The U-shaped beam is an advanced and novel concrete beam structure form. It has an ideal and beautiful appearance and can significantly reduce the overall structural height and construction complexity of subway viaducts. Currently, U-shaped beams are widely used in the construction of urban subway viaducts. During the prefabrication process, we can start with links such as prefabricated beam platforms, prestressed pipelines, U-shaped beam reinforcement treatment, formwork construction, concrete construction, and curing to improve the application level of U-shaped beams in subway viaduct construction and promote urban construction and development.

1. Prefabricated beam platform construction technology

The prefabricated beam platform is the main construction link of the metro viaduct project and the basic link for carrying out the U-shaped precast beam platform of the subway viaduct. This has a significant impact on the overall project's construction quality. To enhance the construction quality of the precast beam platform, technicians should work in conjunction with the foundation and soil conditions at the construction site of the project and specific construction technologies. Under normal circumstances, technicians can use 30.0 cm of limestone and lime soil with a concentration of 8% for replacement work, and also combine 95% of the standard compacted subgrade to ensure that the construction density and bearing capacity of the bridge base meet the standard requirements. After completing this construction link, technicians can use concrete with a strength of C15 for cushion hardening treatment and control the thickness of the concrete to be about 10.0 cm. During construction, technicians should set up corresponding drainage ditches around the pedestal to prevent water from soaking the foundation and maintain stable construction quality.

2. Prestressed pipeline technology

The prestressed pipeline is the main structure of the U-shaped bridge of the metro viaduct. Technicians should select pipelines with large load-bearing capacity, such as bellows and rubber extraction pipes, and fix the pipelines with steel mesh. Technicians should strictly control construction errors and strictly control the construction link of prestressed pipelines to ensure that the entire construction process follows the design plan details. When extracting rubber pipes, technicians should place the mandrel in the rubber pipe and control the diameter of the mandrel to be less than 8mm. Furthermore, technicians should install the rubber hose joint in the mid-span position. And put a rubber hose to the joint. During the sleeving process of the rubber hose, technicians should control the length of the rubber hose and ensure that the gap between the iron sheet and the rubber hose does not exceed 1mm for sealing. When processing the prestressed beam bellows, it is necessary to strictly follow the relevant regulations, control the deviation data, and ensure it does not exceed 5mm. It 's important to specify the specifications of the reinforcement cage and the bellows and fix them together to prevent displacement during construction.

3. U-shaped beam reinforcement treatment technology

The U girder construction is a crucial component in the U-shaped prefabricated metro viaduct construction. Technicians should make samples that meet construction standards, guarantee bending accuracy, and strictly control the detail dimensions. In the specific construction, technicians should select a special fetal membrane for binding. If abnormal-shaped steel bars are found during the bending process of the beam body, technicians should analyze the steel bar bending method in time, find solutions, control the reinforcement protection layer and size to meet construction standards. Furthermore, technicians should mark the position of the binding steel bar line and bind it with galvanized steel wire at the point where the steel bars intersect. To prevent steel bar leakage, technicians should fix the skeleton with wire tie ends and ensure that the steel bars of the U-shaped beam and the longitudinal bars are vertically intersected. The bar elbows are longitudinally distributed along the axis to enhance the stability and strength of the reinforcement cage.

4. Formwork construction technology

Under normal circumstances, the standard bottom plate is composed of the beam body in the U-shaped girder structure and the bases at both ends. The ground beam serves as the foundation. To adjust the bottom formwork, the length of both ends of the beam must be fully considered. If the two ends of the beam are too long, it will affect the overall stability of the U-shaped beam. Technicians should ensure that the surface of the U-shaped beam is flat, use bottom formworks produced in the same batch and with the same model parameters to avoid readjusting the bottom formwork later. Technicians should choose an embedded end formwork and arrange the lower part in the form of a cavity through which the steel bar wire can pass. And strictly control the bottom formwork and the center line position, and height of the side formwork before assembly to improve the safety performance of the application of construction technology, ensure the smooth progress of construction, and prevent accidents. Bolts are required to fix the side formwork. Screws are needed to fix the bottom position of the U-shaped beam and geometrically fix its upper part. Fix the screws on the steel formwork, adjust the bottom with sawdust, connect the outer formwork and the bottom formwork, and set an appropriate sealing strip in the middle. After installation is complete, technicians need to check each part and connection to avoid loose connections and ensure the stability of the U-shaped beam body. Once confirmed, pouring can be carried out.

5. Concrete construction technology

In the concrete construction, technicians should strictly control the quality of materials such as cement. Conduct quality inspections before entering the site, take corresponding samples, and enter the laboratory for testing. Only after meeting the construction standards for cement quality and initial setting time can they be stored on site and construction can begin. During construction, the sand material should be strictly screened to remove excess impurities and select high-quality coarse aggregate for mixing. During mixing, technicians should strictly control the water-cement ratio and improve the slump level. Before pouring construction, check the material details and strictly observe the formwork, steel bars, and concrete parts to ensure the steel bars are in the correct position and improve the construction level. Technicians should oversee vibration technology, select an appropriate vibration device, and control the length of the vibrator to be about 80% of the pouring thickness. At the support plate and the end formwork, technicians should strengthen the vibration intensity to ensure that the concrete is securely attached to the vibrating part and avoid bubbles. Also, make sure the vibrating rod is always parallel to the concrete. If it is inclined, the angle needs to be controlled between 30° and 45°.

6. Concrete curing technology

In the construction of metro viaducts, the main form of concrete curing is steam curing. Technicians select a suitable steam boiler, control the boiler planning, select steel pipes of corresponding specifications as the main steam pipeline, and use steel pipes with a diameter of DN50mm as branch vent pipelines. Drill holes evenly on the pipeline, control the hole size to be φ3mm, and control the hole spacing to be 300mm. Set up drainage ditches. During the curing process, technicians can use 2 to 3 multi-point fully automatic alarm thermometers to monitor and alarm the ambient temperature and surface temperature respectively. Set the alarm temperature between 48°C and 45°C. If the difference between the surface temperature of the U beam body and the ambient temperature is too large, an automatic mechanism to increase or decrease the heat will be activated to avoid beam cracking caused by excessive temperature difference. After curing, it will enter the natural curing stage.

 Summary

This article details the prefabrication construction technology of U-shaped beams for subway viaducts, including prefabricated beam platforms, prestressed pipelines, reinforcement treatment of U-shaped beams, formwork construction, concrete construction and curing technology. All technologies strictly control quality and ensure construction safety and stability.

 Let's pay attention to these advanced construction technologies together and strictly implement them in actual projects to contribute to the construction of metro viaducts.