ML20080T437

Review of Diesel Generator Bldg at Midland Plant

ML20080T437
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Site:	Midland
Issue date:	10/17/1983
From:	Costantino C, Chris Miller BROOKHAVEN NATIONAL LABORATORY
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Text

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Review of Diesel. Generator Building A

at P.idla..; Plant s1 by C.A. Miller and C.J. Costantino

'l Structural Analysis Division Department of Nuclear Energy Brookhaven National Laboratory Upton, NY 11973-n e

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2 Table of Contents I

1.0 Introduction 1

i-2.0 Evaluation of Pertinent Work 2

~2.1 History of' Structure 2

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2.2 Settlement History 3

2.3 Crack Patterns 6

2.4 ' Structural. Analysis 7

4 2.4.1 Bechtel's Computation of Settlement Stress (Ref.2)............................................

8 2.4.2 Bechtel's Analysis Using Measured Settlements (Ref. 3) 9 2.4.3 Matra's Analysis Using Measured Settlenents (Ref. 4)

........................................-10 2.4.4 Estimation of Stresses from Crack Data (Ref. 5) 10 2.5 Stress Totals

............................................. 11 0

2.6 Survey Data...............................................

12 3.0 Assessnent of the Diesel Generator Building 12 4.0 Response to Concerns of R.B. Landsman 13 5.0 Conclusions-....................................................

16 References 18 ahppendix

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1.D INTRODUCTION

This report describes 'a study undertaken by Brookhaven National j

Laboratory (BNL) to evaluate the extent to which settlenent cracks observed in

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-the Diesel-Generator Building (DGB) at the Midland Nuclear Power Plant impact on the ability of the building to satisfy-design requirenents. Dr. R.B

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i 1 Landsman, of Region III.. has raised questions regarding this safety isste (Ref.1). The specific objective of this study is to assess the significance

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-of his comments and to prepare a written response.

This objective was achieved by reviewing the existing pertinent work (published reports, testimony and analytical studies), and by interviewing key f'

personnel so that a correct interpretation of the work perfonned could be

'made. Additional. calculations were specifically omitted frca the scope of this study.- All of the conclusions drawn in this report are based on an assessment of calculations and studies performed by others.

e The study described herein was carried out during the period of August through Septemberi1983. On August 4, a meetin.g was held at NRC to discuss the problem and to obtair. some of the pertinent literature. Some of this litera--

ture was carried back to BNL while other documents were mailed to NRC during the following week. Appendix A contains a listing of all raports used during the program. - On August 24, a meeting was held at Bechtel Corporation of fices in Ann Arbor, Michigan.

Presentations were made by Bechtel and Consumers Power staff summarizing the work performed by project personnel to demonstrate the adequacy of the DGB. Their consultant's (Dr. M. Sozen of the University of' Illinois' and Dr. G. Corley of Construction Technology Laboratories) also i

discussed their work. An inspection of the DGB was held on the evening cf August 24 and during the morning of August 25..At this inspaction, the cracks were observed although no new detailed crack maps were made. Discussions were held with construction personnel to detemine the sequence of concrete place-ment..

Further interviews were held at IRC on September 8.

Individual inter-views'were held with Dr. Harry Singh (soils consultant for NRC from the Amy Corps of Engineers), Joseph Kane (NRC staff), and Lyman Heller (NRC staff).

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A combined interview was also conducted with Frank Rinaldi (NRC staff), John

.. Matra- (structural cobsultant for FRC from Naval Special Weapons Center), and

- Dr. Gunnar.Haarstead (structural consultant for NRC). The purpose of these interviews was to explore the role each played in the design and analysis of l

the nGB and to ~ learn of their concerns regarding the adequacy of the DGB.

4 An' audit of' the DG8 calculations by the task group was held at Bechtel's

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p-E Ann Arbor offices on September 12 and 13. Dr. Sozen was present on September

13. The following items were reviewed in detail. during this audit: numeri-(cal r.cdels used by Bechtel to calculate stresses in the DGB due to settle-

' ment; the msgnitude of stresses due' to the various load cases; the method of P,

determining stresses from crack data; the accuracy of the survey nethods used to moniter settlements; and the concrete pour data. A meeting was held with Dr. Landsaari of Region III on September-13, at dich time his specific con-

- cerns raised in Ref. I were discussed.

This report is organized as follows. An evaluation of the literature is presented in Sectior. 2 of the report. Section 3_ contains BNL's assessment of

. the adequacy of the DGB, while specific responses to Dr. Landsman's concerns are given in 3ection 4.

Conclusions are. listed in Section-5.

p 2.0_ EVALUATION OF PERTINENT WORK l

The_ material on the DGB which was : reviewed during the course of this l

study is divided into six categories; namely, hrtorical description of the structure and its'settlepent behavior; developed crack patterns; structural analyses to evaluate settlement stresses; treatment of other loads and

-stresses; and survey data. The naterial in each cate9ory is described and p

evaluated in this section of the report.

l 2.1- ~ History of Structure ~

The DGE is a reinforced concrete shear wall building consisting of five cross walls connecting a north and south wall. The interior walls are 18" thick while the exterior walls are 30" thick. The structure is 155' by 70' in

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_ plan and is 51high with an intennediate floor slab located 35' above the foun dation. Wall footings are located under each of the walls, the footings being 10' wide and 30" deep. The building is founded on about 30' of various fills overlying the natural glacial till.

- The' fill was placed from 1975 through 1977 with construction of the DGB begun in October 1977.

Concrete was placed in 6 lifts as follows:

October 1977 to Elev. 630.5 (foundation)

December ' 1977 to Elev. 635.0 March 1978 to Elev. 654.0 August 1978 to Elev. 662.0 December 1978 to Elev. 664.0 February 1979 to Eley. 678.3

'Jithin each lift the pours were generally made from east to west. Construc-tion. joints occur. in the middle of the cross walls and at the west end of each bay for th3 north and south walls.

' Large settlements and cracks in the concrete were noticed while the lift going to Elev. 662 was being poured. Construction was halted while the pro-blem was being studied.

It was concluded that the large settlement was due to poor compaction of;the fill naterial. This settlerent caused the structure to

" hang up" on the duct banks which penetrate the footings on the cross walls.

The duct banks were cut loose from the DGB foundation in November 1978 and construction of the building' restarted.

In January 1979, 20' of sand sur-charge was placed.on the site to consolidate the fill. This remained in place until August 1979.

In September 1980, a permanent dewatering system was in-stalled to naintain the water table below Elev. 610.

2.2 Settlement History The DGB is founded on approximately 30' of fill material, underlaid by a veqy stiff glacial till about 190 feet thick. A dense sand layer about 140' thick ~ lies below the till, which is in turn underlaid by bedrock. The,

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majority of-the fill was placed at the site between 1975 and 1977, with actual foundation. construction completed by January 1978. During July 1978, settle-ments of-the order of 3.5 inches (Ref. 7) were noted which were greater than

. the original:40 year. predicted settlements. Apparently consolidation of the j

fill was taking place as structural dead loads were applied.

In addition, the

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- four' electrical ~ duct banks under the structural crosswalis were acting as hard l'

points to the foundation since they were in turn being supported by the stiff

- natural soils below the fill. This caused rotation of the building abcut the duct banks.

. Construction was halted during August 1978, a soil boring program under-L taken to determine the-problem with the fill and Drs. R.B. Peck and A.J.

Hendron' retained to advise on the remedial action. Tha exploratory program i

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. consisted of.32 borings (with no undisturbed sampling) and 14 Dutch cone penetroneters. These confinneo that the fill had been improperly placed (in an extr'emely variable density state)'and consisted of varying amounts of co-hesive as.well as granular backfill. Lean, concrete was also encountered in the backfill..The thickness _of silty cly backf tll was found to be greater

.under the south-east side of the building leadin.g to the. generally larger i

settlements on this side.

A surcharge ' program was implemented to attempt to consolidate the fill more uniformly. - In addition, the duct banks were cut loose from the founda-tion in November 1978 to eliminate the foundation hard points.

Surcha rgi ng began in January 1979 and remained in place until August 1979, when it was determined that prinary consolidation had been completed.

Instrumentation (primarily settlement plates and Borros anchors) placed in the fill was used to arrive at this conclusion.- It should be noted that the consolidation test results, obtained from undisturbed samples taken after canpletion of the sur-charge program, did not confirm this conclusion. Data was sufficiently scattered to indicate that the fill may not be uniformly consolidated. Unfor-teately, the boring program conducted after the surcharge program was com-plated..did not include cone penetrometer soundings for comparison with the readings.taken before the surcharge was applied..

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At'the_ completion of _ the surcharge program, it was decided that since

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loose sands still existed in the fill, a perranent dehttering system would be 1

installed to preclude the potential for soil liquefaction during a seismic event..This dewatering caused additional settlenents to be developed at the n"

site, but apparently these were related to deep seated consolidation of the natural soils under the fill, and would be more uniform than the settlements caused.by the fill consolidation.

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'ItLis questionable whether.the piezometer data was of any significance in

analyzing the excess ~ pore pressure condition developea in the fill during the consolidation process. The readings indicate generally very low pore pres-sures, about 1/20 the magnitude of the applied surcharge pressures.

It is not clear in fact whether the fill was ever fully saturated at the time of the 4 -

surcharge program.

d' Peak settlements anticipated at the end of _2025 (actual settlements to

- o date plus secondary. settlements from now till then) are specified in Ref. 7 to vary from 4.79 inches (under the NW corner) to 9.33 inches (under the SE corner).. However, it should be mentioned that the exact settlement history at the va'rious settlenent markers at the DG,8 is' open to question. For example,

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fit tis mentioned in Ref. 7 that the maximum settlements in August 1978 were about~ 3.5 inches.

Yet the chta used in the stress analyses for the presurcharge period (Figures ES-14.ot: Ref. 7) indicates peak settlements of.

only 1.99 inches.

It was stated-at one of the Bechtel presentations that prior to cutting the duct banks loose from the footing, footings along the

' North wall 'actually lifted off from the soil, with the DGB_ rotating about the 4

duct : banks. There is no indication of this behavior in any of the settlement chta used in the computations. Ref. 8 lists the settlement increment from 8/79 to 12/2025 to be 2.36 inches under the SE corner.of.the building. For the same period Ref._7 lists this data as 1.89 inches. Thus some inconsistencies appear.to exist in the various documents.

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.-v 2.3. Crack-Patterns Af ter it was 'detennined that settlement was a problem, Bechtel initiated g

'a program to conitor cracks'in the structure.

In general cracks were visually

. observed 'and an optical comparator used to detennine crack width. Crack widths greater than 10 mils were of specific interest as this corresponds to

. reinorcing stresses of about 10 ksi. Crack maps were prepared based on

. surveys conducted during December 1978, September 1979, February 1980 and July r

-1981.-.Dr. Corely observed the cracking in January 1982 (Ref. 6) and confirmed ithat the general-pattern of cracks agreed with the July 1981 Bechtel crack

' nap s.

He prepared a detailed crack map for the center interior wall. A comparison of this center wall' map (Fig. 4.21 of Ref. 6) with that prepared by Bechtel in July 1981'(Fig. 4.17) indicates that more cracking had occurred although the widths of.the cracks appear to be about the same.

Cracks' were observed during the BNL inspection of the plant on August 25,

- 1983 and some photographs taken.

In genera) the pattern of cr8ks appear to i

be similar. to the previously mapped cracks.. However cracks, which had not H'

been shown.on any -of the'Bechtiel cracks maps, were noted in both the north.and south walls. These additional cracks are in the lower level (up to Eley. 664)

and run at 45' degree angles to the horizontal up to the cross walls.

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l The first crack maps prepared from the December 1978 survey indicate f vertical cracks in the cross walls sich begin near the bottom of the wall and run.up to Elev. 664 (this was the top of the concrete pour at the time the settlement problem was first. noticed). The pattern of cracking is more severe

-in the east side of the building. This crack pattern is compatible with the E

model that assumes the cracks result from flexural stresses caused by the

. building " hanging up on the duct banks". No cracx maps were prepared for the north or south walls.

Th second set of crack maps were prepared from the September 1979 survey.

In general, mary of the cracks which occurred in the east wall prior to

. placing the surcharge do.not appear on these maps. The east center and center walls show the same type of' crack patterns as shown on the first crack maps except for the appearance of additional cracks. These maps also show cracks

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in the-upper level of the building. These cracks occur near the south side of

' the building in the cross walls.. The cracks tend to be vertical with some inclination of the cracks near the south wall. Soine cracks are indicated in these maps for the south wall.

Primary cracking occurs in the east side of the wall and'are. concentrated in the upper portion of the wall. The north waH :is-shown to' be more severely cracked than the south wall and contains

.mostly vertical cracks in the upper-part of the wall. Tne cracks appear to be centered about the three interior walls.

The third set of crack maps were prepared from the July 1981 survey.

'These. naps indicate the same type of cracking as before althouoh the cross i

wall now contain 'more cracking near the north side of the builuing than was evident before. The west wall.contains many more cracks than were shown previously.. These cracks run from the Eley. 664 level down to the base of the structure.

It appears that many of the cracks wh,ich have occurrea may be attributed

.to the building resting on the duct banks. Other cracks have occurred, how-ever, which were most likely caused by differential settlement of the wall footings. Comparison of successive crack observations generally indicates

.that more cracks are occurring, but that the n.tximum size of the cracks is still, about' 20 mils.

L 2.4 Structural Analyses The various analyses which have been used to evaluata stresses in the DGB are discussed in this section. The first analysis described is the method "used-by Bechtel to estimate stresses due to settlement for use in its load combination study. :This analysis makes use of the straight line a,aproxima-tions to the profiles of the settlements of the north and south walls. The

second and third analyses described are the Bechtel and Matra studies, which L

. attempt to use the actual measured settlements to estinate settlement stresses. - These analyses, though different in detail, lead to the similar

' conclusion that the settlenent measurenents wre (and continue to be) in p

significent error..The fourth analysis describes a cruder model which l

attempts to approximate an upper bound to-settlenent stresses by looking at 1,

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The first three analyses are based on detailed finite elenent nodels, Aile the fourth is based on crack patterns and crack widths.

2.4.1 Bechtel 'r Computation of Settlenent Stresses (Ref. 2)

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Since the building settlenents occurred den the structure was in various l ~

stages,of construction, the settlement stresses were evaluated for four dif-ferent time periods. The first period spans from the beginning of construc-tion:through August 1978 at which time constraction was halted. The second time -period extends from' August 1978 to January 1979 during sich the duct banks were cut loose from the structure and construction resumed. The third

. time period extends from January 1979 to August 1979 during which time the

- surcharge was placed. The last time period scends to the year 2025 and includes measured settlements from Augur'.1979 to December 1981 as well as the predicted ' settlements over the forty year life of the, structure.

The actual measured settlements were used to calculate stresses for the first period. Stresses were calculated in each of the walls by determining the arc of a circle which fit any three adjacent measured displacements.

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. radius of the' arc was then used to find the resulting bending monent in the wall, and the meant used to calculate stress.

The maximum stress in each of 1

the. walls was assumed to exist over the entire. wall. The stress in the south

. wall was 11.3 ~ksi; the east wall-6.6 ksi; and all other walls 2 ksi.

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j-The increnents in stress which occJrred during each of the other three time periods were evaluated using a finite elenent model of the DGB. This model was constructed and run on the Bechtel version of SAP (BSAP). The

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bullding was defined with 853 nodal points.

Plate elements were used to model y

the' walls, and beam elements used for the footings. Eighty-four (84) boundary l

. elenents were used to model the vertical soil stiffness (equivalent to the

_ coefficient of subgrade reaction). An iterative process was then used to

- determine the stiffness of these boundary elements.. A best fit straight line was first fit through the measured settlements for the north wall and another straight line fit to the data for the south wall.

It was shown that the

- measured displacements ' departure from the best fit straight lines is within

' the tolerance of the survey data. Dead load reactions were next estinated at r

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The stiffness of atly soil element was then sdeterndned as the ratio of the dead' load reaction to the displacement of the best fit straight line. The BSAP program was run and the reaction found at

' each' of these boundary elenents. A new~ stiffness was then calculated as the

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ratio of the reaction to the displacement of the best fit straight line. This process was continued for'several iterations.

. It is our opinion that this model will yield unconservative estimates of

! stresses. :If the iteration process were successfully completed, the deforma-tion.of the north and south walls will-be straight lines. The only stresses

.that would be canputed would then occur due to racking of the structure caused

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by the difference in the north and south wall straight lines.

It should be clear that if a best fit plane could be passed through all the settlement points under both the north and south walls, no stresses would be computed arywhere in the building. The stresses computed by this approach are a

function ~ of sich iterative cycle is used to define to soil spring paraneters,

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f and bears no resemblance to the actual soil. conditions at the site. There is no reason to expect that the soil stiffness should vary from point to point as shown by the analyses. We therefore conclude that this approach to compute

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' settlement stresses is inappropriate.

k 2.4.2 Bechtel's Analysis Using Measured Settlements (Ref. 3)

. This' analysis was performed using the same finite elenent model described a bove. This time however, the known survey displacement data was input to the L

program at the ten (10) wall intersection points.- The settlenents used were the displacement increments measured for the fourth time period described above. At the rensining 74 boundary elenent points, the structure was allowed to deform as r1 quired to maintain equilibrium (forces equal zero).

It was

' found that computed stresses were very high in those elenents adjacent to the -

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- wall intersection, but fall off rapidly away from these points.

This indi-cates that the analysis overly penalizes the structure by imposing large con-centrated forces at the wall intersections.

In fact, at some points, the soil is required to pull the structure downward to match these known displacenents.

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A modified analysis was perfonned by Bechtel at the suggestion of the task group. Rather than input only the ten known displacenunts, a smoothed curve was generated.which matched the known settlemeht data, but eliminated the sharp profile changes-developed in the analysis described above. A best Lfit'polynonial was passed through both the north and south wall settlements, p

and 'displacenents computed at all boundary elenent -points of the finite element model. Comparative plots of wall profiles indicate that this approach

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2.4.3 Matra's-Analysis Using Measured Settlenents (Ref. 4)

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The analysis performed by Matra is similar in intent to that described

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above.. -Diffe 9nces between the two are as follows:

First, this finite L

element analys1s was performed for all four time periods described in Section

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2. 4.- l. Three separate finite element models were used to define the DGB at

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various stages of construction. For each problem analyzed, the known settle-

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ment data at the wall intersection points was input to the models.

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does not.specifically state dat input was used at the remaining boundary I

element points between the wall-intersecti.on. However, at the interview,

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Matra stated that a linear displacement profile was assumed between these 1'

points.- The stress results of the analyses are similar to those described above for the Bechtel study, with similar conclusions reached.- In fact, it can'be anticipated that the Matra stress calculations would be even higher than the corresponding Bechtel results due to the linear assumption between data points..lf in; fact this was done, tne conclusions reached in that report would be of:little value since such highLbending stresses would be generated

at these discontinuities.

2.4.4.-Estimation of Stresses from Crack Data (Ref. 5) t

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Sozen considered the problem of predicting reinforcement stresses from a knowledge' of the crack patterns. zHe observed that the usual problem is to

. predict crack width based upon a given reinforcement stress. When these methods are applied to the DGB center wall, a 20 ksi steel stress is

- consistent with a crack width of 20 mils.. He also adds the crack widths for a series of cracks in the center wall and equates this to the total elongation J n

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in thelreinforycenent. Using"a'n estimated, $auge length over which this

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,., ; elongation occurred he obtains an estinated ' stress of 24 ksi, and indicates a probable' range of t20-30 ksi consideririg the urcertainties of the method. This was ' presented by' Sozen at the August 24 meeting).

It is likely that these stress' values would be ' r' educed with time.

A major cause of cracking was the hard points provided by the duct'binks. When the3e were cut free, one would (expect the s, tresses induced by the uneven support to be relieved. Creep in fthe con-crete would also tend to reliivesthe settlement-induced stresses.

Rinaldt-(pg.1108d o' the testimony) reported at the interview of 7

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-Septenber 8, that he calculated stresses' using Sozen's. method in each of the 5 cross. walls, as 'well as the north and south walls. He then added these stresses to the maximuc ' stress reporhd in each of the walls by Bechtel. The resultant maximum reinforcement stress was found to be less than 54 ksi (the allowable limit). ;It was'~ noted'that the Bechtel stresses already included

. settlement stresses.(to an unknown degree however) from the analyses described

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in 2.4.1.

The. crack-based estimates.of settlemer t stresses were added to the I

maximum of the Bechtel stresses without regard to where they occurred. While

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this'is a conservative app) sach,- there is' no documentation of the computa-tions.

It should be; note'd that there would be some question in the applica-tion of this method on those walls 'where relatively few cracks occurred.

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6 2.5 : Stress Totals -

The finite element model described-in 2.4.1 was used to calculate wall-r L

forces from all loadings except for the seismic loading. A lumped mass model

' was csed -to deterairie' forces resulting. from the-seismic loading. These forces

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'were then combined according to the load combinations required in ACI 318 and ACI 349. Critical elements' were then identified 'in each of the walls and

Bechtel's program OPTCON used to evaluate reinforcement stresses. OPTCON i

determines the reinforcement stress resulting from.out-of-plane bending moment-plus in-plane shear loading. The shear capacity of the concrete is deducted from the total shear load with the differedce assumed to be carried by the

reinforcement.- The following are peak reinforcement stresses reported by Becht'el for the critical" load cases:

-north ~ all -- 22 ksi; south wall - 34 w

'ksi; west wall - 29'ksi; east; wall - ' 23 ksi; and interior walls - 20 ksi.

The allowable' steel streesslis 54'ksi.

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' Bechtel. reports that the accuracy of the-survey data describing the DGB p

settlements is 1/8" until the surcharge was removed and 1/16" since that time.

Standard survey techniques and eouipment were used.

'3.0 - ASSESSMENT OF THE DIESEL GENERATOR BUILDING.

. The DGB 'has undergone very large settlements which have undoubtedly caused serious structural distress. This distress is nanifested in the cracks which have occurred in the building.

The purpose of this section of the report is to give an opinion as to (1) dether the building is structurally sound and -(2) whether the building still. meets the criteria as stated in the FSAR.

-An important issue is whether the major part of the settlement has

.' occu rred. The settlement data indicate that settlements are well into the ssecondary consolidation phase so that-large additional settlements would not be anticipated. This leads to confidence that predictions of the adequacy of the structure based on settlenents Wtich have taken place to date should hold for tihe life of the structure.-Certainly, settlements should be monitored and the ' problem reconsidered should more than the anti'cpated additional settle-rents occur. Relative settlements of points on the structure of.005" are 4

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. si gni ficant. : The accuracy of the settlement measurecents should be refined to

? reflect this requirement.

While ~ significant cracking-has occurred in the structure, it would appear that there is little evidence to indicate that the structure is unsound. The structure is very massive and is not subjected to large loadings.

Even the tornado and seismic loadings do not introduce large stresses and usually these

' stresses. occur at -locations that are not critical locations for the settlement

-stresses.1

-.It is-difficult to show that the stresses in the DGB meet the criteria of

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tne FSAR.- Bechtel's straight line analysis (see 2.4.1) is based on the clain.

that the settlement survey data is not sufficiently accurate to calculate r :

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structural stresses.

The adjustment they make to account for this inaccuracy gives results that are likely mconservative.

If conservative assumptions are made then the calculated stresses are too large to satisfy the criteria and not consistent with the cracx patterns observed in the structure (see 2.4.2).

It is doubtful whether any analysis could now be developed which would pro-vide more realistic estimates of settlement stresses with the required degree'.

of confidence.

The most likely source for obtaining. reasonable estimates of settlement stresses are the crack studies (see 2.4.4).

However, these studies must be documentet much more completely than has been done to date.

It is imperative that significantly better methods be used to monitor cract growth than is currently being considered. Vhitemore strain gaget should be used exten-sively. Plugs are attached to the concrete on a 2" gauge. An instrurent is then used to measure the distanc'e between the plugs.

Accuracies of.0001" is routine. Such gauges would give a good picture of the overall behavior of the crack s.

It should be noted that the repair,of cracks would not interfere with the use of these instruments.

No special " windows" need to be maintained during the crack repair program. ' This program of crack monitoring is also important because there is some indication that cracks. in the DGB have not

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stabilized and that the number of cracks. may in fact be increasing.

4.0 ' RESPONSE TO CONCERNS OF R.B. LANDSMAN The Region III inspector has raised four concerns (Ref.-1) regarding the adequacy of the DGB.

Each of these is addressed in the followingi Concern 1:

FINITE ELEENT ANAL YSIS The first concern deals with the Bechtei finite element models (see 2.4.1 i

and 2.4.2) of the DGB used to evaluate stresses due to settlement. There are four objections made to the models.

Concern is raised with regard to the use of uncracked section properties while the concrete is -knowr. to be cracked. All concrete stivctures are.

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cracked and it is standard practice (specifically pennitted in the ACI code) to determine forces in concrete structures based on gross section properties (i.e., neglect the cracks in the concrete and the reinforcenent).

If cracked section properties were used then tht. stresses calculated by Bechtel (2.4.1)

):culd have been smaller. Therefore neglecting cracks in this analysis is a conservative approxination. On the other hand, the analysis reported in 2.4.2

~

was used to show that the measured settlements result in stresses which are so high that much nore severe cracking would be expected than was observed. It was then argued that the measured values must be in error.

If cracket sections were assumed for this analysis the calculated stresses would have been smaller, but probably still not consistent with the observed crack patterns.

Y, The strai@t line representation of the settlenents along the north and south wall for the analysis reported in 2.4.1 is said to be in error. As in-dicated in that section of this report, it is our opinion that this analysis will result in unconservative predictions of stresses due to settlements. As such, it is considered to be an inappropriate analysis.

The third part of this concern raises questions regarding the time effects of the settlements.

Bechtel does calculate stresses for different phases of the settlement. The structure was changing during the significant settlement period. Construction was still in progress during the largest settlement s.

Therefore the structural geometry changed as did the concrete properties (while maturing).

The Bechtel models did not account for these changes. This would have been conservative for the calculation of stresses, but would result in lower stresses in the analyses perfonned using the measured settlenents as input.

The fourth objection deals with the claim that the NRC staff did not approve of the Bechtel analysis.

It appears that this is the case and the intention of the staff was to use settlement stress data based on an analysis of the cracks rather than the finite element analyses.

V

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Concern 2: RELIABILITY OF MEASURED SETTLEMENT VALUES The analyses reported in 2.4.2 and 2.4.3 were used to show that stresses

' computed from structural models subjected to the naasured settlenents' are very I

high and would indicate cracking in the structure where no cracks are ob-i served.. The objection is raised that a linear model was used and that a non-l linear model' accounting for plastic effects would result in a redistribution of stresses and the same conclusion may not apply. This observation is true. -

but, by itself would not change the. conclusions drawn from these analyses.

As stated above, however,' there' are other factors which when coupled with this objection may result in a different conclusion. The other important factors are: the assumed shape of the settlement between the measured points; and.the differing geometry of the DG8 when the various phases of settlement

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occurred.

Concern 3:

STRESSES DETERMINED FROM, CRACK SIZES If the finite element analyses are not reliable then one alternative I

i approach is to find settlement stresses.from c study of the crack sizes. The objection raised is that this approa'ch is not consistent with nonnal engi-

.neering practice and that there are no equations available to evaluate stresses from crack data when the stress fields are as complex as occur in the L DGB( It is true thst this would not be standard practice, but "non-standard"

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analyses may be used provided they are sufficiently. documented and shown to give rer91ts that are ' conservative.

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' An' approach that could predict approximate settlement stresses in tne DGB could probably be used to demonstrate its adequacy. This is true for two

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reasons. First, stresses in the structure due to other loadings are rather low and there 1s a large reserve for settlement stresses.

Second, if large settlement stresses and local yielding of the reinforcement occurs, the resulting defonnations 'of the structure will reduce the settlement induced loadi ngs.

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The documentation of the crack analyses used to determine stresses is not suf ficient. There is no calculation on record which calculates stresses in all of the walls using tMs method. There is also no written justification showing that the' method may be used for structures like the DG8.

Concern 4: CRACK MONITORING

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.This concern deals.with the lack of a good crack monitoring system and specification of action to be taken if the cracks exceed certain limits. As stated in Section 3.0, it is our opinion that the planned crack monitoring system is not adequate. More reliable gauges (e.g., Whitemore Strain Gauges) should be placed in areas where cracking is now evident. These gauges can be used even after crack repairs are made.

Two limits are'now. defined in the current crack monitoring program.

If the' crack width reaches.05" (Action Limit) a meeting will be held to evaluate what, steps to take when the cracks reach the next limit. The next upset limit is set at.06" (Alert Limit).

It is our opinion that the form of this plan is adequate, but that the specific threshold numbers must be based on a resolu-tion of the' current settlement stresses.. A safety margin must be left for the 3

other potential loading events, such as tornado or seismic loads, with the re-maining allowable stress allocated to future potential settlements.

Once_ this limit was reached the only solution would be to make a struc-m l

tural repair. The exact fann of this repair would depend on the location and extent of the crack which exceeded the limit.' The planned response could not

.specify the nature of the repair, but could indicate that an exceedance of the Alert Limit would result in a structural repair rather than performing addi-tional analyses.

L 5.0 COICLUSI0lts Based on the review of the studies perfonned to demonstrate the adequacy of. the DG8, the following conclusions are drawn:

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1.

The settlement data indicates that primary consolidatidn of the fill is completed. However, it is recommended that the ananolies in the documentation of the settlement history be resolved. (See last paragraph of Section 2.2).

2, It is unlikely that a satisfactory stress analysis can be performed based on the measured settlement data.

It is recommended that settlenent stresses be estir:ated from t',e r

crack width data. The exist) 7 work that has been done in this area must be completely documented.

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3.

It appears that the number of cracks in the DGB are con-tinuing to increase.'

It is essential that a better crack monitoring program be established as outlined in Section 3.0.

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The upsec crack width levels spec,ified in the crack

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4.

monitoring program should be chosen so that a sufficient stress margin'is available to resist the critical load combinations.

5, If the Alert Limit (in crack (1dth) were exceeded, specific structural repairs should be mandated.

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f REFERENCES 1.

Memorandum for R.F. Warnick through J.J. Harrison from R.B. Landsman, Subject Diesel Generator Building Concerns at Midland, dated July 19, 1983.

2.

Bechtel Calculetion No. 0Q-52.0 (Q), Rev. 2.

3.

Bechtel Calculation No. DQ-52.7 (Q) - Finite Element Calculation of Settlerent Stresses Using Actual' Displacements.

4.-

Structural Reanalysis of Diesel Generator Building Utilizing Actual Measured Deflections as Load Input, by John Matra, Naval Surface W4apons Center.

5.

Evaluation lof the Effect on Structural Strength of Cracks in the Walls of the Diesel Generator Building Midla,nd Plant Units 1 and 2, by Mete Sosen, February 11, 1982.

6..

Effects of Cracks on Serviceability.of Structures at Midland Plant, by W.G. Corely, A.E. Fiorato, and D.C. Stark, April 19, 1982.

7.

Executive Summary, Diesel Generator Building, Midland Plants Units 1 and

2. August 1983.

8..

Letter from CPCo to NRR dated October 21, 1981; Enclosure 1, Tech.

.. Report, Structural Stresses Induced by Differential Settlement of the DGB.

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APPENDIX A: SUURCE MATERIAL FOR STUDY Site Specific Response Spectra Midland Plant Units 1 & 2 Addendum to Part I Response Spectra--Orginal Ground Surface Jan 81 Weston Geophysical Corp Site Specific Response Spectra

. Midland Plant Units 1 & 2 Part II Response Spectra Applicable for the top of fill Nterial at the plant site April 81 Weston Geophysical Corp Site Specific Response Spectra Midland Plant Units 1 & 2 Part III Seismic Hazard Analysis Feb 81 Weston Geophysical Corp Soil Boring and Testing Program Midland Plant Units 1 & 2 Test Results Foundation Soils Auxiliary Building Woodward-Clyde Consultants Aug 81 Docket Nos. 50-329,50-330 Test Results Perimeter and Baffle Dike Areas Soil Boring and Testing Program Volume II Supporting Data July 81 Docket Nos. 50-329,50-330 Test Results Peri reter and Baffle Dike Areas Soil Boring and Testing Program Volume I Woodward-Clyde Consultants July 81 Docket Nos. 50-329,50,330 Estimates 6f Maximum Past Consolidation Pressu're of Cohesiv'e Fill Materials Utesel Generator Building July 81 Woodward-Clyde Consultants Docket Nos. 50-329,50-330 USA /NRC Before.The Atomic Safety and Licen:ing Board 12/7/82 testimony of; Frank Rinaldi John Matra i

Gunnar Harstead ~

(

with respect to the Structural Adequacy of The Diesel Generator Building at Midland Official Transcript Proceedings Before NRC Atomic Safety and Licensing Board DKT/ CASE No. 50-329,50-330 GL & OM 12/10/82 pages 11008 through 11228 A.1

Evalcation Report for Concrete Cracks in the Diesel Generator Building

~~

Consumers Power Company 2/16/82 Evaluation of the Effect-on Structural Strength of Cracks in the Walls of

-the Diesel Generator Building Mete A. Sozen 2/11/b2 Relationship of Observed Concrete Crack Widths and Spacing to Reinforcement

-Residual Stresses Consumers Power CompIny 6/14/82

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Observed Cracks in Walls of Midland Plant Structures 6/14/82 Corley and Fiorato Portlar.d Cement Association

' Safety ~ EvaluationL Report related to the operation of Midland Plant j

Docket Nos. 50-329 and 50-330 Consumers Power Company USNRC 5/82 Effects of Cracks on~ Serviceability of Concrete Structures and Repair of Cracks Consumers Power Company 4/30/82

' Effects-of Cracks on Serviceability of Structures at Midland Plant Corley, Fiorato, Stark t.

. Portland Cenent Association

' Sunmary of Sept. 8,1981 Meeting 'on Seismic

• Input Parame_ters Midland Plant 1

USNRC 12/3/81

~~ USA /NRC Before the Atomic Safety and Licensing Board 50-329,50-330 testinopy of Jef frey K. Kimball 9/29/81

}

50-330 OM,0L' NRC Atomic Safety and Licensing Board 50-329 OM,0L witnesses;

. Johnson Burke Corley Sozen l

Goul d

-NRC Before tne Atomic Safety and Licensing Board (no date)

NRC staff testimony of Joseph Kane on Staniris Contention 4.8 '

g Docket Mos. 50-329 ON,0L-50-330 OM,0L

. Safety Evaluation Report related to the operation of Midland Plant October 82 1

b Docket Nos.60-329 50-330 I

USNRC 'NUREG-0793 Supplement No. 2

' Safety Evaluation-Report related to the operation of Midland Plant June 82 Docket Nos. 50-329 50-330 USNRC NUREG-0793 Supplement No.1 t-A-2 V

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s-.

-NRC Atomic Safety and Licensing Board 9/29/U1 Applicant's Brief on Compatibility of Site Specific Response Spectra Approach with 10 CRF part 100 Appendix A S4fety Evaluation Report related to the operation of Midland Plant May 82 Docket Nos. 50-329 50-330 3

NUREG-0793 i

b.

JResponse to the NRC Staff request for Settlement Related Analyses for the Diesel Generator Building 6/1/82 i

Consume rs Technical Report ~

Structural Stresses Induced-by Differential Settlement L

of the Diesel Generator Building

-}.

Consumers Power Company Test Results of Soil Boring and Testing Program for Diesel Generator Building.

Docket Nos. 50-329 50-330 7/31/81 Consupers Power Company Final Re'sults-of Soil Boring and Testing -Program for Ferimeter and Baffle Dike Areas 7/27/81 Docket Nos. 50-329 50-330 Consumers Power Company NRC Atomic Safety and Licensing Board Docket Nos.

50-329 OM,0M 50-330 OM,0L Witnesses; Hood 12/3/81 Kane Singh Rinal di NRC' Atomic' Safety and Licensing Board Docket Nos.

50-3 29 OM,0L 50-330 OM,0L witnesses; Kennedy 2/17/82 Campbell Rinaldi Kane Matra Hood Si ngh -

CSE Input to the Midland' SER Supplement Aug, 82 Geotechnical, structural, mechanical and hydrologic inputs for the Midland Ser Suppleiaent i

1/6/81 Transcript of Proceedings USA /NRC

- Deposition of Frank Rinaldi Transcript of Proceedings USA /NRC 1/9/81 Deposition of Pao C. Huang Transcript of Proceedings USA /NRC - Docket Nos. 50-329 OM, OL-50-330 OM,0L Deposition of John P. Matra 1/7/81 A-3

o USA /NRC Before the Atomic Safety and Licensing Board Docket Nos. 50-329 OM-OL 50-330 0M-OL N2C Staff Brief in Support of the use of a Site Specific Response Spectra to comply with the Requirements if 10 CFR Part 100, Appendix A 9/29/81 USA /NRC Before the Atomic Safety and Licensing Board Docket Nos. 50-329 OM-OL 50-330 OM-OL 1

Testimony of Dr. Paul F. Hadala with Respect to the Study of Amplication of Earthquake Induced Ground Motions and the Stability of the Cooling Pond Dike Slopes Under Earthquake Loading 9/29/81 USA /NRC Before the Atomic Safety and Licensing Board Docket Nos. 50-329 OM,0L 50-330 OM,0L Witnesses; Boos Hendron Hanson Testimony of Ralph B. Peck before the Atomic Safety and Licensing Board, in the the matter of Consumers Power Company (Midland Plant, Units 1 and 2), Docket Nos.

50-329 (M. 50-330 OM, 50-329 OL, 50-330 OL, notarized Nov. 3,1982.

Letter from CPCe to H.R. Denton dated June 14, 1982 with Enclosure " Response to the NRC Staff Request for Additional Infonnation Required for Completion of Staff Review of Soils Remedial Workd dated June 14, 1982.

, Summary of August 17,'1982 Meeting on Soils-Related Construction Release, dated

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September 7,1982, by Darl Hood.

" Structural Reanalysis of Diesel Generator Building Utilizing Actual Measured Deflections-as Inout", by John Matra.

, Letter from CPCo to H.R. Denton <iated October 21, 1981 with

Enclosures:

" Structural Stresses Induced by Differential Settlement of DGB",

"Subgrade Modulus & Spring Constant Values for DGb Structural Analysis",

" Bearing Capacity Evaluation of DGB Foundation" L

"Logterm Monitoring of Settlenent for DGB",

" Relative Density and Shakedown Settlement of Sand under DGB",

"Esticates for Relative Density of Granular Fill Materials, DGB",

" Review and Control of Facility Charges to DGB",

"DGB Bearing Pressure due to Equipment and Commodities",

Report form Woodward-Clyde to CPCo dated June 10,1981, " Preliminary Test Results, Soil-Boring.8 Testing Program, Perimeter and Baffle Dike Areas",

" Seismic Margin Revier, Midland Energy Center Project":

Volunne 1, Methodology and c

Criteria, dated February 1983, Volume V, Diesel Generator Building, dated July 1983, prepared for CPCo by Structural Mechanics Associites.

A-4

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Applicant's Propsed Findings of Facts and Conclusions of Law on Remedial Soils issue Docket hos. 50-329-0M 50-330-0M 50-329-0L 50-330-OL Testimony of Karl Weidner for the Midland Plant Diesel Generator Building September 8, 1982 Docket Nos. 50-329-OL 50-330-OL'

/

50-329-0M 50-330-0M

' Find Report on the ADINA Concrete Cracking Analysis for the Diesel Generator Building by Gygna Energy Services, September lu, 1981,

e A-5 L