US3653634A

US3653634A - Stepwise-operating power apparatus

Info

Publication number: US3653634A
Application number: US83534A
Authority: US
Inventors: Rene Bechi
Original assignee: GRANDS SOC D
Current assignee: GRANDS SOC D
Priority date: 1970-10-23
Filing date: 1970-10-23
Publication date: 1972-04-04
Anticipated expiration: 1989-04-04

Abstract

Hydraulic power apparatus operating stepwise and comprising essentially a body having arranged therein a fixed retaining device, an annular piston and a movable traction device connected to the tubular rod of said piston, said fixed retaining device and said movable traction device comprising clamping members adapted to grip and release by turn cables, rods or the like, the clamping members of one device gripping the cables when the clamping members of the other device release said cables, and vice-versa. The invention may be used either as a traction ram when it is held in a fixed position for exerting a tractive effort, for example on a cable for prestressing a concrete mass, or as a ''''re-advancing'''' device for displacing step-by-step a mass or load to which it is connected along a rail-forming cable or rod.

Description

[S4] STEPWISE-OPERATING POWER APPARATUS [451 Apr. 4, 1972 Primary ExaminerOthell M. Simpson Attorney-Amster & Rothstein [72] Inventor: Rene Bechl, Bois Colombes, France [73] Assignee: Soclete des Grands, Travaux de Marseille, [57] ABSTRACT France Hydraulic power apparatus operating stepwise and comprising [22] Filed. on. 23 1970 essentially a body having arranged therein a fixed retaining device, an annular piston and a movable traction device con- [2l] Appl. No 83,534 nected to the tubular rod of said piston, said fixed retaining device and said movable traction device comprising clamping members adapted to grip and release by turn cables, rods or E CCll. the like, the p g members of one device g pp g the cm 58] g i 4/68 29 A bles when the clamping members of the other device release o 'T said cables, and vice-versa. The invention may be used either as a traction ram when it is held in a fixed position for exerting [56] References Cited a tractive effort, for example on a cable for prestressing a UNITED STATES PATENTS concrete mass, or as a re-advancing? device for displacing step-by-step a mass or load to which it IS connected along a 3,338,553 8/ l 967 Perslcke ..254/29 A il f i cable or 3,35l,320 11/1967 Harvey ..254/29 A 3,399,865 9/1968 Kelly ..254/29 A 9'Clalms, 8 Drawing Figures 21a 1 2 11 10 12 Y/ 4 v 1 16 13a is 2 7a 5" E 1 h L 1 w v a r WM '*ll| I! #1 H 92"9- Q. P 5 \g 7 f a 1* 2 ll, -l F t/I glam l'" 1 a; s"

a a I a e 6 a "w x I lie I 15 16a $3 16b 15 hr x PATENTEDAPR 4l972 3,653,634

sum 2 OF 3 a F1.g.2.

5 A M m ms/vs'asaw glam Mam/70R.

STEPWISE-OPERATING POWER APPARATUS BACKGROUND OF THE INVENTION This invention relates to a power apparatus adapted to generate a relative displacement between an elongated member of constant cross-sectional area, on the one hand, and itself, or a mass to which it is connected on the other hand.

This invention is concerned more particularly with a traction ram adapted, when held in a fixed position, to exert a tractive effort on at least one elongated member of constant cross-sectional area, for example a cable for prestressing concrete.

In the specific example of the prestressing of a concrete beam, a considerable tractive force is applied to one end of at least one cable or rope of which the opposite end is anchored to one end of the beam to be prestressed, this cable following a predetermined path within said beam. To this end, a traction unit is used as a rule, this unit being mounted to the first aforesaid cable end and connected directly or indirectly to the piston of a power ram. In conventional tractive units of this character, such as the one disclosed in the French Pat. No. l.530,660, the tractive effort is applied to the cable at one go, so that the stroke of the piston of the traction ram must necessarily be at least equal to the desired elongation of the cable to which the tractive effort is applied. Now the cable elongation is an increasing function of the cable length and also of the intensity of the tractive force to which it is submitted, so that when it is contemplated to prestress beams of relatively great length the cable elongation may be of the order of 40 or more. As a result, according to the length of the beams to be prestressed, there must be provided either several traction rams of different lengths, thus compelling acontractor specialized in prestressing works to have a complete range of rams having different lengths, or a single ram but of considerable length, which in this case constitutes an extremely long and cumbersome device difficult to handle in case of prestressing operations requiring a relatively reduced cable elongation.

SUMMARY OF THE INVENTION It is the essential scope of the'present-invention to avoid these inconveniences by providing a traction ram or relatively reduced length, permitting of prestressing beams of any desired length.

The present invention is also concerned with a power apparatus, notably a traction ram, operating stepwise, as will be explained hereinafter.

Furthermore, the invention is concerned with a power apparatus capable of generating a relative step-by-step movement between an elongated member of constant cross sectional area, on the one hand, and this apparatus or a mass to which said apparatus is connected, on the other hand.

To this end, the power apparatus operating stepwise according to this invention is characterized in that it comprises a body formed with a cylindrical bore, a retaining device secured by one of its ends to said body, in a coaxial position in said bore of said body, and having a cylindrical surface of smaller diameter than said bore, so as to provide between its external surface and the wall of said bore an annular space closed at the end of the retaining device which is secured to said body, an annular piston adapted to slide axially in said annular space so as to form therein two axially spaced annular chambers each provided with an inlet port for introducing a fluid under pressure into the relevant chamber, a tubular coaxial piston rod having one end connected to said annular piston and extending from said piston in the direction opposite to said closed end of said annular space, a sealing member disposed between the inner wall of the bore of said body and the external surface of the tubular piston rod for closing in a fluid-tight manner the other end of said annular space, and a movable traction device positioned in alignment with said fixed retaining device and connected to the other end of the tubular piston rod, the fixed retaining device and the movable traction device being adapted to receive therethrough, in the axial direction, at least one elongated member of constant cross-sectional area, with which the power apparatus is adapted to co-act, and enclosing each a plurality of clamping members co-acting by frictional contact with said elongated member, for automatically releasing and re-gripping said elongated member when a fluid under pressure is directed into one of said two annular chambers and when the piston is moved in a first direction corresponding to a power stroke, so as to generate a relative displacement between the power apparatus and said elongated member, and, vice-versa, for automatically gripping and releasing said elongated member when fluid under pressure is fed into the other annular chamber and the piston is moved in a direction opposite to said first direction, which corresponds to an inoperative piston stroke.

Thus, the power apparatus according to the present invention can be utilized either as a traction ram when it is held in a fixed position for exerting a tractive effort on at least one elongated member of constant cross-sectional sectional area, for example a cable for prestressing concrete or any other material, or as a driving device or re-advancer" for displacing stepwise or step-by-step a mass to which it is connected, for example a cable or a rail-forming bar. In this last instance, the power apparatus according to this invention is particularly suited for all applications in which it is desired to produce the step-by-step, slow and accurate movement of a considerable mass.

In case the power apparatus according to this invention were intended more particularly for use as a traction ram for prestressing concrete beams, it is clear that it can be designed with a view to produce a relatively short piston stroke and, therefore, have a total length also relatively short, since it is adapted to operate stepwise or, in other words, by causing its movable traction device and its fixed retaining device to coact by turns with the traction cable or cables in order to pull them and then retain said cable or cables in the position obtained after said pulling action, during the power or operative and inoperative strokes of the piston, r,espectively. In spite of the moderate length of the apparatus of this invention, it is thus advantageously possible to prestress beams of any desired length, since it is only necessary to actuate its piston a certain numberof times, in either direction, until the desired degree of prestress is obtained.

BRlEF DESCRIPTION OF THE DRAWING Now a typical form of embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a longitudinal section showing a stepwise-operating power apparatus according to the present invention, designed more particularly for use as a traction ram in the prestressing of concrete elements, this view showing in its upper portion and its lower portion respectively two positions of operation of the component elements of the traction ram;

FIG. 2 is a cross section taken along the line IIII of H0. 1;

FIG. 3 is a section taken along the line IIIIII of FIG. 1 showing on a larger scale clamping members of the traction ram according to this invention;

FIG. 4 is a section taken along the line IV-IV of HG. 3;

FIG. 5 is a detail view showing a component element of the clamping members illustrated in FIGS. 3 and 4;

FIGS. 6, 7 and 8 are fragmentary diagrammatic views showing in axial section the traction ram of this invention for illustrating the various stages of its operation.

DESCRIPTION OF THE PREFERRED EMBODIMENT.

The traction ram 1 illustrated in the drawings is intended more particularly for use in the operation consisting in prestressing a concrete member, for example a concrete beam 2, of which only one end is shown in FIG. 1. To this end, the beam 2 has embedded therein, the longitudinal direction and along a suitable path, a tube 3 having secured to one end a bearing plate 4 engageable by the ram 1. This tube 3 permits the passage of at least one cable 5 having one end (not shown) connected in the conventional manner to device (not shown) bearing against the opposite end of beam 2. In the example illustrated seven cables 5 are provided and constitute either separate cables or the elementary strands of a same cable. Secured in a conventional manner to the cables 5 is a substantially cylindrical anchoring device 6 having a screw-threaded external surface; when the cables 5 are in their inoperative condition, this anchoring device 6 is somewhat engaged into the tube 3. As in the structure of conventional traction rams designed for prestressing a concrete beam, the traction ram according to this invention bears against said bearing plate 4 through the medium of an intermediate bearing member 7, for pulling the cables 5 and thus elongate same as a consequence of the traction force exerted thereon, whereby the anchoring device 6 is eventually positioned within the bearing plate 4 (FIG. 1 A nut 8 previously engaged on the cables 5 may then be screwed on the anchoring device 6 until it bears against the plate 4 for holding the cables 5 in their taut condition, as already known in the art.

According to an essential feature characterizing this invention the traction ram 1 operates by successive steps; in other words, it is adapted to pull the cables 5 according to a cycle comprising alternating traction phases and inoperative return phases during which however the cables are retained in the position obtained during the preceding traction phase. To this end, the traction ram according to this invention comprises essentially a substantially cylindrical body 10 having mounted concentrically therein a fixed retaining device 11, an annular piston 12 and a movable traction device 13 connected to the tubular rod 14 of annular piston 12. The fixed retaining device 11 and the movable traction device 13 incorporate similar clamping members 15 to be described more in detail presently, these devices being adapted to alternatively grip and release the cables 5; to this end, the cables 5 are gripped by the clamping members 15 of the movable traction device 13 when the clamping members 15 of the fixed retaining device 11 release them, and vice-versa. The cylindrical body 10 of traction ram 1 comprises a cylindrical concentric bore 10a internally screw-threaded at either end, and the member 7 through which the body 10 engages the bearing plate 4 con sists of a tubular member having one end formed with inner and outer screw threads so that on the one hand it can be screwed into the end of body 10 adjacent the beam 2 and, on the other hand, it can receive the screw-threaded end of the fixed retaining device 11. The intermediate bearing member 7 further comprises a pair of longitudinal apertures 7a through which access may be had to the nut 8 for tightening same to the anchoring device 6. In order to facilitate the actuation of this nut 8 the latter has preferably a cylindrical outer configuration with a pair of flat faces 8a engageable by corresponding flat portions of a control socket 9 formed with radial holes 9a adapted to receive the studs of a tightening spanner (not shown).

The fixed retaining device 11 secured in the manner explained hereinabove to the intermediate bearing member 7 is thus rigid with the body 10 of the traction ram. Moreover, its body 11a is of cylindrical external configuration and extends coaxially within the bore 100 so as to provide between its peripheral surface and the inner wall of said bore 100 an annular space 16 in which an annular piston 12 is adapted to slide. This annular piston 12 divides the annular space 16 into two axially

spaced chambers

16a and 16b; an orifice for introducing fluid under pressure opens into each chamber. These two

orifices

17 and 18 are formed respectively through the wall of the cylindrical body 10 of the traction ram and communicate through suitable ducts and pipe lines and a distributor (not shown) with a source of fluid under pressure (also not shown). The tubular piston rod 14 sliding with piston 12 on the outer cylindrical surface of the body 11a of the fixed retaining device 11 extends into the chamber 16b beyond the aforesaid fixed retaining device 11. In the end portion of cylindrical body 10 which is opposite to the concrete beam 2 an annular plug 19 is screwed for closing in a fluid-tight manner the chamber 16b and acting as a rear abutment member to said annular piston 12. The end of said tubular piston rod 14 (which is opposite to piston 12) is formed with an internally screw-threaded portion adapted to engage a corresponding externally screw-threaded cylindrical portion of the body 130 of said movable traction device 13. Thus, the movable traction device 13 is aligned with the fixed retaining device 11 and moves bodily with the annular piston 12.

The body 11a of the fixed retaining device 11 and the body 13a of the movable traction device 13 are both formed with an axial bore shaped to provide a certain gradient in order to coact with the external surface of the clamping members 15 formed with a similar or corresponding gradient. This gradient is so designed that when the clamping members are moved in relation to their respective bores formed in said bodies and 130, as a result of the frictional contact between the cables 5 and the clamping members, in combination with the movement of said body 13a as a consequence of the thrust of piston 12, said clamping members grip the cables when the formers are moved in the direction of the arrow F (FIG. 1) in relation to the relevant bodies 11a and 13a, and move away from said cables, so as to release same, when said clamping members move in the opposite axial direction shown by the arrow F in FIG. 1 in relation to the same bodies 11a and 13a.

In order to reduce the outer diameter of these bodies 110 and 13a, it is particularly advantageous that the inclined surfaces of the bores formed in these bodies, as well as the corresponding inclined surfaces formed on clamping members 15, be shaped somewhat in the fashion of inner and outer threads respectively, each thread comprising a front face 20a of relatively great width with a moderate inclination to the axis of the assembly, and a rear face 20b of considerably shorter width and greater inclination in relation to said axis than the front face 20a. This surface may advantageously be machined in the relevant bores of bodies 110 and by using a lathe, exactly as in the machining of internal screw threads.

Now the shape of the clamping members 15 of the fixed retaining device 11 and of the movable traction device 13 will be described more in detail, together with the manner in which these members can be obtained, with reference to FIGS. 3 and 4 illustrating these members on a larger scale. The clamping members 15 comprise a number of keys 15a to 15g (equal in number to the number of cables 5 to be gripped) having substantially the shape of cylinder sectors and which, when assembled as shown in FIG. 3, constitute an assembly of substantially cylindrical configuration formed with radial slots 21 extending throughout its length. Moreover, in the lateral faces of these keys 15a to 153 determining said radial slots 21, longitudinal grooves 22 having a semi-circular cross-section are formed; these grooves are adapted to surround by pairs of cable 5 of which they accommodate the major portion of the peripheral surface. The ends of grooves 22 adjacent to the concrete beam 2 are bevelled as shown at 22a in FIG. 4, in order to facilitate the positioning of the cables. To obtain these keys 15a to 15g and give the afore-mentioned screw thread appearance to the outer surface of the assembly constituted by these keys with the front faces 20a and the rear faces 20b, the following procedure may advantageously be adhered to. It is only necessary to start from a cylindrical block and form on its outer surface, for example on a lathe, the above-defined special screw-threads. Upon completion of the external screws, the central hole 23 is drilled and the assembly is cut into sectors. The faces of each sector are then milled to form the holes 24 permitting the passage of the strands or cables 5. This machining method is more accurate than the drilling performed before cutting the block into sectors. Of course, the number of holes 24 must be be equal to the number of cables with which the traction device is intended to co-operate. Then the cylindrical block is cut along planes containing the axis of the block nd also the axis of each hole 24, so as to obtain the keys 15a to 15g having substantially the shape of cylinder sectors, each hole 24 forming in the parallel adjacent faces of two keys the longitudinalgrooves with semicircular cross-sectional contour of these keys.

In order to keep the keys properlyspaced from one another and facilitate the positioning of cables 5 in said holes 24, and also the release of these cables by said keys, there is provided according to a specific feature of the present invention a set of elastic return members each bearing against two lateral parallel registering faces of two adjacent keys. In the preferred from of embodiment of, the present invention each elastic return member may advantageously consist of a spring steel blade 25 of corrugated configuration so that the peak of its corrugations bears by turns on the lateral parallel registering faces of two adjacent keys parallel to their grooves 22, between these grooves and the key edge parallel to their peripheral surface. In order to hold the blades 25against axial movement in their relevant grooves 26, these blades are bent at one end so as to form a stop lug 25a engageable into a hole 26a formed in the bottom of said grooves 26.

Referring again to the construction of FIGS. 1 and 2, it will be seen that the traction ram 1 according to the present invention is adapted to be suspended from any suitable supporting device by means of a collar 27 comprised of two

semi-circular members

27a, 27b assembled by bolts and nuts 28. Moreover, two

grids

29 and 30, having a function to be explained presently, are provided; these grids comprise countersunk or

bevelled holes

29a and 30a, respectively, aligned with the holes 24 of clamping members 15. The grid 29is secured to the end of'the fixed retaining device 11 which is adjacent .to the movable traction device 13, and the grid 30 is normally adapted to move freely between the nut 8 and the end of the fixed retaining device which is adjacent to the concrete beam 2. Two lock pegs 31 may be inserted into transverse holes 32 drilled through the intermediate'bearing member 7 for holding the grid 30 in contact with the end of the clamping members 15 of the .retaining device ll, so that the rear faces 20b of the threads formed on said clamping members 15 can bear against the corresponding faces of the female threads of block 11a, as shown in the lower portion of FIG. 1. In this position the keys lower portion of FIG. 1 and clamp these cables. During this clamping action, the piston 12 and movable traction block 13 move along a distance d, without exerting any efficient tractive effort on the cables 5. This stroke d 'IFIG. 1) corresponds substantially to the relative movement of keys with respect to the body 13a of traction device 13. When va sufficient clamping action is produced, the movable traction block 13 carries along its keys 15 with pull the cables 5 so as to elongate them in the direction of the arrow F,. Meanwhile, the cables 5 carry along by frictional contact the keys 15 of the fixed retaining device 11 in thedirection of the arrow F inorder to move them to the release position if they are not already in this position. This positive traction stroke takes place until the annular piston 12 engages the plug 19. The various component elements of the ram are then in the position illustrated in FIG. 7. If from this position the pressure is released in chamber 16a and fluid under pressure is fed to chamber 161: through orifice 18, the piston 12. and the movable traction block 13 will move firstly'through a distance d, in the direction of the arrow F and, during this stroke, the cables 5 are partially slackened and carry along, by frictional contact, the keys 15 of retaining device 11, so that these keys will move to the position illustrated in'FIG. 8 was to clamp and hold the cables 5 in the taut position. The stroke 11;, substantially equal to stroke d corresponds to a slight loss of tension in the cables 5 and to a very moderate loss of useful stroke of piston 12. From the position illustrated in FIG. 8, in which the cables 5 are of the fixed retaining device 11 are released. Similarly, when the keys of the movable traction device 13 are in the position illustrated in the upper portion of FIG. l,- they are also released. I

Now, reference will be made to FIG. 1 andalso to FIGS. 6, 7 and 8for describing the manner in which the traction ram 1 of this invention can be positioned on the cables 5, and its mode of operation. Firstly, in order to ascertain whether the holes 24 of the various clamping members and the holes'of the grids are properly aligned, the operators insert at least two rigid aligning bars into these holes, and-these are thus re-aligned, if necessary. While maintaining these aligning bars in said holes of the clamping members and grids, the traction ram 1 is brought to a position adjacent the ends of cables 5 which emerge from the opening of bearing plate 4. Having previously slipped the nut 8.0n these cables 5, the ends of the cables 15 are subsequently inserted in succession into the holes of grid 30, into the holes of the clamping members of the fixed retaining device 11, into those of grid 29 and finally into those of the movable traction device 13, so as to push back the aligning bars and permit their removal. The ram is then applied against the bearing plate 4 and the pegs 21 areremoved, in case they are still positioned in the device, so thatthe grid 30 can move freely along the cables between the device 11 and nut 8. Moreover, it will be assumed that the orifices l7 and 18 are connected to a suitable source of fluid under'pressure. Under these conditions, the traction ram is ready to operate. The

keys l5 and movable traction device 13 are positioned as shown in FIG. 6; then, fluid under pressure is delivered through orifice 17 into chamber 16a. As a consequence, the piston 12 is moved back into the direction of the arrow F (FIG. 1). The keys 15 of traction device 13, whichare in frictional contact with the cables 5, are firstly retained by these cables, so that they move to the position illustrated in the locked by the retaining device 11, if thepiston 12'continues its movement in the direction of the arrow'F fthe keys I5 of traction block 13 will move, as a consequence of their frictional engagement with cables 5, to the position illustrated in the same FIG. 8, and the assembly comprising the piston 12 and traction block 13, with its keys 15, will continue its movement until it attains the position'shown in the upper portion of FIG. 1 in which the piston 12 abuts against the rear end of the intermediate bearing member 7. The cycle of the above-described operations may then be repeated in order to exert another traction on the cables, by switching'thesupply of fluid under pressure from orifice 18 to orifice 17, and then operating exactly as described hereinabove. By performing a: certain number, of traction cycles the anchoring device 6 eventually penetrates into the 'opening of bearing plate 4 and the nut 8 can then be screwed on this anchoring device until. it engages the plate 4, so that the cable's5 canproperly' held in their taut condition. Then the ram 11 can be removed for performing another prestressing operation, if required. However, to remove the ram, 11 it is necessary to take certain 'care. In fact, after the last traction stroke, the componentelements of the ram are in the position shown in FIG.'7, so that the cablesec'-- I tions disposed between the anchoring device 6 and thekeys 15 of traction block 13 are still strongly tensioned. Therefore, to prevent the cables 5 from carrying along by friction the keys 15 of retaining block 11 during the return stroke of piston 12 in the direction of the arrow F L which would cause these keys to be clamped on the cables and, therefore, prevent the removal of the traction ram, the pair of lock pegs 31 are inserted behind the grid 30 so that the latter can hold the keys 1 5 of retaining block 11in their release position, as shown in the lower portion of FIG. 1. Then fluid under pressure can be introduced through the orifice 18 so as to move the piston 12 and the movable traction block 13 from the position shown in FIG. 7 to the position shown in FIG. 6. In this last position, the

keys 15 of traction block 13 are pushed back by grid 29 to tions, it could easily be modified with the view to utilize same as a step-by-step driving device for displacing a bulky assembly or a load attached in any suitable manner to the body 10 of the ram in relation to one or a plurality of cables or to one or a plurality of parallel fixed bars or rods acting as rails. Under these conditions, the intermediate bearing member 7 and grid 30 can be dispensed with, but the retaining device 11 must nevertheless be properly connected to the body 10 of the traction ram. Moreover, the clamping members of the fixed retaining device 11 and of the movable traction device 13 must be designed to suit the number and shape of the cables, strands, rods or bars acting as guide rails.

lclaim:

l. A power apparatus operating by successive steps, comprising a body formed with a cylindrical bore, a retaining device secured at one end to said body in a coaxial position in the bore thereof and having an external cylindrical surface of smaller diameter than said bore so as to provide between its outer surface and the wall of said bore an annular space closed on the side of the end of said retaining device secured to said body, an annular piston adapted to slide axially in said annular space so as to separate therein two axially spaced annular chambers each provided with an inlet orifice for supplying fluid under pressure thereto, a coaxial tubular rod of said piston connected at one end to said piston and extending from said piston in the direction opposite to that of said closed end of said annular space, a sealing member disposed between the inner wall of said bore of said body and the outer surface of the tubular piston rod for closing in a fluid-tight manner the other end of said annular space, and a movable traction device aligned with said fixed retaining device and connected to the other end of said tubular piston rod, and fixed retaining device and said movable traction device being arranged with a view to receive axially therethrough at least one elongated member of constant cross-sectional area, with which the power apparatus is adapted to co-operate, each one of said retaining and traction devices enclosing a set of clamping members coacting by frictional contact with said elongated members, for releasing and automatically gripping, respectively, said elongated member when a fluid under pressure is delivered into one of said annular chambers and the piston is moved in a first direction corresponding to a power stroke, so as to produce a relative movement between the power apparatus and said elongated member, and vice-versa for automatically gripping and releasing said elongated member, respectively, when said fluid under pressure is delivered into the other annular chamber and the piston travels in a direction opposite to said first direction, which corresponds to an inoperative return stroke.

2. Power apparatus as set forth in claim 1, wherein said fixed retaining device and said movable traction device comprise each a hollow cylindrical body of which the inner surface is inclined in relation to the axis of said cylindrical body and receives therein said set of clamping members associated therewith, said assembly having an outer surface having the same inclination as the inner surface of the hollow cylindrical body, whereby a relative axial displacement of the set of clamping members with respect to said hollow body is attended, according to the direction of said relative displacement, by the clamping or release of said elongated member by the clamping members.

3. Power apparatus as set forth in claim 2, wherein said inner inclined surface of said hollow body and said outer surface of set of clamping members associated therewith are shaped to correspond to internal and external screw threads, respectively, said threads comprising a front face of relatively great width and slightly incllned in relation to the axis of said hollow body, and a rear face of considerably shorter width and steeper inclination in relation to said axis in comparison with said front face.

4. Power apparatus as set forth in claim 3, wherein each set of clamping members is designed for co-acting with a plurality of cables or bars having a constant cross-sectional area and comprises in this case as many identical clamping members as there are cables or rods, each clamping member having sub stantially the shape of a cylinder sector with an external surface such that, when all the clamping members are assembled, the outer surface of their assembly as the shape of said screw threads, each clamping member further comprising in each one of its lateral faces a longitudinal groove accomlodating the shape of a cable or bar to be clamped, the grooves formed in the two registering lateral surfaces of two adjacent clamping members being adapted to co-act for surrounding a same cable or bar.

5. Power apparatus as set forth in claim 4, wherein resilient return means tending to move adjacent clampingmembers away from each other are disposed between each pair of registering lateral faces of adjacent clamping members.

6. Power apparatus as set forth in claim 5, wherein said resilient return means consist of a corrugated spring steel blade of which the peaks of the corrugations bear alternatively on said registering faces.

7. Power apparatus as set forth in claim 6, wherein said corrugated blade is inserted in a pair of longitudinal grooves opening towards each other, which are formed in said registering lateral faces respectively, parallel to said cable or barreceiving grooves, between said last-named grooves and the corresponding edges of said registering faces which are adjacent to the external surface of said clamping members, and that means are provided for preventing any longitudinal displacement of said blade in said grooves.

8. Power apparatus as set forth in claim 1, adapted for use as a traction ram for pulling the end of at least one cable extending through a member of body to be compressed and of which the opposite end is anchored to a first side of same member or body to be compressed, said traction ram bearing on a second side, opposite to said first side, of said member or body to be compressed, and stop means provided for co-acting with said cable and said other side in order to keep said member or body to be compressed in its compressed condition when a predetermined tractive effort is applied to said cable, and wherein a tubular bearing member constitutes the extension of the body of said ram beyond said end and bears against the other side of said member of body to be compressed, said tubular member comprising at least one relatively wide longitudinal slot permitting the access to said stop means.

9. A traction ram as set forth in claim 8, wherein a movable grid receiving said cable therethrough and adapted to be brought into engagement with the ends of the clamping members of the fixed retaining device in order to push same back to its release position is disposed on the side of the end of said fixed device which is adjacent to the member or body to be compressed, and wherein the other end of said fixed retaining device has secured thereto another grid against which the clamping members of the movable traction device are adapted to abut at the end of the return stroke of said piston so as to be pushed back to a release position, means being also provided for holding when desired said movable grid in its position of engagement with the clamping members of the fixed retaining member and holding said clamping members in their release position.

UNITED STATES PATENT OFFICE CERTIFICATE CF CORRECTION v Patent 3,653,634 Dated- April 4 1972 Rene Behi Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected a s shown below:

Inventor: RENE BEGHI, Bois Colombes,- France Assignee: SOCIETE DES GRANDS TRAVAUX DE MARSEILLE,

NANTERRE, FRANCE Signed and sealed this 3rd day of October- 1972.

(SEAL) Attest:

- RO-BER'I'. GOTTSCHALK USCGMM-DC 6037e-P6 I v.1. oovnmlnn "mums ovnc: 1 "n o-su-u FORM 5 0-1050 (10-69}

Claims

1. A power apparatus operating by successive steps, comprising a body formed with a cylindrical bore, a retaining device secured at one end to said body in a coaxial position in the bore thereof and having an external cylindrical surface of smaller diameter than said bore so as to provide between its outer surface and the wall of said bore an annular space closed on the side of the end of said retaining device secured to said body, an annular piston adapted to slide axially in said annular space so as to separate therein two axially spaced annular chambers each provided with an inlet orifice for supplying fluid under pressure thereto, a coaxial tubular rod of said piston connected at one end to said piston and extending from said piston in the direction opposite to that of said closed end of said annular space, a sealing member disposed between the inner wall of said bore of said body and the outer surface of the tubular piston rod for closing in a fluid-tight manner the other end of said annular space, and a movable traction device aligned with said fixed retaining device and connected to the other end of said tubular piston rod, and fixed retaining device and said movable traction device being arranged with a view to receive axially therethrough at least one elongated member of constant cross-sectional area, with which the power apparatus is adapted to co-operate, each one of said retaining and traction devices enclosing a set of clamping members co-acting by frictional contact with said elongated members, for releasing and automatically gripping, respectively, said elongated member when a fluid under pressure is delivered into one of said annular chambers and the piston is moved in a first direction corresponding to a power stroke, so as to produce a relative movement between the power apparatus and said elongated member, and vice-versa for automatically gripping and releasing said elongated member, respectively, when said fluid under pressure is delivered into the other annular chamber and the piston travels in a direction opposite to said first direction, which corresponds to an inoperative return stroke.

4. Power apparatus as set forth in claim 3, wherein each set of clamping members is designed for co-acting with a plurality of cables or bars having a constant cross-sectional area and comprises in this case as many identical clamping members as there are cables or rods, each clamping member having substantially the shape of a cylinder sector with an external surface such that, when all the clamping members are assembled, the outer surface of their assembly as the shape of said screw threads, each clamping member further comprising in eacH one of its lateral faces a longitudinal groove accomlodating the shape of a cable or bar to be clamped, the grooves formed in the two registering lateral surfaces of two adjacent clamping members being adapted to co-act for surrounding a same cable or bar.

5. Power apparatus as set forth in claim 4, wherein resilient return means tending to move adjacent clamping members away from each other are disposed between each pair of registering lateral faces of adjacent clamping members.

7. Power apparatus as set forth in claim 6, wherein said corrugated blade is inserted in a pair of longitudinal grooves opening towards each other, which are formed in said registering lateral faces respectively, parallel to said cable or bar-receiving grooves, between said last-named grooves and the corresponding edges of said registering faces which are adjacent to the external surface of said clamping members, and that means are provided for preventing any longitudinal displacement of said blade in said grooves.