Confinement Effect of U-shaped Ties in Columns

Abstract

Recently, mega columns are mainly used in tall buildings, large factory and plant for structural efficiency and constructability. However, as the height of tall buildings rise, the size of mega columns also increases. With increasing the size of columns, it is hard to install continuous hoop and cross tie. In the present study, instead of the use of conventional hoop and cross-tie, cross-section of mega column with U-shaped tie was proposed. Not only general size of columns but also scaled model of mega column with U-shaped tie experiments were performed and evaluated the structural safety of columns with U-shaped ties. As a result of compression test, the column using U-shaped tie performed similar load-carrying capacity and deformation capacity despite descending more rapidly. Under compression force, premature expansion of midpoint section was not occurred. In case of cyclic loading test, the mega column using U-shaped tie exhibited the load-carrying capacity and deformation capacity which are similar to those of the mega column using conventional lateral bar details. Under cyclic loading, premature pulling out of the U-shaped tie was not occurred. Closely placed U-shaped tie for cross-tie prevented premature buckling of longitudinal bars. As a result, in the mega column using U-shaped tie, strength deterioration due to premature cover concrete crushing and premature fracture of longitudinal bars was not occurred. In conclusion, the column using U-shaped tie has similar performance comparing with the column according to design criteria. Therefore, U-shaped tie could be used for columns instead of cross the section.