Concrete columns are members that mainly bear vertical and horizontal loads, and columns are easily damaged under the action of seismic loads. Its typical failure modes mainly include the following four categories: shear failure, bending failure, longitudinal reinforcement lap failure, and bending shear failure.

The use of external bonding carbon fiber reinforcement method can significantly improve the seismic performance of the column, so that the column can have better inelastic deformation before the above-mentioned damage occurs.

At present, the most commonly used method of seismic reinforcement is to stick carbon fiber wrap outward along the column ring. The carbon fiber wrap pasted in the circumferential direction can be regarded as an additional stirrup to restrain the lateral deformation of the concrete, thereby improving the ductility of the concrete column. Carbon fiber wrap can also be applied longitudinally to improve the seismic performance of the column.

The use of carbon fiber wrap to reinforce the column can significantly improve its seismic performance. There are two main types of reinforcement methods: sticking carbon fiber wrap along the column ring and longitudinally bonding carbon fiber wrap.

1. The reinforcement method of sticking carbon fiber wrap along the column ring direction

The ring-shaped pasted carbon fiber wrap is used to form the ring-shaped surrounding beams for the seismic reinforcement of the concrete column, and the reinforcement method is the same as the normal section reinforcement method of the column.

Carbon fiber wrap mainly plays a similar role to stirrups. The carbon fiber wrap forms an effective constraint on the core concrete, which can suppress the spalling of the concrete and the buckling of the longitudinal bars, so that the column has a good inelastic bending deformation ability. In addition, the binding force provided by the carbon fiber wrap can prevent the bond damage and slippage of the longitudinal reinforcement lap joint, and the carbon fiber wrap can improve the shear resistance of the column.

Therefore, sticking carbon fiber wrap along the column circumferential direction can prevent the column from shearing damage, bending plastic hinge damage and longitudinal reinforcement overlap damage, and improve its seismic performance.

2. The method of reinforcing carbon fiber wrap along the longitudinal direction of the column

Its main purpose is to improve the bending resistance of the column. This method of bonding requires reliable anchoring of the carbon fiber wrap at the end. Generally, it is also necessary to stick the carbon fiber wrap along the column ring.

However, it should be noted that this reinforcement method will also produce a large additional force on adjacent components. Therefore, when longitudinally sticking carbon fiber wrap to reinforce a column, attention should also be paid to the degree of improvement of the bending capacity of the reinforced column. Too large an increase in the column bending capacity is not desirable.

Construction requirements

When the method of strengthening the column by externally sticking carbon fiber wrap to improve its ductility, the following structural requirements should be met:

1. The number of layers of the fiber sheet in the circumferential direction is not less than 2 layers of cylinders; not less than 3 layers of square and rectangular columns.

2. The lap length between the upper and lower fiber sheet layers of the circumferential encircling bundle should not be less than 50 mm, the extension length of the circumferential truncation point should not be less than 200 mm, and the overlapping positions of the strips should be staggered from each other.

3. The corners of square and rectangular columns need to be chamfered. When reinforced with carbon fiber and glass sheets, the chamfer radius should not be less than 25 mm.

4. The height of the encryption area shall be the maximum value of the long side dimension of the column section, 1/6 of the column height and 500mm.

5. It should be wrapped along the entire height of the column. For corner columns with seismic grades one and two, they should be wrapped along the entire height of the column.