Accurate installation of permanent bearings and temporary bearings, and at the same time, check the top elevation and elevation difference of bearings with a level gauge and spirit level to ensure that the installation of bearings meets the specification requirements.
Third, the underlying structure
(1) Pile caps and tie beams
1, foundation pit excavation
It is proposed to adopt the construction scheme of combining mechanical excavation with manual trimming. Backhoe hydraulic excavator is used for excavation, and the slope is controlled at about 1∶0.75. After digging to the basement design elevation, pour 10cm thick low-grade concrete cushion. Use submersible pump or well point for dewatering and drainage.
2. Steel structure
After the digging pile is completed, the reinforcement at the pile head is made into a trumpet shape, and then the reinforcement is bound. Clean the pad and pop up the control line. Tie and shape according to the requirements of construction drawing.
3, template support
The formwork adopts large-area steel formwork, and sponge strips are pasted between flat-fell seams to prevent slurry leakage at the joints of the formwork.
4, concrete pouring
The concrete is mixed by the mixing station, transported to the site by the concrete mixer and poured by the pump. Concrete shall be poured in layers, with the thickness of each layer being 30cm, and vibrated by six 50-type vibrators. After concrete pouring is completed, the surface shall be leveled immediately. In order to avoid shrinkage cracks, secondary pulp collection treatment should be adopted. Except for the column part (rough surface), the surface of the bearing platform and tie beam should be calendered. After concrete pouring, cover it with straw curtain or sack and spray water for curing.
(2) Pier and abutment
The piers and abutments of bridges and passages are reinforced concrete masonry. There are column piers, column platforms, ribbed platforms and thin-walled platforms.
1, steel processing and binding
Firstly, the contact range between concrete and concrete is chiseled to remove laitance. Steel processing is carried out in the steel processing plant, and steel bars are bound and welded after being transported to the construction site. Welding and binding of steel bars shall be carried out according to the requirements of specifications.
2. Template
Large-scale composite steel formwork processed by the factory is used for the concrete construction formwork of pier and abutment, and the steel formwork must be brushed with release agent before installation. In order to facilitate the use and installation, the pier formwork is made into 2-4m segments, which are assembled on site according to different heights. After the template installation is completed, check and correct it, and reinforce it after the error meets the design requirements. The formwork is reinforced by steel pipe scaffolding, and a layer of wind rope is set every 4 meters in the vertical direction for the column pier formwork to ensure the stability of the formwork and prevent the overall deformation. Use rubber pad at the interface of formwork to prevent slurry leakage. Place concrete cushion blocks between steel bars and formwork to ensure the thickness of protective layer of steel bars and the appearance quality of concrete.
3, concrete pouring
Concrete is mixed by concrete mixing station, transported by concrete mixer truck, and hoisted into the mould by truck crane. Concrete shall be poured and molded once, and string drums shall be used to prevent concrete segregation caused by excessive drop. The free dumping height of concrete shall be within1.5m. The concrete shall be vibrated by internal vibrator, and the vibrating time and method shall be controlled as required, so as to make the poured pier fully dense and smooth. In order to prevent shrinkage cracks on the pier top, secondary vibration and ballast treatment must be carried out.
4. Maintenance
Concrete curing adopts the method of wrapping plastic sheets on the surface and spreading wet sand with a thickness of 10 cm on the top of the column to prevent concrete surface from cracking.
(3) Pier cap
1. Support: Bowl-button support is adopted, and 50cm thick gravel cushion is paved after the ground is compacted, or 30cm 10% lime soil is used to treat it, and the square wood is used as the support foundation, so the Bowl-button support is erected. In order to ensure the stability of the support, oblique shear braces should also be set up. Vertical and horizontal squares are laid on the support, and the bottom die is laid on it.
2. Formwork: large-area steel formwork shall be used for formwork, the pull screw shall be fastened, the diagonal brace shall be stable, and plastic foam shall be added at the joint of formwork to prevent slurry leakage.
3. Reinforcement: After the reinforcement is processed in the processing plant, it is transported to the site, bound and shaped, and then hoisted into the mold, or bound and shaped on the bottom mold.
4. Concrete pouring: concrete is mixed in the mixing station, transported by concrete mixer, and put into the mould by truck crane. The pouring sequence is: first in the middle, then at both ends, and finally at the top of pier, so as to prevent concrete from cracking due to deformation of support.
5. Form removal: the side form can be removed when the compressive strength of concrete reaches 2.5MPa, and the bottom form can be removed when the concrete strength reaches 90% of the design strength. The concrete surface is covered with sacks and cured by sprinkling water.
(4) capping beam
Low pier adopts steel pipe scaffold to install capping formwork, and high pier can adopt hoop support construction method, and hoop should have sufficient safety factor during construction. Put the cross beam and longitudinal beam on the hoop, then lay the bottom die, install and process the semi-finished capping beam reinforcement, and pay attention to the equipment for supporting the embedded reinforcement of the cushion stone. Set up formwork, build pouring platform, check, accept and pour concrete of pile caps. The capping beam formwork adopts large steel formwork, sponge strips are clamped at the joints to prevent slurry leakage, and the board surface is brushed with release agent to ensure the concrete quality is solid inside and beautiful outside. When pouring concrete, the elevation must be strictly controlled to prevent the elevation of beam bottom from exceeding or lower than the design elevation.
The leveling of the pier top surface and the bearing of the capping beam should be cast and molded at one time, and mortar mixing is prohibited. When the construction is difficult, the thickness of leveling layer should be reserved when pouring the capping beam, and the capping beam should be chiseled and shaped.
(5), construction matters needing attention
This project is located in the alluvial plain of the Yellow River, with serious salinization, and the following points should be paid attention to during construction:
1, the reinforced concrete substructure works below the normal water level shall be coated with epoxy resin or materials agreed by the supervision engineer for anticorrosion treatment, and the depth shall reach the bottom of the cap or tie beam.
2. Drinking well water must be used for concrete mixing and curing.
3. The thickness of concrete protective layer should be strictly guaranteed during construction.
4, capping beam bracket or hoop bottom die to preloading test, after passing, and then the steel binding process.
Fourth, the superstructure
The Tuhaihe Bridge adopts simply supported box girder first and then continuous box girder, the middle bridge and separation overpass adopt pretensioned prestressed concrete hollow slab, the overpass bridge adopts ordinary concrete continuous box girder and prestressed concrete continuous box girder, and the passage adopts hollow slab and solid slab. According to the number and distribution of precast slabs, the prefabrication factory decided to set them on the right side of K4 1+300, which will be beneficial to assembly line and industrial production when making beams.
The prefabrication yard shall be leveled by bulldozer and rolled by smooth roller, especially the beam groove and beam storage area must be compacted tightly, and the drainage equipment should be unblocked to prevent the beam groove from cracking or the beam body from tilting due to uneven ground settlement during beam storage. On-site roads, yards, concrete mixing stations and living quarters are hardened with 10cm gravel cushion and 10cm plain concrete.
(1) Tension the prestressed concrete hollow slab first.
There are 10m and 20m pre-tensioned prestressed concrete hollow slabs in this contract section.
1, prefabricated pedestal
Make a drainage groove around the beam groove to facilitate the flushing of the beam groove. 30# concrete is used for the beam slot force transmission column, and 25# concrete is used for the beam-making pedestal. The surface is terrazzo surface, which is smooth and polished.
2, template processing
The external mold adopts the large steel template processed by the factory, and the core mold adopts the wooden mold. According to the requirements of the quantity and time limit for a project of various hollow slabs, the processing templates are reserved.
3, steel strand tension
(1) Preparation before tensioning
Firstly, the tensioning equipment is calibrated to determine the relationship curve between tensioning force and instrument data. Before and after the steel strand enters the site, it should be sampled and inspected separately, and it can be used only after it meets the design requirements. Steel strand is cut by grinding wheel cutter, and electric welding is strictly prohibited. When the steel strand passes through the beam, the surface of the pedestal should be padded with colored cloth strips to prevent the release agent on the bottom die from polluting the steel strand. Before formal tensioning, try to pull and check the pedestal. After the bottom die and pedestal meet the requirements and are accepted by the supervision engineer, formal tensioning can be carried out.
(2) tensioning procedure
Use YC300 small jack to pull a single steel strand to the initial stress, and then use two YC2000 long-stroke pedestal jacks for overall tensioning.
0→ initial stress →σcon (anchor with load for 2 minutes)
Tension should be carried out in strict accordance with the operation procedures of jack and high-pressure oil pump, and there should be special personnel to direct tension at both ends.
When tensioning, the elongation value should be measured after adjusting to the initial stress. In addition to the measured elongation value, the actual elongation value should be added with the elongation value calculated according to the initial stress. Through the dual control of stress and strain, the difference between the actual elongation value and the theoretical elongation value is controlled within 6%.
4, steel processing, binding
Steel processing is completed in the steel processing plant. After 24 hours of tensioning, the steel bars will be transported to the pedestal and directly bound and formed on the pedestal.
5. Model
After the reinforcement cage binding is completed, the formwork can be erected. When the formwork is installed, the joints must be tight and reinforced firmly to prevent slurry leakage and formwork leakage during concrete pouring.
6, concrete pouring
After the concrete is mixed in the mixing station, it is transported by a small dump truck, poured into a hopper, and hoisted into the mold by a gantry crane. Plug-in vibrators are used for vibration. When vibrating, it is forbidden for the vibrator to collide with the prestressed steel strand. Concrete shall be poured in layers, each layer shall not exceed 30cm, and the bottom plate, rear side plate and top plate shall be used for construction in turn. Concrete curing adopts gunny bag covering and water spraying curing.
The above are collected and sorted by Zhong Da Consulting Company.
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