Reinforcement of overrun bridges in active service

Bridge Overview

The old bridge, built in 1966, has a net width of 10.5m and a bridge length of 26.4m. 3-span, combined beam-type simply-supported beam, design load steam-l0 level, calculated span length 8.8m In 1986, in order to meet the traffic requirements, the two sides of the original bridge were widened by 8m, and the widened part was a 3-span continuous beam. The design load was steam-20. The old bridge has been in overload service and has been listed as a dangerous bridge according to the industry standard.

The main problems of the old bridge

Each main beam has some cracks, the average crack spacing is 45cm, and each beam has 10 to 15 cracks. Each beam has several cracks extending to the top of the beam, the remaining cracks are about 40em high, and the width of the crack is about 0.2mm

The test result shows:

① There are many cracks along the tendon at the bottom of the main beam, and the concrete of the protective layer is cracked severely, resulting in bare steel bar corrosion;

② There is a curved crack in the overhanging part of the cover beam, and there are a few fine cracks in the reverse bending area;

③The average value of carbonation depth is 25.11mm, the average value of steel reinforcement cover is 32.8mm, and the strength grade of concrete of main beam and cover beam is C20 after testing;

Maintenance and repair

The maintenance and reinforcement adopts the scheme of sticking carbon fiber on the bottom and sides of the main girder and the cover girder 

1 Test to strengthen the side elevation of the small beam

The carbon fiber cloth pasted on the top and sides has a limit of 40% higher load capacity than only bonded carbon fiber cloth on the bottom.

2 Main girder and slight bend plate

3 Main girder reinforcement

4 Cap reinforcement

Conclusion

1) Use carbon fiber cloth to repair and strengthen the old bridge. The construction period is short and the impact on traffic is small. The reinforced bridge beam is still in use today.

2) Comparing maintenance and repair with dismantling and reconstruction, the funds are only equivalent to 22.23% of the reconstruction, and the construction period is only one-third of the reconstruction. The economic and social benefits are significant.