Performance of square reinforced concrete columns externally confined by steel angle collars under combined axial and lateral load

Providing good ductility has become research interest in the area of seismic resistant structures. Particularly in Reinforced
Concrete (RC) structure, such ductility is commonly achieved by providing good confinement. Confinement can be
conventionally provided by internal stirrups, and also additional external elements which are commonly used as strengthening or
retrofit works. Attaching external steel collars on concrete columns is one of many techniques in enhancing the ductility. In this
study, performance of such retrofitting method is investigated through laboratory experiment. Totally five specimens are built for
this investigation. The first two specimens (CS1-1, and CS1-2) are control specimens, which are conventionally confined by
stirrups. The other three specimens (S1-3, S1-4, and S1-5) are only confined externally with the steel angle collars. All five
specimens are tested under combined axial and lateral load. The axial load is kept constant at 30% of plain concrete axial
capacity to model the gravity load. The lateral load given is according to ACI 374.1-05 quasi-static cyclic loading protocol.
Lateral load resistance is recorded throughout the cyclic loading, and plotted against the corresponding lateral displacement.
Results show that specimens with smaller volumetric ratio of confining element suffered brittle failure (poor ductility).
Specimens with adequate confinement show good deformability and ductile failure. In conclusion, the retrofitting method by
providing external steel angle collars is very promising.