ML18004A007

La -

ML18004A007
Person / Time
Site:	Seabrook
Issue date:	01/02/2018
From:	NRC
To:	Division of Operating Reactor Licensing
References
17-953-02-LA-BD01
Download: ML18004A007 (14)

Text

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170444-L-001 Rev. 0.pdf

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6 November 2017 Mr. Edward Carley Engineering Supervisor - License Renewal NextEra Energy Seabrook, LLC.

P.O. Box 300, Lafayette Road Seabrook, NH 03874 Project 170444 -

License Amendment Request & NRC Review Support, NextEra Energy Seabrook Station, Seabrook, NH Reference -

Evaluation of Containment Enclosure Ventilation Area (CEVA),

Calculation 160268-CA-055HY (FP101122), 22 March 2017 Document Number: 170444-L-001

Dear Mr. Carley:

The structural evaluation of the Containment Enclosure Ventilation Area (CEVA), referenced above, showed that its north wall between EL +3 and +19 ft was bowed outward with a maximum out-of-plumbness of 1.25 in., measured during SGH field observation in February 2017. The referenced calculation showed that the wall can move by an additional 25% (reaching to 1.5 in.

at the point of maximum bowing) before conducting a more robust analysis or repairing the wall becomes necessary.

The bowing limit of 1.5 in. was calculated conservatively in the referenced calculation by neglecting the compression reinforcement in calculating the moment-curvature behavior of the wall. The limit of bowing is recalculated as shown in Attachment A considering the compression reinforcement in the moment-curvature calculation, and including the effects of upward vertical movement of CEVA. The upward movement of CEVA can impose vertical tension in the north wall of CEVA. Accordingly, moment-curvature relationships are calculated at different levels of tension.

At each level of axial force, a limiting curvature is determined to avoid unacceptable behavior. As explained in Attachment A, the curvature value of 0.003 1/in. corresponds either to the buckling of compression reinforcement (for cases with low level of axial tension) or rupture of tension reinforcement (for cases with high level of axial tension). Conservatively, 90% of this curvature value (0.0027 1/in.) is selected for computing the maximum bowing that the wall can resist.

The computed moment-curvature relationships are assigned to a finite element model of the wall, and nonlinear analyses are performed to determine the lateral displacement at which the curvature of the wall at the point of maximum bowing reaches the limiting curvature. Figure A2 in Attachment A shows that 2 in. of lateral wall deformation induces curvature of 0.0027 1/in. in the wall with a low level of axial force, while the same displacement induces curvature of 0.0023 1/in.

in the wall with a high level of axial tension. Therefore, the wall can resist a lateral bowing of 2 in.

Mr. Edward Carley - Project 170444 6 November 2017 Document No. 170444-L-001 Revision 0 before buckling or rupture of the vertical reinforcement will occur (with 10% margin), and it is recommended that the wall be retrofitted prior to it experiencing 2 in. of bowing.

The site visit report (170444-SVR-01-R0, FP101192-00) for the recent measurements indicates that the wall moved outward since the previous measurements; bulging has increased to 1-7/16 in. Additionally, at a localized area, hammer sounding indicated portions of the concrete cover potentially susceptible to separation, especially at areas with larger horizontal cracks. Therefore, sensitive equipment or processes should be protected against possible falling pieces of concrete cover from this wall before it is retrofitted.

Sincerely yours, Said Bolourchi Michael Mudlock, P.E.

Senior Principal Senior Project Manager NH License No. 14808 I:\\BOS\\Projects\\2017\\170444.00-LARS\\Workspace\\CEVA North Wall\\170444-L-001 Rev. 0.docx

PROJECT NO:

170444 DATE:

Nov 2017 CLIENT:

NextEra Energy Seabrook BY:

MR.M.Gargari

SUBJECT:

Evaluation of Additional Displacement for the North Wall of CEVA VERIFIER:

I. Baig ATTACHMENT A MOMENT CURVATURE RELATION FOR THE CEVA NORTH WALL A1.

REVISION HISTORY Revision 0: Initial document.

A2.

OBJECTIVE OF CALCULATION The objective of this calculation is to compute moment-curvature diagrams for the north wall of Containment Enclosure Ventilation Area (CEVA) structure subjected to different tensile force.

A3.

RESULTS AND CONCLUSIONS Figure A2 presents moment-curvature diagram for the wall section subjected to different tensile force. As can be seen from the figure, by increasing the magnitude of tensile force, the failure mode changes from compressive rebar buckling to tensile rebar rupture. For all cases, the point of severe damage initiation approximately corresponds to curvature value of 0.003 (1/in.). Accordingly, this point is selected as a limiting curvature and the wall is allowed to deform up to this curvature.

Figure A3 provides a comparison between two cases, one with accounting for the effect of compressive rebars and the other one without considering the compressive rebars. As can be seen from the figure, including the resistance offered by compressive reinforcement does not affect the ultimate capacity noticeably, however, it increases the ductility of a section.

A4.

DESIGN DATA / CRITERIA See Section 4 of the calculation main body (160268-CA-05 Rev.0).

A5.

ASSUMPTIONS A5.1 Justified assumptions There are no justified assumptions.

A5.2 Unverified assumptions There are no unverified assumptions.

Attachment A

- A Revision 0

A6.

METHODOLOGY To calculate the moment-curvature diagrams, sectional analysis based on fiber section method for integrating over the cross section is used. In this method, the cross section is discretized into fibers (or layers subjected to unidirectional bending), and an appropriate material model is assigned to each fiber.

Figure A1 demonstrates a typical fiber section discretization. In this study, each section is discretized into 20 fibers/layers. The concrete material is represented by Kent and Park [A5] model in compression and Stevens exponential softening model in tension [A3]. Reinforcing steel bars are modeled using elastic perfectly plastic material with strain cutoff of 0.007 in tension and accounting for inelastic buckling model of Kashani et al. [A4] in compression.

Moment-curvature diagrams are then calculated for axial tension of 0, 10, 30 and 60 kips. Each point is derived by selecting an axial force, and then changing curvature value and calculating the moment. Figure A2 presents the computed moment-curvature diagrams.

An additional study is conducted to show the effect of including or excluding compressive reinforcement.

The study shows accounting for the effect of compressive rebars increases the ductility of a member as presented in Figure A3; therefore, the member can accommodate more displacement.

A7.

REFERENCES

[A1]

Simpson Gumpertz & Heger Inc., Evaluation of Containment Enclosure Ventilation Area, 160268-CD-05 Rev. 1, Waltham, MA, Mar. 2017.

[A2]

United Engineers & Constructors Inc., Seabrook Station Structural Design Drawings.

[A3]

Yuan Lu, and Marios Panagiotou. "Three-dimensional cyclic beam-truss model for nonplanar reinforced concrete walls." Journal of Structural Engineering, 2013, 140(3): 04013071.

[A4]

Mohammad M.

Kashani, Laura N.

Lowes, Adam J.

Crewe, Nicholas A.

Alexander, Phenomenological hysteretic model for corroded reinforcing bars including inelastic buckling and low-cycle fatigue degradation, Computer and Structures, 156 (1), 58-71, 2015.

[A5]

Dudley. C. Kent, and Robert Park, Flexural members with confined concrete, ASCE Journal of Structural Division, 97 (ST7), 1969-1990, 1971.

Attachment A

- A Revision 0

A8.

COMPUTATION Geometry Rebar diameter db 1.128in



Reinforcement ratio

2 1 in2 12in 24

in 6.944 10 3



u



Concrete Material Model Compressive strength of concrete fc 3

 ksi



Kent & Park Model Strain at Peak compressive strength co 0.002





Strain at 50% compressive strength 50u 3

0.002 fc psi



fc psi 1000



4.5



10 3



u



Model parameter Z

0.5 50u co



200





Residual compressive strength fc.res fc 0.025

75



psi



Steven's Model Young's modulus of concrete Ec 3120ksi



Tensile strength of concrete ft 5

fc psi

273.861 psi



Strain at cracking cr ft Ec 8.778 10 5



u



Model parameter that controls residual M

75mm db 0.018



Model parameter that controls softening slope t

540 M

4.005 103 u



MATconc

( )

min fc.res fc 1 Z

co









¬

º1/4



¬

º1/4

co



if fc 2

co

co

§¨©

• ¸¹ 2



¬

º 1/4

co

d 0



if Ec

0

d cr



if ft 1

M



(

) e t



cr







M



¬

º1/4

cr

d if



Constitutive model for concrete Attachment A

- A Revision 0

0.01



5



10 3



u 0

4



2



0 Strain Stress (ksi)

MATconc c

 

ksi c

Steel Material Model Yield strength of steel fy 60ksi



Young's modulus of steel Es 29000ksi



Yield strain y

fy Es 2.069 10 3



u



Rupture strain sr 0.07



Account for buckling Buckling 1



Put 0 to ignore, put 1 to consider Kashani Model (buckling)

Unbraced length/Diameter LD 15



Slenderness ratio p

fy 100MPa LD

30.509



Model parameters 1

4.572 p

74.43



65.057



2 318.4 e 0.071



p

36.495



star 3.75 fy LD

15 ksi



Attachment A

- A Revision 0

Constitutive model for steel MATsteel

( )

fy



Buckling 0

=

if star fy star





 e 1 2

y











y







¬

º1/4



¬

º 1/4



otherwise

y





if fy y

d sr



if 0

sr

d if Es



 otherwise



0.05



0 0.05 50



0 50 Strain Stress (ksi)

MATsteel s

 

ksi s

Concrete Fibers Width of fibers b

12in



Ref. 2, 2ft thick wall Total thickness or height h

24in



Number of fibers ConcNum 20



Height of fibers ConcH h

ConcNum 1.2 in



Concrete fiber coordinates Concy ansi h

2



ConcH 2



i 1



(

) ConcH



m i

1 ConcNum



for ans



Concrete fiber strain Conc o







ansi o

Concyi



m i

1 ConcNum



for ans



Attachment A

- A Revision 0

Concrete fiber stress Conc o







ansi MATconc Conc o





i





m i

1 ConcNum



for ans



Concrete fiber force ConcF o







ansi Conc o





i b ConcH





m i

1 ConcNum



for ans



Reinforcement/Steel fibers Depth to reinforcement d

20.5in



Ref. 2, 2ft thick wall Area of tensile reinforcement

(#9@12 in.)

As 1in2



Number of reinforcement in row, e.g. equal to 2 for tensile and compressive SteelNum 2



Depth to reinforcement fiber Steely1 d

h 2



§¨©

• ¸¹



8.5



in



Steely2 d

h 2



8.5 in



Area of reinforcement fiber SteelAs1 As 1 in2



SteelAs2 As 1 in2



Steel fiber strain Steel o







ansi o

Steelyi



m i

1 SteelNum



for ans



Steel fiber stress Steel o







ansi MATsteel Steel o





i





m i

1 SteelNum



for ans



Steel fiber force SteelF o







ansi Steel o





i SteelAsi

m i

1 SteelNum



for ans



Attachment A

- A Revision 0

Axial Equilibrium Force o







ans1 0

m ans1 ans1 ConcF o





i



m i

1 ConcNum



for ans2 0

m ans2 ans2 SteelF o





i



m i

1 SteelNum



for ans ans1 ans2



m



Moment Equilibrium Moment o







ans1 0

m ans1 ans1 1



ConcF o





i

Concyi



m i

1 ConcNum



for ans2 0

m ans2 ans2 1



SteelF o





i

Steelyi



m i

1 SteelNum



for ans ans1 ans2



m



Solution Known parameters Axial force P

60kip



Iteration Curvature

0.003 1 in



Solve for strain at centroid Axial strain at centroid (initial guess) xo 0.03



Requires iteration Axial force equilibrium f x

( )

Force x



(

)

P





cent root f xo

  xo







0.027



Sectional forces Force cent







60 kip

Moment cent







48.079 kip ft

Attachment A

- A Revision 0

Stress and strain in concrete and steel Steel fiber stress and strain Rebar Steel cent







0.052 1.266 10 3



u

§

¨

©

¸

¹



Rebar Steel cent







60 36.723

§¨©

• ¸¹ ksi



SteelF cent







60 36.723

§¨©

• ¸¹ kip

Concretey Concy



Concrete fiber stress and strain Concrete Conc cent









Concrete Conc cent









Maximum compressive strain in concrete max.comp Rebar2 Rebar1



Steely2 Steely1



h 2

Steely1



§¨©

• ¸¹

Rebar1



9.234



10 3



u



Attachment A

- A Revision 0

A9.

TABLES There are no tables.

A10.

FIGURES Figure A1: Schematic representation of fiber section method Figure A2: Moment - curvature diagrams for different axial force Attachment A

- A Revision 0

Figure A3: Moment - curvature diagram considering the effect of including or excluding compressive rebars Attachment A

- A Revision 0