Transition section structure of offshore wind turbine generator jacket foundation and construction method thereof

Abstract

The application provides a jacket foundation transition section structure of offshore wind turbine generator and a construction method thereof, which comprises a main cylinder, a truss type inclined support structure, a deck and a support structure, the bottom of the main cylinder is connected with the deck, a plurality of truss type inclined support structures are connected between the outer sidewall of the main cylinder and the deck, and the bottom of the deck is connected with the support structure connected with the lower foundation; the main cylinder, the truss type inclined support structure and the support structure are all arranged as a steel pipe-ultra high performance concrete combined structure. The application solves the defects of the traditional pure steel transition section, such as excessive dependence on expensive thick steel plates, easy local buckling of large-diameter single pipes and short board of fatigue cracking caused by complex internal stiffening structure, and overcomes the defects of the full concrete transition section, such as large weight, easy cracking under tension and complicated offshore formwork.

Description

Technical Field

[0001] This invention relates to the field of offshore wind power engineering technology, specifically to a transition section structure for an offshore wind turbine jacket foundation and its construction method. Background Technology

[0002] The transition section of the offshore wind turbine jacket foundation is a key core structure connecting the upper wind turbine tower and the lower underwater jacket. Its main responsibility is to safely transfer the enormous vertical loads, horizontal shear forces, and overturning moments generated by the wind turbine operation to the lower foundation. As offshore wind power develops towards deeper waters and larger megawatt capacities, the complex dynamic loads and fatigue stresses borne by the transition section increase dramatically, posing severe challenges to structural design.

[0003] Currently used traditional pure steel transition sections face significant bottlenecks when dealing with large-megawatt units: First, to meet rigidity and fatigue resistance requirements, the steel plate thickness must be significantly increased, leading to high costs for the procurement, rolling, manufacturing, and transportation of ultra-thick steel plates. Second, there is a high risk of local buckling and fatigue; thin-walled, large-diameter steel pipes are extremely prone to buckling in the pressure zone, necessitating the arrangement of numerous complex internal stiffening ribs. This results in extremely dense welds, which easily induce stress concentration under alternating marine loads, becoming a fatal source of fatigue cracking.

[0004] On the other hand, the all-concrete transition section also has serious drawbacks: its structural weight is extremely large, which not only increases the load on the foundation but also greatly increases the difficulty of offshore transportation and equipment hoisting. At the same time, ordinary concrete has weak tensile strength, and under extreme working conditions, the root is very prone to tensile cracking, leading to seawater leakage and structural corrosion. In addition, the complex formwork erection, dismantling, and curing procedures at sea also seriously restrict the construction period and project quality. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the first objective of this invention is to provide a transition section structure for offshore wind turbine jacket foundations. This invention solves the problems of traditional pure steel transition sections, which rely excessively on expensive thick steel plates, are prone to local buckling of large-diameter single pipes under large-megawatt wind turbine loads, and suffer from fatigue cracking due to complex internal stiffening structures. Simultaneously, it overcomes the drawbacks of all-concrete transition sections, such as heavy weight, susceptibility to cracking under tension, and cumbersome offshore formwork. This invention provides a solution for deep-sea, large-capacity wind power projects that optimizes the force transmission path, effectively shifts the stress mode from tension in steel to compression in the core concrete, eliminates the need for formwork removal during construction, and ensures structural reliability throughout its entire lifecycle.

[0006] In a first aspect, the present invention provides a transition section structure for a jacket foundation of an offshore wind turbine, comprising a main cylinder, a truss-type diagonal bracing structure, a deck, and a support structure. The bottom of the main cylinder is connected to the deck, and several truss-type diagonal bracing structures are connected between the outer side wall of the main cylinder and the deck. The bottom of the deck is connected to the support structure connected to the lower foundation. The main cylinder, the truss-type diagonal bracing structure, and the support structure are all configured as a steel pipe-ultra-high performance concrete composite structure.

[0007] As a preferred technical solution of the present invention: the truss-type diagonal bracing structure includes a diagonal bracing upper chord structure, a diagonal bracing lower chord structure, and multiple diagonal bracing web members connected between the diagonal bracing upper chord structure and the diagonal bracing lower chord structure. One end of the diagonal bracing upper chord structure and the diagonal bracing lower chord structure are both connected to the deck, and the other end is respectively connected to different height positions on the outer side wall of the main cylinder to form a triangular truss structure.

[0008] As a preferred technical solution of the present invention: the multiple diagonal bracing struts are arranged in any one of the following arrangements: cross arrangement, K-shaped arrangement, N-shaped arrangement or W-shaped arrangement.

[0009] As a preferred technical solution of the present invention: at least three sets of truss-type diagonal bracing structures are provided on the outer wall of the main cylinder, and the three sets of truss-type diagonal bracing structures are spaced apart on the outer wall of the main cylinder.

[0010] As a preferred technical solution of the present invention: at least three sets of the support structure are provided at the bottom of the deck, and each set of the support structure is respectively provided below the connection position between the corresponding truss-type diagonal brace structure and the deck.

[0011] As a preferred technical solution of the present invention: the main cylinder includes an inner steel pipe and an outer steel pipe, and an annular cavity is formed between the inner steel pipe and the outer steel pipe. The inner steel pipe and the outer steel pipe serve as permanent inner formwork and permanent outer formwork for ultra-high performance concrete pouring, respectively, and the annular cavity is filled with ultra-high performance concrete.

[0012] As a preferred technical solution of the present invention: the upper chord structure of the inclined brace includes an upper chord steel pipe and ultra-high performance concrete filled inside the upper chord steel pipe; the lower chord structure of the inclined brace includes a lower chord steel pipe and ultra-high performance concrete filled inside the lower chord steel pipe; both the upper chord steel pipe and the lower chord steel pipe of the inclined brace serve as permanent templates for the pouring of ultra-high performance concrete.

[0013] As a preferred embodiment of the present invention: the support structure includes a support steel pipe and ultra-high performance concrete filled inside the support steel pipe, wherein the support steel pipe serves as a permanent template for the ultra-high performance concrete pouring.

[0014] Secondly, a second objective of this invention is to provide a construction method for a transition section structure of an offshore wind turbine jacket foundation, comprising the following steps:

[0015] S1. Perform steel structure assembly and welding, connecting the main tube, truss-type diagonal bracing structure and supporting structure with the deck to form an overall steel frame system;

[0016] S2. Shear connection components are installed on the inner wall of each steel pipe component, and prestressed ducts, grouting holes and vent holes are reserved to form a grouting channel system;

[0017] S3. The inner steel pipe, outer steel pipe, upper chord steel pipe of the diagonal brace, lower chord steel pipe of the diagonal brace, and supporting steel pipe are used as permanent formwork for ultra-high performance concrete pouring, and temporary support structures are set up.

[0018] S4. Adopting a bottom-up jacking and grouting process, ultra-high performance concrete is continuously poured into the interior of each steel pipe component through the grouting hole, and the internal gas is discharged through the vent hole until the grouting is completed.

[0019] S5. During the setting process of ultra-high performance concrete, grouting and pressurization are carried out. After the strength reaches the design requirements, the temporary support is removed and prestressing tensioning and anchoring are carried out to finally form a combined structure in which steel pipe and ultra-high performance concrete work together to bear the load.

[0020] As a preferred technical solution of the present invention: In step S5, after the ultra-high performance concrete completes its first jacking and pouring, before and after its initial setting, before and after its final setting, and during the shrinkage-sensitive stage, a secondary grouting and pressure stabilization process is implemented through reserved grouting holes to compensate for and fill the small voids that may be formed in the pipe due to settlement, gas leakage, or early shrinkage, so that the ultra-high performance concrete always maintains a full fit with the inner wall of the steel pipe; if necessary, a staged, segmented, and pressure-maintaining grouting method can be adopted to further improve the filling fullness of narrow interfaces and complex joints, and establish a favorable interface compaction state and micro-expansion compressive stress under the constraint of the steel pipe on the core concrete, thereby effectively suppressing interface voids, shrinkage joints, and bond degradation.

[0021] The beneficial effects provided by this invention are as follows:

[0022] This invention employs a truss-type diagonal bracing structure, transforming complex bending and shearing forces into axial tensile and compressive forces on the chord tubes. Combining the synergistic effect of the tensile strength of the outer steel tube and the compressive strength of ultra-high performance concrete, it fully leverages the advantages of the materials, effectively enhancing the structure's ultimate bearing capacity and overall spatial stiffness.

[0023] The ultra-high performance concrete filling the steel pipes in this invention provides reliable internal support and suppresses local buckling; at the same time, the truss-type diagonal bracing structure enhances overall stability and reduces the slenderness ratio effect of individual pipes. The combination of these two aspects significantly reduces the reliance on internal dense stiffening ribs, reduces stress concentration in welds, and significantly improves the fatigue resistance of the structure.

[0024] In this invention, each steel pipe can be directly used as a formwork for ultra-high performance concrete pouring without dismantling, simplifying the offshore formwork process. Compared to large-diameter single-pipe bracing, the structural pipe diameters of the members in the truss-type bracing structure are smaller, reducing the difficulty of steel pipe rolling and hoisting; by using the truss-type bracing structure to replace ultra-thick steel plates for load-bearing, the amount of steel used is effectively reduced, which helps control project costs. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 A three-dimensional structural view of the transition section structure of the offshore wind turbine jacket foundation provided in an embodiment of the present invention;

[0027] Figure 2 An exploded view of the transition section structure of the offshore wind turbine jacket foundation provided in an embodiment of the present invention;

[0028] Figure 3 This is a schematic diagram of the truss-type diagonal brace provided in an embodiment of the present invention;

[0029] Figure 4 This is a schematic diagram of the main cylinder structure provided in an embodiment of the present invention;

[0030] Figure 5 This is a schematic diagram of the deck structure provided in an embodiment of the present invention.

[0031] Reference numerals: 1. Inner steel pipe; 2. Ultra-high performance concrete; 3. Outer steel pipe; 4. Truss-type diagonal bracing structure; 5. Upper chord steel pipe of diagonal bracing; 6. Support structure; 7. Lower chord steel pipe of diagonal bracing; 8. Diagonal bracing web member; 9. Deck; 10. Main tube; 11. Supporting steel pipe. Detailed Implementation

[0032] To enable those skilled in the art to better understand the technical solutions of the present invention, preferred embodiments of the present invention are described below in conjunction with specific examples. However, it should be understood that the accompanying drawings are for illustrative purposes only and should not be construed as limiting the present invention. For better illustration of this embodiment, some components in the drawings may be omitted, enlarged, or reduced, and do not represent the actual dimensions of the product. It is understandable that some well-known structures and their descriptions may be omitted in the drawings for those skilled in the art. The positional relationships described in the drawings are for illustrative purposes only and should not be construed as limiting the present invention.

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0034] like Figures 1 to 5 As shown, a transition section structure for an offshore wind turbine jacket foundation includes a main cylinder 10, a truss-type diagonal bracing structure 4, a deck 9, and a support structure 6. The bottom of the main cylinder 10 is connected to the deck 9, and several truss-type diagonal bracing structures 4 are connected between the outer side wall of the main cylinder 10 and the deck 9. The bottom of the deck 9 is connected to the support structure 6, which is connected to the lower foundation. The main cylinder 10, the truss-type diagonal bracing structure 4, and the support structure 6 are all configured as a steel pipe-ultra-high performance concrete composite structure. The main cylinder 10 is vertically fixedly installed in the middle of the deck 9.

[0035] The truss-type diagonal bracing structure 4 includes an upper diagonal bracing structure, a lower diagonal bracing structure, and multiple diagonal bracing web members 8 connected between the upper diagonal bracing structure and the lower diagonal bracing structure. One end of the upper diagonal bracing structure and the lower diagonal bracing structure are connected to the deck 9, and the other end is connected to different height positions on the outer side wall of the main cylinder 10 to form a triangular truss structure.

[0036] The upper chord structure, lower chord structure, and web members 8 of the truss-type diagonal bracing structure 4 are connected and arranged in a reasonable spatial manner, which further enhances the local stiffness of the nodes on the outer wall of the main tube 10. This effectively disperses the concentrated stress transmitted from the truss-type diagonal bracing structure 4 to the outer wall of the main tube 10, and avoids premature fatigue cracking at the stress concentration points of traditional single tube connections.

[0037] The multiple diagonal bracing struts 8 are arranged in any one of the following configurations: cross-shaped, K-shaped, N-shaped, or W-shaped.

[0038] At least three sets of the truss-type diagonal bracing structure 4 are provided on the outer wall of the main cylinder 10, and the three sets of truss-type diagonal bracing structures 4 are spaced apart on the outer wall of the main cylinder 10.

[0039] At least three sets of the support structure 6 are provided at the bottom of the deck 9, and each set of the support structure 6 is respectively located below the connection position between the corresponding truss-type diagonal brace structure 4 and the deck 9.

[0040] The main cylinder 10 includes an inner steel pipe 1 and an outer steel pipe 3, with an annular cavity formed between the inner steel pipe 1 and the outer steel pipe 3. The inner steel pipe 1 and the outer steel pipe 3 serve as the permanent inner formwork and the permanent outer formwork for the pouring of ultra-high performance concrete 2, respectively. The annular cavity is filled with ultra-high performance concrete 2.

[0041] The upper chord structure of the diagonal brace includes an upper chord steel pipe 5 and ultra-high performance concrete 2 filled inside the upper chord steel pipe 5. The lower chord structure of the diagonal brace includes a lower chord steel pipe 7 and ultra-high performance concrete 2 filled inside the lower chord steel pipe 7. Both the upper chord steel pipe 5 and the lower chord steel pipe 7 serve as permanent formwork for the pouring of ultra-high performance concrete 2.

[0042] The support structure 6 includes a support steel pipe 11 and ultra-high performance concrete 2 filled inside the support steel pipe 11. The support steel pipe 11 serves as a permanent template for the pouring of ultra-high performance concrete 2.

[0043] This invention utilizes hollow steel pipes in each layer as a skeleton and permanent inner and outer molds, and pours ultra-high performance concrete (UHPC) into the cavity inside the steel pipes to form a whole. During the stress process, the huge wind turbine load is transferred to the main cylinder 10 and the truss-type diagonal bracing structure 4 through the tower. The truss-type diagonal bracing structure 4 transforms the complex bending and shearing actions into axial tension and compression forces on the chord tube. The large cross-section and ultra-high compressive strength of the inner core concrete withstand the huge pressure and bending moment. The inner steel pipe 1 and the outer steel pipe 3 mainly bear the pull-out force and form a tight constraint on the inner concrete.

[0044] This invention forms a basic framework by welding steel pipes and diagonal bracing 8 in each layer. Compared with traditional pure steel structures, it can meet the ultimate load-bearing requirements without the need for expensive extra-thick steel plates. The ultra-high performance concrete 2 filled in each steel pipe provides excellent overall spatial stiffness and bending stiffness, which effectively changes the overall stress mode of the transition section from steel being mainly under tension to core concrete being mainly under compression, effectively resisting the severe fatigue load in the deep-sea environment. At the same time, the bottom deck 9 and the supporting structure 6 work together to safely and evenly transfer the upper load to the underwater jacket foundation.

[0045] Shear keys are provided on the outer wall of the inner steel pipe 1, the inner wall of the outer steel pipe 3, the inner wall of the upper chord steel pipe 5 of the diagonal brace, the inner wall of the lower chord steel pipe 7 of the diagonal brace, and the inner wall of the supporting steel pipe 11. The shear keys are integrally cast and encased in the corresponding core concrete to ensure the coordinated stress of the steel pipe and the concrete.

[0046] This invention also provides a construction method for the transition section structure of the offshore wind turbine jacket foundation, including the following steps:

[0047] S1. Perform steel structure assembly and welding, connecting the main tube 10, truss-type diagonal bracing structure 4 and supporting structure 6 with the deck 9 to form an overall steel frame system.

[0048] Specifically, the inner steel pipe 1, outer steel pipe 3, upper chord steel pipe 5, lower chord steel pipe 7, and web member 8 are assembled and welded according to the designed spatial angle to form a truss-type diagonal bracing structure 4, and the bottom of each component is welded and fixed to the deck 9; at the same time, support steel pipe 11 is welded at the corresponding position below the deck 9 to complete the assembly of the overall steel frame system.

[0049] S2. Shear connection components are installed on the inner wall of each steel pipe component to enhance the interfacial bonding and synergistic stress performance between the steel pipe and the ultra-high performance concrete 2, and prestressed ducts, grouting holes and vent holes are reserved to form a grouting channel system.

[0050] Specifically, prestressed ducts are reserved in the corresponding pouring area according to the arrangement path of the prestressed tendons, and jacking grouting holes are set at the bottom of each steel pipe component to be grouted and venting grouting holes are set at the top. At the same time, the anchor plate and related grouting and venting accessories are positioned and installed, thus forming a complete jacking grouting and grouting channel system.

[0051] S3. The inner steel pipe 1, outer steel pipe 3, upper chord steel pipe 5 of the diagonal brace, lower chord steel pipe 7 of the diagonal brace, and support steel pipe 11 are used as permanent formwork for the pouring of ultra-high performance concrete 2, and a temporary support structure 6 is set up to suppress local deformation or instability caused by the side pressure of the grout during the jacking and pouring process, and to ensure the geometric accuracy and overall stability of the component during the pouring stage.

[0052] S4. Using a bottom-up jacking and grouting process, ultra-high performance concrete 2 is continuously poured into the interior of each steel pipe component through the grouting hole, and the internal gas is discharged through the vent hole until the grouting is completed.

[0053] Specifically, during the grouting process, the jacking pressure is used to push the grout to rise steadily, and the air and free gas inside the steel pipe are fully discharged through the top vent grout outlet until the grout is discharged continuously and evenly from each vent grout outlet, and then the grouting of the corresponding part is stopped.

[0054] S5. During the setting process of ultra-high performance concrete 2, grouting and pressurization are carried out. After its strength reaches the design requirements, the temporary support is removed and prestressing tensioning and anchoring are carried out to finally form a combined structure in which the steel pipe and ultra-high performance concrete 2 work together to bear the force.

[0055] Specifically, after the initial jacking and pouring of the ultra-high performance concrete 2 (UHPC 2), during the initial setting, final setting, and shrinkage-sensitive stages, a secondary grouting and pressure stabilization process is implemented through pre-reserved grouting holes. This process compensates for and fills the small voids that may be formed in the pipe due to settlement, gas leakage, or early shrinkage, ensuring that the UHPC 2 always maintains a full fit with the inner wall of the steel pipe. If necessary, a staged, segmented, and pressure-maintaining grouting method can be adopted to further improve the fullness of filling narrow interfaces and complex joints. Under the constraint of the steel pipe on the core concrete, a favorable interface compaction state and micro-expansion compressive stress are established, effectively suppressing interface voids, shrinkage joints, and bond degradation. After the UHPC 2 reaches the design strength, the temporary supports inside the steel pipe are removed, steel strands are threaded, and prestressing tensioning and anchoring are performed. Finally, overall curing is carried out, forming a high-load-bearing, high-rigidity steel-concrete composite transition section structure where the core concrete is under pressure and the steel pipe and UHPC work in synergy.

[0056] The above construction method, through steps such as prefabrication of the steel structure frame, using the steel pipes of each layer as formwork and setting shear keys and temporary internal supports, bottom-up jacking and pouring of ultra-high performance concrete (UHPC), subsequent grouting and pressurization, and prestressed tensioning and anchoring, has the following advantages:

[0057] The construction process is simplified by using each steel structure directly as a permanent inner and outer formwork, eliminating the complicated formwork erection and dismantling procedures and shortening the construction cycle. The temporary support inside the pipe effectively solves the problem of local deformation or buckling of thin-walled steel pipes under the lateral pressure of ultra-high performance concrete 2, ensuring the accuracy of structural dimensions. At the same time, the jacking and grouting and subsequent pressurization process effectively avoids air entrapment and concrete shrinkage, ensuring a tight fit and density between the core concrete and the inner wall of the steel pipe. The ultra-high performance concrete is cast integrally, and combined with the relatively small pipe diameter of the truss members, it avoids the dense and complex node welding and cumbersome closed-space weld inspection of traditional pure steel large-diameter pipe structures, reducing the difficulty of manufacturing and on-site hoisting construction. The formed structure has good overall integrity, possessing both the high ductility and toughness of the outer thin-walled steel pipe and the high rigidity and strong pressure bearing capacity of the inner ultra-high performance concrete 2, comprehensively improving construction efficiency and project quality.

[0058] Furthermore, the steel pipe-ultra-high performance concrete composite structure effectively changes the stress mode of the transition section from steel being mainly under tension to core concrete being mainly under compression. This significantly reduces the amount of expensive extra-thick steel plates used, reduces the residual stress and fatigue cracking risk caused by the dense welding of complex stiffening ribs, provides a guarantee for the long-term safe operation of the structure and construction operations, significantly reduces the maintenance cost throughout the entire life cycle, and comprehensively improves the reliability of large-capacity offshore wind power foundations in deep-sea areas.

[0059] Based on the description and accompanying drawings of this invention, those skilled in the art can easily manufacture or use the offshore wind turbine jacket foundation transition section structure and its construction method as described in this invention, and can achieve the positive effects described in this invention.

[0060] Unless otherwise specified, in this invention, terms such as "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe orientation or positional relationships in this invention are for illustrative purposes only and should not be construed as limiting this invention. For those skilled in the art, the specific meaning of the above terms can be understood in conjunction with the accompanying drawings and according to the specific circumstances.

[0061] Unless otherwise explicitly specified and limited, the terms "set up," "connected," and "linked" in this invention should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0062] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A transition section structure for a jacket foundation of an offshore wind turbine, characterized in that: It includes a main tube, a truss-type diagonal bracing structure, a deck, and a support structure. The bottom of the main tube is connected to the deck, and several truss-type diagonal bracing structures are connected between the outer wall of the main tube and the deck. The bottom of the deck is connected to the support structure that is connected to the lower foundation. The main tube, the truss-type diagonal bracing structure, and the support structure are all set as steel pipe-ultra-high performance concrete composite structures.

2. The transition section structure of the offshore wind turbine jacket foundation according to claim 1, characterized in that: The truss-type diagonal bracing structure includes an upper diagonal bracing structure, a lower diagonal bracing structure, and multiple diagonal bracing web members connecting the upper diagonal bracing structure and the lower diagonal bracing structure. One end of the upper diagonal bracing structure and the lower diagonal bracing structure are connected to the deck, and the other end is connected to different height positions on the outer side wall of the main cylinder to form a triangular truss structure.

3. The transition section structure of the offshore wind turbine jacket foundation according to claim 2, characterized in that: The multiple diagonal bracing members are arranged in any one of the following configurations: cross-shaped, K-shaped, N-shaped, or W-shaped.

4. The transition section structure of the offshore wind turbine jacket foundation according to claim 1, characterized in that: At least three sets of the truss-type diagonal bracing structure are provided on the outer wall of the main tube, and the three sets of truss-type diagonal bracing structures are spaced apart on the outer wall of the main tube.

5. The transition section structure of the offshore wind turbine jacket foundation according to claim 4, characterized in that: At least three sets of the support structure are provided at the bottom of the deck, and each set of the support structure is respectively located below the connection position between the corresponding truss-type diagonal brace structure and the deck.

6. The transition section structure of the offshore wind turbine jacket foundation according to claim 1, characterized in that: The main cylinder includes an inner steel pipe and an outer steel pipe, with an annular cavity formed between the inner and outer steel pipes. The inner and outer steel pipes serve as permanent inner and outer formwork for ultra-high performance concrete pouring, respectively, and the annular cavity is filled with ultra-high performance concrete.

7. The transition section structure of the offshore wind turbine jacket foundation according to claim 2, characterized in that: The upper chord structure of the diagonal brace includes an upper chord steel pipe and ultra-high performance concrete filled inside the upper chord steel pipe; the lower chord structure of the diagonal brace includes a lower chord steel pipe and ultra-high performance concrete filled inside the lower chord steel pipe; both the upper chord steel pipe and the lower chord steel pipe serve as permanent formwork for the pouring of ultra-high performance concrete.

8. The transition section structure of the offshore wind turbine jacket foundation according to claim 1, characterized in that: The support structure includes a support steel pipe and ultra-high performance concrete filled inside the support steel pipe, with the support steel pipe serving as a permanent formwork for the ultra-high performance concrete pouring.

9. A construction method for a transition section structure of an offshore wind turbine jacket foundation, characterized in that, The construction of the transition section structure for the offshore wind turbine jacket foundation as described in any of claims 1-8 includes the following steps: S1. Perform steel structure assembly and welding, connecting the main tube, truss-type diagonal bracing structure and supporting structure with the deck to form an overall steel frame system; S2. Shear connection components are installed on the inner wall of each steel pipe component, and prestressed ducts, grouting holes and vent holes are reserved to form a grouting channel system; S3. The inner steel pipe, outer steel pipe, upper chord steel pipe of the diagonal brace, lower chord steel pipe of the diagonal brace, and supporting steel pipe are used as permanent formwork for ultra-high performance concrete pouring, and temporary support structures are set up. S4. Adopting a bottom-up jacking and grouting process, ultra-high performance concrete is continuously poured into the interior of each steel pipe component through the grouting hole, and the internal gas is discharged through the vent hole until the grouting is completed. S5. During the setting process of ultra-high performance concrete, grouting and pressurization are carried out. After the strength reaches the design requirements, the temporary support is removed and prestressing tensioning and anchoring are carried out to finally form a combined structure in which steel pipe and ultra-high performance concrete work together to bear the load.

10. The construction method for the transition section structure of the offshore wind turbine jacket foundation according to claim 9, characterized in that: In step S5, after the ultra-high performance concrete completes its first jacking and pouring, during the initial setting, final setting, and shrinkage-sensitive stages, a secondary grouting and pressure stabilization process is implemented through pre-reserved grouting holes. This process compensates for and fills the small voids that may be formed in the pipe due to settlement, gas leakage, or early shrinkage, ensuring that the ultra-high performance concrete always maintains a full fit with the inner wall of the steel pipe. If necessary, a staged, segmented, and pressure-maintaining grouting method can be adopted to further improve the fullness of filling narrow interfaces and complex joints. Under the constraint of the steel pipe on the core concrete, a favorable interface compaction state and micro-expansion compressive stress are established, thereby effectively suppressing interface voids, shrinkage joints, and bond degradation.

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