damping modification factor, B, and either Bs or Bl,
the viscous forces so that the horizontal displacement
for periods in the vicinity of the mode under
of each floor level is zero.
consideration; note that the value of B will be
different for each mode of vibration. The damping
iii.
At the stage of maximum floor
acceleration. Design actions in components of the
modification factor in each significant mode should
be determined using Table 8-2 and the calculated
rehabilitated building should be determined as the
effective damping in that mode.
The effective
sum of [actions determined at the stage of maximum
drift] times [CF1] and [actions determined at the stage
damping should be determined using a procedure
of maximum velocity] times [CF2], where
similar to the described in Paragraph 8-4e(2)(a).
[
]
CF1 = cos tan -1 (2β eff )
2.
If the maximum base shear force
(8-23)
calculated by dynamic analysis is less than 80 percent
of the modified equivalent base shear of Paragraph 8-
[
)]
CF2 = sin tan (2βeff
-1
(8-24)
4e(2)(a), component and element actions and
deformations shall be proportionally increased to
in which $eff is defined by either Equation 8-20 or
correspond to 80 percent of the modified equivalent
Equation 8-22.
base shear.
(3) Linear Dynamic Procedure (LDP). The
(b) Velocity-dependent devices.
modal analyses procedure, described in Paragraph 3-
2(c)(2), may be used when the effective damping in
1. For analysis by the Response Spectrum
the fundamental mode of the building, in each
Method, the 5 percent damped response spectrum
principal direction, does not exceed 30 percent of
may be modified to account for the damping afforded
critical.
by the velocity-dependent energy dissipation devices.
The 5 percent damped acceleration spectrum should
(a)
Displacement-dependent
devices.
be reduced by the modal-dependent damping
Application of the LDP for the analysis of buildings
modification factor, B, either Bs or Bl, for periods in
incorporating displacement-dependent devices is
the vicinity of the mode under consideration; note
subject to the restrictions set forth in Paragraph 8-4-
that the value of B will be different for each mode of
e(2)(a).
vibration. The damping modification factor in each
significant mode should be determined using Table 8-
1. For analysis by the Response Spectrum
2 and the calculated effective damping mode.
Method, the 5 percent damped response spectrum
may be modified to account for the damping afforded
The effective damping in the m-th
2.
the
displacement-dependent
energy-dissipation
mode of vibration ($eff-m) shall be calculated as:
devices.
The 5 percent damped acceleration
spectrum should be reduced by the modal-dependent
8 - 35
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