Methods for producing gravity-borne structures (GBS) at special production sites.

Abstract

The present invention relates to the production of gravity-based structures (GBS). The GBS comprises a core and a protrusion with a common lower platform. For the core of the GBS, the outer and inner walls and the upper platform are cast in concrete, so that the GBS takes the shape of a rectangular parallelepiped. When the casting of the individual sections of the outer wall of the core is completed, a reinforcing frame is assembled, a temporary frame is installed, and the outer and inner walls of the protrusion of the GBS are cast in concrete. The outer wall of the GBS is formed along the entire periphery of the lower platform, and the height of the outer wall of the protrusion is lower than the height of the outer wall of the core. When the casting of the individual sections of the walls of the protrusion is completed, a reinforcing frame is assembled, a temporary frame is installed for the upper platform of the protrusion, and the upper platform of the protrusion is cast in concrete. When the casting of the core and the upper platform of the protrusion is completed and the concrete of the structure to be tensioned is sufficiently hardened, the introduction of post-tensioning is carried out on the upper platform of the core, as well as on the outer and inner walls of the core and the protrusion. As a result, the buoyancy of the GBS and the structure as a whole increases and its draft decreases during transportation to the installation site.

Description

[Technical Field]

[0001] The present invention relates to the fabrication (construction) of gravity-based structures (GBS), which can be used as part of the deployment of various types of onshore and offshore production, transportation, transshipment, and storage facilities (including natural gas liquefaction, ammonia, methanol, hydrogen production, and power generation). [Background technology]

[0002] A gravity-based structure (GBS) is a platform that is anchored to the seabed with the aid of its own weight. Gravity-based structures are used in coastal and offshore waters where the water depth is sufficient to support a superstructure of the required height above water level after the GBS is installed on the seabed. GBSs can feature internal chambers that allow them to be buoyant during transportation to their installation site. GBSs are designed to be floatable and have a ballast system that allows them to be transported and installed over long distances for operation at the intended offshore site without the use of expensive lifting and transportation equipment. GBSs are primarily constructed of reinforced concrete and steel.

[0003] GBS is produced in specialized production facilities and shipyards.

[0004] There is a method for fabricating a reinforced concrete gravity structure (GBS) having a rectangular parallelepiped shape with a base slab, an upper slab, and side walls for supporting a floating power plant and storing liquefied natural gas. The method comprises placing reinforcing bars, concrete-casting the GBS elements, and prestressing and post-tensioning the GBS elements (Korean Patent Application Publication No. 20150136823, published August 12, 2015).

[0005] The closest approach to what has been proposed features the fabrication of a gravity-based structure (GBS) for Adriatic LNG, an offshore liquefied natural gas receiving and regasification terminal constructed at the Algeciras production site in Spain (Design and Construction on Gravity Based Structure and Modularized LNG Tanks for the Adriatic LNG Terminal, Lisa B. Waters et al., ExxonMobil Development Company, 2007, http: / / www.ivt.ntnu.no / ept / fag / tep4215 / innhold / LNG%20Conferences / 2007 / fscommand / PS6_7_Waters_s.pdf).

[0006] The GBS is made in the form of a rectangular parallelepiped with a top slab, a base slab, an intermediate support slab for the freestanding LNG tanks, external walls, and internal longitudinal and transverse walls for separating the chambers.

[0007] The above production method is characterized by the following: The GBS construction site is prepared, including the installation of concrete cavities for the steel skirts, and the installation of these steel skirts, which hang loosely within the concrete cavities, thus transferring the GBS weight to the gravel backfilled site and concrete foundation. A rectangular reinforcing cage is assembled for the base slab, formwork for the base slab is installed, and then the base slab is concreted. Once the concrete pouring of each base slab area is complete, the reinforcing cages for the exterior and interior walls will be erected, and the exterior and interior walls will be constructed in slip form, except for the short end wall on one side of the GBS (the side where the LNG tank is located). Simultaneously with the concrete pouring of the walls, the reinforcing cage for the intermediate slab is assembled, formwork is erected and the intermediate slab is concreted. ·Roof beams are fabricated and installed. When the separate wall sections are concreted, the reinforcing cage for the top slab is erected, the top slab formwork is installed, and then the top slab is concreted. ·Insulation and secondary barriers for the LNG tank room will be installed. Compartments for free-standing LNG tanks will be built. The short end wall on one side of the GBS (the side where the LNG tank is installed) is concreted. The top and base slabs and interior and exterior walls are post-tensioned with reinforcing strands.

[0008] This method has the following drawbacks:

[0009] The concrete cavity for the steel skirt and the installation of the steel skirt increase the scope and duration of the work in the preparation stage, and the presence of the concrete cavity makes the preparation of the foundation more complicated.

[0010] The use of roof beams complicates construction work and requires the use of cranes with higher lifting capacities.

[0011] The concreting of one short end wall of the GBS (where the LNG tank is located) is done last, after the tank is installed in the GBS room, which increases construction time and violates the monolithic nature of the reinforced concrete structure due to the presence of "cold joints" in this section.

[0012] The rectangular parallelepiped shape of the GBS has a large draft when transported to the installation site, which makes it impossible to transport through shallow waters.

[0013] The rectangular parallelepiped shape of the GBS does not provide protection from external influences such as drifting ice and emergency ship impacts. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Korean Patent Application Publication No. 20150136823 [Non-patent literature]

[0015] [Non-Patent Document 1] Design and Construction on Gravity Based Structure and Modularized LNG Tanks for the Adriatic LNG Terminal, Lisa B. Waters et al., ExxonMobil Development Company, 2007, http: / / www.ivt.ntnu.no / ept / fag / tep4215 / innhold / LNG%20Conferences / 2007 / fscommand / PS6_7_Waters_s.pdf. Summary of the Invention

[0016] The technical problem solved by the present invention is the following: Considering that an increasing proportion of production and infrastructure facilities are located in less developed areas, including the coasts and waters of the Arctic Ocean, there is an urgent need to develop new and efficient methods for the construction of gravity structures that can accommodate production, transport, transshipment and storage complexes for various purposes on the coasts and in waters, and that can be adapted for use in waters with icy conditions.

[0017] To solve the above problems, a method has been proposed for producing a GBS that represents a three-dimensional reinforced concrete structure having internal walls separating chambers, intended for installation on the bottom of a target body of water, and capable of serving as a base for housing a top surface for various purposes. Furthermore, the GBS can remain afloat during transport through a waterway from the production site to the installation site, and can withstand ice loads from an icy basin when installed on the seabed. The top surface can be erected immediately after GBS production, after GBS placement on the seabed, or at one of the temporary locations during transport of the GBS from the production site to the installation site.

[0018] The technical problem was solved by the method of gravity-based structures (GBS) production, i.e. A reinforcing cage is assembled about the rectangular base slab, the base slab formwork is installed, and then the base slab is concreted; When the separate sections of the base slab are concreted, the reinforcing cages for the interior and exterior walls are erected and concreted in slipform; When the separate wall sections are concreted, the reinforcing cage for the top slab is erected, the top slab formwork is installed, and then the top slab is concreted; The top and base slabs and interior and exterior walls are post-tensioned with reinforcing strands. At the same time, according to the present invention, The GBS is fabricated including a central section and protruding sections with a common base slab; For the central part of the GBS, the inner and outer walls and the upper slab are concreted, which takes the form of a rectangular parallelepiped; When separate sections of the central exterior wall are concreted, the reinforcement cage is assembled, formwork is installed and concrete pouring is carried out for the inner and outer walls of the GBS protrusion, and the outer wall is made along the perimeter of the base slab, while the height of the outer wall of the protrusion is lower than that of the outer wall of the central section; When the separate wall sections of the projection are concreted, the reinforcing cage is assembled and formwork is installed for the upper slab of the projection, which is then concreted; When the central and protruding top slabs are concreted, the central base and top slabs and the central and protruding inner and outer walls are post-tensioned and the concrete of the post-tensioned structure gains the required strength.

[0019] In addition, it is desirable to concrete the upper slab with its center bent upward so that it will later drop under its own weight to its design position.

[0020] Furthermore, in a preferred option of the present invention, when the separate sections of the central upper slab are concreted, the reinforcing cage is assembled, the formwork is installed, the embeds are fitted and the supports for the equipment are concreted onto the upper slab.

[0021] Furthermore, when the outer and inner walls of the central section are concreted, it is desirable to leave openings for the removal of formwork and for further installation of equipment inside the GBS chamber defined by the walls and slab.

[0022] If the GBS is to accommodate at least one tank for storing liquids, simultaneously with the concrete pouring of the central wall, the reinforcing cage is assembled, formwork is installed, the intermediate slab is concreted, post-tensioning is introduced, and the tank for storing liquids is assembled with panels inside at least one chamber defined by the wall, intermediate slab and top slab and delivered through the wall opening.

[0023] The technical results achieved by the GBS manufactured with protrusions are as follows: The protrusions increase the buoyancy of the GBS and the entire structure, reducing its submergence during transport to the installation site. The provision of additional ballast chambers around the periphery of the GBS inside the protrusions makes it easier to balance the GBS, i.e., to sink it evenly without trimming or listing. The increased width of the GBS lower part increases the stability of the entire structure during its transport, allowing for the installation of a higher and heavier superstructure on top of the GBS.

[0024] Unlike platforms towed and installed in deepwater regions, a GBS that uses protrusions rather than having the same volume throughout its height has clear advantages in terms of draft and overall weight-to-buoyancy ratio, allowing for much larger displacements for a relatively small increase in the platform's dead weight.

[0025] The protruding part of the GBS also protects the central section, which can house the main storage compartment, from the impact of drifting ice and emergency ships.

[0026] Erecting both the side walls and short end walls before the top slab is formed, as well as having the possibility to assemble the tank from separate panels within a confined chamber, expedites GBS fabrication and helps to reduce the number of "cold welds" in reinforced concrete construction.

[0027] To reduce the overall GBS production time, certain stages are performed in parallel. [Brief explanation of the drawings]

[0028] [Figure 1] 10 shows the fabrication of the base slab and the central wall of the GBS between the base slab and the intermediate slab. [Figure 2] 10 shows the fabrication of the base slab, intermediate slab and inner wall of the central part of the GBS. [Figure 3] FIG. 10 shows the fabrication of the inner and outer walls of the central GBS. [Figure 4] 1 shows the fabrication of the outer wall of the central part of the GBS, the upper slab, the upper support on the upper slab, the outer wall of the GBS protrusion, and the liquid storage tank inside the GBS. [Figure 5] 1 shows the fabrication of the GBS central upper slab, the GBS protruding upper slab, and the superstructure support. [Figure 6] This is a front view of the fabricated GBS as it is pulled out of the dock. [Figure 7] A side view of the fabricated GBS as it is pulled out of the dock. DETAILED DESCRIPTION OF THE INVENTION

[0029] The fabrication program refers to the mass production of the GBS as part of a phased process at a specialized fabrication site with a dry dock. The location of the fabrication site facilities allows for the production of material for each separate phase of fabrication, within the confines of the separate facilities, and subsequent transportation to the dry dock for use in GBS fabrication. The GBS fabrication sequence is designed to optimize the use of equipment and personnel and reduce construction time through the parallel execution of some of the work phases.

[0030] The GBS is produced as follows.

[0031] The dry dock is isolated from the adjacent waters using a dock gate, and then the dock is pumped out. The bottom of the dock is then prepared with a compacted crushed stone cover for the fabrication of the GBS foundation slab.

[0032] The reinforcement is cut and bent, and the reinforcement cage is fabricated and labeled in the reinforcement shop. The reinforcement elements are transported by road to the dry dock and delivered by loader or lift crane to the GBS reinforcement cage assembly site. The GBS reinforcement cage is assembled by crimping, tying, and sleeve joining.

[0033] Simultaneously with the reinforcing cages, duct pipes for the post-tensioning reinforcing strand bundles are installed in the tensioned structure, as well as anchors and penetrations for the equipment to be installed.

[0034] Three types of formwork are used for GBS concreting: conventional formwork, stock formwork, and permanent formwork. In the formwork shop, conventional and permanent formwork is produced and stock formwork assembly bays are assembled. Completed bays are stored in the formwork laying area and, when needed, transported to the dry dock and installed for concreting the GBS structure.

[0035] Conventional formwork panels are produced in formwork factories from cut timber and laminated plywood. Conventional formwork is primarily used for concreting lower height objects, such as slabs and supports.

[0036] The basic elements of stock formwork are panels or blocks, frames, load-bearing structures, connectors, and fasteners. Depending on the structure to be concreted, two types of stock formwork are applied: panel formwork and slipform formwork.

[0037] Panel formwork is foldable and made up of large elements, facilitating the construction of large structures. Slipforms consist of two identical rows of panels, 1.0–1.2 m high, rigidly connected to each other by bolts and mounted on a special frame. They are moved upward by jacks as the structure is concreted. Slipforms are used in the concreting of GBS walls. When applied, the concrete is monolithic, i.e., there are no "cold seams," thus improving the structure's performance parameters. Furthermore, the use of slipforms allows GBS walls to be concreted very rapidly, upwards of 2.5 meters or more per day.

[0038] If formwork removal is not possible, such as during the concreting of intermediate ceiling slabs when equipment is installed inside the chamber, permanent formwork is used. This type of formwork is also used in the construction of pit structures for LNG tanks and other parts of GBS, and its removal requires a lot of labor after the outer structure is closed.

[0039] Concrete, the main construction material for GBS production, is mixed in a concrete processing plant located close to the dry dock. The location of the concrete processing plant ensures that the distance the concrete has to be transported to the pouring point is minimal.

[0040] Bulk materials for concrete mixing may be delivered to the fabrication site via a wharf located in front of the concrete processing plant, which ensures the shortest route for the materials from the point of shipment to where they are stored and subsequently used.

[0041] GBS production utilizes a special high-strength concrete mix design with the required density and durability characteristics. The use of different densities of concrete, combined with weight control, allows for optimal targets for the structure's mass, buoyancy, and stability. The concrete mix is ​​delivered to the dry dock by mixer truck. The concrete is then pumped into the formwork with a concrete pump.

[0042] Concreting begins with the sectioned concrete casting of base slab 1, which is common to the central and protruding sections of the GBS (Figure 1). A reinforcing cage is assembled for the rectangular base slab 1, formwork is installed for the base slab 1, and then the base slab 1 is concreted. Once the individual sections of base slab 1 are completed, reinforcing cages are assembled for the interior walls 2 with the aid of stock formwork in the central section of the GBS. In parallel, reinforcement installation is carried out for the interior and exterior walls 3 and 4 of the central GBS (Figures 2 and 3), which are constructed using slipform construction. During this process, the central GBS section is shaped as a rectangular parallelepiped. A relatively small service opening is left in the wall for the purpose of removing the formwork and subsequently installing equipment in the GBS room, and is then completely closed and sealed once the work inside the room is complete.

[0043] If the GBS is constructed with an intermediate slab 7 for housing at least one liquid storage tank 8 (Fig. 4), the concreting of the GBS intermediate slab 7 begins when the concreting of the individual sections of the central wall 2 between the base slab 1 and the intermediate slab 7 is completed, in parallel with the concreting of the internal and external walls 3 and 4 of the GBS central section. For this purpose, the reinforcing cage is assembled, the formwork is erected and the intermediate slab 7 is concreted.

[0044] As the individual sections of the central exterior wall 4 are concreted, the reinforcing cage is erected, formwork is installed, and the external and internal walls of the protrusions are concreted section by section using slipforms. The GBS protrusion exterior walls 5 are erected along the entire perimeter of the base slab, and are lower than the central exterior wall 4.

[0045] In parallel with this, where the concrete pouring of the central GBS walls 3 and 4 has been completed, the concrete pouring of the central GBS upper slab 9 begins. To this end, a reinforcing cage is assembled for the upper slab 9, formwork is erected for the upper slab 9, and the upper slab 9 is concreted. Additionally, scaffolding and trestles are installed inside the GBS chamber to erect the formwork, eliminating the need for roof beams. The use of scaffolding in combination with formwork provides universal use for both the construction of the upper slab 9 and the subsequent preparation and installation of the structural elements of the tank 8 at different heights, ultimately facilitating the overall construction process.

[0046] To offset the downward bowing of the top slab 9 due to its weight, the center of the slab is bent upward before concreting to ensure an opposing bowing. Once concreting is complete and the formwork is removed, the slab will sink under its weight, assuming a design configuration that allows for partial offset of the downward bowing. The use of a beamless design for the top slab 9, with a non-uniform thickness (not shown) resembling an arc where the slab is thicker near the edges than at the spans, allows for better target specifications for weight and stiffness, as well as facilitated formwork installation, through the simplification of the slab bottom surface with no protruding parts.

[0047] The liquid storage tank 8 is locally erected in at least one of the chambers formed by the internal reinforced concrete wall 3, the intermediate slab 7 and the top slab 9 from panels delivered through openings in the walls.

[0048] In parallel, when the external wall 5 of the GBS projection is completed, the concreting of the top slab 6 of the GBS projection begins (Figures 4 and 5). The top slab 6 of the GBS projection is connected to the central external wall 4 by extending and tying the projection reinforcement into sleeves and anchor rods that have been previously installed flush in the slipform of the wall 4 according to the design.

[0049] If the intended use of the GBS includes berthing of ships, supports are constructed from reinforced concrete along the outer edges of the GBS projection above the top slab 6 for the purpose of installing berthing structures and fenders for berthing and mooring of ships, allowing the GBS structure to be used as a berthing position. These supports are erected with the help of stock formwork.

[0050] If it is required to fabricate a GBS with supports 10 for topside equipment installed on the top slab 9, the reinforcing cage is assembled, forms are installed, fillers are fitted, and supports 10 are concreted to provide support for the load-bearing structure of the topside cage that may house the process equipment (FIG. 5).

[0051] The post-tensioning materials workshop accommodates the storage of reinforcing strands, duct pipes, and anchors, and the preparation of materials and equipment for carrying out post-tensioning. Equipment is installed in the dry dock in areas where a series of operations will allow this type of work to begin. Once the equipment is ready, the post-tensioning materials are transported to the dry dock, where the strand bundles are installed and tensioned to the design value by anchoring and transferring tension to anchorages on the reinforced concrete structure of the GBS.

[0052] Concrete structures are post-tensioned using "tension against concrete" with bonded repair, which means that after the concrete of the GBS-tensioned reinforced concrete structure is poured, the strands are pushed / pulled through pre-installed corrugated steel duct pipes. After the concrete reaches the required minimum strength, the strand bundles are tensioned and fixed, thus transferring the tension to pre-installed steel anchorages at the short ends of the structure. The reinforcing strands are tensioned with hydraulic jacks. After the strand bundles are tensioned and pull-out tested, the duct pipe is filled with non-shrink cement mortar and all temporary openings and niches are sealed. The duct pipe protects the reinforcing strands from external impacts and partially transfers the load from the strands to the concrete along the entire length of the structure.

[0053] The introduction of post-tensioning during construction of the GBS allows the targeted performance to be achieved more efficiently, especially for limit state Group II, such as crack resistance and impermeability. As a result, it reduces the amount of non-tensioned reinforcement required, contributing to a reduction in the structure weight and increasing the overall spatial stiffness of the GBS's load-bearing reinforced concrete cage.

[0054] Finally, the process openings in the GBS wall are closed, post-tension anchors are concreted, and the concrete surface is cleaned.

[0055] After GBS fabrication is completed, equipment 11 is installed inside the room and on the top slab 9, and modular top structure 12 is installed on supports 10 on top slab 9 (see Figures 6 and 7). Top modules 12 may be fabricated independently in parallel with the GBS construction schedule and then installed on supports 10 with the aid of a specialized jacking and skid system. Supports 10 are also the main load-bearing elements supporting the load-bearing guardrails of the top skid system.

[0056] In addition to the skid system, cranes are also used in the dry dock to allow heavy machinery and steel structures to be placed on the GBS from areas near the dock.

[0057] After the construction of the GBS and the installation of the equipment are completed, the dry dock 13 with the GBS inside is gradually filled with water 14 from the nearby body of water with the help of pumps. At each stage of dock flooding, the GBS room is checked for leak tightness by hydraulic and pneumatic tests. Along with the dock flooding, the GBS ballast room is also flooded to increase the weight of the structure and therefore ensure its stability against the dock bottom.

[0058] Once testing is complete, the GBS is secured inside the dry dock by mooring lines and holding and guiding mooring piles located at the bottom of the dry dock. Once testing and mooring of the GBS is complete, water is pumped out of the moored GBS's chamber to ensure the GBS remains afloat during high tides.

[0059] The GBS is retrieved from the dry dock by a tugboat. After being retrieved from the dry dock, the GBS is towed to the installation site. The GBS is then installed at its destination around the quayside by a land-based winch and tug, where it is connected to land-based communication lines within the storage area. Once its position is confirmed as correct, the GBS is ballasted and installed on a foundation previously placed on the bottom of the water.

Claims

1. 1. A method of fabricating a gravity-based structure (GBS), comprising: a reinforcing cage is assembled about a rectangular base slab, a base slab form is installed, and then the base slab is concreted; When the concrete pouring of each section of the base slab is completed, the reinforcing cages for the interior and exterior walls are assembled, and the interior and exterior walls connected to the base slab are concreted by slipform; Upon completion of the concrete pouring of each section of the interior and exterior walls, a reinforcing cage for the upper slab is assembled, an upper slab formwork is installed, and then the upper slab connected to the interior and exterior walls is concreted; The method of claim 1, wherein the top slab, the base slab, and the interior and exterior walls are post-tensioned with reinforcing strands; The GBS is fabricated to include a central portion and a protruding portion having a common base slab, and the inner and outer walls and the upper slab are concreted for the central portion of the GBS, so that the central portion of the GBS has a rectangular parallelepiped shape; When the concrete pouring of each section of the outer wall of the central part is completed, for the inner and outer walls of the protruding part of the GBS connected to the base slab, a reinforcing cage is assembled, formwork is installed and concrete pouring is carried out, and the outer walls are made along the outer edge of the base slab, and at the same time, the height of the outer wall of the protruding part is lower than the height of the outer wall of the central part; Upon completion of the concreting of each section of the interior and exterior walls of the protrusion, a reinforcing cage is erected and a formwork is installed for the upper slab of the protrusion, which is then concreted; Simultaneously with the concrete pouring of the inner and outer walls of the central portion, a reinforcing cage is assembled, formwork is installed, an intermediate slab is concreted, and post-tensioning is introduced, the intermediate slab is located closer to the base slab than the upper slab of the protruding portion, and the width and length of the intermediate slab are smaller than the width and length of the central portion, and a tank for storing liquid is arranged by panels inside at least one chamber defined by the inner and outer walls, the intermediate slab, and the upper slab, and liquid is delivered through a temporary wall opening; Upon completion of concreting the top slab of the central section and the protruding sections, the base slab and the top slab of the central section and the interior and exterior walls of the central and protruding sections are post-tensioned, and the concrete of the post-tensioned structure is allowed to harden.

2. 2. The method of claim 1, wherein the top slab is concreted with a central portion of the top slab bowing upward so that the central portion of the top slab drops under its own weight to a design position.

3. 10. The method of claim 1, wherein, once the individual sections of the top slab in the central section are completed concreting, a reinforcing cage is erected, forms are installed, embeds are fitted, and supports for equipment are concreted onto the top slab.

4. 2. The method of claim 1, wherein during the process of concrete pouring the exterior and interior walls of the central section, an opening is left for removal of the formwork and for further installation of equipment inside the chamber of the GBS defined by the exterior and interior walls and slab.

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