Carbon fiber reinforced polymer strengthening compression members

(1) Carbon fiber reinforced polymer strengthening axial compression member

The axial compression member wrapped with carbon fiber reinforced polymer can increase the compressive strength of concrete and effectively improve the deformation performance of concrete. The effect becomes more significant as the amount of carbon fiber reinforced polymer increases. In engineering practice, it is appropriate to wrap 2 to 3 layers in a ring. In the case of the same amount of carbon fiber reinforced polymer, the effect of strip wrapping is better than the effect of whole wrapping. Through engineering practice and tests, the width of 100mm is appropriate.

(2) Carbon fiber reinforced polymer strengthening large eccentric compression member

The use of carbon fiber reinforced polymer to reinforce strengthening concrete columns can effectively improve the normal section bearing capacity of large eccentric compression members, especially when the strength of the member concrete is low (C15 ~ C30). After being strengthening by carbon fiber reinforced polymer, its flexural capacity is significantly improved.

As the number of layers of longitudinally pasted carbon fiber reinforced polymer increases, the strengthening effect will become more obvious. However, the number of fiber cloth layers and the increase in component bearing capacity do not show a linear growth relationship. When sticking more than two layers of carbon fiber reinforced polymer, a joint work reduction factor needs to be considered. The tensile strength of carbon fiber reinforced polymer has a size effect. As the width of the fiber cloth increases, its ultimate tensile stress is reduced to a certain extent, so the width should be ≤200mm when pasting in the longitudinal direction.

When carbon fiber reinforced polymer is longitudinally pasted to strengthen the column, effective anchoring should be considered, and steel plate bead is usually used at both ends of the column.

(3) Seismic strengthening of concrete columns with carbon fiber reinforced polymer

Wrap the carbon fiber reinforced polymer horizontally in the range of h/4～h/3 (h is the height of the column) at the root of the column that needs seismic strengthening, which can effectively improve its ductility. In the case of no loading angle, this seismic strengthening method has a significant strengthening effect. For high-strength concrete with a relatively large shear span, the seismic strengthening effect is more obvious. The essential reason why the carbon fiber reinforced polymer wraps the concrete column laterally to increase its ductility is that the circumferential restraint effect of the outer carbon fiber reinforced polymer effectively improves the deformation performance of high-strength concrete. Moreover, the restraining effect of the outer carbon fiber reinforced polymer on the internal concrete is more direct and effective than stirrups.

Carbon fiber reinforced polymer strengthening bending member

(1) strengthening of normal section of strengthening concrete bending members

When carbon fiber reinforced polymer is used to reinforce the normal section of a flexural member of a strengthening concrete beam, the flexural capacity is significantly improved, and the ultimate flexural capacity is even more significant. There is a problem of efficiency in the application of carbon fiber reinforced polymer. With the same amount of carbon fiber reinforced polymer, the strengthening effect of striped paste is slightly better than that of whole strip. The flexural bearing capacity of components increases with the increase of the amount of carbon fiber reinforced polymer, and the increase is relatively large when the number of layers of carbon fiber reinforced polymer is small. With the increase in the number of layers of carbon fiber reinforced polymer, due to the effect of efficiency, this increase is reduced accordingly. Therefore, the reduction factor of the number of layers should be considered when designing.

The amount of carbon fiber reinforced polymer will also affect the failure mode of the bending member. When the amount of carbon fiber reinforced polymer is too much, the damage of the component will be the damage caused by the broken carbon fiber reinforced polymer into the damage of the concrete being crushed. At the same time, because carbon fiber reinforced polymer is a completely elastic material, its joint work with steel bars will weaken the effect of plastic deformation of steel bars on improving the ductility of components. When the amount of carbon fiber reinforced polymer is too much, the ductility of components will decrease. Therefore, it is prevented that the amount of carbon fiber reinforced polymer sticking is too large, causing "super-strengthening damage".

(2) strengthening of oblique section of strengthening concrete bending members

Practice has proved that the use of carbon fiber reinforced polymer to improve the shear capacity of concrete members is effective. After the carbon fiber reinforced polymer is pasted, the cracking load and shear capacity of the beam are obviously improved, and the increase in shear capacity is even more remarkable. The mechanism of carbon fiber reinforced polymer for improving the shear capacity is similar to that of stirrups. Therefore, while improving the shear bearing capacity of strengthening concrete beams, it can also significantly improve the deformation capacity of the components, and increase the ductility of the components. The diagonal section of the concrete beams strengthening with carbon fiber reinforced polymer. Before the failure, there are signs of damage such as tearing, bulging and wrinkling of the carbon fiber reinforced polymer strip, which improves the brittleness of the original concrete beam against shear failure. While improving the shear resistance, it can increase the anchoring of the bent carbon fiber reinforced polymer.

In the strengthening of concrete structural members, carbon fiber reinforced polymer has the characteristics of strong adaptability, wide strengthening range, high strength and efficiency, and simple construction, which are not available in traditional strengthening methods. Carbon fiber reinforced polymer is widely used in the strengthening of concrete structures, which has a positive role in promoting the development of strengthening projects.