Application of Carbon Fiber Reinforcement Technology in Repair of Civil Engineering

Carbon fiber (CFRP) reinforcement method is highly valued and widely used in the field of civil engineering reinforcement and repair due to its high strength, light weight, corrosion resistance, and easy construction.

Application of Carbon Fiber Reinforcement

Project overview

A salt industry warehouse in Chongzuo, Guangxi is a one-story frame structure building with a span of 15m. The original roof is a general non-sovereign roof, and the use of the roof needs to be changed. After structural calculations, the reinforcement of the frame beams is too small, and the original roof beams cannot bear the added load and must be reinforced.

Comparison and selection of structural reinforcement technology

According to the actual situation of the project, several traditional reinforcement methods such as enlarged section reinforcement method and outer steel reinforcement method and carbon fiber reinforcement method can be selected. The enlarged section reinforcement method is also called the outer concrete method, which mainly widens and heightens the beam and column section to accommodate the new reinforcement. It is effective to strengthen the structure with the enlarged section method. But it will increase the volume and weight of the structure, resulting in fat beams and fat columns. In addition, there are many construction procedures, long construction period and many machines, which require a large construction site and construction space. The outer steel reinforcement method is also called the stick steel reinforcement method. The effect of sticking steel plate method to strengthen the structure is also better, but the construction process is relatively complicated. In addition, the construction process requires high flatness between the structural base layer and the steel plate, and the rigidity of the steel plate is difficult to operate. When the steel plate is pasted, it is prone to hollowing, and it is not corrosion-resistant. It must be regularly rust-proof. Therefore, the use of the above traditional reinforcement methods will be subject to various restrictions in practical applications.

The carbon fiber reinforcement method is to use a specially formulated matching bonding material to stick a carbon fiber sheet composed of continuous carbon fibers with high strength or high elastic modulus in one-way or multi-directional bundles along the direction of the force ribs on the tensile surface of the structure. After the bonding material is solidified, it is coordinated with the original structure through deformation to form a new force-bearing composite body, so that the carbon fiber sheet and the original structure are stressed together. The tensile strength of the high-strength carbon fiber sheet can reach 3400N/mm2, which is 8-10 times higher than the steel of the same section, and the elastic modulus is between 2.35×105N/mm2 and 3.8×105N/mm2. It is slightly higher than steel bars, and the elongation rate of high-strength carbon fiber is less than steel bars when under stress, so when the structure is under stress, it receives force first. With the gradual increase of the load, the deformation of the two is coordinated, and the force is shared and distributed according to a certain proportion. The performance of working together with the steel bar is very good. Since the reinforced carbon fiber material shares part of the tensile force, the stress of the original structural steel bar is greatly reduced, the structure is strengthened, and the bearing capacity is improved. Moreover, the carbon fiber is light and soft, easy to stick, and easy to construct. It does not require large-scale machinery and other fixing measures. The increase in the weight of the structure after the reinforcement is almost negligible. It has high fatigue strength, good durability and corrosion resistance, and the reinforcement work can be completed in a short time. 

By comparison, it was decided to use carbon fiber (CFRP) for reinforcement.

Application of carbon fiber reinforcement

1 beam-slab structure reinforcement

(1) Anti-bending reinforcement. The carbon fiber sheet is pasted on the side under tension, that is, the lower part of the beam and the middle of the beam and the upper part of the continuous plate, continuous beam, cantilever plate and other supports, and pasted along the direction of the force rib.

(2) Shear reinforcement. The reinforcement position is usually at the end of the beam, the area where the main tensile stress is large, and where there is a secondary beam or concentrated load. When reinforcing, stick carbon fiber sheets vertically on both sides of the beam, or form a U-shaped loop with the bottom of the beam, which is equivalent to adding shear stirrups to share the shear force of the original stirrups.

2 column reinforcement

(1) Flexural reinforcement of the column. The eccentric compression column is pasted with carbon fiber sheet along the longitudinal axis of the column axis on the side of the tension bend, which can be effectively reinforced.

(2) Compressive reinforcement of the column. The middle part of the column is wrapped with a carbon fiber transverse ring to produce a ring constraint effect on the compression zone to improve the compressive capacity of the column and reduce the buckling coefficient of the column. Relevant experiments have proved that the compressive bearing capacity of concrete columns can be improved to varying degrees by using CFRP sheets of different specifications for reinforcement.

(3) Shear and seismic reinforcement of the column. Under the action of lateral force, the bending moment and shear force at the column end are very large. If longitudinal pasting and ring wrapping are performed at the same time, the lateral shear resistance of the column can be improved, and the ductility of the column can be significantly improved, the hysteretic energy dissipation capacity is enhanced, and the seismic capacity is significantly increased.

3 Shear wall reinforcement Paste carbon fiber sheets along the direction of shear reinforcement on one or both sides of the shear wall.

4 Reinforcement of masonry structure Use CFRP sheet to strengthen the masonry structure horizontally and diagonally, which can improve its seismic performance.

In addition, carbon fiber reinforcement can also be widely used in other civil engineering such as bridges, tunnels, chimneys and silos.

In summary, carbon fiber reinforcement can be a reliable and convenient method of structural reinforcement, and it has extremely broad application prospects.

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