Industrialized construction method and construction system of urban rail transit thin-walled cast-in-place U-shaped beam

Abstract

The disclosed urban rail transit thin-wall mixed U-shaped beam industrial construction method and construction system carries out the construction of U-shaped beam beam manufacturing pedestal and beam storage tensioning pedestal in the site; carries out the U-shaped beam steel bar binding and the installation of the prestressed steel bundle on the U-shaped beam mold frame, and hoists the U-shaped beam steel cage to the beam manufacturing pedestal through a hanger; after the U-shaped beam steel cage is positioned, the embedded part, the U-shaped beam inner mold and the support system are installed; the thin-wall mixed U-shaped beam structure is optimized; the first tensioning prestressed bundle is constructed; the beam body concrete is poured; the first tensioning prestressed bundle is released and cut; the two U-shaped beams are respectively hoisted to the beam storage tensioning pedestal by using a gantry crane; the second tensioning prestressed bundle is constructed; the hole is grouted and sealed; after the overall operation is completed, the quartz sand is discharged through the steel sand box sand discharge hole, so that the U-shaped beam is lowered to the concrete base of the beam storage tensioning pedestal. The present application comprehensively and systematically solves the problems of large waste of original technical resources and low production efficiency.

Description

Technical Field

[0001] This invention relates to the field of U-beam production technology, specifically to an industrialized construction method and system for thin-walled, mixed-tension U-beams used in urban rail transit. Background Technology

[0002] Prestressed concrete U-shaped beams possess technical advantages such as low building height, good noise reduction, high cross-sectional space utilization, guaranteed driving safety, aesthetically pleasing appearance, low overall cost, and easy maintenance. However, the application of U-shaped beams is still limited in my country, and the corresponding construction technology reserves are not yet fully developed.

[0003] Constant-section precast U-beams are mostly prestressed concrete structures constructed using the pre-tensioning method. Prestressed steel strands are tensioned on a platform before concrete is poured, and prestress is established through bond force transfer. Due to the structural design characteristics of U-beams, constant-section U-beams cannot meet the requirements for safe vehicle operation, cable tray installation, and aesthetics in sections with small curve radii. Therefore, they need to be designed as variable-section thin-walled, mixed-tension U-beams. In addition to the prestressed steel strands in the base area, variable-section thin-walled, mixed-tension U-beams require additional bent-up prestressed steel strands in the thin-walled areas on both sides. Due to the technical limitations of pre-tensioning construction, the bent-up prestressed strands cannot be tensioned directly; post-tensioning must be used after the concrete has been poured and reached the design strength.

[0004] The second construction section of the Nanjing-Jurong Intercity Rail Transit Project DS6-TA02 consists of one station and one section, employing an irregular and complex shape of double U-shaped variable cross-section segmental beams. The thin-walled, tensioned U-shaped beams will present the following problems during construction:

[0005] 1. The lengths of the variable cross-section U-shaped beams in the Nanjing-Jurong Intercity Railway are 26m, 28m, and 30m. Taking the 28m variable cross-section U-shaped beam with a cross-section of 5.21-5.41 as an example, the cross-sectional area of ​​the prestressed steel strands is 0.014㎡, and the total number of prestressed tendons is 102. There are many problems such as different relaxation coefficients and different lengths of individual prestressed tendons, which make tensioning each tendon time-consuming and laborious, and making it difficult to control the overall tension stress.

[0006] 2. According to the simulation calculation based on the established model, the stress on the tensioning groove of the post-tensioned prestressed tendons in the U-shaped beam is the greatest, which makes it prone to concrete cracking.

[0007] 3. The construction of thin-walled mixed tension U-shaped beams involves three more steps than the standard section construction, which takes longer to occupy the beam fabrication platform and formwork, thus increasing the project cost and construction period accordingly. Summary of the Invention

[0008] Purpose of the invention: The purpose of this invention is to address the shortcomings of existing technologies by providing an industrialized construction method and system for thin-walled, mixed-tension U-shaped beams in urban rail transit, solving problems such as difficulty in controlling tensile stress, easy structural damage, and resource waste in the production process of thin-walled, mixed-tension U-shaped beams, thereby improving construction efficiency and increasing benefits.

[0009] Technical solution: The industrialized construction method for thin-walled, tensioned U-shaped beams in urban rail transit according to the present invention includes the following steps:

[0010] S1. Construct the U-shaped beam fabrication platform and the beam storage and tensioning platform on site. The fabrication platform can support the production of 2 U-shaped beams at a time. When constructing the fabrication platform, install the bottom formwork, outer formwork and steam curing shed of the U-shaped beam at the same time.

[0011] S2. The U-shaped beam reinforcement bars are tied and the prestressed steel strands are installed on the U-shaped beam formwork to obtain the U-shaped beam reinforcement cage. The U-shaped beam reinforcement cage is then lifted onto the beam fabrication platform using a gantry crane and a lifting frame.

[0012] After the S3 and U-shaped beam steel cages are in place, install the embedded parts, and then install the U-shaped beam inner formwork, inner formwork support, inner formwork moving system, and end formwork.

[0013] S4: Optimize the side wall structure of thin-walled mixed-tension U-beams, including calculating the side wall thickness of U-beams based on the stress characteristics of U-beams with different spans, analyzing the stress on each part of the beam, and strengthening the area with the greatest stress.

[0014] S5: Prestressed tendon construction is carried out using a construction process of simultaneously tensioning two U-shaped beams. The tensioning process is as follows: initially adjust each tendon at one end to 15%σcon → tension the whole to 100%σcon and hold the load for 3 minutes → anchor σcon. Steam curing is used during construction. The tension control stress is taken as 0.7fpk+2*At based on the actual temperature difference At between the steel tendon and the platform.

[0015] S6: After the steel reinforcement, formwork, and prestressing have passed the acceptance inspection, pour the beam concrete;

[0016] S7: First, release and cut the prestressed tendons. After the concrete strength reaches 85% and the elastic modulus reaches 90%, release the prestressed tendons.

[0017] S8. After the tension is released, the two U-shaped beams are hoisted to the beam storage tensioning platform by a gantry crane. At this time, the beam storage tensioning platform is in the state of being topped by the steel sand box, and the steel sand box bears the force, and automatic spray curing continues.

[0018] S9. Post-tensioned prestressed tendon construction: Post-tensioned prestressed tendon construction shall be carried out after the concrete strength reaches 95% of the design value, the elastic modulus reaches 100% of the design value, and the age is not less than 7 days. Simultaneous tensioning at both ends shall be adopted. The tensioning process is as follows: 0→0.1σcon→0.2σcon→tensioning control stress σcon→holding load for 5 minutes and anchoring.

[0019] S10, duct grouting, anchor sealing, and after final tensioning, vacuum-assisted grouting of the pipeline is carried out within 48 hours. Epoxy mortar is used for the end sealing of the pre-tensioned sleeve, and C60 fine stone micro-expansion concrete is used for the anchor sealing of the post-tensioned sleeve.

[0020] S11. After the overall operation is completed, quartz sand is released through the sand discharge hole of the steel sand box, so that the U-shaped beam is lowered to the concrete base of the beam tensioning platform. The stress point of the U-shaped beam changes from the end stress to the support position stress. After the U-shaped beam is stored for a specified time, it is transported to the site for erection.

[0021] To further improve the above technical solution, the beam-making platform in S1 includes a platform foundation, reaction piers, tension beams, force transmission rods, and a bottom formwork platform. The bottom formwork platform is provided on the top of the platform foundation, and tension beams are provided on both sides of the bottom formwork platform. Reaction piers are provided on the outer side of the tension beams. The reaction piers are connected to the platform foundation by pre-embedded 600×300×20mm I-beams to form steel-reinforced concrete. Tensioning holes are reserved inside the reaction piers, and 660×1360×20mm steel plates are provided on both sides of the tensioning holes for reinforcement.

[0022] Furthermore, the tensioning platform for the beam in S1 includes a concrete base and a steel sand box. The steel sand box is located at the outer corner of the concrete base and is connected to the concrete base by pre-embedded steel bars. The steel sand box contains a base and quartz sand filled on the base. A top cover is supported above the quartz sand, and a sand discharge hole is provided in the middle of the steel sand box.

[0023] Furthermore, in S4, based on the stress characteristics of U-shaped beams with different spans, the sidewalls of the U-shaped beams are used to resist the centrifugal force generated by the train operation. The sidewall thickness is calculated using the formula h=(F×S×V^2) / 127g, where h is the sidewall thickness, F is the tension control force, S is the span, V is the train speed, and g is the gravitational acceleration. At the same time, a design verification model is established using Midas Civil to analyze the stress on various parts of the beam, identify the area of ​​the steel strand with the greatest stress, and reinforce it with C12 threaded steel bars to form spiral reinforcement and steel mesh.

[0024] Furthermore, in step S5, anchor clamps are first installed one by one at the fixed end of the platform to anchor the prestressed tendons, and the clamps are tightened by tapping the sleeves of the clamps. Then, connectors are installed one by one and section by section towards the tensioning end. The two sleeves are tightened with a half-moon wrench and the prestressed tendons are straightened. Finally, anchor clamps are installed one by one at the tensioning end. Tensioning is carried out using two 30t jacks. After all prestressed tendons are tensioned to 15%σcon, they are then tensioned using four 600t jacks. At this time, the reaction piers bear the force. The construction requirements are met by strengthening the reserved tensioning holes of the reaction piers and pre-embedding the I-beams. After holding the load for 3 minutes, the stress sensor data is checked. If there are no errors, the tendons are anchored. If the stress is less than σcon, the tendons are tensioned to the control stress before anchoring.

[0025] Furthermore, the S7 tensioning process involves simultaneous tensioning from both ends, with the tensioning steps being 10%-10%-20%--20%--20%--20%, and a 1-minute interval between each tensioning step. After tensioning, the exposed steel strands at the beam ends are cut using a manual abrasive wheel cutter, and the exposed steel strand ends are coated with anti-rust material according to design requirements.

[0026] Furthermore, the entire construction process is controlled by information technology, and is divided into three major processes: information collection, data processing, and information output.

[0027] The information collection includes: adjusting concrete mix parameters according to different seasons, verifying the performance indicators of raw materials, and ensuring that production can only proceed if the design requirements are met; adjusting and optimizing the tensioning control stress before construction based on the collected control stress of a single prestressed tendon and the measured temperatures of the abutment and prestressed tendons; determining whether tensioning is in place based on the actual stress feedback from the stress acquisition device during tensioning; collecting data on curing temperature, humidity, and strength growth, and proceeding to the next step only after the strength requirements are met; and collecting monitoring data on the formed U-shaped beams.

[0028] The data processing includes: establishing a standard database based on the design content of concrete mix proportion, performance indicators of raw materials, and design standards for prestressed tendon control stress; formulating control indicators; comparing data through information collection during construction; and determining compliance with construction requirements and proceeding to the next process once relevant requirements are met; and adjusting the standard database by collecting monitoring data of the formed U-shaped beam.

[0029] The information output includes: creating a separate file for each U-beam after construction, containing three main contents: materials, construction, and monitoring; and creating a QR code based on the file content and posting it in a prominent place on the U-beam, linking to the file content.

[0030] The construction system for realizing the above-mentioned industrialized construction method of thin-walled mixed-tension U-shaped beams for urban rail transit includes: a beam-making platform for preparing thin-walled mixed-tension U-shaped beams, a U-shaped beam template system, a steam curing shed, intelligent tensioning equipment, and a beam-storage tensioning platform for storing thin-walled mixed-tension U-shaped beams.

[0031] The beam fabrication platform includes a platform foundation, reaction piers, tension beams, force transmission rods, and a bottom formwork platform. The force transmission rods are installed in the middle of the platform foundation. The bottom formwork platform is installed above the platform foundation to support the U-shaped beam formwork system. Tension beams are installed on both sides of the bottom formwork platform. The intelligent tensioning device is installed at the tension beams. The reaction piers are installed on the outside of the tension beams. The reaction piers are connected to the platform foundation through pre-embedded I-beams to form reinforced concrete. Tensioning holes are pre-reserved inside the reaction piers. Steel plates are provided on both sides of the tensioning holes for reinforcement. Jacks are provided on the outside of the reaction piers.

[0032] The beam tensioning platform includes a concrete base and a steel sand box. The steel sand box is located at the outer corner of the concrete base and is connected to the concrete base by pre-embedded steel bars. The steel sand box contains a base and quartz sand filled on the base. A top cover is supported above the quartz sand. A sand discharge hole is provided in the middle of the steel sand box.

[0033] Beneficial Effects: Compared with existing technologies, the advantages of this invention are as follows: 1. The modified beam-making platform addresses the high control stress of pre-tensioned prestressed tendons by optimizing the original reaction pier structure. By pre-embedding I-beams and connecting them to the foundation, a steel-reinforced concrete structure is formed. The simultaneous stress of the steel-reinforced concrete resists the shear force generated by prestressing tension, while the I-beams resist the bending moment caused by the tension force, further increasing its load-bearing capacity. The pre-embedding of the I-beams also reduces platform slippage, increases friction, and enhances safety. The pre-embedded bolt holes and pre-assembled steel plates in the pre-reserved openings of the reaction piers further improve the crack resistance of the openings, preventing damage to the reaction piers due to excessive local stress. The pre-assembled steel plates can also be reused, effectively reducing construction costs and making the invention highly scalable. 2. The hydraulic steel formwork and support system used in this invention can be adjusted and recycled for different structures, reducing resource waste and improving production efficiency. 3. The beam-making platform used in this invention can produce two beams at a time, improving production efficiency. Post-tensioning of prestressed tendons can be carried out on the beam tensioning platform, which can reduce the time occupied by the beam fabrication platform and formwork, saving construction time and costs.

[0034] 2. A new beam storage and tensioning platform was designed. The original beam storage platform only had the function of storing beams. In order to reduce the time occupied by the beam fabrication platform, the beam storage platform was modified to also have the function of tensioning. According to mechanical analysis, the stress at both ends of the tensioning is the weak zone, and the support point must be at the end. The beam storage needs to simulate the working condition after the beam is erected, and the support point is at the position of the beam support. By combining the steel sand box with the original beam storage platform, the tensioning and support can be effectively combined. The steel sand box can resist the local dispersion of tension stress, successfully complete the stress conversion, and achieve the expected construction goal.

[0035] 3. The design method for thin-walled post-tensioned U-beams was optimized. Through design verification with different spans and radii, and by comprehensively considering factors such as centrifugal force and vehicle speed, a design formula for the sidewall thickness of the U-beam was derived. This formula can effectively guide the design and application of other similar projects. The thin-walled, mixed-tensioned U-beams used reinforced the weak tension areas, preventing tension cracks from appearing in the beam.

[0036] 4. The construction method for the U-shaped beam with mixed tensioning was optimized by employing a single-strand-then-whole construction process. First, the structure was simulated to obtain the control stress of each individual steel strand. Qualified jacks were then used to tension each strand to 15% of its control stress to eliminate slack. Finally, qualified jacks were used for overall tensioning to 100% of the control stress, achieving the design requirements. To reduce beam fabrication time, a steam curing and beam storage platform method was adopted for post-tensioning of the prestressed tendons, enabling efficient and safe construction of the thin-walled mixed-tensioned U-shaped beam.

[0037] 5. The entire construction process is controlled by information technology, divided into three main workflows: information collection, data processing, and information output. This comprehensive approach ensures control over the construction process and guarantees quality. This invention continuously optimizes construction parameters through information-based management and control measures, monitors the entire U-shaped beam construction process, improves overall beam fabrication quality, and significantly reduces waste of resources. Attached Figure Description

[0038] Figure 1 Cross-sectional view of the steel strands of the U-shaped beam;

[0039] Figure 2 Longitudinal section view of the steel strands of the U-shaped beam;

[0040] Figure 3 : Reinforcement diagram for tensioning grooves;

[0041] Figure 4 Overall drawing of beam fabrication platform, formwork system, and curing shed;

[0042] Figure 5 Longitudinal section view of the beam fabrication platform;

[0043] Figure 6 : Schematic diagram of the connection between the force transmission rod and the bottom formwork platform;

[0044] Figure 7 Cross-sectional view of the reaction pier;

[0045] Figure 8 Longitudinal section view of the reaction pier;

[0046] Figure 9 : A schematic diagram of the structure supporting the U-shaped beam using a beam tensioning platform;

[0047] Figure 10 Plan view of the beam tensioning platform;

[0048] Figure 11 Cross-sectional view of the beam tensioning platform (initial state);

[0049] Figure 12 Cross-sectional view of the beam tensioning platform (after unloading sand from the steel sand box);

[0050] Figure 13 U-shaped beam verification model diagram;

[0051] Figure 14 : Model diagram of mixed prestressed tendon arrangement;

[0052] Figure 15 : Connection diagram of prestressed tendons;

[0053] Figure 16 Monitoring point layout diagram;

[0054] Figure 17 Information control flowchart.

[0055] The components include: 1. Thin-walled post-tensioned U-shaped beam; 2. Pre-tensioned prestressed tendons; 3. Post-tensioned prestressed tendons; 4. Threaded steel bars; 5. Beam fabrication platform; 6. Beam storage and tensioning platform; 7. Platform foundation; 8. Reaction pier; 9. Tensioning crossbeam; 10. Dowel bar; 11. Bottom formwork platform; 12. Tensioning holes; 13. Steel plate; 14. I-beam; 15. High-strength threaded steel bars; 16. Connector; 17. Intelligent tensioning equipment; 18. 600t jack; 19. U-shaped beam formwork system; 20. Steam curing shed; 21. Monitoring points; 22. Concrete base; 23. Steel sand box; 24. Top cover; 25. Quartz sand; 26. Sand discharge hole; 27. Base; 28. Embedded steel bars. Detailed Implementation

[0056] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the embodiments described.

[0057] Example 1: The industrialized construction method for thin-walled, tensioned U-shaped beams used in urban rail transit provided by this invention produces U-shaped beam structures such as... Figure 1As shown, the thin-walled, mixed-tension U-shaped beam 1 is designed with pre-tensioned prestressed tendons 2 and post-tensioned prestressed tendons 3. (Refer to...) Figure 2 The post-tensioned prestressed tendon 3 is a bent-up prestressed tendon with a large bending amplitude. The U-shaped beam formwork system adopts an all-steel structure and an integral design scheme. The complete formwork consists of bottom formwork, outer formwork, inner formwork, inner formwork support, inner formwork moving system and end formwork. It also includes accessories such as outer formwork diagonal bracing, inner formwork diagonal bracing and horizontal bracing, tie rods between outer formwork and tie rods between inner and outer formwork.

[0058] The industrialized construction method for thin-walled, tensioned U-shaped beams in urban rail transit provided by this invention includes the following steps:

[0059] S1. Construction of Beam Fabrication Platform and Beam Storage Tensioning Platform: After leveling the site and treating the soft foundation, construct the beam fabrication platform and beam storage tensioning platform. During the construction of the beam fabrication platform, simultaneously install the U-shaped beam bottom formwork, outer formwork, outer formwork diagonal braces, tie rods between outer formwork sections, and steam curing shed. Figure 4 As shown.

[0060] Reference Figure 5 , Figure 6 The beam fabrication platform consists of a platform foundation (7), reaction piers (8), tensioning beams (9), force transmission rods (10), and a bottom formwork platform (11). Among these, the reaction piers (8), as the components directly bearing the tension force, must meet the tensioning requirements in terms of strength and stiffness. (Refer to...) Figure 7 , Figure 8 The reaction pier 8 is reinforced with 660×1360×20mm steel plates 13 on both sides of the reserved tension hole 12. The reaction pier 8 is connected to the base foundation 7 by a pre-embedded 600×300×20 H-beam 14 to form a steel-reinforced concrete structure, which effectively enhances the shear resistance of the reaction pier and ensures the safety of the load.

[0061] Reference Figure 9 The tensioning platform supports the bottom sides of the six pairs of thin-walled, mixed-tension U-shaped beams. (See also...) Figure 10 The beam tensioning platform 6 consists of a concrete base 22 and a steel sand box 23. (See also...) Figure 11 The steel sand box 23 is connected to the concrete base 22 via pre-embedded reinforcing bars 28. The steel sand box 23 consists of a top cover 24, quartz sand 25, a sand discharge hole 26, and a base 27. When quartz sand is released through the sand discharge hole of the steel sand box, the U-shaped beam descends onto the concrete base of the beam tensioning platform, and the stress point of the U-shaped beam changes from end stress to support stress. Figure 12 As shown.

[0062] S2. U-shaped beam reinforcement processing: The U-shaped beam reinforcement is tied and the prestressed steel strands are installed on a special U-shaped beam formwork frame. The U-shaped beam reinforcement cage is lifted to the beam fabrication platform 5 by a gantry crane.

[0063] After the S3 and U-shaped beam reinforcement cages are in place, install the embedded parts, U-shaped beam inner formwork, inner formwork support, inner formwork moving system, tie rods between inner and outer formwork, end formwork, etc.

[0064] S4. Thin-walled mixed-tension U-beam structure optimization: Based on the stress characteristics of U-beams with different spans, the sidewalls of the U-beams are used to resist the centrifugal force generated by train operation. Figure 13 The U-shaped beam verification model diagram shown can be used to calculate the sidewall thickness using the formula: h = (F × S × V^2) / 127g, where h = sidewall thickness, F is the tension control force, S is the span, V is the train speed, and g is the acceleration due to gravity. (Refer to...) Figure 1 The thin-walled, mixed-tension U-shaped beam 1 is designed with pre-tensioned prestressed tendons 2 and post-tensioned prestressed tendons 3, as shown in the reference. Figure 2 Post-tensioned prestressed tendon 3 is a bent-up prestressed tendon with a large bending amplitude. See also Figure 14 A mixed-tension prestressed tendon arrangement model diagram was used. A design verification model was established using Midas Civil to analyze the stress on various parts of the beam, concluding that the post-tensioned prestressed tendon region experiences the highest stress. To prevent failure in this region, [further details are needed]. Figure 3 C12 threaded steel bars 4 are used to make spiral bars and steel mesh for reinforcement.

[0065] S5. Prestressed tendon construction: Two tendons are tensioned simultaneously using a construction process, referring to... Figure 15 The prestressed tendon 2 is connected to the high-strength threaded steel bar 15 via connector 16. The tensioning process is as follows: initial adjustment of each tendon at one end to 15%σcon → overall tensioning to 100%σcon and holding for 3 minutes → σcon anchoring. Steam curing is used during construction. The tensioning control stress is taken as 0.7fpk + 2*At based on the actual temperature difference At between the steel tendon and the platform.

[0066] First, anchor clamps are installed one by one at the fixed end of the platform to anchor the prestressed tendons 2, and the clamps are tightened with special clamping sleeves. Then, connectors 15 are installed one by one and section by section towards the tensioning end. The two sleeves are tightened with a half-moon wrench and the prestressed tendons 2 are straightened. Finally, anchor clamps are installed one by one at the tensioning end. Tensioning is carried out using two 30t jacks to eliminate the original slack state of the prestressed tendons 2. At this time, the tensioning beam 9 bears the force. After all the prestressed tendons 2 are tensioned to 15%σcon, four 600t jacks 18 are used to control the tensioning equipment 17. At this time, the reaction piers 8 bear the force. The construction requirements can be met by strengthening the reserved openings 12 of the reaction piers 8 and pre-embedding the I-beams 13. After holding the load for 3 minutes, the stress sensor data is checked. If it is correct, the tendons are anchored (if it is less than σcon, it should be tensioned to the control stress before anchoring).

[0067] S6. Concrete Pouring and Curing: After the reinforcement, formwork, and prestressing have passed inspection, the beam concrete is poured. Pouring is done using a method of diagonal segmentation and horizontal layering, pouring symmetrically and continuously from one end to the other, with both webs facing outwards. In addition to immersion vibrators, attached vibrators are added every 2m below the outer and inner formwork to compact the thin-walled post-tensioned areas. After pouring, the steam curing shed 16 is moved along rails to the beam casting platform for curing. Monitoring points 21 are set up on both sides of the beam and at the mid-span. Figure 16 As shown.

[0068] S7. Prestressed Tendon Release and Cutting: After the concrete strength reaches 85% and the elastic modulus reaches 90%, the prestressed tendons are released. Release is performed simultaneously at both ends, with the release steps being 10%-10%-20%--20%--20%--20%, with a 1-minute interval between each step. After release, the exposed steel strands at the beam ends are cut using a manual abrasive wheel cutter (symmetrical cutting, from both sides towards the middle, from top to bottom). The exposed steel strand ends outside the beam are coated with anti-rust material according to design requirements.

[0069] S8. Beam Transfer: After tensioning, the two U-shaped beams are hoisted to the beam storage tensioning platform by a gantry crane. At this time, the beam storage tensioning platform is in the state of being supported by the steel sand box, and the automatic spray curing continues.

[0070] S9. Post-tensioned prestressed tendon construction: Post-tensioned prestressed tendon construction shall be carried out after the concrete strength reaches 95% of the design value, the elastic modulus reaches 100% of the design value, and the curing period is not less than 7 days. The tensioning process is as follows: 0→0.1σcon→0.2σcon→tensioning control stress σcon (including anchor friction loss)→holding load for 5 minutes and anchoring.

[0071] S10, duct grouting and anchor sealing: After the final tensioning is completed, vacuum-assisted grouting of the pipeline is carried out within 48 hours. The end of the pre-tensioned sleeve is sealed with epoxy mortar, and the anchor sealing of the post-tensioned section is sealed with C60 fine stone micro-expansion concrete.

[0072] S11. After the overall operation is completed, quartz sand is released through the sand discharge hole of the steel sand box, allowing the U-shaped beam to descend onto the concrete base of the beam tensioning platform. The stress point of the U-shaped beam changes from end stress to support stress. Figure 16 As shown, the U-shaped beams will be transported to the site for erection after being stored for a certain period of time.

[0073] This embodiment comprehensively and systematically solves the problems of large waste of original technical resources and low production efficiency by using beam fabrication platform, hydraulic formwork system, steel bar processing jig, and steel bar hanger, forming a set of industrialized production methods for thin-walled mixed-tension U-shaped beams for urban rail transit.

[0074] Example 2: The entire construction process is controlled by information technology, such as... Figure 17 As shown, the process is divided into three main stages: information collection, data processing, and information output. Information collection involves: 1) adjusting mix proportions according to different seasons and verifying the performance indicators of raw materials to ensure they meet design requirements before production. 2) collecting data on the actual temperature difference between the steel strands and the support, and the actual control stress of individual steel strands before construction, adjusting and optimizing the tension control stress, and using the stress acquisition device to monitor the actual stress during tensioning to determine if tensioning is adequate. 3) collecting data on curing temperature, humidity, and strength growth; proceeding to the next step once the required strength is met. 4) collecting monitoring data on the formed U-shaped beams and analyzing the main factors causing discrepancies in the monitoring data. After collecting and summarizing this information, the following benefits are achieved: 1) providing real-time and comprehensive information on U-shaped beam production; 2) optimizing construction process control through information to improve the tensioning and curing levels of U-shaped beams; and 3) providing foundational data for subsequent U-shaped beam erection, trial operation, and operation. Through information-based control, tension stress control can be verified, concrete quality improved, and process intervals reduced.

[0075] Data Processing: A standard database is established based on the concrete mix design, raw material test data, and prestressed tendon control stress design standards, and control indicators are formulated. Data is collected and compared during construction; once relevant requirements are met, the construction is deemed compliant, and the process proceeds to the next stage. Monitoring data from the formed U-shaped beams is collected to further adjust the standard database, ensuring the quality of the U-shaped beams.

[0076] Information Output: A separate file is created for each U-beam after construction, containing information on materials, construction, and monitoring, ensuring full-process quality traceability. Based on the file content, a QR code is created for each U-beam and affixed to a prominent location on the beam, linking to the file content for timely access to relevant information.

[0077] Example 3: The present invention also provides a construction system for implementing the industrialized construction method of thin-walled mixed-tension U-shaped beams for urban rail transit in Example 1, including: a beam-making platform for preparing thin-walled mixed-tension U-shaped beams, a U-shaped beam template system, a steam curing shed, intelligent tensioning equipment, and a beam-storage tensioning platform for storing thin-walled mixed-tension U-shaped beams;

[0078] The beam fabrication platform includes a platform foundation, reaction piers, tension beams, dowel bars, and a bottom formwork platform. Dowel bars are installed in the middle of the platform foundation. The bottom formwork platform is set above the platform foundation to support the U-shaped beam formwork system. Tension beams are set on both sides of the bottom formwork platform. Intelligent tensioning equipment is set at the tension beams. The reaction piers are set on the outside of the tension beams. The reaction piers are connected to the platform foundation through pre-embedded I-beams to form reinforced concrete. Tensioning holes are reserved inside the reaction piers. Steel plates are installed on both sides of the tensioning holes for reinforcement. Jacks are installed on the outside of the reaction piers.

[0079] The beam tensioning platform includes a concrete base and a steel sand box. The steel sand box is located at the outer corner of the concrete base and is connected to the concrete base by pre-embedded steel bars. The steel sand box contains a base and quartz sand filled on the base. A top cover supports the quartz sand. A sand discharge hole is provided in the middle of the steel sand box.

[0080] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. An industrialized construction method for thin-walled, mixed-tension U-shaped beams in urban rail transit, characterized in that, Includes the following steps: S1. Construct the U-shaped beam fabrication platform and the beam storage and tensioning platform on site. The fabrication platform can support the production of 2 U-shaped beams at a time. When constructing the fabrication platform, install the bottom formwork, outer formwork and steam curing shed of the U-shaped beam at the same time. S2. The U-shaped beam reinforcement bars are tied and the prestressed steel strands are installed on the U-shaped beam formwork to obtain the U-shaped beam reinforcement cage. The U-shaped beam reinforcement cage is then lifted onto the beam fabrication platform using a gantry crane and a lifting frame. After the S3 and U-shaped beam steel cages are in place, install the embedded parts, and then install the U-shaped beam inner formwork, inner formwork support, inner formwork moving system, and end formwork. S4: Optimize the side wall structure of thin-walled mixed-tension U-beams, including calculating the side wall thickness of U-beams based on the stress characteristics of U-beams with different spans, analyzing the stress on each part of the beam, and strengthening the area with the greatest stress. S5: Prestressed tendon construction is carried out using a construction process of simultaneously tensioning two U-shaped beams. The tensioning process is as follows: initially adjust each tendon at one end to 15%σcon → tension the whole to 100%σcon and hold the load for 3 minutes → anchor σcon. Steam curing is used during construction. The tension control stress is taken as 0.7fpk+2*At based on the actual temperature difference At between the steel tendon and the platform. S6: After the steel reinforcement, formwork, and prestressing have passed the acceptance inspection, pour the beam concrete; S7: First, release and cut the prestressed tendons. After the concrete strength reaches 85% and the elastic modulus reaches 90%, release the prestressed tendons. S8. After the tension is released, the two U-shaped beams are hoisted to the beam storage tensioning platform by a gantry crane. At this time, the beam storage tensioning platform is in the state of being topped by the steel sand box, and the steel sand box bears the force, and automatic spray curing continues. S9. Post-tensioned prestressed tendon construction: Post-tensioned prestressed tendon construction shall be carried out after the concrete strength reaches 95% of the design value, the elastic modulus reaches 100% of the design value, and the age is not less than 7 days. Simultaneous tensioning at both ends shall be adopted. The tensioning process is as follows: 0→0.1σcon→0.2σcon→tensioning control stress σcon→holding load for 5 minutes and anchoring. S10, duct grouting, anchor sealing, and after final tensioning, vacuum-assisted grouting of the pipeline is carried out within 48 hours. Epoxy mortar is used for the end sealing of the pre-tensioned sleeve, and C60 fine stone micro-expansion concrete is used for the anchor sealing of the post-tensioned sleeve. S11. After the overall operation is completed, quartz sand is released through the sand discharge hole of the steel sand box, so that the U-shaped beam is lowered to the concrete base of the beam tensioning platform. The stress point of the U-shaped beam changes from the end stress to the support position stress. After the U-shaped beam is stored for a specified time, it is transported to the site for erection. The beam-making platform in S1 includes a platform foundation, reaction piers, tension beams, force transmission rods, and a bottom formwork platform. The bottom formwork platform is located on the top of the platform foundation, and tension beams are located on both sides of the bottom formwork platform. Reaction piers are located on the outer sides of the tension beams. The reaction piers are connected to the platform foundation by pre-embedded 600×300×20mm I-beams to form reinforced concrete. Tensioning holes are pre-reserved inside the reaction piers, and 660×1360×20mm steel plates are provided on both sides of the tensioning holes for reinforcement. The tensioning platform for the beam in S1 includes a concrete base and a steel sand box. The steel sand box is located at the outer corner of the concrete base and is connected to the concrete base by pre-embedded steel bars. The steel sand box contains a base and quartz sand filled on the base. A top cover is supported above the quartz sand, and a sand discharge hole is provided in the middle of the steel sand box. In S4, based on the stress characteristics of U-shaped beams with different spans, the sidewalls of the U-shaped beams are used to resist the centrifugal force generated by train operation. At the same time, a design verification model is established using Midas Civil to analyze the stress on various parts of the beam, identify the steel strand area with the greatest stress, and reinforce it with C12 threaded steel bars to make spiral bars and steel mesh.

2. The industrialized construction method for thin-walled, mixed-tension U-shaped beams in urban rail transit according to claim 1, characterized in that: S5 first installs anchor clamps one by one at the fixed end of the beam casting platform to anchor the prestressed tendons, and then uses the sleeves of the clamping plates to tighten the clamps; then installs connectors one by one and section by section towards the tensioning end, and uses a half-moon wrench to forcefully tighten the two sleeves and straighten the prestressed tendons; finally, installs anchor clamps at the tensioning end one by one; tensioning is carried out using two 30t jacks. After all prestressed tendons are tensioned to 15%σcon, they are then tensioned using four 600t jacks. At this time, the reaction pier bears the force. By strengthening the reserved tensioning holes of the reaction pier and pre-embedding the I-beams, the construction requirements are met. After holding the load for 3 minutes, the stress sensor data is checked. If it is correct, it is anchored. If it is less than σcon, it should be tensioned to the control stress before anchoring.

3. The industrialized construction method for thin-walled, mixed-tension U-shaped beams in urban rail transit according to claim 1, characterized in that: The S7 tensioning process is as follows: tensioning is carried out simultaneously from both ends, with the tensioning steps being 10%-10%-20%--20%--20%--20%, and the time interval between each tensioning step being 1 minute. After tensioning, the exposed steel strands at the beam ends are cut off using a manual abrasive wheel cutter, and the exposed steel strand ends outside the beam are coated with anti-rust material according to the design requirements.

4. The industrialized construction method for thin-walled, mixed-tension U-shaped beams in urban rail transit according to claim 1, characterized in that: The entire construction process is controlled by information technology and is divided into three major processes: information collection, data processing, and information output. The information collection includes: adjusting concrete mix parameters according to different seasons, verifying the performance indicators of raw materials, and ensuring that production can only proceed if the design requirements are met; adjusting and optimizing the tensioning control stress before construction based on the collected control stress of a single prestressed tendon and the measured temperatures of the abutment and prestressed tendons; determining whether tensioning is in place based on the actual stress feedback from the stress acquisition device during tensioning; collecting data on curing temperature, humidity, and strength growth, and proceeding to the next step only after the strength requirements are met; and collecting monitoring data on the formed U-shaped beams. The data processing includes: establishing a standard database based on the design content of concrete mix proportion, performance indicators of raw materials, and design standards for prestressed tendon control stress; formulating control indicators; comparing data through information collection during construction; and determining compliance with construction requirements and proceeding to the next process once relevant requirements are met; and adjusting the standard database by collecting monitoring data of the formed U-shaped beam. The information output includes: creating a separate file for each U-beam after construction, containing three main contents: materials, construction, and monitoring; and creating a QR code based on the file content and posting it in a prominent place on the U-beam, linking to the file content.

5. A construction system for implementing the industrialized construction method of thin-walled mixed-tension U-shaped beams for urban rail transit as described in claim 1, characterized in that, include: Beam-making platform, U-beam template system, steam curing shed, intelligent tensioning equipment, and storage tensioning platform for storing thin-walled mixed-tension U-beams are used for preparing thin-walled mixed-tension U-beams. The beam fabrication platform includes a platform foundation, reaction piers, tension beams, force transmission rods, and a bottom formwork platform. The force transmission rods are installed in the middle of the platform foundation. The bottom formwork platform is installed above the platform foundation to support the U-shaped beam formwork system. Tension beams are installed on both sides of the bottom formwork platform. The intelligent tensioning device is installed at the tension beams. The reaction piers are installed on the outside of the tension beams. The reaction piers are connected to the platform foundation through pre-embedded I-beams to form reinforced concrete. Tensioning holes are pre-reserved inside the reaction piers. Steel plates are provided on both sides of the tensioning holes for reinforcement. Jacks are provided on the outside of the reaction piers. The beam tensioning platform includes a concrete base and a steel sand box. The steel sand box is located at the outer corner of the concrete base and is connected to the concrete base by pre-embedded steel bars. The steel sand box contains a base and quartz sand filled on the base. A top cover is supported above the quartz sand. A sand discharge hole is provided in the middle of the steel sand box.

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