examples of passive control systems.
Some
CHAPTER 8
examples of these devices are presented in Figure 8-
SEISMIC ISOLATION AND ENERGY
DISSIPATION SYSTEMS
1. It is interesting to note that many of these devices
can be used at the base of a structure as part of an
isolation system, or in combination with braced
8-1.
Introduction.
frames or walls as energy dissipation devices.
The purpose of this chapter is to provide a brief
(a)
Seismic isolation systems.
The
overview of many new technologies that are rapidly
objective of these systems is to decouple the building
becoming more prevalent in the seismic design of
structure from the damaging components of the
building structures, and to provide guidance for the
earthquake input motion, i.e., to prevent the
consideration and evaluation of the use of these
superstructure of the building from absorbing the
systems in selected buildings. These technologies all
earthquake energy. The entire superstructure must be
involve the use of special details or specific devices
supported on discrete isolators whose dynamic
to alter or control the dynamic behavior of buildings.
characteristics are chosen to uncouple the ground
The structural systems that utilize these technologies
motion.
Some isolators are also designed to add
can be broadly categorized as passive, active, or
substantial damping. Displacement and yielding are
hybrid control systems. Definitions of these terms
concentrated at the level of the isolation devices, and
are provided below, although the primary focus of
the superstructure behaves very much like a rigid
this chapter is on passive control systems. Additional
body.
guidelines and design provisions for base isolation
systems are provided in FEMA 302.
Similar
(b) Passive energy dissipation systems. The
guidance for energy dissipation systems is provided
objective of these systems is to provide supplemental
in FEMA 273.
damping in order to significantly reduce structural
response to earthquake motions. This may involve
a.
System Definitions.
the addition of viscous damping through the use of
viscoelastic dampers, hydraulic devices or lead
(1) Passive control systems. These systems
extrusion systems; or the addition of hysteretic
are designed to dissipate a large portion of the
damping through the use of friction-slip devices,
earthquake input energy in specialized devices or
metallic yielding devices, or shape-memory alloy
special connection details that deform and yield
devices.
Using these systems, a building will
during an earthquake.
Since the deformation and
dissipate a large portion of the earthquake energy
yielding are concentrated in the device, damage to
through
inelastic
deformations
or
other elements of the building may be reduced.
concentrated in the energy dissipation devices,
These systems are passive in that they do not require
any additional energy source to operate, and are
activated by the earthquake input motion. Seismic
isolation and passive energy dissipation are both
8-1
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