Equivalent Damping Ratios of Structures with Supplemental Viscous Dampers

The current design formulas such as those provided by FEMA273/274 for building structures with supplemental viscous dampers were derived based on the shear building assumption. However, for medium-rise to high-rise buildings that deform in a combined form of shear and bending when subjected to seismic loading, the design using existing formulas may result into an actual damping ratio much lower than what is expected by the design. Therefore, the actual seismic performance of the structure may be worse than what is expected by the design. In this study, modified design formulas are derived considering both shear and flexural deformations of the building structures subjected to ground excitations. The modified formulas are derived for two often used installation schemes of viscous dampers including diagonal-brace-damper system and K-brace-damper system. Numerical verifications have indicated that the modified design formulas predict a more accurate viscous damping ratio contributed by linear viscous dampers and ensure a more conservative design for the structure with nonlinear viscous dampers. _____________ J.S. Hwang , National Center for Research on Earthquake Engineering, Taiwan , Taipei 106,Taiwan, R.O.C S.L. Yi and S.Y. Ho , Department of Construction Engineering, National Taiwan University of Science and Technology, Taipei 106,Taiwan, R.O.C .