Linear Static and Dynamic Procedures for Structures With Velocity-Dependent Supplemental Dampers.
Linear Static and Dynamic Procedures for Structures With
Velocity-Dependent Supplemental Dampers.
Sadek, F.; Mohraz, B.; Riley, M. A.
NISTIR 6329; 55 p. May 1999.
Available from: National Technical Information Service
(NTIS), Technology Administration, U.S. Department of
Commerce, Springfield, VA 22161.
1-800-553-6847 or 703-605-6000;
Order number: PB99-139859
dampers; structures; codes; dissipation; velocity
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.