A prestressed concrete box girder cast-in-situ and beam dropping construction method

Abstract

The application discloses a prestressed concrete box girder cast-in-situ and beam falling construction method, which comprises the following steps: step 1, high-position beam body cast-in-situ; step 2, supporting the beam body on a temporary support, installing a guide beam system, installing a jack and a receiving member on the top of a pier; step 3, lifting the beam body through the jack, removing the temporary support, installing a permanent support, retracting the jack, supporting the beam body on the receiving member, completing the first beam falling, and repeating the above steps until the beam is positioned to the design position; and step 4, completing support grouting, removing the jack, the receiving member and the guide beam system, and completing the beam falling. The application effectively solves the problems of the box girder cast-in-situ, prestressed tension, beam falling positioning and support installation construction under the conditions of large span, large weight, insufficient construction clearance under the bridge and limited bridge end tension sequence by reasonably utilizing the limited space on the top surface of the bridge pier and comprehensively using a temporary cross-road scaffold, a temporary support, a jack and a guide beam system without affecting the normal traffic of the road under the bridge.

Description

Technical Field

[0001] This invention relates to the technical field of bridge construction, and in particular to a method for the cast-in-place and lowering construction of prestressed concrete box girders. Background Technology

[0002] With the rapid development of modern urban infrastructure construction, box girder bridges spanning highways and railways are becoming increasingly common. To ensure the normal operation of traffic beneath these bridges and to meet the clearance and safety requirements during construction, bridge construction often faces numerous restrictions. Box girders are typically installed by first jacking them to a pre-set position or by hoisting them to a pre-set position using large lifting equipment, followed by lowering them into place. However, this jacking or hoisting method places high demands on the work site and access roads, impacting existing road traffic beneath the bridge, incurring high handling costs and significant financial waste, and making girder lowering difficult to control, increasing the risks during construction.

[0003] Chinese patent application number 201821874502.7 discloses a "high-position beam lowering device," whose structure mainly involves setting up temporary support piers and distribution beams outside the pier body, along with lifting jacks and pier top support components, to achieve high-position beam lowering construction for large-tonnage bridges. The drawbacks of this device are: the beam lowering support piers are located outside the pier body, and due to their large size, they occupy limited construction space under the bridge, making them unsuitable for use on adjacent roads; the beam lowering support piers are temporary facilities, resulting in high temporary construction costs; the beam lowering device does not consider horizontal limiting requirements, making it impossible to guarantee the precise placement of the beam; the beam lowering process is complex, and the precise positioning of the distribution beam and jacks cannot be guaranteed between each beam lowering cycle, affecting the stability of the beam's stress points and potentially leading to accidents during beam lowering. Summary of the Invention

[0004] This invention provides a method for the in-situ casting and placement of prestressed concrete box girders. By making reasonable use of the limited space on the top surface of the bridge piers and by comprehensively utilizing temporary cross-road scaffolding, temporary supports, jacks and guide beam systems, it effectively solves the problems of in-situ casting, prestressing tensioning, girder placement and support installation of box girders under conditions of large span, heavy weight, insufficient construction clearance under the bridge and limited tensioning sequence at the bridge ends, without affecting the normal traffic flow under the bridge.

[0005] The technical problem to be solved is that the existing beam-dropping technology is greatly affected by the environment, the temporary facilities are complicated, the operation is inconvenient, it cannot guarantee accurate placement, and there are significant safety risks.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: This invention discloses a method for cast-in-place and lowering prestressed concrete box girder, comprising the following steps: Step 1: Complete the construction of the bridge substructure, erect cross-road scaffolding and steel supports as the beam formwork support system, and at the same time set up temporary supports on the pier caps and pier top scaffolding as the formwork support system. Then, install the formwork, tie the reinforcing bars, thread the steel strands and pour the concrete to complete the prestressing tensioning and grouting of the beam. Step 2: Remove the formwork and support system, support the beam on temporary supports, and install the guide beam system according to the design coordinates. The guide beam system includes a guide beam crossbeam and guide beam columns located on both sides of the guide beam crossbeam. A gap is reserved between the guide beam columns and the guide beam crossbeam. The guide beam crossbeam is fixed to the bottom of the manhole at the end of the beam by pre-embedded anchor bolts. The guide beam columns are located at the center of the pier top and connected to the pier top by pre-embedded anchor bolts. Install jacks and supporting components on the pier top. Step 3: Simultaneously lift the beam with jacks until it detaches from the temporary supports, remove the temporary supports, and install the support body and bottom plate of the permanent supports. Then, return the jacks to their original position, the cylinders retract, and the beam rests on the support, completing the first beam lowering. Remove one section of the steel pipe column from the jacks, and lift the beam again with jacks until it detaches from the support, remove one section of the steel pipe column from the support, return the jacks to their original position, the cylinders retract, and the beam rests on the support again, completing the second beam lowering. Repeat the above steps and monitor the horizontal and longitudinal displacement changes on both sides of the beam in real time. Use the guide beam system to adjust the beam position in real time until the beam is lowered to the design position. Step 4: Connect the upper and lower base plates of the permanent support. After confirming the precise placement of the beam, complete the grouting of the support. Once the grouting strength meets the standard, retract the jacks, remove the jacks and supporting components, and dismantle the guide beam system. The weight of the beam is finally transferred to the permanent support, completing the beam placement.

[0007] The present invention discloses a method for cast-in-place and lowering construction of prestressed concrete box girders. Further, in step 2, two jacks and two sets of bearing components are respectively set on the inner side of the preset permanent support.

[0008] This invention discloses a method for cast-in-place and lowering construction of prestressed concrete box girders. Further, the supporting component is composed of multiple detachable thick short steel pipe columns spliced ​​together, with each steel pipe column connected by a mortise and tenon joint and reinforced by bolts, and a steel plate on its upper part connected to the beam body; the jack is equipped with detachable thick short steel pipe columns, and a steel plate on its upper part is connected to the beam body.

[0009] This invention discloses a method for cast-in-place and lowering prestressed concrete box girder construction. Furthermore, the jacks are self-locking jacks, and multi-directional flow dividers are installed. A shut-off valve is added to each jack, and a shut-off valve is added to the oil pump.

[0010] This invention discloses a method for cast-in-place and lowering prestressed concrete box girder construction. Further, a circular steel plate sleeve is installed outside the piston of the jack. The sleeve is added as the piston of the jack extends and removed as the piston of the jack shortens.

[0011] This invention discloses a method for the cast-in-place and lowering construction of prestressed concrete box girders. Further, in step 3, real-time monitoring is implemented by setting displacement sensors and establishing leveling observation points at the bottom of the girder. The method monitors the descent of the bottom plates on both sides of the girder during the lowering process and continuously reports the descent amounts on both sides and at both ends of the girder. The difference in descent amount between the bottom plates on both sides of the girder is controlled within 2mm by adjusting the jacks. The difference in height between the bottom plates at both ends of the girder is also controlled within 10mm by adjusting the jacks. Simultaneously, the method observes the changes in the gap between the guide beam crossbeam and the guide beam column, and adjusts the girder in a timely manner to ensure the accuracy of the girder's placement.

[0012] This invention discloses a method for cast-in-place and lowering construction of prestressed concrete box girders, wherein the temporary support is a hardwood stack.

[0013] The present invention discloses a method for cast-in-place and lowering construction of prestressed concrete box girders, wherein the gap between the guide beam column and the guide beam crossbeam is no more than 10mm.

[0014] This invention discloses a method for cast-in-place and lowering prestressed concrete box girder construction. Furthermore, before the girder is poured, the position of the bolt holes of the top plate and the reserved guide beam is adjusted in advance, taking into account the design eccentricity value of the support and the tension offset value.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. By making reasonable use of the limited space on the top surface of the bridge piers and by comprehensively using temporary cross-road scaffolding, temporary supports, jacks and guide beam systems, the construction of box girder casting, prestressing tensioning, beam placement and support installation under the conditions of large span, heavy weight, insufficient construction clearance under the bridge and limited tensioning sequence at the bridge end was effectively solved without affecting the normal traffic of the road under the bridge. 2. By utilizing the permanent structure of the bridge to provide the support reaction force for the beam drop, the amount of engineering work, construction costs and occupation of existing roads of temporary facilities are reduced. In addition, some of the components used in this application can be reused, which further reduces the component processing costs and has good construction economy. 3. The interaction between the guide beam crossbeam and the guide beam column ensures the safety and accuracy of beam lowering during construction; 4. The technical solution adopted in this application is highly applicable, easy to operate, and takes little time, and is not affected by the external environment and geographical conditions of the construction site.

[0016] The invention will now be further described with reference to the accompanying drawings. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the template support system structure of the present invention; Figure 2 A schematic diagram of the temporary support structure for this invention; Figure 3 This is a schematic diagram of the dismantling of the template support system of the present invention; Figure 4 This is a schematic diagram of the installation structure of the guide beam system of the present invention; Figure 5 This is a side view of the guide beam system of the present invention during installation; Figure 6 This is a schematic diagram of the jack installation structure of the present invention; Figure 7 This is a schematic diagram of the installation and receiving structure of the present invention; Figure 8 This is a schematic diagram of the lifting beam body of the jack in this invention; Figure 9 This is a schematic diagram of the jack return mechanism of the present invention; Figure 10 This is a schematic diagram of the beam placement in this invention; Figure 11 This is a schematic diagram of the jacking, support component and guide beam system of the present invention.

[0018] Figure label: 1. Formwork support system; 2. Pier cap; 3. Temporary support; 4. Beam body; 5. Manhole; 6. Guide beam crossbeam; 7. Guide beam column; 8. Jack; 9. Connecting parts; 10. Permanent support. Detailed Implementation

[0019] Combination Figures 1-11 This invention discloses a method for the cast-in-place and lowering construction of prestressed concrete box girders, comprising the following steps: Step 1: Based on the bridge construction drawings, complete the construction of the bridge substructure, and pre-embed the anchor bolts of the guide beam columns before pouring the pier cap. Erect the cross-road scaffolding and steel support system as the box girder formwork support system. At the same time, set up hardwood stacks as temporary supports at the locations where permanent supports are set on the pier cap, and set up pier top scaffolding on the pier cap as the formwork support system. According to the coordinates of the permanent supports and considering the design eccentricity and tension offset of the supports, pre-install the top plate of the supports on the bottom of the beam.

[0020] Construction work includes box girder formwork installation, rebar tying, steel strand threading, and box girder concrete pouring. Before pouring the girder, the design eccentricity and tension offset of the supports are checked to ensure that the top plate is adjusted in place. At the same time, anchor bolt holes required for fixing the transverse guide beam are reserved at the bottom of the box girder manhole. Then, prestressing tensioning and grouting are completed.

[0021] Step 2: Remove the formwork and support system. At this point, the box girder is supported on temporary supports. Position and install the guide beam system according to the design coordinates. The guide beam system includes a guide beam crossbeam and guide beam columns located on both sides of the crossbeam. The crossbeam is fixed to the bottom of the manhole at the end of the girder using pre-embedded anchor bolts. The guide beam columns are located at the center of the pier top and connected to the pier top using pre-embedded anchor bolts. A certain gap, no more than 10mm, is left between the guide beam columns and the crossbeam to ensure fine-tuning of the girder during the lowering process, achieving precise lowering of the girder. Position the jacks and support components precisely, and install them on the pier cap. Specifically, two jacks and two sets of support components are set on the inner side of the pre-set permanent support. The jacks and support components are located on both sides of the center line of the permanent support. The support components are composed of multiple detachable thick short steel pipe columns spliced ​​together. The steel pipe columns are connected by a mortise and tenon joint and reinforced with bolts. A steel plate is installed on the top of the support to connect with the bottom of the beam. Detachable thick short steel pipe columns are installed on the jacks, and a steel plate is installed on the top of the support to connect with the bottom of the beam.

[0022] Step 3: Four jacks simultaneously lift the box girder until it detaches from the temporary supports. The temporary supports are then removed, and the permanent support body and bottom plate are installed. The jacks are then depressurized, the cylinders retract, and the girder rests on the support structure, completing the first lowering. One section of the steel pipe column on each jack is removed, and the girder is lifted again by the jacks until it detaches from the support structure. Another section of the steel pipe column on the support structure is removed, and the jacks are depressurized, the cylinders retract, and the girder rests on the support structure again, completing the second lowering. The above steps are repeated, with real-time monitoring of horizontal and longitudinal displacement changes on both sides. The beam position is adjusted in real-time using the guide beam system until the box girder is positioned at the design location. The jacks used are self-locking jacks, and multi-directional flow dividers are installed to ensure that multiple jacks can be raised and lowered simultaneously. Each jack is equipped with a shut-off valve, and the shut-off valve on the oil pump is also installed to provide dual control of the jacks. A circular steel plate sleeve is installed on the outside of the jack piston. The sleeve is added as the jack piston extends and removed as the jack piston shortens, ensuring that even if the jack fails, the impact load can be controlled within the design allowable range.

[0023] Real-time monitoring is implemented by setting up displacement sensors and leveling observation points at the bottom of the beam. Dedicated personnel observe the descent of the bottom plates on both sides of the beam during the lowering process and report the descent amount on both sides and at both ends of the beam at any time. By adjusting the jacks, the difference in descent amount between the bottom of the beam on both sides is controlled within 2mm to ensure that the beam does not overturn or crack. The difference in height between the bottom of the beam at both ends is also controlled within 10mm by adjusting the jacks. At the same time, the changes in the gap between the guide beam crossbeam and the guide beam column are observed, and the beam position is adjusted in a timely manner to ensure the accuracy of the beam placement.

[0024] Step 4: Bolt the upper and lower base plates of the permanent support. After confirming the precise placement of the beam, complete the grouting of the support. After the grouting strength of the support reaches the standard, the hydraulic cylinder of the jack retracts, the jack and the supporting parts are removed, and the guide beam system is removed. The weight of the beam is finally transferred to the permanent support, and the beam placement is completed.

[0025] This application addresses the challenges posed by limited construction land, including the inability to establish prefabrication sites, install supporting piers outside the piers, and accommodate large machinery due to site constraints. It allows for the completion of prefabrication, tensioning, and beam lowering processes on the original beam location, enabling precise control over the beam lowering position without affecting the design stability of permanent structures such as the piers and beams. It is suitable for construction conditions with high loads; in one application example, the entire box girder weighed 1276 tons, with a lowering height of 1.8 meters. Simultaneously, prestressed grouting and anchoring operations, guide beam installation, and formwork and cross-road steel support dismantling can be carried out without interference.

[0026] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made by those skilled in the art to the technical solutions of the present invention without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.

Claims

1. A method for cast-in-place and lowering construction of prestressed concrete box girders, characterized in that, Includes the following steps: Step 1: Complete the construction of the bridge substructure, erect cross-road scaffolding and steel supports as the beam formwork support system, and set up temporary supports at the locations where permanent supports are set on the pier caps; set up pier top scaffolding on the pier caps as the formwork support system; then carry out formwork installation, rebar binding, steel strand threading and concrete pouring, and pre-install the top plate of the support on the bottom of the beam according to the coordinates of the permanent support. Complete the prestressing tensioning and grouting of the beam; Step 2: Remove the formwork and support system. At this point, the box girder is supported on temporary supports. Install the guide beam system according to the design coordinates. The guide beam system includes a guide beam crossbeam and guide beam columns located on both sides of the guide beam crossbeam. A gap of no more than 10mm is reserved between the guide beam columns and the guide beam crossbeam. The guide beam crossbeam is fixed to the bottom of the manhole at the end of the beam body by pre-embedded anchor bolts. The guide beam columns are located at the center of the pier top and connected to the pier top by pre-embedded anchor bolts. Install jacks and connecting parts on the pier top. Step 3: Simultaneously lift the beam with jacks until it detaches from the temporary supports. Remove the temporary supports and install the permanent support body and bottom plate. Then, return the jacks to their original position, retract the cylinders, and the beam rests on the support, completing the first beam lowering. Remove one section of the steel pipe column from the jacks and lift the beam again with jacks until it detaches from the support, remove one section of the steel pipe column from the support, return the jacks to their original position, retract the cylinders, and the beam rests on the support again, completing the second beam lowering. Repeat the above steps, observing the changes in the gap between the guide beam crossbeam and the guide beam column; monitor the horizontal and longitudinal displacement changes on both sides of the beam in real time, and adjust the beam position in real time using the guide beam system until the beam is lowered to the designed position. Step 4: Connect the upper and lower base plates of the permanent support. After confirming the precise placement of the beam, complete the grouting of the support. Once the grouting strength meets the standard, retract the jacks, remove the jacks and supporting components, and dismantle the guide beam system. The weight of the beam is finally transferred to the permanent support, completing the beam placement.

2. The method for cast-in-place and lowering prestressed concrete box girder construction according to claim 1, characterized in that: In step 2, two jacks and two sets of connecting parts are installed on the inner side of the preset permanent support.

3. The method for cast-in-place and lowering construction of prestressed concrete box girders according to claim 1, characterized in that: The supporting component is composed of multiple detachable thick short steel pipe columns spliced ​​together. The steel pipe columns are connected by a mortise and tenon joint and reinforced with bolts. A steel plate is provided on the upper part to connect with the beam. The jack is equipped with detachable thick short steel pipe columns, and a steel plate is provided on the upper part to connect with the beam.

4. The method for cast-in-place and lowering construction of prestressed concrete box girders according to claim 1, characterized in that: The jacks are self-locking jacks and equipped with multi-directional flow dividers. Each jack is also equipped with a shut-off valve and a shut-off valve on the oil pump.

5. The method for cast-in-place and lowering prestressed concrete box girder construction according to claim 1, characterized in that: A circular steel plate sleeve is installed outside the piston of the jack. The sleeve is added as the piston of the jack extends and removed as the piston of the jack shortens.

6. The method for cast-in-place and lowering construction of prestressed concrete box girders according to claim 1, characterized in that: In step 3, real-time monitoring is conducted by setting up displacement sensors and leveling observation points at the bottom of the beam to observe the descent of the bottom plates on both sides of the beam during the beam lowering process. The descent of the beam on both sides and at both ends is reported at any time during the lowering process. The difference in descent of the bottom plates on both sides of the beam is controlled within 2mm by adjusting the jacks. The difference in height between the bottom plates at both ends of the beam is also controlled within 10mm by adjusting the jacks. At the same time, the change in the gap between the guide beam crossbeam and the guide beam column is observed, and the beam is adjusted in a timely manner to ensure the accuracy of the beam placement.

7. The method for cast-in-place and lowering construction of prestressed concrete box girders according to claim 1, characterized in that: The temporary support is a stack of hardwood.

8. The method for cast-in-place and lowering construction of prestressed concrete box girders according to claim 1, characterized in that: Before pouring the beam, the design eccentricity of the supports and the tension offset should be considered in advance to adjust the position of the bolt holes of the top plate and the reserved guide beam.

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