Generally, the main reasons for structural strengthening are as follows:

(1) The structural load increases, such as caused by changes in the use of the building;

(2) Due to design and construction errors, insufficient reinforcement, insufficient component section or concrete strength cannot meet the design requirements;

(3) The structure is damaged, such as material aging, steel corrosion, unpredictable external load damage (vehicle impact), etc.;

(4) The structure needs to improve its seismic performance.

[Example 1] When the main body of a building in Guangzhou was completed for decoration, the use of some areas changed significantly. The owner changed the ordinary office into a UPs computer room, which greatly increased the floor load. Therefore, carbon fiber plates and carbon fiber cloth were used to reinforce part of the floor beams. Field load tests were carried out before and after reinforcement, and the results show that the reinforced structure meets the requirements for use. At the same time, the negative reinforcement of the floor slab of the building was stepped on and deformed during the construction process, making its position unable to meet the requirements, which is also a common malpractice in building construction. The floor slab is also reinforced with carbon fiber plates to resist the negative bending moment.

[Example 2]  In a commercial and residential building in a certain area, it was found that the strength of the concrete test block was unqualified during the construction process. After testing, it was found that the strength of some of the columns did not meet the design requirements, and analysis believed that it was caused by cement and construction. The design department rechecked the structure after changing the wall to a lightweight wall and lowering the concrete strength level. As a result, the axial compression ratio of some columns still exceeded the specification limit. At the same time, due to the commercial and residential nature of the building, the owner requested that the cross section of the column after reinforcement should not be enlarged, otherwise the use and aesthetics would be affected. After research by the reinforcement construction unit and the owner’s design department, it was decided to use carbon fiber cloth to reinforce this part of the column, which will passively restrain the column concrete in order to improve the compressive strength of the concrete. The building has only the frame part built before reinforcement, and a large amount of load such as the wall has not been applied. After reinforcement, this part of the load is applied, which is more conducive to the restraint of the high-strength carbon fiber material on the column concrete.

At present, the above two carbon fiber structure reinforcement projects have been completed with good results, and the buildings will soon be put into use.

The advantages of carbon fiber structural strengthening reinforcement

Compared with traditional reinforcement methods, the advantages of carbon fiber structural strengthening reinforcement are shown in the following aspects:

(1) It can be widely used in various types and shapes of structures and various parts of the structure. It can be used in buildings, bridges, tunnels, culverts, etc.; it can be used in structures with regular shapes. It can also be used for circular or curved structures. At the same time, carbon fiber reinforcement hardly changes the shape and appearance of the structure, which is unmatched by traditional reinforcement methods.

(2J High strength and high efficiency. Carbon fiber materials have excellent performance, not only high-strength types, but also high elastic modulus types. These characteristics can be fully utilized in reinforcement projects to improve the mechanical performance of the structure and achieve the purpose of efficient reinforcement.

(3) The reinforcement density is much lower than that of steel, so the additional load generated on the structure is small. If the carbon fiber cloth is used for reinforcement, the weight added after pasting is less than 1kg, and the thickness is only about 1mm, which will affect the weight and size of the structure. Very small.

(4) Convenient construction. Due to the low density of carbon fiber material, it is convenient to cut the material, and its reinforcement construction has good operability. There is no need for large construction machinery and heavy equipment, nor too much working space, and the occupied space is also small. No bolts, rivets, etc. are used for temporary fixation during the construction process, which simplifies the construction operation.

(5) The construction quality is easy to guarantee. Because carbon fiber is a flexible material, even if the surface of the structure is not smooth, the effective bonding rate can reach 100%, and it is easy to handle when bubbles are found after construction: this is impossible to achieve with bonded steel plates.

(6) It has good corrosion resistance and durability. Experiments at home and abroad have shown that carbon fiber and structural glue will not react with acids, alkalis, salts, etc. often encountered in the structure. It is also not affected by other harsh environments. This reduces the cost of corrosion and maintenance, and also protects the internal concrete structure.

Compared with traditional reinforcement methods, carbon fiber structural strengthening reinforcement has many advantages, especially in the convenience of construction operations. At the same time, in order to ensure the quality of construction, more detailed requirements are put forward for each construction step than other reinforcement methods. Although the application of carbon fiber structural reinforcement in China is in its infancy, on the basis of plan review, the majority of engineering and technical personnel should actively apply this technology in engineering practice to promote its gradual maturity.