Seismic Design and Detailing

DOE-STD-1020-2002

during the service life, then those code minimum strengths should be further reduced to account

for such degradation. The use of code specified minimum strength values or 95% exceedance

strength levels (i.e., 95% of measured strengths exceed the design/evaluation strength level) is

one location in the design/evaluation process where intentional conservatism is introduced.

In general, for load combinations which include the DBE loading, capacities CC to be

used should be based upon code specified minimum ultimate or limit-state (e.g., yield or

buckling) capacity approaches coupled with material strength properties as specified above. For

concrete, the ultimate strength approach with the appropriate capacity reduction factor, `,

included as specified in ACI-318 or ACI-349 are used. For structural steel, the appropriate

AISC specifications are used. The LRFD Ref. C-51) limit-state strength approach with the

appropriate capacity reduction factor, `, included is preferred. However, the Plastic Design

(applicable IBC Standard, Part 2, Ref. C-52 or Chapter N, Ref. C-53) maximum strength

approach may be used so long as the specified criteria are met. The plastic design strengths can

be taken as 1.4 times the allowable shear stress for members and bolts and 1.7 times other

allowable stresses specified in Refs. C-52 or C-53 unless another factor is defined in the

specified code. For ASME Section III, Division 1 components, ASME Service Level D (Ref.

C-54) capacities should be used. In some cases, functional failure modes may require lesser

limits to be defined (e.g., ASME Mechanical Equipment Performance Standard, Ref. C-55).

For existing facilities, in most cases, the capacity evaluation equations should be based

on the most current edition of the appropriate code, particularly when the current edition is more

conservative than earlier editions. However, in some cases (particularly with the ACI and

ASME codes), current code capacities may be more liberal than those specified at the time the

component was designed and fabricated, because fabrication and material specification

requirements have become more stringent. In these later cases, current code capacities will have

to be reduced to account for the more relaxed fabrication and material specifications that existed

at the time of fabrication. In all cases, when material strength properties are based on code

minimum material strengths, the code edition enforced at the time the component was fabricated

should be used to define these code minimum material strengths.

C.5.2

Seismic Design and Detailing

This section briefly describes general design considerations which enable structures or

equipment to perform during an earthquake in the manner intended by the designer. These

design considerations attempt to avoid premature, unexpected failures and to encourage ductile

and redundant behavior during earthquakes. This material is intended for both design of new

facilities and evaluation of existing facilities. For new facilities, this material addresses

recommended seismic design practices. For existing facilities, this material may be used for

identifying potential deficiencies in the capability of the facility to withstand earthquakes (i.e.,

ductile behavior, redundant load paths, high quality materials and construction, etc.). In

addition, good seismic design practice, as discussed in this section, should be employed for

upgrading or retrofitting existing facilities.

C-41