Due to factors such as overloaded service and seismic effects, the functions of concrete columns in many buildings do not meet the requirements for safe use. Columns are important structural members. Effective reinforcement of concrete columns is very important. If they are not reinforced in time, it may affect the safety of the structure and even cause the structure to collapse. Therefore, it is very necessary to select an economical, reliable, and simple method in time.

Traditional methods of strengthening concrete columns

In the reinforcement methods of concrete columns, several methods such as the outer steel plate method and the enlarged section method are usually used.

In the specific implementation process of the outsourcing steel plate method, the steel is difficult to adhere to the surface of the structure, is not resistant to corrosion, and must be regularly rust-proof, which is a problem we often encounter.

The enlarged section method is mainly to widen and thicken the section while arranging a reasonable amount of steel bars inside. This method is effective but increases the volume and weight of the structure. At the same time, there are many inconveniences due to the numerous construction procedures and long construction period.

Therefore, traditional reinforcement has many limitations. In order to choose a simple, economical and durable reinforcement technology, carbon fiber material reinforcement technology came into being. Compared with bonded steel reinforcement, its basic reinforcement principle is the same as that of bonded steel reinforcement, but its application range is wider.

Carbon fiber reinforced concrete column reinforcement method

The carbon fiber reinforced concrete column is a carbon fiber composite sheet formed by impregnation with epoxy resin and pasted on the structural surface with epoxy resin. After the epoxy resin is cured, a new joint body is formed with the structure, and the carbon fiber sheet and the steel bar are jointly stressed. Because the carbon fiber sheets share the load, the stress of the steel bars is reduced, and the concrete and steel bars in the structure are effectively protected. The repair and reinforcement materials mainly include carbon fiber and adhesive. The reinforcement and repair effect is directly affected by the properties of these two materials.

Advantages of carbon fiber reinforcement technology

(1) Easy and fast construction

Reinforcing concrete columns with carbon fiber sheets only needs to polish the surface of the concrete, paint a specific epoxy resin, then paste the carbon fiber sheets, and finally apply a layer of epoxy resin for natural curing and curing.

(2) Basically no increase in structural weight

  The weight of the carbon fiber sheet is light, and the weight of the epoxy resin is still very light, which has little effect on the weight of the structure, and the adverse effect of the weight of the carbon fiber sheet on the structure can be ignored.

(3) It can adapt to the reinforcement of various structural shapes

Carbon fiber sheets can be cut into various desired shapes and have a very thin thickness, which is not limited by the structural shape. For example, curved beams and variable cross-section beams can be easily pasted.

(4) It can effectively close the cracks of concrete

The carbon fiber sheet is pasted on the surface of the concrete, which can effectively seal the concrete cracks. At the same time, the high-strength and high modulus characteristics of the carbon fiber sheet also restrict the generation and expansion of the concrete structure cracks, thereby effectively improving the rigidity of the concrete member.

Sectional performance of carbon fiber reinforced column

(1) The influence and treatment of the cross-section of carbon fiber reinforced concrete column

Compared with the concrete square column, the bearing capacity of the concrete column is higher than that of the concrete square column. It can be seen that the effect of the carbon fiber reinforced concrete column should fully consider the influence of the shape of the concrete column section. 

(2) Compressive performance of carbon fiber reinforced concrete columns

Under the action of axial force, the concrete cracks, and the circumferential section of the concrete increases, which stimulates the strain of the surrounding fibers, generates circumferential tensile stress, and makes the concrete in a circumferential compression state. Thereby, the compressive strength of the concrete column is improved, and the ductility of the member is greatly improved. It can be seen that the reinforcement of the concrete column with carbon fiber material can effectively improve its axial bearing capacity. When carbon fiber cloth is used to reinforce concrete columns around the circumference, the use efficiency of carbon fiber cloth is the highest.

(3) Carrying capacity performance of normal section of carbon fiber reinforced concrete columns

After the carbon fiber cloth is pasted along the axis of the column for reinforcement, it can effectively improve the flexural bearing capacity of the column and prevent the development of cracks. The effect is related to the number of fiber cloth layers. When the number of carbon fiber cloth layers increases, the reinforcement effect increases significantly. But when the number increases to a certain extent, its influence on the improvement of bearing capacity gradually weakens.

(4) Mechanical properties of oblique section of carbon fiber reinforced concrete columns

After reinforcing the concrete column with carbon fiber cloth, its ductility and shear capacity are greatly improved. The effect of the increase is related to the performance of the concrete column and the number of fiber cloth layers. When the number of layers of carbon fiber cloth increases, the concrete confinement effect will be enhanced, and its strength and ductility will be improved better. The increased shear capacity can transform the column from shear failure to bending failure, thereby effectively improving the ductility of the column. But when the number of stars increases to a certain extent, its influence on the increase in shear capacity gradually weakens. At the same time, the greater the axial compression ratio of the concrete column, the better the ductility effect of the carbon fiber reinforced concrete column. Therefore, the amount of carbon fiber cloth should be set rationally, and attention should be paid to the effect of the component's own performance on the carbon fiber cloth reinforcement effect.

(5) Seismic performance of carbon fiber reinforced concrete columns

After reinforcing the concrete column with carbon fiber cloth, the ductility and hysteresis characteristics of the concrete column are significantly improved, and the hysteresis loop becomes more and more full. At the same time, the reinforcement effect of the full-covered carbon fiber cloth of the concrete column is better than that of the strip fiber cloth. Therefore, for seismic reinforcement, the all-inclusive carbon fiber cloth reinforcement method should be preferred to the strip reinforcement. At the same time, attention should be paid to the influence of the performance of the component on the reinforcement effect of the carbon fiber cloth.