Floating platform structure
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a floating platform structure and more particularly to a floating air port structure. The structure, however, can be used for other purposes such as location for industrial activities at sea. The invention relates also to a method for erecting a structure of the above mentioned kind and structure modules which can be used in combination for building the structure in case. 
     2. Prior Arts 
     Floating structures having great dimensions and comprising deck section, float section and ballast section are formerly known. Most of them are formed as semi-floating structures generally comprising one or more float members supporting vertical columns which again support a deck structure. Frequently, diagonal bracing rods are arranged between the columns. The buoyancy is provided by the float members and partly by the columns. Therefore, the float members must be divided into water-tight compartments and provided with piping systems for draining and ballasting. It may be referred to U.S. Pat. No. 1,670,524, 3,592,155, 3,785,313 and 4,275,679. 
     THE PURPOSE OF THE INVENTION 
     The purpose of the invention is to provide a floating structure particularly a floating air port platform structure which can be produced in an economical manner and allows for easy maintenance and operation. 
     A particular purpose of the invention is to provide a floating platform structure having a deck section and a support section, the structure being formed as a longitudinal trussed girder having an upper and a lower girder chord which are connected by girder members, said trussed girder having a vertical cross section in shape of a triangle or approximated triangle, the base of which is facing upwardly, and the upper chord of which is providing the said deck section, the float means of the platform arranged in the upper portion of the girder members and the ballasting means arranged in the lower portion of the girder members and optionally in the lower chord. 
     A further purpose of this invention is to provide a floating platform structure of the kind defined above which can be easily barged across the sea, if necessary, even during rough weather conditions and which can adjust itself successfully when in moored condition. Further, the cross sectional shape of the platform support structure shall provide for progressive damping of the platform movements owing to the waves. 
     FURTHER OBJECTS OF THE INVENTION 
     A platform structure according to the invention comprises a support section having a succession of groups of at least three girder members in each group, said girder members converging from the deck downwardly towards a common point and being fixedly connected with one another at a junction point in or adjacent said convergency point. 
     Generally, the lower chord comprises at least one pipe as stress absorbing member. 
     A bracing plate is preferably connecting the girder member at a distance upwardly from their lower jointed ends. 
     A floating platform structure according to the invention may comprise two trussed girder structures arranged side by side and fixedly connected with one another, each girder structure having upper and lower chords which are connected with one another by inclined girder members, and which girder structure has a vertical cross section in shape of a triangle or approximately tri-angle with basis thereof facing upwardly, the deck section providing the upper chord of the girder, the float means of the girder structure arranged in the upper portion of the inclined girder members and ballast means arranged in the lower portion of the girder members and optionally in the lower chord. 
     The invention contemplates also a platform structure module for producing a floating structure, said module comprising a deck section having polygonal plane view and supported by four or three columns extending downwardly from the deck and converging towards a junction point, the lower ends of the columns are connected with one another in or adjacent said junction point. 
     The columns of the module may be connected with one another by a bracing plate at a distance from their lower jointed ends. In a platform support section combined of groups having three girder members each, the junction points for each second group are preferably located on a straight line and the junction points for the intermediate groups are located on another straight line being parallel with the first line, the lower chord comprising two pipes of steel extending along one of said two lines, respectively. 
     These and other objects will fully appear from the following description with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of a floating platform structure formed in accordance with the invention for use as a floating air port; 
     FIG. 2 is a schematic side elevation view of the structure of FIG. 1, 
     FIG. 3 is an end elevation view of the structure of FIG. 2, 
     FIG. 4 is a bottom view of the structure of FIG. 1. 
     FIG. 5 is a cross sectional vertical view taken along the line V--V in FIG. 2, showing at a larger scale a portion of the structure deck and of the top of one of the columns, 
     FIG. 6 is a front elevation or side elevation view of a structure module, 
     FIG. 7 is a schematic plane view of the module of FIG. 6, 
     FIG. 8 is a plane view of an alternative embodiment of the structure module of FIG. 6. 
     FIG. 9a is a schematic plane view corresponding to FIG. 4 of a platform structure consisting of structure modules according to FIG. 8. 
     FIG. 9b is an end view of the structure of FIG. 9a. 
     FIGS. 10 a-g illustrate a method of building and erecting a floating air port structure of the kind shown in FIG. 1. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 is an isometric perspective view of a platform structure incorporating the invention in shape of a floating air port. In the following the structure will be denoted as platform because basically, it is an offshore platform. The platform 1 comprises a support section 2 and a deck section 3. The support section 2 comprises a plurality of groups or modules 5 each comprising four inclined columns 6. Geometrically, the columns in each group provide an upside down orientated pyramid with the upper ends of the columns located at the longitudinal side edges of the deck section 3. The columns in each group are converging downwardly towards a common junction point or convergency point 7 located somewhat higher than the geometrical junction point not appearing in the drawing. In the embodiment according to this example the platform is constructed of prestressed or reinforced concrete and the lower end portions of the columns 6 are cast together in the junction point 7. At some distance upwardly from the junction point a horizontal bracing plate 8 is arranged cast monolytic with the columns 6. The columns are cylindric pipes of reinforced concrete. The upper ends of the columns 6 are connected integrally by concrete casting with the deck section 3. Between the junction points 7 and the support section 2 pressure and tension absorbing structural elements 9 are arranged extending in the longitudinal direction of the platform. The structural elements 9 consist of steel pipes filled with concrete and provide a continuous member or chord 10 extending from one end of the support section to the other. 
     FIG. 2 is an elevation of the platform and FIG. 3 is an end view of the platform. It appears clearly from FIGS. 1-3 that the platform 1 is formed as a trussed girder the upper chord of which consists of the deck section 3 and the lower chord of which consists of the pipe 9,10. The chords are connected with one another by diagonal girder members 6. It appears from the FIGS. 1-3 that in side elevation and in end or front elevation the diagonal girder members define a triangle-shaped area. FIG. 4 is a plane view of the platform and it appears from the Figure that the diagonal girder members or columns 6 in the adjacent groups pairwisely meet one another at their upper ends where they provide junction points 11 similar to the junction points 7 of the lower chord. 
     At one end of the deck section 3 a pivotable anchoring device 12 is arranged on the underside of the deck for a plurality of anchoring chains 13 for anchoring the platform to the sea bottom 4 (FIG. 1). 
     In FIG. 4 the longitudinal beams of the deck section 3 are indicated by stretched lines 14 and the cross beams of the deck section by stretched lines 15. 
     In FIG. 5 the adjacent portions of an inclined column 6 and the deck section 3, respectively, are shown in a cross sectional view along the line V--V in FIG. 2. Also a cross beam 15 is indicated by way of example. The inclined column 6 ends with a horizontal surface carrying the longitudinal beam 14. Said beam is formed in shape of a box girder. The longitudinal beam does not cover completely the top surface of the inclined column to provide support areas for overlap mounting of the end portion of a longitudinal beam or a similar member of an adjacent platform module (see the method of erecting the platform disclosed below). The cross beam 15 is formed as a trussed girder having upper and lower chords and vertical trussed girder members and diagonal girder members. Between the beams and on the beams deck plating sections 16 of suitable embodiment are located (see also FIG. 4). The deck slabs 16 provide the upper deck proper 17 of the deck section. The deck section can also be provided with a lower deck 18 as indicated schematically at left in FIG. 5. 
     As it will be described more closely with reference to FIG. 10 the platform is built up of a plurality of units or modules. According to FIG. 1 the platform is comprising six such modules. FIGS. 6-8 show that a platform module can be fitted out as to provide an independent platform by itself. Such a platform module 20 is shown in FIG. 6, and FIG. 7 is the plane view of the module. In this particular case the deck section 23 of the platform is formed with a greater width than in the embodiment of FIG. 1 and the platform is anchored in the sea bottom by means of chains secured to the deck. The inclined columns are denoted by 26, the lower bracing plate by 28 and and the lower junction point by 27. The support section is, therefore, similar to the support section 3 of FIGS. 1-4 apart from the fact that there are no lower chord members 9,10. In FIG. 8 another embodiment 30 of the platform module is shown having the supporting section 32 shaped with triangular plane view, i.e. as a geometric tetraeder. The support section comprises three inclined columns. 36 converging downwardly towards a junction point 37, the upper ends 40 of the columns being cast together in concrete with the deck section 33. FIGS. 9a and 9b show schematically a plane view and an end view of a portion of a platform structure built up of a plurality of platform modules 30 having a support section as shown in FIG. 8. The inclined columns are indicated by 36 and the deck section by 33. (See also below) 
     Production and erection of a floating platform as shown in FIG. 1 will now be described shortly with reference to FIGS. 10 a-g. FIG. 10a shows a schematic cross section of a dry dock where casting of a support section module 5 has been started. The lower junction point, sections of the lower chord 10 and the lower bracing plate 8 are indicated. Upon completing the lower support portion of the support section module this lower portion is towed out from the dock into deeper water. At another location the longitudinal beams 14 (FIG. 10b), the cross beams 15 and the deck slabs 16 for the deck sections are manufactured. The lower portion of the support section is barged out into deeper water (FIG. 10e) and casting of the inclined columns is completed by slip-form-casting. When completed, the columns of the support section of the module, the longitudinal beams and the cross beams of the deck section are floated or transported to the location of the floating support section which is submerged to a suitable depth and the longitudinal beams and the cross beams are mounted on the support section. Then the deck slabs and other outfit which is necessary or desirable on the platform at this time is lifted on board (FIGS. 10e and 10f). The components of the platform module are connected with one another by concrete casting. 
     When a plurality of platform modules have been completed the modules are placed in succession after one another as illustrated in FIG. 10g and connected with one another at the top by concrete casting between the columns and the longitudinal beams (if desirable with mounting of additional intermediate members) and the lower ends of the support section modules are connected by welding together the ends of the lower chord pipes which are of steel. The welding is performed under water using a dry work chamber. After welding, the pipes are covered with concrete and when all deck slab sections are in location the possible joints and interspaces are filled with concrete to complete the main structure. 
     It will be clear to the experts that all portions or members of the structure which shall be connected with one another (by concrete casting) are provided during the manufacturing with means (such as projecting reinforcing irons, anchors, hinge irons, etc.) which make the composing and together casting of the adjacent structure elements more simple and easy. Such techniques are formerly known in connections with producing concrete platforms. It is not necessary that all support section units are completely out-fitted before combining with the deck section members. It can be sufficient that some of the units only are fitted with complete longitudinal beams and cross beams, whereas others can be provided with portions of them only, or such deck section members can be mounted upon the support sections having been combined together. 
     In the examples a longitudinal floating platform comprising a plurality of units has been disclosed with the units arranged in a row one after another, but it will appear that it is also possible to build up a platform by arranging a plurality of platform modules both after one another and laterally of one another to provide a floating structure having great length and great width. In such a case it may be necessary to provide the support sections at their lower ends with two lower chord sections extending at an angle with one another to provide junction means in the longitudinal and in the transversal direction. In an embodiment in accordance with FIG. 9 with tetrahedral-shaped modules it may be suitable to connect the section modules pairwisely with one another before mounting the longitudinal beams, etc. In a floating structure having a deck section with one deck only, the crew facilities, storing rooms, machine rooms, etc. can be placed in the longitudinal beams if it is desirable to keep the deck surface free. If the structure also comprises a lower deck said lower deck can be used for said purposes. In case of a floating airport a terminal for passengers will be arranged on the lower deck. If necessary, suitable building modules may be placed between the cross beams of the deck structure. The lower deck may accommodate hangars for aircrafts. 
     The drawings indicate anchoring of the floating structure by means of chains and anchors. However, it is also feasible that the floating structure is provided with power means such as diesel electric units which drive propelling motors either for complete positioning of the floating structure or as auxiliary for quick changing of the position of an anchored structure, e.g. because of the weather condition. The support for the anchoring chains (12, FIG. 2) is located on the underside of the deck and the dimensions are selected as to allow the structure to pivot freely 360°. In case of a concrete structure having a length of e.g. 600 meter and width of 90 meter and a depth up to 150 meter it can be necessary with e.g. 20 chains for safe anchoring of the structure. The structure is ballasted with sand and water filled into the lower portions of the inclined columns. 
     In the embodiment shown in FIGS. 9a and 9b consisting of modules according to FIG. 8 the lower chord comprises two parallel pipes 39 and there are two geometric locations (two parallel lines) for the junction points 37 of the support sections. These two pipes can be connected with one another, e.g. by girder members 41. 
     The buoyancy of the platform structure is provided by inner cavities in the upper portions of the support columns 6. The lower portion cavities accommodate the ballast.