Wuning Bridge

Summary 

According to the design content of the bridge, in order to improve the construction quality and construction safety, the bridge deck paving, continuous bridge deck maintenance, and replacement of supports and expansion joints were carried out. At the same time, for the crack repair treatment method, two construction techniques of sticking carbon fiber and chemical pressure grouting are given.

Project Overview

The Wuning Bridge is located in the northwest of the county seat of Wuning County. It is a bridge built to cross the Zhelin Reservoir and is an important part of the original S222. It is one of the important passages leading to Yongwu Expressway from Wuning County. The bridge started in November 1999 and was completed in May 2001. With the economic development of Wuning County, there are more and more vehicles in the past, especially heavy or overweight vehicles, and their service life has reached 15 years. Some components have been damaged and the durability of the bridge has been significantly affected, according to the status quo of Wuning Bridge. It is very necessary to repair in time. After the implementation of the maintenance project, the improvement of the quality of use and traffic safety of the Wuning Bridge is of great strategic significance to the promotion of the economic development of Wuning County.

The total length of Wuning Bridge is 847.4m. The bridge deck width is Jingyi 12 lanes + 2x1.5m sidewalk + 2x0.25m pedestrian guardrail, and the total width of the bridge deck is 15.5m. The design load is 20 for steam, 100 for hanging, 3.5KN/M2 for crowd, and the upper structure is 6x40m+5x40m+5x40m+5x40m4 combined with 21 holes. The post-tensioned pre-stressed concrete box girder is composed of small box girder. The joints are connected by expansion joints, and the inner bridge deck is continuous. The superstructure of each span consists of 5 small prestressed concrete box beams. The middle distance of each small box beam is 300cm, the height of the small box beam is 200cm, the actual prefabricated width of the upper edge of each small box beam is 260cm, the middle beam is 220cm, and the wet joint width is 80cm. In order to enhance the overall lateral force performance of the small box girder, a diaphragm is installed at each span of the small box girder.

The piers are double-pillar piers with bored pile foundations, and tie beams are installed between the pillars and piles. Among them, the column diameter of piers 1 to 6 is 1.6m, the diameter of pile foundation is 2.2m, the diameter of piers 7 to 20 is 1.6m, and the diameter of pile foundation is 1.8m. The abutment is a double-ribbed slab platform with a rib width of 1m, a cap height of 2m, and 4 pile foundations with a diameter of 1.5m.

Bridge design content

The damaged part of the bridge is designed, and the design includes the following. The bridge deck paving, sidewalk curbs, diaphragms, main beams, continuous bridge decks, bridge pier cover beams, and abutment back walls have been repaired and designed, and expansion joints, supports and marking lines have been replaced.

This time, the bearings, expansion joints and some severely damaged bridge deck paving were replaced. Generally, the rubber bearing has serious rubber aging and even cracking after its use for about 10 years. If it is not repaired and replaced in time, it will even change the force of the main beam. Therefore, in this maintenance design, the rubber bearing was completely replaced according to the original standard. The expansion joints are blocked, anchored area defects, and rubber waterstops are damaged. All expansion joints of the entire bridge will be replaced this time.

As the existing bridge deck pavement has been in operation for nearly 15 years, the bridge deck pavement has various degrees of polished and exposed bones, transverse cracks, peeling and exposed tendons and other diseases. Therefore, under the principle of appropriately improving driving comfort and saving investment, the severely damaged part of the bridge deck pavement shall be chiseled and repaired, and a few polished and exposed parts shall be maintained intact.

Construction points and precautions、

Bridge repair and construction is a cumbersome systematic project. Although the amount of repair work is not large, the construction process is more complicated and has certain particularities. Therefore, the repair is required to be carried out by a unit with experience in the repair and reinforcement of the old bridge and corresponding qualifications, and the relevant engineering management department is required to conduct quality supervision of the construction. Pay special attention to the following points:

The bottom plate, web and top surface of the small box girder should be carefully inspected again before maintenance. The loose, peeling, and aging concrete of the small box girder should be removed, and the corroded steel bars must be derusted and then repaired with epoxy concrete. At the same time, use the hanging basket when replacing the support for construction, so as to avoid setting up the hanging basket twice.

Precautions for bridge deck paving construction:

①When removing the original bridge deck paving concrete, care should be taken to avoid damage to the small box girder, and the top surface of the small box girder should be roughened. Manually remove the concrete at the butt joint of the new and old bridge decks, and reserve 30cm steel bars for the new and old steel bars to overlap;

②Before pouring the cement concrete pavement, the 30cm steel bars reserved in the old bridge deck paving should be lap welded with the new bridge deck paving steel mesh (strict positioning). Attention should be paid to the sinking of the steel bar net in the process of pouring cement concrete, and the 2% cross slope should be set;

③Before pouring the cement concrete bridge deck pavement, the top surface of the small box girder should be thoroughly cleaned and the top surface of the small box girder should be fully moistened but no water should accumulate.

Precautions for construction process of chemical pressure grouting to repair crack

①Principle of cloth mouth: one every 25cm cloth mouth, vertical cracks require pressure injection from bottom to top: horizontal cracks require pressure injection from one side to the other:

②Chemical grouting adhesives are required to be tested for related performance indicators in accordance with the relevant specifications of A-grade adhesives. The tensile strength of the adhesive is required to be> 3Mpa, and the finished adhesive is required;

③During the construction process, the vertical cracks shall be constructed in the order of grouting first down and then up.

④The grouting nozzle should be pulled out after the grout has initially set (the general initial set time is 4h);

⑤ If new cracks are found during the construction process, they should be repaired in accordance with the above construction techniques at the same time, and the amount of work is subject to actual occurrence:

⑥The plastic injection material should have no harmful effects on the human body and the environment.

Key points of construction technology for reinforcing and repairing with carbon fiber cloth

① Grind and clean the surface of the beam body where the carbon fiber cloth is pasted. It is required to grind a fresh surface of the concrete and ensure that the flatness of the pasted surface reaches 3mm/m;

②Clean the adhesive surface with a powerful blower or vacuum cleaner to remove the dust on the surface, then wipe the surface with acetone and keep it dry;

③After cleaning and polishing the surface of the concrete, if there are depressions, use repair glue to level: the corner paste should be polished into an arc shape, and the arc radius is less than or equal to 20mm:

④ Apply the primer evenly on the surface of the concrete with a roller brush. After the glue is cured, proceed to the next process. Generally curing time is 2d～3d;

⑤Put the cut carbon fiber cloth on the base layer coated with the adhesive, and then use a special roller to roll the surface of the carbon fiber cloth along the fiber direction for many times. Make the adhesive fully soak the carbon fiber cloth, and make it smooth and without bubbles. When cutting and using carbon fiber sheets, keep them away from the power source and pay attention to fire prevention:

⑥After the pasting is completed, the pasting density should be checked, and it is required to reach 99% or more. If foaming or hollowing is found, the needle pipe grouting method should be used to reinforce it. If the density is less than 95%, it is required to re-bond after removal:

⑦The surface should be protected by plastering or spraying fireproof paint. The color and model of plastering or fireproof paint shall be determined by the owner:

⑧After the reinforcement construction with carbon fiber cloth is completed. The bonding strength tester should be used to inspect the construction quality of the carbon fiber sheet and the concrete structure on site:

⑨The glue material used should be harmless to the human body and the environment.

Conclusion

According to the design content of the bridge, the bridge deck paving, sidewalk curbs, diaphragms, main beams, continuous bridge decks, bridge pier cover beams, and bridge back walls are repaired. And for the replacement of expansion joints and supports, construction points and precautions are given. The construction techniques of sticking carbon fiber cloth and chemical pressure grouting are introduced in detail. The bridge passed the completion acceptance inspection and reopened to traffic in July 2016, and its use effect has been significantly improved.