10 The present invention relates to a method for the construc¬ tion of concrete shafts for a platform or similar structure which may for instance rest on the seabed , where one or several shafts will be outfitted with relatively much equip¬ ment .

15

The present invention in addition relates to a section to be used as an internal formwork and/or stiffening for the con¬ struction of a concrete shaft in a platform or similar structure which may for instance rest on the seabed.

20.

So far, it has been common to use traditional slipforming for the construction of a platform or similar structure. This means that the shaft must first be constructed in its full height, and any outfitting in the shaft must be subse-

25 quently performed. Thus, considerable work and time will be spent on the outfitting of the shafts with said equipment after the completed casting of the shafts. This gives sub¬ stantial additional construction cost.

0 By outfitting the individual concrete shaft of the said type with the necessary equipment simultaneously with the casting of the shafts, the present invention is intended to reduce the required construction time and thus also the costs. In other words, the intention, at least for the shafts to be 5 outfitted with equipment, is to construct the shafts in a new way, while other shafts, if any, are constructed by means of traditional slipforming. It should be observed that the advantages of the invention increase with the depth of the water.

The new construction method according to the invention is characterized by the shafts of the said type being construc¬ ted of prefabricated sections which are consecutively installed butt-in-butt on top of each other and which are left in the shaft as an internally fully shaped shaft compo¬ nent, as the sections internally contain the associated equipment and externally feature bodies for mounting of easily removable formwork elements or attachments for slip¬ forming. The sections either serve as internal formwork where the external formwork is subsequently installed, or alternatively, as an attachment for internal formwork as they are built up by means of tubulars on which the internal and external formworks are attached. The space between the formworks is filled with reinforcement and concrete, by a per se known procedure, and is thus moved up to a higher level.

According to the invention, the advantage of this is that said sections may be built in heights of 15 - 20 m, which may in their turn be put together to form longer sections onshore prior to being transferred to the platform. The sections which form the internal formwork or attachment for the internal formwork may.be prefabricated on an appropriate construction site with associated equipment completely installed in sections in an easily accessible way on an appropriate installation site - and said sections may later be consecutively installed in the shaft, which is under construction, in a relatively simple and accurate way. The easily accessible section provides a correspondingly effec- tive installation of the equipment in each individual sec¬ tion. In addition, a particularly rational installation of ^• • the equipment in the different sections is provided, as the sections can be constructed and outfitted with equipment independently of the construction of the actual shaft.

As soon as one section has been installed in the shaft, which is under construction, this part of the shaft has simultaneously been prefabricated internally, and the diffe-

rent sections can subsequently be consecutively attached on top of each other and the shaft can be prefabricated inter¬ nally, as the shaft is gradually constructed. Consequently, when the casting of the shaft is completed, the shaft will simultaneously be fully outfitted internally. Thus, the total time spent on the platform construction or similar structure can to a considerable extent be reduced by a corresponding reduction of the otherwise normal time spent on the outfitting of shafts.

A section according to the invention is characterized by comprising a cylindrically shaped section with a diameter for instance of 10 to 40 m of steel sheet, or alternatively being built up of tubular elements, which internally feature one or several horizontal dividers for support of the equip¬ ment to be installed in the shaft and which externally feature stiffening bodies, at least some of these being adjusted to form an attachment for easily mountable and easily dismountable formwork elements, by said dividers and said stiffening bodies being adjusted to stiffen the section during the transportation of the same from the construction site to the place of installation and being part of the constructed concrete shaft.

In addition to the reduction of time required for the con¬ struction of the platform or similar structure, installa¬ tion-related advantages are obtained, as already mentioned, as there is a better accessibility to the section and diffe¬ rent individual sections respectively than to an extended shaft. In connection with the previously employed slip¬ forming, it was necessary to construct special horizontal dividers at various levels directly in the actual shaft followed by the installation of the equipment on the diffe¬ rent horizontal dividers. By the present invention, where said dividers are built directly into the associated segment and where the segments can be assembled and joined together butt-in-butt to form a continuous structure internally in the shaft, there will be labour-related (assembly-related)

and construction-related advantages. By installing the equipment in a section, the assembly work can be limited to said butt-in-butt assembly and joining together of the sec¬ tions in relation to one another during the construction of the sections in the shaft. Moreover, by means of the hori¬ zontal divider or the horizontal dividers in each section, an effective extra stiffening is obtained for the section during the transportation of the same from the construction site to the installation site, i.e. during the transporta- tion directly to the assembly in the shaft which is under construction.

Further characteristics of the invention will appear from the subsequent description with reference to the enclosed drawings, which show the preferred embodiments, of which:

Fig. 1 is a horizontal sectional view of a section according to the invention for use during the construction of a concrete shaft in a platform which may for instance rest on the seabed.

Fig. 2 is a vertical sectional view of a section accor¬ ding to fig. 1.

Fig. 3 is a horizontal sectional view corresponding to fig. 1, the section featuring external formwork elements.

Fig. 4 is a vertical sectional view "corresponding to the section in fig. 2 featuring external formwork elements, shown during the construction of the.external formwork.

Fig. 5 is a vertical sectional view of the lower founda¬ tion with associated storage cells and the lower part of a shaft according to the invention, shown during the casting.

Fig. 6 is an alternative embodiment by the section being built up of a tubular element on which internal and external formworks have been installed.

Figs. 1-4 generally show the mounting of the formwork for a shaft where a platform or other concrete structure may for instance rest on the seabed.

Fig. 5 shows the actual construction of the shaft 10 in connection with a foundation 11 which may for instance rest on the seabed through a lower base-plate (13) . The shaft 10 rests directly on the base-plate through a tubular lower shaft section 10a, said shaft may be constructed by a per se known procedure in a rigid connection with cells (14) spaced ^• around the circumference, said cells being adjusted to form tanks for ballast and/or for storage of oil or condensate produced from the seabed. After the cells 14 and the lower shaft part 10a have been prefabricated by a per se known procedure in a continuous piece with the base-plate 13, the further construction of the shaft continues by a new proce¬ dure according to the invention, as described below. Alter¬ natively, the lower shaft part (10a) or parts of the same may be constructed in the same way as the rest of the shaft (10) , this is particularly relevant if the lower shaft part contains much equipment.

A separate, section 15 is subsequently constructed, corre¬ sponding to that shown in figs. 1 and 2, on an appropriate construction site separated from the construction site of the actual shaft. The section 15 generally consists of a cylindrical steel sheet 16 {e.g. with a thickness of 25 mm) and a number of horizontal dividers 17. On the different dividers 17, the relevant equipment is pre-instailed as indicated by broken lines 18, and a flight of stairs 19 is indicated between the dividers 17. In addition, hatches may -be installed (not further shown) for coverage of the upper end of the flight of stairs and hatches (not further shown) for vertical transportation of equipment between the diffe- rent stories. In the illustrated embodiment, a section is shown which may comprise a randomly chosen number of story heights, but evidently, when desirable, each section may have only a few or even one single story height.

In the embodiment shown in fig. 1 (and fig. 3) , a schematic location is shown of four equipment components on one hori¬ zontal divider 17, each component being located right above an associated beam section 20a, 20b, 20c, 20d in a cruciform beam structure 20, which forms a stiffening for each story divider. In fig. 2, it is indicated that the beam structure 20 is supported by angle pieces 21 for stiffening of the beam structure 20 internally of the tube 16.

Externally, the section 15 features an annular horizontal stiffening body 22 (only shown in figs. 1 - 3) at the section's upper free end. Alternatively, several such hori¬ zontal mutually parallel stiffening bodies may be installed at various levels in the vertical direction on the tube. Moreover, vertical stiffening bodies 23 have been welded externally of the tube which have a T- shaped cross-section with a typical T-shape dimension of 0.1 m in the full verti¬ cal direction of the section. The different sections may for instance be joined together butt-in-butt by means of a con- tinuous annular weld and may in addition be mutually connec¬ ted through welds by mutually aligned vertical stiffening bodies 23.

By designing the vertical stiffening bodies in a T-shape according to the invention, with the T-shape*s cross piece turned radially outward, appropriate anchoring bodies 24 may be effectively anchored to the internal formwork formed by the sections 15, for clamping of external formwork elements 25 to the internal formwork, as shown in figs. 3 and 4. Bow-shaped anchoring bodies 24 are shown, which are threaded into place on the stiffening bodies 23 and are somewhat radially extended outside the same for support o ^" f the form¬ work elements 25 at a suitable distance radially outside the internal formwork. The bow-shaped anchoring bodies 24 may for instance, as illustrated, feature outwardly extended support surfaces endwise, as mounting bolts 26 may be introduced through corresponding holes in the formwork elements for attachment in threaded fastening holes in said

support surfaces. The formwork elements 25 may moreover be connected sideways in pairs by means of mounting bolts 27 with associated retaining screws 28 introduced through fastening holes in radially outwardly facing flanges on the formwork elements 25.

According to the embodiment shown in fig. 3, sixteen stiffe¬ ning bodies 23 are shown, but only eight of these are used for attachment of the formwork elements.

According to fig. 5, an embodiment is shown where the casting of a first section 15' in the shaft is practically completed, while a second section 15" is installed over the section 15', ready for the mounting of external formwork elements. On the fully cast part of the shaft, i.e. in the illustrated embodiment on the part which contains section 15', an annular work platform 30 is attached which may rest against the shaft through pairs of rollers 32 on diametri¬ cally- oppositely facing sides of the shaft. The work plat- form 30. may be attached to the shaft through brake bodies 33 at the inner end of skewed downwardly and inwardly turned support arms 34. In addition, the work platform may be supported through support.wires 35 attached to the top of the upper section - in the illustrated embodiment, the top of section 15". From the work platform, the joining together may be done butt-in-butt with the abutting sections and parts connected to these, including the installation of the external formwork elements, as the shaft is being construc¬ ted in the vertical direction. As the shaft is gradually cast and hardened, the formwork elements are moved, e.g. by the completely hardened shaft parties being slid upward for installation on a section" above, and when this is completely or more or less completely cast, the formwork is moved further upward, and the process is subsequently continued in a corresponding way to the top of the shaft. When the shaft has been constructed in full height, the associated equip¬ ment in the shaft has been correspondingly installed at the respective levels along the shaft.

Fig. 6 shows an alternative way of installing formwork elements on the sections which contain equipment 18. The sections are built up of horizontal 41 and vertical 42 tubes respectively. On the vertical tubes, T-shaped stiffening bodies 43 are installed with the T-shape's cross piece turned radially outward, on which appropriate anchoring bodies 44 may be effectively anchored for the internal form¬ work 45. The external formwork 46 may be attached to the internal formwork with stiffeners 47 and the formworks may be screwed together wit mounting bolts 48, 49 with associ¬ ated retaining nuts 50 introduced through the fastening holes in the radially outwardly turned flanges on the form¬ work elements 45 and 46.