When carbon fiber reinforced concrete beams, there are many factors that affect its deformation performance. In addition to the number of adhesive layers of carbon fiber itself, the strength grade of concrete, longitudinal reinforcement ratio, cross-sectional height and shear span ratio will all have a certain impact on the deformation performance of carbon fiber reinforcement.

1 number of layers

The number of carbon fiber bonding layers has a greater impact on the reinforced bearing capacity, thereby affecting the deformation performance of reinforced concrete beams. For example, when a layer of carbon fiber cloth is pasted, the ultimate bearing capacity is increased by 13.6% compared with the unreinforced beam. When two layers are pasted, the ultimate bearing capacity is 21.9% higher than that of the unreinforced beam. When three layers are pasted, the ultimate bearing capacity is 3O higher than that of unreinforced beams. 8%. When the four layers are pasted, the ultimate bearing capacity is 41.7% higher than that of the unreinforced beam. When the five layers are pasted, the ultimate bearing capacity is 45.80% higher than that of the unreinforced beam. However, the increase in the bearing capacity is not directly proportional to the number of layers of carbon fiber, but a bilinear relationship. That is, when the number of adhesive layers reaches a certain number, the increase in bearing capacity shows a trend of gradual reduction. That is to say, as the number of layers increases, the growth rate of the increase in the bearing capacity of the carbon fiber reinforced reinforced concrete beams gradually decreases, and the beams will also exhibit higher deformation. Based on the analysis of this influencing factor, we believe that when choosing the carbon fiber adhesive layer, we must weigh various factors and select the best number of layers.

2 Strength grade of concrete

The strength level of concrete will also have an important impact on the reinforcement effect of carbon fiber, and ultimately affect the deformation performance of carbon fiber reinforced concrete beams. The impact limit of the graded strength of concrete on the reinforcement of carbon fiber is C30. That is, when the strength grade of concrete is C30, the reinforcement effect of carbon fiber is the best, and its deformation performance is also the best. When the strength level of concrete is greater than C30, the improvement of the carbon fiber reinforcement effect will show a downward trend with the increase of the concrete strength level, which will affect the deformation performance of carbon fiber reinforced concrete beams. The reason why the best grade strength of concrete is C30 is that when the grade strength of concrete is less than C30, the reinforced beam will crack due to the damage of the steel bars. With the increase of the concrete strength, the height of the compression zone on the concrete during the ultimate failure is reduced, thus increasing the length of the internal force arm of the steel bar and the carbon fiber cloth, so that the contribution of the carbon fiber to the ultimate bending moment is enhanced on the original basis , The increase in bearing capacity is increased. However, when the grade strength of the concrete is greater than C30, the reinforced beam will crack due to the crushing of the concrete, which is limited to the damage of the steel bar being crushed. Therefore, determining the strength level of concrete is of great significance for strengthening the reinforcement effect of carbon fiber and enhancing the deformation performance of reinforced concrete.

3 Longitudinal reinforcement ratio

When pasting the same number of layers of carbon fiber cloth, the higher the longitudinal reinforcement ratio of the beam, the smaller the increase in the ultimate bearing capacity after reinforcement, and the worse the reinforcement effect. The reason is that due to the increase in the area of the longitudinal reinforcement, the height of the compression zone of the concrete during the ultimate failure is increased, and the length of the internal force arm of the steel and carbon fiber cloth is reduced. Therefore, the contribution of carbon fiber to the ultimate bending moment is weakened on the original basis, and the increase in ultimate bearing capacity is reduced. The change of the reinforcement ratio has the greatest impact on the increase in the ultimate bearing capacity of the beam, followed by the increase in the yield load of the reinforced beam, and has almost no effect on the increase in the cracking load of the reinforced beam.

4 Cross section height

The height of the cross section has an important effect on the reinforced bearing capacity, which in turn affects the deformation performance of the reinforced concrete beams reinforced with carbon fiber. According to related research results, a beam cross-sectional height of 500mm is the best cross-sectional height, which is the best effect of carbon fiber reinforcement, and has high anti-deformation performance. When the cross-sectional height is greater than 500mm, the crushing failure of concrete precedes the failure of steel bars. Therefore, the damage of the beam is caused by the crushing damage of the concrete, so the increase in the ultimate bearing capacity is reduced. The reason why the cross section is 500mm is the best height, because when the cross section height of the reinforced beam is less than 500mm, the reinforced beam will crack due to the damage of the steel bar. At the same time, as the cross-sectional height of the reinforced beam continues to increase, the strength of the internal force arm of the steel and carbon fiber so far will be increased, thereby enhancing the bearing capacity of the beam and the corresponding deformation performance. However, when the cross-section of the reinforced beam is greater than less than 500mm, the reinforced two will be damaged due to the crushing of the concrete, which will reduce the bearing capacity of the reinforced beam, resulting in insufficient performance of the superior tensile performance of carbon fiber, thereby reducing The contribution of carbon fiber to the ultimate bending moment is deformed.

5 Shear span ratio

Changing the shear span ratio will also have a certain impact on the bearing capacity of carbon fiber reinforced reinforced concrete, which in turn will affect its deformation performance. Generally speaking, the shear-span ratio and the ultimate bearing capacity of the reinforced beam show a proportional increase. That is, the greater the shear span ratio, the greater the increase in the ultimate bearing capacity of the reinforced beam. For example, when the shear span ratio is 1.61, the ultimate bearing capacity after reinforcement is increased by 10.59%. When the shear span ratio is 2.26, the ultimate bearing capacity after reinforcement is increased by 13.63%. When the shear span ratio is 2.9, the ultimate bearing capacity after reinforcement is increased by 16.44%. This is mainly because, if the shear span ratio is relatively small, the failure of the steel bar will be caused by the stress concentration phenomenon at the two ends of the carbon fiber, which causes the tensile strain near the end of the carbon fiber to exceed the limit. If the shear-span ratio is relatively large, the loading mode of four-point bending gradually transitions to the loading mode with concentrated force acting in the middle of the span, and the failure mode also becomes the tensile strain of the middle-span reinforcement element exceeding the limit. Therefore, by increasing the shear span ratio, the tensile advantages of carbon fiber can be fully utilized, the ultimate bearing capacity of the beam can be enhanced, and the deformation resistance of the beam can be improved.

Carbon fiber reinforcement is a new type of reinforcement technology that has emerged in the reinforcement industry. It has many advantages due to other reinforcement materials. It can reinforce reinforced concrete beams well and has good deformation properties.