Today, the use of FRP in the construction industry has increased rapidly. This paper provides an overview of some developments in the field of fiber reinforced polymers (FRP) for column strengthening.
Why is it necessary to use FRP to strengthen concrete building columns and beams?
The most important reason to strengthen structural components is that it can save human lives and reduce damage by preventing buildings from collapsing. Another reason is the concern for infrastructure and the need for its costly replacement. Reinforcement with FRP materials with preferred properties is an excellent alternative to traditional materials, including steel coating to strengthen reinforced concrete structural components. Existing studies have shown that the use of FRP materials restores or improves the original design of the column.
Also, the potential shear or bending strength allows the structure to withstand a greater load than it was designed for.
Using FRP to strengthen the beam under compressive load
Natural disasters such as storm, hurricane, tsunami, earthquake and random impacts can damage or destroy unfinished structures within seconds. On the other hand, salt water cycles, chemical thawing, and freeze-thawing can cause structural deterioration over a longer period of time.
Most ancient buildings and bridges were built according to ancient design codes. These structures are vulnerable during extreme events and must be modified to meet current codes and standards. Traditional strengthening techniques include concrete and steel cladding. The use of FRP to strengthen the beam under compressive load increases the cross-sectional area of the structural column and, as a result, reduces the probability of destruction due to earthquake or compression. Another new method of repair is the use of fiber reinforced polymers (FRP).
Advantages of FRP
Some of the most important advantages of FRP are:
Provide excellent mechanical properties,
corrosion resistant,
and endurance,
light weight,
Ease, reduced construction time, efficiency, and low life cycle cost.
Using FRP to strengthen the beam under axial load
To increase the axial load bearing capacity of the column with minimal increase in cross-sectional area, FRP sheets or packings can be used. Coated beams and columns involve wrapping them with layers of FRP, prefabricated cladding, or fiber-reinforced panels in the environment. The use of a case increases the lateral stress in them, resulting in greater ductility and an increase in high load capacity. Confinement under axial load is less effective for rectangular and square columns than for finite stresses on concrete.
The confinement effectiveness improves as the beam radius increases. Recent studies show that using FRP materials in the loop direction or laterally can effectively increase the load-bearing capacity.
Strengthening columns
It is the use of FRP to strengthen, repair and strengthen RC reinforced concrete columns through FRP composites, including FRP outer cover and FRP cover. Columns can be made with increased axial, shear and bending capacities for various reasons such as lack of confinement, off-center loading, seismic loading, transverse impacts and corrosion.
Using FRP to strengthen columns under compressive load
In addition to using traditional FRP materials, prestressed FRP strips have been trialled to enclose circular and square columns. Some researchers found no significant effect on the ultimate load capacity due to pre-stressing of FRP, another group of researchers claimed that it has a significant effect on the residual strength of columns after overloading. Residual strength becomes critical in the event of damage to the FRP enclosure due to fire, vandalism or damage to the service life.
The range of increase in axial load capacity of columns varies from 6 to 177 percent. This increase depends on several variables including properties and quantity. FRP reinforcement increases concrete strength, column cross-sectional shape and axial load level. In most of these tests, CFRP caps were chosen to restrain the concrete columns. The tear stress of typical CFRP materials obtained from standard tensile testing of FRP sheets ranges from 1.5% to 2014 polymers.
Strengthening columns under off-center axial load
In field applications, most columns are not concentric under full load. This results in non-uniform confining stress due to the stress gradient, which in turn reduces the column efficiency. Recently, research on axially loaded eccentric columns equipped with FRP panels and various variations on CFRP-reinforced square concrete columns has investigated the effects of using FRP. Their results showed that for both control columns and FRP-coated columns, deflection of the axial load amplitude reduced the corresponding axial deflection.
FRP cladding was also effective in strengthening eccentrically loaded columns. However, its efficiency is proportional to the hardness of the FRP coating and decreases due to the stress gradient in the column. Similar observations were made for eccentrically loaded circular concrete columns wrapped with CFRP and GFRP panels. In addition, CFRP sheathing was more effective for conventional strength than high-strength concrete, and this is one of the most important advantages of FRP in strengthening concrete beams and columns of buildings.
conclusion
Removing the concrete cover, roughening the surface of the beams, cleaning the rebar and covering them with suitable material that prevents corrosion are all advantages of using FRP?