characteristics of the device. In this way, seismic
input energy to the structure is largely dissipated
(a) Review of site-specific seismic criteria,
through the inelastic deformations concentrated in the
including the development of site-specific spectra
devices, reducing damage to other critical elements
and ground motion time histories and all other design
of the building. The benefits resulting from the use
criteria developed specifically for the project;
of
displacement-dependent
energy
dissipation
devices are attributed primarily to the reduction in
(b)
Review of the preliminary design,
spectral demand due to supplemental damping
including the determination of the total design
provided by the devices. A preliminary evaluation of
displacement
of
the
isolation
system
design
these benefits requires the following considerations:
displacement and the lateral force design level;
(1)
From a linear elastic static or modal
(c) Overview and observation of prototype
analysis of the building, determine the story
testing, Paragraph 8-3k;
displacements without the energy dissipation devices.
(d) Review of the final design of the entire
(2) Select target design displacement, DDi, at
structural system and all supporting analyses; and
each story.
From test data furnished by the
manufacturer, determine the effective stiffness, Keff,
(e) Review of the isolation system quality
of the proposed devices at each story using Equation
control testing program, Paragraph 8-3i(2)(i).
8-13.
k.
Required Tests of the Isolation System.
(3)
Based on the effective stiffness of the
Required testing to establish and validate the design
devices and the assumed target displacements,
perspectives of the isolation system shall be in
accordance with the requirements of Section 13.9 of
calculate the effective damping, $, in accordance
FEMA 302.
with Equations 8-18 and 8-19.
(4) Modify the design response spectrum to
8-4.
Energy Dissipation Systems.
represent the effective damping using Table 8-2 and
Figure 8-8.
a.
Design Concept. These systems are designed
to provide supplemental damping in order to reduce
(5)
Modify the mathematical model of the
the seismic input forces.
Most conventional
building to incorporate the effective stiffness of the
buildings are designed assuming 5 percent equivalent
devices in each story.
viscous damping for structures responding in the
elastic range.
For structures that include viscous
dampers or metallic yielding devices, the equivalent
viscous damping may be increased to between 15
percent and 25 percent, depending on the specific
8 - 22
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