Strength and ductility of external steel collared concrete columns under compressive loading

Many studies have revealed that one way to improve the performance of concrete columns is by providing confinement. Recently, external confining methods have drawn interest of researchers due to its main advantage for retrofitting purpose of existing members. Steel jacketing methods have long been proposed by several studies for externally retrofitting circular concrete columns. On the other hand, the lack of research has been found in addressing its impacts on the rectangular and square concrete sections. This paper discusses the experimental results and behavior of concrete columns under concentric static axial loading. Nine column specimens were cast and tested to observe their behaviors. A control specimen (CS01) was cast without confinement, while another one (CS03a) was provided with internal stirrups to conform the seismic requirements of building code. The other seven specimens were retrofitted with a set of L-shaped steel collars. Two specimens (S04a and S04b) consisted of internal stirrups for retrofitting purpose of existing members, whereas the others (S04, S04c, S04d, S04e, and S04f) used various collar configurations to examine the impact of this new retrofitting method. The results have shown significant improvement in both strength and ductility of square concrete column confined externally by L-shaped steel collars