(2) Glass windows should be isolated with
thus permitting the acceptance of an otherwise
adequate clearance and flexible mountings at edges
to allow for frame distortions.
(2) Innovative systems. Systems and devices
(3) Rigid nonstructural partitions should have
are available for controlling and/or limiting the
room to move at the top and sides.
response of structures to earthquake ground motion.
The best known of these systems are seismic
In piping installations, the expansion
isolation systems (sometimes called base isolation
loops and flexible joints used to accommodate
systems). Seismic isolation is based on the premise
temperature movement are often adaptable to
that the structure can be substantially decoupled
accommodating seismic deflections.
from potentially damaging earthquake motions. By
decoupling the structure from the ground motion,
(5) Freestanding shelving can be fastened to
seismic isolation reduces the level of response in the
walls to prevent toppling. Shelves can be provided
structure from the level that would otherwise occur
with lips or edge restraints to prevent contents from
in a conventional fixed-base building, or conversely,
falling off in an earthquake.
offers the advantage of designing with a reduced
level of earthquake load to achieve the same degree
Alternatives to the Prescribed Provisions.
Alternatives to the seismic provisions of this
conventional fixed-base building. Other innovative
document are permitted if they can be properly
substantiated. The most common alternatives are the
devices. Limited guidance for the design of seismic
use of more rigorous analytical procedures or the use
of innovative systems.
in Chapter 8. These systems are relatively new and
sophisticated concepts that require more extensive
design and detailed analysis than most conventional
approximate analyses are generally based on
schemes. Peer review must be an essential part of
assumptions that require a significant degree of
any project that includes seismic isolation or energy
conservatism. A more rigorous analysis may require
characteristics of the structural elements and
materials, but may incorporate less conservatism,
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