A stiffening cable structure and design method for a suspension bridge

Abstract

The present application discloses a stiffening cable structure and design method for a suspension bridge, relating to the technical field of bridge structures. The suspension bridge comprises a main beam and two pylons, and the stiffening cable structure comprises two groups of stay cables and a plurality of slings. The two groups of stay cables are symmetrically arranged along the longitudinal direction of the main beam. Each group of stay cables is anchored transversely to a pylon, and one side of each group of stay cables is anchored to a side span pier or anchorage of the suspension bridge, and the other side is anchored to a quarter-span region of the main beam. The slings located at the same longitudinal position in the quarter-span region of the stay cables are cross-slings. The stay cables are fixed to the anchor points of the main beam and provided with weight blocks of a set weight. Under the action of the stay cables and weight blocks, the dead load cable force of the cross-sling does not exceed the dead load cable force of the non-cross-sling, and the vertical displacement extreme value of the main beam in the quarter-span region is not greater than the vertical displacement extreme value of the main beam in the mid-span. The stiffening cable structure and design method of the present application are intended to solve the technical problem of low vertical stiffness of suspension bridges in related technologies.

Description

Technical Field

[0001] The present application relates to the technical field of bridge structures, and in particular to a stiffening cable structure of a suspension bridge and a design method thereof. Background Art

[0002] Currently, among many bridge types, suspension bridges, due to their high span capacity, are the primary choice for ultra-long span bridges. The largest known suspension bridge span has reached 2,300 meters. However, suspension bridges also have significant drawbacks. Their vertical stiffness is significantly lower than that of cable-stayed bridges of the same span, resulting in poor wind-resistant stability of the main girder, significantly impacting the safety and comfort of trains traveling on them. Therefore, the low vertical stiffness of suspension bridges has become a key factor restricting their application in railway bridges.

[0003] Therefore, those skilled in the art are in urgent need of designing a new solution to solve the problem of low vertical stiffness of suspension bridges. Summary of the Invention

[0004] In view of the defects existing in the prior art, the purpose of this application is to provide a stiffening cable structure of a suspension bridge and a design method thereof, so as to solve the technical problem of low vertical stiffness of the suspension bridge in the related art.

[0005] To achieve the above objectives, the technical solution adopted is as follows: a stiffening cable structure for a suspension bridge, the suspension bridge comprising a main beam and two bridge towers, the stiffening cable structure comprising two sets of stay cables and a plurality of suspenders; the two sets of stay cables are symmetrically arranged along the longitudinal direction of the main beam; each set of stay cables is anchored across a bridge tower, and one side of each set of stay cables is anchored to a side span pier or anchorage of the suspension bridge, and the other side is anchored to a quarter-span region of the main beam; suspenders located at the same longitudinal position in the quarter-span region of the stay cables are cross suspenders;

[0006] The inclined cable is fixed to the anchor point of the main beam and a ballast block of a set weight is added; under the action of the inclined cable and the ballast block, the constant load cable force of the cross cable does not exceed the constant load cable force of the non-cross cable, and the vertical displacement extreme value of the main beam in the four-span area is not greater than the vertical displacement extreme value of the main beam in the mid-span.

[0007] On the basis of the above technical solution, each group of stay cables includes a plurality of stay cables, and two stay cables symmetrically arranged at the same location of the two groups of stay cables are anchored at the same height of the two bridge towers.

[0008] On the basis of the above technical solution, each group of stay cables includes one or more stay cables, and the ends of the stay cables are anchored in the four-span areas of the main beam.

[0009] Based on the above technical solution, several slings of the stiffening cable structure are arranged vertically at equal intervals, and the two ends of each sling are respectively fixed to the main beam and main cable of the suspension bridge; the main cable is bent at the top of the two bridge towers, and its two ends are respectively anchored in two anchors.

[0010] On the basis of the above technical solution, each group of stay cables is divided into main span side stay cables and side span side stay cables along both sides of the bridge tower. The ends of the side span side stay cables are centrally anchored to the side span piers or anchors, and the ends of the main span side stay cables are dispersedly anchored to the four sub-span areas of the main beam; the horizontal components of the dead load cable forces of the main span side stay cables and the side span side stay cables are equal in magnitude and opposite in direction.

[0011] The present application also discloses a method for designing a stiffening cable structure of a suspension bridge, comprising the following steps:

[0012] S1. Establish a finite element model of the suspension bridge and analyze the vertical stiffness of the suspension bridge under the action of vertical moving loads. The W-shaped vertical displacement extreme envelope diagram of the main beam following the main cable is obtained, with the displacement being small in the middle of the span and large at the quarter span.

[0013] S2. Tension two sets of stay cables of initial specifications in the two quarter-span areas with the weakest vertical stiffness. One side of each set of stay cables is anchored to the side span piers or anchorages of the suspension bridge, and the other side is anchored to the quarter-span area of ​​the main beam. Cables located at the same longitudinal position in the quarter-span area of ​​the stay cables are cross-cables. Initial ballast blocks are added at the anchor points where the stay cables are anchored to the main beam.

[0014] S3. Apply vertical moving load and re-extract the vertical displacement extreme value envelope diagram of the main beam; compare the vertical displacement extreme value at the quarter span with the vertical displacement extreme value at the mid-span. If it is greater, go to S4; if not, end;

[0015] S4. Add local weight blocks at the anchor points where the inclined cables are fixed to the main beams. When the dead load tension of the cross cables reaches the dead load tension of the non-cross cables, the dead load tension of the cross cables will no longer increase, and the remaining dead load weight will be distributed to the inclined cables. After updating the dead load tension of the cables and inclined cables after weighting, modify the specifications of the inclined cables and return to S3.

[0016] On the basis of the above technical solution, in step S2 and step S4, after determining the dead load cable forces of the slings and the stay cables, the following steps are included:

[0017] The main cables are shaped to determine the reasonable state of the bridge.

[0018] Based on the above technical solution, the initial specifications of the stay cables are determined in step S2, including:

[0019] The dead load forces of the cross cables and the stay cables are determined according to the principle of equal division of vertical force, and the initial specifications of the stay cables are determined based on the dead load forces of the stay cables; the principle of equal division of vertical force means that the vertical component of the dead load force of the stay cables and the dead load force of the cross cables are both 50% of the total weight of the main beam segment and the ballast block.

[0020] On the basis of the above technical solution, each group of stay cables is divided into main span side stay cables and side span side stay cables along both sides of the bridge tower. The ends of the side span side stay cables are centrally anchored to the side span piers or anchors, while the ends of the main span side stay cables are dispersedly anchored to the four sub-span areas of the main beam.

[0021] In step S2, the horizontal components of the dead load cable forces of the main span side stay cables and the side span side stay cables are equal in magnitude and opposite in direction.

[0022] On the basis of the above technical solution, each group of stay cables includes one or more stay cables, and the ends of the stay cables are anchored in the four-span areas of the main beam.

[0023] The beneficial effects of the technical solution provided by this application include:

[0024] 1. The stiffening cable structure of the present application has a simple structure and an ingenious design. A stay cable is arranged for tensioning at the location with the weakest vertical stiffness, namely the quarter-span area. At the same time, in order to tighten the stay cables and cross suspenders of the stiffening cable structure, a weight block of a set weight is provided at the anchor point where the stay cable is fixed to the main beam, thereby increasing the effective stiffness of each cable body and making the vertical displacement extreme value of the main beam in the quarter-span area less than or equal to the vertical displacement extreme value of the main beam in the mid-span area, thereby greatly improving the vertical stiffness of the suspension bridge as a whole.

[0025] 2. The design method of the stiffening cable structure of the suspension bridge of the present application first uses a finite element model to analyze the weakest position of the vertical stiffness of the suspension bridge, namely the two quarter-span areas, and then tensions the diagonal cables in a highly targeted manner, and adds initial weight blocks at the anchor points where the diagonal cables are anchored to the main beams, so that the diagonal cables and cross cables are both taut, increasing the tensile stress inside the stiffening cable structure, and satisfying the first element of increasing the vertical stiffness.

[0026] Afterwards, an iterative analysis is performed, gradually adding local counterweights. After updating the dead-load tension of the weighted slings and stay cables, the cable specifications are revised, and the vertical displacement envelope of the main beam is re-extracted until the vertical displacement at the quarter-span of the main beam is no greater than the vertical displacement at the mid-span, thus satisfying the second requirement for increasing vertical stiffness. The design method of this application, through cyclical iterative analysis, ultimately ensures that the dead-load tension of the crossed slings is no greater than that of the uncrossed slings, and that both the slings and stay cables are taut. Furthermore, the vertical displacement at the quarter-span of the main beam is no greater than the vertical displacement at the mid-span, achieving the optimal vertical stiffness for the suspension bridge. This design is both ingenious and highly practical. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the description of the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0028] Figure 1 A front view of a suspension bridge structure with a stiffening cable structure provided in an embodiment of the present application;

[0029] Figure 2 A comparison diagram of the envelope curves of the vertical displacement extremes of the suspension bridge girder with a stiffening cable structure provided in an embodiment of the present application and the traditional suspension bridge girder;

[0030] Drawing numbers: 1. main beam; 2. bridge tower; 3. main cable; 4. sling; 41. cross sling; 5. stay cable; 51. main span side stay cable; 52. side span side stay cable; 6. anchorage; 7. pier. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0032] like Figures 1 to 2 As shown, this application discloses an embodiment of a stiffening cable structure for a suspension bridge. The theoretical basis of this application lies in the discovery, during finite element analysis of a conventional suspension bridge, that the main girder 1 experiences significant vertical displacement along with the main cable 3 at the quarter-span position. The envelope curve of the vertical displacement extremes of the main girder is W-shaped, with a small displacement in the middle of the span and a large displacement at the quarter-span position. In other words, the vertical stiffness of the entire suspension bridge is weakest at the two quarter-span positions of the main girder 1. Specifically, the quarter-span position refers to the quarter of the main girder 1 between the two bridge towers.

[0033] The stiffening cable structure of this application aims to improve the vertical stiffness of a suspension bridge. The key to this improvement lies in increasing the tensile stress in the cross-stay cables and diagonal cables, thereby increasing the effective stiffness of each cable body. This ensures that the maximum vertical displacement at the quarter-span of the main beam is no greater than the maximum vertical displacement at the mid-span. Specifically, the vertical stiffness of the cross-stay cables and the effective stiffness of the diagonal cables are collectively referred to as the effective stiffness of each cable body.

[0034] The suspension bridge comprises a main beam 1, a main cable 3 and two bridge towers 2. The stiffening cable structure includes two groups of inclined cables 5 and a number of suspenders. The two groups of inclined cables 5 are symmetrically arranged along the longitudinal direction of the main beam 1. Each group of inclined cables 5 is anchored across a bridge tower 2. Each group of inclined cables 5 is arranged in an inverted V shape on both sides of the bridge tower 2.

[0035] One side of each group of stay cables 5 is anchored to the side span pier 7 or anchor 6 of the suspension bridge, and the other side is anchored to the quarter-span area of ​​the main beam 1. Specifically, the quarter-span area refers to the range of positive and negative set lengths along the length direction of the main beam 1 at the quarter-span.

[0036] The cables 4 located at the same longitudinal position within the four-span region of the stay cables 5 are called cross cables 41. The remaining cables are called non-cross cables. Ballast blocks of a set weight are installed at the anchor points where the stay cables 5 are fixed to the main beam 1. Ballast blocks include the initial ballast blocks and local ballast blocks described below. Ballast blocks provide additional gravity, increasing the dead load force (i.e., internal tensile stress) of the cross cables 41. Under the action of the inclined cables and local ballast blocks, the ratio of the gravity borne by the inclined cables 5 and the cross cables 41 is adjusted so that the constant load cable force of the cross cables 41 is not greater than the constant load cable force of the non-cross cables. At the same time, the effective stiffness of the inclined cables 5 is increased, which satisfies the first key factor for improving the vertical stiffness. At the same time, it is ensured that the vertical displacement extreme value of the main beam 1 in the four-span area is not greater than the vertical displacement extreme value of the main beam 1 in the middle of the span, so that the vertical displacement extreme value of the main beam 1 in the four-span area is less than or equal to the vertical displacement extreme value of the main beam 1 in the middle of the span, which satisfies the second key factor for improving the vertical stiffness.

[0037] The stiffening cable structure of the present application has a simple structure and ingenious design. The inclined cables 5 are set for tensioning at the position with the weakest vertical stiffness, namely the four-span area. At the same time, in order to make the inclined cables 5 and the cross suspenders 41 taut, a weight block with a set weight is set at the anchor point where the inclined cables 5 are fixed to the main beam 1, thereby increasing the tensile stress of the stiffening cable structure. At the same time, the vertical component of the inclined cables 5 ensures that the vertical displacement extreme value of the main beam 1 in the four-span area is less than or equal to the vertical displacement extreme value of the main beam 1 in the mid-span, thereby greatly improving the vertical stiffness of the suspension bridge.

[0038] During the actual construction process, since the vertical displacement extreme value of the quarter-span of the main beam 1 is reduced, the span-rise ratio of the main cable 3 can be increased by 1 / 9 to 1 / 7, which can save construction costs.

[0039] In one embodiment, each group of stay cables 5 includes a plurality of stay cables 5, and two stay cables 5 symmetrically arranged at the same location in two groups of stay cables 5 are anchored at the same height of two bridge towers 2. For example, each group of stay cables 5 includes three stay cables 5, namely, No. 1, No. 2, and No. 3. The No. 2 stay cable of the first group of stay cables 5 is anchored at 100 meters from the bridge tower 2. Similarly, the No. 2 stay cable of the second group of stay cables 5 is also anchored at 100 meters from the bridge tower 2.

[0040] In one embodiment, each group of stay cables 5 includes one or more stay cables, and the ends of the stay cables 5 are anchored in the quarter-span region of the main beam 1. For example, each group of stay cables 5 includes three stay cables 5, with the end of the middle stay cable 5 anchored exactly at the quarter-span of the main beam 1, that is, exactly one-quarter of the length of the main beam 1 between the two pylons 2. The ends of the remaining two stay cables 5 are anchored to the main beam 1 longitudinally forward and backward along the quarter-span. That is, the anchorage positions of the second and third stay cables 5 are staggered relative to the quarter-span, but also fall within the quarter-span region.

[0041] Furthermore, the stiffening cable structure includes several slings 4, each of which is vertically spaced at equal intervals. Each sling has its ends fixed to the suspension bridge's main beam 1 and main cable 3. The main cable 3 is bent at the tops of the two bridge towers 2, with its ends anchored in two anchors 6. During actual construction, the slings 4 and the stay cables 5 interact with each other; changes in one of these cables also affect the other.

[0042] Specifically, each set of stay cables 5 is divided into mainspan-side stay cables 51 and side-span-side stay cables 52 along either side of the pylon 2. The ends of the side-span-side stay cables 52 are centrally anchored to the side-span piers 7 or anchors 6, while the ends of the mainspan-side stay cables 51 are dispersedly anchored to the four sub-span regions of the main girder 1. The horizontal components of the dead load forces in the mainspan-side stay cables 51 and side-span-side stay cables 52 are equal in magnitude and opposite in direction, minimizing the generation of additional horizontal forces that could impact the rest of the suspension bridge structure.

[0043] The present application also discloses a method for designing a stiffening cable structure of a suspension bridge, comprising the following steps:

[0044] S1. Establish a finite element model of the suspension bridge and analyze the vertical stiffness of the suspension bridge under the action of vertical moving load. Obtain a W-shaped vertical displacement extreme envelope diagram of the main beam 1 following the main cable 3, which is small in the middle of the span and large in the quarter span.

[0045] S2. For the two low corners of the W-shaped vertical displacement extreme envelope (corresponding to the quarter-span regions), tension two sets of stay cables 5 in the two quarter-span regions with the weakest vertical stiffness. The cables 4 located at the same longitudinal position in the quarter-span region of the stay cables 5 are cross cables 41.

[0046] When tensioning the stay cables 5 , the dead load cable forces of the cross cables 41 and the stay cables 5 are determined according to the principle of equal division of the vertical force, and the initial specifications of the stay cables 5 are determined according to the dead load cable forces of the stay cables 5 .

[0047] Specifically, the principle of equal distribution of vertical force means that the vertical component of the inclined cable 5 and the dead load cable force of the cross sling 41 each bear 50% of the total weight of the main beam segment and the ballast block.

[0048] Two sets of stay cables 5 are symmetrically arranged along the longitudinal direction of the main beam 1. Each set of stay cables 5 is anchored across a pylon 2. One side of the stay cables 5 is anchored to a side span pier 7 or anchor 6 of the suspension bridge, and the other side is anchored to the quarter-span area of ​​the main beam 1. Initial ballast blocks are added at the anchor points where the stay cables 5 are anchored to the main beam 1.

[0049] S3. Apply vertical moving load, re-analyze the vertical stiffness of the suspension bridge and obtain the vertical displacement extreme value envelope diagram of the main beam; compare the vertical displacement extreme values ​​of the four-span area with the vertical displacement extreme value of the mid-span; if they are greater, go to S4; if not, end;

[0050] S4. Continue to add local ballast blocks at the anchor points where the inclined cables 5 are fixed to the main beam 1. Continue to determine the dead load tensions of the cross cables 41 and the inclined cables 5 according to the principle of equal division of the vertical force. When the dead load tension value of the cross cables 41 reaches the dead load tension value of the non-cross cables, the dead load tension value of the cross cables 41 will no longer increase, and the remaining dead load weight will be distributed to the inclined cables. After updating the dead load tensions of the ballasted cables and inclined cables, revise the specifications of the inclined cables and return to S3.

[0051] The design method of this application ends after S3 and S4 are repeated twice or more, and the final specifications of the inclined cable and the total weight of the final ballast block are obtained, that is, the ballast block with the set weight mentioned above. Finally, the vertical moving load is applied to obtain the following Figure 2 The figure shows a comparison of the envelopes of the extreme vertical displacements of the main beam of a suspension bridge with a stiffening cable structure.

[0052] The design method of the stiffening cable structure of the suspension bridge of the present application first uses a finite element model to analyze the weakest positions of the vertical stiffness of the suspension bridge, the two quarter-span areas, and then tensions the diagonal cables 5 in a highly targeted manner, and adds initial weight blocks at the anchor points where the diagonal cables 5 are anchored to the main beam 1, so that the diagonal cables 5 and the cross cables 41 are both taut, which not only prevents the main beam 1 from deforming upward, but also increases the tensile stress inside the stiffening cables, satisfying the first element of increasing the vertical stiffness mentioned above.

[0053] Afterwards, an iterative analysis is performed, counterweights are added, and the dead load tension of the cables and stay cables after weighting is updated. The specifications of the stay cables are then revised, and the vertical displacement envelope of the main beam is re-extracted until the vertical displacement at the quarter-span of the main beam is no greater than the vertical displacement at the mid-span, thus satisfying the second element of increasing vertical stiffness. The design method of this application uses cyclic iterative analysis to ultimately ensure that the dead load tension of the cross-cable 41 reaches the dead load tension of the non-cross-cable, and the vertical component of the dead load tension of the stay cables is greater than or equal to the dead load tension of the cross-cable 41, thereby tautening both the cables and the stay cables. At the same time, the vertical displacement at the quarter-span of the main beam is no greater than the vertical displacement at the mid-span, achieving the optimal vertical stiffness state for the suspension bridge. This is an ingenious design with strong practicality.

[0054] Furthermore, in step S2 and step S4, after determining the dead load cable forces of the slings and the stay cables, the following steps are included:

[0055] The main cable 3 is form-finded to determine a reasonable bridge state, and the force distribution of the suspenders and the stay cables is always ensured not to affect the linear shape of the main cable 3, and to maintain it in a good linear state.

[0056] Furthermore, in step S2, the initial specifications of the stay cables 5 are determined, including:

[0057] The dead load cable forces of the cross cables 41 and the stay cables 5 are determined according to the principle of equal division of vertical force, and the initial specifications of the stay cables 5 are determined based on the dead load cable forces of the stay cables 5. The principle of equal division of vertical force means that the vertical component of the dead load cable force of the stay cables 5 and the dead load cable force of the cross cables 41 are both 50% of the total weight of the main beam segment and the ballast block.

[0058] In step S4, before the dead load tension of the cross sling 41 reaches the dead load tension of the non-cross sling, the dead load tension of the cross sling 41 and the stay cable 5 is determined according to the principle of equal vertical force division. The dead load tension of the non-cross sling is determined by the weight of the main beam segment.

[0059] Furthermore, each group of stay cables 5 is divided into main span side stay cables 51 and side span side stay cables 52 along both sides of the bridge tower 2. The ends of the side span side stay cables 52 are centrally anchored to the side span piers 7 or anchors 6, and the ends of the main span side stay cables 51 are dispersedly anchored to the four span areas of the main beam 1.

[0060] In step S2, the horizontal components of the dead load cable forces of the main span side stay cables 51 and the side span side stay cables 52 are equal in magnitude and opposite in direction, and no additional horizontal components are generated to affect other structures of the suspension bridge.

[0061] In one embodiment, each group of stay cables 5 includes one or more stay cables, and the ends of the stay cables 5 are anchored in the quarter-span region of the main beam 1. For example, each group of stay cables 5 includes three stay cables 5, with the end of the middle stay cable 5 anchored exactly at the quarter-span of the main beam 1, that is, exactly one-quarter of the length of the main beam 1 between the two pylons 2. The ends of the remaining two stay cables 5 are anchored to the main beam 1 longitudinally forward and backward along the quarter-span. That is, the anchorage positions of the second and third stay cables 5 are staggered relative to the quarter-span, but also fall within the quarter-span region.

[0062] Figure 2 This chart compares the vertical displacement of the main beam of a 1500m single-span suspension bridge before and after the installation of the stiffening cable structure proposed in this application. The figure, combined with actual data, shows that the vertical displacement envelope curve of main beam 1 is flatter after the adoption of the stiffening cable structure proposed in this application, and the vertical stiffness of the structure is increased from 1 / 280 to 1 / 350, a 25% increase.

[0063] In the description of this application, it should be noted that the terms "upper" and "lower" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application. Unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be internal communication between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to the specific circumstances.

[0064] It should be noted that, in this application, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the sentence "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device comprising the element.

[0065] The foregoing is merely a list of specific embodiments of the present application, intended to enable those skilled in the art to understand and implement the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features of the present application.

Claims

1. A design method for a stiffening cable structure of a suspension bridge, characterized in that: The stiffening cable structure comprises two groups of stay cables (5) and a plurality of slings; the two ends of each sling are respectively fixed to the main beam (1) and the main cable (3) of the suspension bridge; the two groups of stay cables (5) are symmetrically arranged along the longitudinal direction of the main beam (1); each group of stay cables (5) is anchored across a bridge tower (2), and each group of stay cables (5) comprises a plurality of stay cables (5), and two stay cables symmetrically arranged at the same location of the two groups of stay cables (5) are anchored at the same height of the two bridge towers (2); Each group of inclined cables (5) is divided into main span side inclined cables (51) and side span side inclined cables (52) along both sides of the bridge tower (2), the ends of the side span side inclined cables (52) are centrally anchored to the side span piers (7) or anchors (6), and the ends of the main span side inclined cables (51) are dispersedly anchored to the four sub-span areas of the main beam (1); the horizontal components of the dead load cable forces of the main span side inclined cables (51) and the side span side inclined cables (52) are equal in magnitude and opposite in direction; The design method comprises the following steps: S1. Establish a finite element model of a suspension bridge, analyze the vertical stiffness of the suspension bridge under the action of vertical moving load, and obtain a W-shaped vertical displacement extreme envelope diagram of the main beam (1) following the main cable (3), which is small in the middle of the span and large in the quarter span; S2. Two groups of initial-specification stay cables (5) are tensioned in two quarter-span regions with the weakest vertical stiffness, one side of each group of stay cables (5) is anchored to the side span pier (7) or anchorage (6) of the suspension bridge, and the other side is anchored to the quarter-span region of the main beam (1); the quarter-span region refers to the range of positive and negative set lengths along the length direction of the main beam (1) at the quarter-span; the slings (4) located at the same longitudinal position of the quarter-span region of the stay cables (5) are cross slings (41), and initial weight blocks are added to the anchor points where the stay cables (5) are anchored to the main beam (1); S3. Apply vertical moving load and re-extract the vertical displacement extreme value envelope diagram of the main beam; compare the vertical displacement extreme value at the quarter span with the vertical displacement extreme value at the mid-span. If it is greater, go to S4; if not, end; S4, adding a local ballast block at the anchor point where the inclined cable (5) is fixed to the main beam (1); when the constant load cable force value of the cross sling (41) reaches the constant load cable force value of the non-cross sling, the constant load cable force value of the cross sling (41) will no longer increase, and the remaining constant load weight will be allocated to the inclined cable (5); after updating the ballasted sling and the constant load cable force of the inclined cable, the specification of the inclined cable is corrected, and the process returns to S3; after S3 and S4 are cycled for more than two times, the process ends, and the final specification of the inclined cable and the total weight of the final ballast block are obtained.

2. The method for designing a stiffening cable structure of a suspension bridge according to claim 1, wherein: In step S2 and step S4, after determining the dead load cable forces of the slings and the stay cables, the following steps are included: The main cable (3) is subjected to shape finding to determine a reasonable bridge state.

3. The method for designing a stiffening cable structure of a suspension bridge according to claim 1, wherein: In step S2, the initial specifications of the stay cables (5) are determined, including: The constant load cable forces of the cross sling (41) and the inclined cable (5) are determined according to the principle of equal division of vertical force, and the initial specifications of the inclined cable (5) are determined according to the constant load cable forces of the inclined cable (5); the principle of equal division of vertical force means that the vertical component of the constant load cable force of the inclined cable (5) and the constant load cable force of the cross sling (41) are both 50% of the total weight of the main beam segment and the ballast block.

4. The method for designing a stiffening cable structure for a suspension bridge according to claim 1, wherein: The plurality of suspension cables (4) of the stiffening cable structure are vertically arranged at equal intervals; the main cable (3) is bent at the tops of the two bridge towers (2), and its two ends are anchored in two anchors (6) respectively.

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