Earthquakes - Geotechnical Engineering Investigation - page 971

TABLE 11.13
Seismic Analysis Progression

Project Stage

Zone Reconnaissance Feasibility Design Memo a

0 and 1 E → SCM → RS b

2A and 2B E → SCM → RS

SCM b → RS b → TH c

SCM → RS → TH

3 and 4 SCM → RS → RS d

RS b → TH c → TH c

Note :E Experience of the structural design engineer; SCM Seismic coefficient method of analysis; RS Response

Time-history analysis.
a If the project proceeds directly from feasibility to plans and specifications stage, a seismic design memoran-
dum will be required for all projects in zones 3 and 4, and projects for which a TH analysis is required.
b Seismic loading condition controls design of an unprecedented structure or unusual configuration or adverse
foundation conditions.
c Seismic loading controls the design requiring linear or nonlinear time-history analysis.
d RS may be used in seismic zones 3 and 4 for the feasibility and design memorandum phases of project devel-
opment only if it can be demonstrated that phenomena sensitive to frequency content (such as soil-structure
interaction and structure-reservoir interaction) can be adequately modeled in an RS.
Source:

spectrum analysis; TH

From USACE, U.S. Army Corps. Of Engineers, ER 1110-2-1806, July 31, 1995. With permission.

11.4.6 The Design Earthquake

Definitions
General
The design earthquake is normally defined as the specification of the ground motion as a
basis for design criteria to provide resistance to a moderate earthquake without damage,
and to provide resistance to a major event without collapse.

Standard Structures (Uniform Building Code, 1997)

Design basis earthquake ( DBE ): The building should not collapse in an earthquake
with a 10% probability of exceedance in 50 years.

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Operating basis earthquake ( OBE ): The building should not collapse in an earth-
quake with a 50% probability of exceedance in 50 years.

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Standard Structures (USACE, 1999)

Operating basis earthquake ( OBE ) is an earthquake with a 50% probability of
exceedance during the service life of the structure, which performs with little or
no damage and without interruption or loss of service.

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Maximum design earthquake ( MDE ) is the maximum level of ground motion for
which a structure is designed, and the structure performs without catastrophic
failure, although severe damage or economic loss may be tolerated.

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Nuclear Power Plants
Two loading levels are given by the U.S. Nuclear Regulatory Commission (USNRC):

Operating-basis earthquake ( OBE ) is the vibratory ground motion through which
the safety features of the plant must remain functional while the plant remains in

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