Influence of maxwell stiffness in seismic response of frames equipped with viscous dampers

Resumen

Added viscous damping systems improve the seismic resiliency of structures through a reduction of key variables related to damage. These systems can be mathematically represented by a serial combination of a linear spring and a non-linear dashpot. The spring stiffness, referred to as Maxwell stiffness, is dominated by the most flexible element of the set, including brace extender, auxiliary mounting hardware and the damper itself. Existing experimental data are used hereby to show that the actual stiffness is a reduced fraction (between 0.25 and 0.50) of the value generally adopted in design, based solely on the brace extender properties. A numerical study involving a 3- and a 5- storey frames equipped with different viscous damping systems, indicates that this stiffness reduction results in a very large increase in structural damage (measured by the plastic strain energy dissipated by the main structure), and a large increase in total acceleration. Additionally, in the 5-storey frame, residual drift ratio and drift ratio show a large to moderate sensitivity to the Maxwell stiffness. These results suggest that, on the absence of accurate experimental information, the Maxwell stiffness used for analysis and damage estimation should be conservatively taken as a fraction (between 0.25 and 0.50, approximately) of the stiffness based on brace extender properties and centerline length. Due to the scarcity of experimental data used, these conclusions must be considered as preliminary