Reinforcement of T-beams and concrete structures began around the 1960s. During these years, different methods of strengthening were used. The first method used was to cover the concrete beams and columns with steel plates. But the disadvantages of these methods were many.
The use of steel panels made the structure heavier and, on the other hand, difficult to implement. But after examining the defects in the 1970s, it was proposed to use synthetic fiber polymers or FRP to strengthen these structures. This method had many advantages and that is why it was more popular day by day.
FRP, with its full name Fiber Reinforced Polymer, (Fiber Reinforced Polymer) is a kind of composite, which is also called synthetic fiber polymer. The use of synthetic fiber polymers made the work of improvement and strengthening easier, and on the other hand, they were lightweight, and because of this, they became very popular. On the other hand, FRP has been very effective in bending, shearing and repairing old structures and buildings.
The cost of using this material is very low. Although the use of FRP is very old in the world, in Iran, the method of strengthening using FRP is still considered a modern method and is not even known. In the following, in order to introduce this method further, we will learn about the characteristics of FRP.
FRP properties
FRP has many advantages and in return has very few disadvantages. Some of the advantages and properties of these synthetic fibers are mentioned below
- Low cost of implementation
- Being non-conductive and suitable for use in structures under electrical and electromagnetic waves
- High bending rate and flexibility
- Ease of installation
- Light weight
- Ease of transportation
- Ease of use
Use of CFRP composite fiber
CFRP composite fibers are widely used in many structures, especially residential buildings, hospitals, radar centers, department stores and many urban centers. These fibers are also used to improve old structures or buildings.
One of the most important cases is the use of these compounds in the renovation of worn-out urban structures. Especially in Tehran, where many buildings are over 40 years old, these natural fibers can be used more than others. On the other hand, these fibers place very little burden and weight on the building and, for this reason, they can perform very well in the reconstruction of old buildings.
Shear and bending reinforcement with fibers
Shear and bending are the most important failure modes of unreinforced beams in buildings. Because bending fracture is soft and shear fracture is brittle, bending fracture is better than shear fracture.
A brittle fracture often spells disaster, while a soft fracture can be a warning. By using external FRP panels, bending reinforcement can be done, and this work makes the beams non-deformable.
Features such as corrosion resistance and high strength, as well as light weight and flexibility of FRPs have made them widely used in beam strengthening and shearing. These fibers can easily fit into other shapes and corners and make for better reinforcement.
Laboratory samples
A test was conducted to determine the behavior of concrete beams reinforced with carbon fiber reinforced polymer, and the results were as follows. In this test, symptoms are tested in two groups. The beams of the first group have a weakness in bending, and the beams of the second group have a weakness in shear. Both beams are strengthened using CFRP fibers and the following results are obtained.
conclusion
It reduces the ductility of beams on which bending and shear reinforcement has been made to a small amount, which can be ignored. The greater the compressive strength of concrete, the greater the load resistance.
The change in the shape of the reinforced beam is almost equal to the change in the shape of the unreinforced beam, which is contrary to expectations due to the weak concrete resistance in the reinforced beam compared to the unreinforced beam.
In reinforced beams, shear failure is in the form of a crack starting from the loading point and continuing until near the support, and in these failures, the part of the CFRP sheet closest to the support is separated from the beam, which should be considered near the support.
last word
This test and various experiments show that the use of CFRP fiber today can significantly reduce the cost of improving and strengthening beams. On the other hand, the use of these vehicles allows large and old cities to be renovated faster than before. For this reason, it is very important to pay attention to these fibers in strengthening them.