New technique for repairing and retrofitting rectangular reinforced concrete columns using anisotropic sandwich structural element

The objective of this research is to introduce a new Sandwich Wrapping Confining System (SWCS) for the repair of square and rectangular columns. Several traditional and non-traditional techniques are used for the repair of square and rectangular columns. Traditional techniques include concrete jackets and steel plates. Concrete jackets and steel plates have a lot of limitations and are not suitable for many repair applications including repair in aggressive environment and repair of structures in earthquake zones. Recently, Jackets made of thin fiber reinforced polymer (FRP) have been used to repair concrete columns. Jackets made of thin FRP have many advantages when compared to traditional techniques. Thin FRP jackets can be used in aggressive environments and in earthquake zones. Thin FRP jackets engage a uniform confining pressure around the entire circumference of circular columns, thereby confining the entire cross-section. However, thin FRP jackets placed on square and rectangular columns engage high confining pressures at the comers, but apply little or no pressure on the flat sides. Therefore, a considerable portion of the concrete cross-section may remain unconfined. Lack of effective confining pressure is the main disadvantage of using thin FRP jackets to strengthen square and rectangular columns.;When one recognizes that the majority of columns (over 85%) are noncircular, one can clearly see that practical applications of thin FRP are limited. Thus, development of a more universal wrapping system—one that is generally applicable to all types of columns—becomes a paramount objective. The sandwich wrapping confining system described here replaces the thin FRP wrapping sheets with a sandwich wrapping system made up of two FRP faces separated by a light incompressible core.;Extensive experimental, theoretical, and finite element investigations of the behavior of concrete columns upgraded and repaired using the Sandwich Wrapping Confining System are presented. A large number of full size square and rectangular columns with different dimensions is tested under compressive loading. The behavior of columns repaired using the Sandwich Wrapping Confining System is modeled using finite element analysis. A comparison is provided between the experimental and the finite element results.;The Sandwich Wrapping Confining System possesses the two most important properties for effective confinement of columns, namely, a high ratio of strength to weight and a high ratio of stiffness to weight. In addition, SWCS possesses adequate transverse flexural stiffness and is therefore capable of entirely confining columns with noncircular cross-sections. In other words, SWCS is a process for improving the axial, flexural, and shear strength—as well as the ductility—of noncircular reinforced concrete columns, which it accomplishes with or without increasing the stiffness of the column.;Although the main focus of this research is on the strengthening of square and rectangular columns repaired and upgraded using the Sandwich Wrapping Confining System, the behavior of circular columns and cylinders upgraded using different types of thin FRP is further investigated theoretically and experimentally. The results indicate that thin FRP jackets can be used to enhance the strength and ductility of circular columns.