ML20235F647

Rev 0 to IM-P-012, Stress Evaluation of Angles

ML20235F647
Person / Time
Site:	Comanche Peak
Issue date:	09/11/1987
From:	Bacon T ABB IMPELL CORP. (FORMERLY IMPELL CORP.)
To:
Shared Package
ML20235F613	List: ML20235F631 ML20235F647 ML20235F681 ML20235F720 ML20235F788 ML20235F820 ML20235F855 ML20235F868 ML20235F882 ML20235F887 ML20235F904 TXX-6773, Forwards Wg Counsil 870923 Cover Ltr & Impell Calculations & Position Papers,Including Rev 0 to IM-P-011, Unbraced Lengths Used to Evaluate Lateral Torsional Buckling of Trapeze Support Post Members, as Requested by Cygna
References
IM-P-012, IM-P-012-R00, IM-P-12, IM-P-12-R, NUDOCS 8709290261
Download: ML20235F647 (3)

Text

CLARIFICATION OF IMPELL CTH DESIGN VERIFICATION CRITERIA / METHODS FOR RESOLUTION OF CYGNA AUDIT CONCERNS Stress Evaluation of Angles Prepared for:

Texas Utilities Electric Company Prepared by:

Impe11 Corporation 0210-040/041 IM-P-012 Revision 0 Prepared by: __, 2dw

')/ // / 8 7 Approved by:

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4 IM-P-012 Concern:

Impe11 applies a 1.2 increase factor to_ the calculated base. angle flexural. stress. This stress is evaluated based on resolving moments about the geometric axes of the cross-section. The 1.2 factor accounts for any potential differences between flexural stress calculated about the base angle geometric axes and stress calculated about the' angle principal axes. CYGNA is concerned that the method used.to develop the 1.2 factor may be unconservative, and that the factor may need to be higher.

Background:

Impell evaluates base angle flexural stress using properties that are developed from the geometric axes rather than the principal axes of the angle. . A 1.2 factor is applied to the geometric axes stress to account for any potential difference from principal axes stress. In determining the 1.2 factor, maximum flexural stresses due to the separate application of major and minor principle axis bending moments on the angle cross-section were occasionally combined using SRSS in order to envelope the maximum bending stress in the angle [1, Section 11]. CYGNA is concerned that the combination should have been performed using an absolute summation method. An absolute combination may increase the' 1.2 factor currently applied to the geometric stress.

Discussion:

Impe11. Calculation M-15 Section 11 contains the de'ivation o. the 1.2 factor which is _ applied to the base angle geometric stress. The factor is based on a ratio of geometric and principal st' ess on the cross-section of a base angle for various loading conditionr. Base angle sizes studied are L5x5x3/4, L6x6x3/4 and L6x4x3/4 Ia Section 11 ,

the maximum bending stresses are calculated by separately applying a I moment about each principal axis. These two maximum bend'ng stresses do I not occur at the same location. As a result, these two aaximum bending stresses are combined using the SRSS method to estimate the maximum ,

combined bending stress across the section. An absolute summation I l

method is not required for ccmbining these stresses since they occur at different locations.

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Attachment B has been added to calculation M-15 to provide further justification for the 1.2 increase factor through a more exact approach. In this attachment combined bending stresses are calculated 4 I

for the critical stress locations. These stresses include the ef fects of simultaneous bending about both the major and minor principal axes, f therefore no SRSS combinations are used. The maximum principal axes l l

stress from this loading is compared to the geometric axes stress, which J is calculated in the same manner as done in Impell's stress evaluation computer program for the cable tray hangers, SUPERPOST. Results of the comparison in Attachment B indicate that principal stress values will not exceed geometric stress values by more than a factor of 1.18 for I

these angle sizes. Therefore, current use of a 1.2 factor multiplied by j the geometric stress does envelope the principal stress acting on the base angle cross-section.

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IM-P-012 .

Impe11 calculation M-15 also uses the 1.2 factor when showing that the anchorage is the controlling component of the base angle assembly [1,  !

Section 12]. Attachment B results verify that the bolts are the contro11ing component for the base angle design. As a result, the previous use of the 1.2 factor and use of the base angle anchorage to l qualify the angle are valid.

Conclusion:

Impe11 applies a 1.2 increase factor to geometric axes bending stress to-envelope flexural stress calculated about the principal axes for base angles. This factor was based on separately applying a moment about each principal axis and combining the resulting maximum stresses by.

SRSS. The factor is also used to show that base angle anchorages are the controlling component in the base angle design. Attachment B of Impell Calculation M-15 uses a more exact method to calculate the maximum flexural stress on the cross section by simultaneously applying:

bending moments about both principal axes. Results confirm that the current use of the 1.2 increase factor on geometric base angle flexural stress is valid.

References:

1. Impe11 Calculation M-15, " Base Plate & Base Angle Interaction Diagram Generation", Revision 4, 9/11/87.

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