Earthquake response of symmetric and asymmetric one-story elastic systems with nonlinear fluid viscous dampers or nonlinear viscoelastic dampers

Investigated are earthquake responses of symmetric and asymmetric one-story elastic systems with nonlinear fluid viscous dampers (FVDs) connected in series to a linearly elastic brace (i.e., Chevron or inverted V-shape brace), which constitutes a nonlinear viscoelastic (VE) damper when the brace is flexible. This investigation aims to improve the fundamental understanding of how and why nonlinear FVDs and VE dampers are effective in reducing structural response and to develop simplified analysis and design procedures for practical applications of these dampers. An innovative technique to parameterize the dynamic characteristics of a nonlinear FVD and a nonlinear VE damper is developed for single-degree-of-freedom (SDF) systems, which is then extended to asymmetric one-story, 2-degree-of-freedom systems. The response of SDF and asymmetric one-story systems is found to be influenced similarly by damper nonlinearity and bracing flexibility. In particular, damper nonlinearity has essentially no influence on earthquake response of SDF systems in the velocity-sensitive region of the spectrum, but differences up to 14% and 17% are observed in the acceleration- and displacement-sensitive spectral regions, respectively. Bracing flexibility increased structural response by less than 10% over the practical range of bracing stiffness and by less than 20% when the brace is very flexible.; Supplemental damping can effectively reduce the response of asymmetric one-story systems; however this effectiveness depends significantly on the planwise distribution of supplemental damping. Asymmetric distributions of supplemental damping that are more effective in reducing the response compared to symmetric distribution are identified. The percentage reduction achieved by a judiciously selected asymmetric distribution can be twice or even larger compared to symmetric distribution. The influence of the planwise distribution of nonlinear VE dampers is found similar to that of linear FVDs because damper nonlinearity and bracing flexibility have little influence on structural response. Finally, an iterative linear analysis procedure is developed to estimate structural response and damper force directly from the earthquake design spectrum for an asymmetric one-story system with nonlinear VE dampers. From these results, a procedure is developed for designing a nonlinear supplemental damping system that satisfies the design criteria for a given earthquake design spectrum. These procedures are simple and accurate, which can be extended to multi-story buildings with symmetric- or asymmetric-plan.