design displacement in the horizontal direction
isolation system shall be designed and constructed to
withstand a minimum lateral seismic force, Vs, using
under consideration.
all of the appropriate provisions for a nonisolated
DD = design displacement, in inches (mm),
structure, where:
at the center of rigidity of the isolation system in the
Vs = kDmaxDD
direction under consideration as prescribed by
(8-7)
Equation 8-1.
where:
RI =
numerical coefficient related to the
kDmax =
maximum effective stiffness, in
type of lateral-force-resisting system above the
kips/inch (kN/mm), of the isolation system at the
isolation system.
design displacement in the horizontal direction under
The RI factor shall be based on the type of lateral-
consideration.
force-resisting system used for the structure above
DD = design displacement, in inches (mm),
the isolation system and shall be 3/8 of the R value
at the center of rigidity of the isolation system in the
given in Table 7-1, with an upper-bound value not to
direction under consideration as prescribed by
exceed 2.0, and a lower-bound value not to be less
Equation 8-1.
than 1.0.
In all cases, Vb shall not be taken as less than the
(4) Vertical distribution of force. The total
maximum force in the isolation system at any
force shall be distributed over the height of the
displacement, up to and including the design
structure above the isolation interface in accordance
displacement.
with the following equation:
(b) Structural elements above the isolation
Vs w x hx
Fx =
(8-9)
system.
The structure above the isolation system
n
∑wh
i
i
shall be designed and constructed to withstand a
i=1
minimum shear force, Vs, using all of the appropriate
provisions for a nonisolated structure, where:
where:
k Dmax DD
Vs = total lateral seismic design force or
VS =
(8-8)
RI
shear on elements above the isolation system as
prescribed by Equation 8-8.
where:
wx =
portion of w that is located at or
assigned to Level x.
kDmax =
maximum effective stiffness, in
kips/inch (kN/mm), of the isolation system at the
8 - 16
Previous Page
