Linear Procedures for Structures with Velocity-Dependent Dampers

Passive energy dissipation devices are used to reduce the damage from earthquakes by absorbing a portion of the earthquake-induced energy in structures. Wide acceptance of these devices in structures will depend on the availability of simplified methods for their analysis and design. The objectives of this study are to (1) investigate the effect of increased viscous damping on the seismic response of structures; (2) assess the accuracy of the linear static and linear dynamic procedures recommended in the NEHRP Guidelines for the Seismic Rehabilitation of Buildings (FEMA 273) for design of structures with velocity-dependent passive energy dissipation devices; and (3) propose modifications to the current design procedures to improve their accuracy. Based on the analysis of single-degree-of-freedom structures subjected to a large number of earthquake records, the study identifies the following limitations of the FEMA 273 procedures: (1) The use of a constant reduction factor for the displacement response of short-period structures; and (2) the assumption of a harmonic response to compute the peak velocity as well as the story and base shears. In many cases, these assumptions result in nonconservative estimates of the peak response and base shear. Comparisons of the results using the methods proposed in this study and in FEMA 273 with time-history analyses for several single- and multi-degree-of-freedom structures indicate that the proposed procedures give more accurate results.