Sectional performance of carbon fiber sheet reinforced columns

1. The influence and treatment of the cross-sectional form of carbon fiber sheet reinforced concrete columns

2. Compressive properties of carbon fiber sheet reinforced concrete columns

3. Carrying capacity of normal section of carbon fiber sheet reinforced concrete columns

4. Mechanical properties of diagonal section of carbon fiber sheet reinforced sheet concrete columns
   

5. Seismic performance of carbon fiber sheet reinforced concrete columns

The influence and treatment of the cross-sectional form of carbon fiber sheet reinforced concrete columns

Experimental research on the use of carbon fiber epoxy resin to reinforce the concrete columns (cylindrical and rectangular columns) with a circumferential ring shows that the concrete column has a higher degree of improvement in bearing capacity than the concrete square column. It can be seen that the effect of carbon fiber reinforced concrete columns should fully consider the influence of the cross-sectional shape of the concrete columns.

Among them, the carbon fiber cloth has the best effect on the circular reinforcement column, followed by the chamfered concrete column, and the rectangular cross-section concrete column is less effective. The main reason is that the effective constrained area and constrained stress of different sections are different. For the circular cross-section concrete columns, the carbon fiber cloth restrains the concrete inside the core uniformly along the circumference. When the concrete expands in the lateral direction under compression, there is a uniform lateral restraint along its circumference, and the carbon fiber cloth in the circumference can effectively exert its tensile effect until it reaches the tensile strength and is destroyed. For a rectangular section column, there are varying degrees of lateral restraint stress along the periphery of the section. Among them, the stress at the corner of the concrete column is too concentrated, and the carbon fiber cloth at the corner often fails in advance due to the stress concentration, and its tensile strength is not fully exerted, so that its reinforcement effect is not as good as that of the concrete column. In engineering practice, concrete members with rectangular cross-sections are often chamfered, and then reinforced with carbon fibers wrapped around the circumference. Generally speaking, as the chamfering radius increases, the restraining effect of carbon fiber cloth on concrete increases.

Compressive properties of carbon fiber sheet  reinforced concrete columns

According to the constraint principle of concrete, the concrete cracks under the action of axial force, the circumferential section of the concrete increases, and the strain of the surrounding fibers is excited, resulting in the circumferential tensile stress. The concrete is put under compression in the circumferential circle, thereby improving the compressive strength of the concrete column, and the ductility of the member is greatly improved.

It can be seen that the carbon fiber reinforced concrete column can effectively improve its axial bearing capacity. When the carbon fiber cloth ring reinforces the concrete column to the circumference, the use efficiency of the carbon fiber cloth is the highest. Experimental research shows that after the carbon fiber cloth reinforces the concrete column, its ductility and ultimate bearing capacity increase significantly, and its increase effect is significantly related to the number of carbon fiber cloth layers and the distance between the fiber cloth strips. When the number of carbon fiber cloth layers increases, the concrete restraining effect increases, and its strength and strain increase accordingly. When the spacing of carbon fiber cloth strips increases, the effect of concrete restraint weakens, so the number of carbon fiber cloth layers and their spacing should be reasonably set.

Carrying capacity of normal section of carbon fiber sheet  reinforced concrete columns

In the research and practice of carbon fiber reinforced concrete columns, the carbon fiber cloth is mainly wrapped around the circumferential ring, and the compressive strength of the concrete column is improved by restraining the core concrete, thereby improving its ductility and deformation performance.  

However, experimental studies have shown that in terms of enhancing the bending resistance of the column, it is better to stick carbon fiber cloth along the axial direction of the column than to stick carbon fiber cloth in the circumferential direction. The reason is mainly to make full use of the tensile properties of carbon fiber cloth, and its stress performance is equivalent to the longitudinal tensile reinforcement, which is equivalent to the increase of the longitudinal tensile reinforcement of the concrete column. Tests and studies have shown that after being reinforced with carbon fiber cloth along the axis of the column, it can effectively improve the bending 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 degree, its impact on the increase of bearing capacity gradually weakens. At the same time, the smaller the number of columns in the longitudinal tensile reinforcement configuration, the more obvious the reinforcement effect. In particular, it should be emphasized that in order to achieve a good reinforcement effect, so that the role of carbon fiber cloth can be effectively exerted, horizontal carbon fiber tape should be pasted along the circumferential direction of the concrete column, in order to prevent the longitudinal carbon fiber cloth from producing adhesive slip or end warpage.

Mechanical properties of diagonal section of carbon fiber sheet reinforced concrete columns

Under the action of earthquakes, shear failures of concrete columns often occur due to insufficient stirrups. For columns with insufficient stirrup reinforcement and shear failure, sticking carbon fiber cloth on the outside is a very effective reinforcement method. Its working mechanism is: when the carbon fiber cloth is wrapped in the circumferential direction, the concrete is in the circumferential compression state, which becomes the constrained concrete. Its compressive strength and ductility have been improved, and its shear resistance has been enhanced. The role of carbon fiber cloth is equivalent to that of stirrups in concrete columns. Experimental research shows that after the carbon fiber cloth reinforces the concrete column, its ductility and shear bearing capacity are greatly improved, and its increase effect is related to the performance of the concrete column and the number of fiber cloth layers. When the number of carbon fiber cloth layers increases, the concrete restraining effect is enhanced, and the better the effect of improving the strength and ductility. The increased shear bearing capacity can transform the column from shear failure to bending failure, thereby effectively improving the ductility of the column. But when the number increases to a certain extent, its influence on the increase of shear capacity gradually decreases. 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 reasonably, and the influence of the performance of the component on the reinforcing effect of carbon fiber cloth should be paid attention to.

Seismic performance of carbon fiber sheet reinforced concrete columns

Under the action of horizontal seismic force, the bending moment and shear force of the concrete column are relatively large, and the carbon fiber cloth can be pasted along the axial and circumferential directions of the column to effectively improve its bending and shear resistance. Thereby, the ductility characteristics of the concrete column are fully utilized, and the lateral resistance capability is improved. In order to improve its reinforcement effect, the upper and lower ends of the concrete column can be reinforced at the same time. When the lateral restraint at the upper end of the column is weak, only the reinforcement at the lower end of the concrete column can be considered. The main action mechanism of the seismic performance of the carbon fiber reinforced concrete column is: after the concrete column is wrapped with carbon fiber in the circumferential direction, the ultimate compressive strain value of the concrete is significantly increased, and the crushing of the concrete in the compression zone is delayed. In order to give full play to the plastic deformation performance of the reinforcement, thereby improving the ductility of the member. At the same time, the restraining effect of the carbon fiber cloth on the concrete is more direct and effective than the stirrup.

After the carbon fiber cloth reinforced the concrete column, the ductility and hysteresis characteristics of the concrete column were significantly improved, and the hysteresis loop became more and more full. At the same time, the reinforced effect of the carbon fiber cloth wrapped in the concrete column is better than that of the strip fiber cloth. Therefore, in terms of anti-seismic reinforcement, it is preferable to use the all-inclusive carbon fiber cloth reinforcement method as compared with strip reinforcement. At the same time, attention should be paid to the effect of the member's own performance on the carbon fiber cloth reinforcement effect.

Conclusion

In this paper, carbon fiber sheet reinforced concrete columns are briefly analyzed in terms of different cross-section forms, normal cross-section bearing capacity, diagonal cross-section bearing capacity and seismic performance. It provides a reasonable theoretical basis for the reinforcement of concrete columns, and provides a reference for more effective reinforcement of concrete columns.

Carbon fiber material is a very promising high-tech product, and its convenient, fast and reliable performance will surely have a broader prospect.