ML20128G773

Review of Waterford III Basemat Analysis

ML20128G773
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Site:	Waterford
Issue date:	04/16/1984
From:	BROOKHAVEN NATIONAL LABORATORY
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Shared Package
ML19263A633	List: IA-84-455, Forwards Evaluation of Concrete in Basemat,Waterford Unit Number 3. Despite Violations of Spec Requirements During Initial Concrete Pouring,Const Adequate to Ensure Structural Safety ML20127A144 ML20127A168 ML20127A834 ML20127A837 ML20127B613 ML20127C060 ML20128G376 ML20128G592 ML20128G691 ML20128G710 ML20128G767 ML20128G773 ML20128G790 ML20128G826 ML20128G847 ML20128G873 ML20128G899 ML20128G920
References
FOIA-84-455, FOIA-84-A-56 NUDOCS 8505300305
Download: ML20128G773 (12)

Text

..- ATTACIMENT 4 l , t . .

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REVIEW 0F WATERFORD III BASEMAT ANALYSIS

- 'e Structural Analysis Division a

Department of Nuclear Energy

• Brookhaven National Laboratory Upton, NY 11973 h

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TABLE OF CONTENTS

-b Page No.

INTRODUCTION ................................................. 1 GENERAL COMENTS ............................................. 2 STRUCTlRAL ANALYSIS TOPIC REVIEWED ........................... 3 .

-1. Dead Loads .......................................... 3

2. Buoyancy Forces .........i........................... 5

3. Variable Springs Used For the Foundation Modulus . .. . 6

• 4. Vertical Earthquake Effects ......................... 6

5. Side Soil Pressure ...........'.'.'..!.~..'...'..~..'..'....

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- 6. Boundary Constraints ................................ 7 o

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• Finite Elenent Mesh and Its Effect .................. 8 -

8. BNL Check Calculations .............................. 8 CONCLUSIONS AND RECOMMENDATIONS .............................. 8 APPE!; DIX A ' LIST OF CONTRIBUTORS ............................. A-1 1

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INTRODUCTION At the request of SGES/NRR, the Structural Analysis Division of the Department of Nuilear Energy at BNL undertook a review and evaluation of the ,

HEA Waterford III mat analysis documented in Harstead Engineering Associates (HEA) Reports, Nos. 8304-1 and 8304-2. Both reports are entitled, " Analysis of

' Cracks and Water Seepage in Foundation Mat" . Report 8304-1 is dated September

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~19, 1983, while Report 8304-2 is dated October 12, 1983. Majortopics .

addressed in the first report are:

(l) Engineering criteria used in' the design, site preparation and con-

! struction of the Nuclear Power Island Structure basemat.

i (2) Discussion of cracking and lea,,k, age,,i,n the ,b,as,em,at.

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o (3) Laboratory tests on basemat water and leakage samples.

l (4) Stability calculations for the containment structure. ,

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The second report concentrates on the finite element analysis aHd its hesults.

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Specifically, it describes:#

(1) The geometric criteria and finite element idealization. ,

(2) The magnitude and distribution of the loads.

(3) The final computer results in terms of moments and shear versus ,, ,

the resistance capacity of the mat structure. -

Supplemental information to these reports were obtained at meetings held in Bethesda, MD, on March 21 and 26,1984, at the Waterford Plant site in * ,

Louisiana on March 27, 1984, and at Ebasco headquarters in New York City on April 4,1984. At t,he close of the EBASCO meeting, a complete listing of the HEA computer run was made available to BNL.

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I The BNL efforts were concentrated on the review of the results presented in report no." B352-2 and on the supplenental information contained in the com .

puter run given to us by HEA. This computer run contains 9 load cases and their various ' combinations. The input / output printout alone consists of roughly two thousand pages of infonnation. Selected portions were reviewed in detail, while the remaining sections were reviewed ir, lesser detail. Com- ,

ments regarding the reviewed work are given in the sections that follow. -

GENERAL COMENTS Basically, the qEA report concludes that large primary moments will pro-duce tension on the b'ottom surface of the mat. .For, this, condition, it is .

shown that the design is conservative. Furthennore, the shear capacity vsy

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the shear produced by load combinations are concluded to be adequate although*

a few elements were found to be close to the design capacity. Accordingly,

! the cracking of the top surface is attributed to " benign" causes such as shrinkage, differential soil settlement, and tenperature changes. ,

I Based on the dinuwiuns held with EBASCO and HEA, and on the review of data given to BNL, it is our , judgement that the bottom reinforcement as well F as th'e mat shear capacicy is adequate. The statenent that the cracking cf the top surface is attributable to " benign" causes however has not been analyti-i cally demonstrated by HEA. In the BNL review of the reports and data, an at tempt was made to ascertain the reasons for the. existing crack patterns that ,

appear around the outside of the reactor shield building as depicted in Figure D-1 Appendix D of the HEA Report 8304-2. Other effects influencing the structural behavior and safety were also investigated. Specifically, the l-strue tural analysis topics reviewed in more detail include:

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(1) Dead loads and their effects.

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(2) Suoyancy forces and their effects.

(3) Variable springs used for the foundation modulus.

-(4) Vertical earthquake effects.

(5) The s'ide soil pressures. , .

(6) The boundary constraint conditions used for the mat.

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(7) Finite element mesh size and 1.ts effects.. _. . . , , ,

(8) BNL check calculations.

l l STRUCTURAL ANALYSIS TOPICS REVIEWED 1 ..

1. Dead Loads f As mentioned EBASCO in their discussion and HEA in their reports have not '

shown ' analytically, the cause of the top surface cracks. In reviewing the HEA-l- computer outputs, it was found that element moments and shears for individual loadings are explicitly given. Thus, for the case involving dead loads only, a nunber of elements in the cracked regions exhibit moments that can produce

- tension and thus create cracking on the top surface. This situation is s,hown ,

in Table I which gives moment data for elements in some of the cracked re-gions. From the HEA report (page C-2-1-9) it seems that the top reinfore,e -

ment, which is n19 6" in each direction

• is the minimum requirement for .

I temperature steel-according to the Anerican Concrete Institute Building Co'de ,

• In a subsequent phone conversation, P.C. Liu of EBASCO stated that some

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l . additional reinforcenent was added on the top surface in one direction. Even if'this is the case the statenent that follows is true for the unstrengthened direction and perhaps even for the strengthened direction.

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TABLE 1 Normal Pressure .

'Mx  % Mxy Side^ Pr:sstre ..

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ELEMENT D 8 0 ,.

- 31 -294 -196 93

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-242 17 3 -574 19 7 116 207 91 106 - 25 -663 -392 79 242 644 595

-605 205 -412 217 -296 48 -2 19 - -416 - 76 211 50

-136 136 - 81 15 -3 19 -193 E 207 99 ,

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,' -170 39 - 12 -347 -489 66 7 441 -l'05 168 172 531 -130 -274 -258 . 11'7

-1193 357 3 E 436 -719 269

- 60 26 -730' -347 27 47 438 269 142 -159 158 88 248 .-- 55 -653 -339 -127 T 44'l 665 59 210 72 -143 28 -361 -420 24 M 204 193 87 569 350 32 898 - 24 -241 75 -354 -771 .- 49 208 -247 30 F 203 -676 260 -995 ~ 236 39 - 21 -574

-705 310 332 - 65 -171 .-486. 61 426 -542 157 8

o 259 62 148 -133 * '81 154 - 36 .

5 71 531 75 0.. 18

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253 41 ;,

30 58 670 5 10 255

- 55 87 , 8 NOTE: D - Dead Load 1 5 252 86 24 611

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• 69 -

9 50 26 412

,, N' 254 8

162 - 23 44 12 8 - Bouyancy E. 251 37

- 38 5

57 15 - 81 - 15

• 9" 257 320 248 255 - 26 29 16 - 29 ,- - 6 267 -236 80 87 118 - 64 , 28 .

269 -17 3 59 434 10 - 82 32 .

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4 19 -314 137 -635 313

' -642 238 270 - 29

!! 410 -371 71

-774 275 - 44 41 400 -315 108

-201 102 108 - 23 3 b' 401 -180 42 ,

-304 118 -130 17 8 44 - 19 A ', 414 - 15

. -200 440 41 - II

• 4 4 17 93

- 32 98 ,- 18 404 - 64 17. 428 I

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) Specification' (i.e. , As = .0018 x 12 x 144 = 3.11 in2/ft). The resisting moment capaci_ty based on working stress design is about M = Asisjd = 3.12 l ,

x 24 x 131/12 = 817 ft-kips /ft. The steel reinforcement strain for this j coment is equal to .

c, (=ce ) = = 29 000 = 0.00083' infin . ,

while, the corresponding concrete stress is, f, = c cE,j, = 0.00083 8

= 3 ksi In checking the data 1.n Table 1, it can be seen that element 208 has exceeded

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the working load capacity under the deaf ~1oad condition and; thus the local -

area could have exhibited a crack when this load acted alone. Similarly, '

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concrete cracking could occur under this load condition in elements 447, 212,

204, 253, 255, 269, 257, 417, and 404. Thus, the cracks on the upper surface 6utside of the shield wall could have been initiated after construction of the l superstructure, before placement of the backfill. It should be noted that '

since no anaissis is available for dead load without the superstructure, the reason for the basemat cracks inside of the shield wall cannot be explained by this reasoning.

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2. Buoyancy Forces

The moment results from this analysis show that these forces when acting alone would mostly cause tensile stress on'the upper surfaces. T'he moments '

. causing these stresses are tabulated in Table 1 for groups of elements in the cracked regionE. As can be seen, these moments are not as severe as those due ,

to dead weight'. By superpositon they could in some cases contribute to higher tensile stress &s and thus result, in further cracking in some of the upper surface areas. .

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3. Variable Springs Used for the Foundation Modulus Moments and hears developed in the basemat were computed using the con-cept of the Winkler foundation; namely the soil is represented as a series of relatively uniform ' independent springs. The stiffness of the springs is ob tained from approxinate analyses dich are based on generalized analytical ,

solutions available for rigid mats on the surface of elastic soils. The

actual design of the sat was based on a series of iterative computer runs in which the soil stiffness was varied'until the computed contact pressures under the nat were fairly uniform and equal to the overburden stress at the eleva-tion of the foundation mat. This approach appears to' be reasonable since the long' term consolidatibn effects can be anticipated to cause effective

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redistribution of loads and cause th' maYto e 6eh' ave'in 'a ' flexible manner. ,

4. Vertical Earthquake Effects Vertical earthquake effect was not discussed in the HEA reports. However, from the finite element analysis print out and conversation with HEA engi-

-neers, it was stated that this effect was included in the load combination cases by specifying an additional factor of 0.067, which was then applied to the dead and equipment loadtcase. From the discussions and the review it is not clear to BNL whether an amplification factor due to vertical mat frequency

, was used or not. A rough check by the reviewers indicates that this factor could have some influence on the results.

5. Side Soil Pressure According to the STARDYNE conputer results obtained from HEA, the nornal side soil pressures produce large noments that are opposite to those causett by i

the dead loads.' As shown in Table 1 tere monents of elenents located in one of the cracked regions outside of the shield building are compared. The total 1 .

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i' moments in some cases (i.e. element 447 or 208) become quite small. In other regions therst is an fact a reversal in the total bending monent which causes .

tension on the bottom surface and compression on the top. This compression f

j would tend to close the cracks on the upper surface. Thus, it appears that this pressure is a very important load case for the mat design.

For the static or normal operating condition the lateral pressures are

} based on the at-rest stress condition and are uniform around the periphery of the structure. For the seismic problems the pressures are computed to ap -

! proximately account for relative movements between the structure and the soil.

l On one side the structure will move away from soil (active side) and reduce the pressures while the opposite will occur on the other side-(passive side).

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The actual computations made use of tiridial~t~est data 'fr'ani site soils to -

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I arrive at the soil pressures rather than use the standard Rankine analyses'. -

However, no dynamic effects on either the lateral soil or pore pressures was included. The sensitivity of the calculated responses to these effects are

surrently unknown. ~

6. Boundary d:r.:trcints /

For equilibrium calculations no special consideration need be made for  :

) vertical case since the soil springs pr, event unbounded structural motion.

However, the same cannot be said for the horizontal case since soil springs are not used to represent the soil reactions. Rather the lateral soil forces .

are directly input to the acdel. To prevent unbounded rigid body motion.

artificial lateral constraints aust be imposed on the model From the output ' '

4 l presented in the EBASCO and HEA reports, it is not possible to evaluate the ~

impact of these assunptions. The stresses caused by the artificial boundaries should be calc'ulated and compared with those presented. '.

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7. Finite Element Mesh and its Effects ,

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In genera 1 finite element models for plate structures require at least '

i four.elenents between supports to obtain reasonable results on stress comp-utatiens. The models used by 'both E8ASCO and HEA violate this " rule of thumb" in the vicinity of the shield wall. The significance of this effect is denonstrated in Figure D-3 which presents a plot of moment taken through the center of the slab. The computed moments in adjacent elements 193,194 and

~ 455 are -3800, -2500 and +400K. The elements used in the HEA analysis are constant curvature elements so that the computed monents will be constant within each element. The steep soment gradient between the elements indi-cates that a finer mesh would be advisable. A similar effect was also noted when investigating the elements fonning -the-junction-between the lateral earth -

retaining walls and the base mat. '

8. BNL Check Calculations Due to the questions raised in the items above (4 through 7), it w'as de-cided to perfem saveral egyilibrium calculations to check the order of mag-nitude of the shear stress computed in the detailed finite element analyses presented by EBASCO/HEA.

Two types of average vertical shear stresses were computed in the base mat. The first type considers the average shear through a vertical section across the entire mat (one section in the E-W direction and the other in the N-S direction)'.' These sections were chosen to include those elements which indicated high shear stresses in the HEA analysis and where the actual crack-

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ing pattern was noted. The highest average shear stress conputed for any de-sign load combination is 50 psi. The allowable shear stress for the case Js 107_ psi (2( Eg%

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The second type of section considered is a circular punching shear section I located a distancd'of d/2 outside the reactor shield wall. The peak value of .

shear stress due to both SSE overturning moments and normal operating loads (plus proper load factors) were always less than the allowable design shear (4tfe).

COICLUSIONS AND RECOMMENDATIONS i (a) ~ The Waterford plant is primarily a box-like concrete structure sup'-

ported on a 12 foot thick continuous concrete mat which houses all Class I structures. The plant island is supported by relatively soft overconsolid'ated soils. To minimize long term settlenent effects, - . . . . . . ,

the foundation mat was designed on the floiting foundation principle. .

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The average contact pressure developed by the weight of the structure .-

is made approximately equal to the existing intergranular stresses developed by the weight of the soil overburden at the level of the bottom of the foundation mat. Thus, net changes in soil stresses due to construction and correspionding settlenents can be ahticipated to .

! be relatively smali.

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~(b) In reviewing the information, reports, and computer outputs sup-plied to BNL by ESASCO, HEA, and LPL, it is concluded that nor-mal engineering practit e and procedures used for the analysis of nuclear power plant structures were employed.

(c) Accepting the infornation pertaining to loadings, geonetries .

of the structures, material properties and finite element mesh, data,'it is the judgenent of the reviewers that:

(1) 'fie t bottom reinforcenent as well as the shear capacity of the base mat.are adequate for the loads considered.

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(ii) the computed dead weight output data can be used to explain some of the net cracks that appear on the top surface. The -

cracks that appear, could have occurred after the construction

'of the superstructure but before the placement of the backfill.

Their growth would then be constrained by subsequent backfill soil pressure. ,

(d) Due to the existance of the cracks, it is recommended that a sur-veilance progran be instituted to monitor cracks on a regular basis.

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Furthermore, an alert limit (in terms of amount of cracks, and or

. crack width,,etc) should be specified. If this limit is exceeded, specific structural repairs. shou.ld be mandated.. . , ,

(e) It is also recommended that a program be set up to nonitor the l water leakage and its chemical content. .

(f) BNL has reviewed the information provided by EBA500, HEA, and, LPL. The following questions concerning their analyses were developed:

l (1) , dynamic coupling in the vertical direction between the reactor building and the base set.

- (ii) dynamic effects of lateral soil / water loadings.

(iii) artificial boundary constraints in finite elements podels.

(iv)4 fineness of base mat mesh.

Based upon "our approximate calculations together with engineering judge-ment, we do not anticipate that the above questions will lead to major changes in calculated stress levels. Thus, it is our opinion that the safety margins in the design of the base mat are adequate. However, it is recommended some detailed confirmatory-calculations be performed in the near future.

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