GB2170538A - Flexible connections - Google Patents

Abstract

A flexible connection in an elongated assembly comprises link members (1A, 1B, 1C...) interposed between two other members (1 and 2) of the assembly. Co-operating pairs of convex and concave bearing surfaces (4/6, 4/5, .... 4/5, 7/5) formed on all these members permit relative pivotal motion to take place between each two adjacent members. Tensioned tendons (8) extending between the members maintain the bearing surfaces in co- operation. The members are hollow such that a continuous duct extends through the elongated assembly as a whole. An elongated assembly described in detail is a hollow rectangular- sectioned column extending from a base structure at the sea bed to the surface. <IMAGE>

Description

SPECIFICATION Flexible connections This invention relates to flexible connections in elongated assemblies.

Flexible connections are needed for many structural assemblies such as otherwise stiff buoyant columns in which flexible connections can be introduced to reduce and limit the bending moments along the length of the column. Such flexible connections generally consist of high strength materials such as alloyed steel. Conventional connections along a hollow concrete column often interrupt the continuity of the column,s internal or external profile and interfere with the passage of pipes or other installations which may require that there be little or no change to the inside or outside diameter of the column at these points.

Articulated columns installed offshore to support vertical pipes (so-called risers) are an example of such structures where there may be a need to reduce bending moments along their length, to limit angular deflections, to control their dynamic behavour and to maintain the continuity of their shape.

According to the present invention there is provided a flexible connection in an elongated assembly, comprising a pair of convex bearing surfaces formed on one member of the assembly and which are in cooperation with a pair of concave bearing surfaces formed on another member of the assembly such that relative pivotal motion can take place between these pairs of bearing surfaces and hence between the members on which these surfaces are formed. The invention further provides tension elements serving to maintain the cooperation between the pairs of bearing surfaces.

In particular forms described hereinafter at least one link member is interposed between the two other members of the assembly respectively carrying the pairs of convex and concave bearing surfaces, the (or each) link member having a pair of convex bearing surfaces and a pair of concave bearing surfaces formed thereon and respectively in co-operation with the first-mentioned pairs of concave and convex bearing surfaces (or such pairs of concave and/or convex bearing surfaces formed on another link member) such that relative pivotal motion about a first axis can take place between the (or a first) link member and one of said two other members of the assembly, and such that relative pivotal motion about a second axis can take place between the (or another) link member and the other of said two other members of the assembly.Where there is a plurality of link members, the first, second and further axes of relative pivotal motion can be angularly displaced from one another at angles other than 90".

When a connection such as defined above is incorporated in a buoyant column extending from a sea or other water bed, it becomes possible to reduce bending moments along the column; to provide freedom for a limited degree of angular deflection (deflections may be caused by horizontal forces from wind, waves, etc); to provide a controlled stiffness for the column, which may be needed for static or dynamic stability of the column; to minimise alteration in the configuration of the column at the zone of the connection; to facilitate a desired distribution of forces (tension, compression and shear) at the zone of the connection; to provide torsional stiffness as required; and to provide capability for the column to deflect in all directions, similar to the capability offered by conventional universal joints.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which: Figure 1 is a schematic perspective view of a rectangular column with a flexible connection incorporated therein; Figure 2 is a side view of the column of Figure 1; Figure 3 is a cross-sectional view of the column; Figure 4 is a detail view on a larger scale; Figure 5 is an exploded perspective view of three link members of the connection; Figure 6 is a perspective view of another form of link member; Figure 7 is a cross-section of the part shown in Figure 6, taken on line VII-VII; Figures 8, 10, 12 and 14 are perspective views of further forms of link members;; Figures 9, 11, 13 and 15 are cross-sections taken on lines IX-IX, Xl-Xl, XIII-XIII and XV XV in Figures 8, 10, 12 and 14 respectively; Figure 14A is a perspective view of part of a modified form of the link member shown in Figure 14; Figure 16 is a schematic view of part of a connection; Figure 17 is a schematic view of a modified form of the connection of Figure 16; Figure 18 is a side view of a connection incorporated in a suspended pipe; and Figure 19 is a cross-sectional view taken on line XIX-XIX in Figure 18.

Referring first to Figures 1 to 5, the connection 1 is incorporated in a base member 2 and an upper member 3 of a hollow, rectangular-sectioned column extending from a base structure to an upper structure, for example from the sea bed to the surface. The column members 2 and 3 as illustrated are of concrete and the connection is composed, in the particular form illustrated, of opposed portions of the column members 2 and 3, and three rectangular-sectioned, also hollow, link mem bers 1A, 1B and 1 C, which are also of concrete.Each of these link members has, formed as parts of the link member, a pair of opposed downwardly convex lower bearing surfaces 4 and a pair of downwardly concave upper bearing surfaces 5, the common axis about which the pair of surfaces 4 of each link member is generated being at right angles to the common axis about which the pair of surfaces 5 of the same link member is generated.

The convex lower bearing surfaces 4 of the lowest link member 1 A bear on concave bearing surfaces 6 formed as parts of the column base member 2. The concave bearing upper surfaces 5 of the uppermost link member 1C have bearing on them convex bearing surfaces 7 formed as parts of the column upper member 3. Each remaining pair of convex lower bearing surfaces 4 bears on the pair of concave bearing surfaces 5 of the adjacent link member IA or IB. Thus, in order from bottom to top, there are bearing upon one another, bearing surfaces 4 on 6, 4 on 5, 4 on 5 and 7 on 5.The co-operation between components 1A, 1B, 1C, 2 and 3 thus achieved is such that each link member can rotate about the axis of its bearing surfaces relative to the link member(s) (or column base or upper member) with which it co-operates, and such that the column upper member 3 can likewise rotate relative to the upper link member 1C.

The co-operation is such that a continuous duct extends through the elongated assembly as a whole.

In the form of Figures 1 to 5 the bearing surfaces are maintained in co-operation by tensioned tendons 8 extending between the link member 1A and the column base member 2, the link members 1B and 1A, and the column upper member 3 and the link member 1C. The tendons 8 are anchored in corbels 9 and can be of high strength steel or manmade fibre. As an alternative, or in addition, tendons could be provided extending directiy between the two column members 2 and 3.

In the Figures the tendons 8 are shown running longitudinally of the connection as a whole in its un-flexed condition. In addition, or alternatively, tendons running in other directions could be provided in the connection, that is they are inclined with respect to the longitudinal direction of the connection as a whole in its un-flexed condition.

The co-operating bearing surfaces can be in sliding co-operation, through suitable bearings, but in the form illustrated, elastomeric bearings 10 (Figure 4) are interposed between each pair of co- operating surfaces. These elastomeric bearings have a sufficient shear deformation capacity to suit requirements.

It will be appreciated that each of the link members 1A, 1B and 1C, and each of the parts 2 and 3, is, in itself, rigid. The flexibility of the connection 1 as a whole is provided by the possibility of relative pivoting motion between the link members and the parts 2 and 3. The number of individual link members is determined by the overall degree of flexibility required. The three link member connection illustrated permits bending in all longitudinai phases. If desired, there could be two, or more than three link members, or no link members at all with the parts 2 and 3 cooperating directly with one another and bending relative to one axis only. Where there is a plurality of link members, the axes of pivotal motion can be angularly displaced from one another at angles other than 90".

The tendons 8 provide bending restraint.

Where elastomeric bearings are utilised, their shear stiffness provides bending restraint in conjunction with that provided by the tendons 8. Transverse and torsional shear loads are taken by the compression forces introduced to the bearings together with the shear stresses which vary along the lengths of the bearings.

The tendons give specified bending stiffness where required, and/or limitation of angular deflection. They can be of any desired length and are prestressed as required. Alternatively, they can be omitted and the shear stiffness provided by the elastomeric bearings may provide the desired flexural restraint, particularly in cases where permanent compressive forces exist between the co-operating bearing surfaces without the use of tendons. It is to be noted that, in a water environment, some components can be in compression and some in tension dependent upon weights and extent of built-in buoyancy.

To avoid bending of the tendons, the anchorage of each can be of the form illustrated in Figure 16, incorporating a sliding or elastomeric bearing 11 permitting pivoting at the tendon anchorages.

It will be appreciated from Figures 1 to 5 that the provision of the illustrated flexible connection 1 results in a minimal interference to the internal void available within the column for passage of pipes and other installations.

The link members of the flexible connection can be of different configurations, as, for example, shown in Figures 6 and 7 where equivalent components are identified by references as used above. In this Figure there is shown an elongated central link member IB. In Figures 8 and 9 also references as already used are utilised, as is also the case in each of Figures 10 and 11, 12 and 13 and 14, 14A and 15. These Figures illustrate various configurations which can be adopted but it will be understood that still other configurations are possible, in particular the link members can have a larger number of side than the six illustrated in Figures 12 and 13, and a corresponding larger number of pivotal axes.

Mention has been made above of provision for pivoting at the tendon anchorages, illustrated in Figure 16. The extent of pivoting motion of cooperating bearing surfaces and tendon anchorages can be limited by stop members 12 as shown in Figure 17.

In all the forms so far described the flexible connection is incorporated in an upright column. Figures 18 and 19 illustrate use in a suspended pipe run. In this form a spigot 20 at the end of a length of pipe has a pair of convex bearing surfaces 21 formed as parts of the spigot and that co-operate with a pair of concave bearing surfaces 22 formed as parts of a first link member 23A. An elastomeric bearing 24 is interposed between the bearing surfaces 21 and 22. Further co-operating bearing surfaces (not shown in detail) are provided between further link members in a manner similar to that already described.

In all cases sealing can be provided wherever there are co-operating bearing surfaces along the length of the flexible connection.

Flexible members or bellows-type sections able to accommodate the angular and longitudinal deflection at the zone to be sealed can be utilised.

By utilising component parts of suitable configuration, flexible connections as described can be incorporated in runs, of any crosssection, of upright columns, and in runs of pipes for example hanging from vessels for depositing materials such as sand and gravel on the water bed, or for taking up (by suction) fine sediments from the water bed. Such pipes can be made up of discrete segments interconnected by flexible connections as described above.

The rigid components of the flexible connections can be constructed in concrete, for example, by slip forming, or casting.

The number of rigid components incorporated in a flexible connection can be two or more depending upon the degree of flexibility required. It will be appreciated that where at least one link member is provided, flexibility is introduced by providing curved bearing surfaces on two opposite sides of the body of the link member if the central part of the structure is to remain uninterrupted. The cross section of the body at this zone has a major axis for sliding and/or shear deflection and another axis for introducing prestressing forces, flexural restraint tendons being provided if required.

Claims (12)

1. A flexible connection in an elongated assembly, comprising a pair of convex bearing surfaces formed on one member of the assembly and which are in cooperation with a pair of concave bearing surfaces formed on another member of the assembly such that relative pivotal motion can take place between these pairs of bearing surfaces and hence between the members on which these surfaces are formed.

2. A flexible connection as claimed in claim 1 and further comprising tension elements serving to maintain the co-operation between the bearing surfaces.

3. A flexible connection as claimed in claim 2, wherein the tension elements are elongate elements at least some of which extend longitudinally of the connection as a whole in the un-flexed condition of the connection.

4. A flexible connection as claimed in claim 2, wherein the tension elements are elongate elements at least some of which are inclined with respect to the longitudinal direction of the connection as a whole in the un-flexed condition of the connection.

5. A flexible connection as claimed in claim 1, 2, 3 or 4, wherein at least one link member is interposed between the two other members of the assembly respectively carrying the pairs of convex and concave bearing surfaces, the (or each) link member having a pair of convex bearing surfaces and a pair of concave bearing surfaces formed thereon and respectively in co-operation with the first-mentioned pairs of concave and convex bearing surfaces (or such pairs of concave and/or convex bearing surfaces formed on another link member) such that relative pivotal motion about a first axis can take place between the (or a first) link member and one of said two other members of the assembly, and such that relative pivotal motion about a second axis can take place between the (or another) link member and the other of said two other members of the assembly.

6. A flexible connection as claimed in claim 5, wherein there is a plurality of link members, and the first, second and further axes of relative pivotal motion are angularly displaced from one another at angles other than 90".

7. A flexible connection as claimed in claim 5 as appendant to claim 2, 3 or 4, or claim 6, wherein at least some of the tension elements extend respectively between each of said two other members and the (or the adjacent) link member, and between each two adjacent link members if there is more than one link member.

8. A flexible connection as claimed in claim 5 as appendant to claim 2, 3 or 4, or claim 6, wherein at least some of the tension elements extend between said two other members.

9. A flexible connection as claimed in any one of claims 2 to 4, 5 as appendant to 2, 3 or 4, 6 or 8, wherein the tension elements are anchored at each end in an anchorage permitting pivoting of the tension elements.

10. A flexible connection as claimed in any one of the preceding claims, wehrein elastomeric bearings are inserted between each two co-operating bearing surfaces.

11. A flexible connection as claimed in any one of the preceding claims, wherein each member having one or two of said pairs of bearing surfaces formed thereon is hollow such that a continuous duct extends through the elongated assembly as a whole.

12. A flexible connection in an elongated assembly, substantially as hereinbefore described with reference to Figures 1 to 5, or Figures 6 and 7, or Figures 8 and 9, or Figures 10 and 11, or Figures 12 and 13, or Figures 14 and 15, or Figure 14A, or Figure 16, or Figure 17, or Figures 18 and 19 of the accompanying drawings.