ML20128K114

Forwards Rev 1 to Attachment to Cygna Energy Svcs Re Phase 4 Open Items - Punching Shear to Omit Ref to Pipe Support Drawing MS-1-002-005-S72R,correct Typo & Revise Statement Describing Approach to Evaluation

ML20128K114
Person / Time
Site:	Comanche Peak
Issue date:	01/31/1985
From:	Williams N CYGNA ENERGY SERVICES
To:	George J TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC)
References
84056.053, NUDOCS 8507100482
Download: ML20128K114 (5)

Text

r

• s 101 California Street, Suite 1000. San Francisco, C A 941115894 415 397 5600 January 31, 1985 84056.053 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 Conanche Peak Steam Electric Station Independent Assessment Program - Phase 4 Job No. 84056

Reference:

N. H. Williams (Cygna) letter to J. B. George (TUGCO), " Phase 4 Open Items - Punching Shear," 84056.051, January 29, 1985.

Dear Mr. George:

The attachment to the above referenced letter has been revised to correct the following three areas:

1. The attachment refers to pipe support drawing MS-1-002-005-572R.

A copy of this drawing was inadvertently omitted when the letter was distributed. Cygna has revised Attachment A to eliminate the statement: "(see attached support drawing)." The drawing was pro-vided as an example only and is not integral to the point being made.

2. In the last sentence of consnent one, change "all" to "an" (typo-graphic error).

3. In the first sentence of coninent two, Cygna has deleted "a yield line analysis of the finite element results" and inserted the words shown, which better describe Cygna's approach to the evaluation.

• l t b

4 San Francisco Boston San Diego Chicago nichland W

1. s\-

7;;, -..

Mr. J. B. George 84056.053 January 31, 1985 Page 2 This letter and attachment therefore supersede letter 84056.051 and its attach-ment. Please call if you have any questions.

Very truly yours, b . W N. H. Williams

. Project Manager NHW/ajb Enclosure cc: Mr. V. Noonan Mr. S. Burwell Mr. S. Treby Mr. D. Wade Mrs. J. Ellis h

V. .- , ,

Mr. J. B. George 84056.053 January 31, 1985 Page 1 of 2 ATTACHMENT (Revision 1)

Calculation of Allowable Punching Shear / Joint Capacity in Tubesteel with Holes For support MS-1-002-005-572R, 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. On October 4, 1984, Cygna requested that TUGC0 review this support ano 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 coments:

A. The AWS equation for calculating the punching shear al-lowable for tubesteel connections is based upon the re-suits 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 sheir allowables since one cannot automtically expect an ir, crease in the AWS punching shear allowable proportional to the increase in thickness provided by the addition of a coverplate. In addition, the close proxi-mity of the load to the edge of the tubesteel also influ-ences the calculation of an allowable punching shear.

B. In the actual problem modeled and reviewed by Cygna, our finite element analysis predicted very little urgin to allowable in the coverplate using an average of the fi-nite element results along a line between the hole and the edge of the coverplate. The TUGC0 calculation re-ceived on October 18, 1984, clearly shows a margin of approxistely 6:1 (12.76/2.21). Thus, the TUGC0 calcu-lations 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 con-sider plate plasticity effecti, in the finite element analysis, Cygna is, nevertheless, concerned with the

U "5, . 7-Mr. J. B. George 84056.053 January 31, 1985 Page 2 of 2 ATTACHENT (Revision 1) 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:

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

$ 2. 01.1-79 assumes the chord is solid. This is not the case for tubesteel with a hole in it.

3. D1.1-79 states that yield-line analysis can be used if 8 < 0.8, which is true for this joint (6 a .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.

.