In bridge reinforcement projects, fiber reinfroced polymer(FRP) wrap is mainly used for strengthening the basic components and joints of concrete bridges. The reinforcement effect is mainly to improve the flexural capacity of the component, the shear bearing capacity and the axial compressive bearing capacity of the compression member, and to improve the stiffness and ductility of the component, the crack width of the reinforced concrete member can be controlled.

Stress analysis of structural strengthening by fiber reinfroced polymer(FRP) wrap

• Compared with other traditional reinforcement methods, the use of CFRP to reinforce the old bridge can minimize the stress distribution of the original structure, so as to ensure the joint force of the original structure within the range of the design load.

  
  

• The carbon fiber cloth with excellent tensile properties is bonded to the bottom of the beam body or on the inner wall of the box girder by bonding material, so that it is involved in the force with the original structure, that is, the carbon fiber cloth can bear the tension together with the steel bar arranged in the original structure, in order to improve the bearing capacity of the old bridge.

  
  

• The carbon fiber cloth is pasted along the direction of the main tensile stress or the orthogonal direction of the crack. The anchorage ends are set at both ends respectively. Accordingly, the cracks in the concrete surface can be restrained to prevent the cracks from expanding, thus the purpose of improving the flexural rigidity of the components, reducing the deflection of the components and improving the stress state of the beam body can be achieved.

  
  

• The carbon fibers used for reinforcement are as follows: unidirectional carbon fiber cloth, unidirectional carbon fiber fabric, two-way carbon fiber interwoven fabric and unidirectional carbon fiber laminates. According to the different structural parts and stress characteristics and direction, the corresponding carbon fiber cloth is selected for reinforcement.

  
  

  
  

  
  

• Carbon fiber reinforced polymer (CFRP) reinforced concrete members may also affect the failure modes of flexural members when improving their flexural capacity. When the amount of carbon fiber cloth is too much, the failure mode of the component will be changed from the failure caused by the breaking of the carbon fiber to the sudden crushing of the concrete. At the same time, because carbon fiber is completely elastic material, its joint work with reinforcing steel will weaken the ductility of reinforced concrete due to its plastic properties. If the amount of carbon fiber cloth is too much, the ductility of components will be reduced. Therefore, when strengthening and reinforcing the reinforced concrete beam bridge with CFRP, it should be used rationally according to the actual situation.

  
  

• The old bridge reinforced by carbon fiber cloth is sudden, and the ultimate state of its bearing capacity can not be defined according to the definition of ordinary reinforced concrete, and the bending bearing capacity should be calculated according to 2/3 of the tensile strength of carbon fiber.

  
  

• CFRP can improve the shear capacity of concrete beams. The mechanism is similar to the stirrup. It can also improve the deformation properties of the components and enhance the anti deformation ability of the members.