Box culvert field prefabrication construction method

Abstract

This invention discloses a method for on-site prefabrication of box culverts, relating to the field of water conservancy and hydropower engineering, including the following steps: S1: Prefabricate U-shaped and I-shaped prefabricated components outside the foundation pit, with reinforcing bars extending from the connection surfaces of the U-shaped and I-shaped prefabricated components; S2: Arrange the U-shaped and I-shaped prefabricated components inside the foundation pit to form a vertically discontinuous box culvert structure, controlling the connection surfaces of the U-shaped and I-shaped prefabricated components to be opposite each other, and the extended reinforcing bars to be staggered; S3: Perform the casting and connection work of the disconnected parts between the U-shaped and I-shaped prefabricated components; In this invention, prefabrication is not required in the foundation pit, saving construction time. The prefabricated U-shaped and I-shaped prefabricated components are reasonably stressed, and with the subsequent staggered reinforcing bars, a high-quality box culvert can be quickly assembled.

Description

Technical Field

[0001] This invention relates to the field of water conservancy and hydropower engineering, and in particular to a method for on-site prefabrication of box culverts. Background Technology

[0002] Box culverts are common underground water conveyance structures in river management, urban flood control and drainage, and water environment improvement projects. They serve functions such as flood control, drainage, sewage interception, and ecological water replenishment. Their structural safety and construction quality directly affect regional flood control standards and water body management effectiveness.

[0003] In current technological practices, box culvert construction is mainly divided into two categories: precast assembly construction and cast-in-place construction. Precast assembly box culverts have advantages such as standardized components, factory production, rapid on-site installation, short construction cycle, and controllable quality. However, their application is highly dependent on factories in the surrounding area with the capacity to produce large precast components and a well-developed road network for transporting oversized components. For geographically remote areas with weak infrastructure, there is usually a lack of supporting precast component factories. If finished box culverts are transported from precast factories at long distances, not only is the transportation cycle long and coordination difficult, but the long-distance transportation cost of large-volume, heavy-tonnage components is also high, and implementation may even be impossible due to road width, height, and load restrictions. Due to the above limitations, box culvert structures in river management projects in remote areas are often forced to adopt in-situ formwork and cast-in-place construction techniques. However, this technique has significant engineering difficulties and technical defects in practical applications: (1) The construction period is long and severely constrained by the environment: Cast-in-place box culverts need to go through the entire process of foundation pit excavation, subbase construction, steel reinforcement binding, formwork support, concrete pouring and curing, etc. The construction line is long. Especially in the case of river management, the construction foundation pit is often flooded or waterlogged due to rainfall, groundwater seepage or fluctuations in river water level, which seriously interferes with normal construction operations and delays the construction period.

[0004] (2) The durability and quality of the structure are difficult to guarantee: The long-term exposure of the foundation pit and the alternating wet and dry environment can easily induce severe corrosion of the steel cage and embedded parts, which weakens the bond and anchorage performance between the steel bars and the concrete. At the same time, the on-site binding of steel bars is limited by the working surface conditions, and its positioning accuracy, spacing control and protective layer thickness uniformity are difficult to achieve the ideal design state, resulting in hidden dangers in the anti-seepage, crack resistance and load-bearing capacity of the box culvert structure.

[0005] (3) High overall construction costs: The delay in construction not only leads to an increase in direct costs such as labor, machinery rental, foundation pit dewatering and cofferdam maintenance, but also indirectly increases project management costs and river flood risk costs.

[0006] In summary, in remote areas where there are no precast component factories or transportation is limited, relying solely on cast-in-place processes cannot simultaneously achieve the triple goals of construction period, cost, and quality.

[0007] Therefore, there is an urgent need for a method for the on-site prefabrication of box culverts that has a reasonable structural stress distribution, is easy to prefabricate in batches under simple on-site conditions, and can achieve rapid assembly and integrated connection. Summary of the Invention

[0008] The purpose of this invention is to provide a method for on-site prefabrication of box culverts to solve the problems existing in the prior art. It eliminates the need for prefabrication in the foundation pit, is suitable for batch prefabrication under simple conditions, and saves construction time. The prefabricated U-shaped and I-shaped prefabricated components are reasonably stressed, and with the subsequent staggered reinforcement, they can be quickly assembled into box culverts with good engineering quality.

[0009] To achieve the above objectives, the present invention provides the following solution: The present invention provides a method for on-site prefabrication of box culverts, comprising the following steps: S1: Prefabricating U-shaped prefabricated components and I-shaped prefabricated components outside the foundation pit. During the prefabrication process of the U-shaped prefabricated components and the I-shaped prefabricated components, reinforcing bars are added to the mold. The reinforcing bars extend out of the connection surfaces of the U-shaped prefabricated components and the I-shaped prefabricated components. S2: The U-shaped precast components and the I-shaped precast components are arranged in the middle and the U-shaped precast components on both sides in the foundation pit to form a vertically disconnected box culvert structure. The connection surfaces of the U-shaped precast components and the connection surfaces of the I-shaped precast components are controlled to be opposite to each other, and the steel bars extending from the opposite connection surfaces are staggered. S3: Perform the casting and connection work for the disconnected parts between the U-shaped precast component and the I-shaped precast component; S4: The box culvert construction is complete.

[0010] Preferably, the U-shaped prefabricated component and the I-shaped prefabricated component are prefabricated using a vertical prefabrication method.

[0011] Preferably, before step S1, an erect prefabrication mold is constructed according to the erection prefabrication method.

[0012] Preferably, after step S1 is completed, wait for the concrete strength to reach the standard, remove the formwork, and use a crane to lift the U-shaped precast component and the I-shaped precast component into the foundation pit.

[0013] Preferably, during the hoisting process, the U-shaped prefabricated component is hoisted first, and the base plate of the U-shaped prefabricated component is adjusted to be located at the design elevation before the I-shaped prefabricated component is hoisted.

[0014] Preferably, the concrete strength grade used in step S3 is higher than that of the U-shaped precast component and the I-shaped precast component.

[0015] Preferably, when the base plate of the U-shaped precast component is cast and connected to the base plate of the I-shaped precast component, the casting space is formed by the foundation pit and two side templates.

[0016] Preferably, when the top plate of the U-shaped precast component is cast and connected to the top plate of the I-shaped precast component, a bottom mold is used to cover the bottom of the casting space. The portions of the bottom mold extending to the lower surface of the top plate are supported by first support strips. A second support strip is placed on the upper surface of the top plate corresponding to the position of the lower first support strip. A side mold is used to cover the side of the casting space. Pre-tensioners are used to connect the upper and lower opposing first support strips and second support strips. At the same time, the pre-tensioners intercept the outer side of the side mold.

[0017] Preferably, a crossbar is inserted between the pretensioner and the side mold, and the crossbar contacts the pretensioner and the side mold at both ends along the direction of the box culvert hole, respectively.

[0018] Preferably, stiffening ribs are welded to the bottom of the bottom mold.

[0019] The present invention achieves the following main technical effects compared to the prior art: When prefabricating U-shaped and I-shaped components, it is not necessary to prefabricate them on a foundation pit; open ground in other locations can be used. This reduces the requirements for prefabrication conditions, improves on-site adaptability, and eliminates dependence on large prefabrication plants. It is suitable for remote areas or transportation-restricted conditions. Furthermore, the excavation of the foundation pit and the prefabrication of components can be carried out simultaneously, effectively saving construction time, reducing the exposure time of the foundation pit, lowering the risk of steel corrosion, saving construction costs, and improving project quality. The prefabricated U-shaped components include the side walls, part of the top slab, and part of the bottom slab of the box culvert; the I-shaped components include the central partition wall, part of the top slab, and part of the bottom slab of the box culvert. The stress of a single component is... With good stability, and the connection nodes between the subsequent I-shaped and U-shaped precast components are located between the side walls and the central partition wall, the stress is relatively small, making the stress distribution more reasonable. This results in a continuous stress path for the subsequently formed box culvert structure, combining the advantages of prefabricated construction efficiency and the overall quality of cast-in-place structures. At the same time, the reasonable stress distribution means that the reinforcing bars of the subsequent I-shaped and U-shaped precast component transition pieces do not need to be precisely aligned or tied (aligning refers to making holes for the reinforcing bars to pass through at opposite positions, and tying refers to tying the reinforcing bars of the two precast components together with tying devices). The requirements for the manufacturing dimensions and hoisting and positioning accuracy of the precast components are low, which significantly reduces the difficulty of on-site construction and installation time.

[0020] Other solutions of the present invention achieve the following technical effects compared with the prior art: Based on the shape design of I-shaped and U-shaped precast components, the vertical precasting method is adopted to precast I-shaped and U-shaped precast components. The original horizontal precast components and irregular parts such as the armpit corners are all converted into vertical precast components that are easy to precast. The formwork is simple, no complex jig is required, the precasting efficiency is high and the quality is controllable.

[0021] The high concrete strength grade at the connection joint between the I-shaped and U-shaped precast components effectively ensures the load-bearing capacity, impermeability, and durability of the connection joint area.

[0022] The bottom connection nodes between the I-shaped and U-shaped precast components adopt conventional sealing, while the top nodes adopt a standardized self-supporting formwork system. There is no need to erect full-span scaffolding, simplifying the process. The formwork can be quickly installed and dismantled and reused, greatly improving construction efficiency. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a flowchart of the on-site prefabrication construction method for box culverts in an embodiment of the present invention; Figure 2 This is a schematic diagram of the structure of the U-shaped prefabricated component and the I-shaped prefabricated component in the embodiments of the present invention; Figure 3 This is a structural schematic diagram of the U-shaped prefabricated component and the I-shaped prefabricated component in the vertical prefabrication state in an embodiment of the present invention; Figure 4 This is a schematic diagram of the assembly structure of the U-shaped prefabricated component and the I-shaped prefabricated component in an embodiment of the present invention; Figure 5 This is a schematic diagram of the connection node structure in an embodiment of the present invention; Figure 6 This is a schematic diagram of the mold structure for the top plate connection node in an embodiment of the present invention; Figure 7 This is a diagram showing the mold structure composition of the top plate connection node in an embodiment of the present invention; Figure 8 This is a schematic diagram of the molded box culvert structure in an embodiment of the present invention; Among them, 1. U-shaped precast components; 2. I-shaped precast components; 3. Armhole corners; 4. Reinforcing bars; 5. Tie rods; 6. Longitudinal steel pipes; 7. Side formwork; 8. Transverse steel pipes; 9. Bottom formwork; 9-1. Square steel; 9-2. Steel plates; 10. Post-cast concrete. Detailed Implementation

[0025] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0026] The purpose of this invention is to provide a method for on-site prefabrication of box culverts to solve the problems existing in the prior art. It eliminates the need for prefabrication in the foundation pit, is suitable for batch prefabrication under simple conditions, and saves construction time. The prefabricated U-shaped and I-shaped prefabricated components are reasonably stressed, and with the subsequent staggered reinforcement, they can be quickly assembled into box culverts with good engineering quality.

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0028] Please refer to the following: Figures 1-8 As shown, a method for on-site prefabrication of box culverts is provided, including the following steps: S1: Prefabricate U-shaped prefabricated component 1 and I-shaped prefabricated component 2 outside the foundation pit. Specifically: select an open space, compact and level it, and lay an isolation layer. During the prefabrication of U-shaped prefabricated component 1 and I-shaped prefabricated component 2, add steel bars 4 to the mold. After the steel bars 4 are laid out, seal the gap between the holes reserved for steel bars 4 on the mold and the steel bars 4. Then pour concrete. After pouring, the steel bars 4 extend out of the connecting surface of U-shaped prefabricated component 1 and the connecting surface of I-shaped prefabricated component 2. S2: Demold the formed U-shaped precast component 1 and I-shaped precast component 2. Arrange the U-shaped precast component 1 and I-shaped precast component 2 in the foundation pit with the I-shaped precast component 2 in the middle and the U-shaped precast component 1 on both sides to form a vertically disconnected box culvert structure. Control the connection surfaces of the U-shaped precast component 1 and the I-shaped precast component 2 to be opposite each other, and the steel bars 4 extending from the opposite connection surfaces are staggered. There is no need to set corresponding holes on the connection surfaces corresponding to the steel bars 4 to allow the steel bars 4 to enter, or to tie the steel bars 4 of the two connection surfaces together with tie-up parts (the commonly used lap splicing method), which reduces construction precision and improves construction efficiency. S3: Perform the pouring and connection work of the disconnected part (connection node of the two precast components) between the U-shaped precast component 1 and the I-shaped precast component 2. The steel bars 4 protruding from the two precast components transmit force only by their natural interlacing in the concrete (referring to the misalignment of the steel bars 4 on both sides) and the bond effect of the concrete. S4: The box culvert construction is complete.

[0029] When preparing the I-shaped precast component 2, the top plate portion of the I-shaped precast component 2 is smaller than the top plate portion of the U-shaped precast component 1, so that the connection node is closer to the central partition wall, which can further reduce the stress on the subsequent connection node casting body.

[0030] Because the prefabricated components are U-shaped and I-shaped, a vertical prefabrication method can be used when prefabricating U-shaped prefabricated component 1 and I-shaped prefabricated component 2. The vertical prefabrication method involves rotating the prefabricated component 90° from horizontal prefabrication for vertical prefabrication. Taking I-shaped prefabricated component 2 as an example, the formed I-shaped prefabricated component 2 lies flat on the ground with its "I" facing the sky. By using the vertical prefabrication method to prefabricate I-shaped prefabricated component 2 and U-shaped prefabricated component 1, the original horizontal prefabricated components and irregular parts such as the armpit corner 3 are all transformed into vertical prefabricated components that are easy to prefabricate. The formwork is simple, no complex jig is required, the prefabrication efficiency is high, and the quality is controllable.

[0031] Since the prefabrication adopts the vertical prefabrication method, before step S1, it is necessary to build a vertical prefabrication mold according to the vertical prefabrication method. During the construction process, holes are reserved on the mold to pass through the reinforcing bars 4 so that the reinforcing bars 4 can be laid out. Then, after subsequent casting and molding, the reinforcing bars 4 can extend out of the surface to be connected of the prefabricated component.

[0032] After step S1 is completed, cover with a curing film for moisturizing and curing for no less than 7 days. Wait for the concrete strength to reach the standard (when the strength reaches more than 75% of the design strength), remove the formwork, and use a crane to lift the U-shaped precast component 1 and the I-shaped precast component 2 into the foundation pit to assemble the discontinuous box culvert structure, and wait for the subsequent connection nodes to be poured and connected.

[0033] During the hoisting process, the U-shaped precast component 1 is hoisted first, and the plane position and elevation of the bottom surface of the foundation pit are continuously adjusted while maintaining the hoisting state, so that the bottom plate of the U-shaped precast component 1 is positioned at the design elevation. Based on the bottom surface of the foundation pit after the adjustment, the I-shaped precast component 2 is then hoisted and placed on the bottom surface of the foundation pit. Hoisting the U-shaped precast component 1 first can help to find the placement position of the U-shaped precast component 1 according to the edge of the foundation pit. After the U-shaped precast components 1 on both sides are placed, the position of the I-shaped precast component 2 will naturally be formed in the middle, reducing the time for marking the placement position of the I-shaped precast component 2. The width of the connection node after forming is generally 200mm to 400mm.

[0034] The concrete strength grade used in step S3 is higher than that of the U-shaped precast component 1 and the I-shaped precast component 2. Specifically, C35 micro-expansion concrete of a higher grade is selected, or RPC concrete is directly selected if economic and technical conditions permit. The concrete strength grade of the connection node is high, which effectively ensures the bearing capacity, impermeability and durability of the connection node area. The compressive strength of RPC concrete can reach 150MPa to 200MPa, the porosity is less than 2%, and the impermeability grade is not lower than P30.

[0035] When the base plate of the U-shaped precast component 1 is connected to the base plate of the I-shaped precast component 2 during casting, the foundation pit and two side templates can be used directly to form the casting space. Specifically, the foundation pit serves as the bottom template of the casting space, and the side templates are covered on both sides of the casting space along the orientation of the culvert opening. The side templates away from the casting space can be supported by diagonal braces and other support components. The casting mold is easy to build and can effectively improve the casting efficiency.

[0036] When the top slab of the U-shaped precast component 1 is connected to the top slab of the I-shaped precast component 2 during casting, a bottom mold 9 is used to cover the bottom of the casting space. The portions of the bottom mold 9 extending to the lower surface of the top slab on both sides are supported by the first support strips (the two sides of the bottom mold 9 extend to the lower surfaces of the top slabs on both sides respectively). A second support strip is placed on the upper surface of the top slab corresponding to the position of the first support strip below. A side mold 7 is used to cover the side of the casting space. When the side mold 7 covers the side of the casting space, its two sides should be in contact with the side end faces of the top slabs on both sides to improve the covering effect. Pre-tensioners are used to connect the upper and lower opposing first support strips and second support strips. At the same time, the pre-tensioners intercept the outer side of the side mold 7. After connecting the first support strips and second support strips with pre-tensioners, no support structure (full-span scaffolding) is required at the bottom of the first support strip to support the bottom mold 9. At the same time, the position of the side mold 7 can be fully limited by the pre-tensioners.

[0037] When a second support bar is installed above and a first support bar is installed below at opposite positions, a rope can be used as a pre-tightening component. One end of the rope is tied to the first support bar, and the other end is pulled taut, wrapped around, and tied to the second support bar to complete the pre-tightening. When two second support bars are installed above and two first support bars are installed below at opposite positions, a tie rod 5 can be used as a pre-tightening component. The tie rod 5 includes a screw rod, nuts at both ends, and two U-shaped clips. The two U-shaped clips have through holes in the middle and are fitted onto the screw rod. The concave surfaces of the two U-shaped clips are arranged opposite each other, and nuts are provided on the opposite sides of the two U-shaped clips. In actual use, the screw rod is inserted between the two first support bars and the two second support bars. The upper U-shaped clips clamp the second support bars on both sides, and the lower U-shaped clips clamp the first support bars on both sides. Then, the two nuts are tightened to complete the pre-tightening. In actual construction, other structures can also be selected as pre-tightening components, as long as they can achieve the pre-tightening.

[0038] Multiple pre-tightening components can be set on the same side end of each corresponding first and second support bars. The multiple pre-tightening components are set along the extension direction of the support bars. The innermost pre-tightening component intercepts the side mold 7, while the other pre-tightening components exist as reinforcement measures.

[0039] Both the first and second support bars can be made of steel pipes, or you can choose according to your needs.

[0040] A crossbar can be inserted between the pretensioner and the side mold 7. The crossbar can be made of steel pipe. Multiple crossbars can be inserted from top to bottom. The two ends of the crossbar along the direction of the box culvert opening contact the pretensioner and the side mold 7 respectively, thereby improving the interception effect on the side mold 7.

[0041] Stiffening ribs can be welded to the bottom of the bottom mold 9. The stiffening ribs can be made of steel pipes. The stiffening ribs can improve the structural strength of the bottom mold 9 and prevent damage during casting. At the same time, the stiffening ribs are perpendicular to the orientation of the culvert openings.

[0042] Multiple bottom formwork 9 can be set up, and multiple bottom formwork 9 can be arranged and spliced ​​together in sequence along the direction of the box culvert opening to form an integral bottom formwork. The bottom formwork 9 can be made of steel plate 9-2 with a thickness of 3mm to 6mm. The stiffening ribs can be made of square steel 9-1 with a cross-sectional size of 40mm×60mm to 50mm×100mm, and the spacing between adjacent stiffening ribs is 250mm to 350mm.

[0043] This invention systematically designs prefabricated components as an organic whole, including the segmentation method (divided into U-shaped prefabricated components 1 and I-shaped prefabricated components 2), prefabrication posture (vertical prefabrication), connection method (staggered reinforcement 4), formwork scheme (casting connection of the top slab without scaffolding) and node reinforcement (increasing the concrete strength of the connection node). The various features complement each other and are mutually conditional, together forming a complete assembly monolithic box culvert construction method system suitable for on-site prefabrication in remote areas.

[0044] The following are specific construction examples: The following explanation uses a double-span box culvert used in a comprehensive river management project as an example. The net width of each span of the box culvert is 3.0m, the net height is 2.5m, and the thickness of the top slab, bottom slab, and sidewalls is 0.3m.

[0045] (1) Precast components A prefabrication area was leveled and compacted at the construction site, and an isolation layer was laid. According to the design drawings, the steel reinforcement frames of U-shaped prefabricated component 1 and I-shaped prefabricated component 2 were fabricated respectively. U-shaped prefabricated component 1 includes part of the top slab, part of the bottom slab, and one side wall of the box culvert. I-shaped prefabricated component 2 includes another part of the top slab, another part of the bottom slab, and another side wall of the box culvert. Outward-extending steel bars 4 were reserved in the connection node area according to the requirement of staggered alignment and partial overlap along the direction of the box culvert openings.

[0046] The reinforcing steel cage is hoisted into the vertical precast mold, ensuring that reinforcing steel 4 protrudes from the pre-drilled holes in the mold. The mold positions the precast components vertically for casting. At this point, the original horizontal precast components, such as the top slab, bottom slab, and haunch 3 of the box culvert, are all flipped into vertical precast components. After verifying that the protective layer thickness of reinforcing steel 4 and the position of the pre-drilled reinforcing steel 4 are correct, C30 concrete is poured and compacted using an immersion vibrator. After pouring, a curing film is applied for moisture retention and curing for no less than 7 days.

[0047] U-shaped precast component 1 and I-shaped precast component 2 can be precast in batches by arranging multiple sets of molds side by side on the same site.

[0048] (2) Hoisting and assembly of prefabricated components When the concrete strength of the precast components reaches more than 75% of the design strength, a crane is used to lift the precast components to the designed position in the foundation pit.

[0049] First, hoist the U-shaped precast component 1 and adjust its plane position and elevation to ensure that the base plate sits on the design elevation of the cushion layer. Then, hoist the I-shaped precast component 2 and slowly lower it so that the protruding steel bars 4 of the I-shaped precast component 2 and the protruding steel bars 4 of the U-shaped precast component 1 are naturally misaligned in the connection node area. Since the misaligned connection method is adopted, the steel bars 4 do not need to be precisely aligned with the holes or tied for fixation, and the hoisting and positioning process is simple and fast.

[0050] (3) Installation of connection node template The bottom connection node is located in the connection area between the bottom plate of the U-shaped precast component 1 and the I-shaped precast component 2. According to the conventional construction method, lateral formwork is set up on the outside of the precast component for sealing. The formwork adopts a fixed steel formwork or wooden formwork and is supported and reinforced to the side wall of the foundation pit or the ground with steel pipes. After the formwork is installed, the tightness of the joint and the reliability of the reinforcement are checked.

[0051] The top connection node is located in the connection area between the top slab of the U-shaped precast component 1 and the I-shaped precast component 2. The formwork system for each post-cast strip is installed in the following order: First, the bottom formwork 9 is placed. Several standardized bottom formwork 9s are placed at the bottom of each post-cast strip. Each bottom formwork 9 is welded from a 5mm thick steel plate 9-2 and a 40mm×60mm square steel 9-1. The square steel 9-1 is arranged longitudinally at 300mm intervals as stiffening ribs. The two ends of the bottom formwork 9 are respectively connected to the support parts reserved on the U-shaped precast component 1 and the I-shaped precast component 2.

[0052] Next, longitudinal steel pipes 6 (first support strips and second support strips) are installed. The longitudinal steel pipes 6 are divided into two groups along the transverse direction of the box culvert. The left group consists of two pipes below the bottom formwork 9 (two first support strips) and two pipes above the top plate (two second support strips). The right group consists of two pipes below the bottom formwork 9 and two pipes above the top plate, for a total of eight pipes, which are arranged longitudinally along the connection nodes.

[0053] Reinstall the side formwork 7 and the transverse steel pipes 8 (horizontal bars). Place one side formwork 7 at each of the longitudinal ends of the node to seal the end. The transverse steel pipes 8 are arranged close to the outside of the side formwork 7 at both ends. Three transverse steel pipes are evenly arranged vertically from top to bottom on the outside of each side formwork 7, for a total of six pipes.

[0054] Finally, tie rods 5 are installed. Four tie rods 5 are installed at the end of each connection node. The two inner tie rods 5 are used to fasten the side mold 7, bottom mold 9 and transverse steel pipe 8. The two outer tie rods 5 serve as a further reinforcement measure. The longitudinal steel pipe 6, transverse steel pipe 8, bottom mold 9 and side mold 7 are tightened together by the tie rods 5 to form a self-supporting structure.

[0055] (4) Concrete pouring at connection nodes After the template is installed and inspected and approved, concrete is poured for the bottom and top connection nodes respectively. C35 micro-expansion concrete is used, which has a higher strength grade than the concrete of precast components. If economic and technical conditions permit, RPC concrete can be used to further improve the load-bearing capacity and durability of the node area.

[0056] The bottom connection node concrete is poured in conventional layers and compacted by vibration. The top node concrete is poured in from the upper discharge port and compacted evenly along the node area with a small vibrator to ensure that the concrete is filled densely. After pouring, it is covered and moisturized in time, and the curing time is not less than 14 days, finally forming a post-poured concrete body 10.

[0057] (5) Formwork removal and finished product acceptance When the concrete strength of the connection node reaches more than 70% of the design strength, the formwork system is removed. The formwork removal sequence is as follows: first, remove the tie rod 5, then remove the transverse steel pipe 8 and the longitudinal steel pipe 6, and finally remove the side formwork 7 and the bottom formwork 9. Check the appearance quality of the node to confirm that there are no defects such as honeycomb, pitting and cracks. After the formwork is removed, the assembled integral box culvert forms a complete load-bearing system.

[0058] Any adaptive changes made according to actual needs are within the scope of protection of this invention.

[0059] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0060] Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. Furthermore, those skilled in the art will recognize that, based on the ideas of this invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for on-site prefabrication of box culverts, characterized in that, Includes the following steps: S1: Prefabricating U-shaped prefabricated components and I-shaped prefabricated components outside the foundation pit. During the prefabrication process of the U-shaped prefabricated components and the I-shaped prefabricated components, reinforcing bars are added to the mold. The reinforcing bars extend out of the connection surfaces of the U-shaped prefabricated components and the I-shaped prefabricated components. S2: The U-shaped precast components and the I-shaped precast components are arranged in the middle and the U-shaped precast components on both sides in the foundation pit to form a vertically disconnected box culvert structure. The connection surfaces of the U-shaped precast components and the connection surfaces of the I-shaped precast components are controlled to be opposite to each other, and the steel bars extending from the opposite connection surfaces are staggered. S3: Perform the casting and connection work for the disconnected parts between the U-shaped precast component and the I-shaped precast component; S4: The box culvert construction is complete.

2. The method for on-site prefabrication of box culverts according to claim 1, characterized in that, The U-shaped prefabricated components and the I-shaped prefabricated components are prefabricated using a vertical prefabrication method.

3. The method for on-site prefabrication of box culverts according to claim 2, characterized in that, Before step S1, an erect prefabrication mold is built according to the erection prefabrication method.

4. The method for on-site prefabrication of box culverts according to claim 1, characterized in that, After step S1 is completed, wait for the concrete strength to reach the standard, remove the formwork, and use a crane to lift the U-shaped precast component and the I-shaped precast component into the foundation pit.

5. The on-site prefabrication construction method for box culverts according to claim 4, characterized in that, During the hoisting process, the U-shaped prefabricated component is hoisted first, and the base plate of the U-shaped prefabricated component is adjusted to be located at the design elevation before the I-shaped prefabricated component is hoisted.

6. The method for on-site prefabrication of box culverts according to claim 1, characterized in that, The concrete strength grade used in step S3 is higher than that of the U-shaped precast component and the I-shaped precast component.

7. The method for on-site prefabrication of box culverts according to claim 1, characterized in that, When the base plate of the U-shaped precast component is cast and connected to the base plate of the I-shaped precast component, the casting space is formed by the foundation pit and two side templates.

8. The method for on-site prefabrication of box culverts according to claim 1, characterized in that, When the top plate of the U-shaped precast component is cast and connected to the top plate of the I-shaped precast component, a bottom mold is used to cover the bottom of the casting space. The portions of the bottom mold extending to the lower surface of the top plate are supported by the first support strips respectively. A second support strip is placed on the upper surface of the top plate corresponding to the position of the first support strip below. A side mold is used to cover the side of the casting space. Pre-tensioners are used to connect the upper and lower opposing first support strips and second support strips. At the same time, the pre-tensioners intercept the outer side of the side mold.

9. The method for on-site prefabrication of box culverts according to claim 8, characterized in that, A crossbar is inserted between the pretensioner and the side mold, and the crossbar contacts the pretensioner and the side mold at both ends along the direction of the box culvert hole.

10. The method for on-site prefabrication of box culverts according to claim 8, characterized in that, Stiffening ribs are welded to the bottom of the bottom mold.

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