Construction method for cast-in-place box girder of cable-stayed bridge

Abstract

The present invention relates to a construction method for a cast-in-situ box girder of a cable-stayed bridge. The present invention utilizes pre-buried beams in conjunction with upper supporting beams located on the top edge of a cast block as a cantilever casting support skeleton for cantilever casting of segment No. 1 on the side span side and main span side to segments with subsequent sequence numbers and adjacent segments to be cast in the joint section, or utilizes pre-buried beams in conjunction with upper supporting beams located on the top edge of a cast block and inclined cables as a cantilever casting support skeleton for cantilever casting of segment No. 1 on the side span side and main span side to segments with subsequent sequence numbers and adjacent segments to be cast in the joint section. The present invention does not require the use of a traditional hanging basket for cantilever casting of the cast-in-situ box girder, and has the advantages of being supported by a formwork system of the box girder to be cast, having a fast moving speed, having less damage to the overall structure of the bridge deck, having a simple process, and saving time and effort.

Description

Technical Field

[0001] The invention belongs to a construction method for a cast-in-situ box girder of a cable-stayed bridge. Background Art

[0002] In the field of bridge construction, the prestressed concrete box girders of the upper main bridge deck structure of cable-stayed bridges are now mostly constructed using traditional hanging basket suspended casting. That is, after each A-type cable tower is built, the scaffolding method is used to first construct the No. 0 block (prestressed concrete box girder) located at the position of each main tower. Then, the hanging basket suspended casting construction method is used to cantilever cast the No. 1 segment on the side span and the main span side to the segments with subsequent sequence numbers. After the suspended casting construction of each segment is completed, the cable hanging and tensioning construction of each segment is carried out, and then the hanging basket is moved forward to the next segment for cyclic construction. Obviously, cantilever hanging basket construction is adopted in the construction of each section. The hanging basket is actually a mobile formwork system built on site. The traditional hanging basket structure includes diamond brackets, front hanging basket slings, rear hanging basket slings, counterweight anchoring structure, forward movement system and hanging basket formwork, etc. Among them, the diamond bracket is the main structure of the hanging basket, and the bottom longitudinal beam of the diamond bracket is placed on the formed box girder bridge deck, and the top longitudinal beam of the diamond bracket extends outward to the air above the upper end of the box girder to be cast and forms a suspended hanging basket formwork system for the box girder to be cast by connecting the front and rear hanging basket slings and the hanging basket formwork.

[0003] Currently, the hanging basket on the formed box girder bridge deck must be moved forward as the cantilevered box girder extends. Traditional hanging baskets all use a track-based integrated forward movement system. That is, before each movement of the hanging basket, the longitudinal track must be laid on the bridge deck in the direction of the hanging basket's movement. Because the center of gravity of the hanging basket is in the front, the lower end of the longitudinal track must be placed on a pad, and both the pad and the longitudinal track must be anchored to the bridge deck box girder. Then, a winch, hydraulic push rod, or hand winch is used to slowly drag the hanging basket forward. After the hanging basket moves forward, the hanging basket and longitudinal track must be re-anchored. Once the hanging basket is in place, the previous set of pads and longitudinal track must be removed to prepare for laying the next set.

[0004] The existing gantry is extremely heavy, and moving the entire gantry forward is time-consuming and inefficient. It also requires repeated anchoring of the gantry and track movement. The excessive number of anchor points can easily damage the overall bridge deck structure, and the operation requires the coordination of at least dozens of people. The track laying process requires the guidance of surveyors, making it a tedious, complex, time-consuming, and labor-intensive process. Furthermore, there is a risk of derailment and slippage during the forward movement. Summary of the Invention

[0005] The purpose of the present invention is to design a construction method for cast-in-situ box girders of cable-stayed bridges, which does not require the use of traditional hanging baskets for suspended pouring of cast-in-situ box girders. The method has the advantages of being supported by a formwork system for the box girder to be poured, having a high moving speed, causing little damage to the overall structure of the bridge deck, and having a simple process and saving time and effort.

[0006] To this end, the present invention provides a construction method for a cast-in-situ box girder of a cable-stayed bridge: after each A-type cable tower is built, first cast-in-situ construction is carried out on block 0 of the prestressed concrete box girder located at the position of each main tower; and one end of a plurality of upper and lower embedded beams distributed at intervals are pre-embedded in the longitudinal two side surfaces of the prestressed concrete box girder No. 0, and the other end of each upper and lower embedded beam is arranged in the longitudinal direction of the bridge and the outer end extends to the space of the next adjacent segment to be cast; then, each embedded beam is used in conjunction with each upper supporting beam located on the edge of the top surface of the completed box beam as a cantilever casting support skeleton for cantilever casting the No. 1 segment on the side span side and the main span side to the subsequent sequence numbered segments and the adjacent segments to be cast of the joint section, or each embedded beam is used in conjunction with each upper supporting beam located on the edge of the top surface of the completed box beam and the inclined cable as a cantilever casting support skeleton for cantilever casting the No. 1 segment on the side span side and the main span side to the subsequent sequence numbered segments and the adjacent segments to be cast of the joint section.

[0007] A construction method for a cast-in-situ box girder of a cable-stayed bridge comprises the following steps:

[0008] (1) Prepare several upper supporting beams. After each A-type cable tower is built, the No. 0 prestressed concrete box beam located at each main tower position is cast in situ by using the scaffolding method. One end of several upper and lower embedded beams distributed at intervals are embedded in the longitudinal two side surfaces of the No. 0 prestressed concrete box beam. The other end of each upper and lower embedded beam is arranged in the longitudinal direction of the bridge and the outer end extends to the space of the next adjacent segment to be cast. Anchor holes are reserved at the anchoring position of the rear end of the upper supporting beam distributed at intervals on the upper end surface of the No. 0 prestressed concrete box beam.

[0009] (2) Installation of each upper joist: On the top surface of the prestressed concrete box girder No. 0 that has been formed, the corresponding reserved anchor holes are placed at intervals by forklift. The front end of each upper joist is located on the top surface of the completed box girder. The upper joist of the two I-beams at the front end of the front end of the pressure support extends to the space of the next adjacent segment to be poured and the end head extends to the outside of the segment to be poured. The rear end of each upper joist passes through the reserved anchor hole of the corresponding part through the anchor rod and is anchored on the top surface of the formed box girder by using the anchor rod pad and the anchor rod fastening nut. The front end of each upper joist is located at the upper end of the adjacent segment to be poured. The front and rear end upper parts of each upper joist are fixed with front and rear connecting beams respectively by bolts. The rear part of each upper joist is provided with a counterweight block.

[0010] (3) Use several suspenders and slings to sequentially pass through the upper supporting beam or front connecting beam at the front, the upper and lower embedded beams at the lower end of the corresponding part, and connect with several longitudinal distribution beams at the lower end of the corresponding section to be poured, so as to form a cantilever casting support skeleton for adjacent sections to be poured;

[0011] Or for those with hanging cable number blocks, the front ends of the left and right upper embedded beams are set to correspond to the positions of the left and right oblique cables. First, cable fixing parts are set on the front ends of the left and right upper embedded beams corresponding to the positions of the left and right oblique cables. Temporary cables or oblique cables are set between the cable fixing parts and the corresponding upper tower column tightening cable parts and force is applied to them. Several hangers and slings pass through the upper supporting beam or front connecting beam at the front, the upper and lower embedded beams at the lower end of the corresponding part and are connected with several longitudinal distribution beams at the lower end of the corresponding segment to be poured. Each embedded beam is used in conjunction with each upper supporting beam and oblique cables or temporary cables located on the edge of the top surface of the completed box beam as a cantilever casting support skeleton for the No. 1 segment on the side span side and the main span side to the subsequent sequence number segments and the adjacent segments to be poured in the joint section;

[0012] (4) A bottom crossbeam is set on the upper end of several longitudinal distribution beams of the cantilever casting support frame. Steel frame brackets are set on both sides of the upper end of the bottom crossbeam. The outer side formwork is set inside the steel frame bracket. The upper front end of the bottom crossbeam is the construction anchor road. The middle part of the upper end of the bottom crossbeam is set with longitudinal square timber, transverse square timber and bottom formwork. Pressure test is carried out on the bottom formwork. After the pressure test, the end formwork, bottom plate reinforcement, web reinforcement, longitudinal corrugated pipe, vertical prestressed reinforcement, inner formwork and top plate reinforcement are installed. The upper and lower embedded beams are fixed to the corresponding reinforcement. The upper and lower embedded beam ends of the next docking section are fixed to the corresponding reinforcement. The longitudinal and transverse corrugated pipes are installed and inspected and accepted.

[0013] (5) Pouring concrete in the formwork of the continuous box girder: first pour the concrete of the box girder bottom plate, pump the concrete into the formwork, and pour the concrete in layers on both sides and then in the middle. Then pour the concrete of the box girder web, and pour the concrete in layers on both sides and then in the middle. The concrete pouring height is within 1m and the height of the layers is within 30cm. The concrete pouring of the box girder top plate and wing plate is carried out from the front to the back, and from the middle of the top plate to the two sides. Finally, pour the wing plate of this section.

[0014] (6) Curing and pouring concrete, removing the end formwork and roughening the end concrete, removing the inner and outer formwork, tensioning the longitudinal, transverse and vertical prestressed tendons, and grouting;

[0015] Or for those with cable number blocks, it corresponds to the layout and traction of the left and right inclined cables;

[0016] (7) Moving forward each upper joist: loosen and remove the suspenders, slings and rear anchor bolts on each upper joist or front connecting beam, remove the front and rear connecting beams on the front and rear ends of each upper joist, remove the counterweights on the rear of each upper joist, and move each upper joist forward using a forklift;

[0017] (8) Repeat steps (2) to (7) to proceed to the next piece of construction;

[0018] (9) Construction of the side span closure section and the middle span closure section.

[0019] As a further description of the above technical solution: the upper and lower embedded beams are arranged in the longitudinal direction of the bridge, the inner ends of the upper and lower embedded beams are located in the completed box beam and are connected to the steel mesh in the corresponding completed box beam, and the outer ends of the upper and lower embedded beams extend to the space of the next adjacent segment to be cast.

[0020] As a further description of the above technical solution: the upper supporting beam is composed of two I30~50 I-beams arranged side by side to form a double I-beam structure, the two I-beams are fixedly connected by a connecting plate, and the front and rear lower ends of the two I-beams are provided with pressure-dividing supports, and the front end pressure-dividing support is located on the front end top surface of the completed box beam. The two I-beams at the front end of the front end pressure-dividing support extend into the space of the next adjacent segment to be cast and the end heads are located outside the space of the segment to be cast, a support frame is provided on the front middle top surface of the two I-beams, a front pull rod is provided between the front top surface of the two I-beams and the top surface of the support frame, a rear pull rod is provided between the rear top surface of the two I-beams and the top surface of the support frame, a counterweight block and an anchor hole are provided at the rear of the upper supporting beam, and the front and rear end top surfaces of each upper supporting beam are connected by the front and rear connecting beams respectively.

[0021] As a further description of the above technical solution: the steel bars installed in the template casting space, the longitudinal non-prestressed bars of each beam section are overlap-welded and connected to the corresponding upper and lower embedded beams.

[0022] As a further description of the above technical solution: the ratio of the total length of the upper supporting beam to the length of the upper supporting beam suspension part located at the front end of the front pressure dividing support is at least 3:1.

[0023] As a further description of the above technical solution: the upper and lower embedded beams are I-beams or channel steels.

[0024] As a further description of the above technical solution: the construction of the side span closure section and the middle span closure section is:

[0025] (1) One end of the upper and lower embedded beams is provided on one side of the butt joint of the adjacent formed box beams in the joint section, and the other end of the upper and lower embedded beams extends into the space of the joint section to be cast, or one end of the upper embedded beam is provided on both sides of the butt joint of the adjacent formed box beams in the joint section, and the other end of the upper embedded beam extends into the space of the joint section to be cast;

[0026] (2) Installation of each upper supporting beam: corresponding pressure bearings are provided on the upper ends of the adjacent formed box beams at the joint section. The lower sides of both ends of each upper supporting beam are respectively overlapped on the pressure bearings on the adjacent formed box beams at the joint section. The middle part of each upper supporting beam is located at the upper end of the space of the adjacent joint section to be cast. The upper parts of the front and rear ends of each upper supporting beam are respectively fixed with front and rear connecting beams by bolts. The embedded beams are used in conjunction with each upper supporting beam as the cantilever casting support skeleton for the adjacent sections to be cast of the joint section.

[0027] As a further description of the above technical solution: the height of the pressure-dividing support is 50 to 100 cm, and the width of the pressure-dividing support is greater than the width of the upper support beam.

[0028] As a further description of the above technical solution: the upper supporting beam is a triangular support structure.

[0029] The present invention has the following beneficial effects:

[0030] 1. The present invention utilizes pre-cast beams in conjunction with upper joists located on the top edge of the completed box girder as the cantilever casting support framework for cantilever casting of segments from segment 1 on the side and main span sides, as well as segments adjacent to the closure section and awaiting pouring. Alternatively, the pre-cast beams, in conjunction with upper joists located on the top edge of the completed box girder and stay cables, serve as the cantilever casting support framework for cantilever casting of segments from segment 1 on the side and main span sides, as well as segments adjacent to the closure section and awaiting pouring. This eliminates the need for conventional cantilevered hanging basket construction, while also addressing the drawbacks of hanging basket construction.

[0031] 2. The layout and displacement of each upper support beam of the present invention only requires a forklift in combination with a crane, or only a crane and 3 to 5 people to complete. It omits the time-consuming and inefficient forward movement of the traditional hanging basket, and the need to repeatedly anchor the hanging basket and longitudinally move the track. Excessive anchoring can easily cause damage to the overall structure of the bridge deck, and at least dozens of people are needed to cooperate during the movement. The track laying process requires the guidance of surveyors, and the procedures are cumbersome, complicated, time-consuming and labor-intensive. At the same time, there is a risk of derailment and sliding during the forward movement. Practice has proved that the layout and displacement time of the present invention is shortened by 70%, the cost is reduced by 60%, and the number of personnel is reduced by more than 60% compared with the traditional hanging basket. The layout and displacement are stable and safe, and have good economic benefits.

[0032] 3. This invention offers excellent performance. The number of upper joists and upper and lower pre-buried beams can be adjusted based on the width of the box girder to be cast, regardless of the width of the box girder or the width of the hanging basket. Because the number of upper joists and upper and lower pre-buried beams can be adjusted based on the weight of the box girder to be cast, the load-bearing capacity of this invention far exceeds that of a conventional hanging basket, given the length and width of the box girder to be cast. This can shorten the construction period by 30-35%, reduce construction costs by 30-35%, save labor, and improve construction efficiency.

[0033] 4. The present invention is easy to move and transfer, with high speed, which improves construction safety and stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of the longitudinal structure of a double-tower, double-cable-plane, low-tower cable-stayed bridge constructed according to the present invention;

[0035] Figure 2 This is a schematic diagram of the upper support beam structure of the present invention;

[0036] Figure 3 This is a schematic diagram of the state structure of block 0 completed in the present invention;

[0037] Figure 4 This is a schematic diagram of the cantilever casting support skeleton structure of the segment to be cast in the present invention;

[0038] Figure 5 This is a schematic diagram of the longitudinal structure of a cantilever casting support frame with a stay cable to be cast section according to the present invention;

[0039] Figure 6 It is a schematic diagram of the transverse structure of the cantilever casting support skeleton with the inclined cable segment to be cast according to the present invention. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. In order to make the technical means, creative features, purpose and efficacy of the present invention easy to understand, the present invention will be further described in conjunction with specific embodiments below. However, the following embodiments are only preferred embodiments of the present invention, not all. Based on the embodiments in the implementation mode, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention. The construction methods in the following embodiments are all conventional methods unless otherwise specified. The materials, devices, equipment, etc. used in the following embodiments are all commercially available unless otherwise specified.

[0041] like Figure 1 As shown, the twin-tower, twin-cable-plane cable-stayed bridge constructed according to the present invention features two main pier caps 11 and two side pier caps 201. Both the main and side pier caps 201 are two-stage structures, each connected to its own pile group foundation 12. The cable towers 15 on the two main pier caps are A-shaped reinforced concrete structures. Each tower has a longitudinal tie beam 14 at its lower longitudinal portion and an H-shaped upper crossbeam 2 at its upper portion. The upper end of the upper crossbeam 2 serves as an upper tower column 1 for the cable-hanging section. The main girder deck is a single-box, double-chamber prestressed concrete box girder structure with a continuously variable cross-section. The main span is divided into forty-three cantilevered cast segments, namely, cantilevered cast segments 101-121, including a mid-span joint section 100. The side spans are divided into twenty-three cantilevered cast segments, including a side span joint section 122 that connects to the side span support box girder 200. The cables 13 are arranged in a fan-shaped pattern, with eight pairs of cables 13 per tower 15.

[0042] The construction sequence of the main beam construction process of the present invention is to first construct block 10 located on the longitudinal lower longitudinal tie beam 14 of each cable tower, then cantilever cast segments 101 to 121 on the side span side and the main span side in sequence, during the construction of segments 101 to 20, construct segment 200 located on the side pier, then construct the side span joint section 122, then cantilever cast segment 122 on the main span side, and finally construct the middle span joint section 100.

[0043] like Figures 1 to 6 As shown, a method for constructing a cast-in-situ box girder for a cable-stayed bridge is described. After each A-type pylon 15 is constructed, prestressed concrete box girder No. 0 is first cast-in-situ at each main pylon location. Furthermore, one end of a plurality of upper pre-embedded beams 3 and lower pre-embedded beams 7 are embedded in the longitudinal side surfaces of the pre-stressed concrete box girder No. 0 at intervals. The upper pre-embedded beams 3 and lower pre-embedded beams 7 are arranged in the upper, lower left, center, and left positions, respectively. The other end of each upper and lower pre-embedded beam is disposed longitudinally along the bridge, with the outer end extending into the space of the next adjacent segment to be cast.

[0044] Then, each embedded beam is used in conjunction with each upper supporting beam 5 located on the top edge of the completed box beam 30 as a cantilever casting support skeleton for the cantilever casting of the No. 1 segment on the side span side and the main span side to the subsequent segments with serial numbers and the adjacent segments to be cast in the joint section, or each embedded beam is used in conjunction with each upper supporting beam and inclined cable located on the top edge of the completed box beam as a cantilever casting support skeleton for the cantilever casting of the No. 1 segment on the side span side and the main span side to the subsequent segments with serial numbers and the adjacent segments to be cast in the joint section.

[0045] like Figure 2 As shown, first prepare the upper supporting beam 5. Each upper supporting beam is formed by two I30-50 I-beams arranged side by side to form a double I-beam structure. The two I-beams are fixedly connected by a number of connecting plates 52 arranged at intervals. The front and rear lower ends of the two I-beams are provided with a pressure dividing support 51. The pressure dividing support is a steel support. The height of the pressure dividing support is 50-100 cm to leave enough construction space. The width of the pressure dividing support is greater than the width of the upper supporting beam. The middle part of the upper end of each pressure dividing support can be welded to the lower end of the corresponding upper supporting beam to form a whole. It can also be temporarily connected by bolts and nuts or clamps. The front end pressure dividing support is located on the top surface of the front end of the completed box beam. The two I-beams at the front end of the front end pressure dividing support extend to the outside of the space of the next adjacent segment to be poured, that is, the two I-beam ends at the front end extend outside the space of the adjacent segment to be poured. A steel support frame 54 is provided on the front middle top surface of the two I-beams, a steel front pull rod 53 is provided between the front top surface of the two I-beams and the top surface of the support frame, and a rear pull rod 55 is provided between the rear top surface of the two I-beams and the top surface of the support frame, thereby forming an upper support beam with a triangular support structure; the total length of the upper support beam and the length ratio of the upper support beam suspension part located at the front end of the pressure dividing support at the front end is at least 3:1.

[0046] The rear of the upper joist is provided with a counterweight 4 and anchor holes. The counterweight 4 is used to press on the rear of the upper joist to balance the load on the front and rear ends of the upper joist. When in use, the front and rear end top surfaces of each upper joist are connected by a front connecting crossbeam 6 and a rear connecting crossbeam 27, respectively, such as by bolts and nuts or clamps.

[0047] like Figures 1 to 6 As shown, a construction method for a cast-in-situ box girder of a cable-stayed bridge comprises the following steps:

[0048] (1) Prepare a number of upper supporting beams 5. After each A-type cable tower is built, the No. 0 prestressed concrete box beam 10 located at each main tower position is cast in situ by using the scaffolding method. In addition, one end of a number of upper embedded beams 3 and lower embedded beams 7 are embedded in the longitudinal sides of the No. 0 prestressed concrete box beam at intervals. The other end of each upper and lower embedded beam is arranged in the longitudinal direction of the bridge and the outer end extends to the space of the next adjacent segment to be cast. The spacing and number of the upper and lower embedded beams are determined according to the overall load-bearing capacity of the segment to be cast and the size and pre-load of each embedded beam. Usually, the horizontal spacing of each upper or lower embedded beam is 2.5 to 3 meters. Each upper embedded beam is located at the upper part of the concrete box beam, and each lower embedded beam is located at the lower part of the concrete box beam. The two upper embedded beams are located at the upper ends of the concrete box beam and the extended ends are on the same longitudinal plane as the cable fasteners 24 of the corresponding left and right inclined cables 13.

[0049] Each upper and lower embedded beam is arranged in the longitudinal direction of the bridge. The inner end of each upper and lower embedded beam is located in the completed box beam 30 and is connected to the steel mesh in the corresponding completed box beam. The outer end of each upper and lower embedded beam extends to the space of the next adjacent segment to be cast.

[0050] The upper and lower embedded beams are I-beams or channel steels.

[0051] Reserved anchor holes 28 are provided on the upper end surface of the No. 0 prestressed concrete box girder at the anchoring positions of the rear ends of the upper supporting beams distributed at intervals, and the reserved anchor holes pass through the top of the concrete box girder.

[0052] (2) Installation of each upper supporting beam: corresponding to the reserved anchor holes 28 on the top surface of the prestressed concrete box beam No. 0 that has been formed, use a forklift to place each upper supporting beam at a distance. The front end pressure-dividing support of each upper supporting beam is located on the front end top surface of the completed box beam. The upper supporting beams of the two I-beams at the front end of the front pressure-dividing support extend into the space of the next adjacent segment to be cast and the end portion extends outside the space of the segment to be cast. The spacing and number of each upper supporting beam are determined according to the overall load-bearing capacity of the segment to be cast and the size and pre-load-bearing capacity of each embedded beam. Usually, the horizontal spacing of each upper supporting beam is 2.5 to 3 meters, and the two upper supporting beams are located on both sides of the main beam in the wing plate on the top surface of the formed box beam.

[0053] The rear end of each upper joist 5 is anchored to the top surface of the formed box girder via steel anchor rods 29 passing through pre-reserved anchor holes 28 in the corresponding portion and anchored using anchor rod pads 16 and anchor rod fastening nuts 26. The front end of each upper joist is located at the upper end of the space between the adjacent segments to be cast. The front and rear ends of each upper joist are respectively fixed to the front connecting crossbeam 6 and the rear connecting crossbeam 27 by bolts. A counterweight block 4 is provided on the rear end of each upper joist.

[0054] (3) Use several suspenders 9, which are made of PSB930MPa 42mm finely rolled threaded steel bars. The suspenders are passed through the upper supporting beam or front connecting beam at the front, the upper and lower embedded beams at the lower end of the corresponding part, and the several longitudinal distribution beams 8 at the lower end of the corresponding section to be poured, connected by gaskets and suspender fastening nuts 25, to form a cantilever casting support skeleton for adjacent sections to be poured. The length of each suspender is based on the exposed end of not less than 10cm after tightening the suspender fastening nut; during installation, each end of the suspender must be equipped with a standard gasket and a suspender fastening nut 25. In order to facilitate the removal of the outer sleeve of the suspender at the corresponding part where it meets the cement.

[0055] Or for blocks with hanging cable numbers (such as block section 106), the front ends of the left and right upper embedded beams are set corresponding to the positions of the left and right inclined cables. First, the cable fixing parts 24 are set on the front ends of the left and right upper embedded beams corresponding to the positions of the left and right inclined cables. A temporary cable or inclined cable is set between the cable fixing parts and the corresponding upper tower column tightening cable parts and subjected to force. Several hangers and slings are sequentially passed through the upper supporting beam or front connecting beam of the front part, the upper and lower embedded beams at the lower end of the corresponding part and the lower end of the corresponding segment to be cast. Several longitudinal distribution beams are connected by gaskets and hanger fastening nuts 25, and the embedded beams are used in conjunction with the upper supporting beams and inclined cables or temporary cables located on the edge of the top surface of the completed box beam as the cantilever casting support skeleton for the No. 1 segment on the side span side and the main span side to the subsequent sequence numbered segments and the adjacent segments to be cast in the joint section; the temporary cables can be steel wire ropes with a diameter of more than 4 cm to cooperate with the upper supporting beams and the upper embedded beams to form a cantilever casting support skeleton for the segments to be cast.

[0056] (4) A bottom crossbeam 19 is installed on the upper end of several longitudinal distribution beams of the cantilever casting support frame. Steel frame brackets 18 are installed on both sides of the upper end of the bottom crossbeam. The outer side formwork 17 is installed inside the steel frame bracket. The upper front end of the bottom crossbeam is a construction anchor road. The middle part of the upper end of the bottom crossbeam is equipped with longitudinal square timber 22, transverse square timber 21, and bottom formwork 20. Pressure test is carried out on the bottom formwork. After the pressure test, the end formwork, bottom plate reinforcement, web reinforcement, longitudinal corrugated pipe, vertical prestressed tendons, inner formwork 23, and top plate reinforcement are installed. The upper and lower embedded beams are fixed to the corresponding reinforcement, and the upper and lower embedded beam ends of the next docking section are fixed to the corresponding reinforcement. The longitudinal and transverse corrugated pipes are installed and inspected and accepted. The reinforcement installed in the formwork casting space and the longitudinal non-prestressed tendons of each beam section are lap-welded and connected to the corresponding upper and lower embedded beams.

[0057] (5) Pouring concrete in the formwork of continuous box beams: first pour the concrete of the box beam bottom plate, pump the concrete into the formwork, and pour the concrete in layers on both sides and then in the middle at a height of less than 1m; then pour the concrete of the box beam web, and pour the concrete in layers within 1m at a height of less than 30cm; pour the concrete of the box beam top plate and wing plate from the front to the back, and from the middle of the top plate to the two sides, and finally pour the wing plate of this section.

[0058] (6) Curing and pouring concrete, removing the end formwork and roughening the end concrete, removing the inner and outer formwork, tensioning the longitudinal, transverse and vertical prestressed tendons, and grouting;

[0059] Or for those with rope number blocks, it corresponds to the layout and traction of the left and right inclined cables.

[0060] (7) Moving forward each upper support beam: loosen and remove the suspension rods, slings and rear anchor rods on each upper support beam or front connecting beam, remove the front and rear connecting beams on the upper front and rear ends of each upper support beam, remove the counterweight blocks on the rear end of each upper support beam, and move each upper support beam forward using a forklift.

[0061] (8) Repeat steps (2) to (7) to proceed to the next piece of construction;

[0062] (9) Construction of the side span closure section and the middle span closure section. The construction of the side span closure section and the middle span closure section is:

[0063] (1) One end of the upper and lower embedded beams is provided on one side of the butt joint of the adjacent formed box beams in the joint section, and the other end of the upper and lower embedded beams extends into the space of the joint section to be cast, or one end of the upper embedded beam is provided on both sides of the butt joint of the adjacent formed box beams in the joint section, and the other end of the upper embedded beam extends into the space of the joint section to be cast;

[0064] (2) Installation of each upper joist: A corresponding pressure bearing is provided on the upper edge of the butt joint surface of the adjacent formed box girders of the joint section. The lower sides of both ends of each upper joist are respectively overlapped on the pressure bearing on the butt joint surface of the adjacent formed box girders of the joint section. The middle part of each upper joist is located at the upper end of the space between the adjacent sections to be cast. The front and rear end upper parts of each upper joist are respectively fixed with front and rear connecting beams by bolts. The embedded beams are used in conjunction with each upper joist as the cantilever casting support frame for the adjacent sections to be cast of the joint section. The rest of the process is the same as that of other sections to be cast, so it will not be repeated here.

[0065] The above is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solutions and inventive concepts of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A construction method for a cast-in-situ box girder of a cable-stayed bridge, characterized in that: The steps include: (1) Prepare several upper supporting beams. After each A-type cable tower is built, the No. 0 prestressed concrete box beam located at each main tower position is cast in situ by using the scaffolding method. One end of several upper and lower embedded beams distributed at intervals are embedded in the longitudinal two side surfaces of the No. 0 prestressed concrete box beam. The other end of each upper and lower embedded beam is arranged in the longitudinal direction of the bridge and the outer end extends to the space of the next adjacent segment to be cast. Anchor holes are reserved at the anchoring position of the rear end of the upper supporting beam distributed at intervals on the upper end surface of the No. 0 prestressed concrete box beam. (2) Installation of each upper joist: On the top surface of the prestressed concrete box girder No. 0 that has been formed, the corresponding reserved anchor holes are placed at intervals by forklift. The front end of each upper joist is located on the top surface of the completed box girder. The upper joist of the two I-beams at the front end of the front end of the pressure support extends to the space of the next adjacent segment to be poured and the end head extends to the outside of the segment to be poured. The rear end of each upper joist passes through the reserved anchor hole of the corresponding part through the anchor rod and is anchored on the top surface of the formed box girder by using the anchor rod pad and the anchor rod fastening nut. The front end of each upper joist is located at the upper end of the adjacent segment to be poured. The front and rear end upper parts of each upper joist are fixed with front and rear connecting beams respectively by bolts. The rear part of each upper joist is provided with a counterweight block. (3) Use several suspenders and slings to sequentially pass through the upper supporting beam or front connecting beam at the front, the upper and lower embedded beams at the lower end of the corresponding part, and connect with several longitudinal distribution beams at the lower end of the corresponding section to be poured, so as to form a cantilever casting support skeleton for adjacent sections to be poured; Or for those with hanging cable number blocks, the front ends of the left and right upper embedded beams are set to correspond to the positions of the left and right oblique cables. First, cable fixing parts are set on the front ends of the left and right upper embedded beams corresponding to the positions of the left and right oblique cables. Temporary cables or oblique cables are set between the cable fixing parts and the corresponding upper tower column tightening cable parts and force is applied to them. Several hangers and slings pass through the upper supporting beam or front connecting beam at the front, the upper and lower embedded beams at the lower end of the corresponding part and are connected with several longitudinal distribution beams at the lower end of the corresponding segment to be poured. Each embedded beam is used in conjunction with each upper supporting beam and oblique cables or temporary cables located on the edge of the top surface of the completed box beam as a cantilever casting support skeleton for the No. 1 segment on the side span side and the main span side to the subsequent sequence number segments and the adjacent segments to be poured in the joint section; (4) A bottom crossbeam is set on the upper end of several longitudinal distribution beams of the cantilever casting support frame. Steel frame brackets are set on both sides of the upper end of the bottom crossbeam. The outer side formwork is set inside the steel frame bracket. The upper front end of the bottom crossbeam is the construction anchor road. The middle part of the upper end of the bottom crossbeam is set with longitudinal square timber, transverse square timber and bottom formwork. Pressure test is carried out on the bottom formwork. After the pressure test, the end formwork, bottom plate reinforcement, web reinforcement, longitudinal corrugated pipe, vertical prestressed reinforcement, inner formwork and top plate reinforcement are installed. The upper and lower embedded beams are fixed to the corresponding reinforcement. The upper and lower embedded beam ends of the next docking section are fixed to the corresponding reinforcement. The longitudinal and transverse corrugated pipes are installed and inspected and accepted. (5) Pouring concrete in the formwork of the continuous box girder: first pour the concrete of the box girder bottom plate, pump the concrete into the formwork, and pour the concrete in layers on both sides and then in the middle. Then pour the concrete of the box girder web, and pour the concrete in layers on both sides and then in the middle. The concrete pouring height is within 1m and the height of the layers is within 30cm. The concrete pouring of the box girder top plate and wing plate is carried out from the front to the back, and from the middle of the top plate to the two sides. Finally, pour the wing plate of this section. (6) Curing and pouring concrete, removing the end formwork and roughening the end concrete, removing the inner and outer formwork, tensioning the longitudinal, transverse and vertical prestressed tendons, and grouting; Or for those with cable number blocks, it corresponds to the layout and traction of the left and right inclined cables; (7) Moving forward each upper joist: loosen and remove the suspenders, slings and rear anchor bolts on each upper joist or front connecting beam, remove the front and rear connecting beams on the front and rear ends of each upper joist, remove the counterweights on the rear of each upper joist, and move each upper joist forward using a forklift; (8) Repeat steps (2) to (7) to proceed to the next piece of construction; (9) Construction of the side span closure section and the middle span closure section.

2. The method according to claim 1, characterized in that: The upper supporting beam is formed by two I30~50 I-beams arranged side by side to form a double I-beam structure. The two I-beams are fixedly connected by a connecting plate. The front and rear lower ends of the two I-beams are provided with pressure-dividing supports. The front end pressure-dividing support is located on the front end top surface of the completed box beam. The two I-beams at the front end of the front end pressure-dividing support extend into the space of the next adjacent segment to be poured and the end head is located outside the space of the segment to be poured. A support frame is provided on the front middle top surface of the two I-beams, a front pull rod is provided between the front top surface of the two I-beams and the top surface of the support frame, and a rear pull rod is provided between the rear top surface of the two I-beams and the top surface of the support frame. A counterweight block and anchor rod hole are provided at the rear of the upper supporting beam, and the front and rear end top surfaces of each upper supporting beam are connected by the front and rear connecting beams respectively.

3. The method according to claim 1, characterized in that: The steel bars installed in the template casting space are longitudinal non-prestressed bars of each beam section, which are overlap-welded and connected to the upper and lower embedded beams at the corresponding positions.

4. The method according to claim 1, characterized in that: The ratio of the total length of the upper supporting beam to the length of the upper supporting beam suspension portion located at the front end of the front pressure dividing support is at least 3:

1.

5. The method according to claim 1, characterized in that: The construction of the side span closure section and the middle span closure section is as follows: (1) One end of the upper and lower embedded beams is provided on one side of the butt joint of the adjacent formed box beams in the joint section, and the other end of the upper and lower embedded beams extends into the space of the joint section to be cast, or one end of the upper embedded beam is provided on both sides of the butt joint of the adjacent formed box beams in the joint section, and the other end of the upper embedded beam extends into the space of the joint section to be cast; (2) Installation of each upper supporting beam: corresponding pressure bearings are provided on the upper ends of the adjacent formed box beams at the joint section. The lower sides of both ends of each upper supporting beam are respectively overlapped on the pressure bearings on the adjacent formed box beams at the joint section. The middle part of each upper supporting beam is located at the upper end of the space of the adjacent joint section to be cast. The upper parts of the front and rear ends of each upper supporting beam are respectively fixed with front and rear connecting beams by bolts. The embedded beams are used in conjunction with each upper supporting beam as the cantilever casting support skeleton for the adjacent sections to be cast of the joint section.

6. The method according to claim 1, characterized in that: The height of the pressure-dividing support is 50-100 cm, and the width of the pressure-dividing support is greater than the width of the upper supporting beam.

7. The method according to claim 1, characterized in that: The upper supporting beam is a triangular support structure.

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