In the current highway, bridge and other engineering construction process, continuous box girder has the characteristics of simple construction, quick installation and centralized prefabrication, so it can be widely used in the current railway and highway engineering construction. Aiming at the problems existing in the operation of precast box girder, this paper briefly analyzes and introduces the corresponding key construction technologies.
A, the operation process of precast box girder
When prefabricating the box girder, according to certain standards, the process is summarized as follows: trimming the pedestal → hoisting the bottom steel skeleton → binding and burying corrugated pipes → installing the internal and external formwork of the box girder → binding the top steel bars → installing corrugated pipes with spacing → pouring the concrete of the roof, webs and bottom plates → dismantling the formwork → making the corresponding prestressed steel strand according to relevant standards → prestressed tensioning → grouting the channel according to standards → constructing the waterproof layer of the bridge deck → constructing the bridge accordingly.
Second, the construction technology of precast box girder
1. Trim the base.
In the process of actual precast box girder construction, the main contents of pedestal trimming include the actual treatment of pedestal foundation and the related design work of pedestal. When dealing with the pedestal foundation, the sundries on the surface should be removed according to certain standards first, and then 6-9% crushed stone should be mixed according to the actual situation of the surface soil layer for corresponding replacement and filling operation, and its thickness should be controlled at 25-32 cm, and heavy roller should be selected for corresponding rolling operation. When designing the pedestal, we should choose to expand its foundation with concrete at both ends of the pedestal, that is, within the range of19 of the total length of the existing pedestal, and install the corresponding rebar mesh according to the standard. In addition, it should be noted that the steel plate laid on the top surface of the pedestal must be welded firmly.
2. Template engineering
(1) bottom formwork engineering. In the process of precast box girder operation, the fixed steel bottom formwork can be made in sections, transported to the site and spliced with the bottom formwork to ensure that the center lines of all construction links are always on the same straight line. When the bottom die is preset, the compression amount is usually reserved, and the corresponding preloading work should be carried out before use. In addition, considering the current settlement situation, attention should be paid to the adjustment of precast box girder bottom formwork during operation, and the corresponding adjustment frequency should be reduced as much as possible after it is stably fixed. Before installing the formwork every time, carefully check the corresponding position of the bottom die support to ensure the flatness of the bottom die section.
(2) External mould engineering. Before installing the external mold, check whether the plate itself is flat, whether there is residual mucilage and whether the template interface is clear and clean. In addition, it should be noted that when installing the external mold, the external mold should be transported to the position connected with the bottom mold along the designated track in advance, and its corresponding hinge connection with the preset shaft should be realized according to certain standards and technology. At the same time, the corresponding height and detail size of the external mold should be adjusted and modified with jacks and corresponding adjustable screws. In addition, the bottom edge of the outer mold and the bottom edge of the pedestal need to be connected with corresponding screws, and the gap between the bottom mold and the template should be handled with high-density adhesive tape.
(3) Internal model engineering. Generally speaking, the internal model project is actually to tie the steel bars inside the bottom web in advance during construction, and then lift the internal model above the trolley in place by gantry crane and other equipment. In addition, in the process of operation, in order to make the internal formwork car pass through the end partition wall safely and make the formwork itself shrink less than the inner cavity specified by the end partition wall under the drive of its internal oil cylinder, it should be ensured that its external dimension in the open state is consistent with the hole size on the box girder surface. In addition, in order to prevent the pouring concrete from moving in the internal mold, the operator should connect the internal mold with the external mold and the corresponding end mold at the ventilation hole with bolts.
(4) end template engineering. At present, in the process of precast box girder operation, due to the dense internal steel bars at the top of the box girder, it involves a wide range, which requires us to ensure that the end formwork is convenient and concise and the joints are dense during the assembly process. It should also be noted that after the end formwork is transported to the site, the reserved holes should be checked in advance, and the actual position, related dimensions and coordinate position of the anchor pad should be carefully checked.
3. Reinforcement engineering
After the steel bar binding and embedded parts operation are completed, they should be firmly bound on the pedestal according to certain standards. For the cushion block needed for concrete protective layer, a professional mold is needed to make the corresponding quadrilateral. Furthermore, it should be noted that wired contact is required between the pad and the template. When the steel skeleton is completely bound, it needs to be hoisted in place with a gantry crane. It should be said that in the process of making steel skeleton, the focus is on the specific positioning and embedding of bellows and its corresponding embedded parts. Before embedding and positioning, the operator needs to check and adjust the pipe fittings, and then it can be finalized. Try to fix the rigidity on the corresponding steel frame by U-shaped positioning method.
Because continuous box girder has many characteristics such as simple construction, quick installation and centralized prefabrication, it can be widely used in railway and highway engineering construction at this stage. Aiming at the problems existing in the operation of precast box girder, this paper briefly analyzes and introduces the corresponding key construction technologies.
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