Concrete columns are the components which are mainly subjected to vertical and horizontal loads. The columns under seismic load are easily damaged. The typical failure modes mainly include the following four types: shear failure, bending failure, longitudinal reinforcement failure, bending and shear failure.

The use of externally bonded CFRP reinforcement method can significantly improve the seismic performance of columns, so that columns can have better inelastic deformation before the above failure occurs.

At present, the most commonly used seismic reinforcement method is ring bonded carbon fiber reinfroced polymer(CFRP). Ring bonded carbon fiber fabric can be regarded as additional stirrup to constrain the transverse deformation of concrete, thus improving the ductility of concrete columns. The longitudinal FRP can also be used to improve the seismic performance of columns.

The CFRP strengthened columns can significantly improve their seismic performance. There are two main methods for reinforcement: CFRP along the column and longitudinal direction.

Strengthening method of CFRP along column ring

The circumferential carbon fiber cloth is used to reinforce the concrete columns with ring girth. The reinforcement method is the same as the normal section reinforcement method of the column. Carbon fiber cloth plays a similar role as stirrup. Carbon fiber cloth restrains the core concrete effectively, restrains the concrete peeling and the buckling of the longitudinal reinforcement, so that the column has a better inelastic bending capacity, and the binding of CFRP can prevent the bonding failure and slip of the longitudinal joint joint, and the carbon fiber cloth. It can improve the shearing ability of the column. Therefore, sticking the carbon fiber cloth along the circumference of the column can prevent the shear failure, bending plastic hinge failure and longitudinal reinforcement lap failure, and improve the seismic performance of the column.

Reinforcement method of CFRP longitudinal column

It is mainly to improve the flexural capacity of the column, which requires the reliable anchorage of the end carbon fiber cloth, and the carbon fiber cloth is usually needed along the column ring. However, it should be noted that this reinforcement method will produce great additional force to the adjacent components at the same time. Therefore, it should also pay attention to the improvement of the flexural ability of the reinforced columns when the longitudinal bonding of CFRP columns, and it is not advisable to increase the flexural ability of the columns too much.