Pushing construction method for buttress-free large-span steel box girder

Abstract

The invention discloses a buttress-free large-span steel box girder incremental launching construction method, and relates to the technical field of bridge construction. The inhaul cables are asymmetrically arranged, the construction range of the incremental launching platform does not need to be additionally expanded, and the incremental launching platform can flexibly adapt to scenes where horizontal curve bridges, vertical curve bridges and incremental launching platform sites are limited, so that the occupied space of the incremental launching platform is greatly reduced, the construction amount and construction cost of temporary engineering are reduced, and the construction efficiency is improved. The problem that a traditional symmetrical inhaul cable arrangement mode is poor in field adaptability is solved. The method can be widely applied to pushing construction of various buttress-free large-span steel box girders, is particularly suitable for engineering scenes of flat curve bridges, vertical curve bridges and narrow pushing sites, does not need to greatly transform existing construction equipment, is easy to popularize and apply, and has good practicability and popularization value.

Description

Technical Field

[0001] This invention relates to the field of bridge construction technology, and in particular to a method for jacking up large-span steel box girders without piers. Background Technology

[0002] The bridge jacking method involves setting up a prefabrication yard behind the abutment along the longitudinal axis of the bridge, prefabricating the beams in stages, applying force with horizontal jacks, and using sliding and jacking devices to push the beams forward segment by segment. After the beams are in place, they are lowered and the permanent supports are replaced.

[0003] Currently, commonly used jacking construction techniques include the inclined cable-stayed jacking method and the temporary support jacking method. The temporary support jacking method requires the placement of multiple temporary supports to support the steel box girder before the jacking operation. Because the inclined cable-stayed jacking method significantly reduces the investment in temporary works and lowers construction costs compared to the temporary support jacking method, it is more widely used. For example, Chinese invention patent application C119571733A discloses a jacking construction device and method for large-span continuous steel beams with a jacking tower, and Chinese invention patent application CN116254773A discloses a jacking construction method for composite beams without supports. Both of these patents employ the inclined cable-stayed jacking method with symmetrically arranged cables.

[0004] However, when bridges have horizontal or vertical curves, or when the launching platform space is limited, the existing jacking construction technology using symmetrically arranged cables and the inclined cable-stayed method is difficult to meet the construction requirements. The main problems are as follows: First, when the launching platform space is limited, if a symmetrical cable arrangement is used, in order to ensure the installation space and stress balance of the cables, the construction area of ​​the launching platform usually needs to be expanded, which increases the amount and cost of temporary works. Furthermore, for horizontal and vertical curve bridges, the symmetrical cable arrangement is difficult to adapt to the curve shape of the bridge, easily leading to uneven stress on the cables and affecting the stability of the jacking. Second, during the jacking process of horizontal curve bridges, the beam is subjected to centrifugal force, and vertical curve bridges are affected by uneven vertical load distribution. If a symmetrical cable arrangement is used... The cable arrangement can lead to an imbalance of forces on both sides of the steel box girder, resulting in additional torque and lateral tilting moment. This can easily cause the girder to deviate or become unstable, posing safety hazards. This is especially true in the case of jacking without supports, where the girder lacks temporary support and the problem of uneven force distribution is even more pronounced. Third, in order to solve the problem of uneven force distribution caused by symmetrical cable arrangement, existing technologies usually use additional counterweights to adjust the load distribution. However, the configuration and adjustment of counterweights is cumbersome, which not only increases the construction process and labor costs, but may also cause the girder to lose control of its posture due to improper adjustment of counterweights, thereby reducing construction efficiency. In addition, symmetrical cable arrangement is prone to girder deviation during jacking, requiring frequent correction operations, which will also lead to an extension of the construction period. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for launching large-span steel box girders without supports, which can reduce temporary construction structures, improve construction efficiency and construction safety.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by this invention is: a method for jacking up large-span steel box girders without supports, comprising the following steps: Step 1: Construct a jacking platform at the starting end of the bridge; Step 2: Assemble the guide beam and some steel box girder segments on the jacking platform. After the assembly is completed, conduct a quality inspection. Then, push the assembled beam forward a preset distance. This preset distance needs to be calculated and determined based on the height of the tower and the installation space of the cables. Step 3: Install the cable tower. Fix the cable tower to the steel box girder, and then install the inner cables and the outer cables on the guide beam side. The layout, quantity and initial cable force of the inner and outer cables are determined by construction mechanics calculations. After the cables are tensioned, the connection between the bottom of the cable tower and the steel box girder is changed from the initial fixed connection to a hinged connection. Step 4: Continue to push the steel box girder forward, and monitor the attitude of the steel box girder, the deflection at the front end of the guide beam, and the changes in the cable tension in real time. When it is detected that the two inner cables and one outer cable cannot meet the jacking balance requirements of the steel box girder, or when it is detected that the deflection at the front end of the guide beam exceeds the allowable range, if the space at the rear end of the steel box girder meets the installation requirements of the remaining outer cables, install the remaining outer cables and adjust the tension of the installed cables. Step 5: Continue to push the steel box girder forward until it passes the front end near the support pier. Then, loosen the inner and outer cables connected to the tower to reduce the cable tension and adjust the cables to a ready-to-tight state. Step 6: Continue pushing the steel box girder forward until the guide beam passes through the end support, remove the outer cables, and then dismantle the guide beam in sections while retaining some sections of the guide beam. Step 7: Remove the remaining guide beam segments; Step 8: Lower the steel box girder as a whole, then install the bridge deck and remove the inner cables and towers.

[0007] As an improvement to the above scheme: In step one, the jacking platform is formed by casting reinforced concrete, an anti-slip mat is laid on the surface of the jacking platform, and guardrails are set at the edge of the jacking platform with a height of not less than 1.2m.

[0008] As an improvement to the above scheme: In step two, the guide beam is assembled from lightweight steel sections, and the length of the guide beam is calculated and determined according to the span of the steel box girder and the stability requirements of the jacking operation; high-strength bolts are used to connect the guide beam and the steel box girder during the assembly process; the initial jacking distance is 1.5 to 3m, the jacking speed is controlled at 0.2 to 0.5m / h, and the displacement and attitude of the beam are monitored in real time during the jacking process.

[0009] As an improvement to the above scheme: In step three, the inner cable and the outer cable are tensioned synchronously, and the cable force changes are monitored in real time during the tensioning process. The deviation between the real-time cable force and the preset cable force does not exceed ±5%.

[0010] As an improvement to the above scheme: In step four, the allowable range of the deflection at the front end of the guide beam is L / 500 to L / 600, where L is the length of the guide beam; when the deflection at the front end of the guide beam exceeds the allowable range, stop pushing and install the remaining outer cables and then adjust the cable force; the cable force adjustment adopts a graded adjustment method, and the adjustment amount of each grade does not exceed 10% of the design cable force.

[0011] As an improvement to the above scheme: in step five, when the cable is adjusted to the tensioning state, the cable force is controlled at 10-20% of the designed tension cable force.

[0012] As an improvement to the above scheme: In step six, the length of the retained guide beam segment is 2 to 3 meters, the retained guide beam segment is close to the end support, and the retained guide beam segment and the end support form a temporary support system.

[0013] As an improvement to the above scheme: In step eight, a synchronous beam-dropping process is adopted when the steel box girder is lowered, and the beam-dropping speed is controlled at 0.1 to 0.2 m / h. The elevation and horizontal displacement of the steel box girder are monitored in real time during the beam-dropping process; the bridge deck installation adopts a symmetrical assembly process on both sides.

[0014] The beneficial effects of this invention are: 1. This invention employs an asymmetrical cable arrangement, eliminating the need to expand the operating range of the launching platform. It can flexibly adapt to horizontal and vertical curve bridges and scenarios with limited launching platform space, thereby significantly reducing the space occupied by the launching platform and reducing the amount and cost of temporary works. This solves the problem of poor site adaptability of traditional symmetrical cable arrangement methods. This invention can be widely applied to the launching construction of various pierless large-span steel box girders, especially suitable for horizontal and vertical curve bridges and engineering scenarios with narrow launching sites. It does not require significant modification to existing construction equipment, is easy to promote and apply, and has good practicality and promotional value.

[0015] 2. This invention, through the asymmetrical arrangement of cables and the dynamic adjustment of cable force based on real-time monitoring data during the jacking process, can effectively balance the centrifugal force of horizontal curved bridges or the vertical load of vertical curved bridges, avoid generating additional torque and lateral tilting moment in the beam, reduce beam deviation during the jacking process, thereby reducing the number of corrections, ensuring the stability of the beam's posture and the balance of forces during the jacking process, and significantly improving construction safety.

[0016] 3. This invention eliminates the need for temporary supports during the jacking process, significantly reducing temporary engineering costs. It also eliminates the need for additional counterweights to adjust load distribution, thus simplifying the construction process. Furthermore, by changing the bottom of the tower from a fixed connection to a hinged connection, the constraint moment at the bottom of the tower is released, allowing the tower to adapt to the displacement and rotation deformation of the beam during the jacking process, avoiding additional stress on the tower and extending its service life.

[0017] 4. This invention maintains the stability of the cable tower by retaining a portion of the guide beam segment after the jacking is completed, thereby improving the reliability of the cable tower and the entire jacking system. The cables, guide beams, and other components removed by this invention can be recycled and reused after cleaning and maintenance, reducing resource consumption and lowering project costs. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the jacking platform during construction of the present invention; Figure 2 This is a schematic diagram illustrating the assembly of the guide beam and steel box girder according to the present invention; Figure 3 This is a schematic diagram of the installation of the tower and some of the cables according to the present invention; Figure 4 This is a schematic diagram illustrating the process of jacking and installing the remaining cables according to the present invention; Figure 5 This is a schematic diagram of the present invention when the steel box girder is pushed to the front end near the support pier; Figure 6 This is a schematic diagram of the invention when it is pushed into place. Figure 7 This is a schematic diagram of the process of dismantling the cable tower and installing the bridge deck according to the present invention.

[0019] The markings in the diagram are: 100-jacking platform, 200-steel box girder, 300-guide beam, 400-tower, 410-inner cable, 420-outer cable, 500-bridge deck. Detailed Implementation

[0020] To facilitate understanding of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0021] In the description of this invention, it should be noted that the terms "front", "rear", "left", "right", "up", "down", etc., 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 description and do not indicate or imply that the device or component 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.

[0022] The jacking construction method for large-span steel box girders without supports disclosed in this invention is carried out according to the following steps: Step 1, such as Figure 1 As shown, a launching platform 100 is constructed at the starting end of the bridge. Based on the self-weight of the steel box girder 200, the launching reaction force, the weight of the construction equipment, and the assembly requirements, the launching platform 100 is planned and constructed at the starting end of the bridge. The launching platform 100 is made of reinforced concrete. The length, width, and thickness of the launching platform 100 are determined according to construction calculations to ensure that the launching platform 100 has sufficient load-bearing capacity and stability to withstand various loads on the steel box girder 200 during assembly and launching. An anti-slip mat is laid on the surface of the launching platform 100 to prevent the construction equipment and the girder from sliding. Protective railings are installed along the edges of the launching platform 100, with a height of not less than 1.2m and a spacing of not more than 0.5m, to ensure the safety of construction personnel. After the construction of the launching platform 100 is completed, a quality inspection is conducted. Only after confirming that the surface of the launching platform 100 is flat, free of cracks, and that its load-bearing capacity meets the design requirements can the next process begin.

[0023] Step Two, as follows Figure 2 As shown, guide beam 300 and some steel box girder segments of steel box girder 200 are assembled on the jacking platform 100. Guide beam 300 is assembled from lightweight steel. The length of guide beam 300 is calculated and determined based on the span of steel box girder 200, jacking stability requirements, and installation space of pylon 400. It is usually 1 / 3 to 1 / 2 of the single span of steel box girder 200, ensuring that guide beam 300 can effectively reduce the deflection at the front end of steel box girder 200 and improve jacking stability. The assembly between guide beam 300 and steel box girder 200 is connected by high-strength bolts and positioned by locating pins to ensure precise alignment between guide beam 300 and steel box girder 200. After assembly, weld inspection and bolt torque inspection are performed to confirm that the assembly accuracy and connection reliability meet the design requirements.

[0024] After assembly, a jacking device is used to push the beam forward a predetermined distance, the specific distance of which is calculated based on the installation space requirements of the pylon 400 and cables. This distance is typically 1.5–3 meters, designed to provide sufficient working space for the installation of the pylon 400 and cables, and to prevent the beam from obstructing the installation work surface. During the jacking process, the jacking speed is controlled at 0.2–0.5 m / h, and the horizontal displacement, vertical displacement, and attitude of the beam are monitored in real time to ensure that the beam is jacked smoothly without any abnormalities such as misalignment or instability.

[0025] Step 3, as follows Figure 3 As shown, the pylon 400 is installed and fixed to the steel box girder 200. The first stage of cable installation is then carried out. Based on construction mechanics calculations, the location, quantity, specifications, and initial cable force of the inner cables 410 and the outer cables 420 on the guide beam side are determined. In this stage, all the inner cables 410 and some of the outer cables 420 are installed. The inner cables 410 are arranged on the steel box girder 200, and the outer cables 420 on the guide beam side are arranged on the guide beam 300 near the steel box girder 200, forming an asymmetrical cable arrangement structure suitable for asymmetrical load conditions. The cables use high-strength galvanized steel strand, which features high strength, corrosion resistance, and low deformation, meeting the stress requirements during the jacking process.

[0026] During cable installation, the anchorages at both ends of the cable are installed first. The anchorages are then fixed to the 400mm pylon, 200mm steel box girder, and 300mm guide beam using high-strength bolts to ensure a secure connection. Next, the cable is threaded and tensioned. A synchronous tensioning process is used, with multiple tensioning devices working in tandem to monitor cable tension changes in real time, ensuring the cable tension reaches the initial design value and that the tension deviation does not exceed ±5%. After tensioning, the cable anchorages are locked to prevent cable tension loss.

[0027] After the cables are tensioned, the bottom of the pylon 400 is changed from its initial fixed connection to a hinged connection. Initially, the bottom of the pylon 400 is connected to the steel box girder 200 using fixed joints to ensure the stability of the pylon 400 during cable installation and tensioning. After tensioning, the original fixed joints are replaced with hinged joints. These hinged joints can rotate 360°, effectively releasing the bottom constraint moment of the pylon 400. This allows the pylon 400 to adapt to the displacement and rotation deformation of the beam during the jacking process, avoiding additional stress on the pylon 400, extending its service life, and improving the flexibility of the jacking process.

[0028] Step 4, as follows Figure 4The steel box girder continues to be pushed forward at a speed of 0.2–0.5 m / h, while the attitude of the steel box girder 200, the deflection at the front end of the guide beam 300, and the changes in cable tension are monitored in real time. Monitoring indicators include the horizontal deviation of the girder, vertical deflection, front end deflection of the guide beam, and the real-time cable tension of each cable. Pushing is stopped and the second stage of cable installation begins when one of the following two situations is detected: First, the combined force of the two inner cables 410 and one outer cable 420 is insufficient to meet the girder pushing balance requirements, resulting in significant girder deviation and tilting; second, the front end deflection of the guide beam 300 is too large, exceeding the allowable range of L / 500–L / 600, where L is the length of the guide beam 300, which may lead to damage to the guide beam or girder instability. Simultaneously, it must be confirmed that there is sufficient space at the rear end of the steel box girder 200 to install the remaining outer cables 420, to avoid interference between cable installation and girder pushing.

[0029] Install the remaining outer cables 420. The installation process for the remaining outer cables 420 is the same as that for the outer cables 420 in the first stage, except that the remaining outer cables 420 are installed at the steel box girder 200 near the jacking platform 100. After installation, adjust the tension of the installed cables according to real-time monitoring data and construction mechanics calculations. Use a tiered adjustment method, with each adjustment not exceeding 10% of the design cable force to avoid sudden changes in cable force that could damage the beam or tower. After adjustment, ensure the beam is under balanced stress and has a stable posture, and keep the deflection at the front end of the guide beam 300 within the allowable range before continuing jacking.

[0030] Step 5, as follows Figure 5 As shown, continue jacking the beam until the steel box girder 200 passes through the front end adjacent pier. At this point, the steel box girder 200 has been supported by the pier, and the supporting role of the tower 400 can be appropriately reduced. Loosen the tension of the inner cable 410 and outer cable 420 connected to the tower 400, and adjust the cables to a pre-tensioned state. The tension is controlled at 10-20% of the design tension. At this point, the cables no longer bear the main support load, but are used as wind ropes to maintain the stability of the tower 400 and prevent the tower 400 from tilting or becoming unstable due to wind load, beam disturbance, or other factors during subsequent jacking.

[0031] After the cable function is converted, the beam body continues to be pushed. During the pushing process, the attitude of the tower 400 and the changes in cable tension are monitored in real time to ensure that the tower 400 remains stable and that there are no abnormalities such as slack or breakage of the cables. At the same time, the displacement and attitude of the steel box girder 200 are monitored, and the pushing speed and direction are adjusted in a timely manner to reduce the number of corrections.

[0032] Step Six, as Figure 6As shown, continue pushing the beam until the guide beam 300 completely passes through the end support. Then, the guide beam 300 and the outer cable 410 can be dismantled. The outer cable 410 is dismantled first, followed by the guide beam 300. The dismantling of the guide beam 300 is carried out in sections, gradually dismantling it from the end furthest from the tower 400 towards the tower. During dismantling, a crane is used to lift the components to prevent them from falling and damaging the already constructed steel box girder 200, supports, and other structures. Safety precautions are also taken for construction personnel. To ensure the stability of the tower 400 during the dismantling of the guide beam 300, a section of the guide beam 300 is retained, with a length of 2-3 meters. This retained section forms a temporary support system with the tower, providing lateral support to the tower 400 and preventing it from swaying or becoming unstable due to the loss of the guide beam 300's restraint.

[0033] Step 7, as follows Figure 7 As shown, the remaining guide beam segments are dismantled. The dismantling process for the remaining guide beam segments is the same as the guide beam dismantling steps in step six, using a crane for lifting and dismantling to ensure safe and efficient operation. The dismantled guide beam components are cleaned and inspected. Components with no damage or minor damage can be recycled and reused, reducing resource consumption and project costs.

[0034] Step 8, as Figure 7 As shown, the steel box girder was lowered as a whole, followed by the installation of the bridge deck and the removal of the inner cables and towers. The lowering of the steel box girder 200 employed a synchronous lowering process, using multiple jacks to retract simultaneously, controlling the lowering speed at 0.1–0.2 m / h. During the lowering process, the elevation and horizontal displacement of the steel box girder 200 were monitored in real time to ensure precise positioning. After lowering, the steel box girder 200 was reliably connected to the piers to ensure its stability.

[0035] After the steel box girder 200 is in place, the bridge deck 500 is symmetrically installed from both sides of the steel box girder 200. The bridge deck 500 is prefabricated and assembled using high-strength bolts to ensure a firm connection and a smooth surface. After the bridge deck 500 is installed, subsequent work such as waterproofing and paving of the bridge deck is carried out. Simultaneously, the inner cable 410 and the pylon 400 are dismantled. The dismantling of the pylon 400 is carried out in sections, gradually removing it from top to bottom. During the dismantling process, hoisting protection measures are implemented to prevent components from falling and ensure construction safety. After the pylon 400 is dismantled, the construction site is cleared, completing the entire jacking construction process.

Claims

1. A method for jacking large-span steel box girders without supports, characterized by: Includes the following steps: Step 1: Construct a jacking platform at the starting end of the bridge; Step 2: Assemble the guide beam and some steel box girder segments on the jacking platform. After the assembly is completed, conduct a quality inspection. Then, push the assembled beam forward a preset distance. This preset distance needs to be calculated and determined based on the height of the tower and the installation space of the cables. Step 3: Install the cable tower. Fix the cable tower to the steel box girder, and then install the inner cables and the outer cables on the guide beam side. The layout, quantity and initial cable force of the inner and outer cables are determined by construction mechanics calculations. After the cables are tensioned, the connection between the bottom of the cable tower and the steel box girder is changed from the initial fixed connection to a hinged connection. Step 4: Continue to push the steel box girder forward, and monitor the attitude of the steel box girder, the deflection at the front end of the guide beam, and the changes in the cable tension in real time. When it is detected that the two inner cables and one outer cable cannot meet the jacking balance requirements of the steel box girder, or when it is detected that the deflection at the front end of the guide beam exceeds the allowable range, if the space at the rear end of the steel box girder meets the installation requirements of the remaining outer cables, install the remaining outer cables and adjust the tension of the installed cables. Step 5: Continue to push the steel box girder forward until it passes the front end near the support pier. Then, loosen the inner and outer cables connected to the tower to reduce the cable tension and adjust the cables to a ready-to-tight state. Step 6: Continue pushing the steel box girder forward until the guide beam passes through the end support, remove the outer cables, and then dismantle the guide beam in sections while retaining some sections of the guide beam. Step 7: Remove the remaining guide beam segments; Step 8: Lower the steel box girder as a whole, then install the bridge deck and remove the inner cables and towers.

2. The method for jacking large-span steel box girders without supports as described in claim 1, characterized in that: In step one, the jacking platform is formed by casting reinforced concrete, an anti-slip mat is laid on the surface of the jacking platform, and guardrails are installed at the edge of the jacking platform with a height of not less than 1.2m.

3. The method for jacking a large-span steel box girder without supports as described in claim 1, characterized in that: In step two, the guide beam is assembled from lightweight steel sections. The length of the guide beam is calculated and determined based on the span of the steel box girder and the stability requirements of the jacking operation. High-strength bolts are used to connect the guide beam and the steel box girder during the assembly process. The initial jacking distance is 1.5 to 3 meters, and the jacking speed is controlled at 0.2 to 0.5 meters per hour. The displacement and attitude of the beam are monitored in real time during the jacking process.

4. The method for jacking a large-span steel box girder without supports as described in claim 1, characterized in that: In step three, the inner and outer cables are tensioned synchronously. During the tensioning process, the cable force changes are monitored in real time, and the deviation between the real-time cable force and the preset cable force does not exceed ±5%.

5. The method for jacking large-span steel box girders without supports as described in claim 1, characterized in that: In step four, the allowable range of the deflection at the front end of the guide beam is L / 500 to L / 600, where L is the length of the guide beam. When the deflection at the front end of the guide beam exceeds the allowable range, the jacking is stopped and the remaining outer cables are installed before adjusting the cable force. The cable force is adjusted in stages, with each adjustment not exceeding 10% of the design cable force.

6. The method for jacking a large-span steel box girder without supports as described in claim 1, characterized in that: In step five, when the cable is adjusted to the tensioned state, the cable force is controlled at 10-20% of the designed tension cable force.

7. The method for jacking large-span steel box girders without supports as described in claim 1, characterized in that: In step six, the length of the retained guide beam segment is 2 to 3 meters. The retained guide beam segment is close to the end support, and the retained guide beam segment and the end support form a temporary support system.

8. The method for jacking a large-span steel box girder without supports as described in claim 1, characterized in that: In step eight, the steel box girder is lowered using a synchronous lowering process, with the lowering speed controlled between 0.1 and 0.2 m / h. The elevation and horizontal displacement of the steel box girder are monitored in real time during the lowering process. The bridge deck is installed using a symmetrical assembly process on both sides.

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