Construction method of long-span low-pylon cable-stayed bridge

Abstract

This invention discloses a construction method for a long-span, low-tower cable-stayed bridge. The method involves installing a variable-stiffness temporary consolidation system, including prestressed steel strands and lockable hydraulic damping cylinders, atop the main pier. Controlled-deflection guide plates are installed on the construction formwork. During typhoon warnings, the guide plates are folded to reduce wind resistance. A servo proportional valve is activated to put the lockable hydraulic damping cylinders into a viscous damping state to dissipate vibration energy. The permanent stay cables are asymmetrically tensioned to actively apply compensating bending moments, achieving coordinated wind resistance. During the semi-floating system transition phase, the prestressed steel strands are cut, and the lockable hydraulic damping cylinders are slowly depressurized, allowing the main beam support reaction force to be smoothly transferred to the movable bearings. Before the mid-span closure, the elevation is precisely adjusted using the slight difference in stroke between the lockable hydraulic damping cylinders on both sides of the main pier. This invention effectively counteracts unbalanced bending moments under extreme wind loads, prevents stress damage to the bottom of the main pier, eliminates stress impacts and abrupt changes in alignment during system transition, and achieves precise closure.

Description

Technical Field

[0001] This invention relates to the field of bridge construction engineering technology, specifically a construction method for a long-span, low-tower cable-stayed bridge. Background Technology

[0002] Long-span, low-tower cable-stayed bridges, as a type of bridge between continuous rigid frame bridges and conventional cable-stayed bridges, combine the technical characteristics of high structural stiffness and strong spanning capacity, and have been widely used in transportation hub projects spanning rivers, seas, and complex terrains. The superstructure typically consists of main beams, bridge towers, and cable stays, and the stress system changes dynamically with the construction progress.

[0003] In the existing construction procedures in the industry, long-span, low-tower cable-stayed bridges are generally constructed using the cantilever casting method. To balance the unbalanced bending moments caused by self-weight and eccentric loading of construction equipment on both sides during the cantilever construction phase, and to maintain the bridge's spatial stability, the construction unit typically sets up a temporary consolidation structure consisting of concrete pads and prestressed steel bars between the top of the main pier and the bottom surface of the No. 0 block of the main beam. This temporarily anchors the pier body and the main beam to form a continuous rigid frame system. Before the closure stage begins after the cantilever beam segment is completed, the aforementioned rigid temporary consolidation structure is removed by mechanical chiseling or blasting, releasing the constraints and completing the transition to a semi-floating, fully-fledged bridge load-bearing system.

[0004] Existing cantilever construction methods face significant structural stress risks when applied in typhoon-prone coastal areas. Traditional temporary fixed structures employ absolute rigid constraints. When the bridge is in its maximum cantilever state and encounters extreme winds, the strong winds act on the end bluffing formwork and the windward side of the main beam, generating enormous wind-induced vibration energy and unbalanced bending moments. Due to the lack of energy dissipation and flexible yielding mechanisms in rigid fixed structures, these wind-induced unbalanced bending moments are directly and rigidly transmitted to the bottom of the main pier and the pier-beam junction, leading to stress concentration in these areas. When the instantaneously superimposed internal forces exceed the design bearing capacity of the concrete material, cracking and failure can occur at the root of the main pier, causing the cantilever structure to face overturning and instability under extreme wind loads. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a construction method for long-span, low-tower cable-stayed bridges, which solves the problems of high wind resistance risk during cantilever construction of long-span, low-tower cable-stayed bridges in typhoon-prone coastal areas, as well as the problems of elevation loss and stress mutation when using a semi-floating system to remove temporary consolidation for mid-span closure.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a construction method for a long-span, low-tower cable-stayed bridge, comprising the following process flow: Substructure construction and installation of supports and variable stiffness temporary consolidation components: permanent supports are installed on the pier top and the movable supports are temporarily longitudinally locked; a variable stiffness temporary consolidation system is installed between the pier top and the bottom surface of the main beam. The variable stiffness temporary consolidation system includes interlocking prestressed steel strands and symmetrically arranged lockable hydraulic damping cylinders connected to servo proportional valves. Construction of cast-in-place beam segment 0 on pier top and bridge tower: Pressure holding and locking can lock the hydraulic damping cylinder, so that it forms a rigid connection with the prestressed steel strands; cast-in-place beam segment 0 and bridge tower are tensioned together with prestressed steel strands; Pneumatic adaptive rhomboid hanging basket assembly and conventional cantilever casting: A pneumatic adaptive rhomboid hanging basket with guide plates hinged to the edge is installed on the beam section at the top of the pier. The guide plates are connected to independent driving hydraulic cylinders. Under normal working conditions, the guide plates are kept in the extended position, the main beam is symmetrically cantilevered and the permanent cable stays of the main beam are installed. Collaborative wind-resistant construction under typhoon warning conditions: When a typhoon warning is received, the independent drive hydraulic cylinder is controlled to change the deflection angle of the guide plate; the servo proportional valve is opened to enable the lockable hydraulic damping cylinder to enter the viscous damping working state; and the permanent stay cables of the main beam are controlled to perform asymmetric pressure adjustment and tensioning to actively apply compensating bending moment. Construction of cast-in-place side span and priority closure of side span: Install temporary rigid connection structure, release longitudinal locking of side pier support, and cast-in-place side span closure segment; System conversion and elevation fine-tuning before mid-span closure: Cut the prestressed steel strands and control the lockable hydraulic damping cylinders to slowly depressurize and achieve stress redistribution to the semi-floating system; Based on the mapping relationship between stroke and elevation difference, use the slight stroke difference of the lockable hydraulic damping cylinders on both sides of the main pier to perform elevation fine-tuning. Mid-span precise closure and bridge cable force adjustment: Cast-in-place mid-span closure section; after the main beam is closed, the cable force of the entire bridge's stay cables is tested and adjusted to the design value.

[0007] In practice, prestressed steel strands provide vertical tensile constraints, while lockable hydraulic damping cylinders provide vertical compressive support. These two components are distributed in parallel on both sides of the central axis at the pier top, forming a bending moment. Embedded steel plates are installed on the bottom slab of beam segment 0. The prestressed steel strands are tensioned, and the tensile force compresses the embedded steel plates onto the pressure-bearing flange of the lockable hydraulic damping cylinder, which is in a pressure-holding and locked state.

[0008] The guide vanes include a bottom guide vane hinged to the front edge of the bottom mold and a side guide vane hinged to the outer edge of the outer mold. The independently driven hydraulic cylinders include a bottom independently driven hydraulic cylinder and a side independently driven hydraulic cylinder, both electrically connected to the central control system. The bottom independently driven hydraulic cylinder is connected to the back of the bottom guide vane, and the side independently driven hydraulic cylinder is connected to the back of the side guide vane.

[0009] During collaborative wind-resistant construction, retraction commands are sent to the bottom and side independently driven hydraulic cylinders, pulling the bottom and side guide plates to fold inward at a preset guide angle towards the inside of the aerodynamic adaptive diamond-shaped hanging basket. This transforms the windward section from a blunt, wind-resistant state to a streamlined guide state. This aerodynamic shape transformation reduces the dynamic drag coefficient and decreases the excitation energy input by wind loads to the bridge cantilever structure.

[0010] By unanchoring and relaxing the prestressed steel strands, an opening electrical signal is sent to the servo proportional valve, which can lock the hydraulic damping cylinder to generate energy-dissipating damping bending moment as it moves relative to the bottom plate of the main beam.

[0011] The pressure fluctuation signal of the lockable hydraulic damping cylinder is extracted to calculate the wind-induced unbalanced bending moment. Subsequently, the tensioning jacks are controlled to increase the tension of the permanent stay cables on the windward side of the main beam and decrease the tension of the permanent stay cables on the leeward side of the main beam.

[0012] The value of the compensating bending moment is obtained by subtracting the sum of the products of the increased tension in the windward stay cables and the corresponding effective bending arm of the stay cables from the sum of the products of the decreased tension in the leeward stay cables and the corresponding effective bending arm of the stay cables. Relying on the physical synergistic feedback of the above three functions, the dynamic equilibrium of the bridge cantilever structure is maintained under the combined action of wind-induced unbalanced bending moment, active compensating bending moment, and energy-dissipating damping bending moment.

[0013] The temporary rigid connection structures installed at both ends of the side span closure include a connecting stiffening frame and temporary prestressed steel strands. The welded connecting stiffening frame bears relative compressive stress, while the tensioned temporary prestressed steel strands bear relative contraction tensile stress, restricting relative displacement between the cantilever end of the main beam and the straight section of the side span. The longitudinal locking of the side pier supports is released to allow the straight section of the side span to undergo longitudinal temperature deformation synchronously with the cantilever end of the main beam.

[0014] During the semi-floating system conversion operation, the prestressed steel strands are cut off, and the main beam load is transferred to the lockable hydraulic damping cylinder, which is in a pressure-holding and locked state. A pressure relief command is sent to the servo proportional valve to control the slow discharge of hydraulic oil in the lockable hydraulic damping cylinder, so that the main beam support reaction force is continuously transferred from the lockable hydraulic damping cylinder to the movable support on the pier top until the lockable hydraulic damping cylinder is released from the pressure-bearing state.

[0015] During elevation fine-tuning, oil is injected and pressurized into the lockable hydraulic damping cylinder on one side of the main pier, causing the piston rod on one side to extend and lift the bottom surface of the main beam on the corresponding side. Simultaneously, the pressure in the lockable hydraulic damping cylinder on the other side of the main pier is released, causing the piston rod on the other side to shorten to provide displacement space for the main beam to descend naturally. The slight difference in stroke created by the lifting on one side and the yielding on the other side forces the main beam to rotate slightly around the movable support for elevation correction.

[0016] After the elevation of the mid-span closure section was precisely adjusted to meet the design tolerance requirements, a lockout command was sent to the servo proportional valve to maintain the pressure and lock the piston rod stroke of the lockable hydraulic damping cylinder to preserve its elevation attitude. Subsequently, the temporary rigid connection structure of the mid-span was installed and the mid-span closure section was poured.

[0017] After the mid-span closure and removal of the lockable hydraulic damping cylinders, the actual tension of the stay cables throughout the bridge was measured and compared with the target values ​​for the completed bridge design established in the finite element analysis software. Cable tension errors accumulated during the earlier construction phase were corrected by additional tensioning or anchorage release.

[0018] This invention provides a construction method for a long-span, low-tower cable-stayed bridge. It has the following beneficial effects: 1. This invention, by configuring guide plates on the construction hanging basket and arranging a variable stiffness temporary consolidation system on the pier top, allows the guide plates to be folded over during typhoon warnings to change their aerodynamic shape and reduce wind resistance. At the same time, the locking of the lockable hydraulic damping cylinder is released so that it outputs viscous damping force to dissipate vibration energy. Combined with the asymmetric tensioning of the permanent stay cables of the main beam to introduce compensating bending moment, this invention achieves dynamic cancellation of unbalanced bending moment of the cantilever structure under extreme wind loads and provides wind-resistant safety assurance by preventing structural damage caused by rigid constraints at the bottom of the main pier.

[0019] 2. This invention achieves a smooth load transition for stress redistribution from a continuous rigid frame to a semi-floating system by cutting off the temporary prestressed steel strands during the transition to a semi-floating system. It utilizes a lockable hydraulic damping cylinder in a pressure-holding state to control the load and unbalanced bending moment of the main beam, and controls a servo proportional valve to slowly discharge hydraulic oil. This guides the main beam support reaction force to be continuously and smoothly transferred from the lockable hydraulic damping cylinder to the movable support on the pier top until the lockable hydraulic damping cylinder is released from pressure. This achieves a smooth transition control effect for stress redistribution from a continuous rigid frame to a semi-floating system and avoids the sudden change in structural stress caused by directly removing the temporary consolidation.

[0020] 3. This invention reuses lockable hydraulic damping cylinders on both sides of the main pier before the mid-span closure. Based on the mapping relationship between stroke and elevation difference, it controls the locking hydraulic damping cylinder on one side to pressurize and extend to lift the main beam upward, while simultaneously controlling the locking hydraulic damping cylinder on the other side to depressurize and shorten to provide clearance for the main beam to descend. The slight stroke difference generated by the locking hydraulic damping cylinders on both sides forces the main beam to rotate slightly around the movable support, thus achieving the effect of actively correcting the elevation error of the cantilever end before pouring the closure section and achieving precise closure control that meets the smoothness requirements. Attached Figure Description

[0021] Figure 1 This is a flowchart illustrating the construction process of the present invention. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Please see the appendix Figure 1 This invention provides a construction method for a long-span, low-tower cable-stayed bridge.

[0024] When constructing long-span, low-tower cable-stayed bridges in typhoon-prone coastal areas, the risk of overturning due to wind loads at the cantilever ends and the challenge of elevation loss during system conversion are frequently encountered. The method provided in this embodiment is applicable to semi-floating low-tower cable-stayed bridges where the main span is constructed using the cantilever casting method and the completed bridge system is a hinged pier-beam and fixed tower-beam system. The method provided in this embodiment includes the following process flow: S1, Substructure Construction and Installation of Supports and Variable Stiffness Temporary Consolidation Components. A steel cofferdam platform is erected for the construction of bored piles, pile caps, and pier bodies. Permanent supports are installed on the pier top, with movable supports temporarily locked longitudinally. Simultaneously, a variable stiffness temporary consolidation system is installed between the pier top and the bottom surface of the main beam. This system specifically includes prestressed steel strands and lockable hydraulic damping cylinders. The prestressed steel strands are interlaced and anchored between the pier body and block 0. The lockable hydraulic damping cylinders are symmetrically arranged around the pier top support surface and are connected to servo proportional valves.

[0025] S2, Cast-in-place construction of beam segment A0 at the pier top and bridge tower construction. After the main pier is installed with brackets, prestressing is performed, and beam segment A0 at the pier top is cast on the brackets. During the casting stage of beam segment A0, the servo proportional valve of the lockable hydraulic damping cylinder is closed and pressure-held and locked. At this time, the hydraulic fluid exhibits near-incompressible characteristics, and the lockable hydraulic damping cylinder provides high axial compressive stiffness, forming a rigid connection with the prestressed steel strands, thus consolidating the pier body and beam together. When the concrete strength and elastic modulus of beam segment A0 reach 100% of the design value, and the concrete age is not less than 7 days, longitudinal and transverse prestressing is tensioned. Subsequently, the tower columns above the bridge deck are constructed, and the middle pier brackets are removed to provide a working surface for subsequent hanging basket construction.

[0026] S3, Pneumatic Adaptive Diamond Formwork Assembly and Conventional Cantilever Casting. The pneumatic adaptive diamond formwork is installed and pre-stressed on the pier top beam segment. The specific structure of the aforementioned pneumatic adaptive diamond formwork includes the main truss, bottom formwork, and outer formwork. Guide plates are hinged to the front edge of the bottom formwork and the edges of the outer formwork, and the guide plates are connected to independently driven hydraulic cylinders. Under conditions without typhoon warning, the independently driven hydraulic cylinders keep the guide plates in an unfolded state flush with the formwork, using the guide plates as load-bearing formwork. The cantilever beam segments are cast symmetrically. After the concrete strength reaches the design value, the prestressed steel strands are tensioned, the stay cables are installed symmetrically, and the pneumatic adaptive diamond formwork is moved to the next segment. The above process is repeated until the construction of each cantilever segment is completed.

[0027] S4, Collaborative Wind-Resistant Construction under Typhoon Warning Conditions. When a typhoon warning is received during cantilever pouring and the bridge structure is in its maximum double-cantilever or single-cantilever state, concrete pouring operations are stopped. The central control system, based on feedback signals from sensors deployed on the bridge structure, uniformly issues hydraulic control commands to execute collaborative wind-resistant operations, specifically including the following sub-steps: The first step is to reduce drag by changing the aerodynamic shape. The independent drive hydraulic cylinders on the pneumatically adaptive diamond-shaped hanging basket are controlled by hydraulic lines to fold the guide plates on the front and side edges of the windward hanging basket inward at a preset guide angle. By changing the windward area and the drag coefficient, the active wind load acting on the cantilever end is reduced.

[0028] The second step is flexible yielding to dissipate energy. The temporary anchorage prestressed steel strands at the pier top are moderately relaxed, the rigid lock of the lockable hydraulic damping cylinder is released, and the servo proportional valve is opened. The lockable hydraulic damping cylinder is controlled to enter a viscous damping working state, allowing the bridge structure to undergo slight rotation under wind load. The equivalent damping bending moment generated by the reciprocating motion of the lockable hydraulic damping cylinder dissipates the wind-induced vibration energy.

[0029] The third step is asymmetric tensioning compensation for the stay cables. Using the already installed permanent stay cables of the main beam, asymmetric tensioning is performed by controlling hydraulic tension jacks. The tension force of the stay cables is increased on the windward side and decreased on the leeward side, actively applying compensating bending moments to the main beam to counteract wind-induced unbalanced bending moments.

[0030] Through the coordinated adjustment of the above three steps, the bending moment at the bottom of the main pier is kept within the allowable range. After the weather warning is lifted, the guide plate resumes its load-bearing state, the stay cables are adjusted to the design cable force corresponding to the current construction stage, the temporary prestressed steel strands are re-tensioned, and the lockable hydraulic damping cylinder is locked.

[0031] S5, Construction of the cast-in-place side span and priority closure of the side span. Cast-in-place supports are installed on the side piers and pre-stressed as appropriate. Straight section A23 is poured on the side span supports. Under non-drastically changing nighttime low temperatures, temporary rigid connection structures for the side span closure section are installed, the longitudinal locking of the side pier supports is released, and the side span closure section is cast in place using suspended supports. After the concrete strength of the side span closure section reaches the design value, the longitudinal steel strands of the side span are tensioned, and the temporary side span supports are removed. To ensure stability during the construction phase, the side span is closed first, the pier-beam anchorages are released, and the structure changes from a double cantilever state to a single cantilever state.

[0032] S6, System Conversion and Elevation Fine-tuning Before Mid-Span Closure. Before pouring the mid-span closure section, a semi-floating system conversion operation was performed. The temporary anchored prestressed steel strands at the pier top were gradually cut off, transferring the main beam's gravity and unbalanced bending moment to the lockable hydraulic damping cylinders at the pier top. The lockable hydraulic damping cylinders were slowly depressurized via servo proportional valves, allowing the support reaction force to be smoothly transferred to the permanent movable supports, achieving stress redistribution to the semi-floating continuous beam system. Subsequently, the elevation difference at the closure section was assessed. Based on a pre-established mapping relationship between stroke and elevation difference, the slight stroke difference between the lockable hydraulic damping cylinders on both sides of the main pier was used to force the main beam to rotate for elevation fine-tuning.

[0033] S7, Mid-span Precision Closure and Cable Stress Adjustment. After the elevation fine-tuning meets the requirements, temporary rigid connection structures for the closure segment are installed under non-drastic nighttime low-temperature conditions. The mid-span closure segment is cast in place using suspension supports. Once the concrete strength reaches the design value, the mid-span longitudinal cables are tensioned, and the temporary structures are removed. After the main girder is closed, cable stress tests are conducted on all bridge stay cables, and the cable stresses of all bridge stay cables are adjusted to the design values.

[0034] The construction of the substructure and the installation of supports and variable stiffness temporary fixed components specifically include the following steps: S11, Construction of the substructure is carried out. A steel cofferdam platform is erected in the water area at the bridge site. Drilled piles are then constructed downwards from the steel cofferdam platform, and a bearing cap is formed on top of the drilled piles. Concrete for the pier body is then poured upwards from the bearing cap.

[0035] S12, Install permanent bearings. Position and install permanent bearings on the pier top support surface according to the bridge's design axis. Permanent bearings include fixed bearings and movable bearings. During the construction phase of the substructure and subsequent cantilever casting, use temporary locking devices to longitudinally lock the movable bearings, restricting longitudinal relative displacement of the main girder relative to the pier. Temporary locking devices employ temporary locking steel plates or pins.

[0036] S13, Install a variable stiffness temporary consolidation assembly. A variable stiffness temporary consolidation system is installed between the pier top and the predetermined position on the bottom surface of the main beam block 0 to be poured. The system consists of prestressed steel strands connected in parallel with lockable hydraulic damping cylinders. The lower ends of the prestressed steel strands are pre-embedded and anchored within the pier body concrete, while the upper ends extend vertically upwards. The prestressed steel strands are reserved with a length extending through the bottom plate of the main beam block 0 for tensioning and anchoring after the main beam block 0 is poured. The prestressed steel strands provide vertical tensile restraint, while the lockable hydraulic damping cylinders provide vertical compressive support. The prestressed steel strands and lockable hydraulic damping cylinders are distributed in parallel on both sides of the central axis of the pier top, forming a tensile and compressive bending moment to resist the unbalanced bending moment of the main beam caused by the asymmetrical loads at the cantilever ends during the cantilever construction stage.

[0037] S14 features a hydraulically controlled mechanical structure. Lockable hydraulic damping cylinders are symmetrically arranged around the perimeter of the pier top support surface. The cylinder base is anchored to the pier top surface using an array of high-strength bolts or pre-embedded steel plates. The piston rod of the lockable hydraulic damping cylinder faces upwards, and a pressure-bearing flange is fitted at the end of the piston rod. The pressure-bearing flange is used to ensure a tight fit with the subsequently poured No. 0 block bottom slab concrete. The internal structure of the lockable hydraulic damping cylinder is divided into a rodless chamber and a rod chamber, connected by an external hydraulic circulation pipeline.

[0038] S15, arranging the hydraulic regulation and servo feedback loop. A servo proportional valve and a high-pressure accumulator are connected in series on the external hydraulic circulation pipeline. All lockable hydraulic damping cylinders arranged around the perimeter of the pier top are connected in parallel to the central hydraulic pump station and main control cabinet via high-pressure hydraulic hoses. The servo proportional valve receives electrical signal commands from the main control cabinet, adjusts the valve core opening inside the servo proportional valve, and controls the on / off state of hydraulic oil between the rodless and rod chambers, as well as the overflow cross-sectional area.

[0039] When the servo proportional valve is fully locked, the piston rod of the lockable hydraulic damping cylinder is rigidly supported by the sealed hydraulic fluid inside the cylinder. In this state, the lockable hydraulic damping cylinder functions as a purely rigid support pad. The equivalent axial compressive stiffness of the lockable hydraulic damping cylinder is directly proportional to the bulk modulus of elasticity of the hydraulic oil and the effective pressure-bearing cross-sectional area of ​​the piston surface, and inversely proportional to the equivalent length of the pressurized sealed oil column. Based on the set equivalent axial compressive stiffness, the lockable hydraulic damping cylinder, in conjunction with the prestressed steel strands, forms a continuous rigid frame system.

[0040] When the servo proportional valve is open, the lockable hydraulic damping cylinder functions as a viscous fluid energy-dissipating damper. The piston rod, under pressure, moves, forcing hydraulic oil through the damping orifice of the servo proportional valve, generating an axial damping force related to the relative velocity of the piston rod. The magnitude of this axial damping force is determined by the nonlinear product of the hydraulic damping coefficient and the axial relative velocity of the piston rod. The hydraulic damping coefficient is dynamically adjusted by the physical cross-sectional area of ​​the servo proportional valve's real-time opening. The lockable hydraulic damping cylinder dissipates the excitation energy from external wind loads by outputting this axial damping force.

[0041] The specific steps involved in the cast-in-place construction of beam segment A0 at the pier top and the construction of the bridge tower are as follows: S21, Main pier bracket installation and preloading. A cantilever bracket for supporting beam segment A0 of the main girder is installed on the outer side of the top of the main pier. After the cantilever bracket is installed, a preload is applied to it. The purpose of applying the preload is to eliminate the inelastic deformation of the cantilever bracket structure and to measure the elastic deformation of the cantilever bracket structure, providing data reference for setting the bottom formwork elevation of beam segment A0.

[0042] S22, State locking and spatial docking of the variable stiffness temporary consolidation assembly. During the laying of the bottom formwork and binding of the reinforcing steel cage for beam segment A0, the temporary anchoring prestressed steel strands pre-embedded inside the pier body pass through the reserved ducts in beam segment A0, and anchorages for anchoring are arranged on the top surface of beam segment A0. Simultaneously, a pre-embedded steel plate is installed at the position corresponding to the top of the lockable hydraulic damping cylinder on the bottom plate of beam segment A0.

[0043] The pressure-bearing flange at the top of the lockable hydraulic damping cylinder located on the pier top is fitted with the pre-embedded steel plate at the bottom of beam segment A0. The pre-embedded steel plate expands the stress-bearing area to prevent local concrete crushing.

[0044] Before pouring concrete for beam segment A0, a lockout electrical signal command is sent to the servo proportional valve via the central control system. This completely closes the servo proportional valve connected to the lockable hydraulic damping cylinder and locks it under pressure. In the pressure-locked state, the hydraulic fluid inside the lockable hydraulic damping cylinder is completely sealed off, allowing the cylinder to provide axial compressive support pads to the bottom surface of beam segment A0.

[0045] S23, the cast-in-place and temporary flexural resistance system for beam segment A0 is activated. Concrete for beam segment A0 is poured on the cantilever support. When the concrete strength of beam segment A0 reaches 100% of the design grade, the elastic modulus reaches 100% of the design value, and the concrete age is not less than 7 days, the longitudinal and transverse prestressed steel strands of the main beam are tensioned within the cross-section of beam segment A0. Simultaneously, the temporary anchored prestressed steel strands passing through the pre-reserved ducts in beam segment A0 are tensioned and pulled to the design control stress.

[0046] The vertical tensile force generated by the temporary anchored prestressed steel strands forces the pre-embedded steel plate on the bottom surface of beam segment A0 to be pressed against the pressure-bearing flange of the lockable hydraulic damping cylinder, which is in a pressure-holding and locked state. Through the coordinated action of the tensile constraint of the temporary anchored prestressed steel strands and the compressive support of the lockable hydraulic damping cylinder, a tension-compression bending moment system is established. This tension-compression bending moment system forms a continuous rigid frame with bending resistance between the main pier and beam segment A0, providing fixed support against asymmetrical construction loads for the main beam and subsequent tower construction, ensuring the stability of beam segment A0's spatial posture at the pier top.

[0047] S24, Bridge Tower Construction and Cantilever Support Removal. The tower structure above the bridge deck will be constructed on the top surface of beam segment A0. During the upward pouring of the tower structure, the unbalanced bending moments caused by the self-weight of the tower structure, the eccentric load of construction equipment, and normal wind loads will all be borne by the aforementioned tension and compression bending moment system. After the tower structure reaches the predetermined height, the cantilever support on the outside of the main pier will be removed, and the working space at the top of the pier and the bottom of beam segment A0 will be cleared to provide a working surface for the subsequent assembly and cantilever movement of the pneumatic adaptive rhomboid formwork.

[0048] The pneumatic adaptive rhomboid hanging basket assembly and conventional cantilever casting process specifically includes the following steps: S31, Pneumatic Adaptive Diamond-Shaped Hanging Basket Assembly and Flow Guiding Component Arrangement. Pneumatic adaptive diamond-shaped hanging baskets are symmetrically installed on both sides of beam segment A0 at the pier top. The pneumatic adaptive diamond-shaped hanging basket includes a main truss system, a suspension system, a traveling system, and a formwork system. The formwork system includes a bottom formwork and outer formwork. A bottom flow guide plate is installed at the front edge of the bottom formwork, and a side flow guide plate is installed at the outer edge of the outer formwork. The rear end of the bottom flow guide plate is connected to the front edge of the bottom formwork via a hinged bearing. The tail end of the cylinder of the bottom independently driven hydraulic cylinder is fixed to the supporting longitudinal rib below the bottom formwork via a pin, and the end of the piston rod of the bottom independently driven hydraulic cylinder is connected to the back of the bottom flow guide plate via a pin. The rear end of the side flow guide plate is connected to the front edge of the outer formwork via a hinged support. The cylinder of the side independently driven hydraulic cylinder is fixed to the supporting frame surrounding the outer formwork, and the end of the piston rod of the side independently driven hydraulic cylinder is connected to the back of the side flow guide plate. Both the bottom-driven hydraulic cylinder and the side-driven hydraulic cylinder are connected in parallel to the hydraulic pump station arranged on the bridge deck through hydraulic pipelines. At the same time, the servo valves on the bottom-driven hydraulic cylinder and the side-driven hydraulic cylinder are electrically connected to the central control system to receive control commands to adjust the deflection angle of the bottom guide plate and the side guide plate.

[0049] S32, Deflector Plate Load-Bearing Status Locked. In a normal construction environment where no typhoon warning signal is received, the central control system sends a command to operate the hydraulic control valves, causing the piston rods of the bottom and side independent drive hydraulic cylinders to extend and retract to the set reference stroke. At the set reference stroke, the surface of the bottom deflector plate is coplanar and flush with the upper surface of the bottom formwork, and the surface of the side deflector plate is coplanar and flush with the inner surface of the outer formwork. The hydraulic control valves are closed to maintain pressure in the bottom and side independent drive hydraulic cylinders. In the pressure-maintaining state, the bottom and side independent drive hydraulic cylinders provide support for the bottom and side deflector plates. At this time, the bottom and side deflector plates, as the load-bearing parts of the formwork system, bear the load of the newly poured concrete.

[0050] S33, Cast-in-place and prestressed tensioning of the cantilever beam segment. The main beam reinforcement cage is tied within the formwork system, prestressed corrugated pipes are positioned and installed, and stay cable sleeves are pre-embedded. The cantilever beam segment concrete is symmetrically poured within pneumatically adaptive diamond-shaped formwork on both sides. After the strength and modulus of elasticity of the cantilever beam segment concrete reach the design parameters, prestressed steel strands are threaded through the prestressed corrugated pipes. Jacks are used to symmetrically tension and anchor the longitudinal and transverse prestressed steel strands, establishing compressive stress within the main beam segment.

[0051] S34, Cable Installation and Formwork Relocation. Using bridge deck lifting equipment, the cable stays are threaded into the cable saddles of the bridge towers and the cable sleeves pre-embedded in the main beam. Tensioning jacks are used at the anchorage end of the main beam to perform symmetrical initial tensioning of the cable stays. The lifting force generated by the cable tensioning is used to balance the downward deflection moment caused by the gravity of the newly poured cantilever beam segment. After the cable tensioning is completed, the rear anchoring system of the pneumatic adaptive diamond-shaped formwork is released, and the traveling system is activated to slide the entire pneumatic adaptive diamond-shaped formwork forward to the construction position of the next cantilever segment. The pneumatic adaptive diamond-shaped formwork is re-anchored, and the formwork system elevation is adjusted. During the sliding and re-anchoring operations, the bottom and side guide plates remain under pressure, acting as the front extension platform of the formwork system. After the formwork system elevation adjustment is completed, the steps from S31 to S34 are repeated to advance the construction progress of the cantilever beam segment.

[0052] During the coordinated wind-resistant construction process of cable-basin-pier under typhoon warning, the following coordinated disaster prevention operations are carried out: S41, Meteorological Monitoring and System Mode Switching. When the bridge structure advances to its maximum double cantilever or maximum single cantilever state, if a typhoon warning signal is received, the concrete pouring at the cantilever ends and the forward movement of the pneumatic adaptive diamond-shaped hanging basket will cease. Based on real-time meteorological electrical signals fed back by wind speed and direction sensors deployed on the bridge structure, the central control system will uniformly issue control commands to switch the overall system from the conventional cantilever load-bearing mode to the collaborative wind-resistant operation mode.

[0053] S42, adaptive aerodynamic shape conversion for drag reduction of the hanging basket. In the cooperative wind-resistant operation mode, the central control system sends retraction commands to the bottom and side independent drive hydraulic cylinders on the pneumatically adaptive diamond-shaped hanging basket via hydraulic lines. The piston rod of the bottom independent drive hydraulic cylinder pulls the bottom guide plate around the hinged shaft seat and folds it inward at a preset guide angle into the pneumatically adaptive diamond-shaped hanging basket. Simultaneously, the piston rod of the independently driven hydraulic cylinder on the side pulls the side guide plate around the hinged support and folds it inward towards the pneumatically adaptive diamond-shaped hanging basket at a preset guide angle. By folding the bottom and side guide plates, the windward section of the aerodynamic adaptive diamond-shaped hanging basket changes from a blunt body wind-blocking state to a streamlined guiding state.

[0054] Active wind load acting on the aerodynamically adaptive diamond-shaped hanging basket at the cantilever end It satisfies the following physical formula: In the formula, The air density at the construction site. This represents the gust wind speed measured by the wind speed and direction sensor. Represents the preset guide angle Dynamic drag coefficient with a functional relationship. This represents the effective windward projected area formed by the aerodynamic adaptive rhomboid hanging basket and the main beam. This is achieved by actively adjusting the preset guide angle. This reduces the dynamic drag coefficient and decreases the excitation energy input by wind load to the bridge cantilever structure.

[0055] S43, Flexible Unlocking and Damping Energy Dissipation of the Temporary Consolidation System. The central control system controls the anchorage on the top surface of the main beam to unanchor, appropriately relaxing the temporary anchored prestressed steel strands connecting the pier body and the No. 0 block beam segment. Simultaneously, the central control system sends an opening electrical signal to the servo proportional valve connected to the lockable hydraulic damping cylinder, releasing the pressure-holding rigid locking state of the lockable hydraulic damping cylinder. At this time, the lockable hydraulic damping cylinder transforms from a rigid support pad into a viscous fluid damper. When extreme gusts force the cantilever structure to rotate, the piston rod of the lockable hydraulic damping cylinder synchronously generates axial relative movement with the bottom plate of the main beam, forcing the oil inside the lockable hydraulic damping cylinder to squeeze through the damping flow channel of the servo proportional valve. The lockable hydraulic damping cylinder outputs axial damping force to the main beam, using the reciprocating motion of the piston rod to generate energy-dissipating damping bending moment, dissipating the mechanical vibration energy caused by wind load, and preventing bending moments exceeding the limits of concrete material from being generated at the bottom of the main pier and the pier-beam joint due to rigid constraints.

[0056] S44, Active Asymmetric Tension Compensation for Stay Cables. The central control system extracts pressure fluctuation signals from the hydraulic sensors located in the rodless chamber of the lockable hydraulic damping cylinder in real time, and calculates the wind-induced unbalanced bending moment data borne by the cantilever structure. Subsequently, the central control system issues asymmetric pressure adjustment commands to the tension jacks configured at the anchorage end of the main beam, using the installed permanent stay cables of the main beam as active actuators. The tension jacks increase the tension force of the stay cables on the windward side and decrease the tension force of the stay cables on the leeward side. Compensating bending moments are actively applied to the main beam based on the asymmetric changes in the cable forces on both sides of the main pier. The value of the compensating bending moment is obtained by subtracting the sum of the products of the increased tension force of the windward stay cables and the effective bending arm of the corresponding stay cable at the neutral axis of the main pier.

[0057] Relying on the physical closed-loop synergy of aerodynamic shape transformation, damping energy dissipation, and active compensation, the bridge structure satisfies the following dynamic equilibrium constraint formula under wind load: In the formula, This represents the wind-induced unbalanced bending moment borne by the cantilever structure. This represents the active compensating bending moment exerted on the main beam by the asymmetric tensioning of the stay cables. This represents the energy-dissipating damping bending moment generated by the reciprocating energy dissipation of a lockable hydraulic damping cylinder. This represents the maximum allowable bending moment at the bottom of the main pier and the pier-beam combined section. Through dynamic closed-loop feedback of these variables by the central control system, the structural safety of the bridge is maintained during typhoon warning periods.

[0058] S45, Post-disaster System Recovery. After the weather warning was lifted and the measured wind speed was confirmed to have decreased to a safe threshold, the central control system extended the piston rods of the bottom and side independent drive hydraulic cylinders, pushing the bottom and side guide plates back to the level with the load-bearing formwork. The tensioning jacks readjusted the tension of each stay cable to match the standard tension value for the current construction stage. The jacks were reused to tension and anchor the temporary prestressed steel strands, while the servo proportional valve was closed and the lockable hydraulic damping cylinder was re-locked. The variable stiffness temporary consolidation assembly was restored to a continuous rigid frame state, the collaborative wind-resistant operation mode was deactivated, and the subsequent cantilever segment cast-in-place construction work continued.

[0059] The construction of the cast-in-place side span and the priority closure of the side span specifically include the following steps: S51, Erection of Cast-in-Place Scaffolding for Side Abutments and Construction of Straight Sections. Cast-in-place scaffolding is erected beside the side abutments. A preload is applied to the scaffolding, and the inelastic deformation is measured and eliminated. The elastic deformation of the scaffolding is recorded to determine the pre-camber of the side span bottom formwork. The reinforcing steel cage for the straight section of the side span is tied to the scaffolding, and the formwork is installed. The concrete for the straight section of the side span is then poured. After the concrete in the straight section of the side span reaches its design strength, the prestressed steel strands inside the straight section of the side span are tensioned.

[0060] S52, Temporary Rigid Locking at the Side Span Closure. Advance the cantilever casting of the main beam to the side span closure position. Clean the concrete connection surfaces on both sides of the side span closure. Select a time of night when temperatures are low and temperature changes are gradual to install temporary rigid connection structures at both ends of the side span closure. The temporary rigid connection structures include a connecting stiffening frame pre-embedded and welded to the cantilever end of the main beam and the straight section end of the side span, as well as temporary prestressed steel strands tensioned across the side span closure. The welded connecting stiffening frame bears the relative compressive stress caused by temperature rise on both sides of the closure, while the tensioned temporary prestressed steel strands bear the relative tensile stress caused by temperature drop on both sides of the closure. Relying on the combined compressive and tensile constraints formed by the connecting stiffening frame and the temporary prestressed steel strands, the spatial relative positions of the cantilever end of the main beam and the straight section of the side span are rigidly locked, restricting relative displacement between them before the concrete in the closure section hardens.

[0061] S53, Release of Side Abutment Supports and Pouring of Closure Segment. After the temporary rigid connection structure is locked, the temporary longitudinal locking device installed on the permanent support of the side pier is removed. Removing the temporary longitudinal locking device releases the longitudinal displacement freedom of the main beam at the side pier position, allowing the straight segment of the side span to undergo longitudinal temperature deformation synchronously with the cantilever end of the main beam, avoiding the side span closure segment concrete from being subjected to temperature tensile stress from the external environment during pouring and early hardening. Suspension supports are installed at the bottom and outside of the side span closure opening. The closure segment formwork is installed on the suspension supports and the steel reinforcement cage is tied, and the side span closure segment concrete is poured in one go.

[0062] S54, Longitudinal Prestressing Tensioning and Force System Transformation. After the concrete strength of the side span closure section reaches the design grade and the elastic modulus reaches the design value, the connecting stiffening frame in the temporary rigid connection structure is cut off, and the temporary prestressing steel strands are released. The longitudinal prestressing steel strands of the main beam are then threaded and tensioned within the cross-section of the main beam side span closure section. After the tensioning operation is completed, the suspension supports at the side span closure opening and the cast-in-place supports next to the side pier are removed. With the main beam completing the side span priority closure operation, the overall stress state of the bridge changes from a double cantilever state at the top of the main pier to a single cantilever stress state.

[0063] During the smooth transition and elevation fine-tuning process of the semi-floating system before the mid-span closure, the following transition and elevation matching operations are performed: S61, Prestress Relief and Gravity Transfer. The temporary anchored prestressed steel strands at the pier top are gradually cut off. After the tension constraint on the main beam is released, the self-weight load of the main beam and the unbalanced bending moment of the cantilever at both ends are transferred to the lockable hydraulic damping cylinder at the pier top. The central control system keeps the servo proportional valve in a pressure-holding and locked state, locking the hydraulic damping cylinder to transfer the main beam load and maintain the spatial attitude of the main beam, preventing sudden displacement of the main beam.

[0064] S62, Hydraulic Relief and Stress Redistribution. The central control system sends a pressure relief command to the servo proportional valve connected to the lockable hydraulic damping cylinder. Adjusting the valve opening controls the slow discharge of hydraulic oil from the lockable hydraulic damping cylinder. As the hydraulic oil is discharged, the piston rod of the lockable hydraulic damping cylinder slowly retracts, and the main beam descends smoothly. During the descent, the support reaction force of the main beam is continuously transferred from the lockable hydraulic damping cylinder to the permanent movable support at the pier top. When the main beam is fully supported by the permanent movable support and the lockable hydraulic damping cylinder is no longer under pressure, the stress redistribution from a continuous rigid frame system to a semi-floating system is completed. Adjusting the valve opening controls the speed of the support reaction force transfer, preventing stress shocks during system transition.

[0065] S63, Measurement and Error Assessment of the Closure Gap Elevation. After completing the system conversion, measure the actual elevation of the cantilever ends on both sides of the mid-span closure gap and calculate the actual elevation difference between the two sides of the mid-span closure gap. If the actual elevation difference exceeds the preset allowable error range, perform fine-tuning of the closure gap elevation.

[0066] S64, Fine-tuning of the closure elevation. The fine-tuning operation is performed using lockable hydraulic damping cylinders on both sides of the main pier. The central control system pressurizes the lockable hydraulic damping cylinder on one side of the main pier via a hydraulic pump station, causing the piston rod on that side to extend and lift the bottom surface of the corresponding main beam. Simultaneously, the system depressurizes the lockable hydraulic damping cylinder on the other side of the main pier, causing the piston rod on that side to shorten, providing displacement space for the corresponding main beam to descend naturally under gravity. Through the lifting on one side and the yielding on the other, a slight stroke difference is generated between the lockable hydraulic damping cylinders on both sides of the main pier. This slight stroke difference forces the main beam to rotate slightly around the permanent movable support, causing a change in the elevation of the cantilever end. The change in elevation at the cantilever end and the slight stroke difference satisfy the following formula: In the formula, This represents the elevation change at the cantilever end of the mid-span closure section. This represents the slight stroke difference established between the lockable hydraulic damping cylinders on both sides of the main pier. This represents the calculated length of the cantilever from the central axis of the main pier to the end of the mid-span closure section. This represents the longitudinal horizontal distance between the force centers of the lockable hydraulic damping cylinders on both sides of the main pier. By controlling a slight difference in stroke, the elevation of the cantilever end is actively corrected until the actual height difference meets the closure locking conditions.

[0067] The following steps are specifically included in the mid-span closure and cable tension adjustment process: S71, Temporary rigid locking at the mid-span closure joint. After the elevation of the mid-span closure joint is finely adjusted to meet the design tolerance requirements, a locking command is sent to the servo proportional valve corresponding to the lockable hydraulic damping cylinder to maintain the pressure and lock the piston rod stroke of the lockable hydraulic damping cylinders on both sides of the main pier, thus maintaining the adjusted elevation and posture of the main beam.

[0068] During periods of lower nighttime temperatures and gradual temperature changes, temporary rigid connection structures for the mid-span are installed at both ends of the mid-span closure section. These temporary rigid connection structures include a mid-span connecting stiffening frame pre-embedded and welded to the cantilever ends of the main beams on both sides, and temporary prestressed steel strands tensioned across the mid-span closure section. The welded mid-span connecting stiffening frame bears the relative compressive stress generated by temperature increases on both sides of the closure section, while the tensioned temporary prestressed steel strands bear the relative tensile stress generated by temperature decreases on both sides of the closure section. The combined compressive and tensile constraints formed by the mid-span connecting stiffening frame and the temporary prestressed steel strands restrict spatial relative displacement at the cantilever ends of the main beams on both sides before the concrete in the mid-span closure section hardens.

[0069] S72, Installation of mid-span suspension supports and pouring of the closure section. Mid-span suspension supports are installed at the bottom and outer side of the mid-span closure joint. The closure section formwork is installed on the mid-span suspension supports, and the reinforcing steel frame is tied. The mid-span closure section concrete is then continuously poured. Once the concrete strength and elastic modulus of the mid-span closure section reach the design grade, the longitudinal prestressed steel strands of the mid-span main beam are threaded through and tensioned within the cross-section of the mid-span closure section.

[0070] S73, Temporary constraint release and overall bridge system finalization. After tensioning, the mid-span connecting stiffening frame in the temporary rigid connection structure of the mid-span is cut off, and the temporary prestressed steel strands in the mid-span are released. Simultaneously, the mid-span suspension support at the mid-span closure point is dismantled. The servo proportional valve is opened to drain the hydraulic oil from the lockable hydraulic damping cylinders on both sides of the main pier, and the lockable hydraulic damping cylinders and related hydraulic pipelines and servo proportional valves are removed. The physical connection of the bridge superstructure is completed, forming a semi-floating continuous beam load-bearing system.

[0071] S74, Cable Stress Testing and Final State Adjustment. After the bridge is fully closed and forms a continuous beam system, the actual tension of all permanent stay cables is measured one by one using cable stress testing instruments. The cable stress measurement data is extracted and compared with the pre-established target values ​​for the completed bridge state using finite element analysis software to obtain the cable stress deviation value of each permanent stay cable. Based on the principle that the internal force distribution of the bridge structure and the geometric shape of the main beam conform to the design specifications, tension jacks located at the anchorage ends are used to perform secondary tensioning on the permanent stay cables with cable stress deviations. By supplementing tensioning with tension jacks or releasing tension by anchoring, the cable stress errors accumulated during the early construction process are corrected, so that the final stress state of each permanent stay cable of the entire bridge reaches the designed stress state of the completed bridge.

[0072] The steel cofferdam platform erection, foundation and pier casting, cantilever bracket and hanging basket assembly, concrete mixing and pouring, prestressed steel strand threading and tensioning anchoring process, wind speed and direction sensor data acquisition, and specific operating methods of cable force testing instruments and tensioning jacks involved in the embodiments of this invention can be performed by those skilled in the art based on bridge construction specifications, engineering mechanics knowledge and electromechanical equipment operation manuals. The aforementioned basic construction process and conventional measurement and control methods are well known technologies in the field and are not described in detail in this invention specification.

[0073] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A construction method for a long-span, low-tower cable-stayed bridge, characterized in that, Includes the following steps: S1, Substructure construction and installation of supports and variable stiffness temporary consolidation components: Install permanent supports on the pier top and temporarily lock the movable supports longitudinally; install a variable stiffness temporary consolidation system between the pier top and the bottom surface of the main beam, the variable stiffness temporary consolidation system including intercalated and anchored prestressed steel strands and symmetrically arranged lockable hydraulic damping cylinders connected to servo proportional valves. S2, Cast-in-place construction of beam segment A0 at pier top and bridge tower: Pressure holding locks the lockable hydraulic damping cylinder, and together with the prestressed steel strands form a rigid connection; Cast-in-place beam segment A0 and bridge tower are tensioned with prestress; S3, Pneumatic adaptive rhomboid hanging basket assembly and conventional cantilever casting: A pneumatic adaptive rhomboid hanging basket with guide plates hinged to the edge is installed on the beam section at the top of the pier. The guide plates are connected to independent driving hydraulic cylinders. Under normal working conditions, the guide plates are kept in the extended position, the main beam is symmetrically cantilevered and the permanent cable stays of the main beam are installed. S4, Collaborative wind-resistant construction under typhoon warning conditions: When a typhoon warning is received, the independent drive hydraulic cylinder is controlled to change the deflection angle of the guide plate; the servo proportional valve is opened to make the lockable hydraulic damping cylinder enter the viscous damping working state; the permanent stay cable of the main beam is controlled to perform asymmetric pressure adjustment and tensioning to actively apply compensating bending moment. S5, Construction of cast-in-place side span section and priority closure of side span: Install temporary rigid connection structure, release longitudinal locking of side pier support, and cast-in-place side span closure section; S6, System Conversion and Elevation Fine-tuning Before Mid-Span Closure: Cut off the prestressed steel strands and control the lockable hydraulic damping cylinders to slowly depressurize to achieve stress redistribution to the semi-floating system; based on the mapping relationship between stroke and elevation difference, use the slight stroke difference of the lockable hydraulic damping cylinders on both sides of the main pier to perform elevation fine-tuning. S7, Mid-span Precision Closure and Bridge Cable Stress Adjustment: Cast-in-place mid-span closure section; After the main beam closure, the cable stress of the entire bridge's stay cables will be tested and adjusted to the design value.

2. The construction method for a long-span, low-tower cable-stayed bridge according to claim 1, characterized in that: In step S1, the prestressed steel strands provide vertical tensile constraints, and the lockable hydraulic damping cylinders provide vertical compressive supports. The two are distributed in parallel on both sides of the central axis of the pier top to form a bending moment together. In step S2, an embedded steel plate is installed on the bottom plate of beam segment A0; the prestressed steel strands are tensioned, and the embedded steel plate is pressed against the pressure-bearing flange at the end of the lockable hydraulic damping cylinder, which is in a pressure-holding and locking state, by using the tension force.

3. The construction method for a long-span, low-tower cable-stayed bridge according to claim 1, characterized in that, In step S3: The guide plate includes a bottom guide plate hinged to the front edge of the bottom mold and a side guide plate hinged to the outer edge of the outer mold. The independent drive hydraulic cylinders include a bottom independent drive hydraulic cylinder and a side independent drive hydraulic cylinder, both of which are electrically connected to the central control system; the bottom independent drive hydraulic cylinder is connected to the back of the bottom guide plate, and the side independent drive hydraulic cylinder is connected to the back of the side guide plate.

4. The construction method for a long-span, low-tower cable-stayed bridge according to claim 3, characterized in that, In step S4, the steps for performing collaborative wind-resistant construction include: The central control system sends a retraction command to the bottom independent drive hydraulic cylinder and the side independent drive hydraulic cylinder, pulling the bottom guide plate and the side guide plate to fold into the pneumatic adaptive rhomboid hanging basket at a preset guide angle, so that the windward section changes from a blunt body wind-blocking state to a streamlined guide state; The anchor is removed and the prestressed steel strands are relaxed. An opening electrical signal is sent to the servo proportional valve, and the lockable hydraulic damping cylinder generates an energy-dissipating damping bending moment as it moves relative to the bottom plate of the main beam.

5. The construction method for a long-span, low-tower cable-stayed bridge according to claim 1, characterized in that, In step S4, the steps of performing collaborative wind-resistant construction also include: The pressure fluctuation signal of the lockable hydraulic damping cylinder is extracted to calculate the wind-induced unbalanced bending moment; then the tensioning jack is controlled to increase the tension of the permanent stay cable of the main beam on the windward side and decrease the tension of the permanent stay cable of the main beam on the leeward side. The value of the compensation bending moment is obtained by subtracting the sum of the products of the increased tension of the windward cable and the effective bending arm of the corresponding cable, and the sum of the products of the decreased tension of the leeward cable and the effective bending arm of the corresponding cable.

6. The construction method for a long-span, low-tower cable-stayed bridge according to claim 1, characterized in that, In step S5: The temporary rigid connection structure installed at both ends of the side span closure includes a connecting stiffening frame and temporary prestressed steel strands. The welding of the connecting stiffening frame bears relative compressive stress, and the tensioning of the temporary prestressed steel strands bears relative shrinkage tensile stress, thus limiting the relative displacement between the cantilever end of the main beam and the straight section of the side span; the longitudinal locking of the side pier support is released so that the straight section of the side span can undergo longitudinal temperature deformation synchronously with the cantilever end of the main beam.

7. The construction method for a long-span, low-tower cable-stayed bridge according to claim 1, characterized in that, In step S6, the steps for performing the semi-floating system conversion operation include: Cut off the prestressed steel strands and transfer the main beam load to the lockable hydraulic damping cylinder, which is in a pressure-holding and locked state; A pressure relief command is sent to the servo proportional valve to control the slow discharge of hydraulic oil in the lockable hydraulic damping cylinder, so that the main beam support reaction force is continuously transferred from the lockable hydraulic damping cylinder to the movable support on the pier top until the lockable hydraulic damping cylinder is released from the pressure state.

8. The construction method for a long-span, low-tower cable-stayed bridge according to claim 1, characterized in that, In step S6, the steps for performing elevation fine-tuning include: Oil is injected and pressurized into the lockable hydraulic damping cylinder on one side of the main pier, causing the piston rod on one side to extend and lift the bottom surface of the main beam on the corresponding side; at the same time, the pressure of the lockable hydraulic damping cylinder on the other side of the main pier is released, causing the piston rod on the other side to shorten to provide displacement space for the main beam to descend naturally; by lifting on one side and yielding on the other side, a slight stroke difference is generated, forcing the main beam to rotate slightly around the movable support for elevation correction.

9. The construction method for a long-span, low-tower cable-stayed bridge according to claim 8, characterized in that, In step S7: After the elevation of the mid-span closure section is finely adjusted to meet the design tolerance requirements, a locking command is sent to the servo proportional valve to maintain the pressure and lock the piston rod stroke of the lockable hydraulic damping cylinder to maintain the elevation attitude. Subsequently, the temporary rigid connection structure for the mid-span was installed and the mid-span closure section was poured.

10. The construction method for a long-span, low-tower cable-stayed bridge according to claim 1, characterized in that, In step S7: After the mid-span closure and the removal of the lockable hydraulic damping cylinder, the actual tension of the entire bridge's stay cables was measured and compared with the target value of the completed bridge state pre-established by the finite element analysis software. The cable force error accumulated during the early construction process can be corrected by supplementing tension or releasing the anchor.

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