Seismic Performance of Full-Scale Reinforced Concrete Frames Retrofitted with Bolted Concrete-Filled Steel Tubes

The effective retrofit strategy of non-seismic designed structures is required to improve the strength and ductility. Jacketing is the most typical method which can enhance seismic resistance capacity, but there are many disadvantages due to its enlarged jacket section. This study developed a non-welded concrete-filled steel tube system (NoWS) which was installed using bolts in the form of tube-type steel-encased beams and columns; the NoWS could increase the capacity of seismic resistance strength and the ductility of members. One reinforced concrete (RC) frame specimen with non-seismic details and one NoWS were manufactured, and cyclic loading tests were conducted until critical failure was observed in the column after reaching maximum load. As experimental results, the specimen retrofitted with NoWS had excellent seismic performance, showing resistance to lateral load, effective stiffnesses, and energy dissipation capacity approximately 2-3 times greater than the results of an RC frame specimen.