Box girder strengthening

Project overview

The bridge length 86m, full width of 12.5m, is 11.5m. The span combination is 4*20m, the superstructure is prefabricated prestressed concrete continuous box girder, 4 beams are transversely arranged, the lower part is columnar pier, and asphalt concrete deck pavement.

Main diseases

There are 33 floor 4-4# box girder cracks and 2 oblique cracks, the maximum crack width of 0.06mm, from 3# 0-1/4 pier on both sides of the web cross range, total distribution of 27 oblique cracks, from 3# 3/8-5/8 pier across the range, there were 19 vertical cracks and 41 oblique cracks, cracks extending to the flange part the maximum width of 0.16mm.

Load test and disease analysis

The load tests on the 3 and 4 span of the bridge show that there is no obvious anomaly in the load test of the bridge.

By means of the box girder deflection, strain and discrete data of horizontal comparison, 4-1# box 4-4# box girder deflection and strain in the test process is symmetrical beam changes slightly larger, indicating that 4-4# box rigidity.

There are dense transverse, vertical and oblique cracks in the 4-4# box girder. From the distribution of the cracks, the bridge 16

Only 4-4# box beams in the box girder produce cracks, which belong to individual cases, and the cracks are mainly distributed in the center of the middle span. According to the stress characteristics of equal span continuous beam, it is concluded that cracks are formed before the transformation of structural system, and then from the quantity and distribution of cracks, the cracks are structural stress cracks.

To sum up, it is inferred that the cracks in the 4-4# box girder are due to the lack of actual prestress (loss), or the strength of the concrete is not up to the design strength.

Reinforcement scheme and construction technology

According to the design of partial prestressed concrete A-type members, the box girder appears more intensive structural stress cracks, which do not conform to the current specifications, and have a certain degree of weakening on the bearing capacity and stiffness of the structure, which affects the structural safety.

1 in the case of insufficient stiffness, the prestressed carbon plate is used to reinforce.

2 in view of the span of the component 20m, the length of the carbon plate is designed to be 16m.

3 according to the distribution of the cracks and the stress characteristics of the box beam, 2 1.4mm thick 100mm wide prestressed carbon plates are arranged, and the tensile force is 1200MPa (16.8t).

Summed up

Theprestressed CFRP reinforcement system is one of the few active reinforcement methods that can be strengthened without unloading. After completion, it can well participate in the stress system of the structure, increase the strength and rigidity of the structure, reduce the deflection and deformation of the structure, and reduce and seal cracks. At the same time, using carbon fiber

The material has the characteristics of light, high strength and aging resistance. It is almost no weight and volume after reinforcement. It is an ideal solution for bridge reinforcement.