ML20215B190

Rev 0 to Clarification of Impell Cth Design Verification Criteria/Methods for Resolution of Cygna Audit Concerns, Seismic Load Combinations

ML20215B190
Person / Time
Site:	Comanche Peak
Issue date:	05/15/1987
From:	Ashley G ABB IMPELL CORP. (FORMERLY IMPELL CORP.)
To:
Shared Package
ML20215B058	List: ML20215B073 ML20215B166 ML20215B190 ML20215B206 ML20215B224 ML20215B384 ML20215B409 ML20215B422 ML20215B444 ML20215B446 ML20215B485 TXX-6517, Forwards Documents Listed in Encl Wg Counsil & Gs Keeley to Nh Williams of Cygna Energy Svcs,Including Assessment of Texas Utils Generating Co As-Built Documentation for Piping & Pipe Supports
References
IM-P-002, IM-P-002-R00, IM-P-2, IM-P-2-R, NUDOCS 8706170251
Download: ML20215B190 (2)

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CLARIFICATION OF IMPELL CTH DESIGN VERIFICATION j CRITERIA / METHODS FOR RESOLUTION OF CYGNA AUDIT CONCERNS l

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Seismic Load Combinations

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i Prepared for:

Texas Utilities Electric Company-Prepared b):

Impell Corporation 0210-040/041 IM-P-002 Revision 0 I

i Prepared by: d. m Au Jug , S/f g/6 7 Approved by: [ [ M T -/ 5~- 3 7 o

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• ' CONCERN: The: response spectrum analysis method provides seismic -

load'results which are unsigned. A concern has.been

. raised regarding the direction and magnitude of the -

critical . load combination of. gravity and seismic load.

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BACKGROUND:

The CPSES cable tray hanger design verification program uses the gravity + seismic (G+S) combination method.

'This method is less corservatTve_-than the [Gl+1Sl-combination, method.

-DISCUSSION: A representative cable tray system which contained a good'-

cross section of typical cable tray supports was ^

selected. Time history.and were run. The response;specresponse spectrum trum_ analysis resultsanalyses-were combined with gravity using both G+S and lGl+lSl.

combination methods.

CONCLUSION: This issue was resolved in the Impell calculation M-49 Rev. O. [1] The results-of thir calculation showed that:

the G+5 and IGj+ ISj envelope the results of the time history analysis, except_ for. two-instances. In those two instances time history analysis results were higher than both G+S and lGl+lSi results. This was due to the fact that tTie seismic ' response from .the time history analysis was higher than the response predicted by the response spectrum analysis, and hence not 'due to the ccmbination method. The slight underpredictions. (5-7%) thyt may result from the response spectrum analysis are compensated by the conservative broadening of the spectra. . For the_ remaining seismic responses (Gl+1Si values were more conservative than G+S however, _ G+S responses more accurately approached ~the time histiiry responses. This calculation has shown that the G+S combination method is adequately conservative in ~

predicting the combination of gravity 'and seismic loadings for the verification of CPSES cable tray systems.

REFERENCES:

1) Impe11 Calculation M-49, " Seismic Load Combination Study", Rev.-0, 2/2 m