ML20104A521

Forwards Summary of Differences Between Cygna & Util Re Acceptability of Using Aws D1.1-79 Methodology for Checking Adequacy of Punched Tubesteel Designs.Cygna Considers Design Std.Item 4,per Nh Williams Closed

ML20104A521
Person / Time
Site:	Comanche Peak
Issue date:	01/29/1985
From:	Williams N CYGNA ENERGY SERVICES
To:	George J TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
References
84056.051, NUDOCS 8502010348
Download: ML20104A521 (5)

Text

~

- i 9

/ I ssevras 101 California Street, Suite 1000, San Francisco, CA 94111-5894 415/397-5600 l s

January 29, 1985 84056.051 Mr. J. B. George Project General Manager Texas Utilities Generating Company Comanche Peak Steam Electric Station Highway FM 201 Glen Rose, Texas 76043

Subject:

Phase 4 Open Items - Punching Shear Texas Utilities Generating Company Comanche Peak Steam Electric Station Independent Assessment Program - Phase 4 Job No. 84056

Reference:

N. H. Williams (Cygna) letter to L. M. Popplewell (TUGCO), "Open Items Associated with Walsh/Doyle Allegations," 84042.22, January 18, 1985

Dear Mr. George:

Cygna and TUGC0 have corresponded on several occasions regarding the punching l shear / joint capacity of tubesteel with holes. The attachment to this letter summarizes Cygna's differences with TUGC0 on the acceptability of using an AWS' D1.1-79 methodology for checking the adequacy of these designs. Cygna does not consider this to be a standard design -- particularly when punched tubesteel is used as the backing plate for a cinched U-bolt. We believe that careful L

consideration should be given to applying AWS without considering the basis for the standard.

l swas SOJMb gZfE b

/

San Francisco Boston San Diego Chicago Richland 8502010348 850129 PDR ADOCK 05000445 A PDR

4 t Tmh Mr. J. B. George 84056.051 January 29, 1985 Page 2 This letter completes Cygna's commitment listed under item 4 of the Open Items List attached to the above referenced letter. Please call at your convenience if further discussion of this position is. necessary.

Very truly yours, 1

N. H. Williams Project Manager Attachment eq: Mr. V. Noonan N r. S. Burwell

-Mr. S. Treby Mr. D. Wade Mrs. J. Ellis Mr. D. Pigott

a

.. J

'",."."'9 ATTACHMENT Mr. J. B. George '

84056.051 January 29, 1985 Pr.ge 1 of 2 Calculation of Allowable Punching Shear / Joint Capacity in Tubesteel with Holes For support MS-1-002-005-S72R, Cygna performed a finite element analysis to determine the effects of tube warping, and check the stresses in the tubesteel and coverplate in the region of the U-bolt hole (see attached support drawing). On October 4,1984, Cygna requested that TUGC0 review this suppo-t and provide calculations justifying the design. TUGC0 submitted calculations on October 18, 1984, which showed that stresses in the tubesteel were acceptable using the " punching shear" method of AWS D1.1-79, Section 10.5.1. Cygna further requested justification for use of " punching shear" as an appropriate check.

TUGC0 provided their justification in their letter dated November 8,1984 (L.

Popplewell, TUGC0 to N. Williams, Cygna).

-Cygna has reviewed the TUGC0 justification and has the following comments:

1. The AWS equation for calculating the punching shear allowable for tubesteel connections is based upon the results of a limit analysis assuming a specific yield-line pattern within the chord of the tubesteel. When a hole is placed in the tubesteel and the edge of the hole is loaded, limit analysis would predict a different yield-line pattern. This new yield-line pattern will result in a lower allowable punching shear. The presence of the coverplate further complicates the problem of determining punching shear allowables since one cannot automatically expect an increase in the AWS punching shear allowable proportional to the increase in thickness provided by the addition of a coverplate. In addition, the close proximity of the load to the edge of the tubesteel also influences the calculation of all allowable punching shear.

2. In the actual problem modeled and reviewed by Cygna, our finite element analysis predicted very little margin to allowable in the coverplate using a yield-line analysis of the finite element results. The TUGC0 calculation received on October 18, 1984, clearly shows a margin of approximately 6:1 (12.76/2.21). Thus, the TUGC0 calculations would predict that this joint is acceptable for approximately six times more load, a fact not borne out by the finite element analysis. While Cygna did not consider plate plasticity effects in the finite element analysis, Cygna is, nevertheless, concerned with the large difference in predicted capability, and attributes much of it to the use of AWS D1.1-79 without assessing the impact of the deviations from D1.1-79. That is, one must consider that:

Y hks ATTACHMENT Mr. J. B. George a 84056.051 January 29, 1985 Page 2 of 2

a. D1.1-79 assumes the brace and chord are welded together. lhus, the brace locally stiffens the chord. This is not the case for the nut loading the tubesteel.

b. D1.1-79 assumes the chord is solid. This is not the case for tubesteel with a hole in it.

c. D1.1-79 states that yield-line analysis can be used if 8 < 0.8, which is true for this joint (8 s .6). Thus, AWS does recognize that yield line theory can also be used to predict joint strength in configurations pictured in AWS.

Based on the above, Cygna does not accept the use of AWS D1.1-79 as an appropri-ate method for establishing an allowable punching shear / joint capacity in the case of tubesteel with loaded holes (with or without coverplates). Cygna re-quests that TUGC0 provide further justification on the design of such unique joints.

I g- ..w. -  % s v. ,-y