displacement due to vertical deformation of the
parameter of interest shall be calculated for each
isolation system, shall not exceed the following
time-history analysis. If three time-history analyses
limits:
are performed, the maximum response of the
parameter of interest shall be used for design.
If
1. The maximum interstory drift of the
seven or more time-history analyses are performed,
structure above the isolation system calculated by
the average value of the response parameter of
response-spectrum analysis shall not exceed 0.015hsx,
interest shall be used for design.
and
(6) Design lateral force.
2. The maximum interstory drift of the
structure above the isolation system calculated by
(a) Isolation system and structural elements
time-history analysis considering the force-deflection
at or below the isolation system.
The isolation
characteristics of nonlinear elements of the lateral-
system, foundation, and all structural elements below
force-resisting system shall not exceed 0.020hsx.
the isolation system shall be designed using all of the
appropriate requirements for a non-isolated structure
Drift shall be calculated using Equation 5.3.8.1 of
and the forces obtained from the dynamic analysis
FEMA 302 with the Cd factor of the isolated structure
without reduction.
equal to the RI factor defined in Paragraph 8-3e(3)(b).
The secondary effects of the maximum considered
(b) Structural elements above the isolation
earthquake lateral displacement ) of the structure
system.
Structural elements above the isolation
above the isolation system combined with gravity
system shall be designed using the appropriate
forces shall be investigated if the interstory drift ratio
provisions for a non-isolated structure and the forces
exceeds 0.010/RI.
obtained from the dynamic analysis divided by a
factor of RI. The RI factor shall be based on the type
g.
Acceptance Criteria.
of lateral-force-resisting system used for the structure
above the isolation system.
(1) Performance Objective 1A. Compliance
with the provisions of Paragraphs 8-3e or 8-3f with
(c) Scaling of results. When the factored
Ground Motion as the design ground motion will be
lateral shear force on structural elements, determined
considered to satisfy this performance objective.
using either response-spectrum or time-history
analysis, is less than the minimum level prescribed by
(2) Enhanced performance objectives. The
Paragraph
8-3f(2)
and
8-3f(3),
all
response
design ground motion for enhanced performance
parameters, including member forces and moments,
objectives will be as indicated in Table 4-4. The
shall be adjusted proportionally upward.
analysis will be performed without the response
modification factor, RI, and the acceptance criteria
(d) Drift limits. Maximum interstory drift
corresponding to the design lateral force, including
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