and connections between braces and the energy
(e)
The components and connections
dissipation devices.
transferring forces between the energy dissipation
devices shall be designed to remain linearly elastic
(c)
Energy dissipation devices should be
for the forces described in items (d)1 or (d)2 above,
modeled as described in the following subsection,
depending upon the degree of redundancy in the
unless more advanced methods or phenomenological
supplemental damping system.
models are used.
(2) Modeling of energy-dissipation devices.
(3) Displacement-dependent devices.
(a) Energy-dissipation devices are classified
(a) The force-displacement response of a
as
either
displacement-dependent,
velocity-
displacement-dependent
device
is
primarily
a
dependent,
or
other.
Displacement-dependent
function of the relative displacement between each
devices may exhibit either rigid-plastic (friction
end of the device. The response of such a device is
devices), bilinear (metallic yielding devices), or
substantially independent of the relative velocity
trilinear hysteresis. The response of displacement-
between each end of the device, and/or frequency of
dependent devices should be independent of velocity
excitation.
and/or frequency of excitation. Velocity-dependent
devices include solid and fluid viscoelastic devices,
(b) Displacement-dependent devices should
and fluid viscous devices. The third classification
be modeled in sufficient detail so as to capture their
(other) includes all devices that cannot be classified
force-displacement response adequately, and their
as
either
displacement-
or
velocity-dependent.
dependence,
if
any,
on
axial-shear-flexure
Examples of "other" devices include shape memory
interaction, or bilateral deformation response.
with recentering capability, and fluid-restoring force-
(c)
For the purposes of evaluating the
damping devices.
response of a displacement-dependent device from
testing data, the force in a displacement-dependent
(b) Models of the energy dissipation system
device may be expressed as:
should include the stiffness of structural components
that are part of the load path between the energy-
dissipation devices and the ground, if the flexibility
F = keff D
(8-12)
of these components is significant enough to affect
the performance of the energy dissipation system.
where the effective stiffness keff of the device is
Structural components whose flexibility could affect
calculated as:
the performance of the energy dissipation system
include components of the foundation, braces that
F+ + F-
work in series with the energy dissipation devices,
keff =
(8-13)
D + D
+
-
8 - 28
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