As the main load-bearing structure in buildings, concrete columns are one of the main components in various buildings. With the increase of the years of building service, due to the previous defects or the continuous changes of the load and the environment, the durability of the column often decreases and the strength and stiffness are insufficient. The destruction of concrete columns is sudden and can easily lead to accidents. Therefore, it is extremely necessary to pay attention to the state of the concrete columns and to strengthen the defective columns. What are the methods for column reinforcement?

Enlarged section reinforcement method

The method of increasing section is used to improve the compressive capacity of the column. Reinforced columns should adopt corresponding reinforcement construction methods according to the type, cross-sectional form, location and stress conditions of the column. The newly-added longitudinally stressed steel bars shall be determined by calculation, but the diameter shall not be less than 14mm. Reinforcing steel bars shall be arranged in the whole length of the reinforced floor. The arrangement of the longitudinal bars should not intersect the beam. If they intersect, they should be anchored in the beam by the technique of planting bars, and should meet the relevant requirements of planting bars. The upper and lower ends of the longitudinally stressed steel bars shall be reliably anchored. The lower end of the longitudinal bars should extend into the foundation to meet the anchoring requirements. The upper end shall pass through the floor slab and be connected to the upper column or be capped and anchored at the roof slab. The newly added stirrups should make the old and new parts work as a whole. The diameter of the stirrups should be the same as the original stirrups and should not be less than 8mm. The stirrups should be encrypted within the specified range, and the spacing and the range of the encrypted zone should meet the relevant specifications. The strength grade of the newly added concrete should be one level higher than that of the original column, and should not be lower than C25.

External bonding steel reinforcement method

The externally bonded steel reinforcement method is used to greatly improve the bearing capacity and seismic resistance of the column section. The method should be based on the type of column, cross-sectional form, location and force conditions, etc., adopt the corresponding reinforcement structure. The longitudinal force angle of the column shall be determined by calculation, but shall not be less than L75*5. The angle steel shall be arranged in the entire length of the reinforced floor. Longitudinal angle steel should be reliably anchored, the lower end of the angle steel should be anchored to the foundation, the middle should pass through each floor slab, and the upper end should extend to the bottom of the upper floor of the reinforcement layer or be anchored to the roof top slab. Along the axis of the column, the hoop plate should be made of flat steel or welded with the angle steel at a certain distance. The cross-sectional area and spacing of the hoop plate and the spacing of the angle steel glue joints are consistent with the beam reinforcement.

Externally pasted carbon fiber cloth reinforcement method

The reinforcement method of pasting carbon fiber cloth is suitable for strengthening the column axis compressive bearing capacity, oblique section bearing capacity and displacement ductility. When the bearing capacity of the front section of the axial compression column is insufficient, the method of continuously pasting carbon fiber cloth along its entire length without intervals (referred to as the hoop bundle method) can be used for reinforcement. When the shear capacity of the oblique section of the column is insufficient, the strip of carbon fiber cloth can be pasted into a ring hoop, and the fiber direction is perpendicular to the longitudinal axis of the column. When the column is seismically strengthened due to insufficient ductility, a hoop bundle composed of hoop-bonded carbon fiber cloth can be used as an additional stirrup. When using carbon fiber cloth hoop bundles to strengthen the normal section of reinforced concrete columns or to improve ductility of seismic reinforcement, the number of layers of carbon fiber cloth for hoop bundles should not be less than 2 for circular cross-sections, and for square and rectangular cross-sections The column should not be less than three floors. The overlap width between the upper and lower layers of the hoop bundle should not be less than 50mm, the extension length of the loop cut-off point of the fiber cloth should not be less than 200mm, and the overlap positions of the strips should be staggered.

The column is an important force-bearing component in the structure. When a disease is found, the correct reinforcement method should be selected for timely reinforcement to ensure the safety of the structure.