Reinforcing Concrete Walls And Columns

The project is a 23-story frame shear wall structure. The section size of the podium column is 400X500, the section size of the main building column is 400X550, and the shear wall thickness of the main building is 25. Commercial concrete was used for pouring during the construction. When the main body was constructed to the second floor, it was found that part of the walls and columns on the first floor were casted incorrectly, and the concrete strength was lower than the design value. Subsequently, the strength of each wall and each column of the entire layer of concrete was tested on the spot strength and rebound strength. The rebound results show that the concrete strength of the main building with six columns and one wall is only about C27 (67.5% of the calculated strength), and the strength of the five-pillar and two-piece wall is only about C32 (80% of the original design strength). Although the concrete strength of some columns in the group room did not meet the design requirements. After checking, it can meet the design requirements without reinforcement. Therefore, this project only reinforces the defective walls and columns of the main building.

1 Determination of reinforcement plan

1.1 External protection carbon fiber sheet reinforcement. For walls and columns with concrete strength grades of about C32, outer carbon fiber sheet is used to improve the compressive strength to meet the design requirements.

1.2 Inner steel plate and outer carbon fiber sheet. For walls and columns with concrete strength grades up to C27, internally bonded thin steel plates (thin steel plates with a width of 500 mm, 6 mm) and outer carbon fiber sheet are used to improve the compressive strength and meet the design requirements.

The basis for using the above methods to reinforce defective walls and columns is:

① Carbon fiber sheet has excellent physical and mechanical properties, the tensile strength is 10-15 times higher than that of ordinary steel, and the modulus of elasticity is close to that of steel plate. Experiments show that defective walls and columns can effectively restrain the concrete through the action of the carbon fiber sheet hoop, significantly improve the ductility of the concrete axially compressed wall columns, and enable the walls and columns to obtain higher compressive strength. The compressive strength of walls and columns reinforced with carbon fiber sheet can reach about 1.4 times that of the same grade concrete;

②Carbon fiber sheet is a material with small thickness, light weight and excellent flexibility. It has extremely high fatigue resistance, acid and alkali resistance, creep resistance, and high temperature resistance. It can meet the requirements of compression, bending and earthquake resistance when used to strengthen the wall column, and basically does not change the external dimensions after reinforcement;

③This kind of reinforcement method has the advantages of not destroying the original structure and simple construction. After the reinforcement is completed, the structure does not need to invest in maintenance costs during the use process and has a long service life. Although the price of its materials is relatively high, it can save construction costs and has long-term comprehensive benefits.

2 Reinforcement construction of fiber sheet

Fiber sheet: width 100. Pitch: 300. 2 layers thick.

The treatment process is: base surface treatment, base surface cleaning, primer brushing, veneer repair, carbon fiber sheet, and maintenance.

3 The effect of wall and column reinforcement

3.1 After reinforcement with carbon fiber, there is basically no trace of reinforcement, and the cross-sectional geometric size is only 2~7 mm larger than the original.

3.2 It is not necessary to consider the maintenance in the future use process after a reinforcement. Although the cost of carbon fiber reinforcement is higher than that of bonded steel reinforcement, its construction speed is fast, which can save construction costs. It also has long-term comprehensive benefits.

3.3 Multiple observations within one year after the completion of the reinforcement showed that the measuring points on the wall, the bottom of the column and the upper part of the reinforcement did not change, and the fixed audio of the hammer tapping on the carbon fiber reinforced part did not change. The on-site rebound strength test was performed again, and the rebound results showed that the minimum strength of the reinforced wall and column concrete was C41 (102.8% of the gauge strength), and the maximum was C45 (113.2% of the gauge strength), all meeting the design requirements (The design strength is C40).