High-efficiency and high-quality double-tower double-cable-plane cable-stayed bridge box-type small-section arched cable bent tower construction method

Abstract

The invention discloses an efficient and high-quality double-tower double-cable-plane cable-stayed bridge box type small-section arch cable tower construction method. The method comprises the following steps that A, a lower tower column is constructed; b, constructing a lower cross beam; c, upper tower column construction; d, closure section construction; and E, tower crown construction. The problem that when an existing double-tower double-cable-plane cable-stayed bridge box type small-section arch cable bent tower is constructed, different construction technologies are not formulated according to the cable bent tower structure so as to improve the construction efficiency and the construction quality is solved.

Description

Technical Field

[0001] The invention relates to the field of construction methods, in particular to an efficient and high-quality construction method for a double-tower double-cable-plane cable-stayed bridge box-type small-section arched cable tower. Background Art

[0002] During the construction of a double-tower double-cable-plane cable-stayed bridge box-type small-section arch cable tower, due to its complex structure, ordinary construction technology cannot take into account both rapid construction and guaranteed construction quality. Therefore, it is necessary to improve the existing construction technology of the double-tower double-cable-plane cable-stayed bridge box-type small-section arch cable tower. Summary of the invention

[0003] The purpose of the present invention is to provide an efficient and high-quality construction method for a double-tower double-cable-plane cable-stayed bridge box-type small-section arched cable tower, so as to solve the problem that different construction processes are not formulated according to the cable tower structure to improve the construction efficiency and construction quality during the construction of the existing double-tower double-cable-plane cable-stayed bridge box-type small-section arched cable tower.

[0004] In order to solve the above technical problems, the present invention adopts the following technical solutions: An efficient and high-quality construction method for a double-tower double-cable-plane cable-stayed bridge box-type small-section arched cable tower comprises the following steps: A. construction of lower tower column; B. construction of lower crossbeam; C. construction of upper tower column; D. construction of joint section; and E. construction of tower crown.

[0005] When the above method is used to construct the arched cable tower, the cable tower is divided into lower tower column construction, lower crossbeam construction, upper tower column construction, joint section construction and tower crown construction according to its structural characteristics. The advantage of this is that the construction method of each part can be well adapted to its structural characteristics. The use of different construction processes can not only make the construction of each part more efficient, but also effectively ensure the quality of construction.

[0006] The tower crane needs to be arranged before construction. The selection of the tower crane during the arrangement mainly considers the following factors: ① Space dimension requirements for formwork and climbing frame during tower column construction; ② Requirements for lifting weight during tower crane construction, including steel bars, rigid skeletons, steel anchor beams and formwork, etc.; ③ The demolition load and spatial position requirements of the tower crane itself; ④Influence of installation, removal and plane position of construction elevator; ⑤ Installation of tower top crane (stayed cable installation equipment); The following factors should be considered when arranging the tower crane position: ①Whether there are places around that are not suitable for tower crane deployment; ② During flood season, the water flow velocity will scour the tower crane foundation, increasing construction safety hazards.

[0007] ③The plane position of the tower crane needs to avoid the position of the hydraulic climbing formwork, and the plane position of the climbing formwork must be at least 3.5m away from the tower crane truss.

[0008] After the tower crane is selected and arranged according to the above method, two tower crane attachments are set up.

[0009] According to the on-site construction conditions and construction requirements, the elevator is selected for layout, and the load that the elevator foundation can bear is not less than P. P = total weight of equipment (kg) × 0.02kN Total weight of equipment = (equipment weight + equipment load) × 125% The foundation ground should be able to withstand a pressure of not less than 0.15Mpa.

[0010] The principles of elevator attachment layout are as follows: The selection of the wall-mounted support is mainly determined by the distance L between the building and the center of the guide frame and the opening B of the wall-mounted support.

[0011] The elevator platform is supported by a triangular bracket and is made of double-jointed 45b I-beams; 25b I-beam distribution beams are laid on the triangular bracket at a rate of 0.6 meters per row; the panel is made of 10mm patterned steel plate, and safety guardrails and anti-fall nets are installed on the edges.

[0012] When the height of the ladder cage reaches near the lower beam, a lower beam access platform is set up; the lower beam access platform is supported by a steel pipe bracket, and M30 / D20 climbing cones are embedded during tower column construction; 2 sets of corbels are installed on the side of the tower column, and the distribution beam uses Ⅰ12.6 I-beam to set up a pedestrian passage between the lower beam access platform and the safety ladder cage.

[0013] The cable tower made of an arched gate tower shape by the above method consists of a lower tower column, a lower crossbeam, and an upper tower column (tower crown). The upper tower column has a variable cross-section along the longitudinal direction of the bridge and a constant cross-section along the transverse direction of the bridge. The lower tower column also has a variable cross-section. A 100x100cm manhole is provided on the lower crossbeam to penetrate the cable tower column.

[0014] In order to facilitate construction and accurate positioning, a rigid frame made of welded steel plates and steel sections is provided inside the tower column. During construction, the position of the rigid frame inside the tower column can be appropriately adjusted according to actual conditions. The rigid frame is required to be welded and positioned with the cableway pipe and steel anchor plate.

[0015] A lightning rod and navigation light are installed on the top of the tower, and a maintenance ladder is installed inside the tower.

[0016] The principle of segmentation during construction: the segmentation of the lower tower column and the middle tower column is mainly based on the turning points and mutation points of the outer contour of the tower body, and the segmentation of the upper tower column is mainly based on avoiding the anchoring teeth of the cable guide tube.

[0017] As a further preference of the present invention, the construction of the lower tower column in step A includes starting section No. 0 and segments No. 1 to 2, the starting section No. 0 and segment No. 1 are constructed by flipping molds, and the segment No. 2 is constructed by hydraulic climbing molds. After the flipping mold construction of starting section No. 0 and segment No. 1 is carried out, the hydraulic climbing mold system is installed, and after the hydraulic climbing mold construction of segment No. 2 is completed, the inner climbing mold is dismantled.

[0018] The climbing formwork frame of the hydraulic climbing formwork construction is a heavy-duty separated truss frame, which adopts a separated structure of formwork and frame. The outer formwork climbing frame is equipped with multi-layer operating platforms, including steel bar binding platform, formwork operating platform, main operating platform, climbing frame climbing control platform and decoration platform from top to bottom; the platform on the top layer is 3 meters above the concrete surface to be poured, providing an operating platform for steel bar binding. The heavy-duty separated truss frame in this scheme adopts fully enclosed protection to provide an operating platform and safety protection for a series of tower column construction such as formwork construction and steel bar bundling, ensuring the safety of construction. The inner and outer sides of the bridge are curved surfaces, and curved guide rails are used to ensure normal construction. The climbing formwork frame along the bridge deck adopts straight guide rails.

[0019] During construction, the structure of the main tower is relatively complex, and the hydraulic climbing formwork needs to change tracks during operation. There are 2 machine positions on each side of the pier body. The single-limb outer formwork of the main tower requires a total of 8 hydraulic lower frames, 8 climbing formwork upper trusses, and 8 rearward shifting devices. The single-limb inner formwork is constructed with a homemade steel platform. The four sides of the outer formwork can climb simultaneously, and the inner formwork is lifted by a tower crane, which shortens the construction period.

[0020] The arrangement method of the operating platform in the hydraulic climbing formwork system is as follows: the steel bar binding platform, formwork operating platform, hydraulic operating platform, and the crossbeams of the hanging platform are connected with [14 channel steel with M20×50 bolts, and the main platform beam is connected with the support between the double 20 slots and the lower frame; steel belts are used to press between the platform plate and the platform crossbeams, and then on the platform plate, φ5×25 drill-tail self-tapping screws are used to connect the steel belts to the platform plate.

[0021] The overall steps for assembling each operating platform of the climbing formwork are as follows: Step 1: Hang the lower frame of the climbing formwork on the embedded part bracket.

[0022] Step 2: Lay the main operation and hydraulic operation platform beams and platform plates on the lower frame of the climbing formwork.

[0023] Step 3: Install the climbing formwork upper frame, and lay the steel bar binding, formwork operating platform beams and platform plates on the climbing formwork upper frame.

[0024] Step 4: Install the climbing formwork hanging platform and lay the hanging platform beams and platform plates on the climbing formwork hanging platform.

[0025] As the construction object is a double-cable arched cable tower with a complex structure, the size of the tower column changes with the tower height. Therefore, the inner and outer molds are made of steel-wood combination templates for easy cutting. The steel-wood combination template panel uses imported boards, the vertical ribs use H20 wood beams, and the horizontal ribs use double 14 grooves 6. The imported board uses birch as the base plate, and the front and back sides are covered with phenolic resin as a whole. The dark brown ester film is covered on both sides of the template by high-temperature hot pressing. The imported board has three layers of film, and the solid and smooth surface of phenolic resin can make It is very easy to demould, meeting the requirements of plain concrete (concrete is vibrated in place), and improving the appearance quality of concrete pouring. For sections with reduced cross-sectional dimensions, the shrinkage of the pier section can be achieved by cutting the template. The R1000 arc chamfer of the outer section of the pier is cast with a fixed steel mold to ensure the linear shape of the pier. The inner and outer sides along the bridge are arc-shaped surfaces and are constructed by replacing the curve with a straight line (except for the inner sides along the bridge of sections 1-4, the bottom mold of the closing section, and the top mold of the 22nd section tower crown, which are constructed with a fixed steel mold). After each section is completed, in order to ensure the overall appearance of the concrete and the safety of the template, the template is pressed against the poured concrete, and the pressing height is not less than 10cm. The template should be in close contact with the poured concrete to ensure no leakage and smooth transition.

[0026] The template cutting mentioned above is carried out on the climbing formwork frame. People stand on the top floor of the formwork frame and the main platform to draw lines on the template with ink cartridges, fix an aluminum alloy ruler next to the ink lines, insert φ30 steel bars into the tension bolt holes of the pier body, lay scaffolding boards to form a simple operating platform, and people stand on the simple platform with electric saws to cut the template to complete the template cutting.

[0027] The top layer of the hydraulic climbing formwork and the hanging platform plate are made of bent patterned steel plates, and the other platforms are made of steel springboards. The outer protection is made of framed wire mesh. There are skirting boards at the bottom of the platform, platform flaps on the wall side of the frame, and platform flaps in the gap between the frames on both sides. Fire extinguishers are installed on each platform of the climbing formwork frame to prevent fire, and there is a lightning rod on the top of the climbing formwork frame to prevent lightning strikes and ensure construction safety.

[0028] The climbing formwork frame has its own anti-fall device. The upper and lower reversing boxes of the climbing formwork frame always have a reversing box support force block supported on the guide rail to ensure the safety of the climbing formwork frame in the climbing state. When the climbing formwork frame climbs, the climbing formwork frame is hung on the rib core frame with a sling. This is the second insurance when the climbing formwork frame climbs.

[0029] The pump pipe can be installed on the tower crane and extended as the tower crane rises. The biggest advantage of this installation method is that the pump pipe is easy to inspect or use the hoisting hopper for concrete pouring.

[0030] The pouring cycle of the standard pouring layer of the hydraulic climbing formwork system is 7 days. The factors that restrict the construction period are not the climbing of the climbing formwork but the steel bar binding, acceptance, concrete pouring, and solidification to reach strength. When the concrete solidification strength reaches 20MPa, the climbing formwork can climb, and it takes about 60 minutes to climb 6 meters.

[0031] The lifting movement of the self-climbing formwork is achieved by alternately lifting the guide rail and the climbing frame with a hydraulic cylinder. The guide rail and the climbing frame can move relative to each other. When the climbing frame is in working condition, both the guide rail and the climbing frame are supported on the embedded support, and there is no relative movement between the two. After the formwork is removed, the force bolts, the hanger body, and the embedded support can be installed on the climbing cone left by the demolding, and the direction of the upper and lower reversing box tongues can be adjusted to lift the guide rail. After the guide rail is lifted into place and located on the embedded support, the operator can go to the lower platform to remove the lower embedded support, climbing cone, etc. exposed after the guide rail is lifted. After all the ties on the climbing frame are released, the climbing frame can be lifted. At this time, the guide rail remains stationary. After adjusting the direction of the upper and lower tongues, the cylinder is started, and the climbing frame moves upward relative to the guide rail. Through the alternate attachment of the guide rail and the climbing frame to the wall, the climbing frame rises along the tower column to achieve layer-by-layer lifting.

[0032] The assembly construction of hydraulic climbing formwork includes ① connection of formwork on the same surface: to ensure smooth joints of formwork, when assembling a single set of formwork, the panels at the edge of the joints are connected in the form of hard interfaces. When assembling each set of formwork, the two panels are connected together, and a core belt is installed on the transverse back rib. The templates on the same surface are tightly connected by inserting the core belt pin into the opening of the core belt and tightening the connection; ② connection of templates on different surfaces: The templates on different surfaces are connected to the back ribs through steel mold hooks and inclined seats. At the same time, in order to avoid the occurrence of mold expansion, the back ribs at the chamfers are also strengthened by tightening the inclined seats with high-strength screws. The inclined seats for vertical chamfers can directly use the standardized products, but for non-vertical chamfers, the seats need to be welded on the back ribs according to the situation on site; ③ Setting of tension and tension screws on large template surfaces: The tension screws of the templates on each surface are vertically penetrated by the pier body, and wedge-shaped pads are used on the climbing and crawling surfaces to ensure the horizontal contact between the tie rod nuts and the channel steel; when the tension length of the tower column template is not more than 3 meters, the tension screws adopt the standard section full-length tensioning method, and the PVC casing is penetrated between the templates on both sides, and the tension screws are passed through the casing, and the tie rods can be used in rotation. When casting solid sections with a thickness greater than 3 meters, use 600mm long tension screws to weld with Φ25 steel bars (or transverse main bars). The welding length is greater than 200mm and is fixed to the steel back rib with a female connecting pad; ④ Hydraulic climbing formwork assembly: The upper and lower frames are connected by pins, and the frame assembly follows the progress of the construction.

[0033] As a further preference of the present invention, the lower cross beam in step B is constructed as segment No. 3, and the lower cross beam is constructed as a cast-in-place bracket, specifically using steel corbels, floor-standing steel pipes and steel brackets for construction. After the lower tower column construction in step A is completed, the lower cross beam bracket is erected.

[0034] As a further preference of the present invention, the upper tower column construction in step C includes sections 4 to 16, section 4 is constructed by cast-in-place formwork, and sections 5-16 are constructed by hydraulic climbing formwork. After the cast-in-place formwork construction of section 4 is completed, the climbing formwork direction is first converted and then the hydraulic climbing formwork construction of sections 5-16 is carried out. Sections 7, 10 and 14 of sections 5-16 all need to be installed with cross braces. After the hydraulic climbing formwork construction of sections 5-16 is completed, the hydraulic climbing formwork system is dismantled.

[0035] The specific construction steps for dismantling the hydraulic climbing formwork system are as follows: Step 1: When the concrete strength reaches 15Mpa or above, remove all the tie rods (including the external angle tie rods). Pull out the safety pins and move the formwork back (the formwork can be moved back 600mm). Then insert the safety pins.

[0036] Step 2: Use a tower crane to lift the formwork, remove the main back rib connector, and lift the formwork to the specified site.

[0037] Step 3: Use a tower crane to hoist the upper platform and upper frame as a whole to the specified site.

[0038] Step 4: Pull the guide rail out of the frame and place it on a level surface.

[0039] Step 5: Cut the main platform and hanging platform in the middle to reduce weight.

[0040] Step 6: Use a tower crane to lift the lower frame of the climbing formwork as a whole to the specified site.

[0041] As a further preferred embodiment of the present invention, before the construction of the joint section in step D, the joint section support needs to be installed. The joint section construction includes 17 sections and 18 sections. The joint section construction is cast in layers according to the sections, specifically using steel corbels + arch trusses for construction, and is completed by casting in layers according to the section height.

[0042] As a further preferred embodiment of the present invention, the tower crown construction in step E includes segments 19 to 20, and the tower crown construction is cast in situ using full formwork and is completed in layers according to segment heights.

[0043] As a further preferred embodiment of the present invention, the rigid frame during the tower construction process is divided into segments synchronously with the main tower segment height, and the segments are processed into segment trusses near the construction area, and the segments are hoisted as a whole by a tower crane; the steel bars are concentrated in the steel bar yard to be processed into semi-finished products, which are transported to the construction site by a flatbed truck. After the rigid frame is installed, the rigid frame is used as a positioning device and hoisted by a tower crane for manual binding and installation.

[0044] The rigid skeleton between the main pier tower columns is set in sections, and the height of the sections is adjusted with the height of the tower column poured in a single time. During the construction of the sections, the exposed reserved length of the rigid skeleton is 50cm. After the skeleton is overlapped with the reserved length of the exposed rigid skeleton after pouring the concrete of the tower body of the foundation section each time, the total height of the rigid skeleton is not higher than 6.5m. It is welded piece by piece in the temporary processing site, and the skeleton is set with flat joints and diagonal braces every 3 meters to form a whole. The rigid skeleton is assembled in blocks at the temporary processing site, and hoisted and installed in blocks to reduce the danger and time of high-altitude installation. The steel used for the rigid skeleton is cut strictly according to the design size, and the assembly inspection is carried out after the production is completed. After the inspection is qualified, it is lifted by the tower crane for installation. In order to speed up the construction progress, the rigid skeleton is processed in sections and sections in the back field and then transported to the site, and then the frame is connected as a whole and hoisted.

[0045] The processing requirements for rigid skeleton processing are as follows: The processing length of each section of the rigid skeleton is determined according to the segment height of the tower column casting. The columns, parallel joints and diagonal braces of the rigid skeleton of the tower column are all made and connected with L75×75×7 steel. In order to facilitate transportation and on-site positioning and installation, the rigid skeleton is composed of small-section trusses and on-site connectors. In order to ensure the processing accuracy of the small-section trusses, they are made on a special pedestal and classified by number.

[0046] The installation method of the rigid frame is as follows: ① Skeleton transportation After the frame is processed in the steel structure processing plant, it is lifted by a crane onto a flatbed truck and transported to the site in sections for assembly on site.

[0047] ②Skeleton installation When installing the rigid frame, reserve bolt holes on the installed frame and use a plumb line and a ruler to control the position of the frame's upper edge. When the position meets the requirements, use bolts to securely connect the current frame to the previous frame. After the frame is fully installed, weld the connecting sections.

[0048] The steel bars of the tower columns should all have factory quality certificates and test reports, and should be sampled and tested for mechanical properties according to regulations. The test results should comply with the design and construction technical specifications.

[0049] The horizontal stirrup reinforcement shall be made according to the reinforcement drawing of the construction drawing, and the reinforcement material notice shall be issued while ensuring the requirements of the protective layer thickness, corner radius and binding lap length.

[0050] The installation of tower column reinforcement should be carried out strictly according to the design drawings. The connection of steel bars with a diameter of ≥22mm in the lower tower column shall be made by rolled straight thread connection. The joint performance shall comply with the relevant requirements of the "General Technical Code for Mechanical Connection of Reinforcement" (JGJ 107-2016). At the same time, the joints should be staggered, and the number of joints in the same section shall not exceed 50% of the total number of steel bars in the section. The operation should be strictly carried out according to the construction specifications to ensure the binding accuracy of the reinforcement construction and the construction quality requirements.

[0051] The steel bars should be straightened and cleaned of dirt before cutting. When mixing the steel bars, use a grinding wheel cutter or a cutting machine to cut the steel bars. The cut end face of the steel bar should be perpendicular to the axis of the steel bar, and the end face deviation angle is not allowed to exceed 4 degrees.

[0052] The threading of the steel bar is carried out on the steel bar threading machine. The tower column stress steel bars are all connected with standard thread heads. The threading of the steel bar and the connection of one end of the threaded sleeve are completed in the steel bar processing plant. In order to ensure the smooth connection of the steel bar, the processed steel bar should be protected during transportation and hoisting, especially the exposed threads of the steel bar and the internal threads of the sleeve.

[0053] The tower column steel bars must be inspected and accepted in batches according to different steel types, grades, brands, specifications and manufacturers, and stacked separately without mixing.

[0054] The processed semi-finished steel bars must be neatly stacked according to the specifications and types on the material cutting list, and be labeled with corresponding signs indicating the number of steel bars, length and quantity of the tower column.

[0055] After the quantity of steel bars is confirmed by the on-site construction team leader or person in charge and the steel bar yard team, they are transported to the construction site by trailers.

[0056] The positioning of vertical reinforcement in the tower column must be carried out strictly in accordance with the requirements of the drawings. If the main reinforcement conflicts with the embedded parts of the formwork support or other temporary construction components, the treatment method of the main reinforcement at the corresponding position must be confirmed by the supervisor and approved by the design unit before construction can be carried out.

[0057] Before tying the steel bars, the concrete dimension line and steel skeleton line of the section should be accurately drawn up according to the axis points laid out by the surveying team, and then the steel bars should be positioned according to the steel skeleton line.

[0058] In order to facilitate the threading of the stirrups and hooks, the horizontal reinforcement should be tied after all the main reinforcements are connected. The horizontal reinforcement should be tied in layers, that is, the construction of the next layer of horizontal reinforcement should be carried out after all the horizontal reinforcements, chamfered reinforcements and hooks of each layer are tied.

[0059] Due to the gap between the rigid frame and the main reinforcement of the tower body, steel bar positioning hoops should be set at the upper and lower ends of the rigid frame before installing the reinforcement. The positioning hoops can be arranged along the long and short sides of the tower body using the horizontal reinforcement of the tower body, and welded to the rigid frame with steel bar scraps. The first row of main reinforcement position lines are laid out on the positioning hoops, and the main reinforcement is spot welded and fixed to the positioning hoops according to the designed spacing. The positioning hoops can be made in advance, and the positioning hoops can be positioned on site according to the lofting axis of the long and short sides of the tower body and the designed distance from the main reinforcement to the axis. When the main reinforcement is spot welded to the positioning hoops, the main reinforcement must not be damaged.

[0060] After each row of main reinforcement is extended, the horizontal reinforcement will be tied. First, mark the horizontal reinforcement on the main reinforcement, and then tie the horizontal reinforcement. The spacing between the reinforcements should meet the design requirements, and the main reinforcement should be tied firmly. The horizontal reinforcement should be tied in layers.

[0061] After tying a layer of horizontal steel bars, mark numbers on the horizontal bars and main bars according to the designed position and inclination angle, and then tie the chamfered bars to ensure that they are tied securely.

[0062] After the chamfer reinforcement is tied, set the hook reinforcement according to the intersection of the main reinforcement and the horizontal stirrups and tie them firmly. The hooks at both ends of the hook reinforcement must be hooked on the outside of the vertical main reinforcement and the horizontal hoop reinforcement.

[0063] If the main reinforcement is made of steel bars with a diameter greater than φ32mm, the reinforcement skeleton is very rigid, and it is difficult to ensure the protection layer of the reinforcement with traditional reinforcement pads. During construction, it is necessary to control the thickness of the protection layer by controlling the binding position of the main reinforcement. At the same time, the reinforcement protection layer uses high-grade mortar pads, which are arranged in a plum blossom shape, with no less than 4 pads per square meter. The thickness of the reinforcement protection layer must be strictly controlled according to the requirements of the installation design drawings.

[0064] As a further preference of the present invention, during the construction of the cable tower, except for the lower tower column cross bridge to the outside and the upper tower column surrounding formwork which are constructed using wooden formwork, the lower cross beam, the upper tower column joint section and the tower crown formwork are all constructed using qualitative steel formwork.

[0065] As a further preferred embodiment of the present invention, the concrete used in the construction of the cable tower is centrally mixed at a commercial mixing station, then transported to the construction site by a concrete tanker, and the concrete is pumped into the mold; the concrete of the lower tower column and the lower beam segment is pumped by a ceiling pump, and the concrete of the upper tower column and the segments above is pumped by a ground pump.

[0066] The raw materials of concrete include cement, admixtures, fly ash, fine aggregate and coarse aggregate. In terms of cement, the tower columns are all C50 steel fiber concrete, and the tower base is C50 ordinary concrete. In order to slow down the hydration reaction rate of cement and the growth rate of early strength of concrete, and reduce the temperature rise value inside the concrete, low and medium heat cement is used; in terms of admixtures, by selecting appropriate water reducers or adjusting the dosage of water reducers, the initial setting time of concrete mixture is reasonably extended to meet the construction time of on-site concrete pouring. The compatibility test of water reducers and cement is carried out, and the effective initial setting time of concrete is ensured by adjusting the composition of water reducers. Polycarboxylic acid high-efficiency water reducers with stable performance and high water reduction rate are preferred, which can effectively reduce the amount of cement per cubic meter of concrete, thereby reducing the hydration heat temperature rise of concrete; in terms of fly ash, in order to reduce the unit water consumption of concrete, reduce the hydration heat of concrete cement, and ensure the working performance of concrete, the low-heat cement mix ratio uses Class I fly ash, and it has passed the self-inspection of the laboratory and the random inspection of the supervision laboratory. In terms of fine aggregate and coarse aggregate, medium sand is used as fine aggregate and 5~25mm continuously graded crushed stone is used as coarse aggregate. After passing the laboratory self-inspection and the supervision laboratory random inspection, the mud content of coarse aggregate is ≤1.0%, and the coarse aggregate is washed in advance.

[0067] The standard mix ratio of ordinary C50 concrete is as follows: cement 415kg / m³, fly ash 80kg / m³, sand 720kg / m³, crushed stone 1080 kg / m³, water 155 kg / m³, admixture 6.930 kg / m³; after trial mixing and testing, the slump of the concrete mixture with a water-cement ratio of 0.31 is 190mm, and it has good workability, water retention and fluidity, no water seepage, and the strength meets the design requirements; the standard mix ratio of C50 steel fiber concrete is as follows: cement 410kg / m³, fly ash 85kg / m³, sand 758kg / m³, crushed stone 1044kg / m³, water 158kg / m³, admixture 6.930 kg / m³, steel fiber 40 kg / m³. After trial mixing and testing, the slump of the concrete mixture with a water-cement ratio of 0.32 was 200mm, and it had good workability, water retention and fluidity, no water seepage, and the strength met the design requirements.

[0068] Things to note when pouring concrete are as follows: ①. In order to prevent the moisture in the tower base concrete from being absorbed by the pedestal or the moisture from penetrating into the concrete, the bottom surface of the pedestal should be treated during construction: sprinkle water in advance to moisten the surface.

[0069] ② During the pouring process, be careful to avoid steel bars and embedded parts; observe whether the steel bars and formwork are displaced at any time. If there is any displacement, deal with and correct it immediately.

[0070] ③. Pay close attention to the condition of the concrete during the pouring process. If there are special circumstances, communicate with laboratory personnel to make adjustments.

[0071] ④. The pouring of concrete should be carried out continuously without interruption.

[0072] ⑤. Concrete pouring adopts layered vibration, each layer is about 30cm thick, and the pouring time of the upper and lower layers should not exceed 90 minutes; the vibrating rod should be inserted vertically into the concrete and into the previous layer of concrete, with a depth of 5 to 10cm. The vibrating rod should be inserted quickly and pulled out slowly. When the current area needs to be moved after the vibration is completed, the moving distance of the concrete vibrating rod should be less than 40cm. The general sign of dense concrete vibration is that the concrete is slurry and no bubbles are generated.

[0073] ⑥. To ensure the quality of concrete connection between each section, make the top surface of concrete 2 to 3 cm higher than the top surface of formwork during pouring, and make the outer edge of concrete flush with the top surface of formwork during roughening.

[0074] ⑦. When the concrete pouring height is greater than 2m, the method of adding a lower barrel should be used to reduce the falling height and falling speed of the concrete to prevent segregation.

[0075] ⑧. When pouring concrete to the top surface of the current segment, if there is too much floating slurry, the surface floating slurry should be cleaned in time.

[0076] ⑨. Use overhead pump to cast the 1st to 3rd sections. From the 4th section onwards, use ground pump and concrete placing machine to place concrete. The pump pipe is arranged along the outer tower body.

[0077] As a further preferred embodiment of the present invention, the tower construction process also includes prestressed engineering construction and cable duct construction of the inclined cable.

[0078] The cross beam under the main tower adopts 25-φs15.2 (fpk=1860MPa) low relaxation steel strands, and 48 strands are set for both piers 2# and 3#. The prestressing adopts single-end tensioning, which is completed in one time, and is tensioned from the middle to both sides from top to bottom. The main tower anchorage area uses a tic-tac-toe prestressed steel strand, 7-φs15.2 (fpk=1860MPa) low-relaxation steel strands are used in the longitudinal direction of the bridge, and 12-φs15.2 (fpk=1860MPa) and 17-φs15.2 (fpk=1860MPa) low-relaxation steel strands are used in the transverse direction of the bridge. The prestressing adopts single-end staggered tensioning; during tensioning, the tensioning force and elongation are controlled, with tensioning as the main control of stress, and the actual elongation value of the elongation is controlled within -6% to 6% of the theoretical design value.

[0079] Prestressed construction requires the preparation of prestressed materials and equipment, including the preparation of steel strands, anchors, corrugated pipes, and equipment, and then the installation of prestressed pipes. The main bridge beams and tower column prestressed pipes are made of plastic corrugated pipes with holes and vacuum grouting technology. The inner diameter of the beam corrugated pipe is 120mm, and the inner diameter of the tower column corrugated pipe is 70, 85, and 90mm respectively according to the different prestressed beams. The installation of tower column prestressed pipes is carried out simultaneously with the steel bars, and the corrugated pipes are fixed by U-shaped steel bar clips. The solution to the conflict between the pipe and the steel bar during the installation of the prestressed pipe is as follows: According to the arrangement of steel bars and prestressed steel bundles, the steel bundles in the anchoring area are single-end staggered tensioned, and the depth of the anchoring groove is 20cm. The thickness of the protective layer of the longitudinal main reinforcement from the outside of the concrete in the construction drawing is 8cm, so there will be no conflict between the two. However, if due to special reasons, the vertical main reinforcement conflicts with the steel beam corrugated pipe, according to the construction drawings, if the prestressed anchor interferes with the tower column reinforcement, the reinforcement will be moved to both sides of the prestressed sleeve; if the prestressed reinforcement conflicts with the tower column reinforcement, the main reinforcement can be fine-tuned, and if it needs to be cut off, equal strength reinforcement measures must be taken. Ordinary steel bars can be set as hangers to avoid prestressed corrugated pipes, and local reinforcement steel bars are set at the bent parts of the steel bars. The specific form can refer to the attached figure, but the design unit and the supervision unit must agree. Cut the steel bars and use steel bar welding connection or lap steel plate welding connection, but this is easy to affect the stress condition of the prestressed steel beam position, and local reinforcement steel bars need to be set at the prestressed steel beam position. The above practices require the consent of the design unit and the supervision unit.

[0080] The installation of prestressed steel bundles during prestressed construction includes the following steps: ① Straighten the steel strands before use, accurately calculate the length of the steel strands, and cut the material with a grinding wheel; ② The prestressed steel strands are constructed by post-bundling, and the metal corrugated pipes are welded and fixed with U-shaped steel bars, and the steel strands are inserted into the corrugated pipes as a whole. During the bundle insertion process, the ends of the steel strands are wrapped with adhesive tape. Pay attention to the bundling of the steel strands and comb them carefully to avoid cross confusion. ③ To ensure the correct position of the pipeline, the prestressed pipeline should be positioned with a U-shaped steel mesh and connected to the adjacent crossbeam steel bars as a whole. The spacing of the positioning steel bars shall not be greater than 50cm, and the curved pipeline should be appropriately encrypted. Since the crossbeam is a pressure-bearing component, it is necessary to ensure that the pipeline does not leak slurry. Pay attention to protecting the pipeline when pouring concrete, strictly check, and strictly prohibit "opening the warehouse". The anchor plate and the pipeline axis must be aligned and straight, and kept on the same axis to ensure that the anchor plate is perpendicular to the prestressed bundle.

[0081] Prestressing during prestressing construction includes the following steps: ① Construction preparation. Before the prestressing construction, detailed instructions, static calculations of prestressing stress and elongation should be submitted to the supervision engineer for approval. In order to ensure that the measured values ​​meet the requirements of the specifications, a qualified unit is commissioned to conduct model tests on the hole size of the cable tower cable anchorage area and the lower beam area to determine the bellows deviation coefficient and friction coefficient, and determine the control value of the prestressing elongation; ② Prestressing of the lower beam. The prestressing of the beam prestressing steel strands needs to wait until the concrete strength and elastic modulus reach 90% of the design, and the age of the concrete is not less than 7 days; after the lower beam is cast, prestressing is carried out, and it is single-end prestressing. For the tensioning sequence, the principle of symmetrical tensioning from the middle of the web is followed. ③ Prestressing of anchorage area: The prestressing of anchorage area prestressing steel strands needs to wait until the concrete strength and elastic modulus reach 90% of the design, and the age of concrete is not less than 7 days. For the anchorage area of ​​the middle cable tower and the upper cable tower, single-end staggered tensioning is adopted to avoid unbalanced prestressing on smaller sections. For the tensioning sequence, follow the principle of "transverse bridge first, then longitudinal bridge", "interior first, then exterior".

[0082] After the prestressed tendons are tensioned, the holes should be grouted as soon as possible and completed within 48 hours using the vacuum grouting process. The working principle of the vacuum grouting process is: use a vacuum pump to suck the air in the prestressed hole so that the hole reaches a vacuum degree of about 0.1MPa, and then use a grouting machine at the other end of the hole to press cement slurry into the prestressed hole with a positive pressure of ≥0.7MPa to increase the saturation of the hole grouting and reduce the impact of bubbles.

[0083] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. When the above method is used to construct the arched cable tower, the cable tower is divided into lower tower column construction, lower crossbeam construction, upper tower column construction, joint section construction and tower crown construction according to its structural characteristics. The advantage of this is that the structural characteristics can be well installed to formulate the construction method of each part. The use of different construction processes can not only make the construction of each part more efficient, but also effectively ensure the quality of construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Figure 1 It is a process diagram of the present invention.

[0085] Figure 2 The present invention is a flow chart of the construction process of hoisting rigid frame.

[0086] Figure 3 This is a schematic diagram of the formwork structure of the hydraulic climbing formwork system of the present invention. DETAILED DESCRIPTION

[0088] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0089] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0090] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0091] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0092] In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the product of the invention is usually placed when in use, or the positions or positional relationships commonly understood by those skilled in the art, which are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0093] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. Specific embodiment 1: Figure 1 , Figure 2 , Figure 3The present invention shows an efficient and high-quality construction method of a double-tower double-cable-plane cable-stayed bridge box-type small-section arched cable tower, which solves the existing problems.

[0095] In order to solve the above technical problems, the present invention adopts the following technical solutions: An efficient and high-quality construction method for a double-tower double-cable-plane cable-stayed bridge box-type small-section arched cable tower comprises the following steps: A. construction of lower tower column; B. construction of lower crossbeam; C. construction of upper tower column; D. construction of joint section; and E. construction of tower crown.

[0096] When the above method is used to construct the arched cable tower, the cable tower is divided into lower tower column construction, lower crossbeam construction, upper tower column construction, joint section construction and tower crown construction according to its structural characteristics. The advantage of this is that the construction method of each part can be well adapted to its structural characteristics. The use of different construction processes can not only make the construction of each part more efficient, but also effectively ensure the quality of construction.

[0097] The tower crane needs to be arranged before construction. The selection of the tower crane during the arrangement mainly considers the following factors: ① Space dimension requirements for formwork and climbing frame during tower column construction; ② Requirements for lifting weight during tower crane construction, including steel bars, rigid skeletons, steel anchor beams and formwork, etc.; ③ The demolition load and spatial position requirements of the tower crane itself; ④Influence of installation, removal and plane position of construction elevator; ⑤ Installation of tower top crane (stayed cable installation equipment); The following factors should be considered when arranging the tower crane position: ①Whether there are places around that are not suitable for tower crane deployment; ② During flood season, the water flow velocity will scour the tower crane foundation, increasing construction safety hazards.

[0098] ③The plane position of the tower crane needs to avoid the position of the hydraulic climbing formwork, and the plane position of the climbing formwork must be at least 3.5m away from the tower crane truss.

[0099] After the tower crane is selected and arranged according to the above method, two tower crane attachments are set up.

[0100] According to the on-site construction conditions and construction requirements, the elevator is selected for layout, and the load that the elevator foundation can bear is not less than P. P = total weight of equipment (kg) × 0.02kN Total weight of equipment = (equipment weight + equipment load) × 125% The foundation ground should be able to withstand a pressure of not less than 0.15Mpa.

[0101] The principles of elevator attachment layout are as follows: The selection of the wall-mounted support is mainly determined by the distance L between the building and the center of the guide frame and the opening B of the wall-mounted support.

[0102] The elevator platform is supported by a triangular bracket and is made of double-jointed 45b I-beams; 25b I-beam distribution beams are laid on the triangular bracket at a rate of 0.6 meters per row; the panel is made of 10mm patterned steel plate, and safety guardrails and anti-fall nets are installed on the edges.

[0103] When the height of the ladder cage reaches near the lower beam, a lower beam access platform is set up; the lower beam access platform is supported by a steel pipe bracket, and M30 / D20 climbing cones are embedded during tower column construction; 2 sets of corbels are installed on the side of the tower column, and the distribution beam uses Ⅰ12.6 I-beam to set up a pedestrian passage between the lower beam access platform and the safety ladder cage.

[0104] The cable tower made of an arched gate tower shape by the above method consists of a lower tower column, a lower crossbeam, and an upper tower column (tower crown). The upper tower column has a variable cross-section along the longitudinal direction of the bridge and a constant cross-section along the transverse direction of the bridge. The lower tower column also has a variable cross-section. A 100x100cm manhole is provided on the lower crossbeam to penetrate the cable tower column.

[0105] In order to facilitate construction and accurate positioning, a rigid frame made of welded steel plates and steel sections is provided inside the tower column. During construction, the position of the rigid frame inside the tower column can be appropriately adjusted according to actual conditions. The rigid frame is required to be welded and positioned with the cableway pipe and steel anchor plate.

[0106] A lightning rod and navigation light are installed on the top of the tower, and a maintenance ladder is installed inside the tower.

[0107] The principle of segmentation during construction: the segmentation of the lower tower column and the middle tower column is mainly based on the turning points and mutation points of the outer contour of the tower body, and the segmentation of the upper tower column is mainly based on avoiding the anchoring teeth of the cable guide tube. Specific embodiment 2: This embodiment further illustrates step A on the basis of specific embodiment 1. The construction of the lower tower column in step A includes starting section No. 0 and segments No. 1 to 2. Starting section No. 0 and segment No. 1 are constructed by flipping molds, and segment No. 2 is constructed by hydraulic climbing molds. After the flipping mold construction of starting section No. 0 and segment No. 1 is carried out, the hydraulic climbing mold system is installed, and after the hydraulic climbing mold construction of segment No. 2 is completed, the inner climbing mold is dismantled.

[0109] The climbing formwork frame of the hydraulic climbing formwork construction is a heavy-duty separated truss frame, which adopts a separated structure of formwork and frame. The outer formwork climbing frame is equipped with multi-layer operating platforms, including steel bar binding platform, formwork operating platform, main operating platform, climbing frame climbing control platform and decoration platform from top to bottom; the platform on the top layer is 3 meters above the concrete surface to be poured, providing an operating platform for steel bar binding. The heavy-duty separated truss frame in this scheme adopts fully enclosed protection to provide an operating platform and safety protection for a series of tower column construction such as formwork construction and steel bar bundling, ensuring the safety of construction. The inner and outer sides of the bridge are curved surfaces, and curved guide rails are used to ensure normal construction. The climbing formwork frame along the bridge deck adopts straight guide rails.

[0110] During construction, the structure of the main tower is relatively complex, and the hydraulic climbing formwork needs to change tracks during operation. There are 2 machine positions on each side of the pier body. The single-limb outer formwork of the main tower requires a total of 8 hydraulic lower frames, 8 climbing formwork upper trusses, and 8 rearward shifting devices. The single-limb inner formwork is constructed with a homemade steel platform. The four sides of the outer formwork can climb simultaneously, and the inner formwork is lifted by a tower crane, which shortens the construction period.

[0111] The arrangement method of the operating platform in the hydraulic climbing formwork system is as follows: the steel bar binding platform, formwork operating platform, hydraulic operating platform, and the crossbeams of the hanging platform are connected with [14 channel steel with M20×50 bolts, and the main platform beam is connected with the support between the double 20 slots and the lower frame; steel belts are used to press between the platform plate and the platform crossbeams, and then on the platform plate, φ5×25 drill-tail self-tapping screws are used to connect the steel belts to the platform plate.

[0112] The overall steps for assembling each operating platform of the climbing formwork are as follows: Step 1: Hang the lower frame of the climbing formwork on the embedded part bracket.

[0113] Step 2: Lay the main operation and hydraulic operation platform beams and platform plates on the lower frame of the climbing formwork.

[0114] Step 3: Install the climbing formwork upper frame, and lay the steel bar binding, formwork operating platform beams and platform plates on the climbing formwork upper frame.

[0115] Step 4: Install the climbing formwork hanging platform and lay the hanging platform beams and platform plates on the climbing formwork hanging platform.

[0116] As the construction object is a double-cable arched cable tower with a complex structure, the size of the tower column changes with the tower height. Therefore, the inner and outer molds are made of steel-wood combination templates for easy cutting. The steel-wood combination template panel uses imported boards, the vertical ribs use H20 wood beams, and the horizontal ribs use double 14 grooves 6. The imported board uses birch as the base plate, and the front and back sides are covered with phenolic resin as a whole. The dark brown ester film is covered on both sides of the template by high-temperature hot pressing. The imported board has three layers of film, and the solid and smooth surface of phenolic resin can make It is very easy to demould, meeting the requirements of plain concrete (concrete is vibrated in place), and improving the appearance quality of concrete pouring. For sections with reduced cross-sectional dimensions, the shrinkage of the pier section can be achieved by cutting the template. The R1000 arc chamfer of the outer section of the pier is cast with a fixed steel mold to ensure the linear shape of the pier. The inner and outer sides along the bridge are arc-shaped surfaces and are constructed by replacing the curve with a straight line (except for the inner sides along the bridge of sections 1-4, the bottom mold of the closing section, and the top mold of the 22nd section tower crown, which are constructed with a fixed steel mold). After each section is completed, in order to ensure the overall appearance of the concrete and the safety of the template, the template is pressed against the poured concrete, and the pressing height is not less than 10cm. The template should be in close contact with the poured concrete to ensure no leakage and smooth transition.

[0117] The template cutting mentioned above is carried out on the climbing formwork frame. People stand on the top floor of the formwork frame and the main platform to draw lines on the template with ink cartridges, fix an aluminum alloy ruler next to the ink lines, insert φ30 steel bars into the tension bolt holes of the pier body, lay scaffolding boards to form a simple operating platform, and people stand on the simple platform with electric saws to cut the template to complete the template cutting.

[0118] The top layer of the hydraulic climbing formwork and the hanging platform plate are made of bent patterned steel plates, and the other platforms are made of steel springboards. The outer protection is made of framed wire mesh. There are skirting boards at the bottom of the platform, platform flaps on the wall side of the frame, and platform flaps in the gap between the frames on both sides. Fire extinguishers are installed on each platform of the climbing formwork frame to prevent fire, and there is a lightning rod on the top of the climbing formwork frame to prevent lightning strikes and ensure construction safety.

[0119] The climbing formwork frame has its own anti-fall device. The upper and lower reversing boxes of the climbing formwork frame always have a reversing box support force block supported on the guide rail to ensure the safety of the climbing formwork frame in the climbing state. When the climbing formwork frame climbs, the climbing formwork frame is hung on the rib core frame with a sling. This is the second insurance when the climbing formwork frame climbs.

[0120] The pump pipe can be installed on the tower crane and extended as the tower crane rises. The biggest advantage of this installation method is that the pump pipe is easy to inspect or use the hoisting hopper for concrete pouring.

[0121] The pouring cycle of the standard pouring layer of the hydraulic climbing formwork system is 7 days. The factors that restrict the construction period are not the climbing of the climbing formwork but the steel bar binding, acceptance, concrete pouring, and solidification to reach strength. When the concrete solidification strength reaches 20MPa, the climbing formwork can climb, and it takes about 60 minutes to climb 6 meters.

[0122] The lifting movement of the self-climbing formwork is achieved by alternately lifting the guide rail and the climbing frame with a hydraulic cylinder. The guide rail and the climbing frame can move relative to each other. When the climbing frame is in working condition, both the guide rail and the climbing frame are supported on the embedded support, and there is no relative movement between the two. After the formwork is removed, the force bolts, the hanger body, and the embedded support can be installed on the climbing cone left by the demolding, and the direction of the upper and lower reversing box tongues can be adjusted to lift the guide rail. After the guide rail is lifted into place and located on the embedded support, the operator can go to the lower platform to remove the lower embedded support, climbing cone, etc. exposed after the guide rail is lifted. After all the ties on the climbing frame are released, the climbing frame can be lifted. At this time, the guide rail remains stationary. After adjusting the direction of the upper and lower tongues, the cylinder is started, and the climbing frame moves upward relative to the guide rail. Through the alternate attachment of the guide rail and the climbing frame to the wall, the climbing frame rises along the tower column to achieve layer-by-layer lifting.

[0123] The assembly construction of hydraulic climbing formwork includes ① connection of formwork on the same surface: to ensure smooth joints of formwork, when assembling a single set of formwork, the panels at the edge of the joints are connected in the form of hard interfaces. When assembling each set of formwork, the two panels are connected together, and a core belt is installed on the transverse back rib. The templates on the same surface are tightly connected by inserting the core belt pin into the opening of the core belt and tightening the connection; ② connection of templates on different surfaces: The templates on different surfaces are connected to the back ribs through steel mold hooks and inclined seats. At the same time, in order to avoid the occurrence of mold expansion, the back ribs at the chamfers are also strengthened by tightening the inclined seats with high-strength screws. The inclined seats for vertical chamfers can directly use the standardized products, but for non-vertical chamfers, the seats need to be welded on the back ribs according to the situation on site; ③ Setting of tension and tension screws on large template surfaces: The tension screws of the templates on each surface are vertically penetrated by the pier body, and wedge-shaped pads are used on the climbing and crawling surfaces to ensure the horizontal contact between the tie rod nuts and the channel steel; when the tension length of the tower column template is not more than 3 meters, the tension screws adopt the standard section full-length tensioning method, and the PVC casing is penetrated between the templates on both sides, and the tension screws are passed through the casing, and the tie rods can be used in rotation. When casting solid sections with a thickness greater than 3 meters, use 600mm long tension screws to weld with Φ25 steel bars (or transverse main bars). The welding length is greater than 200mm and is fixed to the steel back rib with a female connecting pad; ④ Hydraulic climbing formwork assembly: The upper and lower frames are connected by pins, and the frame assembly follows the progress of the construction. Specific embodiment 3: This embodiment further explains step B on the basis of specific embodiment 1. The lower cross beam in step B is constructed as segment No. 3, and the lower cross beam is constructed as a cast-in-place bracket, specifically using steel corbels, floor-standing steel pipes, and steel brackets for construction. After the construction of the lower tower column in step A is completed, the lower cross beam bracket is erected. Specific embodiment 4: This embodiment further illustrates step C on the basis of specific embodiment 1. The upper tower column construction in step C includes segments 4 to 16. Segment 4 is constructed by cast-in-place formwork, and segments 5-16 are constructed by hydraulic climbing formwork. After the cast-in-place formwork construction of segment 4 is completed, the climbing formwork direction is first converted and then the hydraulic climbing formwork construction of segments 5-16 is carried out. Among the segments 5-16, segments 7, 10 and 14 all need to be installed with cross braces. After the hydraulic climbing formwork construction of segments 5-16 is completed, the hydraulic climbing formwork system is dismantled.

[0126] The specific construction steps for dismantling the hydraulic climbing formwork system are as follows: Step 1: When the concrete strength reaches 15Mpa or above, remove all the tie rods (including the external angle tie rods). Pull out the safety pins and move the formwork back (the formwork can be moved back 600mm). Then insert the safety pins.

[0127] Step 2: Use a tower crane to lift the formwork, remove the main back rib connector, and lift the formwork to the specified site.

[0128] Step 3: Use a tower crane to hoist the upper platform and upper frame as a whole to the specified site.

[0129] Step 4: Pull the guide rail out of the frame and place it on a level surface.

[0130] Step 5: Cut the main platform and hanging platform in the middle to reduce weight.

[0131] Step 6: Use a tower crane to lift the lower frame of the climbing formwork as a whole to the specified site. Specific embodiment 5: This embodiment further explains step D on the basis of specific embodiment 1. Before the construction of the joint section in step D, the joint section bracket needs to be installed. The joint section construction includes 17 sections and 18 sections. The joint section construction is layered casting according to the sections. Specifically, it is constructed using steel corbels + arch trusses, and is completed by layered casting according to the section height. Specific embodiment 6: This embodiment further illustrates step E on the basis of specific embodiment 1. The tower crown construction in step E includes segments 19 to 20. The tower crown construction is cast-in-place using full formwork and is completed in layers according to segment height. Specific embodiment 7: This embodiment further illustrates the tower construction process based on the specific embodiment 1. During the tower construction process, the rigid skeleton is divided into segments synchronously with the main tower segment height. The segments near the construction area are processed into segment trusses, and the segments are hoisted as a whole by a tower crane. The steel bars are concentrated in the steel bar yard and processed into semi-finished products, which are transported to the construction site by a flatbed truck. After the rigid skeleton is installed, the rigid skeleton is used as a positioning device and hoisted by a tower crane for manual binding and installation.

[0135] The rigid skeleton between the main pier tower columns is set in sections, and the height of the sections is adjusted with the height of the tower column poured in a single time. During the construction of the sections, the exposed reserved length of the rigid skeleton is 50cm. After the skeleton is overlapped with the reserved length of the exposed rigid skeleton after pouring the concrete of the tower body of the foundation section each time, the total height of the rigid skeleton is not higher than 6.5m. It is welded piece by piece in the temporary processing site, and the skeleton is set with flat joints and diagonal braces every 3 meters to form a whole. The rigid skeleton is assembled in blocks at the temporary processing site, and hoisted and installed in blocks to reduce the danger and time of high-altitude installation. The steel used for the rigid skeleton is cut strictly according to the design size, and the assembly inspection is carried out after the production is completed. After the inspection is qualified, it is lifted by the tower crane for installation. In order to speed up the construction progress, the rigid skeleton is processed in sections and sections in the back field and then transported to the site, and then the frame is connected as a whole and hoisted.

[0136] The processing requirements for rigid skeleton processing are as follows: The processing length of each section of the rigid skeleton is determined according to the segment height of the tower column casting. The columns, parallel joints and diagonal braces of the rigid skeleton of the tower column are all made and connected with L75×75×7 steel. In order to facilitate transportation and on-site positioning and installation, the rigid skeleton is composed of small-section trusses and on-site connectors. In order to ensure the processing accuracy of the small-section trusses, they are made on a special pedestal and classified by number.

[0137] The installation method of the rigid frame is as follows: ① Skeleton transportation After the frame is processed in the steel structure processing plant, it is lifted by a crane onto a flatbed truck and transported to the site in sections for assembly on site.

[0138] ②Skeleton installation When installing the rigid frame, reserve bolt holes on the installed frame and use a plumb line and a ruler to control the position of the frame's upper edge. When the position meets the requirements, use bolts to securely connect the current frame to the previous frame. After the frame is fully installed, weld the connecting sections.

[0139] The steel bars of the tower columns should all have factory quality certificates and test reports, and should be sampled and tested for mechanical properties according to regulations. The test results should comply with the design and construction technical specifications.

[0140] The horizontal stirrup reinforcement shall be made according to the reinforcement drawing of the construction drawing, and the reinforcement material notice shall be issued while ensuring the requirements of the protective layer thickness, corner radius and binding lap length.

[0141] The installation of tower column reinforcement should be carried out strictly according to the design drawings. The connection of steel bars with a diameter of ≥22mm in the lower tower column shall be made by rolled straight thread connection. The joint performance shall comply with the relevant requirements of the "General Technical Code for Mechanical Connection of Reinforcement" (JGJ 107-2016). At the same time, the joints should be staggered, and the number of joints in the same section shall not exceed 50% of the total number of steel bars in the section. The operation should be strictly carried out according to the construction specifications to ensure the binding accuracy of the reinforcement construction and the construction quality requirements.

[0142] The steel bars should be straightened and cleaned of dirt before cutting. When mixing the steel bars, use a grinding wheel cutter or a cutting machine to cut the steel bars. The cut end face of the steel bar should be perpendicular to the axis of the steel bar, and the end face deviation angle is not allowed to exceed 4 degrees.

[0143] The threading of the steel bar is carried out on the steel bar threading machine. The tower column stress steel bars are all connected with standard thread heads. The threading of the steel bar and the connection of one end of the threaded sleeve are completed in the steel bar processing plant. In order to ensure the smooth connection of the steel bar, the processed steel bar should be protected during transportation and hoisting, especially the exposed threads of the steel bar and the internal threads of the sleeve.

[0144] The tower column steel bars must be inspected and accepted in batches according to different steel types, grades, brands, specifications and manufacturers, and stacked separately without mixing.

[0145] The processed semi-finished steel bars must be neatly stacked according to the specifications and types on the material cutting list, and be labeled with corresponding signs indicating the number of steel bars, length and quantity of the tower column.

[0146] After the quantity of steel bars is confirmed by the on-site construction team leader or person in charge and the steel bar yard team, they are transported to the construction site by trailers.

[0147] The positioning of vertical reinforcement in the tower column must be carried out strictly in accordance with the requirements of the drawings. If the main reinforcement conflicts with the embedded parts of the formwork support or other temporary construction components, the treatment method of the main reinforcement at the corresponding position must be confirmed by the supervisor and approved by the design unit before construction can be carried out.

[0148] Before tying the steel bars, the concrete dimension line and steel skeleton line of the section should be accurately drawn up according to the axis points laid out by the surveying team, and then the steel bars should be positioned according to the steel skeleton line.

[0149] In order to facilitate the threading of the stirrups and hooks, the horizontal reinforcement should be tied after all the main reinforcements are connected. The horizontal reinforcement should be tied in layers, that is, the construction of the next layer of horizontal reinforcement should be carried out after all the horizontal reinforcements, chamfered reinforcements and hooks of each layer are tied.

[0150] Due to the gap between the rigid frame and the main reinforcement of the tower body, steel bar positioning hoops should be set at the upper and lower ends of the rigid frame before installing the reinforcement. The positioning hoops can be arranged along the long and short sides of the tower body using the horizontal reinforcement of the tower body, and welded to the rigid frame with steel bar scraps. The first row of main reinforcement position lines are laid out on the positioning hoops, and the main reinforcement is spot welded and fixed to the positioning hoops according to the designed spacing. The positioning hoops can be made in advance, and the positioning hoops can be positioned on site according to the lofting axis of the long and short sides of the tower body and the designed distance from the main reinforcement to the axis. When the main reinforcement is spot welded to the positioning hoops, the main reinforcement must not be damaged.

[0151] After each row of main reinforcement is extended, the horizontal reinforcement will be tied. First, mark the horizontal reinforcement on the main reinforcement, and then tie the horizontal reinforcement. The spacing between the reinforcements should meet the design requirements, and the main reinforcement should be tied firmly. The horizontal reinforcement should be tied in layers.

[0152] After tying a layer of horizontal steel bars, mark numbers on the horizontal bars and main bars according to the designed position and inclination angle, and then tie the chamfered bars to ensure that they are tied securely.

[0153] After the chamfer reinforcement is tied, set the hook reinforcement according to the intersection of the main reinforcement and the horizontal stirrups and tie them firmly. The hooks at both ends of the hook reinforcement must be hooked on the outside of the vertical main reinforcement and the horizontal hoop reinforcement.

[0154] If the main reinforcement is made of steel bars with a diameter greater than φ32mm, the reinforcement skeleton is very rigid, and it is difficult to ensure the protection layer of the reinforcement with traditional reinforcement pads. During construction, it is necessary to control the thickness of the protection layer by controlling the binding position of the main reinforcement. At the same time, the reinforcement protection layer uses high-grade mortar pads, which are arranged in a plum blossom shape, with no less than 4 pads per square meter. The thickness of the reinforcement protection layer must be strictly controlled according to the requirements of the installation design drawings. Specific embodiment 8: This embodiment further illustrates the tower construction process based on the specific embodiment 1. During the tower construction process, except that the lower tower column cross bridge to the outside and the upper tower column formwork are constructed using wooden formwork, the lower cross beam, the upper tower column joint section and the tower crown formwork are all constructed using qualitative steel formwork. Specific embodiment 9: This embodiment further illustrates the cable tower construction process based on the specific embodiment 1. The concrete used in the cable tower construction process is centrally mixed at a commercial mixing station, and then transported to the construction site by a concrete tanker, and the concrete is pumped into the mold; the concrete of the lower tower column and the lower beam segment is pumped by a ceiling pump, and the concrete of the upper tower column and the above segments is pumped by a ground pump.

[0157] The raw materials of concrete include cement, admixtures, fly ash, fine aggregate and coarse aggregate. In terms of cement, the tower columns are all C50 steel fiber concrete, and the tower base is C50 ordinary concrete. In order to slow down the hydration reaction rate of cement and the growth rate of early strength of concrete, and reduce the temperature rise value inside the concrete, low and medium heat cement is used; in terms of admixtures, by selecting appropriate water reducers or adjusting the dosage of water reducers, the initial setting time of concrete mixture is reasonably extended to meet the construction time of on-site concrete pouring. The compatibility test of water reducers and cement is carried out, and the effective initial setting time of concrete is ensured by adjusting the composition of water reducers. Polycarboxylic acid high-efficiency water reducers with stable performance and high water reduction rate are preferred, which can effectively reduce the amount of cement per cubic meter of concrete, thereby reducing the hydration heat temperature rise of concrete; in terms of fly ash, in order to reduce the unit water consumption of concrete, reduce the hydration heat of concrete cement, and ensure the working performance of concrete, the low-heat cement mix ratio uses Class I fly ash, and it has passed the self-inspection of the laboratory and the random inspection of the supervision laboratory. In terms of fine aggregate and coarse aggregate, medium sand is used as fine aggregate and 5~25mm continuously graded crushed stone is used as coarse aggregate. After passing the laboratory self-inspection and the supervision laboratory random inspection, the mud content of coarse aggregate is ≤1.0%, and the coarse aggregate is washed in advance.

[0158] The standard mix ratio of ordinary C50 concrete is as follows: cement 415kg / m³, fly ash 80kg / m³, sand 720kg / m³, crushed stone 1080 kg / m³, water 155 kg / m³, admixture 6.930 kg / m³; after trial mixing and testing, the slump of the concrete mixture with a water-cement ratio of 0.31 is 190mm, and it has good workability, water retention and fluidity, no water seepage, and the strength meets the design requirements; the standard mix ratio of C50 steel fiber concrete is as follows: cement 410kg / m³, fly ash 85kg / m³, sand 758kg / m³, crushed stone 1044kg / m³, water 158kg / m³, admixture 6.930 kg / m³, steel fiber 40 kg / m³. After trial mixing and testing, the slump of the concrete mixture with a water-cement ratio of 0.32 was 200mm, and it had good workability, water retention and fluidity, no water seepage, and the strength met the design requirements.

[0159] Things to note when pouring concrete are as follows: ①. In order to prevent the moisture in the tower base concrete from being absorbed by the pedestal or the moisture from penetrating into the concrete, the bottom surface of the pedestal should be treated during construction: sprinkle water in advance to moisten the surface.

[0160] ② During the pouring process, be careful to avoid steel bars and embedded parts; observe whether the steel bars and formwork are displaced at any time. If there is any displacement, deal with and correct it immediately.

[0161] ③. Pay close attention to the condition of the concrete during the pouring process. If there are special circumstances, communicate with laboratory personnel to make adjustments.

[0162] ④. The pouring of concrete should be carried out continuously without interruption.

[0163] ⑤. Concrete pouring adopts layered vibration, each layer is about 30cm thick, and the pouring time of the upper and lower layers should not exceed 90 minutes; the vibrating rod should be inserted vertically into the concrete and into the previous layer of concrete, with a depth of 5 to 10cm. The vibrating rod should be inserted quickly and pulled out slowly. When the current area needs to be moved after the vibration is completed, the moving distance of the concrete vibrating rod should be less than 40cm. The general sign of dense concrete vibration is that the concrete is slurry and no bubbles are generated.

[0164] ⑥. To ensure the quality of concrete connection between each section, make the top surface of concrete 2 to 3 cm higher than the top surface of formwork during pouring, and make the outer edge of concrete flush with the top surface of formwork during roughening.

[0165] ⑦. When the concrete pouring height is greater than 2m, the method of adding a lower barrel should be used to reduce the falling height and falling speed of the concrete to prevent segregation.

[0166] ⑧. When pouring concrete to the top surface of the current segment, if there is too much floating slurry, the surface floating slurry should be cleaned in time.

[0167] ⑨. Use overhead pump to cast the 1st to 3rd sections. From the 4th section onwards, use ground pump and concrete placing machine to place concrete. The pump pipe is arranged along the outer tower body. Specific embodiment 10: This embodiment further illustrates the cable tower construction process based on the specific embodiment 1. The cable tower construction process also includes prestressed engineering construction and cable duct construction of inclined cables.

[0169] The cross beam under the main tower adopts 25-φs15.2 (fpk=1860MPa) low relaxation steel strands, and 48 strands are set for both piers 2# and 3#. The prestressing adopts single-end tensioning, which is completed in one time, and is tensioned from the middle to both sides from top to bottom. The main tower anchorage area uses a tic-tac-toe prestressed steel strand, 7-φs15.2 (fpk=1860MPa) low-relaxation steel strands are used in the longitudinal direction of the bridge, and 12-φs15.2 (fpk=1860MPa) and 17-φs15.2 (fpk=1860MPa) low-relaxation steel strands are used in the transverse direction of the bridge. The prestressing adopts single-end staggered tensioning; during tensioning, the tensioning force and elongation are controlled, with tensioning as the main control of stress, and the actual elongation value of the elongation is controlled within -6% to 6% of the theoretical design value.

[0170] Prestressed construction requires the preparation of prestressed materials and equipment, including the preparation of steel strands, anchors, corrugated pipes, and equipment, and then the installation of prestressed pipes. The main bridge beams and tower column prestressed pipes are made of plastic corrugated pipes with holes and vacuum grouting technology. The inner diameter of the beam corrugated pipe is 120mm, and the inner diameter of the tower column corrugated pipe is 70, 85, and 90mm respectively according to the different prestressed beams. The installation of tower column prestressed pipes is carried out simultaneously with the steel bars, and the corrugated pipes are fixed by U-shaped steel bar clips. The solution to the conflict between the pipe and the steel bar during the installation of the prestressed pipe is as follows: According to the arrangement of steel bars and prestressed steel bundles, the steel bundles in the anchoring area are single-end staggered tensioned, and the depth of the anchoring groove is 20cm. The thickness of the protective layer of the longitudinal main reinforcement from the outside of the concrete in the construction drawing is 8cm, so there will be no conflict between the two. However, if due to special reasons, the vertical main reinforcement conflicts with the steel beam corrugated pipe, according to the construction drawings, if the prestressed anchor interferes with the tower column reinforcement, the reinforcement will be moved to both sides of the prestressed sleeve; if the prestressed reinforcement conflicts with the tower column reinforcement, the main reinforcement can be fine-tuned, and if it needs to be cut off, equal strength reinforcement measures must be taken. Ordinary steel bars can be set as hangers to avoid prestressed corrugated pipes, and local reinforcement steel bars are set at the bent parts of the steel bars. The specific form can refer to the attached figure, but the design unit and the supervision unit must agree. Cut the steel bars and use steel bar welding connection or lap steel plate welding connection, but this is easy to affect the stress condition of the prestressed steel beam position, and local reinforcement steel bars need to be set at the prestressed steel beam position. The above practices require the consent of the design unit and the supervision unit.

[0171] The installation of prestressed steel bundles during prestressed construction includes the following steps: ① Straighten the steel strands before use, accurately calculate the length of the steel strands, and cut the material with a grinding wheel; ② The prestressed steel strands are constructed by post-bundling, and the metal corrugated pipes are welded and fixed with U-shaped steel bars, and the steel strands are inserted into the corrugated pipes as a whole. During the bundle insertion process, the ends of the steel strands are wrapped with adhesive tape. Pay attention to the bundling of the steel strands and comb them carefully to avoid cross confusion. ③ To ensure the correct position of the pipeline, the prestressed pipeline should be positioned with a U-shaped steel mesh and connected to the adjacent crossbeam steel bars as a whole. The spacing of the positioning steel bars shall not be greater than 50cm, and the curved pipeline should be appropriately encrypted. Since the crossbeam is a pressure-bearing component, it is necessary to ensure that the pipeline does not leak slurry. Pay attention to protecting the pipeline when pouring concrete, strictly check, and strictly prohibit "opening the warehouse". The anchor plate and the pipeline axis must be aligned and straight, and kept on the same axis to ensure that the anchor plate is perpendicular to the prestressed bundle.

[0172] Prestressing during prestressing construction includes the following steps: ① Construction preparation. Before the prestressing construction, detailed instructions, static calculations of prestressing stress and elongation should be submitted to the supervision engineer for approval. In order to ensure that the measured values ​​meet the requirements of the specifications, a qualified unit is commissioned to conduct model tests on the hole size of the cable tower cable anchorage area and the lower beam area to determine the bellows deviation coefficient and friction coefficient, and determine the control value of the prestressing elongation; ② Prestressing of the lower beam. The prestressing of the beam prestressing steel strands needs to wait until the concrete strength and elastic modulus reach 90% of the design, and the age of the concrete is not less than 7 days; after the lower beam is cast, prestressing is carried out, and it is single-end prestressing. For the tensioning sequence, the principle of symmetrical tensioning from the middle of the web is followed. ③ Prestressing of anchorage area: The prestressing of anchorage area prestressing steel strands needs to wait until the concrete strength and elastic modulus reach 90% of the design, and the age of concrete is not less than 7 days. For the anchorage area of ​​the middle cable tower and the upper cable tower, single-end staggered tensioning is adopted to avoid unbalanced prestressing on smaller sections. For the tensioning sequence, follow the principle of "transverse bridge first, then longitudinal bridge", "interior first, then exterior".

[0173] After the prestressed tendons are tensioned, the holes should be grouted as soon as possible and completed within 48 hours using the vacuum grouting process. The working principle of the vacuum grouting process is: use a vacuum pump to suck the air in the prestressed hole so that the hole reaches a vacuum degree of about 0.1MPa, and then use a grouting machine at the other end of the hole to press cement slurry into the prestressed hole with a positive pressure of ≥0.7MPa to increase the saturation of the hole grouting and reduce the impact of bubbles.

[0174] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An efficient and high-quality construction method for a double-tower double-cable-plane cable-stayed bridge box-type small-section arched cable tower, characterized in that: The process includes the following steps: A. construction of lower tower column; B. construction of lower cross beam; C. construction of upper tower column; D. construction of joint section; E. construction of tower crown.

2. The high-efficiency and high-quality construction method of a box-type small-section arched cable tower for a double-tower double-cable-plane cable-stayed bridge according to claim 1 is characterized by: The construction of the lower tower column in step A includes starting section No. 0 and sections No. 1 to 2. The starting section No. 0 and section No. 1 are constructed by flipping the mold, and the section No. 2 is constructed by hydraulic climbing formwork. After the flipping mold construction of starting section No. 0 and section No. 1, the hydraulic climbing formwork system is installed, and after the hydraulic climbing formwork construction of section No. 2 is completed, the inner climbing formwork is dismantled.

3. The high-efficiency and high-quality construction method of a box-type small-section arched cable tower for a double-tower double-cable-plane cable-stayed bridge according to claim 1 is characterized by: The lower crossbeam construction in step B is segment No. 3, and the lower crossbeam construction is cast-in-place, specifically using steel brackets, floor-standing steel pipes and steel brackets for construction. After the lower tower column construction in step A is completed, the lower crossbeam bracket is erected.

4. The high-efficiency and high-quality construction method of a box-type small-section arched cable tower for a double-tower double-cable-plane cable-stayed bridge according to claim 1 is characterized by: The upper tower column construction in step C includes sections 4 to 16. Section 4 is constructed by cast-in-place formwork, while sections 5-16 are constructed by hydraulic climbing formwork. After the cast-in-place formwork construction of section 4 is completed, the climbing formwork direction is first changed and then the hydraulic climbing formwork construction of sections 5-16 is carried out. Sections 7, 10 and 14 of sections 5-16 all need to be installed with cross braces. After the hydraulic climbing formwork construction of sections 5-16 is completed, the hydraulic climbing formwork system is dismantled.

5. The high-efficiency and high-quality construction method of a box-type small-section arched cable tower for a double-tower double-cable-plane cable-stayed bridge according to claim 1 is characterized by: Before the construction of the joint section in step D, the joint section support needs to be installed. The joint section construction includes 17 sections and 18 sections. The joint section construction is cast in layers according to the sections. Specifically, it is constructed using steel corbels + arch trusses and is cast in layers according to the section height.

6. The high-efficiency and high-quality construction method of a double-tower double-cable-plane cable-stayed bridge box-type small-section arched cable tower according to claim 1 is characterized by: The tower crown construction in step E includes segments 19 to 20. The tower crown construction adopts full formwork cast-in-place and is completed by layered casting according to segment height.

7. The high-efficiency and high-quality construction method of a box-type small-section arched cable tower for a double-tower double-cable-plane cable-stayed bridge according to claim 1 is characterized by: During the cable tower construction process, the rigid frame is divided into segments synchronously with the main tower segment height. The segments are processed into segment trusses near the construction area, and the segments are hoisted as a whole by a tower crane. The steel bars are concentrated in the steel bar yard and processed into semi-finished products, which are transported to the construction site by flatbed trucks. After the rigid frame is installed, the rigid frame is used as a positioning device and hoisted by a tower crane for manual binding and installation.

8. The high-efficiency and high-quality construction method of a double-tower double-cable-plane cable-stayed bridge box-type small-section arched cable tower according to claim 1 is characterized by: During the construction of the cable tower, except for the outer side of the lower tower column cross bridge and the formwork around the upper tower column, which are constructed using wooden formwork, the lower cross beam, the joint section of the upper tower column and the tower crown formwork are all constructed using qualitative steel formwork.

9. The high-efficiency and high-quality construction method of a double-tower double-cable-plane cable-stayed bridge box-type small-section arched cable tower according to claim 1 is characterized by: The concrete used in the construction of the cable tower is mixed centrally at a commercial mixing station, then transported to the construction site by concrete tankers, and pumped into the mold; the concrete of the lower tower column and lower beam segments is pumped by overhead pumps, and the concrete of the upper tower column and above segments is pumped by ground pumps.

10. The high-efficiency and high-quality construction method of a box-type small-section arched cable tower for a double-tower double-cable-plane cable-stayed bridge according to claim 1 is characterized by: The tower construction process also includes prestressed engineering construction and cable duct construction.

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