Seismic Anchor Motion

DOE-STD-1020-2002

Seismic Anchor Motion

The seismic anchor motion (SAM) component for seismic response is usually obtained

by conventional static analysis procedures. The resultant component of stress can be very

significant if the relative motions of the support points are quite different. If all supports of a

structural system supported at two or more points have identical excitation, then this component

of seismic response does not exist. For multiple-supported components with different seismic

inputs, support displacements can be obtained either from the structural response calculations of

the supporting structure or from spectral displacements determined from the floor response

spectra. The effect of relative seismic anchor displacements shall be obtained by using the worst

combination of peak displacements or by proper representation of the relative phasing

characteristics associated with different support inputs. In performing an analysis of systems

with multiple supports, the response from the inertial loads shall be combined with the responses

obtained from the seismic anchor displacement analysis of the system by the SRSS



2

rule R = (Rinertia ) + (RSAM )  , where R = response parameter of interest.





Evaluation by Testing

Guidance for conducting testing is contained in IEEE 344 (Ref. 2-11). Input or demand

excitation for the tested equipment shall be based on the seismic hazard curves at the specified

annual probability for the Performance Category of the equipment (OBE provisions of Ref. 2-11

do not apply). When equipment is qualified by shake table testing, the DBE input to the

equipment is defined by an elastic computed required-response-spectrum (RRS) obtained by

enveloping and smoothing (filling in valleys) the in-structure spectra computed at the support of

the equipment by linear elastic analyses. In order to meet the target performance goals

established for the equipment, the Required Response Spectrum (RRS) must exceed the In-

Structure Spectra by:

RRS ≥ (1.1)(In-Structure Spectra)

for PC-1 and PC-2

(2-5)

RRS ≥ (1.4SF)(In-Structure Spectra)

for PC-3 and PC-4

(2-6)

where SF is the seismic scale factor from Equation 2- 1.

The Test Response Spectrum (TRS) of test table motions must envelop the RRS. If

equipment has been tested and shown to meet NRC requirements, then it need not be subjected

to further testing.

Evaluation by Seismic Experience Data

For new design of systems and components, seismic qualification will generally be

performed by analysis or testing as discussed in the previous sections. However, for existing

systems and components, it is anticipated that many items will be judged adequate for seismic

loadings on the basis of seismic experience data without analysis or testing. Seismic experience

data has been developed in a usable format by ongoing research programs sponsored by the

2-19