CFRP wrap for bridge strengthening

Carbon fiber reinforcement method has the characteristics of low relative density, high fatigue strength, good durability, wear resistance, convenient construction, low cost, and is not restricted by construction conditions basically does not affect the shape of the original structure.

At present, many existing bridges in China can not meet the use requirements for various reasons, and need to be strengthened. The maintenance, repair and reinforcement of concrete structures and facilities has become an urgent issue. Traditional materials are often used to reinforce relatively low efficiency, higher degree of mechanization, and usually appear after the poor durability of the problem. The special resin and carbon fiber cloth are applied to the surface of concrete according to the design requirements, so as to achieve the reinforcement effect of the structure. The mechanical properties of beams, culverts and other beams before and after reinforcement have been significantly improved. According to the experimental study, the bending properties of beams, slabs and culverts with a layer of carbon fiber unidirectional cloth can be improved by 5-8%. Compared with other reinforcement techniques such as sticking steel and shotcrete, this technique has the characteristics of small dead weight, simple construction, short construction period and good durability. Because of the advantages of high strength, high efficiency, corrosion resistance and light deadweight, CFRP has been widely used to reinforce reinforced concrete structures.

Engineering Overview

The expressway section from Nanchang to Jiujiang (section) is the main trunk line in Jiangxi Province, with a total length of 133 km. Its construction has undergone many changes, such as secondary highway reconstruction, automobile special highway widening and so on. After more than ten years of operation and use, the pavement has appeared a more serious and diversified late damage phenomenon with potential safety hazards. In view of this, the owners decided to carry out large-scale comprehensive technical transformation of Chang nine expressway. The main content of this technical transformation is to increase the thickness of the pavement structure layer by 16-25 cm on the basis of reinforcing the existing pavement structure layer. At the same time, the single pavement double-sided slope existing in some sections is changed into single-sided slope, in order to fundamentally solve the hidden danger of transverse drainage of Chang-Jiu Highway. In order to achieve the above-mentioned technical transformation purposes, all bridge and culvert structures along the line should be treated and reformed according to the above requirements, and the existing diseases of various structures should be eliminated simultaneously.

There are altogether 849 bridges and culverts along Chang-Jiu expressway, including 79 main bridges and 26 branch bridges. The superstructure is mainly composed of 13m, 16m and 20m pre-tensioned simply-supported hollow slabs. There are a small number of 8m and 10m ordinary reinforced concrete simply-supported hollow slabs, continuous box girder and I-shaped composite girder bridges. There are 303 round pipe culverts, 441 arch culverts and passages with cover plates, box and mortar masonry. Among them, there are nearly 200 open culverts and covered culverts with a small amount of filling at the top. Through investigation, no obvious structural defects were found in the structure, and the overall bearing capacity of all the structures is still good, only in specific parts such as bridge deck continuous, bridge deck pavement, rubber bearings and other weak positions appeared more damage. Therefore, in addition to eliminating all kinds of existing diseases, the emphasis of this reconstruction is to reinforce and reinforce the main line and overpass bridges, culverts and roof slabs and culverts with a small amount of fill, which are greatly affected by the road surface reconstruction, so as to achieve the goal of ensuring traffic safety.

At present, the technical status of structural reinforcement, reconstruction and repair can be generally divided into reinforced concrete thickening method, volume pre-addition method, sheet reinforcement method, isolation and Seismic Absorption method. Carbon fiber reinforcement method has the characteristics of low relative density, high fatigue strength, good durability, wear resistance, convenient construction, low cost, and is not restricted by construction conditions basically does not affect the shape of the original structure. The test results of concrete beams strengthened with FRP show that the bending stiffness increases by 17%~99% and the bending strength increases by 28%~97% under normal service load. In the shear strengthening test, the flexural bearing capacity of the strengthened members is greatly improved, about 65%~95%, which meets the seismic requirements of strong bending and weak shear.

Practice has proved that carbon fiber reinforcement technology has the following characteristics.

(1) CFRP is light in weight, without any heavy equipment during construction, and very thin without large space. It basically does not increase the weight of the structure and section size, especially in the case of the project reinforcement space is tight, it can show this superiority.

(2) The tensile strength is 10 times higher than that of ordinary steel. Reinforcement of reinforced concrete structures with carbon fibers with high bonding strength and high elastic modulus can achieve the same reinforcement effect as steel plates, while the weight of the structure does not increase, the appearance is light and beautiful.

(3) Excellent durability, because the reinforcement only uses carbon fiber and matching resin, so there will be no rust, and has acid, alkali, salt and atmospheric corrosion resistance properties, carbon fiber cloth has excellent chemical resistance.

(4) Simple construction (without large construction institutions and turnover materials), no wet operation, easy operation, good economy.

(5) good flexibility, easy cutting, suitable for any shape, wide application scope and short construction period.

Therefore, the superiority of CFRP in strengthening concrete structures is very obvious. It has wide application prospects in strengthening and reinforcing highway bridges.

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