supported for a substantial period of time while the plurality of relatively in flexible and difficult to manage tendons must be threaded down through the center bore of the ram and tendon couplers then mounted on each tendon. Thus, very heavy and expen sive equipment and personnel are tied up while a time con suming task of manipulating a plurality of tendons is taking place. »

Accordingly, it is an object of the tendon stressing ap paratus and method of the present invention to provide an im proved jacking device construction which allows insertion and removal of the tendons with the pulling head mounted thereon to enable simultaneous tensioning of a plurality of tendons without tying up thejacking device. Another object of the method and apparatus of the present

invention is to provide a tendon alignment means which may be mounted onto the tendons prior to tensioning to maintain them in alignment with the tendon anchorage between the tendon anchorage and pulling head.

Still another object of the apparatus and method of the present invention is to provide a jacking device and tendon aligning means which is formed to insure uniform actuation of the tendon gripping anchorage once a predetermined axial load has been applied to the tendons. Another object of the apparatus of the present invention is

to provide a tendon jacking device which is formed in a manner which insures positive seating and engagement of the pulling head by the jacking device.

SUMMARY OF THE INVENTION

Brie?y, the jacking device of the present invention includes a piston and cylinder formed and mounted for relative axial reciprocation to apply loading forces in a direction of elonga tion of the tendons on tensioning, pulling head engaging means secured to the movable portion of the piston and cylinder for transfer of jacking forces to a pulling head mounted on the portions of the tendons extending beyond the anchorage, the piston and cylinder being formed with a

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passageway terminating in a pulling head receiving opening with the opening and passageway being formed and dimen sioned to allow insertion of the tendons with the pulling head mounted thereon into the passageway to a position allowing the engaging means to be brought into engagement with the pulling head for tensioning of the tendons. Hydraulic driving means operatively connected tothe piston and cylinder and formed to cause the movable portion of the piston and cylinder to be driven in a direction causing tensioning of the tendons is provided, and the jack supporting means secured to the stationary portion of the piston and cylinder for engaging a support to allow application of jacking forces to the. pulling head is also provided. The jacking device is preferably formed with a bore completely therethrough with a pulling head en gaging gate member being slidably mounted for movement transverse to the bore to allow the gate to be disposed to prevent axial withdrawal of the pulling head from the jacking device. Additionally, the jacking device is preferably provided with a second ram which is formed to allow passage of the pulling head to a position for engagement by the jacking ‘

' device and formed to insure actuation of the anchorage by uniformly urging the tendon gripping wedges in the anchorage into engagement of the tendons. ‘

Aligningv means are also provided which maintains the ten don portions in relatively fixed spaced alignment with the ten don anchorage between the tendon anchorage and the pulling head. The alignment means is formed for mounting within the center bore of the jacking device, and preferablyformed to transfer anchorage actuation forces from the jacking device to the anchorage. - >

The method of the present invention is brie?y comprised of mounting the tendons in a tendon gripping anchorage with tensioning portions of each tendon extending beyond the anchorage, mounting a tendon gripping pulling head formed to simultaneously grip the tendons for tensioning thereof on each'of the tensioning portions a spaced distance from the anchorage, thereafter positioning jacking means for engage ment of the pulling head and for support of the jacking means to allow application of jacking forces to the pulling head, en gaging the pulling head with the jacking means, and applying jacking forces to the pulling head. Additionally, a unitary or one-piece pulling head, as mounted on the tendons, is preferably inserted down the central bore of the jacking device, and engaged by pulling head engaging means provided in the jacking device. Tendon aligning means are preferably mounted on the tendons between the anchorage and the pulling head means prior to engagement of the pulling head means by the jacking device. -

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevational view, partially broken away and partially in cross section, of a tendon aligning means and pulling head constructed in accordance with the present in vention and‘ mounted on a plurality of tendons.

FIG. 2 is an enlarged end view of the tendon aligning device illustrated in FIG. I and taken along plane 2—2 thereof.

FIG. 3 is an enlarged end view of the tendon aligning device ' illustrated in FIG. 1 and taken along the plane of line 3-3 thereof. .

FIG. 4 is a side elevational view in cross section of a jacking - device constructed in accordance with the present invention.

FIG. 5 is a front end view of the jacking device. illustrated in FIG. 4.

FIG. 6 is a back end view of the jacking device illustrated in FIG. 4. ' ~

DESCRIPTION'OF THE PREFERRED EMBODIMENT Referring first to'FIG. 1, a typical arrangement of tendons

‘ and an anchorage therefore can be illustrated. Tendons'll are mounted in a member 12 to which they are to be secured. The member 12 is here illustrated asa concrete member having a bore 13 therethrough to receive the tendons and a bearing

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-4 plate 14 having a bore 16 therethrough aligned with bore 13. Thus, when posttensioning of the concrete member 12 is to be effected, bearing plate 14 may be cast into member. 12 and bore or passageway 13 may be lined with a conduit (not shown). After casting of the member 12 tendons 11 are in serted down the bore 13 until a portion 17 thereof projects ’ beyond, the bore and the anchor means or anchorage, generally designated 18, which is here seen to be comprised of an anchor plate 19 formed with frustoconical wedge receiving openings 21 therein and wedge 22. ‘ - .

Immediately adjacent to anchorage 18 it is preferable to mount a tendon aligning means, generally designated 26, which extends along portions 17- to pulling, head means, generally designated 27. Aligning means 26 can be seen to be comprised of a plurality of tubular members 28 held in' spaced fixed relation by end members 29 and 31 and by intermediate member 32. Pulling means 27 is comprised of a pulling head plate 33 formed with frustoconical bores 34 for receipt of frustoconical tendon gripping wedges 36. As illustrated in FIG. 1 the anchor plate, wedges, aligning

means and pulling head means are displaced from one another ~ for the purposes of ease of understanding. In actual'use, how ever, the assembly of FIG. 1 would be constructed as follows. First, tendons 11 would be inserted down bore 13 to be secured at an opposite end thereof by a varietylof means (not shown) including a second anchorage such as anchorage I8. Tendons 11 would be selected of a length so as to allow por‘ tion 17 to'extend beyond the bearing plate 14 a substantial distance. Anchorage 18 would then be mounted ‘on portion 17 with anchor plate 19 abutting bearing plate 14 and wedges 22 positioned in bores 21 for radial gripping of tendons 11. The tendon portion 17 would then be threaded or inserted into the respective tubes 28 in aligning means 26 until they projected beyond end 31 of the aligningmeans. End 29 of the aligning means would be placed adjacent to anchor plate 19. Finally, pulling head 27 is mounted on portion 17 adjacent to end 31 of the aligning means with tendons 11 being threaded through frustoconical bores 34 and wedges 36 mounted thereon.

In‘ the system illustrated in FIG. I there are 24 tendons which will be simultaneously tensioned, with three tendons disposed in each tube 28 and gripped by each of the sets of gripping wedges 22 and 36. As will be understood, the above outlined assembly procedure for 24 relatively in?exible ten dons can be time consuming. However, this assembly is straightforward and can be accomplished by relatively un skilled labor. Moreover and more importantly, the time used to assemble the components in FIG. 1 can all be accomplished without the need of having the tendon jacking device present. Thus, the assembly of the tendons into a 'unitized cartridge structure ready for tensioning can all be accomplished before there is any need to employ the relatively expensive, heavy, and complicated jacking equipment which required highly skilled personnel. As should be understood, the importance of being able to

preassemble the tendons into a unitized cartridge for relatively rapid engagement and tensioning by a jacking device after such assembly increases as the number of tendons increases. For example, using prior techniques for simultaneously ten sioning a plurality of tendons, groups of 24 tendons per cluster or station, as illustrated in FIG. 1, on the order of IO to l5 sta tions or clusters of tendons can be tensioned in a normal work ing day with a single ram. By comparison, using the unitized cartridge technique of the present invention and the ram or jacking device hereinafter described, as many as 40 to 50 clusters of tendons can be tensioned in a single day with a sin gle jacking device.

In order to enable the tendon and pulling head assembly above described to be easily and expeditiously engaged and the tendons tensioned, the jacking device of the present inven tion is preferably formed as a center-hole‘ram, such as is illus trated in FIGS. 4 through 6. The jacking device, generally designated 41, is formed for engagement of pulling head 27 mounted on portions 17 of the tendons. The jacking device is

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provided with a ram or piston 42 and a ram housing or cylinder 43 which is formed and mounted for relative axial reciprocation in the direction of elongation of the tendons. As illustrated in FIG. 4, the cylinder 43 is stationary and piston 42 moves from its position, as illustrated, to the right, which causes elongation of the tendons. As will also be readily un derstood, the other piston and cylinder combinations could be employed wherein the cylinder or outer housing might be movable relative to an inner stationary piston. The movable member of the ram and ram housing, in this case ram or piston 42, has pulling head engaging means, generally designated 44, secured thereto for movement therewith. The ram and ram housing are formed with a passageway 46, here illustrated as a cylindrical bore, terminating in a pulling head receiving open ing 47, with opening 47 and passageway 46 formed and dimensioned to allow insertion of tendon portions 17 with pulling head 27 mounted thereon into passageway 46 to a position allowing engaging means 44 to be brought into en gagem‘ent with pulling head 27 for tensioning of the tendons. The jacking device is also provided with hydraulic driving means 48 (illustrated in FIGS. 5 and 6) operatively connected to the piston and cylinder and formed to cause the movable portion of the piston and its housing to be driven in a direction causing tensioning of the tendons. Jack supporting means 49 secured to the stationary portion of the piston and cylinder and formed for engagement of a support to allow application of jacking forces to pulling head 27 is also provided.

In order to enhance the efficiency of jacking device 41, it is preferably that passageway 46 be formed to extend from the end 51, which faces the anchorage, completely through the jacking device to end 52, which faces away from the anchorage. Thus, the pulling head may be inserted from end 51 through the jacking device until it protrudes past end 52 which allows the jacking device to be positioned between the point of applying tensioning forces to the tendons and the ten don anchorage 18. While this construction affords additional important advantages to the jacking device of the present in vention, it is also within the scope of the present invention to form passageway 46 so that it does not entend to end 52 and to position pulling head engaging means 44 in passageway 46 at a location between end 52 and the front opening 47. As illustrated in FIG. 4, the passageway 46 terminates in a

second opening 53 and pulling head engaging means 44 is positioned beyond and adjacent to opening 53 for engagement of the pulling head 27 upon advancement to opening 53 and past engaging means 44.

In order to facilitate the rapid engagement and disengage ment of the pulling head by the jacking device of the present invention, it is preferable to construct the pulling head engag ing means with at least one gate member 56, and as illustrated, a second gate member 57, best seen in FIG. 5. Gate members 56 and 57 are formed with a pulling head engaging surface 58, which is preferably frustoconical, and are mounted for move ment in a direction transverse to the central axis of passageway 46. As illustrated in FIG. 5 gate 56 is positioned to allow pulling head 27 to be inserted past gate 56, and gate 57 has been slidably urged to superimpose surface 58 over open ing 53 to prevent withdrawal of pulling head 27 from the jacking device. This transverse movement of the gates may be achieved by providing gates 56 and 57 with tongue portions 59 and 60 (see FIG. 4), which are formed ride in tracks 61 and 62, which are in turn bolted to the jacking device by fasteners 63 and cylindrical L-shaped ?ange 64. Secured to gates 56 and 57 are manually engageable handles 66 and 67 which allow the gates to be selectively urged to open or closed posi tion. As will be understood, the opening and closing of the gates can be effected hydraulically or through other mechani cal linkage. '

As best may be seen in FIG. 4, it is preferable that the pulling head engaging means and the pulling head be formed with mating frustoconical bearing surfaces. Thus, surface 58 may be seen to be formed to engage surface 68 on the pulling head. This construction will result in the axial forces which are

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6 generated during jacking being converted into transverse forces which tend to pull gates 56 and 57 towards each other in order to maintain the gates in closed position. Thus, the frustoconical shape of the pulling head engaging means and the pulling head tends to lock the gates into interference fit with the pulling head to insure a positive engagement of the pulling head.

In order to maintain the angular alignment of piston 42 rela tive to the longitudinal axis of the bore 46, it is preferable to construct the jacking device of the present invention with an gular aligning means such as cylindrical bars 71 and 72 which are mounted for reciprocation with piston 42 through guide members 73 and 74 secured to housing 43. Bars 71 are mounted for movement with piston 42 by securement to arms 76 and 77 which in turn are fastened by fasteners 63 to the piston. As may best be seen in FIGS. 5 and 6, guide bars 71 and 72 will prevent rotation of cylinder 42 about central lon gitudinal axis 54. This kind of angular rotation is sometimes encountered when cablelike or strand-type tendons are em ployed, since elongation of these strands tend to unwind the tendons and induce twisting or turning of the jacking device. As above described, the jacking device of the present inven

tion is normally used to simultaneously tension a substantial number of tendons having diameters on the order of about one—half inch. Accordingly, the jacking device must be quite massive and provisions for manipulating the jacking device through the use of a crane or similar equipment is preferable. A center hole ram having a 400 ton loading capacity will typi cally weigh about 4,000 lbs. Accordingly, it is preferable to provide a manipulating structure such as two yoke members 78 and 79 connected by bar 81 having an opening 82 therein for receipt of a crane or hoist connection 83. Yokes 78 and 79 are secured to housing 43 by means of pins 84 and 86.

In order to support the jacking means of pins 84 and 86. In order to support the jacking device of the present inven

tion for application of tensioning forces to pulling head 27 and tendons 11, a jack stand, best seen in FIGS. 4 and 6, is secured to end 51 of the ram housing. The jack stand is here illustrated to be comprised of four L-shaped axially protruding members 87-90 having end surfaces 92 which are formed to engage anchor plate 19 or end member 29. The jack supporting means is secured to housing 43 by means of removable fasteners 93 which would allow for removal of the jacking device and the second ram, hereinafter described.

Since the tendon anchorages which are typically employed to secure a plurality of tendons in a cluster are most often formed with a plurality of wedges, such as wedges 22, it is ad ditionally preferable to form the present jacking device with means for actuating the plurality of wedges into simultaneous uniform gripping of the tendons once tendon tensioning forces have been attained. Accordingly, mounted on the front end of the jacking device of the present invention is a second piston and cylinder which is formed as a center hole or ring-type ram, generally designated I01. Ring ram 101 is formed of a cylinder 102 and movable piston 103 mounted for axial ad vancement in the direction opposite to the direction of elonga tion of the tendons. The second ram is formed to apply a load ing force against the anchorage wedges 22, preferably through plate member 29 in the alignment means, whereby the wedges 22 are uniformly and simultaneously urged into a positive gripping of tendons 11 prior to and during release of the ten sioning forces generated by main piston 42. Ring ram 301 must also be formed with a central passageway 104 which al lows advancement of the pulling head 27, tendon portion 17 and preferably aligning means 26 into the passageway 46. The hydraulic system suitable for operation of the tension

ing ram and wedge actuating ram can correspond to those typ ically employed in jacking devices heretofore used in tension ing tendons. Brie?y, the hydraulic system consists of a fluid pressure source and controlling means 48 having connections I06 and 107 to the ?rst or tensioning ram and connections 108 and 109 to the anchorage actuating ring ram. Referring to FIG. 4, it will be understood that when ?uid is forced through

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hose 109 into passageway riiZild behind piston 103, piston 103 will move from right to left while ?uid is exhausted from

vspace 113 out passageway 112 and through hose 108. Similarly, connection 106 is provided with a bore 114 which communicates with space 116 behind piston 42. Connection 107 is secured to a bore 115 which communicates with space 117. Thus, when ?uid is introduced in space 116 and evacu ated from space 117, piston 42 will be driven from its present position to the right, as viewed in FIG. 4. The reversal of the introduction of ?uid will correspondingly cause the piston to be driven in the opposite direction for relaxing of tensioning forces. Cylinder 43 and piston 42 and cylinder 102 and piston 103 are provided with suitable means for con?ning the hydraulic ?uid in the respective spaces between the pistons and cylinders, such as O-rings mounted at positions 121-124.

Referring now to FIGS. 1,2 and 3, the tendon aligning device of the present invention can be described in greater detail. In order to properly space pulling head 27 a sufficient distance from anchor plate 19 to allow jacking device 41 to be positioned between the pulling head and anchor place, tubes 28 are selected of a length to position end plates 29 and 31 to act as a spacer. Thus, if the aligning means is mounted on ten don portion 17, pulling head 27 will always be mounted on tendon portion 17, a sufficient spaced distance from anchor plate 19 so as to insure that the tensioning ram may be posi tioned betweenthe pulling head and anchorage for tensioning of the tendons. Tubes 28 act as the body of the aligning means to provide guide passageways, in this instance each passageway receiving three tendons, which extend from the anchorage to the pulling head to maintain the tendons in aligned spaced relatively ?xed relation for the full distance between the anchorage and the pulling head. This is important in order to insure that the tensioning forces applied at the remote pulling head 27 are in alignment with the axis of the tendons at the anchorage and wedges 2,2. The aligning means in effect is a cartridge for unitizing the tendons into a con veniently manipulatable and readily engageable structure for the above~described jacking device. The body portion of the cartridge, therefore, has a peripheral con?guration formed and dimensioned to allow insertion of a substantial length of the cartridge with tensioning portion 17 mounted therein into the central bore 46 of jacking device 41. As best may be seen in FIGS. 2 and 3, end member 29 is

formed with a cruciform periphery having protruding portions 131. These protrusions extend between jack stand or chairs 87-90 and are engaged on the back surface 132 thereof by the piston 103 of ring ram 101. Thus, upon urging by ring ram 101 against surface 132, plate 29 will be urged towards plate 19 forcing wedges 22, which engage the front surface of plate 29 adjacent to opening 133, into frustoconical bores 21. Bores 133 are. as may be seen in FIG. 1, suf?ciently large to allow passage of tendon portion 17 but small enough to insure en gagement of wedges 22.

Secured to the back side of plate 29 is a second plate 1341. Plate 134 is formed to have a diameter which is substantially equal to the diameter of passageway 46 whereby the aligning means is seated with plate 134 recessed into passageway 46 and plate 29 acting as a stop means against further axial ad vancement of the aligning means into the jacking device. Fasteners 136 hold plates 29 and 134 together, although other fastening devices could be used. It should be noted also that the fasteners 136 do not protrude beyond the front surface of plate 29 a sufficient distance to interfere with the seating of wedges 22 in frustoconical bores 21.

Intermediate ends 29 and 31, it is preferable to provide a plate member 32 having a diameter slightly less than the diameter of bore 46 to act as a guide means for maintaining cartridge 26 positioned substantially in the > center of passageway 46 over its entire length. Thus,- guide 32 acts as an intermediate support of tubes 28 and rides along bore 26 in the jacking device to support the tendons and cartridge at the approximate center of the passageway. End plate 31 is formed with an external or peripheral diameter which corresponds to

8 the diameter of bore 137 in gate 56. Moreover, when this type of construction is used it is preferable to remove a portion 138 of tubes 28 in order to insure that the tubes will pass inside bore 137 in the gate member. The notch portion 138 of the tubes can best be seen in FIGS. 1 and 3. The tendon aligning means of the present invention may also additionally be pro vided with stiffeners 139 welded or otherwise fastened to tubes 28 to assist in guiding the tubes and reinforcing the overall cartridge structure.

Having set forth the apparatus of the present invention, the operation of this apparatus and the method of the present in vention can be more fully described. In most instances, ten dons will be positioned in a series of parallel adjacent clusters (herein referred to as tensioning stations). Thus, if there are 50 or 100 adjacent tensioning stations, which must be ten

' sioned at one or possibly both ends of the cluster of tendons,

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the advantage of the apparatus and method of the present in vention can be readily appreciated. The concrete member 12 will be formed with a plurality of

passageways 13 to receive the clusters of tendons with a passageway at each work station. Bearing plates 14 will be cast into the member 12, and tendons, cut to predetermined lengths, will be inserted into the passageway 13 for secure ment at both ends by suitable anchorage means. When anchorage 18 is employed, tendon portion 17 will extend a substantial distance beyond bearing plate 14. Anchor plates 18 will be mounted on the tendons adjacent to and bearing upon plate 14. Then wedges 22 will be mounted on the ten dons and urged loosely into frustoconical bores 21 leaving portion 17 extending beyond the anchorage. Next, aligning means 26 will be threaded onto portion 17 with pulling head 27 being ?tted on portion 17 thereafter. Wedges 36 will ?nally be secured to the tendons and urged loosely into the bores 34 in the pulling head. It is preferable that four or ?ve stations be set up as above described with the anchor plates, aligning means and pulling head mounted thereon, with an additional ?ve to 10 stations being set up with the anchor plates only mounted thereon. The jacking device, related equipment and skilled personnel are not required for any of the steps above outlined. The stations are now ready for serial or consecutive tension

ing of the tendons by a single jacking device. The jacking device is brought into proximity with the pulling head end of one station, and the pulling head and aligning device up to plate 29 is inserted past the jack stand, ring ram 101 down bore 46 and out bore 137 until pulling head 27 is positioned beyond surface 58 of the jack engaging means. Gates 56and 57 are open to allow passage of the pulling head therebeyond and closed after such passage to prevent withdrawal of the pulling head. The jack stand front surfaces 92 pass beyond plate 29 through the spaces between projections 131 and en gage anchor plate 19, while ring ram piston 103 will engage plate 29. Wedges 36 are then urged tightly into bores 34 to grip tendon portion 17, and hydraulic ram driving means 48 actuated to drive piston 42 from its position in FIG. 4 to the right, causing axial elongation of tendons 17. The axial loading can be measured by means of the elongation of tendons l7 and checked against the ?uid pressure in the hydraulic actuat ing means 48. When the predetermined elongation and axial loading is achieved, ring ram 101 is actuated and piston 103 drives plate 29 into wedges 22 causing them to be urged into positive locking engagement with tendons 17, whereupon piston 42 may be driven toward the anchorage releasing the tensioning forces which are now taken up or assumed by wedges 22 in anchorage 18. The gates may then be opened and the jacking device pulled back 01? the cartridge and moved to the next station whereupon the procedure above described is repeated. After one or two stations are tensioned, the pulling head and tendon aligning means at the ?rst stations can be removed and mounted at a subsequent tensioning sta tion ahead of the progress of the ram. Thus, as the ram is being employed to tension tendons, new cartridges and pulling heads can be mounted on still further stations so that the

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jacking device is constantly being used in tensioning tendons and not being held in the ?eld while these tendons are threaded into thejack or rain,

It should be noted that seating plate 29 acts to prevent alig ning means 26 from axially traveling in the direction of elon gation of the tendons during the tensioning process.

in most concrete structures, portions 1”] will be sheared off tendons ill at a position adjacent to wedges 2i and the entire anchorage may be subsequently cast into concrete. This shear ing operation can be accomplished by mechanical cutting devices or by burning the portions off through the use ‘of a cutting torch. The construction of the apparatus of the present invention

can be readily accomplished through the use of standard prac tices. The ram is preferably constructed from alloy steels which are commonly presently employed in such jacking devices, with the use of standard auxiliary hydraulic equip ment to effect seals of the cylinder and pistons. The cartridge structure of the aligning device of the present invention can be formed of a plurality of tubes, preferably aluminum for ease in manipulation, which are secured together by welding or other fasteners with plates and gussets which are also aluminum. Wedge eating plate 29, however, is preferably formed of steel (1040) in order to increase its wear resistance during engage ment of wedges 22.

For a 400-ton, iii-inch stroke center hole ram weight will vary between approximately 3,000 and 4,000 lbs. and the car tridge length will be approximately 40 to 50 inches. Center hole 46 may be about 10 inches in diameter and the internal diameter of the tubes 28 may be about 1% inches. As will be readily understood, these dimensions may vary considerably with the size of the ram and the number of tendons which are to tensioned. As the number of tendons to be tensioned in creases, the diameter of the tensioning station may also in crease and require a larger center hole in the ram. The pulling head is preferably formed of the same type of high-strength steel as is the anchorage and pulling head engaging gatev What is claimed is: 1. A jacking device for use with a tendon gripping pulling

head means in simultaneously tensioning a plurality of tendons to be secured by an anchor means, said tendons having por tions extending beyond said anchor means and said pulling head means being mounted on said portions, comprising:

a. a ram and ram housing formed and mounted for relative axial reciprocation; said ram and ram housing being formed with a passageway extending therethrough and terminating at one end in a pulling head receiving open ing and at a second end in a second opening, said ?rst named opening, said passageway and said second opening being formed and dimensioned to allow insertion of said tendons with said pulling head means mounted thereon through said ?rst-named opening, down said passageway and beyond said second opening;

b. pulling head engaging means secured to the moveable member of said ram and ram housing and positioned ad jacent and beyond said second opening, said engaging means being formed with at least one gate member having a pulling head engaging surface, said gate member being mounted for movement in a direction allowing passage of said pulling head means through said second opening to a position superimposing said surface over said second opening for engagement with said puiling head means to selectively prevent and allow withdrawal of said pulling head means from said jacking device and to releasably en gage said pulling head means for the transfer of jacking forces thereto;

c. hydraulic driving means operatively connected to said ram and ram housing and formed to cause the moveable member of said ram and ram housing to be driven in a direction causing tensioning of said tendons; and jack supporting means secured to the stationary member of said ram and ram housing for engagement of a support member to allow application of jacking forces to said pulling head means.

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2. in a jacking device for the tensioning a plurality of ten dons having a pulling head mounted thereon securing said ten dons for simultaneous tensioning, said jacking devices includ ing a ram and ram housing formed and mounted for relative reciprocation and formed with a passageway therethrough, hydraulic driving means operatively connected to said ram and ram housing to cause relative reciprocation thereof, and jack supporting means formed to support said jacking device for relative reciprocation of said ram and ram housing and ap plication of tensioning forces to said tendons, the improve ment comprising:

a. said passageway being formed and dimensioned for receipt and passage of said tendons with said pulling head mounted thereon down said passageway to a positionfor engagement of said pulling head by said jacking device;

b. pulling head engaging means secured to a moveable member of said ram and ram housing and positioned ad jacent said passageway, said pulling head engaging means being formed for passage of said tendons and pulling head there beyond to said position, and said pulling head en gagement means being formed for engagement of said pulling head and application of jacking forces thereto upon relative movement of said pulling head and said pulling head engaging means from a position allowing passage of said tendons and pulling head beyond said pulling head engaging means to a position- preventing withdrawal of said tendons and said pulling head from said passageway.

3. A jacking device as de?ned in claim i for use with a pulling head means having a bearing plate member with a peripheral concaveiy formed frustoconical bearing surface wherein,

said pulling head engaging surface is formed as a convexly protruding frustoconical surface formed to mate with said bearing surface.

4. A jacking device as defined in claim i wherein, said rain and ram housing are provided with angular align ment means for guiding the movable member of said ram and ram housing in a predetermined angular alignment relative to the central axis of said passageway during reciprocation thereof.

5. Ajacking device as defined in claim )1 and a second ram formed and mounted for reciprocation relative to the stationa ry member of said first ram and ram housing, hydraulic ram driving means operatively connected to said second ram, said second ram and hydraulic means being formed for applying a loading force in a direction opposite to the direction of elon gation of said tendons, said second ram being positioned on the end of said first ram and ram housing facing said anchor means upon mounting of said jacking device on said tendons and being formed to allow said tendons and pulling head means to be advanced into said passageway, said second ram being further formed to urge a portion of said anchor means into gripping engagement of said tendons prior to release of tensioning forces generated by said ?rst ram and ram housing.

6. Ajacking device as defined in claim 5 wherein, said second ram is formed with a bore therethrough, said

bore being positioned in alignment with said passageway during reciprocation of said second ram and being dimen sioned for advancement of said tendons and pulling head means therethrough.

7. A jacking device as defined in claim 11 for use with a ten don aligning means demountable positioned on said tendon portions between said anchor member and said pulling head means wherein,

said passageway is formed and dimensioned to receive said tendons with said aligning means mounted thereon, and said jacking device is provided with anchorage actuating means formed to engage said aligning means to urge a portion thereof into engagement with said anchor means to insure actuation of said anchor means into gripping en gagement of said tendons.

3. Ajacking device as de?ned in claim 7 wherein, said anchorage actuating means is provided by a center hole ram axially aligned with said passageway.