The editor of Horse construction wrote this article and saw this news on July 14. "Recently, many pillars in the garage of Vanke Sky City in Nanchang burst, and part of the wall cracked." Columns are important force-bearing components in the structure. When a disease is found, the correct reinforcement method should be selected and reinforced in time to ensure the safety of the structure.  Let's follow this news together to talk about the load-bearing column.

As the main load-bearing structure in buildings, concrete columns are one of the main components in various buildings. With the growth of the service years of the building, due to the previous defects or loads, and the continuous changes in the environment, there are often cases where the durability of the column decreases and the strength and rigidity are insufficient. The destruction of the concrete column is sudden and easily leads to accidents. Therefore, it is extremely necessary to pay attention to the state of the concrete column and strengthen the defective column. What are the methods for column reinforcement? Now Horse Construction introduces you.

Column reinforced with carbon fiber reinforced polymer 

The carbon fiber reinforced polymer reinforcement method is suitable for strengthening the compression capacity of the column axis, diagonal cross-section capacity and displacement ductility.

When the bearing capacity of the cross section of the axial compression column is insufficient, the method of continuously pasting carbon fiber without gaps along its entire length (referred to as the circumferential encircling beam method) can be used for reinforcement. When the shear capacity of the diagonal section of the column is insufficient, the strip of carbon fiber can be pasted into an annular 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 encircled by carbon fiber wrap can be used as an additional stirrup. When the reinforced concrete columns are reinforced with normal cross-sections or reinforced with ductile seismic reinforcement using carbon fiber wrap hoop beams, the number of carbon fiber wrap layers of the hoop beams is required. There should be no less than two layers for circular cross-sections, and no less than three layers for square and rectangular cross-section columns. The overlap width between the upper and lower layers of the hoop should not be less than 50mm, the extension length of the fiber cloth loop to the cutoff point should not be less than 200mm, and the overlap positions of the strips should be staggered from each other.

External bonding steel reinforcement method

The external bonding steel reinforcement method is used to greatly improve the column section bearing capacity and seismic resistance.

The method should adopt the corresponding reinforcement construction method according to the type of column, cross-sectional form, location and stress situation.

The longitudinal stress angle of the column shall be determined by calculation, but shall not be less than L75*5. The angle steel shall be arranged throughout the reinforced floors. Longitudinal angle steel shall be reliably anchored, the lower end of the angle steel shall be anchored to the foundation, the middle shall pass through each floor slab, and the upper end shall extend to the bottom of the upper floor of the reinforced layer or be anchored to the roof roof. Along the direction of the column axis, a flat steel plate should be used to make a hoop plate or a gusset plate and angle steel for welding. The cross-sectional area and spacing of the hoop plate and the spacing of the angle steel joints are consistent with the beam reinforcement.

Enlarged section reinforcement method

The enlarged section method is used to increase the compression capacity of the column.

Reinforced columns should adopt corresponding reinforcement construction methods according to the type of column, cross-sectional form, location and stress.

The newly added longitudinally stressed steel bars shall be determined by calculation, but the diameter shall not be less than 14mm. Reinforcing steel bars should be arranged throughout the reinforced floors. The arrangement of longitudinal bars should not intersect with the beam. If they intersect, they should be anchored in the beam using the technique of planting reinforcement, and should meet the relevant requirements for planting reinforcement. Both the upper and lower ends of the longitudinally stressed steel bars should be reliably anchored. The lower end of the longitudinal bar should extend into the foundation to meet the anchoring requirements. The upper end should be connected to the upper column through the floor slab or capped and anchored at the roof slab. The newly added stirrup should make the new and old parts work together. The diameter of the stirrup should be the same as the original stirrup and should not be less than 8mm. The stirrups should be encrypted within the prescribed range, and the spacing and encryption area should meet the relevant specifications. The newly added concrete strength level should be one level higher than the original column, and should not be lower than C25.

Winding reinforcement method

The winding reinforcement method is suitable for strengthening the displacement ductility of reinforced concrete columns.

The wire for winding should be φ4 cold drawn wire, but it should be used after annealing treatment. Strengthening with this method requires the strength of the original structural concrete to be greater than C10 and less than C50. When the column is a rectangular column, the ratio of the long side dimension to the short side dimension should not be less than 1.5, and the four corner protective layers of the column should be chiseled and polished into rounded corners with a radius of not less than 30mm. The spacing between the windings should be evenly distributed. For important components, it should be no more than 15mm, and the wire should be reliably anchored at the end. Fine stone concrete should be used for winding reinforcement, and the concrete strength should be increased by one grade and not less than C30.