Effect of supplemental viscous damping on the seismic response of structural systems with metallic dampers

Metallic dampers can enhance structural performance by reducing seismically induced lateral displacements, and by reducing inelastic behavior of beams and columns. Limiting story drift also indirectly allows us to mitigate damage of nonstructural components that are sensitive to lateral deformations. However, many nonstructural elements and components are vulnerable to excessive accelerations. Therefore, in order to protect these components, floor accelerations in buildings should be kept below certain limits. In this perspective, this paper investigates the seismic performance of single-degree-of-freedom (SDOF) systems with metallic and viscous dampers installed in parallel, to determine the effectiveness or appropriateness of using metallic dampers to mitigate lateral displacements, simultaneously with viscous dampers to reduce acceleration demands, knowing that their behavior is fundamentally different (i.e., metallic dampers are displacement dependent, whereas velocity dampers are velocity dependent). The effect of a combination of these damping systems is, therefore, studied for SDOF structures as a contribution to the state-of-the-art of seismic protection of nonstructural components. Parametric analyses investigate the effectiveness of adding various levels of viscous damping on the equivalent hysteretic damping and on the spectral floor acceleration for short, intermediate, and long period structures. Argand diagrams are used to explain why in some instances it is observed that adding viscous dampers to strongly inelastic systems can result in increases in floor acceleration (rather than the intended decreases). Results from this study are also applicable to buildings that have been retrofitted with viscous dampers and whose original frame still behaves inelastically after the retrofit.