There are many parameters that affect CFRP strengthening, which can be divided into two categories:reinforcement, the properties of CFRP composite system.

1.Reinforcement

The performance and original condition of the beam itself include load condition, support condition, high span ratio of beam, shear span ratio, concrete banter, reinforcement ratio, stirrup rate, CFRP's nominal "stirrup rate" and stickup mode, etc.

2.The properties of reinforcing materials, including carbon fiber fabric and glue.

It includes the thickness, elastic modulus, anchorage length, shear strength, thickness and ultimate elongation of CFRP.

On the above factors, the shear strength and the damage characteristics of the beam are greatly influenced by the bonding mode of CFRP, the anchorage performance of CFRP, the thickness of CFRP (the number of layers), the shear strength of the adhesive and so on.

1.1 Bonding method and anchorage property of CFRP strengthening

The bonding mode of the beam is the side strip and the bar. The pressure strip can not only anchorage the strips attached to the strip, but also, with the development of the slanting cracks, the pressure can also be involved. Therefore, the strengthening effect of this kind of bonding method is better than that of the previous one, and the shear bearing capacity of the strengthened beam can be increased by 21.3%.

The bonding mode of the beam is U - shaped strip. This kind of bonding method can guarantee the good anchorage length of the carbon fiber cloth at the bottom of the beam. Only the stress concentration will be found at the top of the beam side, so the reinforcement effect is better than the previous two kinds of bonding methods, and the shear strength of the reinforced rear beam is about 23%. At the same time, because the carbon fiber cloth near the support side of the beam has larger anchorage length, the carbon fiber cloth is broken when the damage is destroyed, and the anchorage length of the carbon fiber cloth near the loading point is small, and the bond failure occurs.

The bonding mode of the beam is U strip and pressure bar. Obviously, the anchoring effect of the carbon fiber cloth with this bonding method is better than that of the U strip only, so the bearing capacity is also improved.

The beam sticking is all wrapped in strip. This type of bonding has the best anchorage effect, and its sufficiently large anchorage length can ensure the full exertion of the strength of CFRP. But the actual construction should be restricted by the conditions of the field.

1.2 The layers of carbon fiber fabric

The number of layers of CFRP has little influence on the shear capacity of the beam. If the length of the anchorage is smaller because of a layer of carbon fiber cloth, some carbon fiber cloth on the side of the beam can be broken and the strength is fully exerted when it is destroyed; and the length of the anchorage is also larger with the increase of the number of layers. The anchorage length of reinforcement is limited, so the failure of CFRP is the bond failure and its strength has not been fully exerted.

In practical projects, if reliable measures are taken to ensure the anchorage performance of CFRP, the reinforcement effect will be better with the increase of the number of CFRP layers. Although the increase of storeys has little effect on the shear capacity of beams after reinforcement, the cracks in beams are obviously inhibited.

1.3 Others

The condition of reinforced beams has little effect on the shear capacity of beams. The shear strength and other properties of the adhesive also have a great influence on the reinforcement effect. The higher the shear strength of the adhesive, the better the strengthening effect. In addition, construction quality has great effect on the reinforcement effect.