ML20215B444
| ML20215B444 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 05/15/1987 |
| From: | Ashley G ABB IMPELL CORP. (FORMERLY IMPELL CORP.) |
| To: | |
| Shared Package | |
| ML20215B058 | List:
|
| References | |
| IM-P-008, IM-P-008-R00, IM-P-8, IM-P-8-R, NUDOCS 8706170332 | |
| Download: ML20215B444 (4) | |
Text
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CLARIFICATION OF IMPELL'CTH DESIGN VERIFICATION CRITERIA / METHODS FOR RESOLUTION OF CYGNA AUDIT CONCERNS i
1 Lateral Bracing of Tier Members in Impe11 Calculation CTH-1-1227 Prepared for:
Texas Utilities Electric Company Prepared by:
Impell Corporation 1
0210-040/041 IM-P-008 3
Revision 0 Prepared by: 3%[
LA 5//F/gir eg Approved by: YM 5-/r-g7 r
8706170332 870 g 5 PDR ADOCK 050
-IM-P-008 s.
CONCERN:
In Impe11. Calculation CTH-1-1227 the laterally unsupported length of two tier members take credit for bracing provided by the cable tray against lateral torsional buckling.
Cable trays should not be assumed to provide bracing against lateral torsional buckling.
BACKGROUND: L Per Impe11 Project Instruction PI-03 (see attached excerpt) the unbraced length 1 of.the tier compression flange shall be taken as the full tier length from post to post.
The cable trays should not be assumed to brace the compression flange of tiers.
Impe11 Calculation CTH-1-1227. utilized the Superpipe postprocessor program Superpost for member qualification. All member lengths were input correctly to Superpost except the length for the two tier members.
The tier member lengths were incorrectly specified from post to tray.
DISCUSSION:
Cable tray hanger CTH-1-1227 has unusually high member interactions for one of the two tiers which used incorrect member lengths.
The high interactions are caused primarily by weak axis bending of the tier.
Unsupported length however is used to develop strong axis bending stress allowables and does not impact weak axis i
bending computations.
For this hanger the contribution of strong axis bending interaction to overall member interaction is very small.
An evaluation of the two tier members for worst case loading and incorporating the necessary changes in strong axis bending allowables indicates both tier members remain under acceptable stress limits.
It should also be noted that this cable tray hanger calculation is still in prelimirary stages of review and~
has not been issued final.
An additional review of the calculation is necessary to incorporate changes in design verification criteria.
In all likelihood, the improper unsupported length of the tier members would have been corrected in the close-out review before final issue of the support.
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CONCLUSIONS:
Per -Impe11 Project Instruction PI-03 cable trays should not be 1
assumed to brace the compression flange of tier members.
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C;H-i-1227 used an incorrect unsupported length for two tier.
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members. Further evaluation of the hanger calculation shows l
the impact of the change. in unsupported length is negligible.
Both tiers remain under acceptable stress limits.
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CTlf-i-1227 has not been issued final. A final close-out t
review of the calculation is required' prior to final issue of the. bdeger.
In all. likelihood the improper unsupported length
- would have been corrected during this final review.
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TITLE: DESIGN VERIFICATION OF CABLE TRAY SU e...,. n... - -.
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1 NUMBER: 0210-040 REVISION:
4 PAGE 10 OF 14
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Axial stresses vtil be evaluated using the appropriate AISC equations. - Slenderness ratio limits shall be evaluated for all' support members using the limits given below. Members which exceed these limMS Ball be identified in the individual calculatton filt 1
Post w&ms subject to tensile loads only under static conditions and having' a 1
maximun compressf ve stress ratto of K1/r i 300 and (fa/Fa) 10.5 under other loadtng 1/r i 300 conditions All other n. embers including post members
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j subject to statte compresston loads, K1/r i 200 and
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cant 11evers, tiers, and bracing.
1/r 1300 Note that seismic bracing members shall be considered as main members when computing allowable stresses.
The AISC equations for axial stress do not allow for possible twist buckling of angle members due to the axial load.
Twist l
buckling is not a controlling factor for angles with lengths i
greater thn tabulated below.
When using angles with lengths less i
than tabu, s4ad for other than base angles consult with your Lead for the appropriate evaluation technique.
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Minimum Angle Length for Exclusion of Twf st Buck 1ing Anel a sectt on_
Minimum Lanoth ( ft)
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L4x4x1/2 2.4 L4x4x3/8 3.4 L4x4x1/4 5.9 L3.5x3.5x3/8 2.6 L3.5x3.5x1/4 4.4 L3x3x3/16 4.4 L3x3x3/8 1.7 L2x2x3/8
.5 L2x2x1/4 1.1 4.1.4 For evaluatton of flexural stresses the unbraced length 1 of the tier compression flange shall be conservatively taken as the full
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tier length.
The trays should not be assumed to brace the compression flange of tiers.
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