Prefabricated box girder construction method

Abstract

The invention relates to the technical field of prefabricated box girder construction, in particular to a prefabricated box girder construction method which comprises the steps that self-propelled hydraulic steel formworks are assembled and polished in construction preparation work; processing and installing steel bars; prefabricating a box girder inner mold; mounting bottom web steel bars; pulling down the inner mold; mounting top plate steel bars; mounting the bound top plate reinforcing steel bars to a specified mounting position by using a truss type lifting appliance; pouring concrete; concrete pouring work of the prefabricated box girder is completed in a hoisting mode; removing the template; after box girder concrete is initially set, the hogging moment notch wedge-shaped formwork and the inner formwork are dismantled, and after the strength of the box girder concrete reaches 2.5 Mpa, the outer formwork is dismantled; performing standardized combination and maintenance on the prefabricated box girder; pre-stress tensioning and grouting are conducted; and after the strength of the box girder meets the design requirement, box girder prestress tensioning and grouting work is completed in sequence.

Description

Technical Field

[0001] The invention relates to the technical field of prefabricated box girder construction, in particular to a prefabricated box girder construction method. Background Art

[0002] The construction process of prefabricated box girders is complex and involves numerous technical difficulties. Technical issues can easily lead to quality defects during construction, such as dimensional deviations, poor appearance, insufficient strength, cracks, and other defects. Summary of the Invention

[0003] In view of the deficiencies in the prior art, the present invention provides a prefabricated box girder construction method.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A prefabricated box beam construction method, characterized by comprising the following steps:

[0006] Step 1: Construction preparation

[0007] (1) Pre-adjusted straightening and tying jig production

[0008] Arrange the jig vertical support ribs on both sides of the pedestal width direction, weld the processed jig vertical support ribs to the pre-buried vertical ribs of the jig, arrange the outer reinforcement of the jig vertical support ribs vertically, and arrange the inner reinforcement obliquely according to the slope of the precast beam web, with the height slightly lower than the height of the beam and slab precast reinforcement skeleton. Then weld the jig transverse support ribs about 5 cm downward from the top surface of the jig support ribs, paint the transverse support ribs according to the spacing of the box girder reinforcement skeleton steel bars, and mark them to facilitate control when tying the skeleton steel bars.

[0009] Weld positioning nuts onto the jig's vertical support bars according to the spacing of the frame's horizontal bars. The height of the positioning nuts should be less than half the diameter of the frame's horizontal bars, ensuring that the frame's horizontal bars are at the required height after installation. Then, insert the machined jig's positioning bars into the nuts. The spacing of the jig's positioning bars should be the same as the horizontal bars of the box girder's reinforcement frame, with groups of 3 to 5.

[0010] Use I40 I-beam as the tensioning end fixing, bury the I-beam 1.5m below the ground to ensure that the I-beam does not overturn during tensioning. Use a punch to accurately punch holes in the web according to the design drawings;

[0011] (2) Processing and installation of prefabricated box girder steel pedestals

[0012] When customizing the prefabricated box girder steel pedestal, a crossbeam and hole for pulling down the inner mold are reserved on the main body of the steel pedestal and the steel panel of the pedestal. During the prefabrication of the box girder, the pedestal and the core mold are connected with high-strength bolts through the tie rods (30mm diameter, 65cm long) inside the round steel to form a whole, preventing the core mold from floating up during the concrete pouring process. Transverse channel steel (100mm*48mm*5.3mm) is used inside the core mold to fix the two tie rods to the core mold, and steel plates (10*10cm, wall thickness 10mm) are used inside the steel pedestal to fix the two tie rods to the pedestal. Schematic diagram of the core mold pull-down device;

[0013] Step 2: Assembling and polishing the self-propelled hydraulic steel formwork

[0014] (1) Characteristics of the method:

[0015] ① The self-propelled hydraulic steel formwork has a fast construction speed, low crane occupancy rate in the beam yard, and high production efficiency;

[0016] ② The single-side formwork is divided into two sections, and the 1.5m formwork processing unit is connected into a whole by a crossbeam. The movement of a single prefabricated box beam formwork can be completed in four units, which speeds up the construction.

[0017] ③The hydraulic system supports the formwork in the vertical direction and height direction, which can be finely adjusted and the formwork installation accuracy is high;

[0018] ④ After the formwork is in place, the hydraulic support system is locked and combined with the formwork bottom support rod to ensure that the formwork is stable and reliable. When pouring concrete, the formwork will not be displaced or deformed due to the concrete pressure and the vibration of the attached vibrator.

[0019] ⑤ The self-propelled hydraulic steel formwork has a fast demolding speed. After demolding, it can be quickly moved along the track to another pedestal on the same production line to prepare for the next cycle of operation.

[0020] (2) Operation points:

[0021] ① Move the template longitudinally into place and align the center of the template with the lowest point of the pre-arch.

[0022] ② The hydraulic system lifts the template twice, and the bottom edge of the template is flush with the steel base panel.

[0023] ③The hydraulic system pushes the template close to the steel base.

[0024] ④ Make slight adjustments to ensure that the bottom edge of the steel template is flush with the base surface without any gaps.

[0025] ⑤Lock the formwork hydraulic system and install the steel formwork bottom support rod.

[0026] ⑥ When removing the formwork, first remove the connecting bolts between the mid-span diaphragm and the end beam formwork, remove the mid-span diaphragm and the end beam formwork, then remove the four formwork units in turn and move them along the track to the next platform.

[0027] Step 3: Steel bar processing and installation

[0028] (1) Steel bar processing

[0029] The cutting of steel bars is carried out by CNC bending equipment, which improves the accuracy of steel bar cutting. The steel bars are installed by jigs, which improves the accuracy of steel bar installation. This makes the cutting accuracy of steel bars match the installation accuracy, further improving the accuracy of steel bar skeleton processing.

[0030] (2) Pre-straightening technology

[0031] ①The steel bars are installed on the jig one by one in the order of bottom and web, and the steel bars are installed and tied strictly according to the positions marked on the jig.

[0032] ② The longitudinally distributed horizontal reinforcements of the bottom plate, web plate and top plate are connected to the pre-straightening connectors before tying. One end of the connector is connected to the horizontal reinforcement and the other end passes through the tensioning end fixing for pre-tensioning, so that the reinforcement has a certain straightness and internal stress.

[0033] ③ The tensioning instrument uses a manual anchor cable tensioner. First, anchor a single horizontal rebar at each end of the tire frame. Then, from one side of the tire frame, a pneumatic hydraulic pump and jack assembly are used to tension the horizontal distribution bar. The tensioning stress should not exceed 10kN. Once the horizontal bar is straightened, the jack assembly is slowly removed and the next horizontal bar is tensioned and straightened. The top plate, web plate, and bottom plate horizontal distribution bars are tensioned and straightened sequentially to ensure the straightness and installation accuracy of each horizontal bar.

[0034] ④ After the steel bar binding is completed, loosen the pre-straightening connector and prepare to complete the removal of the steel bar skeleton. After the pre-straightening connector is straightened, prepare for the next cycle of work.

[0035] Step 4: Prefabricated box beam inner formwork

[0036] Assemble and polish the inner mold of the prefabricated box beam, and ensure that the joints between the inner mold segments are tight and without misalignment. Polish the surface smoothly and apply the release agent evenly.

[0037] Step 5: Bottom web reinforcement installation

[0038] Use the steel frame lifting truss to accurately install the tied steel frame from the tying jig into the polished and cleaned formwork.

[0039] Step 6: Pull down the inner mold

[0040] After the inner formwork is installed, a PVC pipe (50mm diameter, 45cm long) is inserted into the reserved round steel hole. A tie rod (30mm diameter, 65cm long) is inserted into the PVC pipe. A transverse channel steel (100mm*48mm*5.3mm) is used inside the core formwork to secure the two tie rods to the core formwork. A steel plate (10*10cm, 10mm wall thickness) is used inside the square steel to secure the two tie rods to the pedestal. The pedestal and inner formwork are then connected with high-strength bolts via the tie rod (30mm diameter, 65cm long) inside the round steel to form a single unit, preventing the inner formwork from floating during concrete pouring. The box girder floor vents are replaced by reserved holes and are no longer separately provided.

[0041] Step 7: Top plate reinforcement installation

[0042] Use a truss-type hanger to install the tied top plate reinforcement to the designated installation location.

[0043] Step 8: Concrete pouring

[0044] The concrete pouring of prefabricated box girders was completed by hoisting.

[0045] Step 9: Template removal

[0046] After the box girder concrete has initially set, remove the negative bending moment notch wedge formwork and inner formwork, and remove the outer formwork after the box girder concrete strength reaches 2.5Mpa.

[0047] Step 10: Standardized combination curing process of prefabricated box beams

[0048] (1) The site selection of boiler room and water room shall take into account the layout of box girder production pedestal and try to locate them in the middle of the production area to ensure sufficient and balanced steam and water supply in each production area. At the same time, the convenience of fuel supply shall be taken into account. The site selection shall be completed after comprehensive consideration of various situations.

[0049] (2) Pipeline layout

[0050] aThe pipeline layout is divided into three levels. The first level is the main pipeline, which is arranged longitudinally on the side of the production area; the second level is the branch pipeline, which is arranged perpendicular to the direction of the beam yard, that is, the horizontal branch pipeline; the third level is the working pipeline, which is led from the second level pipeline to the box beam steel pedestal.

[0051] b. All pipelines at all levels are equipped with control valves, which can adjust the supply in real time according to actual production conditions and optimize the health-care effect.

[0052] (3) Information control

[0053] a. The sprinkler health care system is equipped with an information control system. A main control valve is installed on the main pipeline of the water room. Solenoid valves are installed from the first to the second level to control the branch water source. A telescopic sprinkler head is installed in the third-level maintenance unit. It is extended when in use and retracted into the inside of the box girder steel pedestal when not in use.

[0054] b. The spraying system can be remotely controlled by mobile phone, specifically to a certain box girder pedestal, and timed watering maintenance can also be set for the pedestal that needs spraying curing.

[0055] (4) Health Shed

[0056] In view of the frequent strong winds in the Hexi region, a color steel steam curing shed is used. The color steel steam curing shed has a stable structure and good air tightness.

[0057] (5) Maintenance process

[0058] a. After the box beam is demoulded, it is first sprayed with water for curing to prevent the early water loss and shrinkage cracks. After the steel formwork is moved to the next production pedestal, cement slurry is applied to the exposed steel bars to prevent steel bar corrosion during curing;

[0059] b. Hoist the steam curing shed to the box girder coated with cement slurry, and turn on the second and third level steam curing switches.

[0060] c. The steam curing period is 7 days, during which the curing effect is observed by a temperature and humidity recorder hung on the outer wall of the curing shed.

[0061] (6) Comprehensive health care

[0062] In view of the dry climate and strong winds at the project site, in order to ensure that no cracks appear in the box girder, the spray curing system will continue to operate from the seventh day of maintenance until the box girder tensioning and grouting work is completed.

[0063] (7) Health preservation in special weather conditions

[0064] After the box girder was cast, a sudden cold weather occurred. The movable steam curing hose was extended into the inner mold of the box girder. The top plate and the outside of the formwork were covered with quilts and then wrapped with tarpaulin.

[0065] Step 11: Prestressing and grouting

[0066] After the box girder strength reaches the design requirements, the prestressing and grouting work of the box girder will be completed in sequence.

[0067] The present invention has the following beneficial effects:

[0068] 1. The present invention uses a prefabricated integral steel bar binding jig for beams and slabs that is processed and manufactured. The jig strictly marks and locates the position of the bottom plate and web reinforcement of the prefabricated beams and slabs according to the size and quantity of the design drawings. A CNC bending machine is used to cut the reinforcement bars, and the bottom and web reinforcement bars are installed one by one according to the position and quantity of the bottom plate and web reinforcement bars located in the jig. The installed bottom and web reinforcement bars are strictly tied according to the positions located in the jig, and the longitudinal distribution bars of the web and top plate are pre-tensioned to give the reinforcement bars a certain straightness and internal stress. The distribution bars are tied after precise positioning, and the tied prefabricated steel bar skeleton of the beams and slabs is temporarily fixed by the jig to form an integral steel bar skeleton, and the steel bar skeleton is hoisted into the mold as a whole.

[0069] 2. This integrated, self-propelled hydraulic steel formwork features a single-sided formwork structure divided into two segments, each connected by a main beam. This effectively eliminates the problem of formwork misalignment. Each segment has independent travel and hydraulic jacking systems. The travel system moves longitudinally along the base, while hydraulic system 1 drives the formwork laterally along the base, and hydraulic system 2 drives the formwork vertically. This three-dimensional movement achieves precise formwork support.

[0070] 3. The combined curing method of the present invention employs a curing sequence of steam curing followed by spray curing, employing a three-stage spray curing pipeline and steam curing pipeline. The spray and steam pipelines are installed inside the box girder steel pedestal. Each of the three pipelines is equipped with a branch valve to adjust the water and steam supply according to production conditions, ensuring optimal curing results.

[0071] 4. The present invention adopts a pre-buried inner mold pull-down device to transfer the buoyancy of the inner mold to the pedestal during the box girder casting process (converting the buoyancy into internal force), avoiding the traditional situation where the buoyancy is entirely applied to the outer mold through the pressure rod, ensuring the stability of the outer mold, and at the same time avoiding the occurrence of the inner mold floating accident due to the deformation of the pressure rod and other reasons, ensuring the thickness of the prefabricated box girder top plate, web plate and top plate and the thickness of the top plate steel bar protective layer, thereby improving the construction quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 is a process flow chart of the present invention;

[0073] Figure 2 This is a schematic diagram of the core mold pull-down device of the present invention; in the figure: 1, box beam web; 2, embedded Ф63mm steel pipe; 3, steel pedestal body; 4, high-strength bolts; 5, cross bar; 6, box beam bottom plate; 7, pedestal steel panel; 8, reserved channel of pedestal body; 9, gasket; 10, high-strength bolts. DETAILED DESCRIPTION

[0074] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0075] Example 1

[0076] A prefabricated box beam construction method, such as Figure 1 As shown, the following steps are included:

[0077] Step 1: Construction preparation

[0078] (1) Pre-adjusted straightening and tying jig production

[0079] Arrange the jig vertical support ribs on both sides of the pedestal width direction, weld the processed jig vertical support ribs to the pre-buried vertical ribs of the jig, arrange the outer reinforcement of the jig vertical support ribs vertically, and arrange the inner reinforcement obliquely according to the slope of the precast beam web, with the height slightly lower than the height of the beam and slab precast reinforcement skeleton. Then weld the jig transverse support ribs about 5 cm downward from the top surface of the jig support ribs, paint the transverse support ribs according to the spacing of the box girder reinforcement skeleton steel bars, and mark them to facilitate control when tying the skeleton steel bars.

[0080] Weld positioning nuts onto the jig's vertical support bars according to the spacing of the frame's horizontal bars. The height of the positioning nuts should be less than half the diameter of the frame's horizontal bars, ensuring that the frame's horizontal bars are at the required height after installation. Then, insert the machined jig's positioning bars into the nuts. The spacing of the jig's positioning bars should be the same as the horizontal bars of the box girder's reinforcement frame, with groups of 3 to 5.

[0081] Use I40 I-beam as the tensioning end fixing, bury the I-beam 1.5m below the ground to ensure that the I-beam does not overturn during tensioning. Use a punch to accurately punch holes in the web according to the design drawings;

[0082] (2) Processing and installation of prefabricated box girder steel pedestals

[0083] like Figure 2 As shown, when customizing the prefabricated box girder steel pedestal, crossbeams and holes for pulling down the inner mold are reserved on the steel pedestal body and the pedestal steel panel. During the box girder prefabrication process, the pedestal and the core mold are connected with high-strength bolts through the tie rods (30mm diameter, 65cm long) inside the round steel to form a whole, preventing the core mold from floating up during the concrete pouring process. Transverse channel steel (100mm*48mm*5.3mm) is used inside the core mold to fix the two tie rods to the core mold, and steel plates (10*10cm, wall thickness 10mm) are used inside the steel pedestal to fix the two tie rods to the pedestal. Schematic diagram of the core mold pull-down device;

[0084] Step 2: Assembling and polishing the self-propelled hydraulic steel formwork

[0085] (1) Characteristics of the method:

[0086] ① The self-propelled hydraulic steel formwork has a fast construction speed, low crane occupancy rate in the beam yard, and high production efficiency;

[0087] ② The single-side formwork is divided into two sections, and the 1.5m formwork processing unit is connected into a whole by a crossbeam. The movement of a single prefabricated box beam formwork can be completed in four units, which speeds up the construction.

[0088] ③The hydraulic system supports the formwork in the vertical direction and height direction, which can be finely adjusted and the formwork installation accuracy is high;

[0089] ④ After the formwork is in place, the hydraulic support system is locked and combined with the formwork bottom support rod to ensure that the formwork is stable and reliable. When pouring concrete, the formwork will not be displaced or deformed due to the concrete pressure and the vibration of the attached vibrator.

[0090] ⑤ The self-propelled hydraulic steel formwork has a fast demolding speed. After demolding, it can be quickly moved along the track to another pedestal on the same production line to prepare for the next cycle of operation.

[0091] (2) Operation points:

[0092] ① Move the template longitudinally into place and align the center of the template with the lowest point of the pre-arch.

[0093] ② The hydraulic system lifts the template twice, and the bottom edge of the template is flush with the steel base panel.

[0094] ③The hydraulic system pushes the template close to the steel base.

[0095] ④ Make slight adjustments to ensure that the bottom edge of the steel template is flush with the base surface without any gaps.

[0096] ⑤Lock the formwork hydraulic system and install the steel formwork bottom support rod.

[0097] ⑥ When removing the formwork, first remove the connecting bolts between the mid-span diaphragm and the end beam formwork, remove the mid-span diaphragm and the end beam formwork, then remove the four formwork units in turn and move them along the track to the next platform.

[0098] Step 3: Steel bar processing and installation

[0099] (1) Steel bar processing

[0100] The cutting of steel bars is carried out by CNC bending equipment, which improves the accuracy of steel bar cutting. The steel bars are installed by jigs, which improves the accuracy of steel bar installation. This makes the cutting accuracy of steel bars match the installation accuracy, further improving the accuracy of steel bar skeleton processing.

[0101] (2) Pre-straightening technology

[0102] ①The steel bars are installed on the jig one by one in the order of bottom and web, and the steel bars are installed and tied strictly according to the positions marked on the jig.

[0103] ② The longitudinally distributed horizontal reinforcements of the bottom plate, web plate and top plate are connected to the pre-straightening connectors before tying. One end of the connector is connected to the horizontal reinforcement and the other end passes through the tensioning end fixing for pre-tensioning, so that the reinforcement has a certain straightness and internal stress.

[0104] ③ The tensioning instrument uses a manual anchor cable tensioner. First, anchor a single horizontal rebar at each end of the tire frame. Then, from one side of the tire frame, a pneumatic hydraulic pump and jack assembly are used to tension the horizontal distribution bar. The tensioning stress should not exceed 10kN. Once the horizontal bar is straightened, the jack assembly is slowly removed and the next horizontal bar is tensioned and straightened. The top plate, web plate, and bottom plate horizontal distribution bars are tensioned and straightened sequentially to ensure the straightness and installation accuracy of each horizontal bar.

[0105] ④ After the steel bar binding is completed, loosen the pre-straightening connector and prepare to complete the removal of the steel bar skeleton. After the pre-straightening connector is straightened, prepare for the next cycle of work.

[0106] Step 4: Prefabricated box beam inner formwork

[0107] Assemble and polish the inner mold of the prefabricated box beam, and ensure that the joints between the inner mold segments are tight and without misalignment. Polish the surface smoothly and apply the release agent evenly.

[0108] Step 5: Bottom web reinforcement installation

[0109] Use the steel frame lifting truss to accurately install the tied steel frame from the tying jig into the polished and cleaned formwork.

[0110] Step 6: Pull down the inner mold

[0111] After the inner formwork is installed, a PVC pipe (50mm diameter, 45cm long) is inserted into the reserved round steel hole. A tie rod (30mm diameter, 65cm long) is inserted into the PVC pipe. A transverse channel steel (100mm*48mm*5.3mm) is used inside the core formwork to secure the two tie rods to the core formwork. A steel plate (10*10cm, 10mm wall thickness) is used inside the square steel to secure the two tie rods to the pedestal. The pedestal and inner formwork are then connected with high-strength bolts via the tie rod (30mm diameter, 65cm long) inside the round steel to form a single unit, preventing the inner formwork from floating during concrete pouring. The box girder floor vents are replaced by reserved holes and are no longer separately provided.

[0112] Step 7: Top plate reinforcement installation

[0113] Use a truss-type hanger to install the tied top plate reinforcement to the designated installation location.

[0114] Step 8: Concrete pouring

[0115] The concrete pouring of prefabricated box girders was completed by hoisting.

[0116] Step 9: Template removal

[0117] After the box girder concrete has initially set, remove the negative bending moment notch wedge formwork and inner formwork, and remove the outer formwork after the box girder concrete strength reaches 2.5Mpa.

[0118] Step 10: Standardized combination curing process of prefabricated box beams

[0119] (1) The site selection of boiler room and water room shall take into account the layout of box girder production pedestal and try to locate them in the middle of the production area to ensure sufficient and balanced steam and water supply in each production area. At the same time, the convenience of fuel supply shall be taken into account. The site selection shall be completed after comprehensive consideration of various situations.

[0120] (2) Pipeline layout

[0121] aThe pipeline layout is divided into three levels. The first level is the main pipeline, which is arranged longitudinally on the side of the production area; the second level is the branch pipeline, which is arranged perpendicular to the direction of the beam yard, that is, the horizontal branch pipeline; the third level is the working pipeline, which is led from the second level pipeline to the box beam steel pedestal.

[0122] b. All pipelines at all levels are equipped with control valves, which can adjust the supply in real time according to actual production conditions and optimize the health-care effect.

[0123] (3) Information control

[0124] a. The sprinkler health care system is equipped with an information control system. A main control valve is installed on the main pipeline of the water room. Solenoid valves are installed from the first to the second level to control the branch water source. A telescopic sprinkler head is installed in the third-level maintenance unit. It is extended when in use and retracted into the inside of the box girder steel pedestal when not in use.

[0125] b. The spraying system can be remotely controlled by mobile phone, specifically to a certain box girder pedestal, and timed watering maintenance can also be set for the pedestal that needs spraying curing.

[0126] (4) Health Shed

[0127] In view of the frequent strong winds in the Hexi region, a color steel steam curing shed is used. The color steel steam curing shed has a stable structure and good air tightness.

[0128] (5) Maintenance process

[0129] a. After the box beam is demoulded, it is first sprayed with water for curing to prevent the early water loss and shrinkage cracks. After the steel formwork is moved to the next production pedestal, cement slurry is applied to the exposed steel bars to prevent steel bar corrosion during curing;

[0130] b. Hoist the steam curing shed to the box girder coated with cement slurry, and turn on the second and third level steam curing switches.

[0131] c. The steam curing period is 7 days, during which the curing effect is observed by a temperature and humidity recorder hung on the outer wall of the curing shed.

[0132] (6) Comprehensive health care

[0133] In view of the dry climate and strong winds at the project site, in order to ensure that no cracks appear in the box girder, the spray curing system will continue to operate from the seventh day of maintenance until the box girder tensioning and grouting work is completed.

[0134] (7) Health preservation in special weather conditions

[0135] After the box girder was cast, a sudden cold weather occurred. The movable steam curing hose was extended into the inner mold of the box girder. The top plate and the outside of the formwork were covered with quilts and then wrapped with tarpaulin.

[0136] Step 11: Prestressing and grouting

[0137] After the box girder strength reaches the design requirements, the prestressing and grouting work of the box girder will be completed in sequence.

[0138] Example 2 Benefit Analysis

[0139] Economic benefits

[0140] 1.1 Economic benefits of pre-straightening process:

[0141] Before the prefabricated box girder reinforcement skeleton binding and pre-straightening construction method was adopted, the average time required to bind the reinforcement of each box girder was 18 working days. After using this method, the reinforcement binding efficiency was significantly improved, and the average reinforcement binding time for each beam was shortened to 6 working days. Calculated based on a labor cost of 200 yuan per working day, the average cost of each beam can be saved by 2,400 yuan.

[0142] 1.2 Economic benefits of pre-adjusted straight connectors:

[0143] Currently, precast box girder framing generally utilizes horizontal rebar pre-straightening technology, which improves the straightness of the horizontal bars and thus the qualified rate of the rebar cover. During this operation, the horizontal rebar is cut 1.6 meters long to pass through the pre-straightening mold holes for tensioning and pre-straightening. After the bottom web reinforcement framing is completed, the 0.8-meter-long bars at each end of the horizontal bars are cut, and then the rebar framing is hoisted and installed.

[0144] Taking the beam and slab production of the Jie'an project as an example: the steel bar loss was 16.16T, with a value of 57,000 yuan.

[0145] Table 1 Economic Benefits of Pre-adjusted Straightening Connectors

[0146]

[0147] The average cost saving per box girder is 100 yuan.

[0148] 1.3 Economic benefits of self-propelled hydraulic steel formwork:

[0149] Self-propelled hydraulic steel formwork uses a motor to quickly move to the next position on the production line's tracks, reducing reliance on and occupation of cranes while also reducing the number of formwork workers. Analysis shows that each box girder can save 370 yuan in costs.

[0150] 1.4 Economic benefits of pull-down inner mold:

[0151] The pull-down inner formwork simplifies the construction method of the traditional pressure bar fixed inner formwork, making the operation easier and reducing mutual interference in the process. After comparative analysis, each prefabricated box girder can save 90 yuan in costs.

[0152] Based on the above four points, the average economic benefit of each prefabricated box girder is 2,960 yuan.

[0153] 2. Social benefits

[0154] The use of a complete set of prefabricated box girder processes for precise control of construction methods effectively improves the construction quality of prefabricated box girders without significantly increasing costs. Each construction link is closely connected, the process is optimized, and production efficiency is greatly improved. This construction method is technologically advanced, safe, and reliable, and has important guiding significance for construction under similar conditions, with positive social benefits.

[0155] Example 3 Application Example

[0156] 1. (G85) Pengyang to Pingliang to Daqiao Village Expressway Civil Engineering Project PDSG2

[0157] Project location: Kongtong District, Pingliang City, Gansu Province

[0158] Project Overview: Located in Sisilipu Town, Kongtong District, Pingliang City, Gansu Province, the project starts at K26+400, connecting with the PDSG1 section, and ends at K37+400, connecting with the PDSYSG-4 section. The total length is 9.98 km. The entire route includes two tunnels, 21 bridges, and 22 culverts.

[0159] Construction start and completion dates: Start on October 10, 2019 and completion on June 20, 2021.

[0160] Project cost: 1256.533 million yuan.

[0161] 2. JASG-1 section of the G312 line Jiepai Village to Anmen (including the Tianzhu transit section) upgrade and reconstruction project

[0162] Project location: Tianzhu County, Wuwei City, Gansu Province

[0163] Project Overview: The project begins in Jiepai Village, Tianzhu County, and connects with the G312 Kushui to Jiepai Village section reconstruction project, which terminates in Chenjiagou, Tianzhu County, connecting to the existing G312. The total length of the route is 45.13 km. The project primarily includes seven large bridges, four medium bridges, 13 small bridges, and 117 culverts.

[0164] Construction start and completion dates: Start on November 1, 2021 and completion on December 12, 2023.

[0165] Project cost: 457.8768 million yuan.

[0166] 3. Application effect

[0167] Two projects used this method, including the pre-adjustment straightening frame binding process to accurately control the spacing between steel bars, the inner mold pull-down process to accurately position and control the outline size of the box beam, the hydraulic formwork to control the accuracy of the box beam size, and the standardized composite curing process. These construction methods have achieved precise control of the entire set of construction processes for prefabricated box beams, improved the construction quality of the box beams, accelerated the construction progress, and are advanced and reliable, with good economic results.

[0168] The embodiments of the present application are described above in conjunction with the accompanying drawings, but the present application is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of this application, ordinary technicians in this field can also make many forms without departing from the purpose of this application and the scope of protection of the claims, all of which are within the protection of this application.

Claims

1. A prefabricated box girder construction method, characterized in that: The steps include: Step 1: Construction preparation; Step 2: Assembling and grinding the self-propelled hydraulic steel formwork; Step 3: Processing and installation of steel bars; Step 4: Prefabricate the inner mold of the box girder; assemble and polish the inner mold of the prefabricated box girder, ensure that the joints of the inner mold segments are not misaligned and are tightly connected, polish the surface smoothly, and apply the release agent evenly; Step 5: Install the bottom web reinforcement: Use the reinforcement frame hoisting truss to accurately install the tied reinforcement frame from the tying jig into the polished and cleaned formwork; Step 6: Pull down the inner mold; After the inner mold is installed, a PVC pipe is inserted into the reserved hole round steel. The diameter of the PVC pipe is 50mm and the length is 45cm. A tie rod is inserted into the PVC pipe. The diameter of the tie rod is 30mm and the length is 65cm. A transverse channel steel is used inside the core mold. The specification of the transverse channel steel is 100mm*48mm*5.3mm. The two tie rods are fixed to the core mold. Steel plates are used inside the square steel. The specifications of the steel plates are 10*10cm and the wall thickness is 10mm. The two tie rods are fixed to the pedestal. The pedestal and the inner mold are connected together with high-strength bolts through the tie rods in the round steel to form a whole to prevent the inner mold from floating up during the concrete pouring process. The vent holes of the box beam bottom plate are replaced by reserved holes and are no longer set separately. Step 7: Install the top plate reinforcement: Use a truss-type hanger to install the tied top plate reinforcement to the designated installation position; Step 8: Concrete pouring: Use hoisting method to complete the concrete pouring of prefabricated box beam; Step 9: Formwork removal: After the initial setting of the box girder concrete, remove the negative bending moment notch wedge formwork and inner formwork, and remove the outer formwork after the box girder concrete strength reaches 2.5Mpa; Step 10: Standardized combination and curing of prefabricated box beams; Step 11: Prestressing and grouting: After the box girder strength reaches the design requirements, complete the prestressing and grouting work of the box girder in sequence.

2. A prefabricated box girder construction method according to claim 1, characterized in that: In step 1, the construction preparation work includes the following steps: (1) Pre-adjusted straight tying jig production Arrange the jig vertical support ribs on both sides of the pedestal width direction, weld the processed jig vertical support ribs with the pre-buried vertical ribs of the jig, arrange the outer steel bars of the jig vertical support ribs vertically, and arrange the inner steel bars obliquely according to the slope of the precast beam web, with a height slightly lower than the height of the precast steel bar skeleton of the beam and slab, and then weld the jig transverse support ribs about 5 cm downward from the top surface of the jig support ribs, paint the transverse support ribs according to the spacing of the box beam steel bar skeleton steel bars, and make marks to facilitate control when tying the skeleton steel bars; Weld positioning nuts on the vertical support bars of the jig according to the spacing of the horizontal bars of the frame. The height of the positioning nuts is lower than half of the diameter of the horizontal bars of the frame, so that the horizontal bars of the frame are at the required height after installation. Then insert the processed jig positioning bars into the nuts. The spacing of the jig positioning bars is equal to the horizontal bars of the box girder steel frame, and they are grouped in groups of 3 to 5. Use I40 I-beam as the tension end fixing part, bury the I-beam 1.5m below the floor to ensure that the I-beam does not overturn during tensioning, and use a puncher to accurately punch holes on the web according to the design drawings; (2) Processing and installation of prefabricated box girder steel pedestal When customizing the prefabricated box girder steel pedestal, crossbeams and channels for pulling down the inner mold are reserved on the steel pedestal body and the pedestal steel panel respectively. During the prefabrication of the box girder, the pedestal and the core mold are connected together with high-strength bolts through the tie rods in the round steel to form a whole, so as to prevent the core mold from floating up during the concrete pouring process. Transverse channel steel is used inside the core mold to fix the two tie rods to the core mold, and steel plates are used inside the steel pedestal to fix the two tie rods to the pedestal.

3. A prefabricated box girder construction method according to claim 1, characterized in that: In step 2, the self-propelled hydraulic steel formwork assembly and grinding includes the following steps: (1) The template is moved longitudinally into place, and the template is aligned with the lowest point of the pre-camber; (2) The hydraulic system lifts the template twice, and the lower edge of the template is flush with the steel pedestal panel; (3) The hydraulic system pushes the template close to the steel pedestal; (4) Make minor adjustments to ensure that the bottom edge of the steel template is flush with the surface of the pedestal without any gaps; (5) Lock the template hydraulic system and install the steel template bottom support rod; (6) When removing the formwork, first remove the connecting bolts between the mid-span partition and the end beam formwork, remove the mid-span partition and the end beam formwork, and then remove the four formwork units in turn and move them along the track to the next pedestal.

4. A prefabricated box girder construction method according to claim 1, characterized in that: In step three, the steel bar processing and installation includes the following steps: (1) Steel bar processing The cutting of steel bars is carried out by CNC bending equipment, which improves the accuracy of steel bar cutting. The steel bars are installed by jigs, which improves the accuracy of steel bar installation. Thus, the cutting accuracy of steel bars matches the installation accuracy, further improving the accuracy of steel bar skeleton processing. (2) Pre-straightening technology ① The steel bars are installed on the jig one by one in the order of the bottom and web plates, and the steel bars are installed and tied strictly according to the positions marked on the jig; ② The longitudinally distributed horizontal reinforcements of the bottom plate, web plate and top plate are connected with the pre-straightening connectors before tying. One end of the connector is connected with the horizontal reinforcement and the other end passes through the tensioning end fixing piece for pre-tensioning, so that the reinforcement has a certain straightness and internal stress; ③ The tensioning instrument uses a manual anchor cable tensioning instrument. When in use, first use the anchor to fix a single horizontal steel bar through both ends of the tire frame, and then tension the horizontal distribution bar from one side of the tire frame through the pneumatic hydraulic pump and the jack group. The tensioning stress should not exceed 10KN. After the horizontal steel bar is tensioned and straightened, slowly remove the jack group to tension and straighten the next horizontal bar. The horizontal distribution bars of the top plate, web plate, and bottom plate are tensioned and straightened in turn to ensure the straightness and installation accuracy of each horizontal bar; ④ After the steel bar binding is completed, loosen the pre-straightening connector and prepare to complete the steel bar skeleton removal. After the pre-straightening connector is straightened, prepare for the next cycle of work.

5. A prefabricated box girder construction method according to claim 1, characterized in that: In step ten, the standardized assembly curing of prefabricated box beams includes the following steps: (1) The site selection of boiler room and water room should take into account the layout of the box girder production pedestal and try to locate them in the middle of the production area to ensure sufficient and balanced steam and water supply in each production area. At the same time, the convenience of fuel supply should be taken into account and the site selection should be completed after comprehensive consideration of various conditions. (2) Pipeline layout a. The pipeline layout is divided into three levels. The first level is the main pipeline, which is arranged longitudinally on the side of the production area; the second level is the branch pipeline, which is arranged perpendicular to the beam yard, that is, the horizontal branch pipeline; the third level is the working pipeline, which is led from the second level pipeline to the steel pedestal of the box beam; b. All pipelines at all levels are equipped with control valves, which can adjust the supply in real time according to the actual production situation and optimize the health-care effect; (3) Information control a. The sprinkler health system is equipped with an information control system. A master control valve is installed on the main pipeline of the water room. Solenoid valves are installed from the first to the second level to control the branch water source. A telescopic sprinkler head is installed in the third-level maintenance unit. It is extended when in use and retracted to the inside of the box beam steel pedestal when waiting for use. b. The spray system can be remotely controlled by mobile phone, specifically to a certain box beam pedestal, and can also set a scheduled watering maintenance for the pedestal that needs spraying maintenance; (4) Health Shed In view of the frequent strong winds in Hexi region, the color steel steam curing shed is used. The color steel steam curing shed has a stable structure and good air tightness. (5) Maintenance process a. After the box beam is removed from the formwork, it is first sprayed with water for curing to prevent early water loss shrinkage cracks. After the steel formwork is moved to the next production pedestal, cement slurry is applied to the exposed steel bars to prevent steel bar corrosion during curing; b. Hoist the steam curing shed to the box girder where the cement slurry has been applied, and turn on the secondary and tertiary steam curing switches; c. The steam curing period is 7 days, during which the curing effect is observed by a temperature and humidity recorder hung on the outer wall of the curing shed; (6) Comprehensive health care In view of the dry climate and strong winds at the project site, in order to ensure that no cracks occur in the box beam, the spray curing system will continue to work from the seventh day of maintenance until the box beam tensioning and grouting work is completed; (7) Health preservation in special weather conditions After the box girder was cast, a sudden cold weather occurred. The movable steam maintenance hose was extended into the inner mold of the box girder. The top plate and the outside of the formwork were covered with quilts and then wrapped with tarpaulin.

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