Externally bonded carbon fiber reinfroced(CFRP) fabric on RC column

3 columns in the building have vertical cracks, the corrosion of the main tendons and stirrups is heavy, which leads to the reduction of the effective area of the original force and the serious loss of the concrete in the root. So choose carbon fiber reinfroced polymer fabric(CFRP) for column strengthening

Externally bonded carbon fiber reinfroced(CFRP) fabric on RC column


Project overview

An office building with a length of 68 m, a width of 16m, a building area of about 8900 m2, an underground layer, seven floors on the ground, a frame structure and a raft foundation, invested in 1980 and put into use in the following year. When redecorated, it is found that there are 3 middle columns in the two and three stories in the middle of the building, and the cracks in the root of the column are serious. The concrete peeling in the column root is serious, and the corroded column longitudinal tendons can be seen obviously. It is found that the above 3 columns in the building have vertical cracks at about 1 m from the root of the column, the maximum seam width is 2.5 mm, the corrosion of the main tendons and stirrups is heavy, which leads to the reduction of the effective area of the original force and the serious loss of the concrete in the root, which has reduced the column section to a different degree. In addition, there are several serious cracks in the frame beams, all of which need reinforcement. This article only introduces the columns reinforcement .


Based on the project, choose carbon fiber reinfroced(CFRP) fabric for columns strengthening.


Choice of strengthening method

At present, the commonly used methods for strengthening reinforced concrete columns are: enlarging column section method, wrapping steel jacketing method and wrapping FRP material method. The wrapped steel method is more effective than the reinforced concrete section method, because the enlarging section method makes the structure's weight and section size increase greatly. The two methods are more artificial and sometimes difficult to construct. In addition to heavier steel, the ability of steel encircling to resist adverse environmental erosion is poor.


In recent years, FRP material (including CFRP, GFRP, AFRP, etc.) has been used to reinforce reinforced concrete columns as a new reinforcement method instead of steel encased. The method has the advantages of high strength, high efficiency, convenient construction, good durability and corrosion resistance, thin thickness, light weight and so on. Among them, the most common form of FRP reinforced columns is wrapped fiber cloth or strip. The project chooses carbon fiber cloth to reinforce it.


There are several different processes for reinforcing the reinforced concrete column with FRP material. According to the forming process, the reinforcement method can be divided into three kinds: wet stick method, continuous filament winding method and prefabricated shell method. The most commonly used method is the wet bonding method, which has the outstanding advantages of large flexibility and easy to operate in the field. This method is selected by this method, and the unidirectional fiber cloth is wrapped on the surface of the column by resin infiltration, so that the direction of the main fiber is along the ring of the column. The column can be completely wrapped by single layer or multi-layer fiber cloth, and can also be partially wrapped by a continuous spiral hoop or spacer hoop. In this project, carbon fiber cloth is completely wrapped and strengthened.


The section size of the rectangular column in this project is 500 mm x 550 mm. Considering that the confinement effect of the CFRP hoop to the rectangular column is poor, it can provide a very effective constraint to the circular column, so the section of the rectangular column in this project is cross section. The shape is first modified to ellipse and constrained by carbon fiber cloth hoop.


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