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.

(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, *K*s, 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

(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 *C*0 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

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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