Construction method for reducing tension stress of main beam of cable-stayed bridge with composite beam

Abstract

The application discloses a kind of combined beam cable-stayed bridge girder tensile stress reduction control construction methods, comprising the following steps: S1, the pre-arch height theoretical value of each section steel beam is calculated, and each section steel beam reaches corresponding pre-arch height before assembly;S2, each section steel beam is pushed to design position using push method, and steel girder installation is completed;Each section steel beam is supported by temporary buttress;S3, from small mileage to large mileage direction, deck is installed in block;S4, the concrete is poured at the wet joint between adjacent two deck panels;S5, deck prestressed construction: tensioning the prestressed steel strand in each deck panel, completing girder construction;S6, each cable is installed, and each cable on both sides of bridge is sequentially symmetrically tensioned from far tower end to near tower end.The application can effectively reduce the tensile stress of girder concrete, and guarantee the durability of bridge structure.

Description

Technical Field

[0001] This invention relates to the field of composite beam cable-stayed bridge construction. More specifically, this invention relates to a construction method for controlling the tensile stress reduction of the main girder of a composite beam cable-stayed bridge. Background Technology

[0002] The main girder of a combined cable-stayed bridge is generally a "steel main girder-precast PC bridge deck" structure. Cantilever assembly is commonly used in combined cable-stayed bridges, typically employing a bridge deck crane for main girder construction. After the bridge deck is constructed and prestressed, the stay cables are tensioned immediately. For combined cable-stayed bridges where the girder is constructed first and then the cables are tensioned, the main girder is often constructed using a scaffolding method. The steel main girder is constructed first, then the precast concrete bridge deck is installed using equipment such as gantry cranes. The wet joints of the bridge deck are constructed, followed by prestressing of the main girder. Once all prestressing is completed, the stay cables are tensioned. In the case of a large spacing between the supports for the main girder in the first-beam-then-cable-stayed construction, the stay cables are usually tensioned by first installing them near the tower end and then at the far tower end. This can cause the overall displacement of the main girder structure to cause an upward arch, easily leading to excessive tensile stress in the concrete near the wet joints and anchor plates. This can result in prestress loss within the girder and even cracking of the wet joint concrete, affecting the durability of the bridge structure. Summary of the Invention

[0003] One object of the present invention is to solve at least the above-mentioned problems and to provide at least the advantages that will be described later.

[0004] To achieve these objectives and other advantages according to the present invention, a construction method for controlling the tensile stress reduction of the main girder of a combined beam cable-stayed bridge is provided, comprising the following steps:

[0005] S1. Calculate the theoretical value of the pre-camber height of each steel beam segment and ensure that each steel beam segment reaches the corresponding pre-camber height before assembly.

[0006] S2. The steel beam segments are pushed to their designed positions using the jacking method to complete the installation of the main steel beam; each steel beam segment is supported by temporary supports.

[0007] S3. Install the bridge deck in sections from the smaller mileage to the larger mileage.

[0008] S4. Pour concrete at the wet joint between two adjacent bridge deck panels;

[0009] S5. Bridge deck prestressing construction: Tensioning the prestressed steel strands in each bridge deck to complete the main beam construction;

[0010] S6. Install each stay cable and tension each stay cable on both sides of the bridge symmetrically from the far tower end to the near tower end.

[0011] Preferably, in step S1, finite element software is used to simulate the vertical deformation at each node on each segment of the steel beam under the standard working condition of constant load; the longitudinal displacement of each segment of the steel beam is taken as the horizontal axis and the vertical deformation as the vertical axis, the longitudinal displacement of each node on each segment of the steel beam is extracted, and the lower disturbance curve of each segment of the steel beam is obtained by fitting, and the value of each node corresponding to the lower disturbance curve is the pre-camber height of each node.

[0012] Preferably, when the combined beam cable-stayed bridge is a double-tower double-cable-stayed bridge, in step S5, the prestressed steel strands in the bridge deck at the mid-span are tensioned first, and then the prestressed steel strands in the bridge deck at the side span are tensioned.

[0013] Preferably, the prestressed steel strands include multiple long prestressed strands and multiple short prestressed strands arranged alternately along the transverse direction of the bridge; at the same location of the bridge deck, the long prestressed strands are tensioned first, and then the short prestressed strands are tensioned.

[0014] Preferably, the prestressed tendons are tensioned in a direction from the center of the main beam to both sides, whether tensioning long or short prestressed tendons or not, and the prestressed tendons on both sides of the center of the main beam are tensioned symmetrically.

[0015] Preferably, in step S6, during the tensioning process of the stay cables, the tension of each stay cable is controlled by monitoring the changes in the main beam alignment and the cable force of the stay cables.

[0016] Preferably, strain gauges are installed at the mid-span of the side span, at the main tower, at 1 / 4 of the middle span, at the mid-span of the middle span, and at 3 / 4 of the middle span of the main beam.

[0017] Preferably, in step S3, the bridge deck is laid by a gantry crane, and a track is provided on the main steel beam, along which the gantry crane moves; the trolley transporting the bridge deck uses the laid bridge deck as the transport channel.

[0018] Preferably, the concrete poured at the wet joint between two adjacent bridge deck panels contains steel fibers.

[0019] The present invention has at least the following beneficial effects:

[0020] 1. This invention calculates the pre-camber height of each steel beam segment and ensures that each steel beam segment reaches the corresponding pre-camber height before assembly. This not only guarantees the overall alignment of the main steel beam but also reduces the risk of concrete panel cracking caused by downward disturbance of the main steel beam under load.

[0021] 2. This invention pre-stresses the bridge deck, thereby applying pre-compression stress to the upper part of the main beam. This can offset some of the tensile stress generated by the subsequent tensioning of the stay cables, reducing the risk of concrete cracking.

[0022] 3. This invention employs a prestressing tensioning method for bridge deck prestressing by first tensioning the long prestressed tendons and then the short prestressed tendons, and by tensioning the mid-span first and then the side spans. This avoids tensile stress caused by uneven stress distribution in the main beam and reduces the risk of concrete cracking.

[0023] 4. This invention effectively reduces the tensile stress on the main beam during the tensioning process of the stay cables by installing the tensioning cables sequentially from the far end of the tower to the near end of the tower, thereby reducing the risk of concrete cracking.

[0024] 5. The construction method for controlling the tensile stress reduction of the main beam of the cable-stayed bridge provided by this invention is simple to operate. The prestressing of the main beam and the tensioning of the cable stays are basically formed in one step, and the tensile stress of the main beam concrete is close to zero, thus achieving the target of controlling the tensile stress reduction of the main beam and providing better protection for the durability of the bridge structure.

[0025] Other advantages, objectives and features of the present invention will become apparent in part from the following description, and in part from those skilled in the art through study and practice of the invention. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the main beam in one embodiment of the present invention;

[0027] Figure 2 This is a schematic diagram of the arrangement structure of the prestressed steel strands described in the above embodiments of the present invention;

[0028] Figure 3 This is a schematic diagram of the cable numbering sequence in the above embodiments of the present invention;

[0029] Figure 4 The stress diagram of the main beam is simulated using finite element software under the condition of prestressing the cable stays first and then the main beam, with the cable stays being tensioned from the near end of the tower to the far end of the tower.

[0030] Figure 5 The stress diagram of the main beam is simulated using finite element software under the condition of prestressing the main beam first and then tensioning the cable stays, with the cable stays being tensioned from the near end of the tower to the far end of the tower.

[0031] Figure 6 The stress diagram of the main beam is simulated using finite element software under the condition of prestressing the main beam first and then tensioning the cable stays, with the cable stays being tensioned from the far end of the tower to the near end of the tower. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to the accompanying drawings, so that those skilled in the art can implement it based on the description.

[0033] It should be noted that, unless otherwise specified, the experimental methods described in the following embodiments are all conventional methods, and the reagents and materials described are all commercially available unless otherwise specified. In the description of this invention, the terms "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0034] like Figures 1-6 As shown, the present invention provides a construction method for controlling the tensile stress reduction of the main girder of a combined beam cable-stayed bridge, comprising the following steps:

[0035] S1. Calculate the theoretical value of the pre-camber height of each steel beam segment 1, and ensure that each steel beam segment 1 reaches the corresponding pre-camber height before assembly;

[0036] S2. The steel beam segments 1 are pushed to their designed positions using the jacking method to complete the installation of the main steel beam; each steel beam segment 1 is supported by temporary supports 2.

[0037] S3. Install the bridge deck in sections from the smaller mileage to the larger mileage.

[0038] S4. Pour concrete at the wet joint between two adjacent bridge deck panels;

[0039] S5. Bridge deck prestressing construction: Tensioning the prestressed steel strands in each bridge deck to complete the main beam construction;

[0040] S6. Install each stay cable and tension each stay cable on both sides of the bridge symmetrically from the far tower end to the near tower end.

[0041] The above-mentioned technical solution has been successfully applied to a bridge project in Zhangzhou. The main bridge of this project is a double-tower, double-cable-stayed bridge with span combinations of 70m, 160m, and 70m. The bridge is 300m long and 36m wide. The main girder is a steel-concrete composite beam, and the main towers are teardrop-shaped towers. The entire bridge has 32 pairs of cables arranged in a spatial double-cable-stayed fan shape. Before step S1, the construction of the main piers and towers of the cable-stayed bridge has been completed.

[0042] First, in step S1, finite element software is used to simulate the vertical deformation at each node of each segment of the steel beam 1 under the standard working condition of constant load. Using the longitudinal displacement of each segment of the steel beam 1 as the horizontal axis and the vertical deformation as the vertical axis, the longitudinal displacement of each node of each segment of the steel beam 1 is extracted. The lower disturbance curve of each segment of the steel beam 1 is obtained through fitting, and the value corresponding to each node on the lower disturbance curve is the pre-camber height of each node. Based on the obtained pre-camber height, the steel beam 1 is set with the corresponding pre-camber height during processing and manufacturing, and then assembled.

[0043] Furthermore, in step S2, the steel beam segments 1 are pushed to their designed positions using a jacking method to complete the installation of the main steel beam, such as... Figure 1 As shown; before the stay cables are tensioned, each segment of the steel beam 1 is supported by temporary supports 2.

[0044] After the main steel beam is installed, step S3 is implemented, proceeding from the smaller mileage direction to the larger mileage direction, to install the bridge deck in sections. Specifically, in step S3, the bridge deck is laid using a gantry crane. Tracks are installed on the main steel beam, and the gantry crane moves along these tracks. A trolley transporting the bridge deck uses the already laid bridge deck as a transport channel to transport the bridge deck to the laying position. After the bridge deck is installed, concrete is poured at the wet joint between adjacent bridge deck sections. In step S4, to prevent the development of concrete cracks and improve its tensile strength, flexural strength, and shear strength, steel fibers are added to the concrete poured at the wet joint.

[0045] Before step S5, the tensile stress of the main beam under the standard value of dead load is simulated using finite element software. Calculations and analyses are performed, and the stress range of the bridge deck concrete under the "cable stays first, then main beam prestressing" condition is found to be -5.5 MPa to +2.0 MPa. Figure 4 As shown; under the condition of "prestressing the main girder first, then the stay cables", the stress range of the bridge deck concrete is -5.2MPa to +1.4MPa, as follows. Figure 5 As shown. Therefore, in this application, the construction sequence of first performing prestressed construction of the main beam and then installing tensioned stay cables is selected. By setting a pre-camber height for the steel beam 1 and simultaneously applying pre-compression stress to the upper part of the steel beam, some of the tensile stress generated by the subsequent tensioning of the stay cables can be offset, thereby reducing the risk of concrete cracking.

[0046] In the prestressed construction of the main girder, for a double-tower, double-cable-stayed bridge project in Zhangzhou, an intelligent tensioning system was used for tensioning, with tension force as the primary factor and the elongation of the prestressed steel strands as a reference for tension control. Specifically, the prestressed steel strands in the bridge deck at the mid-span were tensioned first, followed by the prestressed steel strands in the bridge deck at the side spans.

[0047] The prestressed steel strands include multiple long prestressed strands and multiple short prestressed strands alternately arranged along the transverse direction of the bridge; at the same location on the bridge deck, the long prestressed strands are tensioned first, followed by the short prestressed strands. That is, the long prestressed strands 3 in the middle span are tensioned first, followed by the short prestressed strands 4 in the middle span, then the long prestressed strands 5 in the side spans are tensioned, and finally the short prestressed strands 6 in the side spans are tensioned.

[0048] Furthermore, when tensioning long or short prestressed tendons, tensioning is carried out from the center of the main beam to both sides, and the prestressed tendons on both sides of the center of the main beam are tensioned symmetrically.

[0049] Before step S6, the tensile stress of the main beam under the standard value of dead load was simulated using finite element software. The calculation and analysis revealed that under the condition that the tensioning sequence of the stay cables was "from near the tower end to the far tower end," the stress range of the main beam was -5.2 MPa to +1.4 MPa. Figure 5 As shown; under the condition that the tensioning sequence of the stay cables is "from the far end of the tower to the near end of the tower", the stress range of the main beam is -4.9MPa to +0.1MPa. Figure 6 As shown. Therefore, in step S6, the stay cables on both sides of the bridge are tensioned symmetrically from the far tower end to the near tower end to further reduce the tensile stress on the main beam. Corresponding to the double-tower, double-cable-stayed bridge project in Zhangzhou, the stay cables on both towers are tensioned symmetrically and synchronously, both from the far tower end to the near tower end on both sides of the tower. Specifically, refer to... Figure 3 The stay cables on both sides of the bridge tower are arranged from the far tower end to the near tower end in l1, l2, l3 to l n If numbered, the tensioning sequence is to symmetrically tension l1, l2, l3 to l on both sides of the bridge in sequence. n .

[0050] In step S6, during the tensioning of the stay cables, the tension of each stay cable is controlled by monitoring the changes in the main beam alignment and the cable tension. The changes in the main beam alignment and the cable tension are monitored using conventional methods.

[0051] Furthermore, strain gauges were installed at the mid-span of the side spans, the main tower, the 1 / 4 mark of the middle span, the mid-span of the middle span, and the 3 / 4 mark of the middle span of the main girder. These strain gauges monitored the strain of the main girder during the cable tensioning process, and the stress of the main girder was calculated. In a bridge project in Zhangzhou, vibrating wire strain gauges were installed at all the above locations. The calculated stress of the main girder was consistent with the stress results obtained through finite element software simulation analysis under the condition of cable tensioning sequence from the far tower end to the near tower end.

[0052] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. They can be applied to various fields suitable for the present invention. For those skilled in the art, other modifications can be easily made. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A construction method for controlling the tensile stress reduction of the main girder of a combined beam cable-stayed bridge, characterized in that, Includes the following steps: S1. Calculate the theoretical value of the pre-camber height of each steel beam segment, and ensure that each steel beam segment reaches the corresponding pre-camber height before assembly; S2. The steel beam segments are pushed to their designed positions using the jacking method to complete the installation of the main steel beam; each steel beam segment is supported by temporary supports. S3. Install the bridge deck in sections from the smaller mileage to the larger mileage. S4. Pour concrete at the wet joint between two adjacent bridge deck panels; S5. Bridge deck prestressing construction: Tensioning the prestressed steel strands in each bridge deck to complete the main beam construction; S6. Install each stay cable and tension each stay cable on both sides of the bridge symmetrically from the far tower end to the near tower end.

2. The construction method for controlling the tensile stress reduction of the main girder of a combined beam cable-stayed bridge as described in claim 1, characterized in that, In step S1, finite element software is used to simulate the vertical deformation at each node of each segment of the steel beam under the standard working condition of constant load. The longitudinal displacement of each segment of the steel beam is taken as the horizontal axis and the vertical deformation as the vertical axis. The longitudinal displacement of each node on each segment of the steel beam is extracted. The deflection curve of each segment of the steel beam is obtained by fitting. The value of each node corresponding to the deflection curve is the pre-camber height of each node.

3. The construction method for controlling the tensile stress reduction of the main girder of a combined beam cable-stayed bridge as described in claim 1, characterized in that, When the combined beam cable-stayed bridge is a double-tower double-cable-stayed bridge, in step S5, the prestressed steel strands in the bridge deck at the mid-span are tensioned first, and then the prestressed steel strands in the bridge deck at the side span are tensioned.

4. The construction method for controlling the tensile stress reduction of the main girder of a combined beam cable-stayed bridge as described in claim 3, characterized in that, The prestressed steel strands include multiple long prestressed strands and multiple short prestressed strands arranged alternately along the transverse direction of the bridge; at the same location on the bridge deck, the long prestressed strands are tensioned first, followed by the short prestressed strands.

5. The construction method for controlling the tensile stress reduction of the main girder of a combined beam cable-stayed bridge as described in claim 4, characterized in that, When tensioning long or short prestressed tendons, tensioning is carried out from the center of the main beam to both sides, and the prestressed tendons on both sides of the center of the main beam are tensioned symmetrically.

6. The construction method for controlling the tensile stress reduction of the main girder of a combined beam cable-stayed bridge as described in claim 1, characterized in that, In step S6, during the tensioning process of the stay cables, the tension of each stay cable is controlled by monitoring the changes in the main beam alignment and the cable force of the stay cables.

7. The construction method for controlling the tensile stress reduction of the main girder of a combined beam cable-stayed bridge as described in claim 3, characterized in that, Strain gauges are installed at the mid-span of the side span, at the main tower, at 1 / 4 of the middle span, at the mid-span of the middle span, and at 3 / 4 of the middle span of the main beam.

8. The construction method for controlling the tensile stress reduction of the main girder of a combined beam cable-stayed bridge as described in claim 1, characterized in that, In step S3, the bridge deck is laid using a gantry crane. A track is installed on the main steel beam, and the gantry crane moves along the track. The trolley transporting the bridge deck uses the laid bridge deck as the transport channel.

9. The construction method for controlling the tensile stress reduction of the main girder of a combined beam cable-stayed bridge as described in claim 1, characterized in that, The concrete poured at the wet joint between two adjacent bridge deck panels contains steel fibers.

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