Subassembly Tests of Seismic Retrofit Technique Using Curved Members for Steel Frames

A retrofit technique leveraging the advantages of curved members previously was developed to address the drawbacks of conventional retrofit methods for steel column bases, which typically enhance local strength and stiffness and result in increased acceleration input and seismic demand. The proposed curved-member retrofit technique was verified to have moderately enhanced strength and stiffness with low structural disturbances. To extend the application of the proposed retrofit technique from column bases to other brittle or older structural components in buildings, this study presents experimental and analytical work. A series of experiments was conducted on pre- and postretrofit subassemblies of column bases and beam–column connections to verify their seismic performance and validate the proposed design approach. The retrofitted frame achieved increases in initial stiffness, yield strength, and ultimate strength, consistent with the design targets. Additionally, the structural ductility was doubled, with stable hysteretic responses maintained up to 6% story drift, while reducing the rotational demand at the column base and the beam–column connection. A general numerical modeling approach is proposed and was verified to accurately capture all yield mechanisms as well as measured responses. The necessity of continuity plates at the curved-member– beam connections also was evaluated.