estimated by multiple analyses of the building frame,
displacement response of the device under all sources
using limiting values for the spring and dashpot
of loading (e.g., gravity, seismic, thermal).
constants.
e.
Linear Analytical Procedures.
(c) Fluid viscous devices.
(1) General.
1. The cyclic response of a fluid viscous
device is dependent on the velocity of motion; may
(a) Linear procedures are only permitted if
be dependent on the frequency and amplitude of the
it can be demonstrated that the framing system
motion; and is generally dependent on the operation
exclusive of the energy dissipation devices remains
temperature (including temperature rise due to
essentially linearly elastic for the level of earthquake
excitation). Fluid viscous devices may exhibit some
demand of interest after the effects of added damping
stiffness at high frequencies of cyclic loading. Linear
are considered.
Further, the effective damping
fluid viscous dampers exhibiting stiffness in the
afforded by the energy dissipation shall not exceed
30 percent of critical in the fundamental mode. Other
a fluid viscoelastic device.
limits on the use of linear procedures are presented
below.
2.
In the absence of stiffness in the
(b) The secant stiffness, Ks, of each energy
viscous device may be expressed as:
dissipation device, calculated at the maximum
displacement in the device, in a manner similar to
that
indicated
in
Figure
8-7
for
the
target
α
F = CO D sgnD
(8-17)
displacement of the building, shall be included in the
mathematical model of the rehabilitated building.
For the purpose of evaluating the regularity of a
where C0 is the damping coefficient for the device, "
building, the energy dissipation devices shall be
is the velocity exponent for the device, D is the
included in the mathematical mode.
relative velocity between each end of the device, and
sgn is the signum function that, in this case, defines
the sign of the relative velocity term.
(d)
Other types of devices.
Energy
dissipation
devices
not
classified
as
either
displacement-dependent
or
velocity-dependent
should be modeled using either established principles
of mechanics or phenomenological models.
Such
models should accurately describe the force-velocity-
8 - 30
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