Two earthquake engineers from Canada, Dr. Murat Saatcioglu and Cem Yalcin, recently received U.S. Patent No. 6,247,279 for their process of "Retrofitting Existing Concrete Columns By External Prestressing." The patent is assigned to the University of Ottawa.
The new retrofitting process has been developed to improve strength and "deformability" of existing reinforced concrete columns. The process involves:
- Determining critical column regions,
- Identifying critical stresses that may lead to brittle shear or compression failures,
- Determining external prestressing to overcome some of these stresses, and
- Providing lateral confining pressure to improve the ductility of concrete in compression.
External prestressing is provided by placing prestressing hoops around the column at predetermined locations.
Each hoop includes a strand that encircles the column with its ends fixed to an anchor while under tension. The invention is applicable to concrete columns of any geometric cross-section. Prestressing may be applied directly on the surface of circular columns by the strands. For columns with non-round geometry such as square, rectangular, or other polygonal cross-sectional shapes, it's necessary to install additional hardware between the strand and the flat surfaces to distribute the prestressing force as evenly as possible on the surfaces of the column. External protection of hardware against corrosion, fire, and vandalism may be carried out by means of fiber-reinforced or plain concrete jackets, shotcreting, or similar sprayed applications of cement-based materials or different types of paints.