Effects of Earthquakes

DOE-STD-1020-2002

by an instrument on a small pad. These reductions are due to vertical spatial variation of the

ground motion (reduced motion with depth), horizontal spatial variation of the ground motion

(basemat averaging effects), and wave scattering effects (modification of earthquake waves

striking a rigid structure foundation).

Earthquake ground shaking generally has lateral, vertical, and rotational components.

Structures are typically more vulnerable to the lateral component of seismic motion; therefore, a

lateral force-resisting system must be developed. Typical lateral force-resisting systems for

buildings include moment-resisting frames, braced frames, shear walls, diaphragms, and

foundations. Properly designed lateral force-resisting systems provide a continuous load path

from the top of the structure down to the foundation. Furthermore, it is recommended that

redundant load paths exist. Proper design of lateral force-resisting systems must consider the

relative rigidities of the elements taking the lateral load and their capacities to resist load. An

example of lack of consideration for relative rigidity are frames with brittle unreinforced infill

walls that are not capable of resisting the loads attracted by such rigid construction. In addition,

unsymmetrical arrangement of lateral force-resisting elements can produce torsional response

which, if not accounted for in design, can lead to damage. Even in symmetrical structures,

propagating earthquake ground waves can give rise to torsion. Hence, a minimum torsional

loading should be considered in design or evaluation.

Earthquake ground shaking causes limited energy transient loading. Structures have

energy absorption capacity through material damping and hysteretic behavior during inelastic

response. The capability of structures to respond to earthquake shaking beyond the elastic limit

without major damage is strongly dependent on structural design details. For example, to

develop ductile behavior of inelastic elements, it is necessary to prevent premature abrupt failure

of connections. For reinforced concrete members, design is based on ductile steel reinforcement

in which steel ratios are limited such that reinforcing steel yields before concrete crushes, abrupt

bond or shear failure is prevented, and compression reinforcement includes adequate ties to

prevent buckling or spalling. With proper design details, structures can be designed to withstand

different amounts of inelastic behavior during an earthquake. For example, if the goal is to

prevent collapse, structures may be permitted to undergo large inelastic deformations resulting in

structural damage that would have to be repaired or replaced. If the goal is to allow only minor

damage such that there is minimal or no interruption to the ability of the structure to function,

only relatively small inelastic deformations should be permitted. For new facilities, it is assumed

that proper detailing will result in permissible levels of inelastic deformation at the specified

force levels, without unacceptable damage. For existing facilities, the amount of inelastic

behavior that can be allowed without unacceptable damage must be estimated from the as-is

condition of the structure.

Potential damage and failure of structures, systems, and components (SSCs) due to both

direct earthquake ground shaking and seismic response of adjacent SSCs must be considered.

The interaction of SSCs during earthquake occurrence can produce additional damage/failure

modes to be addressed during seismic design or evaluation. Examples of interaction include: (1)

seismic-induced failure of a relatively unimportant SSC which falls on a SSC which is important

to safety or to the mission; (2) displacements of adjacent SSCs during seismic response resulting

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