d.
Design Criteria.
3.
The structure above the isolation
interface is not more than four stories or 65 feet (20
m) in height;
(1) Basis for design. The procedures and
limitations for the design of seismically isolated
4.
The effective period of the isolated
structures shall be determined considering zoning,
structure, TM, is less than or equal to 3.0 sec.;
site characteristics, vertical acceleration, cracked
section properties of concrete and masonry members,
5.
The effective period of the isolated
Seismic Use Group, configuration, structural system,
structure, TD, is greater than three times the elastic,
and height in accordance with Section 5.2 of FEMA
fixed-base period of the structure above the isolation
302, except as noted below.
system, as determined by Equations 5.3.3.1-1 or
5.3.3.1-2 of FEMA 302;
(2)
Stability of the isolation system.
The
stability of the vertical-load-carrying elements of the
6.
The structure above the isolation
isolation system shall be verified by analysis and test,
system is of regular configuration; and
as required, for lateral seismic displacement equal to
the total maximum displacement.
7. The isolation system meets all of the
following criteria:
(3) Selection of analytical procedure.
The effective stiffness of the isolation
(a)
General.
Any seismically isolated
structure is permitted to be designed using the
system at the design displacement is greater than
dynamic lateral response procedure of Paragraph 8-
one-third of the effective stiffness at 20 percent of
3f, as are certain seismically designed structures
the design displacement;
defined below.
The isolation system is capable of
(b)
Equivalent lateral-force procedures.
producing a restoring force as specified in Paragraph
The
equivalent
lateral-response
procedure
of
8-3i(2)(d);
Paragraph 8-3e is permitted to be used for design of a
seismically isolated structure, provided that:
The isolation system has force-
deflection properties that are independent of the rate
1. The structure is located at a site with S1
of loading;
less than or equal to 0.60g;
The isolation system has force-
2. The structure is located on a Class A,
deflection properties that are independent of vertical
B, C, or D site;
load and bilateral load; and
8 - 12
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