IE55105B1

IE55105B1 - Cable anchorage

Info

Publication number: IE55105B1
Application number: IE903/84A
Authority: IE
Original assignee: Joseph Ferdinand O Halloran
Priority date: 1985-04-11
Filing date: 1985-04-11
Publication date: 1990-05-23
Also published as: GB8509339D0; GB2157354A; IE55105L; GB2157354B

Abstract

The anchorage for securing cables under stress around the external peripheral wall (11) of a containment vessel (10) has a main body portion (31) for accommodating at least one cable (14) to be gripped by the anchorage, means for gripping the said at least one cable while accommodated in the main body portion (31), and spacing means (35) adapted for maintaining the main body portion (31) clear of the external wall (11) to permit the passage of at least one further cable below the main body portion (31) without being gripped by the anchorage. The spacing means (35) is preferably adapted to permit the passage of a plurality of cables below the main body portion (31). <IMAGE> [GB2157354A]

Description

- 2 - - 2 - S5105 The present invention relates to an anchorage bridge for securing cables under stress around a containment vessel.

The cylindrical walls of circular containment vessels must withstand hoop tension and concrete walls in 5 such vessels are usually prestressed to counteract the hoop tension. One known method of achieving the prestress is a wire winding method which comprises externally winding steel wire about the vessel. The wire may be spaced out over the full height of the vessel or 10 concentrated in bands and is protected by a layer of sprayed concrete.

A second known method is a ducted cable system which comprises using bonded or unbonded cable which is stressed at special anchorage bridge piers. A third 15 known method is an external cable system which uses bonded cable which is stressed in stages at floating anchorage bridges and is protected by sprayed concrete.

By the term bonded cable is meant cable which is bonded directly to concrete, whereas unbonded cable is provided 20 with a sheath which prevents the cable from being bonded directly to concrete.

It is an object of the present invention to provide a novel anchorage bridge for use in the prestressing of e.g. containment vessels, and a novel construction of 25 vessel using such anchorage bridges.

Accordingly, the present invention provides an anchorage bridge for securing cables under stress around the external peripheral wall of a containment vessel, the anchorage bridge comprising a main body portion for 30 accommodating at least one cable to be gripped by the 3 anchorage bridge, means for gripping the said at least one cable while accommodated in the main body portion, and spacing means for maintaining the main body portion clear of the external wall to permit the passage of at least one further cable below the main body portion without being gripped by the anchorage bridge.

The invention also provides a containment vessel comprising an external peripheral wall and at least one substantially horizontal band of stressed cables extending side-by-side surrounding the external peripheral wall, the band being secured in position by a plurality of anchorage bridges according to the invention spaced around the peripheral wall of the vessel, each anchorage bridge gripping one end of at least one cable such that the ends of all the cables are gripped, and the cables ungripped by any anchorage bridge passing beneath the main body portion thereof.

The cable may be in bonded or unbonded form.

Unbonded cable having a grease filled polypropylene sheath is preferably used with the invention, because it provides excellent protection against corrosion and has a very low coefficient of friction. In the embodiment of the invention, to provide each full cable about the circumference of the vessel being prestressed, two cable sections each of which is greater in length than half the circumference of the vessel are used with the two pairs of adjacent ends of the cable sections being gripped at two diametrically opposite anchorage bridge points.

The invention will now be more particularly described with reference to the accompanying drawings which show, by way of example only, two embodiments of the invention.

In the drawings: Figure 1 is a plan view of a circular containment vessel; 4 Figure 2 is a side view of a typical wall section of the vessel; Figure 3 is an elevation of one embodiment of an anchorage bridge and associated cables; Figure 4 is a side view of the anchorage bridge of Figure 3 secured to the external peripheral wall of the vessel; Figure 5 is a front view of a portion of a cable rack and retaining clip for use in the embodiment of the invention; Figure 5A is a plan view of the clip of Figure 5; Figure 6 is a side view of the cable rack and retaining clip shown in Figure 5; Figure 7 is a section view of a band of cables mounted in a cable rack in a recess of the external wall of the vessel; Figure 8 is a side view of the anchorage bridge of Figure 3; Figure 9 is a sectional view of the anchorage bridge along 9-9 of Figure 8 showing a cable and a cable grip; Figure 10 is a perspective view of the anchorage bridge of Figures 8 and 9; Figure 11 is an elevation of a second embodiment of an anchorage bridge and associated cables; and Figure 12 is an enlarged sectional view on the line 12-12 of the anchorage bridge shown in Figure 11, showing cables and grips.

Referring to Figures 1 to 9 of the drawings, containment vessel 10 is approximately twelve metres high and is sixty metres in diameter (Figures 1 and 2 are not drawn to the same scale). The external peripheral wall 11 of the vessel is provided, with nine substantially horizontal reinforcing bands 12 of cables 14, Figure 2, the cables in each band extending side-by-side fully around the vessel. The pressure exerted by the contents 5 of the vessel 10 on the vessel wall 11 decreases with height and accordingly the spacing between the bands 12 increases with height. The seven lowermost bands 12 comprise sixteen reinforcing cables 14 and the two 5 uppermost bands comprise eight reinforcing cables 14.

One of the sixteen cable bands 12 will now be described in more detail. The sixteen cables 14 may be regarded as constituting four subsets or groups (designated A,B,C,D) of four cables each (designated 10 1,2,3,4). The sixteen cables 14 are disposed one vertically above the other (see for example Figure 7) in the order (beginning from the bottom) Al, Bl, Cl, Dl, A2, B2 etc in a recess 20 (Figures 3 and 7) in the wall of the containment vessel 10. At one metre intervals along 15 the recess 20, there are provided four retaining racks 25 and clips 26 (see Figures 5, 5A and 6) for holding the four groups of cables in position. Each of the sixteen prestressed cables 14 comprises two half cable sections. Four pairs A,B,C,D, of anchorage bridges 30 are provided 20 at equally spaced intervals along the recess 20 (see Figure 1) for anchoring the ends of the halt cable sections of the A,B,C and D groups of cables respectively.

For example, Figure 3 shows One of the A anchorage 25 bridges, wherein it is clear that the adjacent ends of the half cable sections of the group of cables Al, A2, A3 and A4 are gripped, while the other three groups of cables B,C and D pass freely below the main body of the anchorage bridge. It will be noted that each of the two 30 half cable sections corresponding to the same full cable, for example the cable Al, enters the anchorage bridge from opposite directions, and is gripped by a respective cable grip 36. It is to be understood that in Figure 3 only the ends of the A cables are shown, except for the path of the A4 cable shown as a dashed line.

The A anchorage bridge 30 will now be described in more detail with reference to Figures 8 and 9. At the anchorage bridge 30 shown, the A cables are accommodated in slots 32 in the main body 31 of the anchorage bridge while the B,C and D cables pass freely below the main body portion 31 through channels 34 defined by spacing elements 35 which maintain the main body portion 31 clear of the wall 11 seen in Figures 3 and 8. The anchorage bridge 30 is in the form of a generally rectangular block which may be cast in steel, ductile or malleable iron.

To secure the cables to the anchorage bridge 30 use is made of the aforementioned cable grips 36 which may be double or single units as seen in Figures 3 and 8. The anchorage bridge 30 shown in Figures 3, 8 and 9 is known as a 16/4 anchorage bridge (see Figure 2) since the anchorage bridge accommodates sixteen cables in total, the four A cables being accommodated in the slots 32 and the twelve B,C and D cables passing through the channels 34. It is to be understood that a similar arrangement applies to the B,C and D anchorage bridges. There are also provided two 8/2 anchorage bridges approximately half the size of the anchorage bridge 30 and which accommodates eight cables in total and grips two cables. These are for the upper two cable bands, Figure 2.

The method by which the cables 14 are put in position on the external wall of the vessel 10 will now be described. When the vessel 10 is being constructed, a fixing plate 50 (Figure 4) for each anchorage bridge 30 is embedded in the wall of the vessel. The fixing plate 50 is a B.S. Channel placed with the flanges 52 extending into the wall of the vessel 10. Six holes 54 are provided on each flange 52 for accommodating anchoring dowels 56 (only one shown). Six fixing holes (not shown) are provided in the fixing plate 50 to coincide with holes 39 of the anchorage bridge 30. A high strength 7 friction grip nut 58 and a bearing plate 60 are welded to the inside surface of the fixing plate 50 behind each fixing hole. Protective domed cups 53 are placed over the nuts 58 to protect the threads of the nuts during the casting of the wall. Also, retardant impregnated foam is bonded to the formwork for the wall, above and below the fixing plates 50, to facilitate the exposure of the aggregate by brushing with water after stripping of the forms. The exposed aggregate forms a better bonding surface for the in situ concrete cover to the anchorage bridge 30. Bach fixing plate 50 is temporarily retained to the external formwork for the wall using standard black bolts. To permit striking of the formwork, the black bolts are removed, regreased and replaced in the holes until the anchorage bridges 30 are ready for fixing.

The cable retaining racks 25 are fixed to the wall using pneumatically driven short steel nails 27. To mount the cables 14 in the racks 25, the eight A half cable sections are laid out on the perimeter pathway of the vessel 10 with their opposite ends below the diametrically opposite A anchorage bridges 30 respectively. Then, starting from one end, a first half cable section is lifted manually into the bottom position of the bottom rung of a rack 25 and is fixed with a steel retaining clip 26. The clipping operation is continued until the other anchorage bridge is reached. The operation is repeated with the other three A half cable sections on the same side of the vessel, with each one occupying a bottom position in each of the other three rungs of the rack. The four A half cables at the other side of the containment vessel are mounted onto the vessel in a similar manner. The operation is repeated for the B, C and D cables in that order.

With all the cables 14 in position, each anchorage 8 bridge 30 is bolted to its fixing plate 50 using high strength friction grip (HSFG) bolts 65 in place of the black bolts. The polypropylene sheath at the ends of each half cable is circumferentially cut at the centre line of the anchorage bridge 30, so that the sheath can be easily removed just prior to the prestressing operation. The overlapping ends of the half cable sections are then passed through the appropriate slots 32 in the anchorage bridges 30 and tied to each other until the stressing operation is commenced.

The stressing of the cables 14 is effected after stressing the vertically disposed cables of the containment vessel, if such cables are provided in the construction. Stressing of the horizontally disposed cables 14 is then effected commencing with A anchorage bridges 30 at the base of the wall working upwards until bands 1, 3, 5 and 7 are completed and then working downwards until bands 8, 6, 4 and 2 are completed. All the C anchorage bridges 30 are sequentially stressed working in an upward direction. Then all the B anchorage bridges 30 are sequentially stressed working in a downward direction and finally all the D anchorage bridges 30 are sequentially stressed working in an upward direction. Such a method of applying stress prevents an excessive unbalancing of forces.

To perform a stressing operation on a cable 14, the pre-cut polypropylene sheath 15 is removed and a cable grip 36 is fitted over the end of the cable and tapped snug. Before stress is applied to the cable 14, it is necessary to check that the HSFG bolts 65 have been fully torqued. This check may be accomplished using load indicating washers (not shown) with the bolts 65. The ends of the cable 14 are synchronously stressed using identical jacks. With reference to Figure 3, the order in which the cables 14 are stressed at each anchorage bridge 9 30 is 4, 3, 6, 5, 2, 1, 7 and 8. The operation should not normally be interrupted before all eight cable ends at the anchorage bridge have been stressed and every effort should be made to avoid a stoppage when only an odd number of cable ends have been stressed.

When all the cables 14 have been stressed, the anchorage bridges 30 are filled with grout which is injected under pressure through holes 75. The anchorage bridges 30 are then surrounded by mesh reinforced concrete 76. The retaining clips 26 are then removed from the racks 25, and mild steel mesh 78 (Fig 7) is placed in the recess 20 and a number of the clips 26 are replaced to hold it firmly in place with the remainder of the clips being stored for re-use. A concrete cover is then sprayed over the cables 14 and the mesh 78.

Instead of mounting the cables 14 in the recess 20, the cables may be mounted on the surface of the containment vessel 10 or in a shallow recess. In such a case metal flashings are used above and below the band of cables to weatherproof and support the concrete cover.

In a second embodiment of the invention shown in Figures 11 and 12, an anchorage bridge 130 is provided which is fabricated in mild steel. Inside the anchorage bridge 130 are stiffeners 131 and a number of spacers 135 are provided on the underside of the anchorage bridge to allow it to be positioned over the ungripped cables. The anchorage bridge 130 allows cables 14 to be stressed using cable grips 36 and is fixed to a fixing plate 50 in a manner similar to the anchorage bridge 30. The other reference numerals used in Figures 11 and 12 refer to the same components as in the earlier Figures.

It will be appreciated that the anchorage bridge according to the invention may be used for securing cables under stress in other structures such as bridges.

It is to be understood that the invention is not 10 limited to the specific embodiments described above, details of which are given by way of example only and that various modifications and alterations are possible without departing from the scope of the invention.

Claims

11 CLAIMS :-

1. An anchorage bridge for securing cables under stress around the external peripheral wall of a containment vessel, the anchorage bridge comprising a main body 5 portion for accommodating at least one cable to be gripped by the anchorage bridge, means for gripping the said at least one cable while accommodated in the main body portion, and spacing means for maintaining the main body portion clear of the external wall to permit the 10 passage of at least one further cable below the main body portion without being gripped by the anchorage bridge.

2. An anchorage bridge according to claim 1, wherein the main body portion is adapted to accommodate at least one pair of cables entering the anchorage bridge from 15 opposite directions, and a respective gripping means is provided to grip each cable of the pair.

3. An anchorage bridge according to claim 2, wherein the spacing means is adapted to permit the passage of a plurality of cables below the main body portion.

4. An anchorage bridge according to claim 1, 2 or 3, wherein the anchorage bridge is adapted to be rigidly secured to a fixing means mounted on the wall of the vessel.

5. A containment vessel comprising an external 25 peripheral wall and at least one substantially horizontal band of stressed cables extending side-by-side surrounding the external peripheral wall, the band being secured in position by a plurality of anchorage bridges according to any preceding claim spaced around the 30 peripheral wall of the vessel, each anchorage bridge 12 gripping one end of at least one cable such that the ends of all the cables are gripped, and the cables ungripped by any anchorage bridge passing beneath the main body portion thereof.

6. A containment vessel according to claim 5, wherein each cable of the band comprises at least two cable sections extending consecutively around the wall, the adjacent ends of consecutive sections of the same cable being gripped in the same anchorage bridge.

7. A containment vessel according to claim 6, wherein each cable of the band comprises two cable sections each extending around substantially half of the external peripheral wall of the vessel, each pair of adjacent ends of the two cable sections being gripped by the same respective anchorage bridge.

8. A containment vessel according to claim 6 or 7, wherein different mutually exclusive subsets of the cables of the band are each gripped by a respective different mutually exclusive subset of the anchorage bridges.

9. A containment vessel according to claim 6, 7 or 8, wherein all of the cable sections are substantially the same length and the anchorage bridges are equally spaced around the external peripheral wall.

10. An anchorage bridge substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

11. A containment vessel substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings. F. R. KELLY & CO., AGENTS FOR THE APPLICANTS.