Grouping Method - CAESAR II - Help

CAESAR II Users Guide

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CAESAR II
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CAESAR II Version
13

This method is defined in USNRC Regulatory Guide 1.92. The grouping method attempts to eliminate the drawbacks of the Absolute and SRSS methods. It assumes that modes are completely correlated with any modes with similar closely spaced frequencies and are completely uncorrelated with those modes with widely different frequencies. The total system response is calculated as

Where:

R = total system response of the element

N = number of significant modes considered in the modal response combination

Rk = the peak value of the response of the element due to the kth mode

P = number of groups of closely-spaced modes (where modes are closely-spaced if their frequencies are within 10% of the base mode in the group), excluding individual separated modes. No mode can be in more than one group.

i = number of first mode in group q

j = number of last mode in group q

Rlq = response of mode l in group q

Rmq = response of mode m in group q

The responses of any modes which have frequencies within 10% of each other are added together absolutely, and the results of each of these groups are combined with the remaining individual modal results using the SRSS method.

The 10% value controlling the definition of closely spaced frequencies can be changed by using the Closely Spaced Mode Criteria/Time History Time Step (ms) parameter.