Construction Technology and System of Cable-Stayed Bridges with Multiple Low Towers in High-Altitude and Windy Regions

Abstract

This invention discloses a construction technology and system for the cable-stayed bridge system of multi-tower cable-stayed bridges in high-altitude, cold, and windy areas, including the following steps: a low-temperature anchorage reliability assessment process for cables; calculation of temperature effects based on bridge site temperature data, acquisition of material performance parameters through mechanical tests of steel strands in low-temperature environments, and simulation of concrete stress and deformation in the anchorage zone using finite element software; an optimized closure and jacking construction process; establishment of a finite element model of the bridge, construction of a two-stage hierarchical weighted evaluation system using the empirical entropy weight method, and determination of the optimal closure sequence and closure jacking force; and an optimized setting process for cable-stayed viscous dampers; derivation of the motion equations of the cable-damper system, analysis of the vibration reduction effect under wind load and cable end displacement excitation through finite element simulation, and determination of the damper installation position and key parameters. This invention solves the technical problems of unreliable cable anchorage, complex stress control during closure construction, and poor vibration reduction effect of cables in existing multi-tower cable-stayed bridges in high-altitude, cold, and windy environments.

Description

Technical Field

[0001] This invention relates to the field of bridge construction technology, and more specifically, to a construction process and system for cable-stayed bridges with multiple low towers in high-altitude, cold, and windy areas. Background Technology

[0002] Currently, in infrastructure construction, long-span bridges serve as transportation nodes, and the status control during their construction process directly affects their safe operation and usability after completion. Low-tower cable-stayed bridges, with their advantages of good structural performance and convenient construction, are widely used in bridge construction, especially suitable for long-span scenarios. However, in high-altitude, cold, and windy regions, the construction of such bridges faces unique challenges. For example, typical multi-tower, low-tower cable-stayed bridges, when subjected to long periods of extreme minimum temperatures and complex wind environments, present severe challenges to the construction of the cable-stayed system.

[0003] While existing technologies have developed certain technical solutions for the construction of cable-stayed bridge cable systems, significant drawbacks remain in high-altitude, cold, and windy environments, as detailed below: Firstly, in terms of cable anchorage, existing research mainly focuses on the low-temperature performance changes of a single material, without fully considering the coupling effect of the overall structural stress and temperature effect. This leads to inaccurate stress distribution analysis in the anchorage zone, making it difficult to ensure the reliability of anchorage in low-temperature environments. Secondly, in terms of closure and jacking construction, traditional methods focus more on the peak response of a single component and do not establish an evaluation system for the comprehensive response of multiple components under the same index in multi-tower structures. The selection of closure sequence and jacking force lacks scientific basis, which can easily lead to problems such as excessive pier displacement and structural internal force imbalance. Thirdly, in terms of cable vibration reduction, existing damper designs focus more on overall bridge vibration control and do not take into account the synergistic effect of wind load and cable end displacement excitation in detail. The vibration reduction parameters are not optimized enough, and the service life of the cables is seriously affected by vibration.

[0004] The aforementioned problems make it difficult to guarantee the construction quality and structural safety of cable-stayed bridges with low towers in high-altitude, cold, and windy areas, which seriously restricts the promotion and application of this type of bridge in extreme environments. Summary of the Invention

[0005] To address these issues, this invention provides a construction process and system for cable-stayed bridges with multiple low towers in high-altitude, cold, and windy areas, in order to solve the technical problems in existing technologies, such as unreliable cable anchorage, complex stress control during closure construction, and poor vibration reduction effect of cables in multi-low tower cable-stayed bridges in high-altitude, cold, and windy environments.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A construction technology and system for cable-stayed bridges with multiple low towers in high-altitude, cold, and windy areas includes the following steps: S1: Low-temperature anchorage reliability assessment process for cables; Temperature effects were calculated based on bridge site temperature data. Material performance parameters were obtained through mechanical tests of steel strands under low-temperature conditions. The stress and deformation of concrete in the anchorage zone were simulated using finite element software. S2: Optimized construction process for closure and jacking; A finite element model of the bridge was established, and a two-stage hierarchical weighted evaluation system was constructed using the empirical entropy weight method to determine the optimal closure sequence and closure thrust. S3: Optimized setting process for viscous dampers in cable-stayed bridges; The equations of motion for the cable-damper system were derived, and the vibration reduction effect under wind load and cable end displacement excitation was analyzed through finite element simulation. The installation position and key parameters of the damper were then determined.

[0007] Based on the above technical solution, the present invention is further described as follows: As a further aspect of the present invention, S1 specifically includes: By combining extreme temperature data at the bridge site, key parameters of the structural temperature field were determined, a finite element model of the whole bridge planar truss system was established, various temperature conditions were simulated, cable force changes and structural deformation were calculated, and the degree of influence of each temperature factor was clarified. Select steel strands consistent with the actual engineering, set multiple temperature gradients and prepare specimens in groups, conduct tensile tests in equipment simulating low temperature environment, and test the core mechanical performance parameters. A refined model of the main beam segment and anchorage system containing key components was established to simulate various temperature load conditions, calculate the stress distribution and local deformation of the concrete in the anchorage zone, and add reinforcement structures in the anchorage zone.

[0008] As a further aspect of the present invention, S2 specifically includes: A full bridge model is constructed using professional finite element software. The corresponding simulation elements are selected according to the component type. Reasonable nodes, number of elements and construction stages are divided. Material property parameters of each component are set and boundary conditions are set according to the actual structural form. The control indicators for closure were determined, an original matrix was constructed for multiple closure schemes and evaluation indicators, the objective weights of the indicators were calculated by the entropy weight method, the comprehensive weights were determined by introducing empirical factors, and the overall values ​​of the sub-indicators and the overall evaluation results of the schemes were calculated in two stages. Multiple closure schemes were proposed to address the symmetrical structural characteristics of the bridge. The closure sequence was selected through finite element simulation and evaluation system calculations. Various jacking force conditions were set and the structural response was simulated. The jacking force range was determined through comprehensive evaluation.

[0009] As a further aspect of the present invention, S3 specifically includes: Based on the structural characteristics and mechanical behavior of cables, the natural vibration equation of undamped cables is established, and the vibration equation of cables with dampers is derived by introducing a damping term. The calculation method of key parameters related to vibration reduction is also derived. A typical cable-stayed cable was selected as the research object. A cable element model was established using professional finite element software and constraints were set. The cable end displacement excitation and wind load excitation conditions were simulated, and the influence of different damper design parameters and installation positions on vibration reduction was analyzed.

[0010] Based on the cable length classification, the design parameters and installation position of the damper are determined, and the cable body correction, beam end vibration damper installation and fixing, tower end vibration damper installation and sealing, and pre-embedded steel plate positioning and fixing are carried out in sequence.

[0011] As a further aspect of the present invention, it also includes: S4: Closure temperature effect control technology, which controls the closure temperature effect through equal displacement counterweight, selection of construction timing and locking of stiffening frame.

[0012] As a further aspect of the present invention, S4 specifically includes: The influence of closure temperature on cantilever end displacement, cantilever root stress and cable force was analyzed to clarify the correlation between temperature change and structural response. The equal displacement counterweight method was adopted, and the corresponding counterweight value was determined according to different temperature conditions. Counterweights were then applied to the box girders on both sides of the closure section. Select a period of relatively stable structural temperature for measuring the elevation of the hanging basket formwork and constructing the closure section. Before the concrete is poured for the closure section, a rigid frame is used to temporarily lock the closure joint.

[0013] As a further aspect of the present invention, the equal displacement counterweight method includes: By combining the data on the influence of temperature on the displacement of the cantilever end, a correspondence between temperature and counterweight is established, and a matching counterweight value is selected based on the real-time ambient temperature before the closure construction.

[0014] As a further aspect of the present invention, the selection of the construction timing specifically includes: Monitor the temperature changes of the bridge structure at different times to determine the period when the structural temperature is relatively stable. During this period, complete the following procedures: measuring the elevation of the hanging basket formwork, binding the reinforcing bars of the closure section, installing the formwork, and pouring concrete.

[0015] As a further aspect of the present invention, the rigid frame locking specifically includes: Based on the dimensions of the closure joint and the stress requirements, a rigid frame was designed and installed and fixed at the closure joint before the concrete of the closure section was poured.

[0016] A construction system for the cable-stayed bridge cable system, the system comprising: The cable anchorage assessment module is used to calculate the temperature effect based on the bridge site temperature data, obtain material performance parameters through mechanical tests of steel strands in low-temperature environments, and simulate the stress and deformation of concrete in the anchorage zone using finite element software. The closure and jacking optimization module is used to establish a finite element model of the bridge, and to construct a two-stage hierarchical weighted evaluation system using the empirical entropy weight method to determine the optimal closure sequence and closure jacking force. The viscous damping optimization module is used to derive the motion equations of the cable-damper system, analyze the vibration reduction effect under wind load and cable end displacement excitation through finite element simulation, and determine the installation position and key parameters of the damper.

[0017] The present invention has the following beneficial effects: This construction technique, through the coordinated efforts of low-temperature anchorage reliability assessment of cables, optimization of closure jacking construction, optimized setting and installation of viscous dampers for cable stays, significantly improves the construction efficiency and structural safety of cable-stayed bridges with multiple low towers in cold and windy environments. It provides a complete and reliable technical reference for the construction of similar bridges in extreme environments and has broad prospects for promotion and application. Attached Figure Description

[0018] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. The structures, proportions, sizes, etc., drawn in this specification are only used to complement the content disclosed in the specification, so that those skilled in the art can understand and read them. Any modifications to the structure, changes in the proportional relationships, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0019] Figure 1 This is a schematic diagram illustrating the overall construction process of the cable-stayed bridge with multiple low towers in a high-altitude, cold, and windy region, as provided in an embodiment of the present invention. Detailed Implementation

[0020] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0021] The terms "upper," "lower," "left," "right," and "middle" used in this specification are merely for clarity of description and are not intended to limit the scope of the invention. Any changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the invention.

[0022] like Figure 1 As shown, this embodiment of the invention provides a construction process for the cable-stayed bridge system of a multi-tower cable-stayed bridge in a high-altitude, cold, and windy region, specifically including the following steps: S1: Low-temperature anchorage reliability assessment process for cables, which calculates the temperature effect based on bridge site temperature data, obtains material performance parameters through mechanical tests of steel strands in low-temperature environments, and uses finite element software to simulate the stress and deformation of concrete in the anchorage zone. This process effectively ensures the safety and reliability of cable anchorage in low-temperature environments by accurately calculating temperature effects, testing the low-temperature mechanical properties of steel strands, and simulating the stress and deformation of concrete in the anchorage zone. The specific process is as follows: S101: Temperature effect calculation; Based on statistical data of extreme temperatures, key parameters of the structural temperature field were determined: A finite element model of the entire bridge's planar truss system was established using MidasCivil to simulate five working conditions: overall temperature rise, overall temperature drop, cable-beam negative temperature, beam gradient temperature drop, and tower gradient temperature drop. The changes in cable force and structural deformation under different working conditions were calculated. The analysis showed that the vertical displacement at mid-span caused by temperature can be calculated by linearly superimposing the thermal expansion and contraction effects of cable temperature, average main beam temperature, temperature difference between the top and bottom plates of the main beam, and average tower temperature. Among these, the influence of cable temperature and average main beam temperature accounts for more than 90%. When the overall temperature drops by 40℃, the cable force of the longest cable, C14, increases by 402.4kN (an increase of 5.7%). The cable force of the long cable on the Keshiketeng side of Tower 8 increases while the cable force of the short cable decreases. The cable forces of Towers 9 and 10 both show an increasing trend, clearly demonstrating the impact of temperature changes on cable force. S102: Mechanical property test of steel strand under low temperature environment; 1860MPa epoxy-coated steel strand (15.2mm in diameter and 140mm² in area) consistent with the actual engineering was selected. Eight temperature gradients were set: 30℃, 20℃, 10℃, 0℃, -10℃, -20℃, -30℃, and -40℃. Three specimens were used in each group to ensure the reliability of the test results.

[0023] First, the corresponding low-temperature environment was simulated in the atmospheric environment simulation test chamber. Then, the yield strength, ultimate tensile strength and elongation after fracture of the steel strand were tested by the material tensile testing equipment.

[0024] The test results show that as the temperature gradually decreases, the yield strength and ultimate tensile strength of the steel strand increase linearly, but the increase in ultimate strength is greater than that in yield strength, resulting in a gradual decrease in the strength-to-yield ratio and a reduction in strength reserve; the elongation after fracture continues to decrease, and the plasticity gradually deteriorates.

[0025] S103: Finite element analysis of concrete in the anchorage zone under low temperature conditions; A refined finite element model of the main beam segment and anchorage system was established based on ABAQUS. The model includes key components such as steel strand anchor group, wire branch tube, and concrete diaphragm, accurately simulating the complex structure of the anchorage zone. The stress distribution and local deformation of the concrete in the anchorage zone were calculated under five temperature load conditions: design reference temperature, overall temperature drop of 10℃, 20℃, 30℃, and 40℃. The results showed that the maximum tensile stress and maximum compressive stress in the anchorage zone of the stay cable increased linearly with decreasing temperature. When the overall temperature dropped by 40℃, the maximum tensile stress was 1.89 MPa (less than the design tensile strength of C60 concrete, 2.04 MPa), and the maximum compressive stress was 13.37 MPa (less than the design compressive strength of C60 concrete, 27.5 MPa), meeting the specifications. The vertical deformation at mid-span of the main beam and the local deformation in the anchorage zone also increased linearly with decreasing temperature. When the temperature dropped by 40℃, the vertical deformation at mid-span was 167.1 mm, and the local deformation in the anchorage zone was 1.15 mm, both within the design allowable range. By adding reinforcing steel mesh and spiral reinforcement in the anchorage zone, the stress concentration of the prestressed steel was effectively alleviated, concrete cracking was avoided, and the anchorage reliability was further improved.

[0026] This process, through the organic combination of temperature effect calculation, material testing and finite element simulation, systematically grasps the stress and deformation laws of the cable anchorage system in high-altitude and cold environments, providing a scientific basis for cable tensioning and subsequent operation and maintenance, and ensuring the safety and stability of cable anchorage in low-temperature environments.

[0027] S2: Optimize the closure and jacking construction process, establish a bridge finite element model, and use the empirical entropy weight method to construct a two-stage hierarchical weighted evaluation system to determine the optimal closure sequence and closure jacking force; This process, through the establishment of a finite element model and a two-stage hierarchical weighted evaluation system, scientifically determines the optimal closure sequence and jacking force, achieving precise control of the closure construction process. Specifically, it includes the following: S201: Establishment of numerical calculation model for bridge; Based on the spatial finite element software MIDASCivil2021, a full bridge model was established in accordance with the "General Specifications for Highway Bridge and Culvert Design". The main beam, main tower, pier, abutment and pile foundation were simulated by beam elements, and the stay cables were simulated by truss elements. The full bridge model was divided into 5643 nodes, 5212 elements and 86 construction stages.

[0028] Model material parameter settings: The main beam is made of C60 concrete with an elastic modulus of 3.6 × 10¹. 0 N / m², Poisson's ratio 0.2, coefficient of linear expansion 1×10 -5 / ℃, density 25kN / m³; the main tower is made of C55 concrete, the piers are made of C50 concrete, the elastic modulus of the steel is 1.95×10¹¹N / m², Poisson's ratio is 0.3, and the coefficient of linear expansion is 1.2×10⁻ 5 / ℃, density 78.5kN / m³; the stay cables are made of prestressed steel strands with a standard strength of 1860MPa and an elastic modulus of 1.95×10. 5 MPa.

[0029] Boundary condition settings: The main bridge adopts a rigid frame system with towers, piers and beams fixed together, and supports are only set at the transition piers at the connecting ends to accurately simulate the actual stress state of the bridge.

[0030] S202: Construction of a two-stage hierarchical weighting evaluation system based on the empirical entropy weighting method; Determine the closure control indicators: Based on the structural characteristics of the Xilamulun River Bridge and the correlation and importance of each response, six core indicators were selected as the evaluation basis for the closure scheme: tower longitudinal displacement, beam vertical displacement, pier bottom stress, cable stress, main beam section bending moment, and support reaction force. Constructing an evaluation system: For m closure schemes and n evaluation indicators, first construct the original matrix. A =( α ij ) m×n ,in α ij Let j be the value of the evaluation index for the i-th scheme; Then, the weight p of the i-th scheme under the j-th evaluation index is calculated. ij and index entropy value e j ; In the formula, k>0, k=1 / ln m; Secondly, calculate the entropy weight of the j-th evaluation index. w j ; Introducing an empirical factor δ=0.3, through... Determine the overall weight; v j The subjective weights are based on engineering experience, with the experience weights for the longitudinal displacement of the pylon and the vertical displacement of the beam both at 25%, the experience weights for the pier bottom stress and the beam section bending moment both at 15%, and the experience weights for the stay cable tension and support reaction force both at 10%. Two-stage evaluation process: The first stage is based on the response of multiple components of each indicator, and the overall value of the sub-indicators is calculated using comprehensive weights; the second stage uses the overall value of the sub-indicators as the evaluation object to calculate the overall evaluation result of the scheme. In the formula: S represents the evaluation result of the closure of the low-tower cable-stayed bridge; β i The weight of the i-th evaluation index is calculated according to the weighting method. θ i The result is the normalized result of this evaluation index. The smaller the evaluation result, the closer the various indicators of the scheme are to the optimal value.

[0031] S203: Optimization of closure sequence; The proposed closure schemes based on the current main multi-span structural closure processes include: ① from side to center; ② from center to side; ③ first statically determinate small closure followed by super-statically indeterminate large closure; ④ closure of all spans in one go; ⑤ closure from one side to the other sequentially. Among these, ①②③ are applicable to symmetrical bridge types, while ④⑤ are applicable to asymmetrical bridge types.

[0032] The established finite element model was used to simulate the structural response of the bridge 10 years after its completion, and data such as the longitudinal displacement of the pylon, the vertical displacement of the beam, the stress at the bottom of the pier, the internal forces of the beam section, and the support reaction force were extracted. Analysis results show that the longitudinal displacement of the tower piers decreases from both ends towards the middle. The vertical displacement at mid-span is upward only in the side spans, downward in all other spans, with the peak values ​​occurring in the left mid-span. Significant differences exist in the internal forces of the left span across different schemes, while the internal forces of the beam sections in the other spans are relatively similar. The maximum positive bending moment and the maximum negative bending moment occur at the right root of the right mid-span and the left root of the left mid-span, respectively, with maximum and minimum values ​​of 21.93 × 10⁻⁶. 4 kN・m and -26.91×10 4 kN・m. The evaluation results of each scheme were calculated using a two-stage graded weighted evaluation system. Scheme ② (from the middle to both banks) performed best with an evaluation result of 0.9326. This scheme was superior to other schemes in terms of pylon displacement along the bridge, pier bottom stress, beam section bending moment and peak support reaction force. It can effectively balance the internal forces of the structure and reduce the deformation after the bridge is completed. Therefore, it was determined to be the optimal closure sequence.

[0033] S204: Optimization of closure top thrust; The jacking force conditions with an interval of 250kN from 0 to 3000kN were set up to simulate the structural response under each condition and analyze the influence of the jacking force on the longitudinal displacement of the tower, the vertical displacement of the beam, the stress at the bottom of the pier, the bending moment of the beam section, and the support reaction force. Finite element simulation results show that the internal forces of the beam section and the stress at the bottom of the pier are less affected by the jacking force, while the longitudinal displacement of the tower piers, the vertical displacement at the mid-span of the side spans, and the support reactions are more significantly affected. As the jacking force increases, some towers gradually develop longitudinal displacements towards both sides, while the vertical displacement at the mid-span of the side spans increases downwards with the increase of the jacking force. The support reactions of some tower piers show a significant reaction towards the middle as the jacking force increases. The longitudinal displacement of some towers and the support reactions of other tower piers are not sensitive to changes in the jacking force. A comprehensive evaluation of each jacking force scheme was conducted using a two-stage graded weighted evaluation system. When the jacking force was 1500kN, the evaluation results of the tower's longitudinal displacement and support reaction were the best. When the jacking force was 2000kN and 2250kN, the evaluation results of the mid-span vertical displacement were the best. Based on the comprehensive secondary evaluation results, 1500-1750kN was the optimal jacking force range. Within this range, the internal forces and deformation of the bridge structure were balanced, which could effectively offset the pier displacement caused by concrete shrinkage and creep, and improve the stress state of the completed bridge. This technology, through a scientific evaluation system and precise numerical simulation, optimizes the selection of closure sequence and jacking force, effectively solving the problem of complex stress during the closure construction of multi-tower structures, and improving the closure construction quality and structural safety.

[0034] S3: Optimization of the installation process of the viscous damper for cable-stayed bridges, derivation of the motion equation of the cable-damper system, analysis of the vibration reduction effect under wind load and cable end displacement excitation through finite element simulation, and determination of the damper installation position and key parameters.

[0035] This process determines optimal parameters by deriving motion equations and simulating vibration reduction effects under multiple working conditions, and ensures effective vibration reduction by combining these with standardized installation procedures. Specifically, it includes the following: S301: Derivation of the equations of motion for a cable-damper system; Based on the cable sag effect and geometric nonlinearity, assuming that the cable has a small sag-to-span ratio, vibrates only in the xy plane, has a parabolic geometry, and its self-weight is constant in the y direction, the natural vibration equation of the undamped cable is established as follows: Where EI is the cable bending stiffness, υ(x,t) is the cable vertical vibration displacement, and T is the cable force. The increment of cable force due to cable vibration is given by , and m is the mass per unit length of the cable.

[0036] For second-order and higher vibration modes, the effect of the cable force increment ∆T is negligible, and the equation simplifies to: Assuming the two ends are hinged, the formula for calculating the natural frequency is: Where n is the frequency order of the cable. For the length of the cable, For cable tension, The mass per unit length of the cable, The stiffness correction factor is given by the following formula: In practical cable-stayed bridges, the cables are generally made of braided steel wire, which has relatively low bending stiffness, and its influence on frequency is negligible. Assuming that both ends are fixed, the approximate formula for calculating the natural frequency can be obtained as follows: For cable stays, wind loads mainly cause lateral vibration response, and the viscous damper constrains this effect. Therefore, it is believed that the effective length of the cable stays in the horizontal direction is reduced.

[0037] When a damping term is introduced, considering the cable's own damping and the effect of the viscous damper, the vibration equation of the cable with damper is derived: Where c is the damping coefficient per unit length of the cable, a is the reduced length of the cable, and δ(xa) is the Dirac function.

[0038] Under harmonic excitation, the equivalent damping ratio is: Assuming the frequency of the external excitation force is close to the first natural frequency of the cable, the corresponding logarithmic decay rate is: Determine the damping coefficient of the damper to achieve vibration reduction of the stay cables.

[0039] Where, ε= -a represents the reduced length of the cable, and ω1 represents the first-order natural frequency of the cable.

[0040] S302: Simulation of parameter optimization for cable-stayed viscous dampers; The bridge structure with a cable length of 110m, diameter of 0.099m, inclination angle of 21°, dead load of 7000kN, cable area of ​​0.007699m², density of 7850kg / m³, and elastic modulus of 1.95×10¹¹Pa was constructed as the research object. Ansys was used to establish a cable element finite element model, and fixed constraints were applied to both ends of the cable. First, the natural frequencies and mode shapes of the cables are analyzed. The results show that the first six modes of vibration of the cable-stayed bridge include horizontal bending, vertical bending, antisymmetric horizontal bending, symmetrical horizontal bending, antisymmetric vertical bending, and symmetrical vertical bending. The frequency of the first horizontal bending mode is 1.4263 Hz, the frequency of the second vertical bending mode is 1.4278 Hz, the frequency of the third antisymmetric vertical bending mode is 2.8529 Hz, the frequency of the fourth antisymmetric horizontal bending mode is 2.8529 Hz, the frequency of the fifth symmetrical horizontal bending mode is 4.2802 Hz, and the frequency of the sixth symmetrical vertical bending mode is 4.2802 Hz.

[0041] Then, the vibration reduction effect under cable end displacement excitation and wind load excitation was simulated: Simulation of cable end displacement excitation: Both longitudinal and vertical cable end displacement excitation adopt random excitation displacement loads with a period of 200s and an amplitude of 0-50mm. The damping forces of the dampers are designed to be 5kN, 10kN, 20kN, and 30kN, respectively, and the installation positions are 1m, 2m, 3m, 4m, and 5m away from the anchorage end of the main beam.

[0042] The results show that the greater the damping force of the damper and the farther the installation position is from the anchor end of the main beam, the better the vibration reduction effect. When the 30kN damper is installed at a position of 5m, the vertical vibration amplitude under longitudinal displacement excitation is reduced by 3.88%, and the vertical vibration amplitude under vertical displacement excitation is reduced by 9.80%. Moreover, the damper has a more significant vibration reduction effect on vertical displacement excitation.

[0043] Wind load excitation simulation: The harmonic synthesis method is used to simulate the time-history wind load coupled with mean wind and fluctuating wind. The static wind load calculation formula is as follows: Where ρ = 1.25 kg / m³ is the air density, and V g For calm gust wind speed, C H A is the drag coefficient. n Projected area in the downwind direction (m²) 2 ); The vibration response under random wind loads in the X, Y, and Z directions was simulated. The results showed that the amplitude of the stay cable in the Z direction was the largest under wind load in the Z direction, and the vertical damper had no obvious vibration reduction effect. Under wind load in the X direction, when the 30kN damper was installed at a position of 5m, the amplitude in the X direction decreased from 3.38mm to 3.04mm (a reduction of 10.43%), and the amplitude in the Y direction decreased from 8.73mm to 8.08mm (a reduction of 7.96%). Under wind load in the Y direction, the vibration reduction was relatively small (3.4% in the X direction and 3.41% in the Y direction).

[0044] Based on the comprehensive simulation results under multiple working conditions, the optimal parameters for the stay cable viscous dampers were determined as follows: the damping force of the long cable (C9-C14) damper is 30kN, and the installation position is 2-2.5m away from the anchorage end of the main beam; the damping force of the short cable (C1-C8) damper is 20-30kN, and the installation position is 1-1.5m away from the anchorage end of the main beam. This combination of parameters achieves a balance between vibration reduction effect and economy while meeting the requirements of the specifications.

[0045] The installation process for cable-stayed bridge viscous dampers is divided into tower-end dampers (all-rubber structure, combining sealing and vibration damping functions) and beam-end dampers (steel-rubber hybrid structure, solely for vibration damping). The installation process is as follows: a. Cable alignment: Before installing the shock absorber, carefully check whether the stay cable is tilted. If the tilt is large, use tools such as a hand hoist or jack to correct the tilt of the stay cable to ensure that the cable is vertical and to provide a good foundation for the installation of the shock absorber.

[0046] b. Installation of beam end vibration damper: Insert the beam end vibration damper into the pre-embedded pipe, and tighten the four locking screws on the vibration damper with a special tool to tighten the four sliders of the vibration damper towards the inner wall of the pre-embedded pipe until the sliders are in close contact with the inner wall of the pre-embedded pipe, ensuring a firm connection between the vibration damper and the pre-embedded pipe; then use a wrench to lift the locking plate below the screw head on the vibration damper to fix the screw head and prevent the screw from loosening during use.

[0047] c. Tower end vibration damper installation: Use tools to press the tower end half-type rubber vibration damper into the anti-slip anchor cylinder to ensure that the vibration damper is tightly pressed against the cable body to achieve reliable vibration reduction; use putty to completely seal the gaps between the steel strands of the vibration damper to prevent impurities from entering and affecting the vibration reduction effect, and use thin steel bars to weld a mesh structure on the outside of the vibration damper to prevent it from falling out when epoxy mortar is poured into the anti-slip anchor cylinder.

[0048] d. Fixing the embedded steel plate: Each damper is equipped with a set of embedded steel plates for the support frame and a set of embedded steel plates for the diagonal bracing tube. Accurately locate the installation position of the embedded steel plate according to the parameter table provided by the manufacturer; insert the reinforcing bars of the embedded steel plate into the wet joint reinforcing bars of the cable area, ensuring that the top surface of the embedded steel plate remains horizontal and consistent with the height of the top surface of the concrete. The overlap is fully welded firmly. When pouring concrete, take care to avoid covering the embedded steel plate with concrete.

[0049] This technology, through precise parameter optimization and standardized installation operations, significantly improves the vibration reduction effect of stay cables under wind loads and cable end displacement excitation, effectively extends the service life of the stay cables, and ensures the long-term safe operation of the bridge structure.

[0050] S4; Closure temperature effect control technology, which achieves control of closure temperature effect through equal displacement counterweight, selection of construction timing and locking of stiffening frame; This process effectively mitigates the adverse effects of temperature changes on the closure construction through equal-displacement counterweights, appropriate timing of construction, and rigid frame locking measures. Specifically, it includes the following: The calculation was performed under the condition of overall temperature rise and fall during the closure of the central span. The temperature difference was set to be 2.5℃. The influence of the closure temperature on the vertical displacement of the cantilever end, the stress at the root of the cantilever and the cable force of the stay cable was analyzed.

[0051] The results show that as the temperature rises during the closure construction, the vertical displacement of the cantilever end decreases linearly, while the longitudinal displacement of the cantilever end increases linearly with increasing temperature. As the temperature rises, the internal force at the 1 / 2 point of the cantilever beam increases, while the internal force at the root of the cantilever end decreases. As the closure temperature rises, the cable force of the longest cable increases significantly, the cable force of the middle cable does not change significantly, and the cable force of the shortest cable decreases slightly, but the magnitude is small.

[0052] Under different temperature conditions, the bridge alignment, stress, and cable tension of the main girder after closure all changed significantly. A temperature increase of 20℃ caused a downward vertical displacement of 5.43 mm at the mid-span of the main girder, and the internal force at the mid-span decreased by 1.43 × 10⁻⁶ mm. 6 N·m; As the distance between the cross section and the root of the main beam increases, the vertical displacement variation increases, while the internal force variation of the main beam decreases; and as the overall temperature rises with the closure, the vertical displacement and internal force variation of the closure span become more pronounced.

[0053] Further application of the equal displacement counterweight method: The equal displacement counterweight method was adopted to mitigate the adverse effects of temperature during the closure construction phase. Closure counterweight refers to the addition of weights to the box girders on both sides of the closure section before closure, serving multiple purposes such as preventing beam disturbance, adjusting beam elevation, and mitigating later-stage stress in the bridge. Since temperature effects during the closure construction phase will also cause displacement at the cantilever ends, this displacement is taken into account during the closure counterweight construction process. The corresponding counterweight values ​​are determined based on different temperature conditions, as shown in the table below. By applying corresponding counterweights, the cantilever end does not shift after the concrete of the closure section is poured, thus ensuring the closure accuracy.

[0054] The timing of the closure construction is chosen because the temperature difference caused by sunlight during the closure construction process is significant. Sunlight causes the temperature at the upper edge of the main beam to be higher than that at the lower edge, causing the main beam to bend and deform downwards. Since the temperature field changes in the structure caused by sunlight are very complex and are related to many factors such as season, sunlight conditions, structural form, and time, in order to avoid their influence, the elevation measurement of the hanging basket formwork and the construction of the closure section are carried out from midnight to before sunrise when the structural temperature is relatively stable, thus eliminating the influence of temperature on construction control.

[0055] Further, the closure section is locked in place using a robust frame structure: Before concrete pouring, a rigid frame is used to temporarily lock the closure joint. The rigid frame has sufficient rigidity to resist the deformation of the closure joint caused by temperature changes, prevent the beam from being disturbed during the closure process, and ensure that the structure is connected in the optimal state, further guaranteeing the closure accuracy and structural stability.

[0056] This process, through the synergistic effect of multiple measures, effectively controlled the adverse effects of temperature on the closure construction, ensuring that the completed bridge alignment and structural internal forces met the design requirements, and improving the quality and reliability of the closure construction of multi-tower cable-stayed bridges in high-altitude, cold, and windy areas.

[0057] Although the present invention has been described in detail above with general descriptions and specific embodiments, modifications or improvements can be made to it, which will be obvious to those skilled in the art. Therefore, all such modifications or improvements made without departing from the spirit of the present invention fall within the scope of protection claimed by the present invention.

Claims

1. A construction technique for the cable-stayed system of a multi-tower cable-stayed bridge in a high-altitude, cold, and windy region, characterized in that, Includes the following steps: S1: Low-temperature anchorage reliability assessment process for cables; Temperature effects were calculated based on bridge site temperature data. Material performance parameters were obtained through mechanical tests of steel strands under low-temperature conditions. The stress and deformation of concrete in the anchorage zone were simulated using finite element software. S2: Optimized construction process for closure and jacking; A finite element model of the bridge was established, and a two-stage hierarchical weighted evaluation system was constructed using the empirical entropy weight method to determine the optimal closure sequence and closure thrust. S3: Optimized setting process for viscous dampers in cable-stayed bridges; The equations of motion for the cable-damper system were derived, and the vibration reduction effect under wind load and cable end displacement excitation was analyzed through finite element simulation. The installation position and key parameters of the damper were then determined.

2. The construction technology of the cable-stayed bridge system for multi-tower cable-stayed bridges in high-altitude, cold, and windy areas according to claim 1, characterized in that, S1 specifically includes: By combining extreme temperature data at the bridge site, key parameters of the structural temperature field were determined, a finite element model of the whole bridge planar truss system was established, various temperature conditions were simulated, cable force changes and structural deformation were calculated, and the degree of influence of each temperature factor was clarified. Select steel strands consistent with the actual engineering, set multiple temperature gradients and prepare specimens in groups, conduct tensile tests in equipment simulating low temperature environment, and test the core mechanical performance parameters. A refined model of the main beam segment and anchorage system containing key components was established to simulate various temperature load conditions, calculate the stress distribution and local deformation of the concrete in the anchorage zone, and add reinforcement structures in the anchorage zone.

3. The construction technology of the cable-stayed bridge system for multi-tower cable-stayed bridges in high-altitude, cold, and windy areas according to claim 2, is characterized in that, S2 specifically includes: A full bridge model is constructed using professional finite element software. The corresponding simulation elements are selected according to the component type. Reasonable nodes, number of elements and construction stages are divided. Material property parameters of each component are set and boundary conditions are set according to the actual structural form. The control indicators for closure were determined, an original matrix was constructed for multiple closure schemes and evaluation indicators, the objective weights of the indicators were calculated by the entropy weight method, the comprehensive weights were determined by introducing empirical factors, and the overall values ​​of the sub-indicators and the overall evaluation results of the schemes were calculated in two stages. Multiple closure schemes were proposed to address the symmetrical structural characteristics of the bridge. The closure sequence was selected through finite element simulation and evaluation system calculations. Various jacking force conditions were set and the structural response was simulated. The jacking force range was determined through comprehensive evaluation.

4. The construction technology of the cable-stayed bridge system for multi-tower cable-stayed bridges in high-altitude, cold, and windy areas according to claim 3, is characterized in that, S3 specifically includes: Based on the structural characteristics and mechanical behavior of cables, the natural vibration equation of undamped cables is established, and the vibration equation of cables with dampers is derived by introducing a damping term. The calculation method of key parameters related to vibration reduction is also derived. A typical cable-stayed cable was selected as the research object. A cable element model was established using professional finite element software and constraints were set. The cable end displacement excitation and wind load excitation conditions were simulated, and the influence of different damper design parameters and installation positions on vibration reduction was analyzed. Based on the cable length classification, the design parameters and installation position of the damper are determined, and the cable body correction, beam end vibration damper installation and fixing, tower end vibration damper installation and sealing, and pre-embedded steel plate positioning and fixing are carried out in sequence.

5. The construction technology for the cable-stayed bridge system of multi-tower cable-stayed bridges in high-altitude, cold, and windy areas according to any one of claims 1-4, characterized in that, Also includes: S4: Closure temperature effect control technology, which controls the closure temperature effect through equal displacement counterweight, selection of construction timing and locking of stiffening frame.

6. The construction technology of the cable-stayed bridge system for multi-tower cable-stayed bridges in high-altitude, cold, and windy areas according to claim 5, is characterized in that, S4 specifically includes: The influence of closure temperature on cantilever end displacement, cantilever root stress and cable force was analyzed to clarify the correlation between temperature change and structural response. The equal displacement counterweight method was adopted, and the corresponding counterweight value was determined according to different temperature conditions. Counterweights were then applied to the box girders on both sides of the closure section. Select a period of relatively stable structural temperature for measuring the elevation of the hanging basket formwork and constructing the closure section. Before the concrete is poured for the closure section, a rigid frame is used to temporarily lock the closure joint.

7. The construction technology of the cable-stayed bridge system for multi-tower cable-stayed bridges in high-altitude, cold, and windy areas according to claim 6, is characterized in that, The equal displacement counterweight method includes: By combining the data on the influence of temperature on the displacement of the cantilever end, a correspondence between temperature and counterweight is established, and a matching counterweight value is selected based on the real-time ambient temperature before the closure construction.

8. The construction technology of the cable-stayed bridge system for multi-tower cable-stayed bridges in high-altitude, cold, and windy areas according to claim 6, characterized in that, The selection of the construction timing specifically includes: Monitor the temperature changes of the bridge structure at different times to determine the period when the structural temperature is relatively stable. During this period, complete the following procedures: measuring the elevation of the hanging basket formwork, binding the reinforcing bars of the closure section, installing the formwork, and pouring concrete.

9. The construction technology of the cable-stayed bridge system for multi-tower cable-stayed bridges in high-altitude, cold, and windy areas according to claim 6, is characterized in that, The stiffening frame locking specifically includes: Based on the dimensions of the closure joint and the stress requirements, a rigid frame was designed and installed and fixed at the closure joint before the concrete of the closure section was poured.

10. A cable-stayed bridge cable system construction system that implements the cable system construction technology for multi-tower cable-stayed bridges in high-altitude, cold, and windy areas as described in any one of claims 5-9, characterized in that, The system includes: The cable anchorage assessment module is used to calculate the temperature effect based on the bridge site temperature data, obtain material performance parameters through mechanical tests of steel strands in low-temperature environments, and simulate the stress and deformation of concrete in the anchorage zone using finite element software. The closure and jacking optimization module is used to establish a finite element model of the bridge, and to construct a two-stage hierarchical weighted evaluation system using the empirical entropy weight method to determine the optimal closure sequence and closure jacking force. The viscous damping optimization module is used to derive the motion equations of the cable-damper system, analyze the vibration reduction effect under wind load and cable end displacement excitation through finite element simulation, and determine the installation position and key parameters of the damper.

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