Design of the carbon fiber reinforcement



In Chile there is a park structures both building works and civil that by degradation, requires upgrade to new regulations, changes of use ... To meet these requirements, exist the reinforcement of platabandas steel.
But because of its high manufacturing cost, being very heavy elements, difficult installation and quick deterioration by corrosion, it was restricted their use.

More recently (25 years ago) it use fiber reinforced polymers (FRP, fiber-reinforced polymer) as a substitute for steel facings.

The attractiveness of composites, reinforced with high strength lies in its strength, durability (corrosion resistant); it very interesting properties versus traditional steel reinforcements platabandas. To this we must add its high strength / weight ratio, providing a very handy and quick to attach materials.

Therefore, the reinforcement of concrete structures is the construction field where faster and more successfully being implemented new composite materials (fiber-armed polymers or FRP).
The FRP reinforcements are done very quickly, with few operators and using light aids, minimizing interruptions in the use of the structure and inconvenience to users.
The application of these materials results in a cost savings of labor forces regarding traditional reinforcements around the 40-50%.


A structural reinforcement by a system based on carbon fiber reinforcement, comprising bending stresses, shear and confinement. When anisotropic products, working in one direction, absorbs only tensile stresses, they must be arranged in the drivable elements reinforcing areas.

As an example, used in:

  • Repair damaged structures with loss of section (corrosion, ...)
  • Adapting to new regulations.
  • Changes use involving increased loads.
  • Rehabilitation of structures.
  • Defects in design and / or implementation.
  • Type structures:

    Civil works:

    -Bridges, viaducts: batteries, boards, beams, ...
    -Deposits and Fireplaces

    Building work:

    -Unidirectional reinforcements, reticular slab.



Carbon fibers have high strength at high temperatures (over 600 ° C). However, epoxy resins have a glass transition point between 60-100 ° C, depending on the manufacturer.

Due to the influence of temperature on the reinforcements using an interface resistant resin for collaboration, there are two possibilities of dimensioning a booster:

  1. Ensure a coefficient greater than 1 residual resistance (resistance of the element / applied stress, both ELS). In this case, we guarantee that in an eventual loss of reinforcement in case of fire, the fire resistance time is only determined by the coating of armor.
  2. If the residual resistance coefficient is less than 1, the reinforcement should be protected against fire to ensure fire resistance in accordance with applicable regulations. In this sense, you must ensure that the adhesive reaches its glass transition temperature.


The initial state of the element to reinforce may require some type of repair. This should be in perfect condition when you go to apply the reinforcement and should be considered in the design of reinforcement.

The calculation methods based on Limit States described in Eurocode 2 and in EHE will apply in design. It is important to know the laws of efforts of different charge states to assess the residual safety factor and the required reinforcement section.

The sizing is based on a cross section and on the performance of the main reinforcement materials (composite, fiber sheet), described in the technical specifications of the system manufacturer. But applying the safety factors and taking design deformations (different features) described the design guide reinforcement composites CEB-FIP.


In the calculations of flexural reinforcement a number of assumptions (ACI 440-2R) are assumed:

  • Design based on the existing section (dimensions, materials, ...)
  • The deformations in the fiber reinforced concrete and are proportional to the distance from the neutral axis.
  • Externally bonded reinforcement is perfectly bonded to the concrete.
  • The adhesive shear deformation is negligible because the applied thickness is minimal.
  • The maximum deformation of the compressed concrete is 3.5 ‰ (EHE)
  • The contribution of concrete in tension is negligible.

The fiber reinforcement is perfectly elastic until breaking.
The provision of a carbon fiber section, causes a loss in ductility of the member. Therefore, the CEB-FIP recommends ensuring that the deformation of design must be at least 5 ‰ in concrete type C35/45 or less. Moreover, the recommended maximum design elongation values ​​reach 7.5 ‰ (higher value is recommended), depending on the state of deformation steel at the reinforcement moment.