The structure is made in several "storeys" (D1, D2, D3). These are floated away from their construction site in conventional manner. Once in sufficiently deep water, the storeys are tilted over so that they float on their side, and they are then joined together end-to-end. With tilting and rotating operations performed by suitable ballasting and unballasting of compartments in the storeys, the joining operations can all be performed on members at or near (just above or just below) the surface of the water. Once the storeys are assembled together, the entire structure may be towed on its side to a point of use, and then immersed so that it stands vertically on the sea bed.
An offshore platform comprises a honeycomb foundation (A), a supporting structure (B) and an above-surface section (C), the foundation and the supporting structure being made of prefabricated reinforced concrete elements which are polyhedral hollow prisms (1, 2) set with gaps (6) between the external faces thereof. The prisms (1, 2) are joined by a system of prestressed vertical and horizontal diaphragm walls (4, 3) formed by pre-tensioning reinforcing bars (7, 8) placed in the gaps (6) between the faces of the prisms (1, 2) and casting-in-situ the gaps (6) later on.
A method of constructing and assembling huge modules whose module frame includes sidewalls, a roof, trusswork frames and at least one deck structure secured within and to the module frame involves introducing a separately built deck structure into the module frame at floor level. The introduction is either through a temporary lower opening in a side wall frame, or from beneath the module frame. The deck structure is then positioned within the module frame, controllably elevated therein to a desired level and then secured to the module frame. This sequence is repeated as required such that additional separately built deck structures are similarly introduced into the module frame, positioned, elevated therein and secured thereto. After the desired number of deck structures has been installed, any lower opening in the sidewall frames is closed with trusswork braces.
A jacket tower structure for use in deep water which includes a plurality of tapering jacket sections adapted to be nested, each section including at least three jacket legs. The base and lower jacket sections include cylindrical legs interconnected by box section bracing, the upper jacket sections including cylindrical bracing. The box section bracing is connected to the legs by a unique joint for transmitting stresses to the legs. The box section bracing is floodable for equilizing hydrostatic pressure during and upon installations. Certain transverse box section bracing at ends of adjacent jacket sections include intermediate connection projections for welding during joining of adjacent jacket sections. The cylindrical legs include a plurality of water tight compartments of selected volume, each compartment having one or more check valves for admitting water into the compartments when external water pressure exceeds air pressurization of the compartments. A method of installing the jacket tower includes floating the tower, to the site, on two of the legs; rotating the tower about a longitudinal axis to submerge one leg while at least the other two are at water level and tilting the structure by flooding certain portions of the base and lower sections and continuing such tilting by automatically flooding the legs by preselected pressure conditions in the water tight compartments until the tower reaches a vertical position. Once vertical, the remaining compartments are flooded to settle the tower vertically on the sea floor.
An improved offshore platform base (12) is disclosed having three sets of substantially parallel bulkheads (24, 26, 28) which intersect one another at about 120.degree. forming a repeatable array of contiguous triangular (30) and hexagonal-shaped (34) chambers.
