Construction process of plastic bellows.
The construction of the plastic bellows adopts the backward wear method, that is, the steel bundle penetrates the hole before the prestressed tension and after the concrete is poured and formed. On the one hand, the prestressed steel strand can avoid the rust caused by the long-term exposure to the hole, and on the other hand, the concrete pouring, bellows installation, and bunching are staggered during the construction process, which can significantly improve the work efficiency.
The specific steps of the construction of the plastic bellows back thread method are as follows:
1) Calculation: The spatial geometry model is used to accurately calculate the length parameters of the vertical bending and finger level of the main control points of the plastic bellows.
2) Marking: The calculated results are compared with the construction drawings, and the positions of different control points are marked with different colors of paint, and the length of the plastic bellows is intercepted according to the position, and the position of the bellows joint and the reserved length should be paid attention to here.
3) positioning curve: pull a reference line along the parallel direction of the bridge bottom plate, mark the bridge section of the control point (including horizontal and vertical curves), and then determine the bridge section of each other control point according to the position of the bridge section and use different colors of paint to assist marking, convenient for installation.
4) Support: Use transverse reinforcement to support the vertical position in the bellows space, and it should be noted that although it is a rough support, it is still necessary to maintain the accuracy of the position of each control point.
5) Reinforcement: Refer to the construction design drawing, according to the positioning of each control point, the layout and encryption positioning of the anti-collapse reinforcement.
Key points of quality inspection in the later stage of plastic bellows construction.
After the vacuum grouting construction is completed, its quality should be checked regularly, and the specific inspection items include:
1. The ball valves at both ends should be removed within 5 hours, and the cement slurry state of the slurry hole and the slurry hole on the anchor backing plate should be observed.
2. Two days after the completion of construction, observe the grouting hole, and the hardened cement slurry in the grouting hole is slightly convex, indicating that the cement slurry is full of filling and has few bubbles.
3. 30 groups of different specimens from 10 work classes are extracted for strength testing, and if the average cement strength exceeds 30MPa, it means that the expected requirements are met.
Plastic bellows material with vacuum-assisted grouting is a set of effective processes to improve the construction quality of highway bridges, and has been used in many projects.