(c) Maximum displacement. The maximum
Motion A or Ground Motion B, as defined in Chapter
displacement of the isolation system, DM, in the most
4.
critical direction of horizontal response shall be
TD = effective period, in seconds (sec), of
calculated in accordance with the formula:
seismically
isolated
structure
at
the
design
displacement in the direction under consideration, as
g
2 S M 1TM
prescribed by Equation 8-2.
4π
DM =
(8-3)
BM
BD = numerical coefficient related to the
effective damping of the isolation system at the
where:
design displacement, $D, as set forth in Table 8-1.
g = acceleration of gravity. The units of the
(b) Effective period. The effective period of
the isolated structure, TD, shall be determined using
units of the design displacement, DD, are inches
the deformational characteristics of the isolation
(mm).
system in accordance with the following equation:
SM1 =
maximum considered 5 percent
W
damped spectral acceleration at 1-second period as
TD = 2π
(8-2)
k Dmin g
determined in Chapter 3.
TM =
effective period, in seconds, of
where:
seismic-isolated
structure
at
the
maximum
displacement in the direction under consideration as
W = total seismic dead load weight of the
prescribed by Equation 8-4.
structure above the isolation interface as defined in
Sections 5.3.2 and 5.5.3 of FEMA 302 (kip or kN).
BM = numerical coefficient related to the
effective damping of the isolation system at the
kDmin = minimum effective stiffness, in
maximum displacement, $D, as set forth in Table 8-1.
kips/inch (kN/mm), of the isolation system at the
design displacement in the horizontal direction under
(d)
Effective
period
at
maximum
consideration.
displacement. The effective period of the isolated
structure at maximum displacement, TM, shall be
g = acceleration of gravity. The units of the
determined using the deformational characteristics of
the isolation system in accordance with the equation:
units of the design displacement, DD, are inches
(mm).
W
TM = 2π
(8-4)
k Mmin g
8 - 14
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