Linear Procedures for Structures with Velocity-Dependent Dampers
Fahim Sadek, B Mohraz, Michael A. Riley
Passive energy dissipation devices are used to reduce the damaging effects of earthquakes. These devices can absorb a portion of the earthquake-induced energy in structures and thus reduce the energy demand on structural members. 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: 1) to investigate the effect of increased viscous damping on the seismic response of structures; 2) to assess the accuracy of the linear static (LSP) and linear dynamic (LDP) 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) to propose modifications to the current design procedures to improve their accuracy and reliability. Based on the analysis of single-degree-of-freedom structures under an ensemble of earthquake records, it is shown that the effect of increased damping on the displacement response is more pronounced in structures with intermediate periods. For long-period structures, however, an increase in damping decreases displacements, but increases the absolute accelerations and consequently, the seismic forces. The study also 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; 2) the assumption of a harmonic response to compute the peak velocity; and 3) the computation of design forces based on the assumption that the structure undergoes a harmonic motion with an amplitude equal to the peak displacement and a frequency equal to that of the fundamental mode. In most cases, these assumptions result in non-conservative estimates of the peak response and design force. Comparisons of the methods proposed in this study and in FEMA 273 for several single- and multi-degree-of-freedom structures indicate that the former produces more reliable results.
Journal of Structural Engineering-Asce
building technology, design codes, passive energy dissipation, structural control, structural dynamics, supplemental dampers