Patent Description:
Recently, suspended type floating structures have been proposed as offshore facilities for wind or solar power generation and mining, manufacturing and storing of various resources.

Such floating structures include various types such as "spar type", "semi-submersible type", "pontoon type" or "TLP (tension leg platform) type". Among them, the so-called "semi-submersible type" floating structure comprises a plurality of vertically extending columnar columns interconnected through a horizontally extending connecting body. Each of the columns is a buoyancy body with an inner cavity and is floatable on water by buoyancy. Such columns are deployed horizontally and are interconnected to increase a metacentric radius of the whole floating structure and thus ensure a sufficient restoring force.

Each of the columns floating on water has a lower portion submerged (a submerged portion) and an upper portion above a water surface on which an upper structure is placeable. For example, when the semi-submersible floating structure as mentioned in the above is employed for an offshore wind power generation facility, a wind turbine as the upper structure is connected to an upper end of one of the columns.

Technical literatures disclosing semi-submersible floating structures are, for example, undermentioned Patent Literatures <NUM>,<NUM> and <NUM>. A floating structure (an offshore platform) disclosed in Patent Literature <NUM> comprises three columns on one of which (a tower support column) a wind turbine tower is placed. The remaining two columns serves not only to ensure a sufficient metacentric radius but also as stabilizing columns for adjustment of buoyancy balance. By contrast, a floating structure for an offshore facility disclosed in Patent Literature <NUM> comprises four columns, i.e., a centrally positioned central floating body and three outer floating bodies arranged therearound; a wind turbine is placed on an upper portion of the central floating body.

In the floating structure disclosed in Patent Literature <NUM>, the three columns are symmetrically arranged to provide respective apexes of an equilateral triangle in planar view. The wind turbine tower is placed on the tower support column which provides one of the apexes of the triangle. Thus, a weight on the tower support column is extremely larger than that on each of the other columns so that a gravity center of the whole floating structure including the wind turbine tower greatly deviates from a center of the equilateral triangle. Such deviation in gravity center may cause tilting of the floating structure; thus, it is generally conducted for prevention of such tilting that each column is provided with an adjustive ballast tank and the columns with no upper structure thereon are increased in weight by pumping water into the ballast tanks of the same, which requires that each column has a large volume for the adjustive ballast tank. Such countermeasure of pumping the ballast water in accordance with the weight of the tower support column to increase weights of the columns other than the tower support column may correct the position of the gravity center to assure horizontality of the whole floating structure; however, it may bring about non-uniformity of load distribution in the floating structure. As a result, a large bending moment may apply on beams interconnecting the columns, leading to necessity of strengthening the connecting structure between the columns to an extent endurable to such bending moment. In this manner, in the floating structure as disclosed in Patent Literature <NUM>, many steel members are required both for the volume of the adjustive ballast tank and strengthening of the beams, disadvantageously leading to increase in construction cost.

In the floating structure for the offshore facility as disclosed in Patent Literature <NUM>, the central floating body is arranged centrally of an equilateral triangle provided by the outer three floating bodies in planar view and the wind turbine is placed on the central floating body so that no deviation in the gravity center occurs. However, such arrangement requires a structure connecting the outer floating bodies with the central floating body, leading to structural complication of the whole and resultant increase in construction cost just the same. Though there is no need of pumping water into adjustive ballast tanks to comply with any deviation in gravity center, non-uniformity in load may occur just the same between the central and outer floating bodies, resulting in required strengthening of the members connecting the central floating body with the outer floating bodies.

In view of the above, the invention has its object to provide a floating structure in which load balance can be corrected while increase in size of the structure and strengthening of the structure are avoided as much as possible to suppress increase in construction cost. Solution to Problems.

The invention is directed to a semi-submersible type floating structure as defined by claim <NUM>. Accordingly, it is disclosed a floating structure with a plurality of columns as vertically extending columnar buoyancy bodies and a connecting body for interconnecting said columns deployed horizontally, an upper structure being connected to an upper portion of at least one of said columns, whereby the whole floating structure is supported on water, the floating structure constructed such that the column among said columns on which applied downwardly from said upper structure is a load larger than that on each of the other columns is larger in buoyancy than each of the other columns.

In the floating structure of the invention, the column on which applied downwardly from said upper structure is the load larger than that on each of the other columns may have a submerged portion with a volume larger than that of a submerged portion of each of the other columns.

In the floating structure of the invention, the column on which applied downwardly from said upper structure is the load larger than that on each of the other columns are provided with a lower hull having an inner cavity and projecting horizontally from said column.

In the floating structure of the invention, equipment for an operation of said upper structure or of said floating structure may be arranged in the column on which applied downwardly from the upper structure is the load larger than that on each of the other columns.

In the floating structure of the invention, the connecting body for interconnecting said columns may have a connection provided with a buoyancy body and connected to the column on which applied downwardly from the upper structure is the load larger than that on each of the other columns.

A floating structure according to the invention can exhibit an excellent effect that load balance can be corrected while increase in size of the structure and strengthening of the structure are avoided as much as possible to suppress increase in construction cost.

Embodiments of the invention will be disclosed in conjunction with attached drawings.

<FIG> and <FIG> show an embodiment (a first embodiment) of a floating structure according to the invention. As shown in <FIG>, a semi-submersible type floating structure <NUM> comprises vertically extending four columnar columns <NUM> with lower portions interconnected by a horizontally extending connecting body <NUM>. The four columns <NUM> are buoyancy bodies each with an inner cavity and are arranged to provide respective apexes of a square in planar view. An upper structure <NUM> is connected to an upper portion of one (a main column) 2a of the four columns <NUM>. Thus, the four columns <NUM> deployed horizontally support on water the whole floating structure <NUM> to which the upper structure <NUM> is connected.

The main column 2a and the three side columns 2b are columnar bodies each generating buoyancy through at least partial submerging thereof, and have inner cavities <NUM> and <NUM>, respectively. Each of the cavities <NUM> and <NUM> generates buoyancy for the corresponding column <NUM> and is at least partially utilizable as a ballast tank. The connecting body <NUM> also has an inner cavity <NUM> and may be utilized as a buoyancy-generating buoyancy body or a ballast tank as needed.

The main column 2a has a lower portion with a lower hull <NUM> which projects horizontally and radially outwardly. The lower hull <NUM> serves not only as a heave plate to increase water resistance against vertical movements of the main column 2a to thereby attenuate pitches but also to impart buoyancy to the main column 2a through an inner cavity <NUM> formed integrally with the cavity <NUM> in the main column 2a. In other words, the cavity <NUM> in the main column 2a has an increased diameter and an increased volume by the cavity <NUM> provided therebeneath. By contrast, each of the three side columns 2b has a lower portion with a horizontally projecting footing <NUM> which serves as a heave plate to attenuate pitches of the side column 2b but has no inner cavity and provides no buoyancy body.

The lower hull <NUM> of the main column 2a and the footings <NUM> of the side column 2b have mooring lines (not shown) connected thereto so that the floating structure <NUM> is moored through the mooring lines to water bottom and dwells in a predetermined water area.

As shown in <FIG>, placed in the cavity <NUM> beneath the cavity <NUM> of the main column 2a is a pump <NUM> communicated with the cavities <NUM> in the side columns 2b through a water feed pipe <NUM> in the cavity <NUM> of the connecting body <NUM>. Water pumped up from outside of the floating structure <NUM> by the pump <NUM> may be supplied to the cavities <NUM>, <NUM> and <NUM> of the main and side columns 2a and 2b and the connecting body <NUM>, respectively. The cavities <NUM> and/or <NUM> in the main column 2a may also accommodate a machine or other room (not shown) provided with, for example, various controllers and power units as needed.

The upper structure <NUM> is, for example, a wind turbine for wind power generation comprising a brace member <NUM>, a nacelle <NUM> and blades <NUM> as shown in <FIG>. The brace member <NUM> is erected on the main column 2a through a connection <NUM> on an upper end of the main column 2a. The nacelle <NUM> is internally provided with a dynamo (not shown) to generate power through rotation of the blades <NUM>. The upper structure <NUM> is not limited to the wind power generation facility as illustrated. For example, it may be a solar power generation facility; otherwise assumable as the upper structure <NUM> are various facilities placeable on water such as observation, communication and mining facilities.

Next, mode of operation of the above-mentioned first embodiment will be described.

When the floating structure <NUM> is to be placed in position on an ocean or the like, the floating structure <NUM> and the brace member <NUM>, the blades <NUM> and the like of the wind turbine <NUM> as the upper structure are separately fabricated, for example, in a plant in a maritime area and then these are towed by a ship or the like to a sea area on which the floating structure is to be placed. Upon towing, it is preferable that the floating structure <NUM> has minimum submerged portions so as to suppress resistance from water and fuel consumption of the ship. Thus, a minimum amount of ballast water is poured into the inner cavities <NUM>, <NUM>, <NUM> and <NUM> in the columns <NUM> (the main and side columns 2a and 2b) and connecting body <NUM>, and the towing is conducted in a state where a draft line is, for example, near an upper surface of the lower hull <NUM>.

Upon arrival at the sea area on which the floating structure is to be placed, the brace member <NUM> of the wind turbine <NUM> is erected on the connection <NUM> on the upper portion of the main column 2a in the floating structure <NUM> and the blades <NUM> are attached to the nacelle <NUM>. In this case, ballast water is properly supplied from the pump <NUM> in the cavity <NUM> underneath the cavity <NUM> in the main column 2a through the water feed pipe <NUM> to the cavities <NUM> and <NUM> in the side columns 2b and connecting body <NUM> to thereby adjust the floating structure <NUM> in balance and stabilize the same in water, partly using the cavities <NUM> and <NUM> as adjustive ballast tanks. As needed, water may be also poured into the cavities <NUM> and <NUM> in the main column 2a and lower hull <NUM>. Through such process, the floating structure <NUM> is placed horizontally as shown in <FIG> and <FIG> to support thereon the wind turbine <NUM>. In this case, the draft line is positioned vertically midway of the columns <NUM>.

Among the columns <NUM>, the main column 2a with the wind turbine <NUM> connected to the upper portion thereof has extremely large weight applied thereon in comparison with each of the other side columns 2b. Meanwhile, by the lower hull <NUM> on the lower portion, the main column 2a has the submerged portion large in volume and thus large resultant buoyancy in comparison with each of the side columns 2b. Due to the buoyancy, the main column 2a resists the load applied by the upper structure <NUM> so that load disequilibrium of the same with the side columns 2b is corrected to keep balance of the whole floating structure <NUM>.

Distributions of weights, buoyancies and resultant bending moments and the like in the floating structure <NUM> as mentioned in the above will be explained in conjunction with <FIG>. <FIG> is a schematic view of the floating structure <NUM> along a section passing through the main column 2a and the side column 2b positioned diagonally thereto and <FIG> shows distributions of weights and buoyancies in the section.

A short dashed line in <FIG> shows weights (downward loads) applied to portions shown in <FIG>. The main column 2a positioned right, which has the wind turbine <NUM> connected to the upper potion thereof, has larger load applied than the side column 2b positioned left. A dashed-dotted line in <FIG> shows buoyancies (upward loads) applied to the portions of the floating structure <NUM>; the main column 2a with the lower hull <NUM> has buoyancy larger than the side column 2b. A solid line in <FIG> shows total loads as sums of the weights and buoyancies; slight loads are applied downward and upward on the main and side columns 2a and 2b, respectively, so that the total becomes zero into balancing of the floating structure <NUM> as a whole.

<FIG> shows distributions of shearing forces and bending moments in the portions of the floating structure <NUM> due to the load distribution as mentioned in the above. The shearing forces (vertical forces) shown in <FIG> by a short dashed line appear as integration of the load curve shown by solid line in <FIG>; the bending moments shown by a solid line in <FIG> appear integration of the shearing forces. In the embodiment illustrated, the distribution of the bending moments becomes maximum on a left side position of the connecting body <NUM>.

As a reference example, weight and other distributions in a typical conventional floating structure are shown in <FIG>. As shown in <FIG>, a floating structure <NUM> of the first reference example comprises a main column 102a with no additional buoyancy body such as the lower hull <NUM> (see <FIG>) so that there is no difference in volume of the submerged portions between the main and side columns 102a and 102b. Thus, buoyancies on the respective columns <NUM> (the main and side columns 102a and 102b) are the same. In order to keep balance between the main and side columns 102a and 102b in the floating structure <NUM> thus constructed, it is generally conducted to pour ballast water W into the cavity <NUM> of the side column 102b.

In the floating structure <NUM> of the first reference example, as shown in <FIG>, weights (downward loads) shown in a short dashed line become larger in the side column 102b shown left in the figure, by the ballast water W, than that of the side column 2b in the first embodiment (see <FIG>). Buoyancies (upward load) shown in a dashed-dotted line are the same between the main and side columns 102a and 102b.

Loads as sums of the weights and buoyancies as shown by a solid line in <FIG> are applied downward and upward in the main and side columns 102a and 102b, respectively, and absolute values thereof are larger than those of the first embodiment (see <FIG>), respectively. Thus, as shown in <FIG>, the shearing forces as integration of the loads and bearing moments as integration of the shearing forces are larger than those of the first embodiment (see <FIG>), respectively.

As is clear from the above, the floating structure <NUM> of the first embodiment as shown in <FIG> is smaller in shearing force and bending moment generated in the connecting body <NUM> than the floating structure <NUM> of the first reference example as shown in <FIG>. Thus, required strengthening of the connecting body <NUM> is low, leading to reduction in weight of steel members used for the connecting body <NUM>. Moreover, in the floating structure <NUM> of the first reference example shown in <FIG>, the cavity <NUM> in the side column 102b requires a space for an adjustive ballast tank for balancing with the main column 102a to which the upper structure <NUM> is connected; by contrast, the floating structure <NUM> in the first embodiment requires no volume for an adjustive ballast tank so that the whole side column 2b can be made small in size, which also contributes to reduction in weight of the steel members used (though the main column 2a requires additional steel members for the lower hull <NUM>, such added amount is fewer than the reduced amount in the side columns 2b). In provisional calculations by the applicant, the floating structure <NUM> of the fist embodiment can be reduced in displacement by, for example, about <NUM>% in comparison with the floating structure <NUM> of the first reference example.

In the floating structure <NUM> of the first embodiment, the machine room is arranged underneath the cavity <NUM> in the main column 2a for accommodation of the pump <NUM> and other equipment, which is because arrangement of the equipment in connection with the upper structure <NUM> (when the upper structure <NUM> is the wind turbine as shown in <FIG>, equipment for power conversion/delivery, a controller for the wind turbine <NUM> and the like) in a position as near as possible to the upper structure <NUM> is most effective in view of wiring and pipe laying and because arrangement of other equipment (the pump <NUM>, a controller therefor and the like) is simplified by arranging them in a same position as much as possible. In this connection, the first embodiment in which the main column 2a has the lower portion with the lower hull <NUM> contributing to enlargement of the cavity <NUM> by the cavity <NUM> is advantageous in that various equipment as mentioned in the above can be easily laid out there.

As is clear from the above, the first embodiment is directed to the floating structure <NUM> with the plurality of columns <NUM> as vertically extending columnar buoyancy bodies and the connecting body <NUM> for interconnecting the columns <NUM> deployed horizontally, the upper structure (wind turbine) <NUM> being connected to the upper portion of at least one (main column 2a) of the columns <NUM>, whereby the whole floating structure is supported on water, the floating structure <NUM> being constructed such that the column <NUM> (the main column 2a) among the columns <NUM> on which applied from the upper structure <NUM> is the load larger than that on each of the other columns <NUM> is larger in buoyancy than each of the other columns <NUM> (the side columns 2b); thus, imparting of the buoyancy to the main column 2a against the load from the upper structure <NUM> can correct any unbalance of load distribution between the columns <NUM> and reduce bending moments generated on the connecting body <NUM>.

In the first embodiment, the submerged portion of the main column 2a is larger in volume than that of each of the other columns <NUM> (side columns 2b) so that the buoyancy against the load from the upper structure <NUM> can be appropriately imparted to the main column 2a.

In the first embodiment, the main column 2a has the lower portion with the lower hull <NUM> which has the inner cavity and projects horizontally from the main column 2a so that the lower hull <NUM> can increase water resistance against the vertical motions of the main column 2a to thereby attenuate the pitches.

In the first embodiment, equipment in connection with the operation of the upper structure <NUM> or the floating structure <NUM> is arranged inside of the main column 2a, so that a wide space is available for accommodation of the various equipment, resulting in easiness in layout.

Thus, according to the first embodiment, load balance can be corrected while increase in size of the structure and strengthening of the structure are avoided as much as possible to suppress increase in construction cost.

<FIG> shows a floating structure of a further embodiment (a second embodiment) according to the invention which is fundamentally similar in construction to the above-mentioned floating structure <NUM> (see <FIG> and <FIG>) of the first embodiment. A floating structure <NUM> of the second embodiment is different in arrangement of columns from the first embodiment.

Among four columns <NUM> in the floating structure <NUM> of the second embodiment, three side columns 202b are arranged on respective apexes of an equilateral triangle in planar view and a main column 202a is positioned centrally of the triangle provided by the side columns 202b. The central main column 202a is connected with the surrounding side columns 202b through connecting bodies <NUM>, and a wind turbine <NUM> as the upper structure is connected to an upper portion of the main column 202a. Specifically, the floating structure illustrated is similar in arrangement to that disclosed in Patent Literature <NUM>.

However, in the second embodiment, the main column 202a has a lower portion with a lower hull <NUM> as a heave plate and also as a buoyancy body. By contrast, each of the side columns 202b has a lower portion with a footing <NUM> merely serving as a heave plate. Thus, the main column 202a is larger in buoyancy, by the lower hull <NUM>, than that of each of the side column 202b.

In the floating structure <NUM> as mentioned in the above, which has the connecting bodies <NUM> interconnecting the columns <NUM> more complex than the connecting body <NUM> of the first embodiment (see <FIG> and <FIG>), mechanistic unbalance between the columns is properly corrected in comparison with the floating structure disclosed in Patent Literature <NUM>. Explanation will be made thereon hereinafter.

First, in the floating structure <NUM> of the second embodiment, the upper structure <NUM> is connected to the main column 202a as shown in <FIG> and thus a load applied downward on the central main column 202a is extremely larger than that on each of the left and right side columns 202b as shown by a short dashed line in <FIG>. Meanwhile, as shown in <FIG>, the main column 202a has the lower portion with the lower hull <NUM> so that the buoyancy (the upward load) applied on the central main column 202a is larger than that on each of the left and right side columns 202b as shown by a dashed-dotted line in <FIG>. As a result, as shown by a solid line in <FIG>, total loads of the weights and the buoyancies become slight and downward in the main column 202a and slight and upward in each of the side columns 202b.

As a reference example for the second embodiment, <FIG> shows an example of a floating structure (second reference example). The second reference example has a floating structure <NUM> similar in construction to that disclosed in Patent Literature <NUM> and is in common with the second embodiment (see <FIG> and <FIG>) in that a main column 302a is installed centrally of three side columns 302b providing respective apexes of an equilateral triangle in planar view and is connected with the side columns 302b through connecting bodies <NUM>. However, the second reference example is different from the second embodiment in that the main column 302a has no lower hull and each of the side columns 302b has a lower hull <NUM>.

In such a construction, as shown by a short dashed line in <FIG>, downward load distribution is substantially similar to that of the second embodiment (see <FIG>; however, the load on the main column 302a is slightly smaller by no provision of a lower hull; and by contraries, the load on each of the side columns 302b is larger by the provision of the lower hull <NUM>). Meanwhile, buoyancies shown by a dashed-dotted line are small in the main column 302a and large in each of the side columns 302b. As a result, as shown by a solid line, the total loads become larger and downward in the central main column 302a and larger and upward in each of the left and right side columns 302b than those of the second embodiment.

Specifically, unlike the floating structure <NUM> (see <FIG>) of the first reference example, the floating structure <NUM> (see <FIG>) of the second reference example requires no ballast water injected into the side columns 302b for balancing with the load of the upper structure <NUM>; however, there still exists load unbalance between the main column 302a receiving a larger load from the upper structure <NUM> and each of the side columns 302b, which causes a larger shearing force or bending moment on the connecting bodies <NUM>. In the floating structure <NUM> of the second embodiment (see <FIG>), the main column 202a to which the upper structure <NUM> is connected is provided with the lower hull <NUM> to increase buoyancy, thereby counteracting the load of the upper structure <NUM> to reduce load unbalance with the side columns 202b.

As a result, in the floating structure <NUM> of the second embodiment, required strengthening of the connecting bodies <NUM> can be lowered to reduce a required amount of steel members for the connecting bodies <NUM>. Though the large-volume lower hull <NUM> is required for the central main column 202a, no or a smaller lower hull is required for each of the surrounding side columns 202b. Thus, a required amount of steel members for the whole floating structure <NUM> can be reduced.

The other advantageous effects of the second embodiment are omitted since they are similar to those of the above-mentioned first embodiment (see <FIG>). Also in the second embodiment, load balance can be corrected while increase in size of the structure and strengthening of the structure are avoided as much as possible to suppress increase in construction cost.

<FIG> shows a floating structure of a still further embodiment (a third embodiment) of the invention in which an upper structure <NUM> connected to upper portions of the columns <NUM> constituting a floating structure <NUM> is not a wind turbine but a crane, which brings about difference in connecting bodies <NUM> and the like from that or those of the first or second embodiment (see <FIG> and <FIG> or <FIG>).

In the floating structure <NUM> of the third embodiment, upper and lower portions of the four columns <NUM> are interconnected through upper and lower connecting bodies 403a and 403b, respectively. The upper connecting body 403a provides a horizontal surface in the form of substantially quadrate in planar view on upper ends of the four columns <NUM> arranged at respective apexes of the quadrate provided by the upper connecting body 403a. The lower connecting bodies 403b interconnect lower ends of the columns <NUM> to provide sides of the quadrate. The crane as the upper structure <NUM> is placed on the surface provided by the upper connecting body 403a.

In such a construction, none of the columns <NUM> is positioned just below a gravity center of the crane <NUM> as the upper structure, and a downward load by a weight of the crane <NUM> is applied to each of the four columns <NUM> through the upper connecting body 403a. The gravity center of the crane <NUM> is not aligned with the gravity center of all the four columns <NUM> in planar view and is in eccentricity. Thus, loads applied from the crane <NUM> to the four columns <NUM> are not equal, resulting in load deviation between the columns <NUM>. In a state shown in <FIG>, the gravity center of the crane <NUM> deflects right in the figure relative to a gravity center of the four columns <NUM>, resulting in application of an especially large downward load on the column <NUM> positioned at a right end in the figure. Thus, in the floating structure <NUM> of the third embodiment, the lower hull <NUM> of the column <NUM> on the right in the figure is made larger than the lower hulls <NUM> of the other columns <NUM> to produce a large buoyancy on the column <NUM> on the right in the figure to thereby attain load balance between the columns <NUM>.

The other advantageous effects of the third embodiment are omitted since they are similar to those of the above-mentioned first embodiment (see <FIG>). Also in the third embodiment, load balance can be corrected while increase in size of the structure and strengthening of the structure are avoided as much as possible to suppress increase in construction cost.

<FIG> shows a still further embodiment (a fourth embodiment) of a floating structure according to the invention. Though similar in fundamental construction to the first embodiment (see <FIG> and <FIG>), a floating structure <NUM> of the fourth embodiment has a connecting body <NUM> interconnecting columns <NUM> and provided with a buoyancy body <NUM> on a connection with the main column 502a. The buoyancy body <NUM> imparts buoyancy to the main column 502a on which the upper structure <NUM> is connected.

In this case, in order to impart buoyancy to the main column 502a, there is no need of adding structural changes on the main column 502a itself; only design change of the connecting body <NUM> will suffice. Though the main column 502a in which various equipment may be placed may be low in freedom degree with respect to its inner structure and layout, the connecting body <NUM> is meritorious in that provision of the buoyancy body <NUM> thereon is less restrictive in design.

Thus, in the fourth embodiment, the connecting body <NUM> interconnecting the columns <NUM> has the buoyancy body <NUM> on the connection with the column <NUM> (the main column 502a) on which larger load is applied downward from the upper structure <NUM> than each of the loads on the other columns <NUM> so that buoyancy can be imparted to the main column 502a without structural change of the main column 502a.

The other advantageous effects of the fourth embodiment are omitted since they are similar to those of the above-mentioned first embodiment (see <FIG>). Also in the fourth embodiment, load balance can be corrected while increase in size of the structure and strengthening of the structure is avoided as much as possible to suppress increase in construction cost.

<FIG> show still further embodiments of a floating structure according to the invention. The number of the columns may be three as shown in <FIG> or may be five or more (not shown). Appropriate changes may be conducted on arrangement of columns and construction of a connecting body depending on conditions such as kind and construction of an upper structure. Moreover, as in the first embodiment (see <FIG> and <FIG>), a main column may be provided with a lower hull; as in the fourth embodiment (see <FIG>), a connecting body may be provided with a buoyancy body; or as shown in <FIG>, a diameter of a column itself may be changed to impart a large buoyancy. Alternatively, though not shown, a buoyancy body may be attached from outside to an existing column or connecting body to impart buoyancy; in this case, though steel members for construction of the floating structure cannot be reduced, it is effective, for example, upon exchange or addition of an upper structure after the floating structure is constructed. A floating structure of the invention may take various constructions as long as buoyancy can be properly imparted to a column.

Also in each of such embodiments, load balance can be corrected while increase in size of the structure and strengthening of the structure are avoided as much as possible to suppress increase in construction cost.

Claim 1:
A semi-submersible type floating structure (<NUM>; <NUM>; <NUM>; <NUM>) comprising a plurality of columns (2a, 2b; 202a, 202b; <NUM>; 502a, 502b) as vertically extending columnar buoyancy bodies, a connecting body (<NUM>; <NUM>; 403a, 403b; <NUM>) for interconnecting said columns (2a, 2b; 202a, 202b; <NUM>; 502a, 502b) deployed horizontally, and an upper structure (<NUM>; <NUM>) connected to an upper portion of at least one (2a; 202a; <NUM>; 502a) of said columns (2a, 2b; 202a, 202b; <NUM>; 502a, 502b) supporting the whole floating structure (<NUM>; <NUM>; <NUM>; <NUM>) on water,
the column (2a; 202a; <NUM>; 502a) on which applied downwardly from said upper structure (<NUM>; <NUM>) is the load larger than that on each of the other columns (2b; 202b; <NUM>; 502b) has a lower portion with a lower hull (<NUM>; <NUM>; <NUM>) having an inner cavity (<NUM>) and projecting horizontally from said column (2a; 202a; <NUM>; 502a) at a submerged portion,
the column (2a; 202a; <NUM>; 502a) among said columns (2a, 2b; 202a, 202b; <NUM>; 502a, 502b) on which applied downwardly from said upper structure (<NUM>; <NUM>) is a load larger than that on each of the other columns (2b; 202b; <NUM>; 502b) is larger in buoyancy than each of the other columns (2b; 202b; <NUM>; 502b), thereby correcting load balance while increase in size of the structure (<NUM>; <NUM>; <NUM>; <NUM>) and strengthening of the structure (<NUM>; <NUM>; <NUM>; <NUM>) are avoided.