A new type of auxiliary cable-stayed bridge and its form-finding method

Abstract

The present invention relates to the technical field of cable-stayed bridges, and particularly to a novel auxiliary-cable cable-stayed bridge and a form-finding method thereof. The novel auxiliary-cable cable-stayed bridge comprises components including a main tower, a secondary tower, a main beam, a stay cable, a main cable, and auxiliary cables. The secondary tower is arranged at an auxiliary pier or side pier. The main cable crosses the saddle at the top of the secondary tower and the main tower, and is anchored at both ends to an anchor structure. The main cable is higher than the cable surface height of the stay cable, providing auxiliary elastic support for the stay cable. The two ends of the stay cable are respectively connected to the main tower and the main beam. One end of the auxiliary cable is connected to the main cable by a cable clamp, and the other end is connected in series with a plurality of long cables. The corresponding form-finding method includes a form-finding method for the stay cable and a form-finding method for the main cable. The present invention utilizes a method of connecting the auxiliary cables in series with the stay cables to reduce the horizontal projection length and deadweight sag of a single cable unit, increase the equivalent elastic modulus of the long cable, and provide greater support stiffness for the main beam; the form-finding method is very convenient and facilitates determination of the linear shape of the stay cable and the main cable.

Description

Technical Field

[0001] The present invention relates to the technical field of cable-stayed bridges, in particular to a novel auxiliary cable-stayed bridge and a shape-finding method thereof. Background Art

[0002] The superstructure of a cable-stayed bridge consists of a main tower, a bridge deck system, and inclined cables. It is a bridge in which the deck system is mainly subjected to compression (dense cables) or bending (sparse cables), and the supporting system is mainly subjected to tension by inclined cables and compression by the main tower. Due to its advantages such as large spanning capacity, convenient construction, and good mechanical properties, cable-stayed bridges are widely used in both highways and railways.

[0003] The current conventional cable-stayed bridge has a low equivalent elastic modulus of the long cables and a large longitudinal displacement of the structure, which makes it inconvenient to find the form in finite element simulation. Therefore, a new type of auxiliary cable-stayed bridge and its form-finding method are needed to solve the above problems. Summary of the Invention

[0004] The present invention provides a novel auxiliary cable-stayed bridge and a form-finding method thereof, which can overcome the problems of low equivalent elastic modulus and large longitudinal displacement of the structure.

[0005] According to the present invention, a novel auxiliary cable-stayed bridge includes a main beam, a main tower, a secondary tower, a saddle, a main cable, a stay cable, an auxiliary cable, an anchor, a side pier, and an auxiliary pier; the secondary tower is arranged at the position of the side pier or the auxiliary pier; a saddle is provided on the top of the secondary tower and the top of the main tower, and the main cable crosses the saddle on the top of the secondary tower and the main tower; anchors are provided at the foundations on both sides, and both ends of the main cable are anchored on the corresponding anchors; the height of the main cable is higher than the cable surface height of the stay cable, providing auxiliary elastic support for the stay cable; both ends of the stay cable are respectively connected to the main beam and the main tower; one end of the auxiliary cable is connected to the main cable, and the other end is connected in series with multiple stay cables.

[0006] Preferably, the main cable is a space cable, each main cable is composed of a plurality of strands, and each strand is composed of a plurality of zinc-aluminum alloy-coated high-strength parallel steel wires.

[0007] Preferably, the auxiliary cables are parallel steel wire cables arranged obliquely, the steel wires are high-strength steel wires, and each parallel steel wire cable is composed of several steel wires.

[0008] Preferably, one end of the auxiliary cable is connected to the main cable via a cable clamp.

[0009] Preferably, the auxiliary tower can be a reinforced concrete tower, a steel structure bridge tower or a steel-concrete composite bridge tower.

[0010] The present invention provides a novel form-finding method for a cable-stayed bridge with auxiliary cables, which adopts the above-mentioned novel cable-stayed bridge with auxiliary cables. The form-finding method for the cable-stayed bridge is performed in the following four steps:

[0011] 1) Determine the initial positions A, B, M, and N of the segmentation points of the cable according to the catenary expression of the cable. Assume that the auxiliary cable is extended in a straight line in the opposite direction to the main cable and intersects with the empty cable line of the main cable to determine the initial position O of the main cable anchorage point.

[0012] 2) Install a temporary fixed support Z0 on the main cable anchor point O, install the first auxiliary cable unit L1, move point A to the designed position by calculating the tension force, install a temporary fixed support Z1 at point A, and install auxiliary cable units L2...L in this way. N-1 , and install the corresponding temporary fixed support Z2...Z N-1 ;

[0013] 3) Install the last unit L of the auxiliary cable N After the segment point N is stretched into place, there is an unbalanced force on each temporary fixed support. First, calculate and adjust the auxiliary cable unit L. N-1 The cable force makes the support Z N-1 The unbalanced force approaches 0, and the support Z is removed. N-1 , the spatial coordinates of point M have been determined;

[0014] 4) Adjust the tension of the auxiliary cable units from bottom to top in sequence according to the above method. Adjust one unit and remove the corresponding temporary fixed support. After removing the support Z1, the new line shape of all the inclined cables is obtained.

[0015] After the stay cables are completed, the main cables are then found in the following four steps:

[0016] a) After establishing a separate spatial model of the main cables of the entire bridge according to the main cable aerial cable shape, fixed supports are installed at the IP points of the main tower and the auxiliary tower. The constraints of the anchorage positions are consistent with the finite element model of the entire bridge. The auxiliary cable unit L1 force determined by the above method is applied as a concentrated load to the main cable point O. At this time, the main cable shape changes;

[0017] b) By adjusting the horizontal component of the shaping internal force of the main cable of the main span at the IP point, the cable core elevation at the mid-span point is returned to the cable core elevation corresponding to the original design rise-span ratio. The main cable vertical coordinate is iterated once. At this time, the main cable linear shape changes, and the cable core elevation at the mid-span point will still deviate from the cable core elevation corresponding to the original design rise-span ratio. Repeated iterations according to the above method are performed. When the main cable displacement of the two previous iterations is less than the convergence criterion, the new design elevation of the main cable is reached. The main cable linear shape of the main span at this time is the cable linear shape of the completed bridge.

[0018] c) Based on the principle of equal horizontal forces, the horizontal components of the internal forces of the main cables of the second side span and the first side span at the IP point of the secondary tower are adjusted in sequence to make the longitudinal force of the support at the IP point of the secondary tower equal to 0. The cable core elevations of the main cables of the second side span and the first side span are iterated. When the displacements of the main cables of the two previous and subsequent iterations are less than the convergence criterion, the new design elevation of the main cables is reached.

[0019] d) After obtaining the main cable linear shape, substitute the new linear coordinates of the main cable back into the full-bridge spatial finite element model.

[0020] The stay cables and main cables are in equilibrium under the action of the dead load, and the model of the completed bridge is thus established.

[0021] This invention utilizes auxiliary cables in series with the stay cables, aiming to add auxiliary cable constraints to the long stay cables, splitting the long cables in two. This reduces the horizontal projection length of a single cable unit, resulting in a higher equivalent elastic modulus while also reducing the deadweight sag of the individual cables. The auxiliary towers provide support for the main cables and vertical and lateral support for the main beams. The form-finding method of this invention is highly convenient, facilitating the determination of the linear shape of the stay cables and main cables. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a structural schematic diagram of a novel auxiliary cable-stayed bridge in an embodiment;

[0023] Figure 2 Schematic diagram of the structure of the auxiliary tower in the embodiment;

[0024] Figure 3 Schematic diagram of the equivalent elastic modulus reduction coefficient of the semi-structured cables of a conventional cable-stayed bridge in the embodiment;

[0025] Figure 4 : is a diagram of a full-bridge spatial finite element model in the embodiment;

[0026] FIG5( a ) is a schematic diagram of tensioning the first auxiliary cable in an embodiment;

[0027] FIG5( b ) is a schematic diagram of tensioning the Nth auxiliary cable in an embodiment;

[0028] Figure 6 This is a schematic diagram of the main span main cable line shape after adding concentrated force balance in the embodiment;

[0029] FIG7( a ) is a schematic diagram of the main cable line shape of the first span of the side span after balancing in an embodiment;

[0030] FIG7( b ) is a schematic diagram of the main cable line shape of the second span of the side span after balancing in an embodiment. DETAILED DESCRIPTION

[0031] In order to further understand the content of the present invention, the present invention is described in detail with reference to the accompanying drawings and embodiments. It should be understood that the embodiments are merely for explaining the present invention and are not intended to limit the present invention.

[0032] Example

[0033] like Figure 1As shown, this embodiment provides a novel auxiliary cable-stayed bridge, which comprises a main beam 1, a main tower 2, a secondary tower 3, a saddle 4, a main cable 5, a stay cable 6, an auxiliary cable 7, an anchor 8, a side pier 9, and an auxiliary pier 10; the secondary tower 3 is arranged at the side pier 9 or the auxiliary pier 10 (the side pier 9 and the auxiliary pier 10 are both located below the main beam 1). Figure 1 The middle auxiliary tower 3 is arranged at the auxiliary pier 10; saddles 4 are provided on the top of the auxiliary tower 3 and the top of the main tower 2, and the main cable 5 crosses the saddles 4 on the top of the auxiliary tower 3 and the top of the main tower 2. Anchors 8 are provided at the foundations on both sides, and both ends of the main cable 5 are anchored on the corresponding anchors 8; the height of the main cable 5 is higher than the cable surface height of the inclined cable 6, providing auxiliary elastic support for the inclined cable 6; the two ends of the inclined cable 6 are respectively connected to the main beam 1 and the main tower 2; one end of the auxiliary cable 7 is connected to the main cable 5, and the other end is connected in series with multiple long inclined cables 6.

[0034] This embodiment adds a main cable 5, auxiliary cable 7 and auxiliary tower 3, while the main beam 1 and main tower 2 structures remain unchanged. The main cable 5 adopts a space cable with a span ratio of 1 / 10. Each main cable 5 is composed of 79 strands, each of which is composed of 91 zinc-aluminum alloy coated high-strength parallel steel wires with a diameter of 5.1 mm and a standard tensile strength of 2060 MPa. The net area of ​​a single main cable is 146858.37 mm 2 The auxiliary cable 7 is arranged in a parallel wire rope and passes through the cable clamp on the inclined cable 6. The steel wire is a high-strength steel wire with a diameter of 7mm and a standard tensile strength of 1960MPa. Each parallel wire rope consists of 190 steel wires, and the total area of ​​each wire rope is 7312.1mm. 2 .

[0035] like Figure 2 As shown, the auxiliary tower 3 adopts C60 reinforced concrete tower with three steel-concrete composite beams. The upper tower column is 86m high, the middle tower column is 110m high, and the lower tower column is 80m high. The total height of the auxiliary tower is 284m, and the tower column wall thickness is 2m.

[0036] The novel auxiliary-cable cable-stayed bridge of this embodiment builds upon a conventional cable-stayed bridge by adding a main cable 5, auxiliary towers 3, and auxiliary cables 7. This solution addresses the low equivalent elastic modulus and large longitudinal displacement of the long cables in conventional cable-stayed bridges. By connecting the long mid-span cable in series with the auxiliary cables 7, the equivalent elastic modulus of the long cables is increased, thereby increasing their axial stiffness. The additional main cables 5 also reduce the longitudinal deflection of the towers, and consequently, the longitudinal displacement of the main beam 1. This bridge type differs from conventional cable-stayed and suspension-coordinated bridges in that the main cables 5 serve as a support structure for anchoring the auxiliary cables and are not connected to the main beam via slings. The load acting on the main beam is primarily transmitted to the towers via the cables, thus remaining within the scope of a cable-stayed bridge.

[0037] From the perspective of structural layout, the purpose of setting up the auxiliary tower 3 is: ① The main cable 5 serves as the anchoring platform for the auxiliary cable 7 and must be higher in spatial elevation than the cable-stayed cable 6. However, the cable-stayed bridge adopts a side-to-mid-span ratio of 0.5, and the main cable with a large side span is difficult to meet the anchoring requirements. Therefore, the auxiliary tower 3 is required to provide support for the main cable 5; ② The auxiliary tower 3 is used to replace the auxiliary pier 10 to provide vertical and lateral support for the main beam 1.

[0038] Conventional auxiliary cables are usually made by connecting a certain number of stay cables in series and then anchoring them on the main beam to form a cable net structure with the stay cables. They are used as a vibration reduction measure for the extra-long stay cables of ultra-long span cable-stayed bridges. However, the auxiliary cables of this embodiment lift the stay cables by tensioning them, thereby reducing the sag of the stay cables and increasing their axial stiffness.

[0039] The sag effect of the cable is part of the geometric nonlinearity calculation of the cable-stayed bridge. The linear shape of the cable under the action of its own weight is a catenary. When establishing the finite element model, if linear truss elements are used for simulation, the elastic modulus of the material needs to be reduced using the Ernst formula:

[0040]

[0041] Where E eq represents the equivalent elastic modulus after reduction, E0 is the elastic modulus of the cable material, γ is the bulk density of the cable material, L is the horizontal projection length of a single cable, and σ0 is the axial stress of a single cable.

[0042] As can be seen from the above formula, the factors affecting the equivalent elastic modulus of a stay cable are primarily its material, horizontal projection length, and cable stress. This embodiment utilizes auxiliary cables in series with the stay cables to add constraints to the long stay cables, splitting them in two and reducing the horizontal projection length of a single cable unit. This results in a higher equivalent elastic modulus while also reducing the deadweight sag of the individual cables.

[0043] Auxiliary cables are provided to improve the equivalent elastic modulus of the cable-stayed cables. First, the equivalent elastic modulus of all cables on a conventional cable-stayed bridge should be calculated. In this embodiment, the cable with the lowest equivalent elastic modulus on a single cable plane of a conventional cable-stayed bridge is used as the control standard. The equivalent elastic modulus of all cables on a single cable plane must meet a certain standard to determine the number of cables that need to be connected in series. For ease of explanation, the elastic modulus reduction coefficient is defined as the ratio of the equivalent elastic modulus of the cable to the elastic modulus of the cable steel wire material, i.e., E / E0. The equivalent elastic modulus reduction coefficient of the semi-structural cable-stayed cables of a conventional cable-stayed bridge is as follows: Figure 3 shown.

[0044] Make the equivalent elastic modulus of all inclined cables greater than or equal to 0.85E0. At this time, 36 inclined cables need to be connected in series. If the series connection starts from the midpoint of the end inclined cable, there is not enough space for the series connection of the auxiliary cables. The series connection can be started from the three-point point of the end inclined cable. The auxiliary cables are perpendicular to the midpoint of the end inclined cable to obtain the best lifting efficiency. A inclined cable is represented by a cable unit before anchoring. After the auxiliary cables are connected in series, one cable unit is divided into 2-3 cable units by the segmentation point and connected to the auxiliary cable unit at the same node.

[0045] Finite element simulation

[0046] The full bridge spatial finite element model is as follows Figure 4 As shown, the material properties used are consistent with those of a cable-stayed-suspension bridge. The main cables, main towers, and auxiliary towers are connected at the IP point using a master-slave connection to constrain the nodes' six degrees of freedom. The loose cable saddles are simulated as rigid arms, releasing the longitudinal rotational degrees of freedom. The remaining boundary conditions are the same as for cable-stayed bridges.

[0047] First, a conventional cable-stayed bridge model is established and the main cable unit is installed. At this time, the main cable and the stay cable are in the catenary shape, and the main cable is still in the empty cable state. Then the auxiliary cable unit is installed and tensioned. Because the main cable and the stay cable are simultaneously affected by the tension of the auxiliary cable, changes in the cable force and the cable anchorage position will affect the cabling shape of the stay cable and the main cable. Therefore, it is necessary to consider the cable net structure and the main cable and find an accurate modeling method for finding the static equilibrium position after taking into account the geometric nonlinearity.

[0048] This embodiment adopts a modeling method for batch tensioning of the inclined cables using a multiple-tensioning method. Taking the tensioning of an auxiliary cable as an example, as shown in Figures 5(a) and 5(b), the auxiliary cable L1 and the outer inclined cables A1A2 are first connected and tensioned. After the anchor point A moves to the design position, the auxiliary cable L2 is connected to the second inclined cable B1B2 and tensioned. At this time, the anchor point A is forced to move downward, and L1 and L2 need to be re-tensioned to return points A and B to the design position. After multiple tensioning, the position of each anchor point is ensured to be at the design position, completing the tensioning and anchoring of one auxiliary cable. Figure 5(a) is a schematic diagram of tensioning the first inclined cable, and Figure 5(b) is a schematic diagram of tensioning the Nth inclined cable.

[0049] In actual modeling, the form-finding method of a new auxiliary cable-stayed bridge in this embodiment is:

[0050] The form-finding method for the stay cable is carried out in four steps:

[0051] 1) Determine the initial positions A, B, M, and N of the segmentation points of the cable according to the catenary expression of the cable. Assume that the auxiliary cable is extended in a straight line in the opposite direction to the main cable and intersects with the empty cable line of the main cable to determine the initial position O of the main cable anchorage point.

[0052] 2) Install a temporary fixed support Z0 on the main cable anchor point O, install the first auxiliary cable unit L1, move point A to the designed position by calculating the tension force, install a temporary fixed support Z1 at point A, and install auxiliary cable units L2...L in this way. N-1 , and install the corresponding temporary fixed support Z2...Z N-1 ;

[0053] 3) Install the last unit L of the auxiliary cable N After the segment point N is stretched into place, there is an unbalanced force on each temporary fixed support. First, calculate and adjust the auxiliary cable unit L. N-1 The cable force makes the support Z N-1 The unbalanced force approaches 0, and the support Z is removed. N-1 , the spatial coordinates of point M have been determined;

[0054] 4) Adjust the tension of the auxiliary cable units from bottom to top in sequence according to the above method. Adjust one unit and remove the corresponding temporary fixed support. After removing the support Z1, the new line shape of all the inclined cables is obtained.

[0055] After the stay cables are completed, the main cables are then found in the following four steps:

[0056] a) After establishing a separate spatial model of the main cable of the entire bridge according to the main cable aerial cable shape, fixed supports are installed at the IP points of the main tower and the auxiliary tower. The constraints of the anchorage position are consistent with the finite element model of the entire bridge. The auxiliary cable unit L1 force determined by the above method is applied as a concentrated load to the main cable point O. At this time, the main cable shape changes, as shown in the following example. Figure 6 As shown;

[0057] b) By adjusting the horizontal component of the internal force of the main cable of the main span at the IP point (i.e., adjusting the stress-free length of the main cable), the cable core elevation at the mid-span point is returned to the cable core elevation corresponding to the original design rise-span ratio. The main cable vertical coordinate is iterated once. At this time, the main cable linear shape changes, and the cable core elevation at the mid-span point will still deviate from the cable core elevation corresponding to the original design rise-span ratio. Repeated iterations according to the above method are performed. When the main cable displacements of the two previous and subsequent iterations are less than the convergence criterion, the new design elevation of the main cable is reached. The main cable linear shape of the main span at this time is the cable linear shape of the completed bridge.

[0058] c) According to the principle of equal horizontal forces, the horizontal components of the internal forces of the main cables of the second side span and the first side span at the IP point of the secondary tower are adjusted in sequence to make the longitudinal force of the support at the IP point of the secondary tower equal to 0. The cable core elevations of the main cables of the second side span and the first side span are iterated. When the displacements of the main cables in the two previous and subsequent iterations are less than the convergence criterion, the new design elevation of the main cables is reached. The corrected equilibrium line of the main cables of the side span is shown in Figures 7(a) and 7(b).

[0059] d) After obtaining the main cable linear shape, substitute the new linear coordinates of the main cable back into the full-bridge spatial finite element model.

[0060] The redesigned stay cables and main cables are in equilibrium under the action of the dead load, and the model of the completed bridge is thus established.

[0061] The above is a schematic description of the present invention and its embodiments, which is not restrictive. The drawings show only one embodiment of the present invention, and the actual structure is not limited thereto. Therefore, if a person skilled in the art is inspired by this and, without departing from the purpose of the present invention, designs a structure and embodiment similar to this technical solution without inventiveness, they shall fall within the scope of protection of the present invention.

Claims

1. A new form-finding method for a cable-stayed bridge with auxiliary cables, characterized by: The novel auxiliary cable-stayed bridge comprises a main beam (1), a main tower (2), a secondary tower (3), a saddle (4), a main cable (5), a stay cable (6), an auxiliary cable (7), an anchor (8), a side pier (9), and an auxiliary pier (10); the secondary tower (3) is arranged at the position of the side pier (9) or the auxiliary pier (10); the top of the secondary tower (3) and the top of the main tower (2) are both provided with a saddle (4), and the main cable (5) crosses the saddle (4) on the top of the secondary tower (3) and the top of the main tower (2); anchors (8) are respectively provided at the foundations on both sides, and both ends of the main cable (5) are anchored on the corresponding anchors (8); the height of the main cable (5) is higher than the cable surface height of the stay cable (6), providing auxiliary elastic support for the stay cable (6); both ends of the stay cable (6) are respectively connected to the main beam (1) and the main tower (2); one end of the auxiliary cable (7) is connected to the main cable (5), and the other end is connected in series with multiple stay cables (6); The form-finding method for the stay cable is carried out in four steps: 1) Determine the initial positions A, B, M, and N of the segmentation points of the cable according to the catenary expression of the cable. Assume that the auxiliary cable is extended in a straight line in the opposite direction to the main cable and intersects with the empty cable line of the main cable to determine the initial position O of the main cable anchorage point. 2) Install a temporary fixed support Z0 on the main cable anchor point O, install the first auxiliary cable unit L1, move point A to the designed position by calculating the tension force, install a temporary fixed support Z1 at point A, and install auxiliary cable units L2...L in this way. N-1 , and install the corresponding temporary fixed support Z2...Z N-1 ; 3) Install the last unit L of the auxiliary cable N After the segment point N is stretched into place, there is an unbalanced force on each temporary fixed support. First, calculate and adjust the auxiliary cable unit L. N-1 The cable force makes the support Z N-1 The unbalanced force approaches 0, and the support Z is removed. N-1 , the spatial coordinates of point M have been determined; 4) Adjust the tension of the auxiliary cable units from bottom to top in sequence according to the above method. Adjust each unit and remove the corresponding temporary fixed support. After removing support Z1, the new line shape of all the inclined cables is obtained; After the stay cables are completed, the main cables are then found in the following four steps: a) After establishing a separate spatial model of the main cables of the entire bridge according to the main cable aerial cable shape, fixed supports are installed at the IP points of the main tower and the auxiliary tower. The constraints of the anchorage positions are consistent with the finite element model of the entire bridge. The auxiliary cable unit L1 force determined by the above method is applied as a concentrated load to the main cable point O. At this time, the main cable shape changes; b) By adjusting the horizontal component of the shaping internal force of the main cable of the main span at the IP point, the cable core elevation at the mid-span point is returned to the cable core elevation corresponding to the original design rise-span ratio. The main cable vertical coordinate is iterated once. At this time, the main cable linear shape changes, and the cable core elevation at the mid-span point will still deviate from the cable core elevation corresponding to the original design rise-span ratio. Repeated iterations according to the above method are performed. When the main cable displacement of the two previous iterations is less than the convergence criterion, the new design elevation of the main cable is reached. The main cable linear shape of the main span at this time is the cable linear shape of the completed bridge. c) Based on the principle of equal horizontal forces, the horizontal components of the internal forces of the main cables of the second side span and the first side span at the IP point of the secondary tower are adjusted in sequence to make the longitudinal force of the support at the IP point of the secondary tower equal to 0. The cable core elevations of the main cables of the second side span and the first side span are iterated. When the displacements of the main cables of the two previous and subsequent iterations are less than the convergence criterion, the new design elevation of the main cables is reached. d) After obtaining the main cable alignment, the new main cable alignment coordinates are substituted back into the full-bridge spatial finite element model. The alignments of the stay cables and main cables are in equilibrium under the action of the dead load, and the model of the completed bridge is thus established.

2. The form-finding method for a novel auxiliary cable-stayed bridge according to claim 1 is characterized in that: The main cable (5) adopts a space cable, and each main cable (5) is composed of a plurality of cable strands, and each cable strand is composed of a plurality of zinc-aluminum alloy-coated high-strength parallel steel wires.

3. The form-finding method for a novel auxiliary cable-stayed bridge according to claim 2 is characterized in that: The auxiliary rope (7) is arranged in an inclined manner using parallel steel wires, the steel wires are high-strength steel wires, and each parallel steel wire rope is composed of a plurality of steel wires.

4. The form-finding method for a novel auxiliary cable-stayed bridge according to claim 3 is characterized by: One end of the auxiliary cable (7) is connected to the main cable (5) through a cable clamp.

5. The form-finding method for a novel auxiliary cable-stayed bridge according to claim 4 is characterized in that: The auxiliary tower (3) can be a reinforced concrete tower, a steel structure bridge tower or a steel-concrete composite bridge tower.

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