Construction method for cast-in-place box girder crossing existing overpass

Abstract

This invention discloses a construction method for cast-in-place box girder spanning an existing overpass, comprising the following steps: Step 1: Construction preparation stage, including foundation treatment, formwork processing, and steel reinforcement processing; Step 2: Erection and reinforcement of full-span scaffolding. First, the scaffolding is erected. After the scaffolding is erected, the bottom formwork and outer side plates of the box girder are installed. Then, the scaffolding is pre-stressed. After unloading, the elevation of the bottom formwork is adjusted as needed. Finally, the inner side formwork and the bottom formwork of the top plate of the box girder are installed; Step 3: Casting of the box girder. After the entire cross-section of the box girder is cast, it is cured. Tensioning is performed when the concrete strength reaches 85% of the design strength, and finally, grouting is carried out; Step 4: Dismantling of the scaffolding. In this invention, disc-lock full-span scaffolding is used to reinforce existing highway bridges. Disc-lock full-span scaffolding is then erected on top of the existing highway bridge as cast-in-place scaffolding. Installation and dismantling are convenient and can save construction time.

Description

Technical Field

[0001] This invention relates to the field of bridge construction technology, specifically a method for constructing cast-in-place box girders across existing overpasses. Background Technology

[0002] When a cast-in-place box girder intersects with an existing highway bridge, the cast-in-place box girder needs to cross the bridge, but it must not damage the existing highway bridge. It is necessary to find an effective method that can save resources, reduce energy consumption, and save construction time to solve the problem of cast-in-place box girders crossing existing highway bridges.

[0003] The current main method is to use steel pipe piles to cross existing highway bridges with less scaffolding. However, this method has the disadvantages of high cost, difficulty in dismantling (heavy structure), large deflection of temporary structure (large span), and long construction period. Summary of the Invention

[0004] The purpose of this invention is to provide a construction method for cast-in-place box girders spanning existing overpasses to solve the problems encountered in practical use.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for constructing cast-in-place box girders spanning existing overpasses includes the following steps:

[0007] Step 1: Construction preparation stage, including foundation treatment, formwork processing, and steel reinforcement processing;

[0008] Step 2: Construction and reinforcement of full-span scaffolding. First, erect the scaffolding. After the scaffolding is erected, install the bottom formwork and outer side plate of the box girder. Then, preload the scaffolding. After the preloading is completed and unloaded, adjust the elevation of the bottom formwork according to the current construction requirements of the bridge. Finally, install the inner side formwork and the bottom formwork of the top plate of the box girder.

[0009] Step 3: Casting of the box girder. After the box girder is cast across the entire cross section, it is cured. Tensioning is carried out when the concrete strength reaches 85% of the design strength, and finally grouting is performed.

[0010] Step 4: Dismantle the scaffolding. The dismantling order is as follows: dismantle the inner formwork, dismantle the outer formwork and the top and bottom formwork, remove the bottom formwork, and dismantle the scaffolding.

[0011] Preferred method: During foundation treatment in step one, No. 20 I-beams are laid longitudinally under the bottom support of the scaffolding on the bridge, and 20×5cm wooden boards are laid transversely under the I-beams. The wooden boards are placed on the web of the original hollow slab of the viaduct. The scaffolding under the bridge is also supported on the web of the original hollow slab of the highway bridge, so that the original highway bridge only bears the vertical pressure, and the construction load is directly transferred from the bridge to the foundation under the bridge.

[0012] Preferred method: When erecting scaffolding in step two, determine the structure of the disc-lock scaffolding. For scaffolding under 10m, set one scissor brace for every 5 rows of horizontal uprights and one scissor brace for every 5 rows of horizontal uprights. For scaffolding between 10m and 15m, set one scissor brace for every 4 rows of horizontal uprights and one scissor brace for every 4 rows of horizontal uprights. For scaffolding between 15m and 20m, set one scissor brace for every 3 rows of horizontal uprights and one scissor brace for every 3 rows of horizontal uprights.

[0013] Preferred method: After the scaffolding is erected in step two, measure and mark several elevation control points, then lay out the bottom support with lines, and install the disc-lock scaffolding on it. Install the adjustable top support on the top of the scaffolding uprights. The adjustable top support is used to adjust the height of the scaffolding and to remove the formwork. The adjustable top support used in this scaffolding has an adjustable range of about 35cm, and the adjustable bottom support has an adjustable range of 25cm.

[0014] Preferred method: In step two, the scaffolding preloading is carried out using sandbags and sand loads.

[0015] Preferred method: When installing the inner formwork of the box girder in step two, the specific process is as follows: tying the bottom side plate reinforcement - installing the corrugated pipe - threading the steel strand - erecting the inner formwork - reserving the manhole - tying the top plate reinforcement.

[0016] Preferred method: After the prestressing is completed in step two, the elevation of the bottom formwork should be adjusted in a timely manner, and the reinforcement and concrete construction of the box girder should be carried out.

[0017] Preferred timing for dismantling the scaffolding in step four: after the box girder concrete has reached its design strength, the steel strands have been tensioned, and the ducts have been grouted and anchored.

[0018] Preferred method: The scaffolding dismantling method in step four is as follows:

[0019] A. Use a wrench or similar tool to loosen the top support bolts to unload the material, allowing the bottom formwork to detach from the bottom of the box girder;

[0020] B. Loosen the connecting bolts between the bottom mold and the side mold, and between the bottom molds;

[0021] C. Use a crane to remove the flange plate and side formwork template, manually move the bottom formwork to the flange plate position in sections, and then use a crane to lift it to the ground;

[0022] D. Remove the I-beams and top supports;

[0023] E. Dismantle the disc-lock scaffolding in order from top to bottom;

[0024] F. Move the dismantled scaffolding to the next construction span for construction.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] This patent utilizes full-span scaffolding to reinforce existing highway bridges. The advantages of this invention are as follows:

[0027] 1) Use disc-lock full-span scaffolding to reinforce existing highway bridges. Then, erect disc-lock full-span scaffolding on the top of the existing highway bridge as cast-in-place scaffolding. Installation and dismantling are relatively convenient and can save construction time.

[0028] 2) Disc-lock full-span scaffolding can be used to reinforce existing highway bridges. It can be reused after dismantling, with less wear and tear, which can save resources and reduce costs.

[0029] 3) The disc-lock type full-span scaffolding is used to reinforce existing highway bridges without affecting the structure of the existing highway bridges, and is safe and reliable. Attached Figure Description

[0030] Figure 1 This is a flowchart of a construction method for a cast-in-place box girder crossing an existing overpass. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0032] Please see Figure 1 In this embodiment of the invention, a method for constructing a cast-in-place box girder spanning an existing overpass includes the following steps:

[0033] Step 1: Construction preparation stage, including foundation treatment, formwork processing, and steel reinforcement processing;

[0034] During foundation treatment, No. 20 I-beams were laid longitudinally under the scaffolding supports on the bridge, and 20×5cm wooden planks were laid transversely under the I-beams. The planks were placed on the original hollow slab web of the viaduct. The scaffolding under the bridge was also supported on the original hollow slab web of the highway bridge, so that the original highway bridge only bore vertical pressure, and the construction load was directly transferred from the bridge to the foundation. After the foundation pit was cleared, silty clay was backfilled in layers and leveled and compacted. Then, 20cm of crushed stone was laid on the treated clay layer, leveled manually, and compacted with a road roller. If the installation is less than four times, lay 5×20cm square timber on the gravel layer according to the positions corresponding to the installation of the scaffolding steel pipe uprights. The width of the compacted clay layer and gravel layer should be approximately 15m. To prevent the properly treated foundation from being soaked in water, dig 40×30cm drainage ditches on both sides. The drainage ditches should be excavated in sections to form a slope, and sump pits should be dug at the lowest points on both sides. If the existing foundation is the original asphalt pavement and the foundation is in good condition, no treatment is required. Lay 5×20cm square timber according to the positions corresponding to the installation of the scaffolding steel pipe uprights.

[0035] Step 2: Construction and reinforcement of full-span scaffolding. First, erect the scaffolding. After the scaffolding is erected, install the bottom formwork and outer side plate of the box girder. Then, preload the scaffolding. After the preloading is completed and unloaded, adjust the elevation of the bottom formwork according to the current construction requirements of the bridge. Finally, install the inner side formwork and the bottom formwork of the top plate of the box girder.

[0036] When erecting scaffolding, based on stress calculations, the structure of the disc-lock scaffolding was determined as follows: the scaffolding layout dimensions at the end beams are 600×600cm; at the mid-span web, the layout dimensions are 900×600cm; and at the flanges and mid-span box girder, the layout dimensions are 900×(900+1200+900)cm. That is, the row spacing at the beams is 600cm, and the row spacing at other locations is 900cm, with the row direction perpendicular to the centerline of the highway bridge. All scaffolding horizontal members are spaced 1.2m apart, meaning that a row of longitudinal and transverse connecting disc-lock steel pipes is installed every 1.2m along the height, connecting all uprights into a whole. The maximum allowable stress is 30kN, and the calculated maximum stress on the scaffolding for this project is 27.9kN. To ensure the overall stability of the scaffolding, for scaffolding under 10m in height, one scissor brace is installed every 5 rows of horizontal uprights and every 5 rows of horizontal uprights; for scaffolding between 10m and 15m in height, one scissor brace is installed every 4 rows of horizontal uprights and every 4 rows of horizontal uprights; for scaffolding between 15m and 20m in height, one scissor brace is installed every 3 rows of horizontal uprights and every 3 rows of horizontal uprights. After the foundation is properly prepared, sleepers are laid longitudinally, and then the scaffolding can be erected. After the scaffolding is erected, several elevation control points are measured and marked, then the base supports are laid out, and the disc-lock scaffolding is installed on top. Adjustable top supports are installed at the top of the scaffolding uprights. The adjustable top supports are used to adjust the height of the scaffolding and for removing formwork. The adjustable range of the adjustable top supports used in this scaffolding is about 35cm, and the adjustable range of the adjustable base supports is 25cm. After the scaffolding pipes are installed, I10 I-beams are laid on the adjustable top supports. The I10 I-beams below the bottom plate of the box girder are arranged laterally, with a length of 8m and a spacing of 0.6-0.9m; the I10 I-beams are also arranged perpendicular to the bridge direction. After the I-beams are laid, 10×10cm timbers are laid on them, with a spacing of 30cm.

[0037] During preloading, the preloading is carried out in stages according to 115% of the box girder's self-weight to obtain basic data. The formwork elevation is set according to the ballast data and the precamber of the structural design. The scaffolding preloading is carried out by adding sandbags and sand load for easy operation.

[0038] After the box girder scaffolding is erected, the bottom formwork is installed and the elevation is initially adjusted so that the bottom formwork elevation is about 1.0 cm higher than the design elevation. Measurement control points are set up at key points on the cross section of the construction box girder. Their positions must be fixed and can meet the observation range. According to the load requirements, 1m×1m×1m fixed-length sandbags are made by a professional manufacturer.

[0039] For each box girder scaffolding preloading, the preloading is carried out at the web and bottom plate of the box girder, while the flange plate is selected for preloading based on the actual situation of the static cone penetrometer.

[0040] The specific process for installing the inner formwork of the box girder is as follows: tying the bottom side plate reinforcement - installing corrugated pipes - threading steel strands - erecting the inner formwork - reserving manholes - tying the top plate reinforcement.

[0041] During ballast loading, several settlement and displacement observation points are set up on the scaffold foundation to monitor settlement and displacement. In principle, the observation points are set up at the mid-span, pier top, and scaffold foundation of each span, with no less than 3 measuring points per section. A temporary leveling point is set up on the nearby completed pier or next to the box girder. The elevation and displacement changes of each measuring point are observed throughout the ballast loading process using the third-order leveling method. The data are analyzed and compiled to obtain the values ​​for controlling the formwork elevation and setting the pre-camber.

[0042] Sandbags were arranged in three layers, with the first layer added first, followed by the second and third layers. A crane was used for stacking the sandbags, with manual assistance, and the ballast load was distributed as evenly as possible with the construction load.

[0043] During preloading construction, graded loading is adopted. After loading reaches 50% and 115%, loading is stopped and continuous monitoring of scaffold settlement and displacement is carried out for 12 hours. The next grade of load can be applied only after the application and monitoring of each grade of load are completed and no abnormalities are found. After all loading is completed, continuous monitoring is carried out in 12-hour units. If the settlement and displacement of the scaffold are less than 1 mm for two consecutive days, the foundation settlement can be considered to be basically stable, and the load can be unloaded at this time.

[0044] After unloading, the measurement points are observed again to calculate the elastic and inelastic deformation.

[0045] After preloading is completed, the elevation of the bottom formwork should be adjusted promptly, and the reinforcement and concrete construction of the box girder should proceed. During the concrete construction of the box girder, observation points should be established at the preloading observation points, and observations should continue.

[0046] Step 3: Casting of the box girder. After the box girder is cast across the entire cross section, it is cured. Tensioning is carried out when the concrete strength reaches 85% of the design strength, and finally grouting is performed.

[0047] Step 4: Dismantle the scaffolding. The dismantling order is as follows: dismantle the inner formwork, dismantle the outer formwork and the top and bottom formwork, remove the bottom formwork, and dismantle the scaffolding.

[0048] Demolition time: After the box girder concrete reaches the design strength, the steel strands are tensioned, and the ducts are grouted and the anchors are sealed.

[0049] To facilitate the dismantling of the scaffolding system and accelerate the dismantling process, unloading is carried out in symmetrical groups from both ends towards the middle. The dismantling method is as follows:

[0050] A. Use a wrench or similar tool to loosen the top support bolts to unload the material, allowing the bottom formwork to detach from the bottom of the box girder;

[0051] B. Loosen the connecting bolts between the bottom mold and the side mold, and between the bottom molds;

[0052] C. Use a crane to remove the flange plate and side formwork template, manually move the bottom formwork to the flange plate position in sections, and then use a crane to lift it to the ground;

[0053] D. Remove the I-beams and top supports;

[0054] E. Dismantle the disc-lock scaffolding in order from top to bottom;

[0055] F. Move the dismantled scaffolding to the next construction span for construction.

[0056] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for constructing cast-in-place box girders spanning existing overpasses, characterized in that, Includes the following steps: Step 1: Construction preparation stage, including foundation treatment, formwork processing and steel reinforcement processing; during foundation treatment, No. 20 I-beams are laid longitudinally under the bottom support of the scaffolding on the bridge, and 20cm×5cm wooden boards are laid transversely under the I-beams. The wooden boards are placed on the hollow slab web of the existing overpass. The scaffolding under the bridge is also supported on the hollow slab web of the existing overpass, so that the existing overpass only bears the vertical pressure, and the construction load is directly transferred from the bridge to the foundation under the bridge. Step Two: Erection and Reinforcement of Full-Span Scaffolding; First, erect the full-span scaffolding. After the scaffolding is erected, install the bottom formwork and outer side panels of the box girder, and then perform graded preloading on the scaffolding; After unloading after preloading, adjust the elevation of the bottom formwork of the box girder according to the current bridge construction requirements. Finally, install the inner side formwork and the bottom formwork of the top slab of the box girder; After the scaffolding is erected, measure and mark several elevation control points, then lay out the bottom support with lines, and install the disc-lock scaffolding on it. Install adjustable top supports on the upper part of the scaffolding uprights, and lay I-beams on the adjustable top supports; The adjustable top supports are used to adjust the height of the scaffolding and remove the box girder formwork, and its adjustable range is about 35cm; Step 3: Casting of the box girder; After the box girder is cast across the entire cross section, it is cured. Tensioning is performed when the concrete strength reaches 85% of the design strength, and finally grouting is carried out. Step 4: Dismantling of scaffolding; the dismantling order is as follows: dismantle inner formwork - dismantle outer formwork, top slab bottom formwork - remove bottom formwork - dismantle scaffolding.

2. The construction method for a cast-in-place box girder spanning an existing overpass according to claim 1, characterized in that, In step two, when erecting scaffolding, the structural form of the disc-lock scaffolding is determined as follows: for scaffolding under 10m, a scissor brace is set up for every 5 rows of horizontal uprights and for every 5 rows of horizontal uprights; for scaffolding between 10m and 15m, a scissor brace is set up for every 4 rows of horizontal uprights and for every 4 rows of horizontal uprights; for scaffolding between 15m and 20m, a scissor brace is set up for every 3 rows of horizontal uprights and for every 3 rows of horizontal uprights.

3. The construction method for a cast-in-place box girder spanning an existing overpass according to claim 1, characterized in that, In step two, the adjustable range of the base is 25cm.

4. The construction method for a cast-in-place box girder spanning an existing overpass according to claim 1, characterized in that, In step two, the scaffolding preloading is carried out using sandbags and sand loads.

5. A construction method for a cast-in-place box girder spanning an existing overpass according to claim 1, characterized in that, In step two, the specific process of installing the inner formwork of the box girder is as follows: tying the bottom side plate reinforcement - installing the corrugated pipe - threading the steel strand - erecting the inner formwork - reserving the manhole - tying the top plate reinforcement.

6. A construction method for a cast-in-place box girder spanning an existing overpass according to claim 1, characterized in that, In step four, the scaffolding dismantling time is set as follows: after the box girder concrete reaches the design strength, the steel strands are tensioned, and the ducts are grouted and anchored.

7. A construction method for a cast-in-place box girder spanning an existing overpass according to claim 1, characterized in that, In step four, the scaffolding dismantling process is as follows: A. Use a wrench to loosen the bolts of the adjustable top support to unload the material, allowing the bottom formwork to detach from the bottom of the box girder; B. Loosen the connecting bolts between the bottom mold and the side mold, and between the bottom molds; C. Use a crane to remove the flange plate and side formwork template, manually move the bottom formwork to the flange plate position in sections, and then use a crane to lift it to the ground; D. Remove the I-beam and the adjustable top support; E. Dismantle the disc-lock scaffolding in order from top to bottom; F. Move the dismantled scaffolding to the next construction span for construction.

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