ML19208D590

Forwards Revised Response to IE Bulletin 79-02, Pipe Support Base Plate Designs Using Concrete Expansion Anchor Bolts. Design Review in Progress Re Base Plate Flexibility & Determination of Concrete Anchor Bolt Loads

ML19208D590
Person / Time
Site:	Farley
Issue date:	08/05/1979
From:	Clayton F ALABAMA POWER CO.
To:	James O'Reilly ALABAMA POWER CO.
References
NUDOCS 7909280667
Download: ML19208D590 (8)

Text

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August 5,1979 Docket No. 50-348 IE Bulletin 79-02 Mr. James P. O'Reilly L U. S. Nuclear Regulatory %= mission .,_

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Region II .

101 Marietta Street, N. W.

Suite 3100 Atlanta, Georgia 30303

Dear Sir:

Enclosed is the revised response to IE Bulletin 79- 32 con-cerning pipe support base plate designs using concrete expansion anchor bolts . The specific responses to the bulletin are < aclassd.

Yours very truly.

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b F. L. Clayto , Jr.

FLCj r/ KAP /c=b Enclosure cc: Messrs. R. A. 'Ihomas G. F. Trowbridge I&E Reactor Operations Washington, D. C.

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rf Response to Item 1: ,

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Originally, flexibility of the base plate was not specpfically taken into account in determining the concrete anchor bolt Joads. Alaba5a# Power Company is in the process of perfor=ing a design review that takes bas / plate flexibility into account in deter =ining the concrete anchor bolt loads. This design review is describec below.

Grinnell, Southern Company Services, Inc. (SCS) and Bechtel Power Corporation (as appropriate) are utilizing the calculated Westinghouse /Bechtel piping system hanger / seismic restraint design loads and the ICES STRUDL Program to . develop design loading condition; (forces and =oments) at the centroid of each attachment to the hanger / seismic restraint base plates. For simple cases the forces and moments are obtained by hand calculations. Bechtel then utilizes this information in con-junction with the inspection and test data for analyses of all base plate anchor bolts to determine if the existing base plate anchorage is adequate to meet the design loads with the prescribed safety factor or if corrective action is necessary.

This determination is perfor=ed in accordance with FNP-1-ETP-123 (a Farley Nuclear Plant Engineering Technical Procedure) which has been reviewed by NRC, I&E Region II Staff.

More specifically, a su==ary of the evaluation of base plate design by Sechte' is as follows:

1. The method of analysis is based on an empirical-analytic technique developed by Bechtel which takes into account design pars =eters such as flexibility of the base plate and concrete anchor stiffness (based on actual pre-loaded load-displacement curves furnished by the manufacturer). This method has been verified with appropriate finite element analytical solutions . Description o f this empirical-analytic technique is provided in Attachment I.

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A computer program for the empirical-analytical technique has been implemented for determining the anchor bolt loads for the majority of applications. For other cases refer to. Item 3 below. This program requires plate dimensions, nu=ber of bolts, bolt size, bolt spacing, bolt stif fness, the applied forces and the allowable bolt shear and tension loads as inputs.

The allowable loads for a given bolt are determined based on the con-crete edge distance, bolt spacing, embedment length, shear cone over-lapping, manuf acturer's ultimate capacity, and safety factor.

The program computes the forces on the bolt and calculates a shear-tension interaction based on allowable loads. An interaction value greater than the allowable is accepted as failure of the bolt (safety f actor less than required) . Unit 1 shear-tension interactions analyses are computed utilizing a linear relation. Even though a subsequent squared interaction formula is acceptable and its use has been justified by Bechtel in representing the shear-tension interaction, Alaba=a Power has chosen to continue with the use of linear relationship rec-ognizing that the results f rom this technique tre more conservative.

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The empirical-analytic method does not consider prying action for the follow-ing reasons:

a. Where the anchorage system capacity is governed by the concrete shear cone the prying action would result in an application of an external compressive load on the cone and would not affect the anchorage capacity.

b. Where the bolt pull out determines the anchorage capacity, the additional load carried by the bolt due to the prying action will be self-limiting since the bolt stif fness decreases with increasing load. At higher loads the bolt extensions will be such that the corners of the base plate will separate from the concrete and the prying action will be relieved. This phenomena 'aas been found to occur even when the bolt stiffnesses in the fisite element analysis were varied from a high to a low value correrponding to both typical initial stiffnesses and to values be. yond the allowable design load.

2. Calculated bolt loads are used to check stresses in the support base plate to ensure they are less than the allowable stress as specified by the Anerican Institute of Steel Construction (AISC) code.

3. For special cases where the design of the support plate does not lend itself to this method, standard engineering analytical techniques with conservative assumptions are being employed.

All anchor bolts within the scope of this program are being evaluated by Bechtel in accordance with the bolt acceptance criteria, "as built" drawings reflecting the existing plant conditions, and the bolt design loads to determine if corrective action is required.

If any bolt on a base plate f ails the Bechtel evaluation as described in FNP-1-ETP-123, one or more of the following actions are being taken:

a. Re-analyze the base plate assuming that the bolt is f ailed (bolts carries zero load) .

b. Re-analyze the base place incorporating bolt replace =ent as corrective ac tion.

In those instances where repair e tetions result in a piping c.

support modification, Bechtel Westine ._ ase (as appropriate) will analyze the effect of such modifications on the analysis of the piping system.

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Response to Item 2:

In the original design of Unit 1 at Farley Nuclear Plant a factor of safety of four was used for wedge type and shell type anchor bolts. Because of this (the original design factor of safety of four), the current verification program (described in the response to Item 4) requires the existing anchor bolts to withstand a load equivalent to 1/4 of the manufacturer's published pullout load.

The original design f actor of saf ety of four is consistent with the current in-dustry design practices. In general, the current industry approach concerning the use of safety f actors for various design loading conditicas are described below. This information is provided as additional support for the factor of safety used in our evaluation / repair program.

1. Factors of safety (i.e. ratio of bolt ulti= ate capacity to design load) of four for vedge type and shell type anchor bolts, for service (operating) load cases, are used.

2. For factored loadings (which include accident / extreme environmental loads) safety factors of 1.2 and 3.0 are used consensurate with the provisions of Section B.7.2 of the Proposed Addition to Code Require-ments for Nuclear Safety Related Concrete Structures (ACI-349-76)

Augus t , 1978. The f actors of safety are consistent with the ulti= ate strength design me thod. A f actor of safety of 1.2 is used if the f ailure mechanism for the anchor is controlled by the bolt =aterial.

If the f ailure mechanism is controlled by concrete shear cone action, a factor of safety of 3.0 is used. The utili:stion of sampling and quality control methods used are integral to selecting the factor of safety of 3.0.

3. For general structural design in steel, the AISC Specification has an approximate factor of safety of 1.7 for services loading (for example, a colu=n buckling) . For factored accident / extreme en-vironmental loads, a f actor of safety of 1.1 is used on nuclear

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structures for both ductile (yielding) and non-ductile (colu=n buckling) failures. In concrete design for factored loads, a factor of safety of 1.1 is used for flexural and tension ac, tion and 1.2 for shear action.

It can be observed that a higher factor of safety is assigned to the expansion anchor only if its capacity is governed by the shear cone.

Based on the above interaction of design para =eters and on the following addi-tional factors, Alaba=a Power Company has concluded that a safety factor of 2 is sufficient to ensure operability of Seismic Category I piping system in the event of a seismic event:

100% verification testing program with .a1 Quality Control coverage a.

of scoped syste=s (described in questics 4) which minimizes installation uncertainties (e.g. verification of torq2 e, embedment depth, nut engage =ent,*

plate configuration, expansion of shell, etc.) which were allowed for in the original design by the factor of safety of four.

b. Verification that plates are not overstressed by bolt loadings (e.g.

consideration of mini =u= edge distance and proper bolt spacing) .

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Response to Item 3_:

In the original design of the piping systems Bechtel/ Westinghouse considered -

deadweight, thermal stresses, seismic loads, and dynamic loads (e.g. certain rapid valve openings and closings) in the generation of the static equivalent pipe support design loads.

The safety f actors used for concrete expansion anchors, installed on supports for safety related piping systems, were not incraased for loads which are cyslic in nature. The use of the same safety factor for cyclic and static loads is based on the Fast Flux Test Facility (FFTF) Tests *. The test results indicate:

1. The expansion anchors successfully withstood two million cycles of long term f atigue loading at a maximum intensity of 0.20 of the static ultimate capacity. When the maximum load intensity was steadily increased beyond the aforementioned value and cycled for 2,000 times at each load step, the observed f ailure load was about the same as the static ultimate capacity.

2. The dynamic load capacity of the expansion anchors, under simulated seismic loading, was about the sa=e as their corresponding static ultimate capacities.

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• Drilled - In Expansion Bolts Under Static and Alternating Loads, Report No.

BR-5853-C-4, Rev.1, by Bechtel Power Corporation, October 1976.

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Response to Item 4_:

Since existing Q.C. docuaentation is not adequate to document the installation parameters associated with each anchor bolt, the following programs have been undertaken:

Test Program Alaba=a Power Company initiated a program to randomly select and test a sample of anchor bolts installed in Seismic Category I Safety Ralated, 2-1/2 inch and greater piping systems. Initial results of that program revealed that statistical sampling would not be suf ficient to provide a 95% confidence level in anchor bolt reliability.

As a result, the anchor bolt testing program was expanded to include 100% verifi-cation of anchorages associated with pipe hangers for those systems or portions of systems required to meet design basis accidents and those required to bring the plant to cold shutdown condition. These piping syste=s included in the program are:

a. Seismic Category I; Safety Related 2-1/2 inches and above,

b. Seismic Category I; Safety Related ASME Section III, Class 1 piping, under 2-1/2 inch,

c. Seismic Category I; Safety Related of other classes for which the designer perfor=ed detailed analysis,

d. All piping through contain=ent penetrations.

The scope of this program given above has been reviewed and approved by the NRC I&E Region II Staff.

79-21/01T, The specific systems involved in this testing program are listed in LER

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Anchor bolts on hangers within the scope of this program are tested for the follow-ing parameters:

a. embedment - Actual embedment depth is determined.

b. grout - The presence of grout and leveling nuts is determined to ensure proper torque test.

c. type of bolts - Verification is made that installed bolts are in accordance with design bill of material.

d. number of bolts - Verification is made that the installed number of bolts is in accordance with design bill of material,

e. bolt dimensional measurements - Dimensional measurements are taken to determine the degree of compliance with the manufacturers' recommended bolt installation requirements.

f. torque - Bolts are torqued to a level such that the resultant tensile load on the anchor is equal to 1/4 of the manufacturers' published pull-out load. For shell type bolt torque tests to be considered valid, the shell shoulder must not touch the base plate.

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NOTS: A torque / tension relationship was developed Jor Hilti vedge type anchors based on tests performed at Farley. Torque / tension relationships were developed for Phillips shell type anchors under the direction of Bechtel Corporation with technical consultation from ITT-Phillips Drill Division at Plant Hatch. Since these relationships were completed and the majority of anchor bolt field verification was perfor=ed prior to ISE Bulletin 79-02 Revision 1 issuance no site specific testing for the shell type anchors was performed. Torque requirements for Wej-it vedge type anchors were obtained f rom vendor data.

g. base plate dimensional measurements - Dimensional maasurements of base plate parameters which could affect bolt loading or capacity (e.g. bolt spacing, edge distance) are taken.

Based on the results of the test program and the empirical-analytic evaluation, anchors are being repaired according to the following criteria:

1. Repair individual base plate anchorages not having a safety f actor of at least 2.0.

11. Repairs are done so that all repaired bolts have a safety factor of at least 4,0 and all base plate anchorages have a safety f actor of at least 2.0.

iii. All repairs are done in accordance with written procedures and quality control checks.

The f ailure to test inaccessible anchor bolts will be justified by analysis which substantiates operability of the af fected systems

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without assuming integrity of the anchorages which are not tested.

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Preloading Even though Alabama Power is preloading all knchor bolts to the design load, availab7e test data indicatas that it is not necessary that the bolt preload should be equal to or greater than the bolt design load because pipe supports and anchors are subjected to both static and dynamic loads. The dynamic loads such as the seismic loads are short duration cyclic loads and are not f atigue type loads, therefore, the amount of preload on the bolts will not greatly affect the performance of the anchorage. The initial installation torque on the bolt accomplishes the purpose of setting the anchor, but the ultimate capacity of the bolt is not affected by the amount of preload present in the bolt at the time of cyclic loading. For vibratory loads, the expansion anchors have successfully withstood long term f atigue conditions as discussed in the previous section (FFIT tests) .

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rf Response to Item 5: f The Alabama Power Company testing, analysis and repaiz/ program vill not be completed by July 6,1979; however, Farley Nuclear Pynt Unit 1 is currently shutdown during the present critical power dee and' pdiod to complete the above program. The testing, analysis and repair program described in Itens 1 and 4 will be completed prior to return to power generation.

Response to Item 6:

A program for the verification of Unit 2 anchorages, similar to that of Unit 1, will be developed incorporating the experience gained from the Unit 1 activities. A full and detailed description of the Unit 2 program vill be trans-mitted to the NRC by a supplement to this bulletin response. Currently, the construction activities associated with Unit 2 are temporarily suspended due to the Company's financial condition. The verification program for Unit 2 anchorages vill be completed prior to the initial criticality of the unit.

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