ML19242B279

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Responds to IE Bulletin 79-02 Re Pipe Supports Using Concrete Expansion Anchor Bolts.Verifies Satisfactory Pipe Support Base Plate Flexibility,Concrete Expansion Anchor Bolts Safety & Related QC Documentation
ML19242B279
Person / Time
Site: Beaver Valley
Issue date: 07/06/1979
From: Woolever E
DUQUESNE LIGHT CO.
To: Grier B
NRC OFFICE OF INSPECTION & ENFORCEMENT (IE REGION I)
References
NUDOCS 7908070812
Download: ML19242B279 (3)


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(41?) 456-6000 435 Sixth Avenue Pittsburgh, Pennsylvania 152,s p ly 6, 1g79 United States Nuclear Regulatory Commiss. inn Region I 631 Park Avenue King of Prussia, PA 19406 ATTENTION: MR. BOYCE H. GRIER, DIRECTOR

SUBJECT:

Beaver Valley Power Stat ion - Unit No. 2 Pipe Support Base Plate Design Using Drilled-In Anchors Response to IE Bulletin 79-02 Docket No. 50-334 Gentlemen:

The following is the response of the Duquesne Light Company to IE Bulletin 79-02 as it applies to Beaver Valley Power Station, Unit 2. The item numbers listed below are referenced to simi-larly numbered items in IE Bulletin 79-02.

Item (1)

" Verify that pipe support base plate flexibility was accounted for in the calculation of anchor bolt loads."

The primary means of attaching pipe supports is by field welding to plates embedded in concrete, thus minimizing the use of concrete expansion anchors. For those relatively few cases where base plates and concrete anchors are used, design guides are utilized, which account for the increased loads on concrete ex-pansion anchors due to base plate flexibility ef fects .

A pr.cedure has been developed which is applied to common pipe support base plate configurations, to account for plate flex-ibility in determining the load induced in the drilled-in anchor bolts. This procedure includes load factors to be applied to the anchor bolt lead to provide for the ef fects of plate flex-ibility. The load factors were developed using finite element analysis techniques.

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United States Nuclear Regulatt.y Commission Page 2 July 6, 1979 A finite element model was used to determine load in the drilled-in anchor. Plate flexibility, anchor stiffness, stiffening effects of members attached to the plate, as well as concrete flexibility are represented in the model. The centact boundary conditions at the interface of the plate and concrete-, and plate and drilled-in anchors are satisfied in the solution.

The ANSYS III finite element package was used for the analysis .

The alement model considers pure plate 5ending whi :h is appropri-ate for the analysis of a flexible base plate. '.e concrett and drilled-in anchor are both modeled with the comb..tation gap element which iodels the stiffness of these components as well as represents the contact Loundary ccnditions discussed previously.

Finally, the forces are applied as couples and axial forces dis-tributed to the nodes of the attached members.

Item (2)

"Verir, that tha concrete expansion anchor bolts have the follow-ing minimum facto. of safety between the bolt design load and the bolt ultimate capacity."

2(a) Proj ect design procedures and the specification for drilled-in anchors for the BVPS-2 project specify the allowable design loads, purchasing requirements, and installation re-quirements for wedge type anchor bolts.

The average ultimate capacity of bolts is a minimum of four times the allowable design load used in the design procedure.

This minimum factor of safety of 4 is based on the average ultimate capacity determined from static load tests conducted by anchor manufacturers in 3,000 psi concrete. The project specifications require an on-site prequalification test program to establish torgtes and turn-of-the nut requirements to properly set the anchors in the concrete at BVPS-2, as well as to verify the average ultimate capacity o f the bolts .

2(b) Shell type anchor bolts are not used for BVPS-2 Category I pipe support design.

Item (3)

" Describe the design requirements, if applicable, for anchor bolts to withstand cyclic loads."

To account for cyclic loadings, the BVPS-2 design procedures use a conservative allowable design load which has a minimum factor of safety of 4 with respect to the average ultimate bolt capacity.

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United States Nuclear Regulatory Commisaion Page 3 July 6, 1979 Conclusions of the FFTF Report on " Drilled-in Expansion Bolts under Static and Alternating Load" (BR-5853-C-4 dated January, 1975), indicate that properly installed anchors perform satis-factorily under cyclic loads. Installation requirements of the speciLication ensure proper bolt ins t allatio:i .

Item (4)

" Verify from existing QC documentation that design requirements have been met."

4 (a) BVPS-2 specification for drilled-in anchors requires that, during the on-site prequalification test program, the n.inimum ins talla tion torque for proper setting of the anchors be established. This required installation torque will develop a bolt preload at least 1.5 times the bolt design load as verified by tension tests performed in the same on-site test program. Category I anchors are randomly torque tested to 80 percent of this torque value in accord-ance with specified frequency of testing, assuring a properly installed bolt.

4 (b) The BVPS-2 specification for drilled-in anchor requires all anchor bolts to be permanently marked with a standard mark-ing sy stem on the expcsed end of the anchor which will identify the overall length of the anchor. This enables Site Quality ntrol to determine that the proper length anchors have oeen installed.

DUQUESNE LIGHT COMPANY By - . .

(Ai. J. Woolever Vice President cc: United States Nuclear Regulatory Commission Office of Inspection and Enforcement Division of Reactor Operations Washington, D.C. 20555

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