glazing, utilities, computer equipment, piping and
mechanical systems, and other critical building
(a)
Structural Damage to Conventionally
components must be reviewed in order to assess the
Designed Buildings.
Based on observations from
post-earthquake functionality of essential facilities.
past earthquakes and laboratory tests, it is assumed
that a properly detailed structure, designed to remain
(a) Conventional Design. In order to meet
elastic for reduced seismic forces, will have sufficient
restrictive
post-earthquake
functionality
strength and energy absorption capability to resist a
requirements,
most
conventionally
designed
major earthquake without collapse.
The energy
buildings must be designed to remain elastic for
absorption
capacity
of
conventional
structural
larger earthquake forces, with less reliance on
systems is a result of the yielding and degradation,
ductility, increased damping, or significant inelastic
i.e., damage to the structural and non-structural
behavior.
elements of the building. This includes degradation
of beam-column joints, buckling of steel braces,
(b)
Passive Control Systems.
Seismic
cracking of shear panels and interior partition walls,
isolation and energy dissipation systems offer
etc.
Following a major earthquake, buildings
attractive alternatives to conventional design, since
designed to meet the minimum life-safety standard
all these schemes can be used to reduce the
are not expected to be functional, and may not be
earthquake input energy and concentrate the inelastic
repairable.
deformations in the isolators or damping devices,
protecting critical elements of the structural frame
(b) Passive Control Systems. To date, most
from damage. Isolation and dissipation devices all
projects
where
these
technologies
have
been
have a yield threshold, and exhibit elastic behavior
employed involve structures that were designed to a
below this threshold and inelastic behavior after
standard higher than life safety. In the future, these
initial yielding. It is therefore especially important
technologies may be useful in providing structures
that response to both small and large earthquake
that meet the life safety objectives with lower life-
motions be investigated, in order to capture the
cycle costs than for conventional design, or providing
effective range of behavior of the particular device.
cost-effective seismic upgrades for older construction
that does not comply with current life safety
requirements.
8-3.
Seismic Isolation Systems.
(2)
Damage control and post-earthquake
functionality. In order to reduce or avoid damage to
a.
Design Concept. The design of a seismic
structures and building systems, a building' behavior
s
isolation system depends on many factors, including
must be investigated for a range of earthquake
the period of the fixed-base structure, the period of
motions from smaller, more frequent events, to
the isolated structure, the dynamic characteristics of
larger, infrequent events.
Seismic demands on
the soil at the site, the shape of the input response
structural elements, stairs, ceiling systems, cladding,
spectrum, and the force-deformation relationship for
8-5
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