Combined with engineering inspection, this paper expounds some common problems in bridge beam slab prefabrication, including tunnel blockage of prestressed beam slab, excessive arch of precast beam slab, thickness of top slab of formed beam slab, cracks in top slab of precast beam slab, flatness of top slab of precast beam slab, premature bearing of bridge, etc., and puts forward corresponding countermeasures.

Keywords: bridge engineering; Prefabrication of beams and slabs; Solution measures

introduce

Bridge beam and slab is a very important load-bearing structure in bridge engineering. The prefabrication quality of beam and slab directly affects the quality of the whole project and even its service life. Therefore, the construction personnel should focus on analyzing all the problems existing in the bridge construction process, and choose the best treatment measures according to the actual situation, so as to comprehensively improve the bridge engineering quality, avoid excessive frequent maintenance in operation and reduce the operation and maintenance costs.

1 summary of bridge slab prefabrication

Bridge beam slab is an important load-bearing structure of the bridge, which is mainly composed of beams and slabs, and is an integral reinforced concrete slab. According to the structural form, it can be divided into beam-slab rib and tic-tac-toe beam rib, and the volume synthesis of beam and slab should be considered comprehensively in the design and calculation process. Beam-slab is composed of one or two beams and plates, and other parts do not belong to this part of the structure. Beam-slab mainly refers to the plate and beam structure part which are parallel and coincident with the beam. During the prefabrication of bridge beam and slab, serious quality problems are also prone to occur, which seriously affects the quality of the whole bridge structure.

2 bridge beam slab precast common problems and solutions

2. 1 Blocking of prestressed beam and slab channels

Hole blockage in beam and slab is a very common problem, which usually occurs in the process of beam and slab prefabrication. Failure to take timely treatment measures has brought great trouble to the subsequent construction. Through the analysis of engineering practice, it is found that the reasons of channel blockage are as follows: ① the corrugated quality is poor, and a large amount of cement slurry is accumulated in the pipeline during the project; (2) The corrugated joint caused by unreasonable operation is not tight, and the pipeline is blocked during vibrating construction. In addition, the excessive number of bellows joints is also the main reason for a large number of slurry leakage. Solution: In the construction process, the quality inspection of corrugated pipe should be carefully carried out, which must include structural strength and stability. Only in this way can the construction quality of corrugated pipe meet the engineering requirements. When installing, carefully check whether the joint of the pipeline meets the design requirements and whether the quality is up to standard. Compared with plastic corrugated pipe, it is found that the latter has higher strength and better quality, mainly to avoid internal blockage. Construction personnel should fully grasp the specific contents of the design drawings, fully understand the structural form of the beam body, and scientifically and reasonably arrange all the steel bars, beams and corrugated pipes. Choosing reasonable vibrating and pouring methods, or using vibrating rod combined with vibrating equipment for construction, can comprehensively improve the compactness of concrete and improve the quality of vibrating construction, thus effectively avoiding concrete construction cracks. After the beam-slab formwork is installed, it is necessary to set an exhaust pipe in the pipeline to avoid blocking the pipeline. The construction of bellows is generally completed in the construction site, and reducing the number of joints can improve the quality of the whole project.

2.2 precast slab beam arch is too large.

Before the installation of precast beam and slab, it is easy to see that the mid-span deflection is much higher than the design parameters. The main reason for this situation is that the tension construction time is short, and the concrete strength is difficult to meet the design standard, or because the prestress is greater than the design parameter value. After the tensioning construction is completed, if the beam and slab are placed for more than a predetermined time, the concrete will shrink and the camber value will increase. Shrinkage mainly refers to the volume shrinkage in the process of concrete hardening. After this problem exists, the prestress will be reduced, resulting in the pre-camber of the bridge. Concrete creep is caused by long-term load, and the strain time is too long, which leads to concrete creep. Creep phenomenon leads to the pre-camber value of beam structure increasing by nearly 1 times, and the factors affecting this phenomenon are mainly divided into stress factors, environmental factors and internal factors. If there is excessive stretching in engineering practice, the pre-camber will continue to increase. Solution: In the construction process, the corresponding construction specifications and process parameters should be strictly implemented to determine the most accurate tensioning method. It is necessary to determine the construction period according to the actual situation and grasp the construction period and progress of the project. As long as the storage time of precast beam and slab exceeds the specified time, measures must be taken to control the preloading of the whole beam.

2.3 Forming beam slab roof thickness problem

The construction of precast beam and slab needs to choose one-time pouring construction technology. In the process of pouring, the final beam and slab thickness will be unqualified due to the selected template fixing method and unreasonable internal molding rod setting. The main performance is uneven thickness, and some of them are caused by the thickness not reaching the standard. In order to effectively avoid this problem, the following control measures should be taken: (1) to ensure that the collapse degree meets the design requirements. (2) Choose the best vibration treatment method and reasonably determine the vibration time. (3) Select the compression bar with higher rigidity.

2.4 Precast beam slab roof crack

In the process of beam slab prefabrication, due to various factors, many cracks will appear in the roof. There are many factors that lead to this situation: ① There is a big difference between water temperature and cement content during construction, which leads to the lag of maintenance, which in turn leads to large cracks in beam and slab; (2) During bridge construction, the temperature will be higher in summer, and if it is not maintained in time, it will lead to cracks; (3) The foundation strength is insufficient during construction, and many parts of the bridge are unevenly stressed, which leads to different degrees of settlement in local positions at this time, thus causing the bottom plate to break; (4) During the construction process, due to the unreasonable selection and stacking of tower cranes, the stress fulcrum is unstable and cracks appear. In the construction, engineers should deal with these problems according to the actual situation, and comprehensively improve the safety of construction. Solution: In the process of beam and slab prefabrication, constructors need to determine the best technical parameters of concrete mixture ratio in combination with the successful experience of the project and the site environment, so as to better ensure the pouring quality and maintenance quality. In the process of construction, if cracks are found in the top plate of beam and slab, a correct evaluation should be made according to the actual situation. If the crack exceeds the standard range, reasonable measures should be taken to deal with it. At this time, all cracks in the roof should be chiseled away, and then remedial measures should be taken to appropriately increase the steel structure.

2.5 Prefabricated beam slab top surface flatness and bristle treatment

In the installation process of precast beam, there is a link that is easily overlooked by engineers, that is, the quality treatment of the top surface of beam and slab, and the surface treatment quality of the top plate directly affects the quality of beam and slab. If measures are not taken to treat the bristles in time, the bridge deck will be damaged to varying degrees, because the bridge will be affected by external loads during use, and the connection performance will not meet the engineering requirements. Solution: In order to comprehensively improve the flatness of the top surface of precast beam slab, it is necessary to ensure the stability of beam slab connection. At this time, it is necessary to brush the top surface of beam and slab, and its depth should be 3 ~ 5 mm, and then clean the slab. Before the steel binding construction, the flatness and cleanliness of the board surface and precast beam and slab should meet the engineering quality requirements. If it is difficult to avoid treatment, it is necessary to clean up the exposed cement mortar, and wash it with a high-pressure water gun when appropriate to ensure thorough cleaning.

2.6 premature bearing of the bridge

When the pre-tensioned plate beam is prefabricated and installed, if the construction is completed, but the surface of the prefabricated beam plate does not form an integral structural form, its bearing capacity will be relatively low. At this time, if the vehicle load on the bridge deck is too large, the whole bridge will be damaged, the safety will continue to decrease and the bridge will be excessively damaged. Solution: After the completion of the bridge construction, before the beam and slab form a whole, it is necessary to designate a special person to manage it, and vehicles are not allowed to drive. If necessary, it shall be managed in coordination with the regulatory authorities.

3 Conclusion

To sum up, there are still many quality problems in bridge beam slab prefabrication. In the construction, we should correctly analyze these problems and take active measures to improve the engineering quality in an all-round way, achieve higher economic benefits and ensure the safety of bridge operation.

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