GB2178373A

GB2178373A - Supporting leg for an artificial island

Info

Publication number: GB2178373A
Application number: GB08618349A
Authority: GB
Inventors: Bart Boon
Original assignee: RSV GUSTO ENG BV
Current assignee: RSV GUSTO ENG BV
Priority date: 1985-07-30
Filing date: 1986-07-28
Publication date: 1987-02-11
Also published as: GB2178373B; FI863116A; NO863036D0; FI863116A0; NO863036L; NL8502158A; GB8618349D0

Abstract

The supporting leg or its vertical chords (3) consist of preferably centrifugally cast tube having spaced apart thickened portions (4) which can be the nodal points of a lattice (Figure 1). The locking means or means for the vertical displacement of a leg with respect to the pontoon are clamp jaws (10, 11,Figure 3) which act upon the tubes between the thickened portions (4), and which are moved vertically by cylinders (8, 9). At each leg or chord sets of locking means (10, 11) can be provided one spaced above the other. By means of two of said sets moments can be generated suitable activation of the cylinders to counteract additional loads in the leg such as occur under survival conditions. <IMAGE>

Description

SPECIFICATION Artificial island and supporting leg therefor Supporting leg for an artificial island, and an island respectively provided with supporting legs according to the invention.

The invention relates firstly to a supporting leg for an artificial island consisting of a pontoon and a number of supporting legs adapted to be made fast and to be displaced vertically relative to the pontoon, said supporting leg being provided with a row of parts projecting in the horizontal direction, which project beyond the periphery of the supporting leg or beyond the periphery of a vertical chord of a lattice supporting leg respectively and which are adapted to cooperate with the apparatus effecting the relative displacement of the supporting leg in relation to the pontoon, said projecting parts cooperating with locking means which are displaceable transversely in relation to the longitudinal axis of the supporting leg.

A supporting leg of this kind and the artificial island in which this supporting leg is used are generally known, for example from Published European Patent Application No. 0.024.939.

This known supporting leg is provided with outwardly projecting racks meshing with pinions of the apparatus, fastened on the pontoon, for bringing about the relative displacement of a supporting leg in relation to the pontoon, which can also be called a lifting mechanism. With the aid of this arrangement this leg can be lowered and, after all the legs have been placed on the bed of the water, the pontoon can be raised out of the water. When the pontoon has been lifted out of the water and rests on the supporting legs, each leg is locked in relation to the pontoon, for example by means of toothed bars which are displaceable in the transverse direction and can be pressed into the rack or racks on the supporting leg, and which in their locked position are secured against horizontal or vertical displacement with the aid of supporting or adjusting means, such as bolts.When this method of locking is employed, as is customary, it is possible with this fastening system not only to transmit the static load from the pontoon to the legs, but also to take the moments emanating from the horizontal load due to wind, currents and waves acting on each supporting leg on the pontoon. The lifting mechanism itself can then be disconnected, for example by releasing the brakes on the operating mechanism of the pinions.

This locking system must be so constructed that it can take the load originating from the fraction of the weight applied to each leg and from the maximum moments occurring there,under difficult conditions, such as the so-called survival conditions. This usually means that the locking system must be able to take twice the static load plus a generally greater load originating from the moments.

This known locking system imposes strict requirements in the construction of the supporting leg and of the pontoon, and is therefore expensive. Moreover, the correct adjustment of the toothed bars effecting the locking is time-consuming. The invention seeks to provide a means of solving these problems in a simple manner.

According to the invention this aim is achieved in that the projecting parts consist of thickened portions of the supporting leg or of a chord or the chords of a lattice type supporting leg respectively, these thickened portions being disposed at regular distances from each other, viewed in the longitudinal direction of the supporting leg or the chords respectively. This means firstly that there are now no toothed racks and that the means for securing the supporting legs in relation to the pontoon and for the relative displacement must therefore be adapted accordingly. Instead of acting on the toothing of the racks, they should in fact now act on the thickened portions of the tubular supporting leg or of the tubular chords respectively of a lattice type supporting leg.Locking means supported on the thickened portions of a Sectional member can usually be of a simple form, and this is certainly the case when said sectional member - that is to say the tube from which the supporting leg is made or of which the chords of a lattice type supporting leg are composed - has a cylindrical section. The locking means then act on or around the thinner parts and are supported in the vertical direction by the thickened portions, or the thickened portions are supported on the locking means.

If the supporting leg is a lattice type leg, the thickened portions are preferably situated at the nodal points of the lattice. The volume of material of the thickened portions can then be usefully employed for forming the nodal point and for the transmission of forces there.

Between the nodal points at least one additional thickened portion can be provided, and this may project a shorter distance outwards than the thickened portions at the nodal points, since there no material is required for forming a nodal point. Furthermore, the guides adapted to the larger diameter at a nodal point cannot in that case introduce moments at an undesirable point situated between the nodal points.

Cylindrical tubes, in which each thickened portion is a cylindrical part of a larger outside diameter, are preferably used. The inside diameters are then preferably equal to one another in order to ensure a good weld connection.

For supporting legs for artificial islands a prerequisite is great strength. This means that when tubes are used, they must have a thick wall. It is known to produce thick tubes by centrifugal casting.

According to the invention, the supporting leg or the chord of a lattice type supporting leg may consist of pieces of tubing which are welded together in the longitudinal direction, are produced by centrifugal casting, and are each provided at at least one end with at least a part of a thickening formed by casting.

Pieces of tubing of this kind can thus comprise a long portion of the smaller diameter with, at the ends, parts of larger diameter, each forming half of a thickened portion. It is also possible for a piece of tubing to be used which has an integrally cast thickening at only one end. It is also conceivable for the pieces of tubing of smaller diameter to be inserted into the inside diameter of the thickened portion.

According to the invention it is also possible for the supporting leg or the chord respectively of the lattice type supporting leg to consist of pieces of tubing which are produced by centrifugal casting and are welded together in the longitudinmal direction, and which consist alternately of short and long pieces, the short pieces having the larger diameter. Use is then made solely of pieces of tubing of smaller diameter and pieces of tubing of larger diameter.

An artificial island provided with supporting legs of this kind may in addition be characterized in that the locking means consist of horizontally displaceable clamp jaws acting on both sides on the tube or on the chords and substantially embracing the tube or the chord, the shape of the jaw being adapted to the parts of the tube or chord which lie between the thickened portions.

According to the invention it is now possible for a plurality of sets of locking means to be disposed one above the other on each tube or chord respectively, and for these locking means to be disposed in a separate frame for each set of locking means, this frame being adjustably connected to the pontoon with the aid of adjusting means, such as pressure medium cylinders. It is thus possible to use the locking means both for the relative displacement of the supporting leg with respect to the pontoon and for taking the loads after the pontoon has been lifted out of the water, that is to say both the static loads and a part of the dynamic loads, in other words the moments which occur as the result of wind and wave loads. If both the sets of locking means disposed one above the other are load-carrying, twice the static load per leg can be taken by them.The arrangements for taking the moments under survival conditions, usually consisting of fastenings spaced apart, can then be simpler because these means can be disposed respectively above and below the locking means, while for the purpose of taking the moments these means can then also act on the parts of the supporting leg tube or chord tube which are situated between the thickened portions without any complicated adjustment operations being required, such as are always needed when a rack has to engage in another rack. If the locking means with their associated adjustment means act separately, but in turn, the relative displacements can then be effected; if they act simultaneously, a heavier load can be taken.

If the supporting legs consist of lattice type legs and if sets of locking means and associated adjustment means are used for each chord, these means can once again be controllable independently of each other, in such a manner that in one chord a different vertical force can be transmitted from that in another chord.

In the case of small islands, supporting legs will be adequate which are formed by a single tube, and therefore in accordance with the invention by one single tube per supporting leg, provided with thickened portions. In the case of larger islands use is made of lattice type legs whose chords are formed by tubes having a diameter comparable with that of the tube which can constitute the supporting leg of a small island. Lattice type legs of this kind are therefore of large dimensions.

This makes it possible for the locking means, with their adjustment means, to be allowed to supply an opposing moment, taking the place of the fastenings spaced apart one above the other for the purpose of taking the moments. The force components of this opposing moment are directed vertically.

The invention will now be further explained with the aid of the drawings.

Figure 1 shows a schematic side view of an artificial island having supporting legs according to the invention.

Figure 2 is a top plan view of Figure 1.

Figure 3 is likewise a schematic side view of a part of an artificial island having a leg structure according to another embodiment of the invention.

Figure 4 shows schematically the action of the locking means on a cylindrical leg.

Figure 5 is a side view of a part of an open lattice leg.

Figure 6 is the top plan view of the leg shown in Figure 5.

Figure 7 shows a part of a chord of a lattice supporting leg on a larger scale.

Figure 8 shows schematically the action of the locking means on the chord of a lattice supporting leg.

Figure 1 shows a pontoon (1) having openings (2) through which legs (3) pass. The embodiment shown in Figures 1 and 2 comprises open lattice leg structures of triangular configuration in horizontal section.

The construction of a leg of this kind is shown in greater detail in Figure 5.

Figure 3 shows a pontoon (1') having guide openings (2') for supporting legs (3'), which consist of a single tube. This tube may be constructed from pieces of tubing which are welded together and which are produced, for example, by centrifugal casting and during the casting process are provided with regularly spaced cylindrical thickened portions (4'). A possible position for the weld joint between successive pieces of tubing is indicated at 5.

In the lattice supporting leg shown in Figures 1,2 and 5 to 8 the chords of the lattice are formed by tubes (3) having thickened portions (4). Each chord can be constructed in the same way as the single tube shown in Figure 3.

The thickened portions (4 or 4') form the supporting members for locking means adapted to act on the parts of smaller diameter of the tube (3 or 3'), either above the thickened portions or below them.

Figure 3 shows two lock frames (6 and 7) which are joined to the pontoon (1') by means of pressure medium cylinders such as 8 and 9 respectively. This connection is only shown schematically. Other forms of construction are conceivable for this purpose.

A locking frame (6 or 7) carries horizontally displaceable locking means (1 0a, 1 0b and 11 a, 11 b respectively) which are guided in the horizontal direction in the frames and by means of pressure medium cylinders (not shown), which are known per se, can be displaced horizontally between a position in which they act on the tube and in a position in which they release the tube in such a manner that a thickened portion (4') can pass through.

As shown in Figure 4, each locking means has a circular recess whose radius corresponds to that of the portion (3') of the supporting leg.

In the lattice supporting legs shown in Figures 1 and 2, locking means (12a and 12b) and (13a, 13b respectively) are disposed on each chord, acting on both sides of the chord, these locking means merely being indicated schematically in Figure 1; their arrangement and operation are however entirely comparable to those shown in Figure 3, it being understood that they are horizontally displaceable in vertical planes which extend parallel to the opposite side of the lattice supporting leg and in which support stands (14 and 1 5 respectively) are also disposed, as indicated in Figure 3, and (14', 15' respectively) as indicated in Figure 2.

All the locking systems (1 0a, 1 0b and 11 a, 11 b respectively) with their associated adjusting cylinders (8 and 9 respectively) can be used in the usual manner to bring about a relative displacement of a supporting leg with respect to the pontoon. In view of the fact that the locking means and their associated adjusting means must each be able to carry in turn a part of the weight of the pontoon, that is to say a one-third part in the case of three legs, it is possible with two locking means and associated adjusting means for twice this weight, that is to say two thirds of the weight, to be carried per leg.For the purpose of taking moments, fastening can then be effected, for example, by means of clamp jaws (16 and 17 respectively), which likewise act between the thickened portions and which are guided for horizontal displacement in the opening (2') in the pontoon (1') and are adapted to be secured, in conjunction with comparable means (not shown) situated to the right of (16', 17') in Figure 1 and acting on another chord.

This can be done both for a supporting leg consisting of a single tube and for each chord of a lattice supporting leg.

With a lattice supporting leg, however, there is another possible method, since with the aid of the cylinders (8 and 9), with both sets of locking means in action, divergent forces can be generated for each chord of each lattice leg to counteract the bending moment occurring at the level of the pontoon through the action of wind and waves.

In Figure 1 the direction of the wind is indicated by the arrow 20, and the resulting ground reactions are indicated by (21) in the case of horizontal reaction and (22) and (23) respectively in the case of vertical reactions.

Based on a pontoon weight of, for example, 9,000 tonnes, the static load per supporting leg will be 3,000 tonnes. Assuming a total moment due to wind and wave forces of, for example, 150,000 tonne-metres, this means, for example with a leg spacing of 50 metres, that the leg situated on the leeward side will carry an additional load of 3,000 tonnes. This most heavily loaded leg thus has to carry a total vertical load of 6,000 tonnes.

If the locking mechanism with its associated adjusting cylinders is already so constructed that it can carry 3,000 tonnes per leg, the two mechanisms, when both are in action, can carry 6,000 tonnes, so that the static load which can occur under survival conditions can thus all be taken by this mechanism alone.

With a lifting apparatus working with racks and pinions this can of course also be achieved in theory, but in practice so many expensive drive motors together with operating mechanisms and pinions are required that this system becomes too expensive, while slippage of the brakes on the operating mechanism pinions can lead to problems.

The simple leg construction according to the invention now makes this easily possible.

For the purpose of enabling moments to be taken, the fastening of the leg at the level of the pontoon is necessary.

If it is now assumed that in this example the moment per leg under survival conditions amounts to 90,000 tonne-metres, this has the consequence that under survival conditions the most heavily loaded chord of a substantially triangular lattice leg structure, with a distance between chords of for example 18 metres, carries an extra load of 5,000 tonnes.

With 6,000 tonnes per leg, this means 2,000 tonnes per chord, so that the most heavily loaded chord has to carry 5,000 + 2,000 = 7,000 tonnes, and the least heavily loaded chord has to take -5,000 + 2,000 = -3,000 tonnes. For the third chord the load due to moments is equal to zero and that due to static load is 2,000 tonnes.

According to the invention it is now possible, even with a lattice leg, to use fastenings at the points 16', 17' as indicated in Figure 1, and above in the support stands 14, 15, at the height of 14', 15'.

However, opposing forces producing the desired opposing moment can also be generated for each chord with the aid of the locking means and their adjusting cylinders 8, 9 which are disposed on both sides of each chord.

For the sake of clarity it is observed that in Figure 1 the direction of the wind 20 is shown as coming from the left, and in Figure 2 it is shown as coming from a direction displaced by 90 . For the example, however, this is of no importance, because for survival conditions the most heavily loaded leg or chord of a leg must always be considered.

Claims

1. Supporting leg for an artificial island, consisting of a pontoon and a number of supporting legs adapted to be made fast and to be displaced vertically relative to the pontoon, said supporting leg being provided with a row of parts projecting in the horizontal direction, which project beyond the periphery of the supporting leg or beyond the periphery of a vertical chord of a lattice supporting leg, and which are adapted to cooperate with the apparatus effecting the relative displacement of the supporting leg in relation to the pontoon, said projecting parts cooperating with locking means which are displaceable transversely in relation to the longitudinal axis of the supporting leg, characterized in that the projecting parts consist of thickened portions of the supporting leg or of a chord or the chords of a lattice supporting leg, these thickened portions being disposed at regular distances from each other, viewed in the longitudinal direction of the supporting leg or the chords.

2. Supporting leg according to Claim 1, characterized in that in a lattice supporting leg the thickened portions are situated at the nodal points of the lattice.

3. Supporting leg according to Claim 2, characterized in that at least one additional thickened portion is provided between successive nodal points.

4. Supporting leg according to Claim 3, characterized in that the interposed thickened portions project a shorter distance outwards than the thickened portions at the nodal points.

5. Supporting leg according to one or more of the preceding claims, in which the supporting leg or the chords of a lattice supporting leg has or have a cylindrical section, characterized in that each thickened portion is a cylindrical part of larger outside diameter.

6. Supporting leg according to Claim 5, characterized in that the supporting leg or the chords of the lattice supporting leg consists or consist of pieces of tubing which are welded together in the longitudinal direction, are produced by centrifugal casting, and are each provided at at least one end with at least a part of a thickened portion formed by casting.

7. Supporting leg according to Claim 5, characterized in that the supporting leg or the chords of the lattice supporting leg consists or consist of pieces of tubing which are produced by centrifugal casting and are welded together in the longitudinal direction, and which consist alternately of short and long pieces, the short pieces having the larger diameter.

8. Artificial island having supporting legs each of which consists either of a single tube provided with thickened portions or of a lattice having chords provided with thickened portions, in accordance with one or more of the preceding claims, characterized in that the locking means consist of horizontally displaceable clamp jaws acting on both sides on the tube or on the chords and substantially embracing the tube or the chord, the shape of the jaw being adapted to the parts of the tube or chord which lie between the thickened portions.

9. Artificial island according to Claim 8, characterized in that a plurality of sets of locking means are disposed one above the other on each tube or chord, and these locking means are disposed in a separate frame for each set of locking means, this frame being adjustably connected to the pontoon with the aid of adjusting means such as pressure medium cylinders.

10. Artificial island according to Claim 9, characterized in that the locking means and the associated adjusting means can act separately from one another or simultaneously on the tubular supporting leg or on the chords of a lattice supporting leg.

11. Artificial island according to Claim 10, in the case of lattice supporting legs, characterized in that the locking means and associated adjusting means for each chord of each lattice supporting leg can be controlled independently of one another, in such a manner that in one chord a different vertical force can be transmitted from that in another chord.