to actual and accidental torsion, required for design of
when the element is deformed beyond the deformation
the isolation system.
corresponding to the development of its nominal
strength. Nonductile elements cannot reliably sustain
Total Design Displacement: The design earthquake
significant deformation beyond that attained at their
lateral displacement, including additional
Equipment Support: Those structural members or
assemblies of members or manufactured elements,
including braces, frames, legs, lugs, snuggers, hangers or
due to actual and accidental torsion, required for
saddles, that transmit gravity load and operating load
design of the isolation system or an element thereof.
between the equipment and the structure.
Total Maximum Displacement: The maximum
Essential Facility: A facility or structure required for post-
capable earthquake lateral displacement, including
additional displacement due to actual and accidental
Factored Resistance (λ D): Reference resistance
torsion, required for verification of the stability of the
isolation system or elements thereof, design of
multiplied by the time effect and resistance factors. This
building separations, and vertical load testing of
value must be adjusted for other factors such as size effects,
isolator unit prototypes.
moisture conditions, and other end-use factors.
Displacement Restraint System: A collection of
Flexible Diaphragm: A diaphragm with stiffness
structural elements that limits lateral displacement of
characteristics indicated in paragraph 5-9b(1).
seismically isolated structures due to the maximum
Flexible Equipment Connections: Those connections
between equipment components that permit rotational
Drag Strut (Collector, Tie, Diaphragm Strut): A
and/or translational movement without degradation of
diaphragm or shear wall boundary element parallel to the
performance. Examples include universal joints, bellows
applied load that collects and transfers diaphragm shear
expansion joints, and flexible metal hose.
forces to the vertical-force-resisting elements or distributes
forces within the diaphragm or shear wall. A drag strut
often is an extension of a boundary element that transfers
forces into the diaphragm or shear wall.
Allowable Bearing Capacity: Foundation load or
stress commonly used in working-stress design (often
Effective Damping: The value of equivalent viscous
controlled by long-term settlement rather than soil
damping corresponding to energy dissipated during cyclic
response of the isolation system.
Deep Foundation: Piles or piers.
Effective Stiffness: The value of the lateral forces in the
isolation system, or an element thereof, divided by the
Differential Compaction: An earthquake-induced
corresponding lateral displacement.
process in which loose or soft soils become more
compact and settle in a nonuniform manner across a
Ductile Element: An element capable of sustaining
Footing: A structural component transferring the
large cyclic deformations beyond the attainment of its
weight of a building to the foundation soils and
nominal strength without any significant loss of
resisting lateral loads.
Foundation Soils: Soils supporting the foundation
Limited Ductile Element: An element that is
system and resisting vertical and lateral loads.
capable of sustaining moderate cyclic deformations
beyond the attainment of nominal strength without
Foundation Springs: Method of modeling to
significant loss of strength.
incorporate load-deformation characteristics of
Nonductile Element: An element having a mode of
Foundation System: Structural components
failure that results in an abrupt loss of resistance