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).
Linear Analytical Procedures.
(c) Fluid viscous devices.
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
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
Further, the effective damping
fluid viscous dampers exhibiting stiffness in the
frequency range 0.5 f1 to 2.0 f1 should be modeled as
30 percent of critical in the fundamental mode. Other
a fluid viscoelastic device.
limits on the use of linear procedures are presented
In the absence of stiffness in the
frequency range 0.5 f1 to 2.0 f1, the force in the fluid
(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
F = CO D sgnD
displacement of the building, shall be included in the
mathematical model of the rehabilitated building.
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.
Other types of devices.
should be modeled using either established principles
of mechanics or phenomenological models.
models should accurately describe the force-velocity-
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