CFRP and concrete member connection method

Carbon fiber-reinforced reinforced concrete members generally use structural adhesive to paste carbon fiber on the concrete member, and there are two commonly used connection methods between carbon fiber and concrete members, namely surface pasting method and surface layer embedding method.

Main factors affecting the effect of side-adhesive CFRP reinforcement

There are many factors that affect the effect of CFRP reinforcement, which can be roughly divided into two categories, including the performance of the structure itself and the performance of the reinforcement material. Among them, the reinforcement ratio, concrete strength, carbon fiber elastic modulus, number of layers and side adhesion height have the greatest influence on the bearing capacity and failure form of the reinforced beam.

1. Reinforcement ratio

When the reinforcement ratio is small, the strain value of the carbon fiber is larger, indicating that the carbon fiber bears a larger proportion of the load and contributes more to the bearing capacity. When the reinforcement ratio exceeds a certain range, the load value that the reinforced beam can withstand is smaller.

When reinforced concrete beams are strengthened with CFRP side bonding, the bearing capacity of reinforced concrete beams with lower reinforcement ratio has a larger increase. When the reinforcement ratio is higher, the tensile strength exerted by the carbon fiber is smaller, and the reinforcement effect is not obvious.

2. Concrete strength

With the improvement of concrete grade, the ultimate bearing capacity of reinforced beams has increased to a certain extent, but because the elastic modulus of concrete is small, the increase in bearing capacity is smaller.

3. Carbon fiber elastic modulus

When the reinforced beam is in the state of concrete crushing failure, the elastic modulus of carbon fiber has a greater impact on the bearing capacity. The larger the elastic modulus, the higher the ultimate tensile strength of the carbon fiber cloth and the greater the bending moment of the reinforced beam. If the reinforced beam is in the failure state of carbon fiber, the elastic modulus of carbon fiber has no effect on the ultimate bearing capacity.

4. CFRP side sticky layer number

The cross-sectional bearing capacity of carbon fiber reinforced beams is not completely proportional to the number of CFRP bonding layers. The main reason is that as the number of bonding layers increases, the bonding quality between each layer of carbon fiber cloth cannot be easily guaranteed. With the increase of the load, when the strength of the structural adhesive does not reach the standard, the cooperative performance between the fibers of each layer will become worse, peeling failure will occur easily, and the tensile strength of CFRP will not be fully exerted. With the increase of the number of adhesive layers, the slope of the curve decreases significantly, indicating that the increase in the bearing capacity of the reinforced beam decreases when the number of layers increases, and the reinforcement efficiency decreases. Therefore, the CFRP layer reduction factor must be considered in the specific bearing capacity calculation and reinforcement construction process.

5. CFRP side sticky height

With the increase of the side adhesion height, the slope of the curve gradually decreases, and the increase in the ultimate bearing capacity of the reinforced beam will be reduced. Therefore, in the calculation of the specific bearing capacity and the reinforcement design, the reduction factor of the CFRP paste height must be considered and converted into the effective height. In order to facilitate calculations, the reduction factor of the bonding height can be converted into the area reduction factor in the reinforcement design, and the less stressed parts of the side-bonded carbon fiber member can be reduced, so the area reduction factor of the CFRP side-bonded reinforcement is introduced .