Hydraulic and earth engineering – Marine structure or fabrication thereof – With anchoring of structure to marine floor
Patent
1985-11-25
1987-11-03
Corbin, David H.
Hydraulic and earth engineering
Marine structure or fabrication thereof
With anchoring of structure to marine floor
52152, 405195, E02B 1700
Patent
active
047040513
DESCRIPTION:
BRIEF SUMMARY
This invention relates to an offshore bottom supported platform structure comprising a vertical tower structure of low bending stiffness which is laterally supported at several elevations by inclined, pre-tensioned stay cables. The tower structure being of low bending stiffness entails the major part of any horizontal loading on the tower is transferred down to the sea bottom--or down to the platform foundations--as changes in the stay cables tension forces.
The invention describes the configuration of a tower structure feasible for such platform. Further, the invention includes a platform construction alternative where the tower is erected on a floating box-like foundation structure whereafter the completed platform is towed out to location and installed. The invention also may be used as a subsea well-head platform for large water depths.
In a structural sense, conventional, fixed platforms like piled steel jackets and gravity platforms of concrete or steel are stiff tower structures spanning from the sea bottom up above the sea surface. For such structures the environmental loads are transferred down to the platform foundations as sear and bending forces in the structure. With increasing water depth the size and weight of such conventional platform structures increase dramatically. The structurally weight of a conventional steel jacket platform increases approximately in proportion to the square of the increase of the water depth. The reasons are the environmental loads acting on the platform increase in proportion to the size of the structure, while the bending moments at the platform foundations produced by said loads further increase with increasing height of the structure. Exploitation of hydrocarbons and other resources at increasing water depths implies a need to identify more efficient and appropriate concepts for offshore platform structures than those in use today. The disclosed invention represents such a concept.
Guyed towers used as offshore platform structures have been proposed earlier. This previously proposed structure--Exxon's `Guyed Tower` (FIG. 1)--comprises a steel jacket structure which is laterally stayed at one single elevation some distance below the sea surface by means of inclined, pre-tensioned guy lines. All the guy lines have the same length and inclination and are attached to anchorages at the sea bottom. The jacket structure may be founded on piles or on a gravity `spud can` foundation penetrated into the sea floor.
Horizontal loads acting on the `Guyed Tower` platform will in part be balanced by changes in the guy line tension forces. However, the tower still needs to have significant bending stiffness as it spans from the sea bottom up to the elevation where the guy lines are attached. The requirement for bending stiffness limits the acceptable horizontal deflections of the tower; reducing the efficiency of the guy line stay arrangement. In a structural sense the `Guyed Tower` platform is a stiff tower structure.
Concepts for offshore platform structures which do not make use of inclined stay arrangements, do not affect the invention presented here.
The main structural configuration of the platform invention disclosed here is sketched on FIG. 2a. FIG. 2b shows a plan view of the structure. The platform structure comprises a vertical tower 1 which is laterally supported at a number of elevations by means of inclined stay cables 2. The stay cables are pretensioned to a level which excludes slack in any cable for extreme environmental loading on the platform. The pre-tensioning of the stay cables introduces a compressive force T into the tower. The stay cbles 2 are attached to the stay anchorages 3; the horizontal and vertical components of the resultant anchorage forces due to cable pre-tensioning are denoted V and S. The platform tower 1 may be founded on piles or on a boxlike foundation structure (gravity type platform). The stay anchorages 3 may be integrated into the tower foundation 4.
FIG. 3 illustrates the load carrying principles of the proposed structure. When the
REFERENCES:
patent: 3284972 (1966-11-01), Werner
patent: 3388512 (1968-06-01), Newman
patent: 3636716 (1972-01-01), Castellanos
patent: 4127003 (1978-11-01), Vilain
patent: 4170186 (1979-10-01), Shaw
patent: 4222682 (1980-09-01), Vilain
patent: 4269542 (1981-05-01), Mueller
patent: 4273470 (1981-06-01), Blomsma et al.
patent: 4378178 (1983-03-01), Roach
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