US3882585A

US3882585A - Method and device for positioning prestressing hoops

Info

Publication number: US3882585A
Application number: US440137A
Authority: US
Inventors: Didier Costes; Jack Picaut
Original assignee: Commissariat a lEnergie Atomique CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 1973-02-06
Filing date: 1974-02-05
Publication date: 1975-05-13
Anticipated expiration: 1992-05-13
Also published as: FR2216056A1; CA1020333A; FR2216056B1; DE2405286A1; SE394339B; JPS49106620A; GB1461811A

Abstract

In a method of positioning hoops of steel wire or strip for the application of circular prestress to pressure vessels provided at uniform intervals with peripheral support saddles, a winding core is placed between the saddles and the prestressing hoops and is displaced in rotational motion so as to wind the hoops. The device for carrying out the method comprises radial rollers and adjacent axial rollers so arranged as to form a roller track corresponding to the internal diameter of the winding core, at least one pressure roller for displacing the core and the hoop and at least one stationary drum for feeding steel strip.

Description

United States Patent [191 Costes et al.

[451 May 13, 1975 METHOD AND DEVICE FOR POSITIONING PRESTRESSING HOOPS [75] Inventors: Didier Costes; Jack Picaut, both of Paris, France [73] Assignee: Commissariat a IEnergie Atomique,

Paris, France [22] Filed: Feb. 5, 1974 [21] App]. No.: 440,137

[30] Foreign Application Priority Data Feb 6, 1973 France 73.04168 [52] U.S. Cl 29/150; 29/200 B; 29/452 [51] Int. Cl... B23p 13/00; B23p 19/00; B2ld 39/00 [58] Field of Search 29/150, 153, 200 B, 208 B,

[56] References Cited UNITED STATES PATENTS 2,743,514 5/1956 Duecy 29/452 3,216,079 11/1965 Keyworth 29/150 X 3,221,401 12/1965 Scott et al 29/208 D Primary Examiner-Thomas H. Eager Attorney, Agent, or Firm-Cameron, Kerkam, Sutton, Stowell & Stowell [5 7 ABSTRACT In a method of positioning hoops of steel wire or strip for the application of circular prestress to pressure vessels provided at uniform intervals with peripheral support saddles, a winding core is placed between the saddles and the prestressing hoops and is displaced in rotational motion so as to wind the hoops.

The device for carrying out the method comprises radial rollers and adjacent axial rollers so arranged as to form a roller track corresponding to the internal diameter of the winding core, at least one pressure roller for displacing the core and the hoop and at least one stationary drum for feeding steel strip.

11 Claims, 6 Drawing Figures METHOD AND DEVICE FOR POSITIONING PRESTRESSING HOOPS This invention relates to the fabrication of prestressing hoops by winding and to the prestressing of these latter on a vessel which contains an internal pressure.

It is a known practice to make use of hoops formed by winding unstressed wire or cable followed by tensioning of the hoops by means of radial jacks and wedges. As an alternative to wires or cables, it is also known to make use of thin steel strip. The superposition of turns of strip accordingly permits the formation of prestressing hoops of substantial thickness without any need to provide embracing support saddles as in the case of cables and wires.

By analogy with the known practice adopted for hoops formed by wires or cables, the arrangements contemplated up to the present time in the case of hoops made of steel strip have consisted in forming these latter in situ by supplying the strip from a cable drum and winding the strip round the cylindrical shell of the vessel which is intended to contain an internal pressure. This accordingly entails the need to cause the cable-drum support or frame to revolve about the axis of the cylindrical shell as well as the need to provide a.

substantial clearance space, with the result that difficulties are liable to arise in erection and operation on a construction site.

The primary aim of this invention is to overcome the difficulties which arise in known methods either at the time of formation of the hoops by winding or during prestressing of these latter.

To this end, the invention proposes a method which essentially consists in placing between the support saddles and the prestressing hoops a winding core which is caused to rotate in order to wind said hoops.

The winding hoop can be constituted by a rigid annular band which is mounted around the cylindrical shell by welding.

In a preferred alternative embodiment, the winding core is constituted by a number of turns of mild steel strip having the same thickness and width as the hardened-steel strip of the prestressing hoop to which said winding core can be joined by welding unless it constitutes a softened extremity of the hardened-steel strip.

In order to facilitate winding of said turns of mild steel, provision is made for preliminary forming at the moment of winding.

It is apparent that the method leads to the preferred use of steel strip with softened ends. It is in fact an advantage to make use of softened ends for the purpose of welding in end-to-end relation two lengths of strip delivered from a drum and thus to permit of practically continuous operations in which each hoop is wound without any change in thickness.

The advantage of the method in accordance with the invention lies in the fact that steel strip elements for the winding core and the hoop are taken from stationarilyfixed feed drums.

Positioning of hoops formed in accordance with the method hereinabove described can be carried out at a suitable height after winding and prior to tensioning.

A device for carrying out the method aforesaid is also contemplated by the invention and essentially comprises radial rollers and adjacent axial rollers so arranged as to form a roller track which conforms to the internal diameter of the winding core, at least one actuating pressure-roller for displacing the strip of the winding core and of the hoop, at least one stationarilyfixed drum for feeding the steel strip.

Provision is made for shaping rollers which serve to facilitate starting of the mild steel strip as this latter undergoes the winding operation. In order to prevent damage to the hardened-steel strip of the prestressing hoop when the actuating pressure-roller is outside, said roller is provided with a rim of elastic material.

In an alternative embodiment, arrangements are made to couple the prestressing hoops in pairs in order to endow these latter with higher tilting inertia. This coupling is carried out at the moment of prestressing by means of the jacks themselves.

To this end, the bodies of the common jacks are joined together by means of a bridge which also serves as a support for the two hoops.

Moreover, each jack is fitted with a wedge which is capable of sliding between the jack body and the piston, said wedge being subjected by a spring to a tractive effort in the direction of wedging inorder to ensure progressive action of the jacks when these latter are actuated in order to apply tension to the hoop.

The following specification relates to examples of construction which are described with reference to the accompanying drawings, wherein:

FIG. 1 illustrates a mode of positioning of hoops which have been prepared in the workshop;

FIG. 2 illustrates another mode of winding hoops placed on a pressure vessel, in which use is made of a drum for delivering wire or strip;

FIG. 3 is a device for winding hoops which are placed on the pressure vessel;

FIG. 4 is a device for the preparation of the wedging element or annular band which serves to support the hoops;

FIG. 5 is a diagrammatic view in sectional elevation showing the coupling of hoops with interposition of common tensioning jacks;

FIG. 6 is a sectional plan view of FIG. 5.

In FIG. 1, the hoops 1 are fabricated in the workshop by known methods of winding around an annular band in accordance with the invention, whereupon said hoops are conveyed to a location above the tank 2 and displaced vertically in downward motion around the tank to the desired level. It will be noted that, after fabrication, the strip-steel hoop 1 has a fairly high degree of rigidity, especially with respect to deformations outside its plane. As shown at 1a in the figure, the hoop can thus be readily transported by means of an accompanying support structure 3 of relative elementary design. j

From FIG. 2 it is seen that the steel-strip hoops are fabricated directly around the cylindrical shell of the pressure vessel by causing these latter to rotate about their own axes instead of displacing the feed drum 4. This mode of fabrication in accordance with the invention results in a considerable reduction in the clearance space which it is necessary to provide around the pressure vessel shell. The drum 4 can be placed at a substantial distance from the hoop and the steel strip is simply intended to be directed along a path which is compatible with freedom of bending movements.

The hoop 1 shown in FIG. 2 can be constructed at a predetermined height of the cylindrical shell 2 and then either raised or lowered to its final level. The method of winding in situ can be adopted for any subsequent repairs while the pressure vessel is in service.

FIG. 3 represents one mode of execution of the winding operation in accordance with the invention. Radial rollers 5 of slightly conical shape and capable of free rotation determine a roller track which supports the hoop 1 during fabrication. Cylindrical bearing rollers 6 having a vertical axis and capable of free rotation are disposed at uniform intervals around the shell 2 and determine the winding diameter ofthe wedging element 10. Rotational displacement is carried out by means of at least one actuating pressure-roller 7 driven by a motion-transmission system 8 and a motor 9; the pressureroller 7 is placed externally in oppositely-facing relation to the bearing rollers 6. The roller such as 7 which produces direct action on the flexible strip element is provided with an elastic covering 7a or a rubber tire (tyre).

In the case of preliminary winding of the hoop on a winding core or annular band 10 (as shown in detail in FIGS. 3 and 4), said annular band also rests on radial rollers 5 and is displaced by means of at least one actuating pressure-roller 7. It is also possible to displace the hoop or the annular band by means of driving belts in contact with a peripheral zone of its elements (not shown in the drawings). The annular band 10 performs a useful function in preventing the flexible element of hardened steel from being damaged in direct contact with the bearing rollers 6. It is difficult to form said annular band by mechanical welding. An easier method of construction consists in forming an initial winding of metallic strip which is identical in cross-section to the hardened-steel strip employed for prestressing but is formed of steel which has higher ductility and tolerance to deteriorative effects. In order that the winding operation may readily be started (as shown in FIG. 4), a strip 10 is passed through a set of actuating pressurerollers 12 and emerges from these latter with the degree of curvature which is necessary to ensure that the strip will wind round the cylindrical shell 2 of its own accord. The final extremity of said strip is welded to the initial extremity of the prestressing strip which is not required to pass through the rollers 12. The welded joint is clearly ground with very great care.

The same ductile strip 10 can serve to make joints between a number of lengths of hoop strip which are delivered by different feed drums. In fact, when a plurality of hardened-steel strips are wound one above the other simply by overlaying without welding, correct relative anchoring is thereby achieved, subject to slight local slippage resulting from the winding action and from the complementary action of clamping collars (not shown); however, the starting end-portions must be ground so as to be tapered in thickness in order to' prevent stress concentrations in adjacent turns. A predetermined length of ductile strip (not shown in the drawings) is employed for the purpose of end-to-end welding of two lengths supplied from drums, with the result that each hoop is wound in a practically continuous operation without any change in thickness. On the other hand, if a welded joint is not formed, this ductile length permits relative sliding movements which ensure frictional anchorages and suppress any local damage.

It is known to make use of radial jacks applied against the cylindrical shell of the vessel for the purpose of applying prestress to the hoops. However, this tensioning of the hoops may be accompanied by inclination or tilting of the hoop as a result ofrotation about the neutral. axis. It should in fact be noted that the hoop and winding core have limited resistance to tilting during appliw cation of radial prestress when a strip is employed and this entails the need for radial jacks with particularly rigid guiding. I

In accordance with the invention, stabilitycan be obtained by coupling together two adjacent hoops 1m, in as shown in FIG. 5, thereby increasing the fictitious width of hoop and reducing its tendency. to tilt. Furthermore, the center of gravity l5 ofthe transverse sec- I tion of the hoops is located as close as possible to the center of gravity 16 and the transverse section of the I jacks l7 and 18 at the level of the packing-rings of their respective pistons 17a and 18a. Tilting is thus prevented by virtue of the high width-to-heightratio which is thus obtained. To this end, the cylinders 17c and of the corresponding jacks are rigidly coupled together by means of a bridge 27 which also serves as a support for the hoops 1m, 1n. '3

In order that the deformations in the radial plane should be compatible, provision is made for a possibility of vertical sliding motion of the piston 18a of the 1 lower jack 18 by means of a sheet of slippery material 19 which is interposed for example between the base 181) of the piston and the bearing zone 20. Wedges 21a 1 I and 21b to which a tractive force is applied by a spring 22 ensure progressive Wedging during the movement of thrust of the jacks.

In FIG. 6 which is a horizontal sectional view taken along the axis of the upperjack 17, there is shown a detail of the device which is designed to produce Wedging after application of tension..The jacks such as 17,or 18' are placed at the bottom of channels 23 formed by bearing ribs 24 of concrete. Wedging is carried out after prestressing by the jacks such as 17 and .18, first I by fitting in position a packing piece 25 of reinforced concrete and of substantial thickness, then by completing with steel plates 26 of smaller thickness inorder to permit adaptation to structural irregularities.

The entire procedure which has been described in y the foregoing can also apply to windings of wiresand cables. In this case, the annular winding band must be provided with continuous flanges or uniformly spaced Y saddles. Saddles are more compatible with the prestressing deformation but must be completed during the winding operations by continuous sectional members which cooperate with the supporting rollers.

What we claim is: I 1. A method of positioning hoops of steel wire or strip for prestressing a vessel which containsan internal pressure, with interposition of bearing saddles placed at uniform intervals on the periphery of the pressure ves- I sel, wherein a winding core is placed between the hearing saddles and the prestressing hoops and is driven in rotational motion in order to wind said hoops.

2. A method according to claim. 1, wherein the winding core is formed by winding one. turn of-mild steel V strip and welding the two ends thereof in abutting rela I tion.

3. A method according toclai m 1, wherein the wind ing core is formed by windingaplurality of turns of.

mild steel strip having the same thickness as the hardened steel strip of the prestressing hoop. v

4. A method according to claim 3, wherein starting of the winding core is facilitated by preliminary shaping at the moment of winding.

5. A method according to claim 3, wherein the mild steel strip is constituted by the softened end of the prestressing strip.

6. A method according to claim 1, wherein the steel strips of the winding core and of the hoop are taken from stationarily fixed feed drums.

7. A method according to claim 1, wherein the winding core and the hoop are placed at a suitable height after winding.

8. A device for positioning hoops of steel wire or strip for prestressing a vessel comprising radial rollers and adjacent axial rollers so arranged as to form a roller track which conforms to the internal diameter of the winding core, at least one actuating pressure-roller for displacing the core and the hoop, at least one stationarily-fixed drum for feeding the mild steel strip.

9. A device according to claim 8, wherein said device comprises rollers for shaping the mild steel strip.

10. A device for application of tension to prestressing hoops, wherein said device comprises jacks which are common to two adjacent parallel hoops.

1 1. A device according to claim 10, wherein the bodies of the common jacks are joined together by means of a bridge which serves as a support for the two parallel hoops aforesaid.

Claims

1. A method of positioning hoops of steel wire or strip for prestressing a vessel which contains an internal pressure, with interposition of bearing saddles placed at uniform intervals on the periphery of the pressure vessel, wherein a winding core is placed between the bearing saddles and the prestressing hoops and is driven in rotational motion in order to wind said hoops.

2. A method according to claim 1, wherein the winding core is formed by winding one turn of mild steel strip and welding the two ends thereof in abutting relation.

3. A method according to claim 1, wherein the winding core is formed by winding a plurality of turns of mild steel strip having the same thickness as the hardened steel strip of the prestressing hoop.

11. A device according to claim 10, wherein the bodies of the common jacks are joined together by means of a bridge which serves as a support for the two parallel hoops aforesaid.