Ductility and Strength Behavior of Reinforced Concrete Columns Confined by Glass and Carbon FRP Sheets
Authors: Abdulrahman Ahmed R. , Taha Bahman O. , Khdir Muhsin K. 
Published: March 2020

Background:
Fiber reinforced composite materials are becoming popular in civil engineering construction practices. One of the most practical applications of these materials is concerned with the strengthening and retrofitting of reinforced concrete compression members by means of external confinement with the GFRP sheets. The role of FRP for strengthening of existing or new reinforced concrete structures is growing at an extremely rapid pace owing mainly to the ease and speed of construction, and the possibility of the application without disturbing the existing functionality of the structure.

Objective:
The ductility and strength behavior of reinforced concrete columns (Square & Circle) confined by glass and carbon Fiber Reinforced Polymer (FRP) sheets were experimentally investigated

Methods:
In the library, we tested and cast a total of fourteen column specimens. The tested specimens in this study were square and circle columns, the square specimens tested in this experimental study had dimensions of 135x135 mm cross-section while the circle specimens had 150 mm diameter. The columns were loaded at their supports and made prepared to avoid local failure at supports due to steel plates. Two types of fiber reinforcements sheets were used for strengthening the columns (Carbon and Glass fiber polymer sheets). To prevent the highly stressed slender longitudinal bars from buckling outward, adequate amounts of steel ties were utilized in the height of the columns. During the test of the columns, the central deflection and central fiber strains were measured using dia1 gauges and strain gauges

Discussion:
The CFRP strains progressed very slowly before the yielding of longitudinal reinforcement bars but quickly, eventually, due to the concrete expansion in the plastic hinge. The wrapped CFRP sheets contribute to both the shear strength and the confinement of concrete in column specimens.
The results signify that the percentages of increase in the carrying load capacity due to strengthen, using carbon and glass FRP sheets, were greater in the circular columns compared with the square columns for all the types of confinements used in this study.
The ductility factor increased by the strengthen column ranged between 1.35-2.78, while the greatest ductility factor obtained when the circular columns strengthen with glass FRP sheets fully wrapped.

Conclusion:
-The maximum ratio of increase in the carrying load capacity obtained when the column strengthens fully wrapped.
- The columns (circular and square) strengthen with carbon FRP sheets, the greater carrying load capacity obtained when compared the columns strengthen with glass FRP sheets.
-The percentages of increase in the carrying load capacity due to strengthen, using carbon and glass FRP sheets were greater in the circular columns compared with the square columns for all the types of confinements.
- The stains developed in the confined circular columns are greater than stains in the confined square columns.
-The ductility factor increased by the strengthen column, while the greatest ductility factor obtained when the circular columns strengthen with glass FRP sheets fully wrapped.