Hydraulic and earth engineering – Marine structure or fabrication thereof
Patent
1986-07-18
1988-05-10
Taylor, Dennis L.
Hydraulic and earth engineering
Marine structure or fabrication thereof
52648, 405204, 405224, E02B 1700
Patent
active
047431415
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention is related to an offshore truss work type tower structure comprising outer legs and an internal leg arranged in a hexagonal shape with the internal leg equidistant from the outer legs, and leg connecting trusses, and a method for construction of such structure.
SUMMARY OF THE INVENTION
Tower structures of the truss work type which typically are used as offshore platforms are traditionally constructed with vertically inclined legs, having decreasing cross section area towards the top of the tower. This type of design provides a good stability in operational position, however, due to the conical shape, creates certain problems in constructing as well as in launching the structure. Furthermore, the conical tower has some limitations when used in waters with increasing depths. Due to gas and oil exploration at increasing depths, other platform designs have to be taken into consideration and for the fixed platform type, the conically shaped tower is unsuitable.
With the tower structure according to this invention, several problems related to both connecting tower sections and launching these sections are avoided as the tower cross section substantially is the same along the entire tower height; the shape of the tower being prismatic. The advantages of the tower structure according to the present invention will be understood by the features stated in the characterizing clauses of the claims.
By design, a tower structure having a prismatic shape allows for trusses or bracings to be arranged in the outer panels, thereby resulting in a hollow type tower. This, however, would result in a large number of crossing trusses in the panels, which would mean a large number of nodal points.
By providing an internal or center leg, as in the present invention, the necessity of having crossing trusses in the outer panels is avoided.
Furthermore, the prismatic shape of the tower brings the advantage of a large number of uniform nodal points in a minimum number of nodal point types.
By designing the simplest form of the tower structure according to this invention, a prismatic tower structure having a uniform hexagonal cross section with one center leg is provided. In a single hexagon tower structure, a nodal point in an outer leg will have six truss connections, two trusses to each of the adjacent legs and two trusses to the center leg, all trusses thereby being arranged diagonally. At each nodal point level on the center leg, there also will be six truss connections. Such a hexagonal tower structure therefore will have two nodal point types.
In a tower structure having two partly overlapping hexagons, defined as a double hexagon, six of the outer legs also will have six truss connections at every nodal point level, whereas the two outer midlegs will have eight truss connections. In the double hexagon type tower structure, there are provided two internal legs which are connected with horizontal trusses perpendicular to these legs. The internal legs will have two different nodal points, one having seven truss connections and one having five truss connections, where one truss is arranged horizontally and perpendicular to the leg, and the rest are arranged diagonally. The double hexagon type therefore principally will have four different nodal point types.
The double hexagon tower structure type provides remarkably increased strength due to the addition of three outer legs, both in a direction perpendicular to the connection between the internal legs and substantially in this direction.
By the addition of two more outer legs, a triple hexagon tower structure can be achieved which increases the tower strength remarkably in all directions. In the triple hexagon tower structure type the amount of truss connections in the nodal points within the six outer legs and the three outer midlegs are six and eight, respectively, whereas all nodal points of the internal points will have five truss connections between the three internal legs will be arranged horizontally and perpendicular to the legs. The
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Eide Gunnar H.
Simensen Per A.
Saga Petroleum A.S.
Taylor Dennis L.
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