“FRP”
Innovative Retrofitting
One of the innovative methods for retrofitting concrete structures is the use of FRP (Fiber Reinforced Polymer) sheets. This technology was first introduced in Switzerland in 1984, where CFRP (Carbon Fiber Reinforced Polymer) sheets were tested for strengthening concrete beams. FRP sheets can have up to ten times the strength of steel plates while weighing only 20% of the weight of steel plates.
The retrofitting of existing concrete columns using FRP is aimed at improving the axial compressive strength of the column as well as its ductility. Calculations related to the capacity of an FRP-reinforced concrete column cross-section are performed using software designed by the Sazeh Karan-e Bamdad team, in accordance with the latest edition of the ACI 440-2R code.
In general, existing retrofitting methods using FRP are divided into three categories:
- Wrapping (Confinement)
- Jacketing using FRP fibers
- Using pre-made FRP laminates
Modifying the Cross-Section Shape:
FRP wraps effectively confine circular columns, but their impact on rectangular columns is significantly less. If the shape of these columns is modified or changed to a circular or elliptical form, the confinement effect of the FRP is greatly enhanced.
Modes of Failure:
When a column confined with FRP materials is subjected to axial compressive load, the column cross-section is laterally constrained, and the FRP applies confining pressure. Since the FRP materials are subjected to tensile forces in the circumferential direction, failure occurs when the FRP materials rupture. Occasionally, failure is observed as the separation of FRP materials at the joints.