Continuous box girder reinforcement

Project overview

The bridge has a full length of 86m, full width of 12.5m, and a net width of 11.5m. The span combination is 4*20m, the superstructure is the assembly prestressed concrete continuous box girder, and 4 beams are arranged laterally; the lower structure is the column pier; the asphalt concrete bridge deck is paved.

The main diseases

There are 33 transverse cracks and 2 oblique cracks in the floor of 4-4# box girder, the maximum crack width is 0.06mm, and there are 27 oblique cracks in the 0-1/4 cross section of the 3# piers on both sides. From the 3/8-5/8 cross section of 3# pier, there are 19 vertical cracks and 41 oblique cracks, and some cracks extend to the flange plate and the maximum width 0.16mm is extended.

Load test and disease analysis

The load tests on the 3 and 4 span of the bridge show that the bridge has no obvious abnormality in the load test. Through the lateral contrast of the deflection, strain and data discreteness of the box girder, the deflection and strain of 4-4# box girder are slightly larger in the 4-1# box beam than the symmetrical box girder in the test process, indicating that the rigidity of the 4-4# box girder is slightly weak.

There are dense transverse, vertical and oblique cracks in the 4-4# box girder. From the distribution of cracks, only 4-4# box beams in the 16 box girder of the bridge produce cracks, which belong to some cases, and the cracks are mainly distributed in the center of the middle span. According to the stress characteristics of the continuous beam, it is inferred that the cracks are formed before the structural system is converted, and then the cracks are analyzed from the number and distribution of the cracks, and the cracks are the structural stress cracks. To sum up, it is speculated that the cracks in 4-4# box girder are caused by inadequate prestressing force (loss), or concrete strength during construction.

Reinforcement scheme and construction technology

1. Inadequacy of stiffness, using prestressed CFRP laminate

2. The span of the component 20m. The length of the carbon fiber lamimate is 16m

3. According to the distribution of cracks and the stress characteristics of box girder, 2pic 1.4mm thick 100mm wide prestressed CFRP laminate are arranged.