Municipal large-span cast-in-place concrete box girder and construction method thereof

Abstract

The invention relates to the technical field of bridge girder boxes, in particular to a municipal large-span cast-in-place concrete box girder and a construction method thereof.The municipal large-span cast-in-place concrete box girder comprises a box girder body arranged between two bridge piers, and the box girder body comprises a U-shaped bottom plate, two web plates arranged at the upper end of the U-shaped bottom plate and a U-shaped top plate connected with the top ends of the two web plates; the two webs are arranged in parallel with the center line of the box girder body, an I-shaped box cavity is defined by the U-shaped bottom plate, the webs and the U-shaped top plate, the sectional area of the box cavity is gradually reduced from the middle of the box girder body to the two ends of the box girder body, and a steel bar keel is arranged in the box girder body. The prestressed tie bars arranged in the length extending direction of the box girder body are arranged in the steel bar keels, variable section design is carried out, the section size of the box girder body is better matched with the bending moment requirement, and therefore the stress performance of the whole structure is improved, and the stress concentration and local yield phenomena are avoided.

Description

Technical Field

[0001] The present application relates to the technical field of bridge girder boxes, and in particular to a municipal large-span cast-in-place concrete box girder and a construction method thereof. Background Art

[0002] A box girder is a beam structure used in bridge engineering. It is characterized by a hollow interior, flanges on both sides of the upper part, and a box-like shape. The beam-box structure can be produced by prefabrication or on-site through cast-in-place technology. The prefabricated beam box is pre-manufactured in the factory and then transported to the construction site for installation. This method is conducive to controlling production conditions, improving production efficiency and product quality, but may involve complex transportation and lifting operations. The cast-in-place beam box is made by directly pouring concrete on the construction site. This method does not require large prefabrication plants and transportation equipment, which can reduce traffic congestion and environmental pollution during construction. At the same time, the cast-in-place beam box can better adapt to the size and shape requirements of the site, reduce the number of joints, and improve integrity and waterproofing.

[0003] Cast-in-place box girders are mostly used in the construction of large continuous bridges. Due to their good integrity, they are suitable for building bridges with larger spans. However, for large-span box beams, the larger the span, the wider the distribution range of the load on the beam. When the load acts on the beam, the beam will produce flexural deformation. During this deformation process, the upper part of the beam is compressed and the lower part is tensile. Since the middle part of the beam is far away from the supports at both ends, the restraining effect of the supports at both ends on the middle part is relatively weak. During the load transfer process, the middle part of the beam needs to bear more bending moment to balance the force of the entire structure. The load is unevenly distributed along the length direction of the beam, resulting in a larger cumulative load on the middle part, thereby generating a larger bending moment. Summary of the invention

[0004] In order to avoid uneven distribution of load in the length direction of the beam due to the large span of the box beam, which leads to a large cumulative load in the middle part and thus a large bending moment, the present application provides a municipal large-span cast-in-place concrete box beam.

[0005] The above technical objectives of this application are achieved through the following technical solutions: A municipal large-span cast-in-place concrete box girder comprises a box girder body arranged between two bridge piers, the box girder body comprising a U-shaped bottom plate, two webs arranged at the upper end of the U-shaped bottom plate and a U-shaped top plate connected to the top ends of the two webs, and the two webs are arranged parallel to the center line of the box girder body, an "I"-shaped box cavity is surrounded by the U-shaped bottom plate, the webs and the U-shaped top plate, and the cross-sectional area of ​​the box cavity gradually decreases from the middle of the box girder body to the two ends of the box girder body, a steel keel is arranged inside the box girder body, and prestressed tension bars are arranged inside the steel keel along the length extension direction of the box girder body, and the prestressed tension bars are evenly distributed in the U-shaped bottom plate, the webs and the U-shaped top plate.

[0006] By adopting the above technical solution, the cross-sectional area of ​​the box-shaped cavity is gradually reduced from the middle of the box girder body to the two ends of the box girder body, and a variable cross-sectional design is performed to make the cross-sectional size of the box girder body more matched with the bending moment requirement, thereby improving the force performance of the entire structure and avoiding stress concentration and local yield.

[0007] Optionally, a plurality of oblique tie bars are provided inside the box-shaped cavity, and two adjacent oblique tie bars are cross-arranged.

[0008] By adopting the above technical solution, it is convenient to enhance the corner stress of the box girder body.

[0009] Optionally, a prestressed installation tube is provided inside the steel keel, the prestressed tensioning bar is installed inside the prestressed installation tube, and a positioning ring is provided on the prestressed installation tube, and a plurality of positioning hoops are provided on the positioning ring.

[0010] By adopting the above technical solution, it is convenient to fix the prestressed reinforcement at the position required by the design.

[0011] Optionally, a transverse mounting tube is provided inside the U-shaped bottom plate, and a vertical projection surface of the transverse mounting tube is perpendicular to a vertical projection surface of the prestressed mounting tube.

[0012] By adopting the above technical solution, the shear resistance of the main cross section of the box girder can be improved.

[0013] Optionally, the vertical projection surfaces of the U-shaped bottom plate coincide with those of the U-shaped top plate.

[0014] By adopting the above technical solution, the box girder body can be subjected to more uniform force up and down when subjected to vertical load.

[0015] Optionally, a solid cross-connecting plate is provided at the upper end of the U-shaped top plate, and the solid cross-connecting plate is covered on the outer surface of the U-shaped top plate.

[0016] The adoption of the above technical solution helps to enhance the overall bearing capacity and deformation resistance of the box girder body.

[0017] A construction method for a municipal large-span cast-in-place concrete box girder comprises the following steps: S1: Foundation treatment, leveling the foundation between the two piers; S2: bracket installation, install the bowl-hook type full-hall bracket on the foundation in step S1, and lay the grouting board on the top of the bracket; S3: pre-compressing the stent, applying a downward force to the stent for pre-compression, and performing data monitoring; S4: Box girder construction, after tying the steel keel, installing the inner formwork and pouring concrete; S5: Demolition work, dismantle the formwork and bowl-hook type full-floor support, adopting the principle of "dismantle the rear support first, and dismantle the front support last".

[0018] S6: Maintenance work, maintenance of the box girder after casting.

[0019] Optionally, when performing the support pre-compression operation in step S3, sand bags or earth bags may be used for pre-compression, and waterproofing and drainage operations on rainy days may be performed to prevent sand and soil from absorbing water and increase the pre-compression weight.

[0020] By adopting the above technical solution, inaccurate measurements can be avoided, which can prevent the performance and deformation of the bracket under excessive loads from being truly reflected.

[0021] By gradually reducing the cross-sectional area of ​​the box-type cavity from the middle of the box girder body to the two ends of the box girder body, a variable cross-sectional design is performed, so that the cross-sectional size of the box girder body is more matched with the bending moment requirement, thereby improving the stress performance of the entire structure, avoiding stress concentration and local yield. At the same time, in some bridge projects, the variable cross-sectional design can adapt to the height difference of different piers, making the bridge line smoother and more beautiful. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the cross-sectional structure of the box girder main body provided in this application; Figure 2 It is a three-dimensional structural diagram provided by this application; Figure 3 It is a schematic diagram of the internal structure of the box girder body provided by this application; Figure 4 It is a structural schematic diagram of the positioning ring provided by the present application installed on the prestressed installation pipe; Figure 5 It is a flow chart provided by this application.

[0023] Explanation of the accompanying reference numerals: 1. Bridge pier; 2. Box girder body; 21. U-shaped bottom plate; 22. Web plate; 23. U-shaped top plate; 3. Box-shaped cavity; 4. Steel keel; 41. Prestressed installation pipe; 42. Positioning ring; 43. Positioning clamp; 5. Prestressed tension bar; 6. Diagonal tension bar; 7. Transverse installation pipe; 8. Solid transverse connecting plate. DETAILED DESCRIPTION

[0024] The present application is further described in detail below in conjunction with the accompanying drawings.

[0025] The present application embodiment discloses a municipal large-span cast-in-place concrete box girder, referring to Figures 1 to 4 As shown, it includes a box girder body 2 arranged between two piers 1, the box girder body 2 includes a U-shaped bottom plate 21, two webs 22 arranged at the upper end of the U-shaped bottom plate 21 and a U-shaped top plate 23 connected to the top ends of the two webs 22, the U-shaped top plate 23 is opposite to the opening of the U-shaped bottom plate 21, the two webs 22 are arranged parallel to the center line of the box girder body 2, and an "I"-shaped box cavity 3 is surrounded by the U-shaped bottom plate 21, the webs 22 and the U-shaped top plate 23. Since the "I"-shaped box cavity 3 is symmetrical, it can provide good stress distribution and avoid stress concentration. At the same time, since the supporting points of the piers 1 at both ends of the large-span box girder body 2 are farther away, the distribution range of the load on the beam is wider. When the load acts on the middle part of the box girder body 2, the upper part is compressed and the lower part is pulled. The load box girder body 2 is unevenly distributed in the length direction, which will cause the middle part of the box girder body 2 to accumulate a large load, so that the bending moment is also larger than that at the two ends. Therefore, The cross-sectional area of ​​the box-shaped cavity 3 gradually decreases from the middle of the box girder body 2 to the two ends of the box girder body 2. Specifically, the mid-span part of the box girder body 2 is subject to the largest bending moment, so a larger cross-section is required to provide sufficient bearing capacity, while the bending moment borne by the beam ends near the supports is smaller, so a smaller cross-section can be used. In this way, since the cross-sections at both ends of the box girder body 2 are smaller, the material usage can be reduced while meeting the mechanical requirements, thereby reducing the project cost. The variable cross-sectional design can reduce the deadweight of the box girder body 2, thereby reducing the burden on temporary supports and tower cranes and other equipment during cantilever construction, and improving construction efficiency. The cross-sectional area of ​​the beam box body gradually decreases from the middle to the two sides. This variable cross-sectional design can make the cross-sectional size of the box girder body 2 more compatible with the bending moment requirements, thereby improving the force-bearing performance of the entire structure, avoiding stress concentration and local yield, and at the same time, it is more beautiful and meets the current architectural aesthetic requirements.

[0026] Among them, reference Figure 3As shown, a steel keel 4 is provided inside the box girder body 2. The steel keel 4 can be tied on site or prefabricated in a factory and then transported to the construction site. The steel keel 4 is provided inside with prestressed reinforcement bars 5 arranged along the length extension direction of the box girder body 2. The prestressed reinforcement bars 5 are evenly distributed in the U-shaped bottom plate 21, the web 22 and the U-shaped top plate 23. After the concrete is poured in the steel keel 4, the beam can be compressed in advance through the tensioning effect of the prestressed reinforcement bars 5, thereby reducing the deflection and cracks caused by the load, improving the rigidity and stability of the structure, and providing additional bearing capacity in the tensioning zone of the box girder body 2, thereby enhancing the bending resistance of the beam and allowing the box girder body 2 to withstand a larger load.

[0027] For further reference, Figure 1 As shown, a plurality of inclined tie bars 6 are provided inside the box-shaped cavity 3, and two adjacent inclined tie bars 6 are cross-arranged. The inclined tie bars 6 can be made of steel bar material with a diameter of 10mm-12mm to enhance the corner stress of the box beam body 2, especially near the end of the box beam body 2, so as to resist shear and torsion.

[0028] For further reference, Figure 1 A prestressed installation tube 41 is provided inside the steel keel 4, and the prestressed tendon 5 is installed inside the prestressed installation tube 41. The prestressed installation tube 41 can be a metal corrugated tube. By installing the prestressed tendon 5 inside the prestressed installation tube 41, the prestressed tendon 5 can be protected from the influence of the external environment, such as moisture, chemicals, etc., thereby preventing corrosion or other damage and increasing the durability of the structure. The metal corrugated tube can evenly disperse the stress of the prestressed tendon 5 to avoid local stress concentration, thereby improving the safety and stability of the overall structure. A positioning ring 42 is provided on the prestressed installation tube 41, and a plurality of positioning clamps 43 are provided on the positioning ring 42. During installation, it is first connected to the steel keel 4 through the positioning clamp 43, and then the positioning ring 42 is installed at a position that meets the design requirements according to the design drawings. The prestressed installation tube 41 is installed to determine the installation position of the prestressed tendon 5.

[0029] For further reference, Figure 3 As shown, a transverse mounting tube 7 is provided inside the U-shaped bottom plate 21, and a prestressed tie rod 5 is also installed inside the transverse mounting tube 7. The vertical projection surface of the transverse mounting tube 7 is perpendicular to the vertical projection surface of the prestressed mounting tube 41. The cooperation with the prestressed tie rod 5 arranged along the length extension direction of the box beam can more effectively control the deformation and stress distribution of the box beam body 2 under various loads, thereby improving the force performance of the box beam body 2.

[0030] Furthermore, the vertical projection surfaces of the U-shaped bottom plate 21 and the U-shaped top plate 23 coincide with each other, that is, the areas of the U-shaped bottom plate 21 and the U-shaped top plate 23 are equal, so that when the box girder body 2 is subjected to vertical loads, the upper and lower forces are more evenly distributed, which is beneficial to improving the overall stability and bearing capacity of the structure. When casting on site, the U-shaped top plate 23 and the U-shaped bottom plate 21 facilitate the installation of the formwork, reduce the difficulty of construction, and help reduce the additional internal force and deformation caused by structural asymmetry.

[0031] Furthermore, a solid cross-connecting plate 8 is provided at the upper end of the U-shaped top plate 23, and the solid cross-connecting plate 8 is covered on the outer surface of the U-shaped top plate 23, which can more evenly disperse the load acting on the box beam body 2, reduce local stress concentration, and also enable the beam box body and the plate to work together to improve the overall bearing capacity.

[0032] refer to Figure 5 As shown, a construction method for a municipal large-span cast-in-place concrete box girder comprises the following steps: S1: foundation treatment, leveling the foundation between the two bridge piers 1; S2: bracket installation, install the bowl-hook type full-hall bracket on the foundation in step S1, and lay the grouting board on the top of the bracket; S3: pre-compressing the stent, applying a downward force to the stent for pre-compression, and performing data monitoring; S4: Box girder construction, after tying the steel keel 4, install the inner formwork and pour concrete. When pouring concrete, use an inserted vibrating device to vibrate the concrete to reduce the bubbles in the concrete. S5: Demolition work, dismantle the formwork and bowl-hook type full-floor support, adopting the principle of "dismantle the rear support first, and dismantle the front support last".

[0033] S6: Maintenance work, the box beam is maintained after pouring. It can be achieved by covering with plastic film, wet cloth or spraying curing agent to prevent the moisture inside the concrete from evaporating too quickly. For beam boxes constructed in winter, they can be covered with insulation blankets, foam boards and other insulation materials for insulation maintenance to control the temperature difference between the inside and outside of the concrete and avoid cracks caused by temperature changes.

[0034] Among them, when pre-stressing the support in step S3, sandbags or earthbags can be used for pre-stressing. The pre-stressing load can be loaded at 60%, 80%, and 100% of the pre-stressing load. The loading should also be done symmetrically and in layers. Pre-stressing and waterproofing and drainage operations should be done on rainy days to prevent sand and soil from absorbing water, increase the pre-stressing weight, avoid inaccurate measurements, and fail to truly reflect the performance and deformation of the support under overdue loads.

[0035] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make modifications to the present embodiment without any creative contribution as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A municipal large-span cast-in-place concrete box girder, comprising a box girder body (2) disposed between two bridge piers (1), characterized in that: The box beam body (2) comprises a U-shaped bottom plate (21), two web plates (22) arranged at the upper end of the U-shaped bottom plate (21), and a U-shaped top plate (23) connected to the top ends of the two web plates (22), and the two web plates (22) are arranged parallel to the center line of the box beam body (2), and an "I"-shaped box cavity (3) is formed between the U-shaped bottom plate (21), the web plates (22), and the U-shaped top plate (23), and the cross-sectional area of ​​the box cavity (3) gradually decreases from the middle of the box beam body (2) to the two ends of the box beam body (2); A steel keel (4) is provided inside the box girder body (2), and prestressed tendons (5) are provided inside the steel keel (4) along the length extension direction of the box girder body (2), and the prestressed tendons (5) are evenly distributed inside the U-shaped bottom plate (21), the web plate (22) and the U-shaped top plate (23).

2. A municipal large-span cast-in-place concrete box girder according to claim 1, characterized in that: A plurality of oblique tie bars (6) are arranged inside the box-shaped cavity (3), and two adjacent oblique tie bars (6) are arranged crosswise.

3. The municipal large-span cast-in-place concrete box girder according to claim 1 is characterized in that: A prestressed installation tube (41) is provided inside the steel keel (4), the prestressed tension bar (5) is installed inside the prestressed installation tube (41), and a positioning ring (42) is provided on the prestressed installation tube (41), and a plurality of positioning hoops (43) are provided on the positioning ring (42).

4. The municipal large-span cast-in-place concrete box girder according to claim 3 is characterized by: A transverse mounting tube (7) is provided inside the U-shaped bottom plate (21), and a vertical projection surface of the transverse mounting tube (7) is perpendicular to a vertical projection surface of the prestressed mounting tube (41).

5. The municipal large-span cast-in-place concrete box girder according to claim 1 is characterized in that: The vertical projection surfaces of the U-shaped bottom plate (21) and the U-shaped top plate (23) coincide with each other.

6. The municipal large-span cast-in-place concrete box girder according to claim 1 is characterized in that: A solid cross-connecting plate (8) is provided at the upper end of the U-shaped top plate (23), and the solid cross-connecting plate (8) is coated on the outer surface of the U-shaped top plate (23).

7. A construction method for a municipal large-span cast-in-place concrete box girder, used to manufacture a municipal large-span cast-in-place concrete box girder as claimed in claim 1, characterized in that: The steps include: S1: foundation treatment, leveling the foundation between the two bridge piers (1); S2: bracket installation, install the bowl-hook type full-hall bracket on the foundation in step S1, and lay the grouting board on the top of the bracket; S3: pre-compressing the stent, applying a downward force to the stent for pre-compression, and performing data monitoring; S4: Box girder construction: after tying the steel keel (4), installing the inner formwork and pouring concrete; S5: Dismantling work, dismantling the formwork and the cup-hook type full-floor bracket, adopting the principle of "dismantling the rear support first, and dismantling the front support later"; S6: Maintenance work, maintenance of the box girder after casting.

8. The construction method of a municipal large-span cast-in-place concrete box girder according to claim 7 is characterized in that: When the support pre-compression operation is performed in the step S3, sand bags or earth bags may be used for pre-compression, and waterproofing and drainage operations are performed on rainy days to prevent sand and soil from absorbing water and increase the pre-compression weight.

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