The CFRP U-shaped hoop is used to fix the CFRP at the bottom of the beam and transmit reliable stress. When pasting CFRP for reinforcement, the method of pasting CFRP U-shaped hoop is often adopted, and it is not allowed to paste strips only on the side of the beam. So, when do you need to paste CFRP U-hoop? How to operate during construction?

U-hoop is an anchoring measure often used in the reinforcement of concrete flexural beams with carbon fiber sheets. It does not directly act on the bottom of the beam, but is fixed on the carbon fiber patch at the bottom of the beam and the side of the beam.

In the process of strengthening concrete beams with carbon fiber sheets, the main forms of damage are the damage of carbon fiber sheets, the damage of beams, and the peeling damage. The failure of the carbon fiber patch is often due to the insufficient use of the carbon fiber patch in the reinforcement. With the increase of the load, the carbon fiber patch will be damaged before the base material.

The compression failure can be likened to the "super-reinforced beam" in the reinforced concrete beam, which is equivalent to the excessive reinforcement and the excessive use of carbon fiber cloth, which will also cause the concrete in the upper tensile zone of the bending beam to be crushed, resulting in the beam damage.

The peeling failure is due to the failure of the bond between the carbon fiber patch and the concrete beam, which leads to slippage or even separation. For the beam with peeling failure, the carbon fiber patch cannot fully exert its due reinforcement strength. The appearance of peeling failure not only causes the waste of carbon fiber adhesive material, but also severely limits the application of concrete beams. Therefore, in addition to the requirements for the quality of carbon fiber adhesive and carbon fiber impregnated rubber, U-shaped hoop is also needed to ensure the integrity of carbon fiber cloth and beam body.

The CFRP U-hoop has different bearing capacity due to its different arrangement in the beam. How to arrange U-shaped hoop when carbon fiber cloth is used for beam reinforcement?

1. Normal section reinforcement

For the U-shaped hoop arranged for the reinforcement of the normal section, when the extension length of the carbon fiber cloth cannot meet the requirements through calculation, it is necessary to uniformly set up at least three U-shaped hoop anchors within the extension length range. When the calculated extension length of carbon fiber cloth is sufficient, it is necessary to set U-shaped hoops with moderate width at both ends of the carbon fiber cloth at the beam bottom and at both sides of the concentrated load.

2. Inclined section reinforcement

When strengthening the diagonal section of flexural members with carbon fiber cloth, there will also be differences in whether to arrange the densified area according to the different types of members. In the diagonal section reinforcement, the CFRP U-shaped hoop must be pasted perpendicular to the direction of the construction axis, and the oblique pasting method is not allowed.