Variable-cross-section multi-box-chamber box girder structure and construction method thereof

Abstract

The invention discloses a variable-cross-section multi-box-chamber box girder structure and a construction method thereof.The variable-cross-section multi-box-chamber box girder structure comprises a bridge body, a first end and a second end, the width size of a bridge floor is gradually reduced in the direction from a first end plate to the second end, and a plurality of box chamber structures are arranged between the first end and the second end in a penetrating mode; at least part of the box chamber structure is symmetrically arranged along the central positions of the first end part and the second end part; a first bridge abutment is arranged on the first end part, and a second bridge abutment is arranged on the second end part; the bridge body is supported on the ground through the first bridge abutment and the second bridge abutment, and the distance from the first end part to the second end part is smaller than the width of the second end part; by means of the structure of the scheme, under the condition that drainage of the wide bridge body structure is guaranteed, the overall stability can be guaranteed, and meanwhile the construction difficulty of the bridge body can be lowered.

Description

Technical Field

[0001] The present invention relates to the technical field of box beams, and in particular to a variable-cross-section multi-chamber box beam structure and a construction method thereof. Background Art

[0002] Prestressed concrete cast-in-place bridges have been widely used in China in areas such as highways, railways, and urban roads, becoming one of the main bridge types. Since the 1950s, my country has begun to research and apply prestressed concrete technology. With the continuous development of technology, prestressed concrete highway bridges have been widely used in my country. Especially since the 1990s, with the rapid development of highway construction and urbanization, prestressed concrete highway bridges have played a significant role in highway bridge construction. Currently, prestressed concrete highway bridges have a wide range of applications, not only becoming one of the main bridge types in highway bridges, but also widely used in urban viaducts, overpasses, railway overpasses, and other occasions.

[0003] The box girder in the existing technology is usually applied to the bridge with a small transverse span and a high vertical height. Therefore, the box girder usually has only 2 or 3 box chambers, and the high vertical height facilitates the construction of the box girder and the box chamber. At present, the existing technology has not yet developed a box girder structure for bridges with large transverse spans and low vertical heights, which brings difficulties to the construction of the existing technology. Summary of the Invention

[0004] The purpose of the present invention is to provide a variable-section multi-box-chamber box girder structure and its construction method to address the above-mentioned shortcomings, thereby solving the problem that the existing technology has no application technology for bridge box girders with large transverse spans and low vertical heights, which brings difficulties to construction.

[0005] The present invention is achieved through the following solutions:

[0006] A variable-section multi-box-chamber box girder structure includes a bridge body, a first end and a second end. The width of the bridge deck gradually decreases from the first end plate in the direction of the second end. Multiple box-chamber structures are arranged between the first end and the second end, and at least some of the box-chamber structures are symmetrically arranged along the center positions of the first end and the second end; a first abutment is arranged on the first end, and a second abutment is arranged on the second end; the bridge body is supported by the first abutment and the second abutment and the ground, and the distance from the first end to the second end is less than the width of the second end.

[0007] This solution discloses a construction method for a variable-section multi-chamber box girder structure, comprising the following steps:

[0008] Step S1, foundation treatment, after leveling the foundation, press the stepped foundation of a predetermined height according to the height difference; Step S2, support system construction, first set up the support system, after the support system is set up, pre-press the support system, and finally perform support system pre-pressing monitoring; Step S3, bottom formwork construction, which includes bottom formwork installation and rapid adjustment of bottom formwork elevation; Step S4, side steel formwork installation; Step S5, first beam construction; Step S6, second beam construction; Step S7, prestressed construction; Step S8, concrete curing; Step S9, formwork frame removal.

[0009] Step S1 is specifically as follows: leveling the original ground, controlling the original ground elevation in a stepped manner according to the elevation requirements of different areas, treating the foundations on both sides separately with the middle of the beam body as the boundary, raising the foundation on the higher side of the bottom plate to a predetermined height for leveling and compacting, forming a predetermined height difference with the foundation on the lower side of the bottom plate, and forming a stepped foundation; rolling and compacting the foundation with a roller, and then pouring a concrete cushion layer; at the same time, setting a transverse slope drainage from the center line of the bridge to both sides.

[0010] The erection of the support system in step S2 is specifically as follows: the cast-in-place beam support adopts a full-span buckle support structure, and the support adopts a buckle type support. When erecting, the line is first laid out for positioning, and then the position of the adjustable base is accurately placed according to the line-laying position, and it should be erected in the order of vertical poles, horizontal poles, and diagonal poles to form a basic frame unit, which should be expanded to form an overall support system; in the first step, the horizontal poles and diagonal poles are locked on the vertical poles to keep them stable, and the lines are hung to adjust whether the vertical and horizontal rows of vertical poles are in a straight line; after each step of the support is erected, the horizontal pole step distance, the vertical and horizontal distances of the vertical poles, the verticality deviation of the vertical poles and the horizontal deviation of the horizontal poles are corrected; since the height of the land passage bridge support is small and the bridge deck is wide, in order to meet the requirements of large vertical and horizontal slope height differences of the bridge bottom plate, the buckle type full-span support is divided into two independent support systems, which are disconnected in the middle of the bridge in the transverse direction, and the distributed beams are laid continuously on the support.

[0011] The support system preload monitoring operation in step S2 specifically includes the following steps: Step S21, support preload monitoring includes: monitoring point elevation before loading, monitoring point elevation after each level of loading, monitoring point elevation every 24 hours after loading to 120% of the concrete structure's dead load, and monitoring point elevation 6 hours after unloading;

[0012] Step S22, Arrangement of Support Prestressing Monitoring Points: Monitoring points are set at both ends of the prestressing area and at intervals of 1 / 4 of the length, with the middle point located at the center of the span. Five monitoring points should be arranged along the centerline of the concrete beam on the foundation and support points of each monitoring section, with five rows arranged in the longitudinal direction of the bridge, with a focus on monitoring the cross-section across the span.

[0013] Step S23, monitoring frequency of stent preload and processing of results;

[0014] Before loading the support, the initial value of each monitoring point should be monitored and recorded; the deformation of the support should be observed 12 hours after each level of loading is completed, and the displacement of each monitoring point should be monitored and recorded at intervals of 6 hours. When the difference between the average displacements of two adjacent monitoring times is less than 2mm, subsequent loading should be carried out; after all preloading loads are applied, the elevation of the monitoring points should be monitored every 24 hours. If the average settlement of each monitoring point in the first 24 hours is less than 1mm, or the average settlement of each monitoring point in the first 72 hours is less than 5mm, the support preloading is judged to be qualified and the preloading load is removed; the support preloading is unloaded once, and the preloading load should be unloaded symmetrically, balanced, and synchronously; 6 hours after the support is unloaded, the displacement of each monitoring point should be monitored and recorded; after the support preloading is completed, the foundation settlement and the elastic deformation, inelastic deformation and plane displacement of the support should be calculated and analyzed based on the monitoring data, and preloading and unloading deformation diagrams should be made respectively. The inelastic deformation and the elastic deformation at 100% design load should be calculated based on the preloading monitoring to obtain the construction pre-camber, and the elastic deformation at 100% design load should be added to the template elevation calculation.

[0015] Step S5, the first beam construction, includes the following steps: Step S5, the first beam construction, includes the following steps: Step S51, rapid binding of bottom web reinforcement in sections; Step S52, installation of web corrugated pipes; Step S53, installation of inner formwork and rapid reinforcement by bracing method; Step S54, first concrete pouring.

[0016] In step S53, the inner mold is installed and the bracing method is used for rapid reinforcement, specifically:

[0017] To ensure the positioning accuracy of the multi-chamber variable-section formwork, a combination of measurement and layout positioning using a total station and level instrument and pre-assembly positioning is used. First, precise measurement and layout are carried out to determine the approximate position of the formwork. Then, during pre-assembly of the formwork, positioning points at key locations are marked. Finally, during on-site installation, precise adjustments are made based on the control lines of the measurement and layout, combined with the pre-assembly positioning points. At the same time, positioning steel bars are installed at the bottom of the formwork to firmly fix the formwork to the lower structure and prevent horizontal displacement of the formwork during concrete pouring. The web inner formwork is all made of bamboo plywood and assembled on-site.

[0018] The inner formwork rapid reinforcement system adopts the bracing method for reinforcement, and the bracing rods are made of ordinary scaffolding steel pipes. Top supports are set at both ends to adjust the bracing width; after the web formwork is installed, the bracing rods are installed, and the rods are arranged in two layers, with a longitudinal spacing of 1m. The bracing rods are arranged and reinforced until a box room is reinforced; to ensure the overall stability of the bracing rods, ordinary steel pipes are set in the longitudinal direction for reinforcement, so that the bracing rods form a frame system; the cast-in-place beams are cast in two times; when pouring concrete for the first time, the inner formwork top plate is not installed; before pouring concrete for the second time, the inner formwork top plate is installed and the top plate concrete is poured.

[0019] The first concrete pouring in step S53 is specifically as follows:

[0020] During the first concrete pouring, the pouring sequence is from the mid-span toward the abutment, and from the middle toward both sides. When placing concrete, working from the middle toward both sides can better ensure uniform distribution of concrete and reduce eccentric loading. A sky pump is placed in the middle of the abutments on both sides. To ensure the flatness and density of the bottom slab concrete and avoid voids, an insert vibrator combined with a flat plate vibrator is used for vibration. After the bottom slab is poured, the middle web is poured, followed by the other webs symmetrically poured on both sides, and finally the side webs. Concrete pouring is appropriately stopped 30 cm above the web chamfer, and pouring continues to the web chamfer until the web chamfer concrete has a certain degree of consolidation and before initial setting. After pouring, the concrete is promptly watered and cured.

[0021] During the concrete pouring process, the material should be discharged evenly and continuously. To prevent concrete segregation, the free fall height of concrete should not exceed 2m, and the pouring time of each truck of concrete should be ensured to be within the specified range; commercial concrete is used and pumped into the mold for pouring; during the concrete pouring process, when the distribution boom changes the pouring position, the distribution boom outlet is sealed with a material bag; the webs on both sides are poured symmetrically; the concrete is vibrated mainly with a φ50 inserted vibrating rod, and a φ30 vibrating rod is used for the anchor parts and cross partitions to ensure the density of the concrete; the vibrating rod is strictly prohibited from directly contacting the corrugated pipe. At the same time, a special person is assigned to follow the load of the bracket and the splicing of the template during the pouring process.

[0022] Step S6, the second beam construction, includes the following steps: step S61, inner formwork top plate reinforcement binding and formwork installation; step S62, second concrete pouring; step S63, construction hole sealing;

[0023] The inner formwork top plate reinforcement binding and formwork installation in step S61 are specifically as follows:

[0024] Before tying the top plate reinforcement, the upper part of the box beam box chamber formwork should be installed first. In order to facilitate the later personnel to enter the box to remove the inner formwork, a construction hole must be reserved at the top of the beam during installation. A construction hole is reserved for each box chamber, and the construction holes between the box chambers are staggered, with a total of 10 holes arranged. During the tying of the top plate reinforcement, construction holes are reserved for overlapping reinforcement, which will be restored later.

[0025] The second pouring of concrete in step S62 is specifically as follows:

[0026] Before the second pouring, the joint surface is roughened. After the top plate reinforcement and end formwork are installed, a sky pump is placed on each side of the abutment before concrete pouring. The pouring sequence is from the mid-span to the abutment in the longitudinal direction of the bridge, and from the middle to both sides in the transverse direction of the bridge. When pouring concrete on an inclined surface, pour horizontally from the lowest point to the highest point. The thickness of each layer of concrete pouring should not exceed 0.3m. The upper layer of concrete should be poured before the lower layer of concrete begins to set or can be reshaped. The pouring process must be continuous, and the formation of cold joints is not allowed.

[0027] The construction hole is sealed in step S63, specifically:

[0028] After the pouring of beam concrete is completed, the reserved construction hole needs to be sealed, and the debris and loose concrete around the construction hole need to be cleaned up, and then the beam concrete around the construction hole needs to be roughened; since the construction hole cuts off the steel bars, the reserved steel bars need to be restored first, and then the steel bars of appropriate length are cut according to the drawings for welding, with a lap length of 10d to ensure the continuity and anchorage length of the steel bars; select appropriate formwork for support, and ensure that the formwork is firm and sealed to prevent concrete leakage; select C55 concrete, and avoid collision with the formwork and steel bars during vibration; when finishing, it must be ensured to be flush with the original structure surface.

[0029] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0030] 1. In this solution, the bridge deck size gradually decreases from the first end to the second end of the bridge body, and the overall cross-section structure is variable. In addition, the distance from the first end to the second end of this solution is less than the width of the second end, making the length of the bridge body less than the width on both sides, resulting in a wider transverse span of the abutment. The existing technology does not have a corresponding box-chamber box girder structure for application. This solution uses multiple box-chamber structures in the box body. On the one hand, it can reduce material consumption while ensuring the mechanical properties of the bridge body. On the other hand, it can meet the requirements of overall structural stability and symmetry under the condition of a large width and drainage slope. Since the bridge body structure in this solution is generally wider in the width direction, and in order to avoid water accumulation in the center during construction, there will be a 2% slope reduction, resulting in a height difference of 60 to 70 cm from the center of the bridge to the two sides of the bridge. Through the structure of this solution, not only can the drainage of the wide bridge body structure be guaranteed, but the overall stability can also be guaranteed, while also reducing the difficulty of bridge construction.

[0031] 2. The present invention's variable-section, multi-chamber box girder construction method addresses a series of construction challenges associated with low-height, multi-chamber, variable-section, cast-in-place beams through research into the technologies of stepped, graded support erection, support preloading, formwork assembly, rapid zoned reinforcement construction, rapid internal formwork reinforcement, concrete pouring, and controlled mobile tensioning. This method addresses numerous challenges, including the significant vertical and transverse gradient differences in the box girder floor, the inefficiency of preloading solutions, the difficulty of formwork assembly and adjustment, the complex and slow multi-zone reinforcement construction, the complex internal formwork reinforcement operation, unsatisfactory concrete pouring results, and the time-consuming and labor-intensive setup of tensioning supports.

[0032] The specific studies have achieved the design details of the elevation and slope of the box girder bottom plate by setting up the scaffolding in stages; achieved cost reduction and efficiency improvement by rationally designing the preloading method; ensured the aesthetic appearance of the beam after pouring by precise measurement and control of the formwork assembly; simplified the construction process and achieved rapid construction by rationally planning and allocating the steel bar construction; achieved rapid reinforcement of multiple box room formwork and improved construction efficiency by combining the design of multiple support methods and carrying out multi-point simultaneous construction; and achieved smooth pouring and forming of the box girder concrete by adjusting the concrete pouring method in stages. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the overall structure of the present invention from above;

[0034] Figure 2 It is a schematic cross-sectional structure diagram of the present invention as a whole;

[0035] Figure 3 is a schematic cross-sectional structural diagram of the first end portion of the present invention;

[0036] Figure 4 is a schematic cross-sectional structural diagram of the second end portion of the present invention;

[0037] Figure 5 It is a construction flow chart of the present invention:

[0038] Description of the drawings: 1. Bridge body; 2. First end; 3. Second end; 4. First abutment; 5. Second abutment; 6. Sidewalk; 7. Driveway; 8. Drain; 9. First foundation top; 10. Second foundation top; 11. First box chamber; 12. Second box chamber; 13. Third box chamber; 14. Fourth box chamber; 15. Fifth box chamber; 16. Sixth box chamber; 17. Seventh box chamber; 18. Eighth box chamber; 19. Ninth box chamber; 110. Tenth box chamber. DETAILED DESCRIPTION

[0039] All features disclosed in this specification, or all steps in the disclosed methods or processes, except mutually exclusive features and / or steps, can be combined in any manner.

[0040] Any feature disclosed in this specification (including any appended claims and abstract), unless otherwise stated, may be replaced by other equivalent or similar features. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0041] In the description of the present invention, it should be understood that the terms "up", "down", "left", "right", etc., indicating directions or positional relationships, are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0042] Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be understood to indicate or imply relative importance or to implicitly indicate the quantity of the technical features being referred to. Thus, a feature defined as "first," "second," etc. may explicitly or implicitly include one or more of such features.

[0043] Example 1

[0044] like Figures 1 to 4 As shown, the present invention provides a technical solution:

[0045] A variable-section multi-box-chamber box girder structure, which at least includes but is not limited to a bridge body 1, a first end 2 and a second end 3. The width of the bridge deck gradually decreases from the first end plate in the direction of the second end 3. A plurality of box-chamber structures are arranged between the first end 2 and the second end 3, and at least some of the box-chamber structures are symmetrically arranged along the center positions of the first end 2 and the second end 3; a first abutment 4 is arranged on the first end 2, and a second abutment 5 is arranged on the second end 3; the bridge body 1 is supported by the ground through the first abutment 4 and the second abutment 5, and the distance from the first end 2 to the second end 3 is less than the width of the second end 3.

[0046] Based on the above structure, in this solution, the bridge deck size gradually decreases from the first end 2 to the second end 3 of the bridge body 1, and the overall cross-section structure is variable from a cross-sectional perspective. In addition, the distance from the first end 2 to the second end 3 of this solution is less than the width of the second end 3, making the length of the bridge body 1 less than the width on both sides, resulting in a wider transverse span of the abutment. The existing technology does not have a corresponding box-chamber box girder structure for application. This solution adopts multiple box-chamber structures in the box body. On the one hand, it can reduce material consumption while ensuring the mechanical properties of the bridge body 1. On the other hand, it can meet the requirements of overall structural stability and symmetry under the condition of a large width and drainage slope. Since the bridge body 1 structure in this solution is relatively wide from the width direction, and in order to avoid water accumulation in the center during construction, there will be a 2% slope reduction, resulting in a height difference of 60 to 70 cm from the center of the bridge to the two sides of the bridge. Through the structure of this solution, not only can the drainage of the wide bridge body 1 structure be guaranteed, but the overall stability can also be guaranteed, and the construction difficulty of the bridge body 1 can also be reduced.

[0047] As an example, sidewalks 6 are provided on both sides of the bridge body 1 and are parallel to the sides of the bridge body 1. The sidewalks 6 are elevated. A center line is provided at the center of the bridge body 1, and two-way carriageways 7 are provided on both sides of the center line.

[0048] Based on the above structure, an inclined sidewalk 6 is set to facilitate walking, and a two-way carriageway 7 is set to facilitate vehicle traffic. Raising the sidewalk 6 can prevent water flowing from the carriageway 7 from flowing onto the sidewalk 6.

[0049] As an example, a drain outlet 8 is provided at a raised portion of the sidewalk 6 , and the sidewalk 6 as a whole is inclined toward the drain outlet 8 , and the single-side carriageway 7 is also inclined toward the drain outlet 8 close thereto.

[0050] Based on the above structure, by arranging the sidewalk 6 and the roadway 7 at an angle, any water flow that may exist can be quickly discharged outward through the drain outlet 8 .

[0051] As an example, the entire inclination gradient of the single-side carriageway 7 from the center line to the drain outlet 8 is 2%, and the entire inclination gradient of the sidewalk 6 from the side to the drain outlet 8 is 1.5%.

[0052] As an example, ten chambers are arranged in sequence along the width direction of the cavity, the first chamber 11, the second chamber 12, the third chamber 13, the fourth chamber 14, and the fifth chamber 15 are respectively arranged at the bottom of the left lane 7, and the sixth chamber 16, the seventh chamber 17, the eighth chamber 18, the ninth chamber 19, and the tenth chamber 110 are respectively arranged at the bottom of the right lane 7; among them, the first chamber 11 and the tenth chamber 110 are respectively arranged at positions away from the center line on the two side lanes 7, and the fifth chamber 15 and the sixth chamber 16 are respectively symmetrically arranged at positions close to the center line on the two side lanes 7.

[0053] From the first chamber 11 to the fifth chamber 15, and from the tenth chamber 110 to the sixth chamber 16, the chambers are arranged with gradually increasing levels, wherein the first chamber 11 and the tenth chamber 110 are the smallest chambers.

[0054] Based on the above structure, this solution sets the height position of the box chamber according to the shape and inclination slope of the bridge body 1, which can make the structure of the entire bridge body 1 more stable and will not cause deformation of the bridge deck.

[0055] As an example, the width of the first end portion 2 is 53 m, the width of the second end portion 3 is 36.5 m, and the length of the bridge body 1 is 29.5 m.

[0056] As an example, a first foundation top 9 can be provided at the bottom of the first abutment 4, and a second foundation top 10 can be provided at the bottom of the second abutment 5. The first abutment 4 and the second abutment 5 are supported by the first foundation top 9 and the second foundation top 10 to avoid overall settlement.

[0057] As an example, the area of ​​the first foundation top 9 is not less than the coverage area of ​​the bottom of the first abutment 4, and the area of ​​the second foundation top 10 is not less than the coverage area of ​​the bottom of the second abutment 5; a height difference is set between the first foundation top 9 and the second foundation top 10.

[0058] Based on the above structure, setting a larger foundation top area can avoid ground settlement and prove the overall structural strength.

[0059] Example 2

[0060] like Figure 5 Based on the above embodiment 1, the present invention provides a technical solution:

[0061] A construction method for a variable-cross-section multi-chamber box girder structure, comprising at least the following steps:

[0062] Step S1: foundation treatment, after leveling the foundation, pressing a stepped foundation of a predetermined height according to the height difference;

[0063] Specifically, the bridge bottom has transverse and longitudinal slopes, and the maximum height difference of the bottom plate reaches 67.2cm. Before setting up the buckle bracket, the bracket system height must be determined and the elevation of the top surface of the foundation treatment must be accurately calculated. The original ground was leveled, and the original ground elevation was controlled in a stepped manner according to the elevation requirements of different areas. The foundations on both sides were treated separately, with the middle of the beam as the boundary. The foundation on the higher side of the bottom plate was raised by 25cm and leveled and compacted, creating a 25cm height difference with the foundation on the lower side of the bottom plate, forming a stepped foundation.

[0064] The foundation was compacted with a roller and tested to have a bearing capacity of no less than 130 kPa before the concrete cushion was poured. A 2% slope was set up for drainage from the centerline of the bridge to both sides, with the water ditch merging into the ditches on both sides of the bridge line.

[0065] Step S2, support system construction, firstly, the support system is erected, after which the support system is erected, the support system is pre-stressed, and finally the support system pre-stressing monitoring operation is performed;

[0066] The erection of the support system includes the following steps:

[0067] The cast-in-place beam supports utilize a full-height, interlocking support structure, with an overall support height of 1-2 meters. The bottom formwork for the cast-in-place beams utilizes 15mm-thick bamboo plywood and 100×100mm longitudinal timbers. Spacing between the webs and the solid sections of the beam ends is 150mm, and the spacing below the box chamber is 300mm. Interlocking scaffolding is installed below the transverse distribution beams, with interlocking scaffolding spacing of 900mm longitudinally and 900mm transversely, with a step-over distance of 1.0m. The support base is placed on a hardened concrete leveling layer.

[0068] The brackets are disc-type brackets, with vertical poles of φ60 mm in diameter, 3.2 mm in wall thickness, and made of Q345. Crossbars are made of Q235 with a diameter of 48 mm and a wall thickness of 2.75 mm. Diagonal braces are made of Q235 with a diameter of φ42 mm and a wall thickness of 2.5 mm. All are hot-dip galvanized. The scaffolding system consists of vertical poles, crossbars, and diagonal braces. All connections are secured with disc-shaped buckles and caliper-type wedge pins.

[0069] When setting up the support, first lay out the lines to position the support. Then, accurately position the adjustable base according to the line. The vertical poles should be set up first, followed by the horizontal poles, and then the diagonal poles. This will form the basic frame unit, which should be expanded to form the entire support system. The first step is to lock the horizontal and diagonal poles onto the vertical poles to maintain stability. Use the lines to adjust the vertical and horizontal poles to ensure they are in a straight line.

[0070] Due to the significant bearing capacity of a single vertical pole, a pad at least 50mm thick (and at least two poles long) should be installed beneath the base support. The latch connection must be secure after self-locking with a hammer, and the pullout resistance must be no less than 3kN. The latch connection between the rod end buckle and the connecting plate should not pull out after self-locking with a hammer. When erecting scaffolding, strike the top surface of the latch at least twice with a hammer weighing at least 0.5kg until the latch is securely fastened.

[0071] After each step of support is completed, the horizontal bar pitch, the vertical and horizontal distances of the vertical bars, the vertical deviation of the vertical bars and the horizontal deviation of the horizontal bars should be corrected in time. The vertical deviation of the vertical bars should not be greater than 1 / 500 of the total height of the formwork support and should not be greater than 50mm.

[0072] As the height of the passage bridge support is small and the bridge deck is wide, in order to meet the requirements of large height difference of the longitudinal and transverse slopes of the bridge bottom plate, the disc-type full-bridge support is divided into two independent support systems, which are disconnected in the middle of the bridge in the transverse direction, and the distribution beams are laid continuously on the support.

[0073] The pre-stressing of the support system includes the following steps:

[0074] To ensure construction safety, the scaffolding was preloaded using ton bags after erection. To expedite construction, foundation preloading and scaffolding preloading were combined. The maximum load the scaffolding could withstand was: 859.6 × 2.6 × 1.2 = 2681.95 tons. After deducting the beam section above the side cap beam, the load at 120% preloading was (859.6 - 62.85 - 92.4) × 2.6 × 1.2 = 2197.5 tons. During the preloading process, if rainy, the ton bags were promptly covered with waterproof tarpaulin.

[0075] The loading pattern is symmetrical, spreading outward from the center to the sides. The ton bag size is 1.1 tons per bag. The preload sequence for the support should be symmetrical, from the mid-span to the support, and from the centerline to the sides. The preload distribution should be consistent with the support construction load, with the load weight deviation controlled within ±5% of the same load level. Loading should be graded according to the concrete pouring sequence.

[0076] The load preload level is divided into three levels (80%, 100%, and 120% of the constant load of the concrete structure). During the loading and holding process, a precision level and a special deformation observation ruler are used to conduct detailed settlement observations on each observation point in stages. Unloading is also carried out according to the same level. Regardless of loading or unloading, the support layout points need to be measured.

[0077] The support system preload monitoring includes the following steps:

[0078] Step S21, monitoring of the support preload includes: monitoring point elevation before loading, monitoring point elevation after each level of loading, monitoring point elevation every 24 hours after loading to 120% of the concrete structure's dead load, and monitoring point elevation 6 hours after unloading;

[0079] Step S22, Arrangement of Support Prestressing Monitoring Points: Monitoring points are set at both ends of the prestressing area and at intervals of 1 / 4 of the length, with the middle point located at the center of the span. Five monitoring points should be arranged along the centerline of the concrete beam on the foundation and support points of each monitoring section, with five rows arranged in the longitudinal direction of the bridge, with a focus on monitoring the cross-section across the span.

[0080] Step S23, monitoring frequency of stent preload and processing of results;

[0081] Before loading the bracket, the initial value of each monitoring point should be monitored and recorded; the deformation of the bracket should be observed 12 hours after each level of loading is completed, and the displacement of each monitoring point should be monitored and recorded every 6 hours thereafter. Subsequent loading can only be carried out when the difference between the average displacements of two adjacent monitoring times is less than 2mm;

[0082] After all preloads are applied, the elevation of the monitoring points is monitored every 24 hours, and the average settlement of each monitoring point in the first 24 hours is less than 1mm, or the average settlement of each monitoring point in the first 72 hours is less than 5mm, then the bracket preload can be determined to be qualified and the preload can be removed; the bracket preload can be unloaded at one time, and the preload should be unloaded symmetrically, evenly and synchronously.

[0083] After the support is unloaded for 6 hours, the displacement of each monitoring point should be monitored and recorded. After the support preloading is completed, the foundation settlement and the elastic deformation, inelastic deformation, and plane displacement of the support should be calculated and analyzed based on the monitoring data. Preloading and unloading deformation diagrams should be drawn separately. Based on the preloading monitoring, the inelastic deformation and the elastic deformation at 100% design load should be calculated to obtain the construction pre-camber. The elastic deformation at 100% design load should be included in the formwork elevation calculation.

[0084] Step S3, bottom formwork construction, which includes bottom formwork installation and bottom formwork elevation rapid adjustment;

[0085] The installation of the bottom template specifically includes the following steps:

[0086] Beam bottom formwork: The bottom formwork uses σ=15mm bamboo plywood, which is directly spread on the longitudinal beam square wood. Sponge double-sided tape is pasted between the formworks. The bottom plate crossbeam uses Ⅰ10 directly supported on the adjustable top support with a spacing of 90cm.

[0087] Use the top support to adjust the longitudinal and transverse slopes of the beam bottom so that the bottom formwork slope meets the requirements.

[0088] The rapid adjustment of the bottom formwork elevation specifically includes the following steps:

[0089] Before installing the base formwork, during the adjustment process, and after the adjustment is completed, measure the key parts of the base formwork and collect coordinate and elevation data. By establishing a high-precision measurement control network, including plane control points and elevation control points, set up 5 sections on the base formwork, with 3 measurement points on each section, to fully reflect the slope of the base formwork. Use a total station to measure the coordinates of the control points on the base formwork, and determine the slope of the base formwork by calculating the coordinate difference of the control points. By monitoring the deformation state of the bracket, obtain the elastic deformation and plastic deformation values, and provide a basis for the base formwork elevation. The elevation adjustment of the ultra-wide base formwork must meet the following requirements:

[0090] 1) When adjusting, the adjustable supports should be arranged evenly and symmetrically to ensure uniform and balanced force on the bottom mold. When adjusting the supports, pay attention to synchronization to avoid excessive local adjustments that may cause uneven deformation of the bottom mold.

[0091] 2) Group adjustment: Divide the extra-wide base mold into several areas and perform symmetrical adjustments in two groups to improve work efficiency. 3) Utilize jacking: Workers can use electric or hydraulic tools to assist in adjustments. By rotating the screw of the jacking, the height of the jacking can be quickly adjusted to adjust the slope of the base mold. 4) Real-time monitoring: During the adjustment process, the slope changes of the base mold are measured in real time, and fine-tuning is performed in a timely manner based on the measurement data to ensure that the slope meets the design requirements. 5) Comprehensive re-measurement: After the base mold slope adjustment is completed, the coordinates and elevations of all key parts of the base mold are re-measured. If there is an error outside the allowable range, analyze the cause and make adjustments again in a timely manner until the requirements are met.

[0092] Step S4: Install the side steel formwork. The side formwork is constructed of steel formwork, and the webs on both sides of the inclined web are constructed with Φ20mm finely rolled threaded steel for through-tensioning, ensuring a smooth and aesthetically pleasing beam shape. I10 I-beams are arranged longitudinally beneath the steel formwork support. A crane is used to lift the steel formwork in sections onto the I10 I-beams and secure them.

[0093] In order to improve efficiency, the bottom plate reinforcement is accurately positioned and the side formwork is installed at the same time as the bottom plate reinforcement is installed.

[0094] Step S5, the first beam construction, includes the following steps: Step S51, fast tying of bottom web reinforcement in different areas; Step S52, installation of web corrugated pipes; Step S53, installation of inner formwork and fast reinforcement by bracing; Step S54, first concrete pouring; Step S51, fast tying of bottom web reinforcement in different areas, specifically:

[0095] In the multi-chamber box girder reinforcement partition rapid construction technology, by dividing the construction workers into one, two, or three groups, the construction efficiency and quality can be effectively improved;

[0096] 1) A team of construction workers is responsible for the binding and installation of the bottom web reinforcement. First, they arrange longitudinally long steel bars on the bottom slab to facilitate positioning of the bottom slab reinforcement. Concrete pads are placed under the long steel bars to reserve a protective layer thickness (40mm). Then, according to the design drawings, they are responsible for installing the box girder bottom slab reinforcement, including the laying and binding of the bottom main and distribution bars, as well as the installation of related support bars and pads, to ensure that the bottom slab reinforcement is accurately positioned and the protective layer thickness meets the requirements.

[0097] 2) The second group of construction workers is responsible for the construction of the box girder web reinforcement; the focus is on the installation and connection of the vertical main reinforcement and horizontal distribution reinforcement. At the same time, they must handle the intersection of the web reinforcement and the bottom plate reinforcement to ensure a firm connection and accurate position, and to meet the requirements of the box chamber gradient;

[0098] 3) Three groups of construction workers are responsible for the installation and welding of the positioning bars and anti-collapse bars of the prestressed pipes, as well as the repair and welding of the missed reinforcement of the bottom plate and web.

[0099] Rebar intersections should be secured with 1.0mm diameter wire. Double wire should be used for larger diameter rebar, and spot welding can be used if necessary. All rebar intersections at the corners of structures or components should be tied. The bottom slab reinforcement should be marked with lines. The position of the rebar should be marked on the formwork or cushion layer, and the ties should be tied according to the markings. To prevent the web reinforcement from tipping over, continuous diagonal tying of the same type of rebar can also effectively position the web reinforcement. When tying the bottom web reinforcement, pay attention to the pre-embedded prestressed tendon pipes and anchor embedded parts. If embedded parts conflict with the beam reinforcement, the embedded parts should be positioned first. The rebar can be avoided accordingly, but it must not be arbitrarily cut. Use durable, plum blossom-shaped fine stone concrete pads of the same grade. The pads should be evenly distributed, with no fewer than 4 pads per square meter on the sides and bottom (with no more than 0.5m between adjacent pads).

[0100] The web bellows are installed in step S52, specifically:

[0101] During construction, the embedded pipes should be positioned according to the drawings. To prevent the corrugated pipes from floating during concrete pouring, U-shaped reinforcement and transverse support bars are welded to the corrugated pipes. The reinforcement is bent into a U-shaped ring with an inner diameter of 10 cm, then clamped around the corrugated pipes and welded to the web reinforcement. Transverse support bars are welded to the U-shaped reinforcement and the web frame for reinforcement. Positioning bars are installed every 0.8 m on straight sections and every 0.4 m on curved sections. These positioning bars should be securely welded to the main reinforcement of the beam section to ensure accurate positioning of the prestressed steel tendons. Corrugated pipe joints must ensure a tight seal, and adjacent corrugated pipe joints should be staggered. The corrugated pipes must not be damaged during construction. The pipe coordinates must be accurate to within 2 cm in beam height and width and within 3 cm in beam length. The spacing between upper and lower pipe layers must be accurate to within 1 cm. Lining pipes should also be installed within the corrugated pipes.

[0102] In step S53, the inner mold is installed and the bracing method is used for rapid reinforcement, specifically:

[0103] To ensure the positioning accuracy of the multi-chamber variable-section formwork, a combination of measurement and layout using a total station and level, and pre-assembly positioning was employed. First, precise measurement and layout were performed to determine the approximate position of the formwork. Then, during pre-assembly, key positioning points were marked. Finally, during on-site installation, precise adjustments were made using the control lines from the measurement and layout as a benchmark, combined with the pre-assembly positioning points. Positioning steel bars were installed at the bottom of the formwork to securely fasten it to the substructure and prevent horizontal displacement during concrete pouring. The web inner formwork was assembled on-site using 15mm bamboo plywood.

[0104] The internal formwork rapid reinforcement system utilizes a bracing method. Bracing rods are constructed from φ48×3.2mm standard scaffolding steel pipes, with supports at each end to adjust the bracing width. After the web formwork is installed, the bracing rods can be installed. Arranged in two layers, with longitudinal spacing of 1m, the bracing rods are reinforced until one chamber is complete. To ensure the overall stability of the bracing rods, conventional steel pipes are installed longitudinally for reinforcement. This creates a framework system, enhancing overall stability and ensuring smooth web concrete pouring.

[0105] Because cast-in-place beams are cast in two stages, the inner formwork top plate is not installed during the first concrete pour. Before the second concrete pour, the inner formwork top plate is installed and the top plate concrete is poured.

[0106] The first concrete pouring in step S53 is specifically as follows:

[0107] During the first concrete pour, the order is from mid-span toward the abutments (along the bridge), and from the center toward the sides (transversely). This method of spreading concrete from the center toward the sides ensures even concrete distribution and reduces off-center loading. A 47m3 / 1.5-meter pump is located in the center of each abutment. To ensure the flatness and density of the bottom slab concrete and avoid voids, an insert vibrator combined with a flat plate vibrator is used. After the bottom slab is poured, the center web is poured, followed by the other webs symmetrically on either side, and finally the side webs. To prevent the bottom slab concrete from tipping over, a grouting plate can be installed at the junction of the bottom slab and web. Concrete pouring is paused 30 cm above the web chamfer. Continue pouring to the web chamfer until the web chamfer concrete has achieved a certain degree of consolidation and initial setting. Watering and curing are carried out promptly after pouring.

[0108] During the concrete pouring process, material must be poured evenly and continuously. To prevent concrete segregation, the free fall height of concrete should not exceed 2m, and the pouring time for each truckload of concrete must be kept within the specified range. Commercial concrete is used and pumped into the formwork for pouring. During the pouring process, when the boom changes its pouring position, the boom outlet is sealed with a special material bag to prevent random dust drop that may affect the appearance of the beam. The webs on both sides are poured symmetrically to prevent internal formwork deviation caused by the significant difference in the concrete surface height of the two webs.

[0109] Concrete vibration is mainly carried out with a φ50 plug-in vibrator. φ30 vibrators are required for anchorage areas and diaphragms to ensure the density of the concrete. The vibrator is strictly prohibited from directly contacting the corrugated pipe. At the same time, a dedicated person is assigned to monitor the load of the bracket and the splicing of the formwork during the pouring process.

[0110] Step S6, the second beam construction, includes the following steps: step S61, inner formwork top plate reinforcement binding and formwork installation; step S62, second concrete pouring; step S63, construction hole sealing;

[0111] In step S61, the inner formwork top plate reinforcement binding and formwork installation are specifically as follows:

[0112] Before tying the top slab reinforcement, the upper half of the box beam chamber formwork should be installed. To facilitate access to the box chamber for removal of the inner formwork, an 80×120cm construction hole should be reserved at the top of the beam during installation. A construction hole is reserved for each chamber, with the construction holes staggered between the chambers, for a total of 10. During the top slab reinforcement tying process, the reserved construction holes are used for overlapping reinforcement and will be restored later.

[0113] The second pouring of concrete in step S62 is specifically as follows:

[0114] Before the second pour, the joint surface was roughened. After the top plate reinforcement and end formwork were installed, a 47m-long sky pump was placed on each side of the abutment before concrete pouring began. The pouring sequence was from the midspan toward the abutment in the longitudinal direction of the bridge, and from the center toward the sides in the transverse direction. When pouring concrete on an inclined surface, pour horizontally in layers from the lowest point to the highest. The thickness of each layer should not exceed 0.3m, and the upper layer of concrete should be poured before the lower layer has initially set or can be reshaped. The pouring process must be continuous, and cold joints are not allowed.

[0115] The construction hole is sealed in step S63, specifically:

[0116] After the beam concrete is poured, the reserved construction hole needs to be sealed, debris and loose concrete around the hole removed, and the beam concrete around the hole roughened. Since the construction hole cuts through the rebar, the reserved rebar is first restored. Then, appropriate lengths of rebar are cut according to the drawings and welded together, with a 10d overlap to ensure continuity and anchorage. Suitable formwork should be selected for support and ensure it is secure and airtight to prevent concrete leakage. Use C55 concrete, avoiding collisions between the formwork and rebar during vibration. Finishing should ensure it is flush with the original structural surface.

[0117] Step S7, prestressing construction: After the main beam concrete strength reaches 100% of the design strength and the age reaches 10 days, the web beams are tensioned symmetrically in sequence. This project has a total of 11 webs, 9 center webs, and 2 side webs. Two sets of tensioning equipment are used for each tensioning operation. The tensioning trolley is moved to the designated position to achieve rapid prestressing of the multi-web box beam. This process includes the following steps:

[0118] Step S71, threading the prestressed steel strand;

[0119] Specifically: When cutting prestressed steel strands, reserve 80cm of working length at both ends. After pouring concrete and curing for 5 days, remove the inner liner pipe and insert the steel strands into the corrugated pipe one by one. Use a winch to assist in the bundle insertion. When inserting the bundle, all the steel strands in a steel bundle must be bundled. Before inserting the bundle, the anchor pads and holes should be fully checked. The anchor pads should be in the correct position. If the anchor pads are displaced, causing the pad plane and the center axis of the hole to be not perpendicular, wedge pads should be used to correct it. The prepared steel wire bundles should be checked for firm binding and whether there are any bends at the ends; the length of the steel wire bundles and the hole positions should be numbered. When inserting the bundles, check the length and insert the corresponding ones into the hole.

[0120] Step S72, prestressing;

[0121] Specifically, the steel strands are tensioned using an intelligent tensioning machine, which requires calibration before use. After the beam concrete reaches 100% strength and is 10 days old, a pipe friction test is conducted. Once the parameters are obtained, the longitudinal prestressing tendons are divided into several batches and tensioned one by one, symmetrically. Tensioning is performed first on the center web, then symmetrically on both sides. This effectively controls the vertical deformation and lateral torsion of the box girder. Tensioning of the same numbered tendons is performed in the center first, then on the sides. After verifying that the oil pipe connections are secure and correct, the oil pump is activated to slightly tighten the steel strands. The jacks are then positioned so that their centers are roughly aligned with the axis of the tunnel. The main cylinders of the jacks are then slowly filled with oil at both ends to maintain consistent elongation. After symmetrically loading to the initial tensioning force (0.1σk), the oil supply is stopped. After verifying the integrity of the clips, a line is drawn to mark the area, and oil loading continues. The prestressing procedure is: 0 → initial stress (10% σcon) with elongation mark → 20% σcon → 100% σcon (hold load for 5 minutes and anchor). The tension value is mainly determined by the oil pressure gauge reading, and is verified by the elongation value of the prestressed steel strand.

[0122] Step S73, grouting and anchor sealing; specifically, grouting is performed on the prestressed pipe within 48 hours after tensioning, and the cement slurry grade is not less than 50 MPa.

[0123] 1) Cutting the steel strands: After 24 hours of tensioning, recheck the strands to ensure there are no slipped or broken wires. Use a grinding wheel saw to cut the strands. The exposed strands should be no less than 30mm after cutting.

[0124] 2) Grouting: Before grouting, flush the channel with pressurized water, pumping water in from one end and out from the other. Grouting should be performed from the lowest point of the curved channel, starting with the grouting hole, first grouting the lower layers and then the upper layers. Grouting should be performed continuously within the same channel, completing the entire process in one go. Grouting should be performed slowly and evenly without interruption. Grouting should be performed until the other end of the channel is full and the vent discharges cement slurry with the specified fluidity.

[0125] 3) Anchor sealing: The prestressed anchor sealing concrete should be constructed as soon as possible after grouting. The anchor groove should be roughened before anchor sealing, and the steel bars welded on the anchor plate should be tied together with the anchor sealing steel bars. The encapsulated wire mesh should be reliably connected to the structural steel bars, and C55 micro-expansive concrete should be used for the tensioning groove.

[0126] Step S8, concrete curing;

[0127] Specifically, concrete should be cured immediately after initial setting. During this curing period, the concrete surface must be kept moist. For exposed concrete surfaces, cover them with geotextiles immediately after the concrete has solidified and set. Water should be sprinkled on the geotextiles and formwork to maintain a moist surface. A drip method should be used: pierce a hole in a PVC pipe and place it along the central axis, allowing water to flow along the transverse slopes and cover the entire surface for curing. Inside the box girder, use an extended water gun for watering and curing.

[0128] Step S9, formwork removal; specifically, step S91, formwork removal: Removal requirements: During formwork removal, the temperature difference between the beam concrete core and surface, between the inside and outside of the box, and between the surface and the ambient temperature should not exceed 15°C. Formwork removal should not occur during periods of rapid temperature fluctuations. The removal order is: flange plate - web plate - bottom plate. The web plate should be removed symmetrically from the center toward the ends to ensure structural stability.

[0129] Step S92, bracket removal: bracket removal starts from the middle of the span, from top to bottom. It is strictly forbidden to carry out dismantling operations at the same time. The order of component removal is opposite to the order of installation. The dismantled components are not allowed to be thrown away. It should be carried out in sequence according to the principle of one step and one clear. The components should be bundled according to their types, classified and stacked, and stored in a centralized manner for transportation as they are dismantled. They should be removed and cleared on the same day. The removed fasteners or wires should be collected and processed separately. After the bracket is dismantled, the construction site should be cleaned up and all construction waste should be removed.

[0130] The innovative points of this scheme include the following: (1) The use of "step-by-step, hierarchical, and full-bridge support" solves the problem of large-section variable cross-sections and the existence of longitudinal and transverse slopes at the bottom of the beam, and the inability of ordinary erection methods to adjust the bottom plate elevation of the beam body, thereby ensuring the linear shape of the bottom plate of a single-box ten-chamber cast-in-place beam. (2) The innovative design of "wood formwork + brace rod combination structure" solves the problem of supporting the construction of variable-section multi-chamber formwork. The combination of wooden formwork and brace rods, and the combination of wooden formwork + brace rods are fast to assemble and of reliable quality, replacing the traditional brace rod reinforcement. The support pipes are made of steel pipes, and the length is adjusted by top supports at both ends to achieve the effect of rapid installation and disassembly of the internal formwork reinforcement system, while ensuring the integrity of the beam body. (3) The innovative use of "mobile tensioning trolley for multi-web tensioning". The use of mobile tensioning trolley for multi-web tensioning is an innovative bridge construction method. Symmetrical tensioning is achieved by hoisting the tensioning jacks, and the trolley is moved as a whole to the next tensioning group position after the tensioning is completed, completing the tensioning operation of the entire bridge in a cycle, ensuring construction safety and quality while improving construction efficiency. (4) Innovate the "Quick Rebar Positioning Tool." Classify and arrange similar types of rebar and plan the binding sequence. Use the steel bars to adjust and fix the spacing between the tied rebars, making the rebar binding quick and effective, reducing the number of measurements and steps, and ensuring proper zoning and classification of rebars. Using the positioning rebars, multiple teams can simultaneously perform simultaneous binding and rapid installation at different locations.

[0131] The following is an explanation of the principles of several innovative points in this solution:

[0132] 1. The technology of step-by-step installation of cast-in-place box girder supports;

[0133] The single-box, ten-chamber, variable-section, cast-in-place beams with full-length, buckled scaffolding utilizes a "stepped, graded" method. Initially, the scaffolding design was affected by the terrain, which included both horizontal and vertical slopes at the bottom of the bridge, with a maximum base plate height difference of 67.2 cm. Ensuring that the scaffolding would accommodate the large, gradual base plate height difference presented a significant challenge. After discussion, the "stepped, graded" method was ultimately chosen.

[0134] The technical principle of the stepped and graded installation of a full-bridge support structure; the support structure for the access bridge on the plot is small and the bridge deck is relatively wide. To solve the problem of the large height difference of the bridge bottom plate, the elevation of the support system is controlled from the beginning of foundation treatment. By calculating the elevation of the bottom of the beam, the support system and the adjustable height of the top support control the elevation of the foundation top surface. During foundation treatment, a horizontal step is set in the middle of the longitudinal bridge, and the foundation on the higher side of the bottom plate is raised by 25 cm for leveling and compaction, forming a 25 cm height difference with the foundation on the lower side of the bottom plate, forming a stepped foundation. The groove in the middle of the step can be used as a temporary drainage ditch. The full-bridge support structure is divided into two independent support systems, which are disconnected in the middle of the bridge in the transverse direction.

[0135] The support is erected longitudinally from the side of the abutment with smaller mileage to the side with larger mileage, and horizontally from the side with smaller mileage to the side with larger mileage, radiating from one point to spread out longitudinally and horizontally.

[0136] When erecting a buckle bracket, the position should be determined after laying out the plan, and then the adjustable base should be placed in sequence. It should be erected in the order of vertical poles, horizontal poles, and then diagonal poles to form a basic frame unit, which should be expanded to form an overall bracket system.

[0137] Key points for the technical construction of the stepped and graded installation of full-floor scaffolding: 1. Before erecting the scaffolding, the height of the scaffolding system must be determined, and the elevation of the top surface of the foundation treatment must be accurately calculated. Level the original ground, control the original ground elevation in a stepped manner according to the elevation requirements of different areas, compact it with a roller, and pour the concrete cushion layer after testing that the bearing capacity of the foundation is not less than 130kpa. 2. Set up a transverse slope drainage from the center line of the bridge to both sides in the transverse direction of the bridge, with a slope of 2%, and the ditch merges into the ditch on both sides of the bridge line. 3. The scaffolding is erected from the side of the abutment with a small mileage to the large mileage in the longitudinal direction, and from the small mileage to the large mileage in the transverse direction, and radiates from one point to the longitudinal and transverse directions.

[0138] Through the research on the technology of step-by-step and graded erection of full-floor brackets, the technical problems of wide box girder bottom plate, large longitudinal and transverse slopes, and large height differences were solved, so that the elevation of the box girder bottom plate meets the requirements of the design drawings.

[0139] 2. Pre-compression technology of variable cross-section whole-width bracket;

[0140] The single-box, ten-chamber, variable-section cast-in-place beam was preloaded using the ton-bag method filled with stone dust slag. Initially, the project was plagued by the challenge of how to achieve rapid and economical preloading. After discussion, the ton-bag method, filled with stone dust slag, was ultimately chosen.

[0141] The principle of variable-section whole-width support preloading technology: In addition to considering the weight of the concrete and steel bars of the beam body, the load determination also needs to consider the weight of the formwork and support, construction loads (construction personnel, stockpiled materials, construction machinery, etc.), the effect of the formwork, and other possible loads (such as wind loads, loads on supporting facilities), etc. The preloading of the support system is a very critical process. The support preloading is used to eliminate the inelastic deformation of the support system and determine the elastic deformation data. The settlement of the support system is determined by measuring and calculating the preloading, and the formwork elevation of the box beam is finally controlled in combination with the construction pre-arch. On-site preloading should completely simulate the load distribution of the box beam during and after construction. According to the construction sequence, first lay square timber on the installed support system. After the square timber is laid, the bottom formwork is installed, and then the pile load preloading is carried out. The load level is divided into three levels (80%, 100%, and 120% of the dead load of the concrete structure).

[0142] To ensure construction safety and improve the quality of cast-in-place beams, the scaffolding was preloaded using the ton-bag method after the box girder supports were erected and the bottom formwork lining was laid. The maximum load the scaffolding could withstand was: 859.6 * 2.6 * 1.2 = 2681.95 tons. After deducting the beam section above the side cap beam, the load at 120% preload was (859.6 - 62.85 - 92.4) * 2.6 * 1.2 = 2197.5 tons. On-site weighing revealed that the ton-bag specification was 1.1 tons per bag. The number of sandbags designed was 1.2 times the cast-in-place beam load. Based on the sandbag specifications and the weight of one bag, a total of 1998 sandbags were calculated. The sandbags were arranged symmetrically, with the loads being applied from the center outwards. The scaffolding preload sequence was from mid-span to the supports, and from the centerline outwards to the sides. Loading was performed according to the loading diagram, distinguishing between the web and the box chamber.

[0143] Prestress monitoring: Since the monitoring points are arranged symmetrically and evenly distributed throughout the bridge, and the bridge bears a very large load, it is easy for the bridge deck and foundation to settle and deform. Therefore, during the construction process, the monitoring of the bridge body should be strengthened to prevent the settlement and deformation of the foundation and the cracking of the variable-section continuous box girder. The observation points should be arranged along the direction of the bridge.

[0144] Monitoring points are set at both ends of the prestressing area and at intervals of 1 / 4 of the length. The middle point is located at the center of the span. Five monitoring points should be arranged on the foundation and support points of each monitoring section along the center line of the concrete beam. Five rows should be set in the longitudinal direction of the bridge, with emphasis on monitoring the cross-section across the span.

[0145] The support pre-compression monitoring includes: monitoring point elevation before loading, monitoring point elevation after each level of loading, monitoring point elevation every 24 hours after loading to 120%, and monitoring point elevation 6 hours after unloading.

[0146] Frequency of monitoring and result processing of support preload: (1) Before loading the support, the initial value of each monitoring point should be monitored and recorded; (2) After each level of loading is completed, the deformation of the support should be observed 12 hours later, and the displacement of each monitoring point should be monitored and recorded at intervals of 6 hours thereafter. Subsequent loading can only be carried out when the difference between the average displacements of two adjacent monitoring times is less than 2mm; (3) After all preload loads are applied, the elevation of each monitoring point should be monitored every 24 hours, and the average settlement of each monitoring point in the first 24 hours is less than 1mm, or the average settlement of each monitoring point in the first 72 hours is less than 5mm. Only then can the support preload be determined to be qualified and the preload can be removed; the support preload can be unloaded at one time, and the preload should be unloaded symmetrically, evenly, and synchronously. (4) After the support is unloaded for 6 hours, the displacement of each monitoring point should be monitored and recorded. After the support preloading is completed, the foundation settlement and the elastic deformation, inelastic deformation and plane displacement of the support should be calculated and analyzed based on the monitoring data, and the inelastic deformation and elastic deformation at 100% design load should be calculated based on the preloading monitoring to obtain the construction pre-arch, and the elastic deformation at 100% design load should be added to the template elevation calculation.

[0147] Key points for preloading construction of variable-section whole-width support: 1. According to the design calculation sheet, the foundation is treated before preloading the support, and the bearing capacity of the foundation is tested by static penetration test. 2. During hoisting, stack according to the preloading diagram, distinguish between the web area and the box area, and truly simulate the stress state of the support. 3. The construction period is the rainy season. After each level of loading is completed, the ton bags are promptly covered with tarpaulins to prevent water accumulation in the stone powder slag and increase the load. Timely monitoring and measurement are carried out to monitor the deformation state of the support, and the elastic deformation and plastic deformation values ​​are obtained to provide a basis for the elevation of the bottom formwork. Through the research on the preloading technology of the variable-section whole-width support, the elevation of the bottom plate formwork of the beam bottom was determined, and the preloading materials were reused to reduce costs and increase efficiency for the project.

[0148] 3. Multi-chamber variable-section formwork assembly technology;

[0149] The bridge beam is 23.5 meters long, with a width that gradually decreases from 36.5 meters at abutment 0 to 53 meters. The bridge covers nearly 1,100 square meters. The bottom formwork surface needed to maintain a 2% slope in the horizontal direction and a 1.5% slope in the vertical direction. How to ensure the quality of the formwork for a variable-section, multi-chamber bridge while ensuring ease of construction was a technical challenge in the early stages of formwork erection. After comparison and discussion, the "wooden formwork plus steel formwork" solution was ultimately chosen.

[0150] The principle behind the assembly technology for multi-chamber variable-section formwork is to determine the formwork's installation location through precise measurement using instruments such as a total station or level. Control lines, such as axes and edges, are set on the construction surface as a reference for formwork installation. To ensure the accuracy of the multi-chamber variable-section formwork, a combination of surveying and setting out positioning and on-site assembly is employed. First, precise surveying and setting out are performed to determine the approximate position of the formwork. Then, during formwork assembly, key positioning points are marked. Finally, during on-site installation, precise adjustments are made using the surveyed control lines as a reference and in conjunction with the positioning points.

[0151] After the bottom formwork is assembled, the steel side formwork is hoisted and installed at both ends of the horizontal direction of the measuring body. The position is roughly adjusted according to the measuring points during the hoisting process, and then fine-tuned manually. The gaps are filled with foam strips.

[0152] Key points of construction technology for multi-chamber variable-section formwork assembly:

[0153] 1. Pre-installation control: Before installing the formwork, the measurement and layout results are reviewed again to ensure the accuracy of the installation position. 2. Installation process control: During the installation process, the centerline position of the formwork is checked at any time by using methods such as a ruler and a hanging line. If any deviation is found, it is adjusted in time. 3. Post-installation inspection: After the formwork is installed, the centerline of the formwork is measured using a total station to ensure that it coincides with the designed centerline. The deviation should be controlled within the allowable range. If it exceeds the allowable range, it should be adjusted until the requirements are met. 4. Bottom fixation: Positioning steel bars or embedded bolts or nails are set at the bottom of the formwork to fix it to the square timber to firmly fix the formwork to the lower structure and prevent horizontal displacement of the formwork during concrete pouring. 5. Top constraint: Tie rods or diagonal braces are set at the top of the formwork to vertically constrain the formwork and prevent it from floating up. 6. Process monitoring: During the concrete pouring process, a dedicated person is assigned to monitor the formwork and take timely measures to deal with any displacement of the formwork.

[0154] 4. Template adjustment measurement and control technology;

[0155] The principle of formwork adjustment measurement and control technology: Before installation, during adjustment, and after completion of the base form, key parts of the base form are measured to collect coordinate and elevation data. A high-precision measurement control network, including both horizontal and vertical control points, is established. A sufficient number of measurement points are set on the base form to fully reflect the base form's slope. A total station is used to measure the coordinates of these control points, and the base form's slope is determined by calculating the coordinate difference between these control points.

[0156] Key points of template adjustment measurement and control technology construction: 1. The same measurement methods and instruments as the initial measurement should be used for re-measurement to ensure the consistency and accuracy of the data. 2. The measurement work should be carried out during a period when the construction environment is relatively stable to reduce measurement errors. 3. After the slope adjustment of the bottom formwork is completed, the coordinates and elevations of all key parts of the bottom formwork should be re-measured. The same measurement methods and instruments as the initial measurement should be used for re-measurement to ensure the consistency and accuracy of the data. Record the re-measured data, conduct a detailed analysis of the re-measured data, compare the deviation with the design requirements, and make timely readjustments for parts that exceed the allowable range. If there is an error outside the allowable range, analyze the cause and make timely readjustments until the requirements are met.

[0157] 5. Ultra-wide bottom mold slope rapid adjustment control technology;

[0158] Principle: When arranging the top supports, reserve a certain adjustment height. By manually adjusting the height of the top supports, the slope of the bottom mold can be quickly changed. When adjusting, the adjustable top supports must be arranged evenly and symmetrically to ensure uniform and balanced force on the bottom membrane. When adjusting the top supports, pay attention to synchronization to avoid excessive local adjustments that may cause uneven deformation of the bottom mold.

[0159] Key points for the rapid adjustment and control technology for the slope of ultra-wide base forms: 1. Group adjustment: Divide the ultra-wide base form into several areas and perform adjustments in groups to improve work efficiency. 2. Utilize jacking supports: By rotating the jacking support's screw, the height of the jacking support can be quickly adjusted to adjust the base form slope. 3. Real-time monitoring: During the adjustment process, the base form slope changes are measured in real time, and fine-tuning is performed promptly based on the measured data to ensure that the slope meets design requirements. Construction personnel should be proficient in jacking support adjustment methods to improve operational efficiency. 4. Tool use: Electric or hydraulic tools can be used to assist in adjustment and speed up adjustments.

[0160] Research on multi-chamber variable-section formwork assembly technology not only optimized the construction process and accelerated the precision of formwork splicing, but also ensured the aesthetic appearance of the beam after pouring. Simultaneously, research on fixed formwork made the pouring process more secure and reliable, ensuring the smooth progress of subsequent pouring operations. Measurement, monitoring, and control ensured the accuracy of formwork dimensions and angles, providing data for subsequent formwork adjustments. This also provided data for formwork deflection monitoring, ensuring the stability of the formwork system and achieving the desired construction results.

[0161] 6. Rapid construction technology of multi-chamber box girder reinforcement partitions;

[0162] The single-box, ten-chamber, variable-section cast-in-place beam has ten chambers and eleven webs. The inner chamber has a gradually varying width of 3 to 5 meters. The wide construction area and the repeatability of the construction area create the necessary conditions for batch construction. Initially, the question of how to quickly complete the reinforcement of the box beams, which exhibit a certain degree of repeatability and independence, became a significant construction issue. After discussion, the zoning reinforcement construction method was ultimately chosen.

[0163] The principle behind the rapid, zoned reinforcement construction technology for multi-chamber box girders is that the bridge structure is bilaterally symmetrical, and the structure and number of the chambers are also symmetrical. If the required reinforcement for the chambers overlaps, the same type of rebar is processed simultaneously, sorted by the order and area of ​​the rebar binding. Symmetrical chambers are constructed simultaneously, with three teams working together. This rapid, zoned reinforcement construction technology for multi-chamber box girders effectively improves construction efficiency and quality by dividing construction personnel into single, secondary, or tertiary groups, enabling rapid zoned reinforcement binding.

[0164] One group of construction workers is usually responsible for the installation of the bottom web reinforcement. First, 11 bars are arranged on the bottom plate, and then according to the design drawings, they are responsible for the installation of the box girder bottom plate reinforcement. This includes the laying and binding of the bottom main reinforcement and distribution reinforcement, as well as the setting of related support reinforcement and pads to ensure that the position of the bottom plate reinforcement is accurate and the thickness of the protective layer meets the requirements. The second group of construction workers is responsible for the construction of the box girder web reinforcement. The focus is on the installation and connection of the vertical main reinforcement and horizontal distribution reinforcement. At the same time, the junction of the web reinforcement and the bottom plate reinforcement must be handled properly to ensure a firm connection and accurate position. The third group of construction workers is responsible for the installation and welding of the positioning reinforcement and anti-collapse reinforcement of the prestressed pipe.

[0165] Key points for the multi-chamber box girder reinforcement zoning and rapid construction technology: 1. Submit rebar models to the rebar processing plant according to the binding sequence to produce rebar that meets the requirements. 2. Organize personnel into groups and arrange rebar binding chambers. 3. Dispatch processed rebar that meets the requirements to the construction site for binding, based on the construction area and work efficiency.

[0166] Through the research on the rapid construction technology of multi-chamber box girder reinforcement partitioning, the construction process was simplified, and at the same time the construction personnel were effectively allocated, which avoided duplication of work and achieved the goal of rapid construction.

[0167] 7. Multi-box indoor formwork rapid reinforcement technology;

[0168] The single-box, ten-chamber, variable-section cast-in-place beam has ten chambers and eleven webs. The inner chamber has a gradually varying width of 3 to 5 meters. The web formwork was quickly reinforced using the double-bracing method. Initial discussions on the design presented a challenge: how to quickly and economically reinforce the formwork. After much discussion, the internal bracing method was ultimately chosen.

[0169] The principle behind the rapid reinforcement technology for the multi-chamber wooden formwork and bracing structure is as follows: Bracing is made of φ48*3.2mm standard scaffolding steel pipe, with supports at each end to adjust the bracing width. After the web formwork is installed, the bracing members can be installed, arranged in two layers, with 1m spacing in the longitudinal direction. To ensure the overall stability of the bracing members, conventional steel pipes are installed in the longitudinal direction for reinforcement. This creates a framework system, enhancing overall stability and ensuring smooth web concrete pouring.

[0170] The formwork should be reinforced using tie rods, steel pipe supports, and timber backing. Tie rods should be evenly spaced, with spacing calculated based on the formwork dimensions and the concrete lateral pressure. Steel pipe supports and timber backing should be properly positioned to ensure formwork stability. To enhance the integrity and stability of the formwork reinforcement system, tie rods should be connected as a single unit between the inner forms. Fasteners can be used to connect adjacent tie rods, forming a crisscrossing pipe support system. Fasteners should be tightened at connection points for a secure connection.

[0171] Key points of technical construction for erecting inner formwork of wooden formwork + strut combination structure: 1. When installing the struts, check the width of the web and adjust the strut width of the struts in time. 2. Control the spacing between the upper and lower layers, and the longitudinal struts during construction. 3. The struts are easy to install, and the box chambers are independent. Each box chamber can install the struts in parallel to achieve a rapid reinforcement effect. 4. The construction is divided into three groups of personnel. The three groups of personnel will start from the first, second, and third box chambers of the bridge's small horizontal mileage and simultaneously carry out the installation and reinforcement of the inner formwork. After completing the first round of box formwork, the first group of personnel will carry out construction on the fourth box chamber, the second group of personnel will carry out construction on the fifth box chamber, and the third group of personnel will carry out construction on the sixth box chamber, completing the installation and reinforcement of all bridge box chambers in turn.

[0172] Through the research on the rapid reinforcement technology of multi-chamber wooden formwork + support rod combined structure inner formwork, the integrity of the structure is guaranteed, and the installation and disassembly are convenient and fast without subsequent redundant processes, thus achieving the goal of rapid construction.

[0173] 8. Concrete pouring technology for small-height multi-chamber variable-section box beams;

[0174] The single-box, ten-chamber cast-in-place beams were constructed using C50 concrete and poured in two stages. The first stage was poured to 20 cm below the chamfer on the web, followed by roughening and then pouring the top slab concrete. Initially, the project was plagued by the question of how to pour concrete for the low-profile, multi-chamber, variable-section cast-in-place box beams. After discussion, the "two-stage pouring method" was ultimately chosen for the concrete pouring.

[0175] A two-pour method is more suitable for this project. First, pour the base plate and webs up to the upper chamfer, then pour the remaining webs and top plate. This method reduces construction difficulty and facilitates construction control. A certain time interval between pours allows the concrete to fully hydrate, reducing the impact of hydration heat. It also facilitates inspection and treatment of the first pour, ensuring construction quality.

[0176] The box beam is poured from one side to the other in a single pass. Its advantages are simple construction, organization, and management. It prevents backflow of concrete during pouring, ensuring its density. However, its disadvantage is that due to the large pouring area of ​​the box beam, uneven concrete settlement may occur during pouring, leading to cracks in the box beam.

[0177] Concrete is poured from the mid-span toward the abutments (along the bridge), and from the center toward the sides (transversely). A 47m-per-day pump is positioned midway between each abutment. After the baseplate is poured, the center web is poured, followed by the other webs symmetrically positioned to either side, and finally the side webs. This method offers the advantage of ensuring even concrete distribution and reducing off-center loading; its disadvantage is the increased difficulty in construction organization and operation. To ensure uniform pouring, the first baseplate pouring method was chosen, with the concrete poured from one side to the other.

[0178] Technical principle of concrete pouring for small-height multi-chamber variable-section box girders: The "two-casting molding method" is mainly to facilitate the first concrete pouring of small-height multi-chamber variable-section box girders and provide construction space for workers.

[0179] When pouring concrete, it is cast in two steps. The pouring order is bottom plate and rear web plate, pouring from the middle to both sides (transverse direction of the bridge). In order to prevent the bottom plate concrete from turning over, a grouting plate can be installed at the junction of the bottom plate and the web plate. The concrete is appropriately stopped 30cm above the chamfer of the web plate when pouring. The pouring to the chamfer of the web plate is continued before the concrete of the chamfer of the web plate has a certain degree of consolidation and initial setting. Before the second pouring, the concrete bonding surface is roughened. After the top formwork of the inner box is installed, the concrete of the wing plates and the top plate on both sides is poured. When pouring concrete on an inclined surface, it should start from the bottom and expand and rise layer by layer, and maintain horizontal stratification. The thickness of the concrete layered pouring should not exceed 0.3m, and the upper layer of concrete should be poured before the lower layer of concrete is initially set or can be reshaped.

[0180] Key construction techniques for pouring concrete for low-profile, multi-chamber, variable-section box girders: 1. The beam is large and densely reinforced, requiring a slow pouring speed. The initial setting time must be controlled to 6-8 hours to ensure that the upper concrete layer is poured before the lower concrete layer has initially set or can be reshaped. 2. During the concrete pouring process, when the pump pipe changes its pouring position, seal the outlet of the distribution pump pipe with a special material bag to prevent dust from falling and affecting the appearance of the beam and contaminating the stirrups at the top of the web. 3. When pouring the web, pay attention to pouring in layers. Each layer should not exceed 30cm in thickness and should be vibrated densely to avoid honeycombing. The pouring speed should be moderate to prevent excessive lateral pressure from the concrete on the formwork. To prevent the bottom slab concrete from flipping up, a grouting plate can be installed at the junction of the bottom slab and the web. 4. Ensure the flatness and density of the concrete to avoid voids. Vibration can be carried out using an insert vibrator combined with a flat vibrator; through research on the concrete pouring technology of small-height multi-chamber variable-section box girders, the concrete pouring form is determined in advance, allowing the box girder concrete to be smoothly poured and formed.

[0181] 9. Multi-web box girder movement and tensioning control technology;

[0182] The bridge's 33 prestressed steel strands are divided into 11 groups and tensioned symmetrically at both ends. Prestressing is repetitive, and for bridges with multiple webs, the project team discussed several methods to avoid duplication and improve construction efficiency. Ultimately, they decided on the mobile tensioning method.

[0183] Principle of Mobile Tensioning Control Technology for Multi-Web Box Girders: This method achieves symmetrical tensioning by hoisting tensioning jacks. After tensioning is complete, a mobile trolley is used to move the entire girders to the next tensioning group, completing the entire bridge tensioning cycle. After completing the tensioning operation of one tensioning group, the trolley moves to the next tensioning group for the next round of tensioning. Throughout the entire process, tension and structural deformation must be strictly monitored. Data analysis allows for timely detection and adjustment of tension to ensure construction quality and safety, while improving efficiency.

[0184] Key points for controlling the mobile tensioning of multi-web box girders: 1. Install tracks or guide rails and hoist the tensioning jacks and other necessary tensioning equipment onto the trolley. 2. Use the jack-tensioning equipment to symmetrically tension the bridge structure to ensure uniform prestress distribution. During the tensioning process, monitor the tension and structural deformation in real time. 3. After completing the tensioning of one tensioning group, move the trolley to the next tensioning group. Repeat the symmetrical tensioning and trolley movement steps until the entire bridge is tensioned.

[0185] The method of using a "mobile tensioning trolley" to tension multiple webs can be reused, which reduces equipment costs, optimizes the tensioning process, and reduces unnecessary manpower consumption. It is innovative, efficient and reliable.

[0186] This method systematically studies the key construction technologies for a single-box, ten-chamber, variable-section, cast-in-place box girder, a rare type in China. By studying the techniques of stepped, graded scaffolding, scaffolding preloading, formwork assembly, rapid zoned reinforcement construction, rapid internal formwork reinforcement, concrete pouring, and mobile tensioning control, it addresses a series of construction challenges for low-profile, multi-chamber, variable-section, cast-in-place girders. These challenges include the significant vertical and transverse gradient differences in the box girder base, the inefficiency of preloading solutions, the difficulty of formwork assembly and adjustment, the complex and slow multi-zone reinforcement construction, the complex internal formwork reinforcement operations, unsatisfactory concrete pouring results, and the time-consuming and labor-intensive scaffolding installation. The specific studies have achieved the design details of the elevation and slope of the box girder bottom plate by setting up the scaffolding in stages; achieved cost reduction and efficiency improvement by rationally designing the preloading method; ensured the aesthetic appearance of the beam after pouring by precise measurement and control of the formwork assembly; simplified the construction process and achieved rapid construction by rationally planning and allocating the steel bar construction; achieved rapid reinforcement of multiple box room formwork and improved construction efficiency by combining the design of multiple support methods and carrying out multi-point simultaneous construction; and achieved smooth pouring and forming of the box girder concrete by adjusting the concrete pouring method in stages.

[0187] The many methods used in project construction have strong adaptability in subsequent projects and are of great reference significance for the project department to save some labor costs.

[0188] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A variable cross-section multi-chamber box girder structure, characterized by: It includes a bridge body, a first end and a second end. The width of the bridge deck is gradually reduced from the first end plate in the direction of the second end. A plurality of box structures are arranged between the first end and the second end, and at least part of the box structures are symmetrically arranged along the center positions of the first end and the second end; a first abutment is arranged on the first end, and a second abutment is arranged on the second end; the bridge body is supported by the first abutment and the second abutment and the ground, and the distance from the first end to the second end is less than the width of the second end.

2. A construction method for a variable-section multi-chamber box girder structure, characterized by: The following steps are involved: Step S1: foundation treatment, after leveling the foundation, pressing a stepped foundation of a predetermined height according to the height difference; Step S2, support system construction, firstly, the support system is erected, after which the support system is erected, the support system is pre-stressed, and finally the support system pre-stressing monitoring operation is performed; Step S3, bottom formwork construction, which includes bottom formwork installation and bottom formwork elevation rapid adjustment; Step S4, installing the side steel formwork; Step S5, first beam construction; Step S6, second beam construction; Step S7, prestressed construction; Step S8, concrete curing; Step S9, dismantling the formwork support.

3. The construction method according to claim 2, wherein: Step S1 is specifically as follows: leveling the original ground, controlling the original ground elevation in a stepped manner according to the elevation requirements of different areas, treating the foundations on both sides separately with the middle of the beam body as the boundary, raising the foundation on the higher side of the bottom plate to a predetermined height for leveling and compacting, forming a predetermined height difference with the foundation on the lower side of the bottom plate, and forming a stepped foundation; rolling and compacting the foundation with a roller, and then pouring a concrete cushion layer; at the same time, setting a transverse slope drainage from the center line of the bridge to both sides.

4. The construction method according to claim 2, wherein: The erection of the support system in step S2 is specifically as follows: the cast-in-place beam support adopts a full-span buckle support structure, and the support adopts a buckle type support. When erecting, the line is first laid out for positioning, and then the position of the adjustable base is accurately placed according to the line-laying position, and it should be erected in the order of vertical poles, horizontal poles, and diagonal poles to form a basic frame unit, which should be expanded to form an overall support system; in the first step, the horizontal poles and diagonal poles are locked on the vertical poles to keep them stable, and the lines are hung to adjust whether the vertical and horizontal rows of vertical poles are in a straight line; after each step of the support is erected, the horizontal pole step distance, the vertical and horizontal distances of the vertical poles, the verticality deviation of the vertical poles and the horizontal deviation of the horizontal poles are corrected; since the height of the land passage bridge support is small and the bridge deck is wide, in order to meet the requirements of large vertical and horizontal slope height differences of the bridge bottom plate, the buckle type full-span support is divided into two independent support systems, which are disconnected in the middle of the bridge in the transverse direction, and the distributed beams are laid continuously on the support.

5. The construction method according to claim 2, wherein: The support system preload monitoring operation in step S2 specifically includes the following steps: Step S21, support preload monitoring includes: monitoring point elevation before loading, monitoring point elevation after each level of loading, monitoring point elevation every 24 hours after loading to 120% of the concrete structure's dead load, and monitoring point elevation 6 hours after unloading; Step S22, Arrangement of Support Prestressing Monitoring Points: Monitoring points are set at both ends of the prestressing area and at intervals of 1 / 4 of the length, with the middle point located at the center of the span. Five monitoring points should be arranged along the centerline of the concrete beam on the foundation and support points of each monitoring section, with five rows arranged in the longitudinal direction of the bridge, with a focus on monitoring the cross-section across the span. Step S23, monitoring frequency of stent preload and processing of results; Before loading the support, the initial value of each monitoring point should be monitored and recorded; the deformation of the support should be observed 12 hours after each level of loading is completed, and the displacement of each monitoring point should be monitored and recorded at intervals of 6 hours. When the difference between the average displacements of two adjacent monitoring times is less than 2mm, subsequent loading should be carried out; after all preloading loads are applied, the elevation of the monitoring points should be monitored every 24 hours. If the average settlement of each monitoring point in the first 24 hours is less than 1mm, or the average settlement of each monitoring point in the first 72 hours is less than 5mm, the support preloading is judged to be qualified and the preloading load is removed; the support preloading is unloaded once, and the preloading load should be unloaded symmetrically, balanced, and synchronously; 6 hours after the support is unloaded, the displacement of each monitoring point should be monitored and recorded; after the support preloading is completed, the foundation settlement and the elastic deformation, inelastic deformation and plane displacement of the support should be calculated and analyzed based on the monitoring data, and preloading and unloading deformation diagrams should be made respectively. The inelastic deformation and the elastic deformation at 100% design load should be calculated based on the preloading monitoring to obtain the construction pre-camber, and the elastic deformation at 100% design load should be added to the template elevation calculation.

6. The construction method according to claim 2, wherein: Step S5, the first beam construction, includes the following steps: Step S5, the first beam construction, includes the following steps: Step S51, fast tying of bottom web reinforcement in sections; Step S52, installing the web bellows; Step S53: installing the inner mold and quickly reinforcing it using the bracing method; Step S54: first concrete pouring.

7. The construction method according to claim 6, wherein: In step S53, the inner mold is installed and the bracing method is used for rapid reinforcement, specifically: To ensure the positioning accuracy of the multi-chamber variable-section formwork, a combination of measurement and layout positioning using a total station and level instrument and pre-assembly positioning is used. First, precise measurement and layout are carried out to determine the approximate position of the formwork. Then, during pre-assembly of the formwork, positioning points at key locations are marked. Finally, during on-site installation, precise adjustments are made based on the control lines of the measurement and layout, combined with the pre-assembly positioning points. At the same time, positioning steel bars are installed at the bottom of the formwork to firmly fix the formwork to the lower structure and prevent horizontal displacement of the formwork during concrete pouring. The web inner formwork is all made of bamboo plywood and assembled on-site. The internal formwork rapid reinforcement system uses the bracing method. Bracing rods are made of ordinary scaffolding steel pipes, with top supports at both ends to adjust the bracing width. After the web formwork is installed, the bracing rods are installed in two layers, with longitudinal spacing of 1m. These bracing rods are arranged and reinforced until one box chamber is reinforced. To ensure the overall stability of the bracing rods, ordinary steel pipes are installed longitudinally for reinforcement, forming a framework system. The cast-in-place beams are cast in two steps; the internal formwork top plate is not installed during the first concrete pour. Before pouring concrete for the second time, install the inner formwork top plate and pour the top plate concrete.

8. The construction method according to claim 6, wherein: The first concrete pouring in step S53 is specifically as follows: During the first concrete pouring, the pouring sequence is from the mid-span toward the abutment, and from the middle toward both sides. When placing concrete, working from the middle toward both sides can better ensure uniform distribution of concrete and reduce eccentric loading. A sky pump is placed in the middle of the abutments on both sides. To ensure the flatness and density of the bottom slab concrete and avoid voids, an insert vibrator combined with a flat plate vibrator is used for vibration. After the bottom slab is poured, the middle web is poured, followed by the other webs symmetrically poured on both sides, and finally the side webs. Concrete pouring is appropriately stopped 30 cm above the web chamfer, and pouring continues to the web chamfer until the web chamfer concrete has a certain degree of consolidation and before initial setting. After pouring, the concrete is promptly watered and cured. During the concrete pouring process, the material should be discharged evenly and continuously. To prevent concrete segregation, the free fall height of concrete should not exceed 2m, and the pouring time of each truck of concrete should be ensured to be within the specified range; commercial concrete is used and pumped into the mold for pouring; during the concrete pouring process, when the distribution boom changes the pouring position, the distribution boom outlet is sealed with a material bag; the webs on both sides are poured symmetrically; the concrete is vibrated mainly with a φ50 inserted vibrating rod, and a φ30 vibrating rod is used for the anchor parts and cross partitions to ensure the density of the concrete; the vibrating rod is strictly prohibited from directly contacting the corrugated pipe. At the same time, a special person is assigned to follow the load of the bracket and the splicing of the template during the pouring process.

9. The construction method according to claim 2, wherein: Step S6, the second beam construction, includes the following steps: Step S61, inner formwork top plate reinforcement binding and formwork installation; Step S62, pouring concrete for the second time; Step S63, sealing the construction hole; The inner formwork top plate reinforcement binding and formwork installation in step S61 are specifically as follows: Before tying the top plate reinforcement, the upper part of the box beam box chamber formwork should be installed first. In order to facilitate the later personnel to enter the box to remove the inner formwork, a construction hole must be reserved at the top of the beam during installation. A construction hole is reserved for each box chamber, and the construction holes between the box chambers are staggered, with a total of 10 holes arranged. During the tying of the top plate reinforcement, construction holes are reserved for overlapping reinforcement, which will be restored later.

10. The construction method according to claim 9, wherein: The second pouring of concrete in step S62 is specifically as follows: Before the second pouring, the joint surface is roughened. After the top plate reinforcement and end formwork are installed, a sky pump is placed on each side of the abutment before concrete pouring. The pouring sequence is from the mid-span to the abutment in the longitudinal direction of the bridge, and from the middle to both sides in the transverse direction of the bridge. When pouring concrete on an inclined surface, pour horizontally from the lowest point to the highest point. The thickness of each layer of concrete pouring should not exceed 0.3m. The upper layer of concrete should be poured before the lower layer of concrete begins to set or can be reshaped. The pouring process must be continuous, and the formation of cold joints is not allowed. The construction hole is sealed in step S63, specifically: After the pouring of beam concrete is completed, the reserved construction hole needs to be sealed, the debris and loose concrete around the construction hole need to be cleaned, and then the beam concrete around the construction hole needs to be roughened; since the construction hole cuts off the steel bars, the reserved steel bars need to be restored first, and then the steel bars of the predetermined length are cut according to the drawings for welding, with a lap length of 10d to ensure the continuity and anchorage length of the steel bars; select appropriate formwork for support, and ensure that the formwork is firm and sealed to prevent concrete leakage; select C55 concrete, and avoid collision between the formwork and steel bars during vibration; when finishing, ensure that it is flush with the original structure surface.

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