GB2142882A

GB2142882A - Fastening legs of jack up rig

Info

Publication number: GB2142882A
Application number: GB08417258A
Authority: GB
Inventors: Peter Adrianus Mart Dijkgraaf
Original assignee: RSV GUSTO ENG BV
Current assignee: RSV GUSTO ENG BV
Priority date: 1983-07-07
Filing date: 1984-07-06
Publication date: 1985-01-30
Also published as: NO842768L; DK331684D0; FR2551785A1; GB8417258D0; JPS6085113A; NL8302433A; DK331684A

Abstract

To fasten the legs of a movable lifting platform in the raised position so that the loads occurring when the platform is subject to swaying movements, are taken up effectively, each leg is fastened by means of welding to the uppermost leg guide situated in the pontoon or in a stand on the pontoon.

Description

SPECIFICATION Method for fastening the legs of a movable lifting platform in the raised position, and a lifting platform for applying this method.

The invention relates to a method of fastening in the raised position the legs of a movable lifting platform consisting of a pontoon, one or more legs movable in the vertical direction relative to the pontoon, a raising mechanism by which the legs can be moved relative to the pontoon, and means for locking the legs relative to the pontoon in a position in which the pontoon is raised and stands on the legs, this fastening of the legs in the raised position being effected by coupling the legs at the uppermost guides to the guides for the legs, which uppermost guides are situated in the pontoon or in a stand disposed on the pontoon.

When a lifting platform has to be moved, the legs must generally be moved upwards so that they extend far above the pontoon floating on the water. Swaying movements of the pontoon caused by waves and wind give rise to corresponding swaying movements of the upwardly projecting legs.

It is known to fasten the legs in this raised position in the guides with the aid of clamp means, such as wedges, and this is done both at the top of the stand and at the bottom of the guide in the pontoon. The swaying movements then have the consequence that the moment exerted by the legs gives rise to heavy horizontal loads on the stand structure and leg structures and these structures must thus also be designed for this exceptional operating condition, which occurs only seldom. The moments in question are a consequence of the accelaration forces occurring during the rolling or swaying.

It is known to solve this problem by constructing the legs of parts which are removed during the raising of the legs and are replaced when the legs are lowered. The length of the parts projecting above the pontoon can thus be reduced, so that the moments occurring are obviously diminished. However, this is particularly cumbersome, time-consuming, dependent on crane capacity, and therefore expensive. If the shortening of the legs is omitted, for example because weather conditions are favourable, it is too late to do so if these conditions suddenly change.

The invention seeks to provide a method by which it is possible to fasten the legs in the raised position in such a manner that the loads occurring can be taken more effectively, and therefore with a relatively lighter construction.

According to the invention this aim is in principle achieved in that each leg is fastened by means of welding to the uppermost guide, preferably the uppermost guide in the top part of an associated stand. Because the legs are welded fast at the top of the stand, the moments resulting from the horizontal and vertical acceleration forces occurring during rolling have the consequence that no horizon tal but only mainly vertical forces are exerted, at the site of the weld joint, on the stand and the leg, which are better able, or can be made better able, to withstand such forces hecause the combination of leg and stand forms a complete structure with the property that the bending moment in the leg in the raised end position is taken by vertical forces in the vertical ribs of the leg.

The weld joint is preferably made in the form of vertical weld seans between strips situated near the vertical ribs of the legs and the adjacent surfaces of the stand.

A weld joint of this kind can generally he made in a simple manner by welding vertical strips between the legs and the stand, these strips being burned through when the connection is to he destroyed.

At the bottom of the guides the known clamping means can he used if desired.

The invention likewise relates to a construction for applying the method according to the invention, particularly when each leg is provided, at each vertical rib of the leg, with a guide plate fitting with clearance between guide strips on the stand. The construction according to the invention is then characterised in that the guide plate carries, internally and between the nodal points of the bars of the truss of the leg, a frame firmly fastened to the guide plate and forming, with the plate, a rigid vertical box, the side walls of which ar provided with strips which are disposed obliquely to the vertical side walls of the box and which by their outwardly directed edges can be welded to vertical walls of the stand which are disposed inwards of the guide strips.

Each leg can then be provided, inward of its corner rib and at a height above the foot, which in the raised state is situated at the top of the stand, with a fastening construction of this kind, which is then supplemented by welding as soon as the leg has reached its end position during the raising movement.

The inclined strips can already be present in advance, but can also be welded in place only as soon as the leg has reached the end raised position.

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

Figure 1 is a diagrarmatical side view of a lifting platform to which the invention can be applied.

Figure 2 shows the lower part of a leg, indicating the position of the fastening means.

Figure 3 is a horizontal section on the line Ill-Ill in Figure 2 through a corner rib of a leg at the site of the fastening means.

Figure 4 is a vertical section on the line IV IV in Figure 3.

Figure 5 is an elevation of the fastening construction viewed in the direction of the arrow 5 in Figure 4.

Figure 1 shows in side view a lifting platform consisting of a pontoon 1 and three legs 2, of which two can be seen and each of which comprises an open truss of triangular configuration in horizontal section, with outwardly projecting toothed strips 3 at the corners. With these toothed strips mesh a plurality of pinions of the raising mechanism which is driven by hydraulic motors and which is accommodated, in a manner which is not illustrated but which is known, in the stands 4 which are disposed on the deck of the pontoon 1, and which are likewise provided with guide means for the vertical corner ribs of the legs 2.

Each leg is provided at 5 with the fastening construction which will be further described below and which is situated at such a height above the foot 6 that, in the raised position, the fastening construction 5 is situated at the height of the top part of each stand 4.

Figure 2 shows a part of a leg on a larger scale and reveals how the fastening construction 5 is situated on the inside of the vertical corner ribs between the nodal points 7 and 8 of the truss and inward of the toothed strip 3.

The section through a vertical rib shown in Figure 3 displays the construction thereof in greater detail. The vertical corner rib of the leg consists of the toothed strip 3, the vertical plates 9 and 10 and the vertical plate 11 which lies transversely to the centre plane of the corner and to which the bars or cross memhers 12, 1 3 of the truss are connected.

Of the stand 4 only the corner plates 14 and 15, 1 6 and 1 7 respectively, are shown, with, fastened thereto, the guide strips 18 and 1 9 which form a guide for the vertical corner ribs at the position of the plates 11.

According to the invention, there is now added hereto the fastening construction 5 consisting of the vertical plates 20, 21 and 22, which, together with the plate 11, form a rigid box which is situated inward of the corner rib and is provided for each corner rib.

In the raised position the fastening for each leg to the stand is effected by means of the strips 23 and 24 respectively, which are welded between the inwardly situated corner 25 or 26 respectively of the box 20, 21, 22 and the plates 1 7 and 14 respectively.

Figure 4 shows a section through the fastening construction on the line IV-IV in Figure 3, and shows that the inner plate 22 of the box-shaped fastening construction is provided, at a plurality of places one above the other, with T-shaped stiffening ribs 27.

In addition, it can he seen from Figures 4 and 5 that this rear plate 22 may bwe interrupted, for example by the opening 28, but that the inclined strips 23, 24 extend over the entire height of the fastening construction 5.

The strips or welding plates 20, 21 must previously be fastened to the plate 11. The plate members 22 can then be fastened in advance to the welding plates 20, 21. Depending on the classification requirements, the plate members 22 may also be welded in position last, after the welds 25, 29, 26, 30 when the leg is already in the raised position.

The strips or welding plates 23, 24 are fastened with the aid of the two vertical longitudinal seams 25, 29 and 26, 30 respectively when the leg has reached its end raised position. The construction shown in Figures 3 to 5 is provided at every corner rib of every leg.

In the example of embodiment illustrated the legs have a triangular horizontal shape.

The same principle can obviously be applied to shapes of a different horizontal section and also to quadrangular legs.

In principle, the method according to the invention is also applicable to cylindrical legs which have radially projecting toothed strips, by welding vertical strips between the guide edges of the stands and the outside peripheral wall of the legs.

Claims

1. Method of fastening in the raised position the legs of a movable lifting platform consisting of a pontoon, one or more legs movable in the vertical direction relative to the pontoon, a raising mechanism by which the legs can be moved relative to the pontoon, and means for iocking the legs relative to the pontoon in a position in which the pontoon is raised and stands on the legs, this fastening of the legs in the raised position being effected by coupling the legs at the uppermost guides to the guides provided for the legs, which uppermost guides are situated in the pontoon or in a stand disposed on the pontoon, characterised in that each leg is fastened by means of welding to the uppermost guide, preferably the uppermost guide in the top part of an associated stand.

2. Method according to claim 1, charcterized in that the weld joint is made in the form of vertical seams between strips situated near the vertical ribs of the legs and the adjoining surfaces of the stand.

3. Lifting platform for applying the method according to claim 1 or 2, wherein each leg is provided at each vertical rib with a guide plate which fits with clearance between guide strips on the strand, characterised in that the guide plate carries, internally and between the nodal points of the cross memhers of the truss of the leg a frame which is firmly fastened to the guide plate and which, with the plate, forms a rigid vertical box, while the side walls of this box are provided with strips which lie obli quely to the vertical side walls of the box and which by their outwardly directed edges can be welded to vertical walls of the stand which lie inward of the guide strips.

4. Lifting platform according to claim 3, characterised in that at least the innermost plate of the box is provided with a number of stiffening ribs extending horizontally and spaced apart one above the other.