GB2254086A - Tendons - Google Patents

Abstract

A structural tendon comprises a plurality (e.g. 2, 4, or 6) of individual strands 1 a-d, ropes, or other elongate load-bearing members, each having a protective jacket 2a-d. The members 1a-d are arranged in a coherent assembly which is substantially torque-balanced under load. Support means (e.g. fluted former 7) supports each member 1a-d over an extended area of its peripheral surface between adjacent members. <IMAGE>

Description

TENDONS The development of ever larger structures, both on and offshore, has led to demands for wire rope tendons in sizes which are rapidly outstripping the available production capacity.

New, bigger machines, capable of manufacturing very large ropes (or stands) have been considered, but their very high capital cost cannot be justified by the expected volume of demand. Even if the economics were favourable, there are major logistical problems involved in transporting such products from factory to site. The present invention aims to alleviate these difficulties.

In one aspect the invention provides a structural tendon comprising a plurality of elongate load-bearing members of more than lOOmm diameter, individually coated with a protective jacket, arranged in a coherent assembly which is substantially torque-balanced under load.

In another aspect the invention provides a structural tendon comprising a plurality of elongate load-bearing members, individually coated with a protective jacket, assembled in a helical array around a substantially incompressible central grooved support member at a pitch selected to minimise the torsional characteristic of the complete assembly under axial load.

Such tendons may be attached to a structure by means of a termination of unitary constructions comprising a plurality of sockets into which ends of the elongate load-bearing members are cast.

A plurality of jacketed load-bearing members may be assembled by means of a modular pre-fabricated facility comprising a series of braked rotatable pay-off reels, an overhead caterpillar traction system, and a driven/traversable take-up reel.

In particular, a structural rope or tendon comprising a plurality of very large strands (or ropes), i.e. more than lOOmm in diameter, may have the following features: i) the strands (or ropes) may be manufactured using existing production equipment; ii) the strands (or ropes) will each be provided with a protective covering (jacket or outer layer); iii) the strands (or ropes may then be transported to site using conventional handling equipment; iv) the covered strands (or ropes) may then be assembled together at a very long lay or pitch, e. g.

from 30 to 75 (or more) times the tendon diameter, using a special purpose closing facility; v) grooved elongate formers may be used to support and separate the strands (or ropes) in a uniform helical array; vi) the assemblies may then be terminated by casting the plurality of strands (or ropes) into a single connector block which provides for an equal number of conical socket housings.

This invention will be described further, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a diagrammatic cross-section through a tenon with two platic-covered steel-wire strands; Figure 2 is a diagrammatic cross-section through a tenon with four plastics-covered steel-wire strands; Figure 3 is a diagrammatic cross-section through a tenon with six plastics-covered steel-wire strans; Figure 4 is a schematic perspective view of an end attachment on a four-strand tenon; and Figure 5 is a diagrammatic cross-section through a tenon with four metal-jacketed steel-wire strands.

Two-Member Tendon (Figure 1) Since no advantage is served by imparting a helical lay, two covered steel wire strands la, ib (or ropes) are laid side-by-side in a straight condition and affixed to one another (by banding or bonding) to form an integral tendon which can then be coiled and handled as a single unit. Left and right-hand lay strands (or ropes) are paired together to ensure freedom from torsional imbalance under load. As shown in Figure 1, the jackets 2a, 2b or the strands are formed with longitundinal bosses 3a, 3b which have plane mating surfaces defining at each side a fillet 4 for forming a weld 6.

Four-Member Tendon (Figure 2) Four identical covered strands la ... id (or ropes) are assembled together at a long helical pitch, around a central fluted former 7 which has an external profile comprising four arcuate concave grooves. The helical pitch may be selected to effect a minimisation of the load-torque characteristic of the complete tendon, having regard to the torsional characteristic of the component strands (or ropes).

The helical lay will impart a natural coherence to the assemblage of strands la ... id, initially due to the inherent (flexural) stiffness of the strands, but supplemented by the radial components of the strand tension, as axial load is applied to the tendon. These compressive radial forces will be resisted by the central fluted support member 7 without causing any damage to the jackets 2a ... 2d of the strands, because of the broad area of contact offered by the supporting grooves and the consequent low level of stress.

Additionally, the central support member 7 is designed to be virtually incompressible so that the axial stiffness of the tendon is maximised (i. e. there is negligible radial movement of the strands with load).

Six-Member Tendon (Figure 3) Six identical covered strands la ... if (or ropes) are assembled together at a long helical pitch, around a central fluted former 7 which has an external profile comprising six arcuate concave grooves. This central fluted member may itself contain a further (seventh) load-bearing strand (or rope) or may, alternatively, contain a transmission means, such as a tube for the conduction of fluids or a conductor for the conveyance of energy.

The helical pitch may be selected to effect a minimisation of the load-torque characteristic of the complete tendon, having regard to the torsional characteristic of the component strands (or ropes). The helical lay will impart a natural coherence to the assemblage of strands, initially due to the inherent (flexural) stiffness of the strands, but supplemented by the radial components of the strand tension, as axial load is applied to the tendon. The tendon may also be banded to provide additional integrity during handling operations, e. g. during installation, and prior to the axial load being applied. This banding (not illustrated) if applied helically and continuously, may also be used to impart additional protection and torsional stability to the tendon during installation.

The compressFive radial forces generated in the outer strands, will be resisted by the central fluted support member without causing any damage to the jackets 2a ...

2f of the strands, because of the broad area of contact offered by the supporting grooves and the consequent low level of stress. However, the central support member 7 is designed to withstand such stresses with minimal distortion, so that the axial stiffness of the tendon is not impaired. The central support member 7 is therefore virtually incompressible, whether or not it contain an additional load-bearing or transmission element.

The aforegoing examples are cited by way of illustration only and other designs of tendon may comprise 3, 5, 7 or more members. Also, the members need not necessarily all be of equal size, but could be of alternate diameter to provide a different geometrical solution, e.g. 2+2F, or 3+3F, 4+4F etc. (F=filler). The filler elements may be profiled to provide a smooth surface to the exterior periphery of the tendon.

ASSEMBLY METHOD The logistical advantage of the above-described tendons is that the component members may be manufactured using existing production machinery (stranding, closing, and extrusion machines) and then transported individually, on reels, to a suitable location close to the proposed installation. The assembly operation is then carried out at this location using a special purpose pre-fabricated and de-mountable facility. This procedure minimises the problems of handling and transporting very large and heavy reels of tendon.

END ATTACHMENTS The preferred method of terminating the finished tendons is to separate the ends of the strands (or ropes) and introduce them into the respective sockets of the termination block 8 illustrated in Figure 6 (exemplary of a block for a 4-member tendon 9). The ends of the individual strands 2a ... 2d (or ropes) are then opened up into their constituent elements (wires) and cleaned, prior to being cast into respective sockets 11 using an appropriate potting (casting) material, e.g. resin or metallic compound. This method ensures accurate adjustment of the strands relative to the end attachment, and good load sharing between them.

An alternative method is to pre-tension the individual strand members (after jacketing), mark and cut accurately to length, and then attach individual cylindrical sockets to each of the ends. After assembly of the tendon, the socketed ends of the members are then introduced into a slotted mother block, which contains and captures the plurality of sockets so that the axial load on the mother block may be transmitted to each of the members of the tendon, and shared between them.

OTHER FEATURES For many applications, protection of the strength-members from degradation due to corrosion is of considerable importance. The jacket applied to the individual strands (or ropes) provides the primary source of protection. Typically, this jacket will comprise a robust extrusion of, for example, a thermoplastic material, such as high density polyethylene, which is impermeable to moisture.

Alternatively, for some applications a helical jacket of a sacrificial or corrosion-resistant material, such as aluminium alloy, may be appropriate. This could take the form of interlocking shaped sections 12, as illustrated in Figure 5.

Additional protection of the load-bearing elements may be provided by fully blocking the interstitial spaces with an impervious blocking material to preclude the migration of media should the jacket be penetrated.

Typically, a corrosion and water-resistant wax compound or gel will be used.

Claims (8)

Claims: -

1. A structural tendon comprising a plurality of individual strands, ropes, or other elongate load-bearing members, each member having a protective jacket, the members being arranged in a coherent assembly which is substantially torque-balanced under load.

2. A structural tendon as claimed in claim 1, including means for supporting each member over an extended area of its peripheral surface between adjacent members.

3. A structural tendon as claimed in claim 2, in which the said supporting means comprises longitudinal bosses integral with the protective jackets.

4. A structural tendon as claimed in claim 2, in which the said supporting means comprises a substantially incompressible central grooved support member.

5. A structural tendon as claimed in claim 4, in which the elongate load-bearing members are arranged in a helical array around the support member.

6. A structural tendon as claimed in any preceding claim, in which the jacket comprises a covering of plastics material.

7. A structural tendon as claimed in any preceding claim, in which each elongate load-bearing member is more than 100 mm in diameter.

8. A structural tendon substantially as described with reference to, and as shown in, Figure 1, Figure 2, Figure 3, or Figure 5 of the accompanying drawings.