ML20140D962
| ML20140D962 | |
| Person / Time | |
|---|---|
| Site: | Waterford  |
| Issue date: | 12/17/1984 |
| From: | Constantino C, Chris Miller, Reich M BROOKHAVEN NATIONAL LABORATORY, NEW YORK UNIV., NEW YORK, NY, NRC OFFICE OF THE EXECUTIVE LEGAL DIRECTOR (OELD) |
| To: | |
| Shared Package | |
| ML20140D809 | List: |
| References | |
| OL, NUDOCS 8412190264 | |
| Download: ML20140D962 (87) | |
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7 UNITED STATES OF AMERICA NUCLEAR REGULATORY COMMISSION BEFORE THE ATOMIC SAFETY AND LICENSING APPEAL BOARD 6
In the Matter of
. LOUISIANA POWER AND LIGHT COMPANY ) Docket No. 50-382 7
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(Waterford Steam Electric Station, )
Unit 3)
AFFIDAVIT OF MORRIS REICH,
. CHARLES A. MILLER, AND CARL J. COSTANTIN0 Q.1. Please state your names, titles and by whom you are employed.
A.1(a). My name is Morris Reich. I am employed as Head of the Structural Analysis Division, Department of Nuclear Energy, Brookhaven National Laboratory, Upton, NY. A statement of my professional qualifications has been provided on the record of this matter.
A.2(b). My name is Charles A. Miller. I am employed as Professor of Civil Engineering and Director of the Materials Testing Laboratory, Department of Civil Engineering, The City College of the City University A
? of New York. A statement of my professional qualifications has been pro'vided on the record of this matter.
J- A.3(c). My name is Carl J. Costantino. I am employed as Professor a of Civil Engineering and Director of the Soil Mechanics Laboratory, Department of Civil Engineering, The City College of the City University
] of New York. A statement of my professional qualifications has been provided on the record of this matter.
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l Q.2, What is the purpose of this affidavit? l A.2. The purpose of this affidavit is to previde a summary of our additional evaluation and conclusions as to the safety significance of the concrete cracking that has been observed in the foundation base mat at Waterford Steam Electric Station, Unit 3 since our affidavit of
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August 7, 1984.
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Q.3. Please describe your involvement with these issues.
6 A.3. The Structural Analysis Division of the Department of Nuclear Energy, Brookhaven National Laboratory (BNL), was requested by the NRC Staff to review various design issues related to the Waterford foundation base mat and to provide its conclusions as to the adequacy and structural integrity of the base mat. BNL's efforts were directed by Dr. Morris Reich and received technical assistance from Drs. Costantino and Miller, whose services were provided under contract to BNL. The other members of the BNL team were A. J. Philippacopoulos, S. K. Sharma a.
and P. C. Wang; the professional qualifications of these individuals have been provided on the record of this matter.
- Our involvement with these issues commenced in March 1984 and has continued to the present. Since our affidavit August 7,1984, we o
met and consulted with members of the NRC Staff on numerous occasions; a
9 reviewed the final NOT and structual evaluation reports prepared by the Applicant's consultant, Muenow and Associates, Inc., and its y architect-engineer, EBASC0; met with and obtained further information i
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from the Applicant, Mr. Muenow arid EBASC0; performed additional independent calculations and conducted tests of beam specimens designed to simulate the structural response of the cracked base mat of Waterford. In addition, we have reviewed and comented on' the separate views of two members of the NRC staff, Drs. John Ma and John Chen.
On July 18, 1984, we issued a report which provided a detailed description of our analyses and conclusions concerning the Waterford foun'dation base mat, entitled " Review of Waterford III Base Mat Analysis" ("BNL Report"); on information and belief, this report was provided to the Atomic Safety and Licensing Appeal Board on July 25, 1984.
On July 31, 1984, following the issuance of the BNL Report, we traveled to the Waterford site to meet with the Applicant and its consultant, Muenow Associates, which had been conducting non-destruc'tive testing of the foundation base mat, and received an explanation of the preliminary NDT results as represented to us by the Applicant and Muenow l Associates. We then prepared an " Addendum" to the BNL Report of July 18, f
1984, which provides further information and confirms the initial conclusions presented in the BNL Report. This Addendum was dated August 3, 1984, and was provided to the Atomic Safety and Licensing' Appeal Board I on August 7, 1984. Based on our activities since the preparation of our 1
]. August 3,1984 Addendum, we have now prepared Addendum 2 to our July 18, j 1984 report. Addendum 2, dated December 14, 1984 is attached to the I Affidavit as Attachment 1.
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. 4 Q.4. Does the BNL Report dated July 18, 1984,-as supplemented >
by the Addenda dated August 3, 1984 and December 14, 1934, provide a true and accurate representation of ycyr views concerning the adequacy and structural integrity of the Waterford fcundation base mat?
A.4. Yes.
Q.5. What is your conclusion relative to the adequacy and structural integrity of the Waterford foundation base mat?
A.S. Based upon the analysis which we have conducted and tne information provided by the Applicant, its consultants, and IbASCO, it is our conclusion that the safety margins in the design of the mat are adequate, and that the concrete cracks in the base mat, ps well as the ,
cracks in certain vertical walls standing on the base mat, do not present a significant issue affecting the safety'of the Waterford facility. We have, however, prev.."s1v r. 1 / i' it certain detailed confirmatory calculations be perfor:3d, e not anticipate that these analy'as will lead t any st fferent results, and we have recommended that a sui eillt . ' itiated to monitor the cracks. Our recommendat. :s , e unchanged at this time. -
Detailed explanations at thu sc ,e Fo: .onclusions may be found in
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ATTACHMENT 1 TO THE AFFIDAVIT OF MORRIS REICH, CHARLES A. MILLER, AND CARL J..COSTANT.'N0 4
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ADDENDUM N0. 2 TO THE REVIEW 0F WATERFORD III BASEMAT ANALYSIS 1-Structural Analysis Division Department of Nuclear Energy j' Brookhaven National Laboratory I~ Upton, NY -11973 4
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- 2-ADDENDUM N0. 2 TO T"E REVIEW OF WATERFORD III BASEMAT ANALYSIS
1.0 INTRODUCTION
-l This addendum is intended to summarize the principle BNL activities a/sociated with the Waterford III basemat safety evaluation since the Ft-suance of the previous addendum early in August 1984. The topics 4 discussed in this report are as follows:
- 1) Non-Destructive Test Programs
- 2) EBASC0/LPL responses to these findings.
. 3) Preliminary experimental results obtained for comparison of strength and stiffness characteristics of uncracked and precracked reinforced concrete beam members, j 4) Analytical assessment of influence of basemat cracks on superstructure floor response, spectra and force resultants.
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, 3 Basemat" included as Appendix F.
- 6) BNL's Review of "Geotechnical Engineering Evaluation of Concrete Cracking in the Basemat Waterford Unit 3" included as Appendix G.
The results of our reevaluation remain essentially unchanged; namely, that
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the basemat is adequate to perform its intended function. The suggested confirmatory analyses are still reconsnended with the exception that item h
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During this review it was noted that Conclusion (c) item (ii) (page 26)oftheJuly 18, 1984 BNL report does not completely reflect the content of the report. This conclusion appeared in an earlier draft of tha report and was not modified as additional work was done. The cause of cracking is clearly stated in the Abstract and on page 11 of the report.
This conclusion should more appropriately be stated as follows:
(ii) The observed cracks developed on the top surface of the mat during the construction phase and were most probably caused by differential settlement induced by the dead loads acting alone or by dead loads acting on the mat already cracked by normal thermal and/or shrinkage effects.
1 2.0 REVIEW 0F NDT PROGRAM A non-destructive test program was undertaken by Muenow and Associates with the objective of defining crack locations in the mat.
- This program was reviewed by BNL during a site visit on July 31, 1984 and the final report was reviewed. Conclusions regarding the NDT determination of crack patterns were presented in the BNL addendum to the Waterford III basemat analysis (dated July 18,1984). Differe; es between j these crack patterns and those defined in Muenow's final report are first
. discussed. An overall assessment of the NDT program is then given.
2.1 COMPARIS0N OF MUENOW AND ASSOC. FINAL REPORT WITH PRELIMINARY RESULTS i As mentioned in the previous BNL addendum to the Waterford III
- basemat analysis, a site visit on July 31, 1984 was made during which the s
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i procedures of the NDT testing program were determined and evaluated, and preliminary results of the tests were pr(vided. Based upon Mr Muenow's presentation at that time, the following characteristics of the L nemat were noted:
- a)' All of the cracks were vertical.
b) The E-W cracks exterior to the shield wall ran from the shield wall-to the side walls. The depths of these cracks varied in an s
undulating manner from seyeral feet (2' to 4') to as much as 9 to 10 feet.
c) Based upon preliminary data, three primary E-W cracks are located under the RCB. Two of these appear to connect to the E-W cracks exterior to the shield wall. The specific depth contours of these cracks are currently unknown, altho. ugh initial speculation indicates that they may be similar to those in (b) above.
d) Cracks emanating in a radial direction from the shield wall are not as deep nor as continuous as the E-W cracks.
e) All of the basemat cracks are tightly closed. This observation is based upon the measured characteristics of the reflected signal.
i Since the issuance of the Muenow Final Report late in October 1984, the only changes in conclusions that have developed are as follows:
'4 a) In the E-W direction, outside the RCB more details on crack depth have been developed. Cracks J L, and P (see Meunow
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Report for location) on the west side, and Fe, Le and Ke on the east side are almost unifonnly deep with the cracks extending approximately to the bottom steel. The remaining cracks vary in depth as previously described.
b) While two cracks under the RCB were originally identified by Muenow as connecting to the external RCB cracks, it appears that I seven major cracks exist under the RCB with 3 of these matching the three deep external cracks, (5 matches J and Fe, 7 matches L and Le, and 1 matches P and Ke). Of the remaining four, three appear to match the shallow external cracks, while one crack (No. 3) terminates under the RCB.
It should be noted that'all other conclusions presented in the original BNL Addendum remain unchanged.
2.2 BNL Assessment of NDT Program As mentioned above, the BNL assessment of the NDT program was reached by considering three separate sources, namely, a site visit conducted on July 31, 1984, a detailed review of the Final Report provided by Muenow &
Associates on the entire program late in October 1984 and a technical meeting in Bethesda on November 2,1984. During the site visit, the procedures utilized by Mr. Muenow to examine the basemat and sidewall crack were determined and evaluated.
At the time of the site visit, the testing program had essentially been completed for the investigation of basemat cracks outside of the shield
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description of his procedures. Based on this visit, an assessment of the NDT program can be presented as follows.
(a) In general, the procedures employed by Muenow & Associates measure the time-of-arrival of a wave reflected off a discontinuity in the concrete. This wave is generated by a small spring. loaded hammer
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applying an impact to the surface of the basemat. For a single impact, a transducer located at a known location with respect to the
- hammer is focused in a restricted (but known) direction and measures the arrival time. Knowledge of the arrival time and focusing direction leads to the determination of the location of the discontinuity. In addition, by restricting the viewing time of the sensor, only the reflection from the discontinuity being mapped can be recorded. From a series of impacts at different locations, j information on the extent (length, depth and orientation) of the f crack can be obtained.
(b) For those cracks visible on the mat surface, external to the shield wall, the NDT procedures utilized a 45 receiving transducer as well as measurements made on both sides of the crack. By starting close j- to the crack and making measurements at intervals away trom the ,
crack on either side, informatien on arrival times of the reflected wave, and viewing time of the sensor are good. It is our opinion ij that this procedure can yield reliable infonnation on the crack l patterns (i.e. depth, orientation and length) external to the RCB.
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- (c) It should be noted that the procedures used are based upon recording j and viewing only the low frequency content of the reflected waves, Therefore, any discontinuity smaller than 10 to 20 inches cannot be i
observed in this study. This cutoff frequency of the program can be controlled to some degree by the operator, if desired. Thus, J
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reflections from single reinforcing bars do not interfere with the crack measurements. However, the layers of closely spaced rebars at the bottom of the slab result in measurable reflections. Data at r
these depths are therefore judged to be less reliable.
(d) Since the procedures utilized to investigate the depth of the sidewall cracks was similar to those employed to investigate the basemat cracks external to the RCB (that is, starting close to e
' known surface crack and marching out in both directions), the conclusions of this investigation should also be reliable.
(e) For measurements underneath the RCB the measurement procedure is different. Specifically, a 60 transducer sensor is utilized to pick
- up reflected waves that must traverse the distance from the sensor located outside of the RCB to the crack and back. Considering that the RCB diameter is approximately 150', it is obvious that the wave must reflect many times from the top and bottom surface (which may not be perfectly level) of the mat before reaching the sensor.
Thus, in our opinion, these cracks measured by this procedure are less accurate than those external to the RCB.
r A report describing the results of the NDT program was published by Muenow in October 1984. BNL reviewed this report and had the following comments:
(a) The report contained the new data and sketches showing the "likely" crack patterns. The method by which the "likely" crack patterns were s.
deouced from the new data was not clearly presented. For example,
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? the cracks in the report were mapped with solid and dashed lines.
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(b) The report did not contain summaries showing the crack depth variation along the various cracks. BNL has prepared such summaries based on the data in the report.
(c) It is not clear what the accuracy of the measurements is for the 60*
sensors used to measure the cracks under the RCB.
(d) The discussion pertaining to the detection and measuring techniques i was incomplete.
A meeting was held on November 2,1984 at which time the above issues were discussed. During this meeting a request was made that the applicant prepare "best estimate" and " worst possible" crack maps showing both location and depth. Crack maps were subsequently provided, but there were some inconsistencies between these maps and the data in the report.
t During the November 2 meeting, Mr. Muenow discussed the accuracy in both the 60* sensor data and the crack width measurements. He stated that the accuracy of the 60' data was 1.5 feet horizontal and 2 feet i vertical. Mr. Muenow also described his method for estimating crack width; he reiterated his conclusion that based on his experience, the
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0.007 inch crack width measurements given in his report for Waterford had j an accuracy of 20%.
In view of the many reflections which occur in the 60" data it was j requested that some additional measurement be undertaken to insure that the fill
,; concrete was not bonded to the mat (so the sonic pulse reflected between i the top and bottom surfaces of the mat and did not propagate into the fill j concrete). Mr. Nuenow took some measurements where he shot downward from around the top of the fill concrete to the fill concrete-basemat interface around the annulus. From this data Mr. Nuenow concluded that
" sufficient non bonding exists at the mat-fill concrete interface to preclude sonic energy from entering and reflecting the fill concrete interior."
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_g. ! It should be realized that the definition of a crack from the NDT
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location, a range to a point on the crack is determined based on the
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measured time delay between the origination of the pulse and the arrival
, time at the sensor. The crack location is then defined by connecting a series of such points. Muenow uses some judgement in this process. While
'this procedure is not well defined in the NDT report, discussions with Muenow have led BNL to conclude that his definition for crack location outside the RCB is reliable.
2 The report review and subsequent meetings basically confirm the five concusions of Section 2.2 which were based on our visit to the site. BNL has reasonable confidence in the crack definitions (depth,- orientation and length) to the side of the RCB, but much less confidence in the crack definition below the RCB. Prudent engineering would be to assume that the cracks under the RCB are uniformly deep and that three of these line up with the known deep cracks outside the RCB.
- 3.0 Assessment of EBASCO Evaluation of NDT Results In light of the ultrasonic test results generated by Muenow and Associates, BNL requested that EBASCO evaluate the structural significance of the reported cracks. As a consequence, EBASCO issued a report entitled
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, " Louisiana Power and Light Company Waterford Steam Electric Station Unit i No. 3, Summary Evaluation Structural Significance of Basemat h- Nondestructive Testing Results". This report was issued on October 25, i
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o.~ .. 1984. It was reviewed by BNL and specific comments sent to NRC are listed below: a) In Section 4.1, families of cracks are identified and are said to be interconnected. Identify all interconnected cracks and reference them to figures (i.e., Drawing No. 7, etc.) shown in the non-destructive testing report. t b) In the text of EBASCO Report and in the tables, it is indicated that some of the deeper crack lengths are not made up from continuous-cracks going from the top towards the bottom, but rather are the results of upper cracks that have interconnected with lower cracks. Since this is difficult to determine from the data in the non-destructive testing report, the contentions made in the report with respee.t to crack " link up" should be clearly identified witt. specific data for each case. c) The use of averaging presented in the' EBASCO Report must be discussed and clarified. As an example, in Table 1 family V contains crack "p" which is shown to have a maximum depth of 10 feet, whereas the family j average is calculated to be only 4 feet. Furthermore, as stated in 4.1.1 the average depth crack is 3' - 6'. This f.gure is obtained by averaging the average depth of families I, II, V, VI, Ie, and IIe. This seems to be an average of the averages of the averages (i.e., the first average corresponds to the average crack depth of the line, the second to the average crack dept' -f the family and third, to the g average crack depth of the families). A full discussion of this
- j technique and the basis for its use must be provided.
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- i l d) Discuss and clarify how family spacings given in Tables 1 and 2 were
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e) In Section 4.1.1, it is stated that the top crack depth decreases as the distance from the E-W centerline increases. This does not seem to be consistent with some of the data presented in the non-destructive test report. This conclusion seems to come about because of the averaging schemes between families mentioned previously und should be discussed in the context of question (c). f) Discuss how the EBASCO crack width field measurements were made. g) With respect to Item 3 of Section 6.0, discuss how through cracks that run from top to bottom were differentiated from through cracks that were formed by the joining of two separate cracks, one originating at the top and one at the bottom of the slab. h) Item 4 of Section 6.0 states that the " stress condition of the top of the basemat has becone compression since the occurrence of the original cracking". If the stresses have changed from tensile to compressive since the cracks have occurred, the conclusion drawn in Item 5 that the rebar stresses were small when the cracks occurred must be justified.
- 1) A statement is made on Page 10 that "when reversal of stresses' occur and a previously cracked tension zone becomes subjected to compressive forces, the cracks close ... provided that the reinforcing steel did not previously exceed the yield strength".
Explain what would preclude cracks from closing even if the steel had yielded. This would seem to be possible especially when the
' reinforcement ratio is as small as in the top of the basemat.
J j) A statement is made on Page 10 that the cracking of the mat due to negative bending moment increases the capacity of the mat to carry h [* '- , = , i = , -
m o positive moments. It is likely that the negative moment was relieved when cracking occurred. If this occurred the conclusion would not be true. In addition the cracking certainly would not enhance the shear capacity of the mat. Discuss this question and provi..e a basis for the above statements.
- EBASCO's views on each of these items plus some others pertaining to clip resistance, and shear considerations were discussed at a meeting held in Bethesda, MD on November 2, 1984. As a consequence of the discussions, EBASCO agreed that the idea of averaging families was not applicable for assessing the adequacy of the mat. The grouping by families was only intended to present an overview of the mat cracking. They also said they would provide a plan view of mat which would show the connectivity of all measured cracks internal and external to the RCB. EBASCO also discussed the method used in 1977 to obtain crack width measurements for cracks internal to the RCB. EBASCO stated that these cracks were found to vary from 0.002 inches to 0.005 inches measured with an optical comparator.
With respect to BNL item 3.0 (1) EBASCO agreed that the steel may have yielded before the closing of the crack. Similarly, with respect to item (j), EBASCO acceded that the scenario raised by BNL is a valid one. 1 Finally, EBASCO agreed that they would enlarge Section 6 of their report which deals with the significance of the cracks and their effects on the structural integrity of the mat. Specifically, they asserted to consider shear behavior in the mat especially shear slip along the cracks. A revised report was made available to BNL on November 7,1984. This report was reviewed and a meeting pertaining to its contents was held in j Bethesda, MD on November 20, 1984. 3 Essentially, this report contained most of the changes and additions discussed previously. Among the new items discussed in this revision is
. an evaluation of the shear friction capacity of the mat. Based on
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ha . calculations presented by EBASCO, the shear capacity of that is 1.9 times the shear demand. This computation of shear friction capacity does not take into acount compressive forces in the mat due to lateral soil and
. water pressures acting on the side walls. These compressive forces would further increase the " shear friction capacity."
Another new item addressed in this addendum concerns shear deformation 1 (slip)acrossajointduringanearthquake. With regards to this topic, EBA5:0 refers to tests that were conducted at Cornell
- to evaluate slip due to shear forces along a cracked surface. A large number of tests were
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run, varying crack width, shear stress applied to the crack and clamping force across the crack. One conclusion of their study is that the slip was less than 0.01 inches for 25 cycles 180 psi shear stress when the clamping stress was less than 20% of the shear stress (36 psi). The crack width was 0.01 inches. L a In reviewing the Cornell data, BNL concluded that in every respect the test conditions are more severe than those in the Waterford basemat. The cracks in this basemat are less than 0.007 inches and, according to data _j supplied by EBASCO in the report, the applied shear stress in the mat is j about 81 psi and the damping force is about 270 psi. Therefore one must conclude that the shear slip along cracks in the Waterford basemat will be less than 0.01 inches. It is difficult to see how this slip could cause a significant change in either superstructure member forces or floor response spectra. I 1. J There were still some further changes, however, requested by BNL in Chapter 4 of the EBASCO report. These were mostly for clarification
- purposes. Nevertheless, EBASCO agreed that these changes would be made.
3 BNL, however, differed with EBASCO on two major issues. The first of these l> involves the maximum stresses seen by the top reinforcement when flexure
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caused the concrete to crack, while the second involves the condition leading to the cracks. BNL felt that the cracks are a result of positive bending which occurred during the construction phase. Furthermore, BNL felt that when crccking occurred the bars were plastically deformed. EBASCO, on the other hand, felt the cracks were primarily due to thermal effects and that cracking was never large enough to cause yielding of the top reinforcements. Both BNL and EBASCO agreed that currently the
', loadings are such that the top of the mat is in compression and the cracks i are tightly closed. Furthermore, both agree that the cracks will not effect the strength of the mat under any of the postulated loadings.
All items pertaining to Revision 1 were discussed at the second Bethesda meeting on November 20, 1984. At this meeting, EBASCO conceeded that the stress calculations in the top reinforcement would only apply for the y present situation and not to the maximum stresses ever seen by the top reinforcent steel. With respect to the causes of the cracking EBASCO agreed that the mechanisms mentioned by BNL could be a possible explanation for the the l deep and narrow cracks of the Waterford mat cracks. All of the above is [ included in Revision 2 issued by EBASCO on November 27, 1984. BNL nonetheless still recourends that the additional confirmatory calculations mentioned on page 27 of the July 18, 1984 BNL report be performed. 4.0 EXPERIMENTAL EVALUATION OF PRECRACKED BASEMAT
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q ., Questions have arisen regardini .ae effect that the primary cracks 5.! may have upon the strength of the basemat, especially with respect to shear j and mat stiffness. The Cornell tests described in the EBASCO report were focused on shear wall type elements while the Waterford basemat is a flexural member. Thus, an experimental evaluation of the effects of the basemat crack on the subsequent performance of the mat was performed. Two beams, having similar reinforcement ratios to the basemat, were tested. i -
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15 - One beam was subjected to a negative bending moment producing tensile stresses at the top of beam. The moment was increased until a crack occurred. This crack propagated to about the depth of the bottom reinforcement as did the negative moment cracks in the actual basemat. The beam was then subjected to a positive bending moment which was increased until the ultimate moment capacity was reached. The second beam was only subjected to the positive bending moment (i.e., it was not h pre-cracked). The load deflection curves for the two beams are identical. They indicate that the negative moment crack in the first beam does not affect the ultimate moment capacity of the beam or the stiffness of the beam. It is therefore concluded that the cracks in the basemat do not effect the capacity or stiffness of the mat, as suggested in the original BNL report. Details of this experiment are contained in Appendix E. 5.0 INFLUENCE OF 8ASEMAT CRACKS ON SUPERSTRUCTURE RESPONSE To assess the impact of basemat cracking on the superstructure response, a simplified but reasonable beam model was analyzed in both the cracked and uncracked mode. This beam model, representing a 22' wide basemat strip running under the RCB in the N-S direction for the entire mat length, was placed on an elastic soil foundation with moduli similar to those used in the Harstead Engineering Associates (HEA) calculation. Masses placed on the beam were also those given in the HEA talculation. A superstructure model representing the RCB and other ancillary structures was placed on top of the mat across the cracked zone. This model had mass and frequency characteristics similar to the structures in the RCB. A parametric study was performed changing the frequency characteristics of the superstructure. A comparison of floor response
- spectra and element moments and shears indicates that the cracked mat has little influence on the resultant responses for both horizontal and vertical earthquake inputs. These analyses are described in detail in
- }** 'fiq F Q ** *(" f* PW* ' W ,'] ' " l*t,V[
- ****Tt' '~, ~* s
* ~ *"'
~~?~W **
} N *f
Appendix D and provide further support for our conclusions regarding the structural adequacy of the mat. 4 's 4 f I 1 i h*I " g O Y N' I Y _M $ ' *k" $"'"W T W, ,V' a . *me g
.i,'"g , <
9
;gu- , -, _ _,p- '.t_'s ,
g
i+ . i
,i
.i
' APPENDIX D EFFECT OF CRACKED BASEMAT ON THE
. RESPONSE OF THE SUPERSTRUCTURE I
i r 1 4 i i l] l t I i l I f I e
* ' ~
9 - A, f
D-1 In order to investigate the effect on superstructure ficor response . spectra due to possible cracking of the basemat, a simplified but reasonable beam model resting on an elastic foundation together with the superstructure was analyzed for response to both vertical and horizontal. earthquake excitation. As shown in Figs. D1 and 02, the model used for the analysis represents a 22 foot wide strip of the basemat running in the N-S directions. The particular strip is located under the center line of the reactor building.
~
1 The total weight on the strip due to the mat, the supported structures, the l, equipment, etc. are the same as those used by EBASCO and HEA in tneir computer analysis. With respect to the finite element idealization, fourteen vertical springs and two horizontal springs were attached to the basemat in order to represent the soil-foundation interaction. The values for the vertical spring constants g i were computed fran the HEA imput data given tc BNL with the mat analysis computer results. The horizontal spring constantron the other hand were conputed according to the theoratical discussion given in [Ref.1]. The mat itself was modeled by beam elements 1 to 15,_while the superstructure i associated with the reactor and shield buildings as well as the other mat I Since an exact supported structures was modeled by beam elements 16 to 27. model of the building was not available, representative models of the superstructure were bsed which have the same mass and similar frequency charac-teristics. Element 8,near the center of the reactor building, represents the cracked portion of the mat and,hence, was idealized so as not to transmit 3- shear force.
?
l In order to evaluate differences in response between the cracked and q uncracked mat, two distinct cases involv1ng element 8 were analyzed, namely,
]- one with normal shear transfer (i.e., the uncracked case) and the other with
[ an infinitely small shear transfer (i.e., the cracked case). Additionally for each of the above cases the superstructure modulus of elasticity was varied
]
2 from case 1 (soft) to case 11 (rigid) so that the fixed base frequencies would enconpass a range of structures in which the actual one would fall. 1 o
.-, ~, A, y r -
+ - - --
r- s-
..;,c,m vj .- - r mer 77- e. * * - - r-
D-2 The mass of the mat section was lumped at the nodes and the specific , values per node are as shown in Table 0.1. The mass of the superstructure is assumed to be distributed along the beam elen.ents with a unit weight of 0.15 2 .The total mass of kips /f t 3 for an approxirate total of 41.63 kip-sec /ft. the mat strip and all structures was, as previously mentioned, taken from the computer output supplied by HEA. The values of the spring constants are shown in Table D.2, the beam element properties of the mat are given in Table D.3 and the superstructure beam element properties are tabulated in Table 0.4. i ror the case with the less rigid superstructure (i.e., case 1) the analysis results are given in the following figures and tables: Table D.5 - Natural frequencies fixed base case; natural frequencies cracked and uncracked flexible mat I Cases. Table D.6 - Structural response due to horizontal El Centro earthquake scaled to 0.075 g. l Figure D.3 - Floor response spectra at node point 36 due to horizontal earthqaake for cracked and uncracked basemat s. Table D.7 - Structural response .due to vertical El Centro
, earthquake scaled to 0.05 g.
i j Figure D.4 - Floor response spectra at node point 33 due to i vertical earthquake for cracked and uncracked basenat. 9 e,* e, o y e t ***'*P+
'% . easWe -, e + y -e -e,-*
g , ,4 e e- 94p ys -+y . &-
, 7 +
m, .
D-3 For the case with the more rigid superstructure (f.e., case 11) the analysis results are given in the following tables and figures: P i Table D.8 - Natural frequencies fixed base case; natural frequencies cracked and uncracked flexible mat Case. 4 '. j. . j Table D.9 - Structural response due to horizontal El Centro 0 . earthquake scaled to 0.075 g. Q Figure 0.5 - Floor response spectra at node point 36 due to e horizontal earthquake for cracked and uncracked basemats.
- i II i Table D.10 - Structural rejsponse due to vertical El Centro O earthquake scaled to 0.05 g.
i Figure D.6 - Floor response spectra at node point 33 due to if vertical earthquake for cracked and uncracked
'! basemat.
,'i s ,7 . In reviewing the results of the analyses,the following conclusions may be drawn: It t i 1) Natural frequency camparisons for the cracked and uncracked d sections for cases i and 11 show negligible differences for i the first three modes, which are the most important ones q ] affecting response. i 4-
- 2) Member shear forces show maximum differences equal to approxi-
. mately 8% for case 1, and 12% for case 11 for the cracked and uncracked computer runs.
- T 4
D-4
- 3) Floor response spectra show negligiole differences for cracked and uncracked results for either cases i or 11.
The above (i.e.,1, 2-and 3) conclusions are true for eit.her horizontal or
- j. vertical earthquake excitations. The results indicate that all responses are l not significantly affected in this particular case due to cracking of the
^ basemat. It should be noted that the cracked model used in the study assumes I no shear transfer across the crack, a most conservative assumption, a 's 4-i i
.k I
L! i
~5
}
L 4.
?
- j a'
^$
q 1 1
't e
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+
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u3 e,ew$n , ~y 777urz,~;.vnin _:-_~ . _- ? w, r 1n. ;+~-
.- __. __ __ _ _ _ _ _g,
. n ,7:___ __ ________ ______ ; _ _ _ _
- l. y ,
D-5
- i. .
?
t REFERENCES
.1 ) Whitman, R.V., and Richart, F.E., Jr., " Design Procedures for Dynami-j: cally Loaded Founaations", Journal of the Soil Mechanics and
[ Foundation Division, ASCE, Proceeding Paper No. 5569, November 1967, I . p p. 169-193. r, i h 6 1 . c
. p-
, j-i
?
I
't .
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d
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4 Is
'l
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i;
- t e
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- l '
j .
%, >, ',4 7
- . t .
mmmmm m . r :.,,
.m.c r m. - ,- - .
, . . cr e - e.
.;....= :..- : .. w u.......z .=.. . . . = = :.: a._...:.. .. ~ . .. = : . . ;;. ; . . , _
yge w..a- . lj l Et ,l
.3 ,
37 Nodes; Nodes 1 to 14 are fixed; Nodes 15 to 37 move on the X and Y directions and rotate about the Z axis; Nodes 38 and 39 are fixed. ]i 16 Translational springs;
.) 27 Beam elements.
3 1 4 'A O
; 36 37 0 -
i e i
@ 6 a
31 32 33 34 35 i 9 0 9 0 8 39
. . @ @.. @ .. @ _ @ ..@GEO@_@.@ @..@ @. 3,8 Y h15 16 17 18 19 20 2 22 23 24 25 26 27 28 29 3o 15 bi 1~~ 2 3
[4 4 5 f6 6 7 8 9 10 0 11 1 12 2 13 13 14 4 4 1X
'I- -
Fig. D.1 Finite Element Model i i - i i
' ~ '
.j t Waterford 3 Basemat, Plan at EL - 41.0
.., ... ,,, ,, ,. ~ ,.. ...
wm 5 . 8
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Jkh Jhak Jki p[ it \ / ssh , se \ )d M F F l3 IY ': n , f > > > > > > J' XXX& b%K#X i l
/ / / f,,-
!XXM EXOh' 7 k Ys X / / /A l
xx x x x x , . ,, gq / r. X X;.iCX X 7 ,/ / /.d 5 >
. 'XXxXjXX ;== en==
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Stardyne Finite Element Model Projection o'n XI - X2 Plane', Case No. 1 , Fig. D.2 -
}
l.I
t TABLE D.1 Mass Computation Total Weight W = 582,400 kips Total Weight Per Foot y , 582,400 . 2181 kips
- 267 Total Mass Per Foot M = 67.73 kip-sec2 ft The mass is distributed as follows:
Mass of the foundation mat. Concentrated masses at nodes 1 to 30 except for nodes 22 and 23. At nodes 21 to 27 the mass of the foundation not was increased to account for the additional weight in the floor of the containnent buil di ng. Node Mass (ki ps) 15 0.91 16 1.48 4 17 2.06 18 2.03 19 1.25
. 20 1.38 21 1.82 24 2.36 25 2.18 26 1.95 27 2.64 1
1 28 2.64 29 1.81 30 0.91 I= 25.42 kips - sec2 ft i L f i t
* . ~ . - . . ,
.c__:,,,,- ._ -. . . . . , . . - - .
~ ~.
,>+,4@.+e#
4 IMAGE EVALUATION
<t it;,
k//7pgj%$>/
/ 4' TEST TARGET (MT-3) , %'+& #'%'kN*
s l.0 lf2 Su y 'y NE i,i Es!! [5 3 1.25 g i.4 g , 4 150mm *
< 6" >
d
> Ay *'% ~
v4 >7/ . +>a%+ o i i t
<+e _
f I'
# #)# o
#8h @ / dig IMAGE EVALUATION TEST TARGET (MT-3)
[// I.0 lf a Baa 5lfDal 1.1
!' E 1.8 1.25 1.4 l 1.6 I
4 150mm >
< 6" >
[*%s
** A ~
/!b #A
++ %+
/7/
o , i 4e t , h _ __- _ _ _ _ _ _ ______- _ .. . _ - _ _ _ _ _ _ _ _J
p TABLE D.2 j; . Translational ~ Springs Stiffness 1 Spri ng tio. Stif fness (kip /ft) d 1 4100 ; ? 2 6200 i; 3 7200 > T 4 6400
- 5 2700
, 6 3000 ,1 - 7 2800 I
8 4500
.i- 9 4700 0- 10 5400 .;. 'll 8000-l' 12 8000
- l 13 8000 1- 14 4000 15 11,100 (horizontal spring)-
16 11,100 (horizontal spring) 2
.k ;}
1
- j. .
1 1 - 1-i
.l .
a a$ .
'S i
l,t - l~ 1 SI i l W 3 3 1- . 4. [^LQMh}'T?*%: ?*;""yvn [T:'* F T *T.~i* T" : ' Y".~ c;Wf t i ~ n?: * * ~ * ~ *
- ~ ' ~ ~
*=":=*':
- * ~~ m - --
TABLE D.3 Mat Beam Element Properties Element tio. Area Inertia Length Material fio. (ft )2 (ft )4 (ft) 1 12 144 31.75. 1 2 12 144 20.5 1 3 12 144 52. 1 4 12 144 20. 1 5 12 144 24. 1
'. 6 12 144 24.5 1 7 12 144 8. 1 8 12 144 4, 1 8. ; . 9 12 -
144 1 10 12 144 37. 1 j 11 12 144 15.5 1 1 12 12 144 32. 1 13 12 144 32. 1 14 12 144 32. I 15 12 144 32. 1 i These are uncracked properties. To imulate the cracks,the shear area of element 8 is changed to 1 x 10-8ft [ Material 1 . E = 521,300 ki ps/ft 2
- . v = 0.30 yy = 0.0 (unit weight)
{ t-t I
- 1
- i.
i
- {
5 a .
'e t!
't i$ y
. r rm- .;- ~m-~<. - s-~~ ~- r ----~,,, e--- - - - . - - - , - - - . - , .,,,,..~..,;.
j.)7g . yv e - v ~~n3 7- ~: ~
Table D.4 Superstructure Bea:n Element Element No. Area Inertia Length Material No. (ft )2 (fg 4) (ft) t 16 10 .55 20 2
- 17 10 .55 20 2 18 10 2.0 20 2 19 10 2.0 20 2 20 10 .55 20 2 21 10 18. 52.25 2 22 10 , 110.5 96 2 23 10 -512. 161 2 24 10 33. 64 2 i+ 25 10- 330. 130 2 26 10 330. 130 2 27 10 512. 161 2 Material No. 2 3
Structural Case Ec (kip /ft2) v ry(kip /ft ) 1; i Ec =8.5 x 106 0.3 0.150 il 11 Ec =8.5 x 107 0.3 0.150 . g .
. ir -
- i as it
.t If , \ - 4-
- c. -
b 4 1; ..
- e*
Table D.5 Case i Natural Frequencies Structure frequencies for the fixed base Mode Frequency (cps)
- -; 1 4.775 2 9.966
'i 3 44.25 4 45.39 5 45.77 _
; 6 62.97 7 82.64 .
8 116.3
! Frequencies of the foundation-structure system for both i uncracked and c6'acked foundation mat 1
Frequency (cps) t Mode Uncracked Cracked
't 1 2.409 2.408 i 2 3.908 3.793 1 3 4.426 4.356 -j 4 6.816 6.804 5 . 7.963 7.312 6 8.270 7.999
,.' 7 8.460 8.292 8 10.75 9.764 a 6 i -[4
-i
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-l
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4 ?.li
- s
.d c4
'I
- \ .
r p: _ :~ * ~;, , ~n - ~~ s v : - ; *:v: vry, r wyr:r;-+~.;s 7 ~;* ' ? ~ :: - -
- i. ;.
Table D.6 (Case 1) I Structural . Response Due to Horizqntal Excitation ! El Centro 1940 amax.= 0.075 g . 1 i i, l
. Maximum Acceleration Node 36 ..J Uncracked Cracked b
- i. amax = 0.175 g amax = 0.172 g a
t = 2.36 see t = 2.36 sec
-{
Shear (kips) Member Uncracked Cracked
. 18 1.353 x 104 1.313 x 104 19 1.423 x 104 1.529 x 104 23 9.183 x 103 9.707 x 103 25 1.522 x 104 1.461 x 104 26 1.277 x 104 1.268 x 104 27 1.081 x 104 1.061 x 104
. !.g r Li u ,Li 9 4 ', l{ , .x
':1 -
.t
- 4
- t. ( -
F k t.} Y 3 w7&~r.?yun;
,' :P n'
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'~~ ~
~ ' ' - v-m
a - . _ . . . . w _. . csen.s._ . . . . _ _ . .. ._1 .1 .. ._ -' - p), _ . y
, m . ._ _ . . _ _ . . , ,
il){
;J. *i -
.. g i Horizontal Excitation Uncracked
- - - Cracked j
.a
'J: 1RMPING - O.02
- , b; -
,i .:
? .
?
J j . g _i y O *
., - n..
L9 i z l
. Ee w d-(
i m w w i W d a o M.< g- l-A ti 9 o Fv w _N
-=
- r-/
8 , o- - 10 t(f 10' 10' Fig. D.3 Floor Response Spectra at Node 36 (Case 1) .
.'{
i s
m
'. 3 3 Table D.7 (Case 1).
Structural Response Due to Vertical Excitation El Centro (1940) Vertical Comp amax = 0.05 g . Maximum Acceleration Node 33 Uncracked Cracked amax = 0.079 g amax = 0.078 g t = 3.32 sec t = 3.32 sec
.i.
i Shear (kips) a Member Uncracked Cracked h 18 7.306 x 103 6.975 x 103 19 7.825 x 103 8.135 x 103 23 6.396 x 103 6.509 x 103 25 8.493 x 103 8.520 x 103 26 7.438 x 103 7.559 x 103 27 6.325 x 103 6.401 x 103 l g . N 1 9 m .g. 1 A i l 1. W Le i 1 P i: 4 -
'k
, ""~*
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, '0 1
)
1 e s
. a C.
(
, 3 3
e d _ o N
. t a
a
\t' Q '0 1
t r c e p S d 2 i ed e _ kck e0 ) s
=_
ac . S n ra0 P .p o cr C nC ( s
- e U
G e d j Y C N R r A E o n N U o o I { O l i
,l C F t P I R - a M F 4 t
i c R l/ . D g u E x W F 0 1 i F l
. a c
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. m
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c . .. . Table D.8 Case 11 Natural Frequencies Structure frequencies for the fixed base Mode Frequency (cps) 1 15.10 2 31.52 4 3 139.9
! 4 143.5 5 144.7 6 '
199.1
! 7 261.3
- 8 367.7 i
l i Frequencies of the foundation-structure system for both I uncracked and cracked foundation mat , f Frequency (cps) Mode Uncracked Cracked j 1. 2.687 2.687
- 1 2 4.648 4.576 i 3 4.984 4.958 i 4' 8.527 7.342
. 5 10.18 9.972 i' 6 12.10 10.39 7 14.36 13.19 8 17.23 15.33 e
l 1 - 4 ,k ' a a a 1 y 6 ,k '5 a I
. . - ,.v-
,g- .t.,,. .. m., ,
, . . ,y . ;- - ,. r : T-- ~+c - ~ * - - --
.rrre v - +
Table D.9 . Structural Response Due to Horizontal Excitation (Case 11) Maximum Acceleration Node 36 Uncracked Cracked l t amax = 0.146 g amax = 0.146 g i t = 2.48 see t = 2.48 sec Shear (kips)
~
- Member Uncracked Cracked 18 3.705 x 103 3.972 x 103 l.
19 1.113 x 104 1.071 x 104 23 - 4.006 x 103 4.159 x 103 - 25 1.312 x 104 1.274 x 104 26 8.130 x 103 7.776 x 103 27 7.899 x 103 7.606 x 103 L a n
?
G 6 c e f i k$
# b I' '
3 h s' # a
, e e. , , ,
uu::. - <
'0 1
d -
. te ot na ni at )
cn 1 e 1 sr ee e nf s if a li C d ( e -
'0 he 1 6
tb 3 tt
. 2 e 0 -
) d d .
S o ed 0 P N ke ck ( C ( t a ac - ? ra ( Y s
. cr C e nC G b' N s U E n
- N y U o I s O p f
C s n P . R e M o F R i t R r D o t i a c m, '01 l F o x r E ' 5 l
^
a g . t i n ! F o ~ z i r
+..
H o s s w a.
'0 w - 1
- u:. R :. R ed onO M" 8
. . - 5 5s.()*U y i4
. . ,. !4 1I ', :. ;s2 ' ; .if 411',
- 3,4).
- .121;i4- - . :.
- 1 7
, - -c i
. Table D.10 (Case 11)
Structural Response Due to Vertical Excitation Maximum Acceleration Node 33 Uncracked Cracked i amax = 0.085 g amax = 0.085 g e
.f' .
t = 1.16 see t = 1.16 sec
.;. Shear (kips)
Member Uncracked Cracked
- 18 1.833 x 103 2.047 x 103
't 19 7.095 x 103 6.928 x 103
- s 23 3.620 x 103 . 3.559 x 103
! 25 5.771 x'103 5.764 x 103 26 3.466 x 103 3.313 x 103 27 3.435 x 103 3.413 x 103 I
i
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ii
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a r nC 2 c U e 0 p 0 1
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n i - / i Y p o t a C s t G N E e R i c N g U x I O r E C o P ( v R o l a M / F l F i t c r R D ) ^
. f(
6 e .D V Ws '1 i g F p m . s_ -
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.=. i ::i.!1 -! ie '
ii' i . e! . k' ".
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+
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-f 1
4 t
' APPENDIX E 3
EXPERDENTAL EVALUATION OF PRECRACKED BASEMAT h
'4 6
5 4 4 1 6 e
~I -t . *l b,
4%
~
l r s s I 0 ( d 79.,..y; s.ga . *- g~"s ,,,e <<, - ' ?- *
.***f7'r
+y -.*~
f 4; -y.y . v,e-t *4 * * , . - - -
E-1 ,- INTRODUCTION , The primary cracks in the basemat are oriented in the E-W direction and are located in the vicinity of the RCB. The cracks originate at the top of the mat, are relatively deep and probably are continuous across most of the
; mat. It is the opinion of BNL that these cracks were caused by negative bending moments (causing tensile stresses at the top of the mat) which occurred during construction.
t 3 When the construction was completed,the bending moments in the vicinity of these primary cracks because positive, causing compressive stresses at the top
! of the mat and thereby closing the cracks. It should be 'noted that all of the expected load combinations result in positive bending moments in the mat. One would therefore not expect the cracks to reopen.
l Questions have been raised regarding the effect these primary cracks may have upon the strength of the mat (especially with respect to shear) and the mat stif fness. An experiment was conducted to assess these effects. Since the cracks run straight across the mat, it is likely that the effects of interest are associated with one-way bending of the mat. Beams were therefore
- used in the experiment. The beam reinforcement ratios were similar to the
] reinforcement ratios in the slab. Two identical beams were tested. The first beam was subjected to a negative bending r'oment causing a flexural crack originating at the top of the beam. The beam was then subjected to a positive bending moment which was increased until the ultimate moment capacity of the beam was reached. The second beam was not precracked and only subjected to the positive moment loading. A comparison of the load-deflection curves of the two beams gives an indication of the effect the initial crack in the first l j bean has on the load carrying capacity of the beam and the beam stiffness. 1 i b u o i o t l l .7_, /.7, . m. 7 r..y. ., - . - . . , , - . , , . . y _. , . , . e . .- _ - _ . . _ . . . -...,y.c...
a- .. E-2 DESCRIPTION OF TEST , I A cross section of the beams is shown in Fig.1(a). The reinforcenent ratios are , p ?d (Top Steel) p' = As' = 0.05 = 0.00167 bd 6x5 i;9 (Bottom Steel) p = As = 2 x 0.11 = 0.00733 1 ]
- i bd 6x5 ,
- f These are similar to the reinforcenent ratios in the baseaat. The concrete had a strength of f 'e= 2100 psi when the tests were performed and the steel if had a yield stress of 60,000 psi.
,q When this cross section is subjected to a negative bending moment (i.e., u! ,3 tensile stresses at top),the neutral axis is located 5.1 inches from the top. The cracking moment for the section is 12.4 kip inches and the yield moment is 15.5 kip inenes. f s When this cross section is subjected to a positive bending moment, the neutral axis is located 1.66 inches from the top. The cracking moment is the
- [ same as above (37.1 kip inches). The yield moment is 61.8 kip inches and the
};' ultimate moment capacity is 63.0 kip inches, in j, .o The loading shown on Fig.1(b)is used to produce the negative bending j nioment. The test setup for this loading is shown on Photo 1. A major crack j developed when the load (P) reached 2.005 kips. This corresponds to a bending moment of . ? M = P1 = 2.005 x 34 = 17.0 kip inches [] m 4 4 l! u h) Lj - f , - ;.+ y ~ 7 . g e. y e : u . : n - , v~ .. .
E-3 This bendinc moment is slightly larger than the yield moment of the section. The crack deptns are shown on Photos 2 and 3. On one side of the beam, the crack depth is about 4 inches (Photo 2) while it is about 5 inches on the opposite side of the beam. Therefore the crack propagated to almost the depth i of the neutral axis (5.1 inches). 3
- The beam was next subjected to the loading shown in Fig. Ic. The load was j placed off center so that the load was not placed directly over the crack.
t The test setup is shown on Photo 4. A 1/2 inch grid was marked on the beam so' that crack development could be followed. The load deflection curve generated i as the loading increased is shown on Fig. 2 as the solid line. The ultimate load of 7.95 kips corresponds to a moment of 67.4 kip inches sich compares very well with the predicted moment capacity of 63.0 kip inches.. The crack pattern at the peak load is shown on Photo 5. The dashed lines indicate cracks that formed as the positive bending moment was increased. 1 The second beam was not precracked but subjected directly to the loading shown in Fig. Ic. The load deflection curve is shown as the dashed curve in Fig. 2. As may be seen,the crack in the one beam had no effect on either the ultimate load capacity of the beam or its stiffness. The crack pattern in the second beam is shown on Photo 6 and Photo 7 shows a camparison of the cracks in both beams. As may be seen, with the exception of the negative moment ., crack in the first beam, the crack pattern in the two beams is very similar.
; CONCLUSION d The following conclusion may be reached based on these data:
- i
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) 1) When the beam is subjected to a negative bending moment close to the yield and cracking moment a deep crack occurs dich penetrates close .
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- 2) The ultimate capacity of the precracked beam is the same as the .
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I i I f I r f I APPENDIX F BNL's REVIEW OF AFFIDAVIT OF JOHN S. MA ENTITLED "WATERFORD UNIT 3 BASEMAT" 1 1 'i ,a I. e a g,.._.........,-
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F-2
1.0 INTRODUCTION
During the past 8-1/2 months BNL has acted as consultant to NRC and j reviewed the significance of the cracks in the Waterford basemat. The findings based on this work are presented in Refs. 1, 2 and 6. The
~
conclusions presented in these reports indicate that the cracks were mosc likely caused by loadings developed during the construction stage (dead loads and soil settlements) and that the cracks should not adversely affect the capability of the mat to safely perform its intended design function, provided that the lateral soil / water loadings are sustained. One NRC staff member, Dr. John S. Ha, has disagreed with these conclusions, and the basis of his argument is presented in Ref. 3. The objective of this report is to respond to the critique of the BNL position
- raised in Ref. 3. This response is organized by areas of primary
- i disagreement, namely, the cause of the cracking, the structural adequacy 3 of the cracked inat to perform its intended function, and soil non
- uniformity. For the sake of completeness, a list of detailed connents pertaining to Ref. 3 is given in section 5.0 of this report.
m l j 2.0 CAUSE OF CRACKS
)
BNL concluded that the primary E-W cracks in the basemat were caused % by positive bending moments (producing tensile stresses at the top of the mat)whichoccurredduringconstruction. The critique of Ref. 3 concludes 3
. that this interpretation is not consistent with reported data. In j general, the critique of Ref. 3 concerns itself with postulated behavior j of the slab af ter construction was completed. The BNL conclusion is that ] cracks occurred during construction. Therefore, much of the discussion in j Ref. 3 does not pertain to the loading conditions which existed when the l cracks most likely were formed, that is, during the construction phase.
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F-3 Section IV.2.1 of Ref. 3 disputes the femation of cracks during construction because "... it would require that portion of the mat to bend 4 into an inverted dish type from an assumed initial fault condition". In j fact, this is precisely the form of the mat displacements measured by EBASCO during construction (Fig. 2 of Ref. 4). The entire argument in this section of Ref. 3 is based on assumed deformation patterns shown in Fig. 1 of Ref. 3. The earliest stage of construction considered is with the reactor and ring wall completed. Clearly it is not possible to use this discussion of Ref. 3 to draw conclusions regarding the deflected j shape of ,the mat which may have existed during construction. In fact, the construction scenario discussed in the second and third paragraphs of II.4 (Pages 6-7) of Ref. 3 would lead to the inverted dish type displacement and corresponding positive bending moments discussed in the BNL report. The applicant did not evaluate basemat bending moments for loadings j which may have existed during construction. BNLreviewed(i.e.,pages 4-13 of Ref. 1) the dead load solution and found that the bending moments were smaller by a factor of approximately 2 than that required to cause l failure. It was argued that the loading induced during construction j combined with thermal and shrinkage cracking could easily have resulted in j sufficiently high bending moments to cause cracking in uncured concrete. Section IV.2.2 of Ref. 3 critiques this conclusion. The following comments are made with reference to this critique: ,t (a) The first paragraph on page 11 of Ref. I clearly states that "while j there is no explicit computation of loading conditions at this point in i the construction of the facility, the dead load portion of the HEA finite element analysis provides a reasonable simulation of the actual loading to 1 permit a conclusion as to the probable cause of the surface cracking". The entire discussion of IV.2.2 of Ref. 3 assumes that BNL concluded that a W t 9 9 0 t
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F-4 cracking occurred for the dead load case alone. This contradicts the discussion on page 11 of the BNL report, which states that... I (b) Section IV.2.2 of Ref. 3 discusses specific moments in Table 1, of Ref. 1. The original draft of Ref. 3 had confused the Mx and My moments of Ref. 1. The My moments are bending moments about an E-W axis and are therefore associated with cracks in the E-W direction. The moments listed in Table 1 of Ref. I were taken from the HEA output case for dead load only using variable soil springs. The data on Fig. 2 of Ref. 3, however,
. were taken from an EBASCO computer run for the same load case. It should be noted that the HEA solution is based on a refined plate element (as compared to the EBASCO solution) and contains some corrections to the applied loadings. A comparison of the two is shown in Fig. 1 of this report for the region outside the RCB. As may be seen the HEA results g show positive moments over 600 k ft/ft while the Fig. 3 of Ref. 3 shows j maximum positive moment of about 200 k ft/ft. Since the HEA analysis is more current and based upon a better plate element, it must be concluded that the HEA results are more correct.
4 (c) The bending moment diagram shown on Fig. 2 of Ref. 3 shows a maximum i positive bending moment of 200 k-ft/ft. This moment diagram is along an E-W section taken through the center line of the RCB. If the same computer solution from HEA is used but the section is taken 75 feet north
. of the RCB center line, then a maximum positive moment of 900 k-ft/ft is found. If one is to look for bending moments which could cause cracking,
{ then all moments in the slab should be considered - not just those at one [ section as was done in Ref. 3. { $i The reinforcement ratio for the top steel in the mat is very low. Therefore the neutral axis location for positive bending moments can be ') shown to be rather deep (ten feet deep) once the concrete cracks. Section i
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F-5 IV.2.4 of Ref. 3 suggests that the locatian of the neutral axis depends on 4- _ the applied moment, and implies a rather gradual variation of neutral axis ] location as the applied moment varies from the value required to cause the concrete to crack to that required to yield the reinforcement. In fact the neutral axis is close to the center of the cross section until the F concrete cracks and as a slightly. higher moment is applied, it jumps to I- the " cracked section" location (10 feet deep for this case). It remains i at tais level until the reinforcement yields. Any standard reinforced
.; concrete text substantiates this behavior.
- i i
The BNL reports (Ref. I and 2) discuss the observed crack characteristics (length and depth) in the light of the neutral axis location. One would expect crack depth close to the " cracked section" neutral axis depth (10 feet). Furthermore, since ti.e neutral axis would
.' move significantly once the crack formed, one could expect the sudden it j motion to cause deeper and longer cracks than for members having more !j reinforcement. This behavior can be illustrated with the very data shown
[ in Fig. 7 of Ref. 3. Before the concrete cracks the tensile load is distributed between the concrete and steel, with 210 kips carried by the concrete in tension and 11 kips carried by the top reinforcing steel. $ Once the concrete cracks the concrete can no longer carry any tensile load
~
~] and the entire 210 kips must be transferred to the steel. There is a
- sudden increase in steel load from 11 kips to 221 kips (implying that the
[ steel stress increases from 3.5 ksi to the yield stress of 60 ksi). This Q - was termed an " abrupt" failure in the BNL report and used to explain cracks running deeper and of longer length than may have occurred if the l{ y, failure would have occurred more gradually. This phenomenon was ]_ experimentally observed in the test described later in Section 3.0 of this j report. The discussion given in Section IV.2.3 and IV.2.4 of Ref. 3 [ ' disagrees with this BNL interpretation but no justification is given to it fr l' p r G-3' [Qgmyygewwz ymsmtww.cy: qw(;7% rwygm v;*w.vv.rv:r- -- " '
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0 0 F-6 explain why the interpretation is not correct. It would appear that the data presented in Fig. 7 of Ref. 3 supports the BNL contention.
; The material of Ref. 3 offers no alternative explanation as to why the mat is cracked. During discussions held at a meeting in Bethesda MD, on December 4,1984, Dr. Ma presented some ideas that the cracking could have resulted from thermal effects. Because of the mat size, we agree and have said previously (Ref. 1) that thermal effects played some role in the f cracking of the mat. The physical description of the crack patterns, however, do not support the contention that thermal effects were the primary cause of cracking. One would expect such cracks to be oriented in a random fashion rather than predominantly in the E-W direction. The mat was poured in about 50' x 50' blocks with adjacent blocks poured at least 1 month apart. There is no reason to expect that for such a pour schedule, themal cracks in one block would connect with thermal cracks in -4 an adjacent block. Rather, one would expect no correlation between the thermal cracks in adjacent blocks.
3.0 ADEQUACY OF THE MAT y Section IV.3 of Ref. 3 agrees with the BNL contention that the cracks do not effect the bending moment capacity of the mat but disagrees with
~
the contention that the cracks do not affect the shear capacity and stiffness of the mat. The BNL contention that the shear capacity of the mat is not affected q by the crack is based on the fact that shear can be transferred across a j cracked section by frictional resistance along the crack. If the section N bends, a compressive force develops normal to the crack creating a force lt component able to resist shear along the crack. This force component is j equal to the normal force times the coefficient of friction. This is a a v Il
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4 F-7 well documented phenomenon and provisions for evaluating " shear friction" strength along a cracked section are contained in the ACI Building Code (Section 11.7 J of ACI 318-83). EBASCO (Ref. 4 pages 21-22) evaluated the
" shear friction" capacity of the mat and found that the shear capacity of
- the mat is 1.9 times the shear demand. This computation of " shear friction" capacity does not take into account compressive forces in the mat due to lateral soil and water pressures acting on the sidewalls.
These compressive forces would further increase the " shear friction" , capacity. At the December 4,1984 meeting, Dr. Ma also raised questions about the shear stiffness of the mat at the crack locations. His concern was that a shear deformation (slip) across the joint during an earthovake would result in changes to the loads applied to the superstructure as well l as floor response spectra in the superstructure. Tests were conaucted at Cornell (Ref. 5) to evaluate slip due to shear forces along cracked surfaces. A large number of tests were run varying crack width, shear stress applied to the crack and clamping force across the crack. One conclusion of their study is that the slip was less than 0.01 inches for 25 cycles of 180 psi shear stress when the clamping stress was less than 20% of the shear stress (36 psi). The crack width was 0.01 inches. In every respect these test conditions are more severe than those in the Waterford basemat. The cracks in this basemat are less than 0.007 inches, l the applied shear stress in the mat is about 81 psi (derived from data on page 21 of Ref. 4) and the clamping force is about 270 psi (derived from data on page 21 of Ref. 4). Therefore one must conclude that the shear (k slip along cracks in the Waterford basemat will be less than 0.01 inches. 3 It is difficult to see how this slip could cause a significant change in
$ either superstructure member forces or floor response spectra.
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p . F-8 The Cornell tests were focused on shear wall type elements while the Waterford basemat is a flexural member. A simple test was conducted at CCNY (Ref. 6, Appendix E) for flexural members having reinforcement ratios similar to the Waterford basemat. Two beams were tested. The first beam was cracked by inducing an upward curvature of the beam such as existed in the basemat during construction. It should be noted that the developed crack propagated imediately to 75% of the member depth. This result supports the discussion of neutral axis location in Section 2 of this report. 3 The loading was then reversed, causing a downward curvature such as exists in the mat under current leadings. The loading was then increased until the ultimate capacity of the beam was reached. A s'econd identical beam was subjected only to the downward loading (i.e., it was not 3 precracked). A comparison of the load-deflection data for the two beams
; indicates that the crack in the first beam had no effect on either the ', ultimate capacity or stiffness of the precracked beam.
Some further work (Ref. 6, Appendix D) was done at BNL to assess the impact of basemat cracking on the superstructure response. A simplified
) beam model was analyzed in both the cracked and uncracked mode. This beam J model, representing a 22' wide basemat strip running under the pCB in the N-S direction for the entire mat length, was placed on an elastic soil - foundation with moduli similar to those used in the HEA calculation. The masses placed on the beam were also those given in the HEA calculation.
f A superstructure model representing the RCB and other ancillary 4 structures was placed on top of the mat across the cracked zone. This model had the same mass and similar frequency characteristics as the i structures in the RCB A parametric study was performed changing the I Pequency characteristics of the superstructure. A comparison of floor i I
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F-9 response spectra and element forces indicates that the cracked mat has little influence on the resultant responses for both horizontal and vertical earthquake inputs. These analyses provide further support for the BNL conclusions regarding the structural adequacy of the mat. Section V.2 and V.3 (pages 28-31) of Ref. 3 raise the question of the effect of cracks in the mat on corrosion and durability problems. Criteria are used in the design of concrete structures so that cracks which occur in the structures are sufficiently narrow so that corrosion of the reinforcement does not occur. The question then is whether the cracks in the Waterford mat satisfy these criteria. As generally agreed, the observed cracks in the mat have a width of less than 0.007 inches; this is well within all standards of acceptability. The cracks which originated during construction resulted from bending moments producing tensile
- stresses at the top of the mat. The current and anticipated future loading on the mat will result in bending moments which produce compressive stresses in the top of the mat. One must conclude, therefore, that these cracks will never be any wider than they are at present. The
, fact that these cracks are now under a 50 ft hydraulic head and there is no evidence of water seepage through the cracks, is further indication that the cracks are very narrow. As the mat is subjected to loadings which result in bending moments producing compressive stresses at the top of the mat (and tensile stresses at the bottom) one would expect bending cracks to develop from the bottom of the mat. The existing cracks starting at the top of the mat should j have no effect on the size of these bottom cracks. On page 13 of Ref. 3
- j it is stated, "If the loads are adequately calculated, I have no doubt that the mat design is adequate for the current soil condition." Dr. Ma
] j apparently is satisfied 6 hat cracks caused by bending moments producing I tensile stresses at the bottom of the mat will be sufficiently small so o en
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F - 10 that corrosion is not a problem. In view of the amount of reinforcement in the mat, we concur with this conclusion.
; Several enclosures are appended to Ref. 3 with respect to the cracking and corrosion problems. The pertinence of this material to the question at hand is unclear. Enclosures I, II and III deal with the fact . that cracks in deep beams may be wider at mid depth than at the level of the reinforcement. Criteria are given to distribute some of the l reinforcement along the face of the member web. This criteria is clearly
, intended for beams and not two way slabs. It would be impractical (from a placement viewpoint) to distribute steel throughout the depth of a slab across its entire width and ineffectual to do it only at the end faces of the wide slab. The discussion in Enclosure II refers to the criteria given in ACI Building-Code Section 10.6.7 (ACI 318-77). The introduction
; to that section of the code (10.6.1) clearly states that the steel distribution in two-way slabs is not covered by these requirements.
Enclosure IV of Ref. 3 deals with control of cracking in mass concrete dams. The discursion in this article deals with much larger pours than was made in the Waterford basemat. Certainly, the larger the
; pour the more significant would be the thermal effects. As discussed in the last paragraph of Section 2.0 of this rep' ort, the characteristics of
^
the observed cracking at Waterford are not consistent with the expected
, characteristics of cracking due to thermal stresses alone. That is not to say that thermal stress did not play a role in the formation and extent of l )
the cracking. 4.0 S0Il NONUNIFORMITY a a ] Throughout the testimony of Dr. Ma, reference is made to " soil p nonuniformity", which generally refers to two separate issues. The first is associated with nonuniformity of actual soil properties of the 3 d 1 4 i
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F - 11 foundation soils immediately below the basemat. This nonunifomity leads to a consideration of the potential for " soft spots" in the soil below the mat. This contention is addressed in Section 4.1 below. A second " nonuniform" soil discussion appears in his affidavit and this is associated with the variable spring finite element analyses performed by EBASC0/HEA. This nonuniformity is in fact associated with a [ consideration of the adequacy of the analytic studies perfomed for the
, NPIS, and has little to do with the actual soil properties existing at the site. A description of this approach is presented in Section 4.2 below.
4.1 S0IL PROPERTIES At several points in Dr. Ma's affidavit, reference is made to the potential nonuniformity of site soils as being a major. contributor to the differential settlement problem. For example, he states on page 27 that
"... the nonuniform nature of soils under the mat was discovered and reported by Dr. J. Chen, but this view has been consistently disputed by BNL." It should be noted, and this has been mentioned to Dr. fia on various occasions, that nonunifom mat displacements which occur during
] the construction stage does not necessarily imply that soil properties are t' nonuniform. It is the BNL opinion that actual displacements experienced ii by the mat are primarily controlled by variations in excavation, z dewatering, recharging, soil stockpiling, dead load construction
- sequences, etc. and not by nonuniform properties of the soil. If the soil 3 .were ideally uniform, these df f ferential slab movements would still have q
j occurred and be significant. N The original discussion with BNL of the impact of " nonuniform" soil re properties developed with Dr. Ma's original concern which focused on the a E Li L.mr._,-_,7 . ., ; , -. _y.~,,_ y. . , - c , ,, - ,. ,- -n ,, . . ,
F - 12 potential for diagonal shear failure of the mat occurring at " soft spots" under the slab. BNL h:sd concluded then, and still does, that (a) such diagonal shear cracking was highly improbable for such a mat foundation (which was later borne out by the NDT study), and (b) all measured slab mocaments were consistent with the field construction sequences at the
- site and were most likely cor. trolled by the medium stiff grey clay layer
[ 3xisting between elevations - 92 and - 108 feet. The primary problems I encountered at the site during construction were concerned with the contro.1 of the dewatering and recharging operations, which in turn led to I settlements being larger than originally planned. These settlements were H nonetheless still consistent with the concept of a un form soil subjected to varying load / unload sequences. Some specific difficulties were noted during construction in the following areas. 1 (a) Erratic behavior was noted in the piezometers located in the shallow foundation silts. In such fine-grained soils, piezometer readings normally are expected to be erratic. However, the phreatic surface (ground water level) was effectively lowered by the dewatering program, as indicated both by the readings of the deeper piezometers located in the sandy soils, as well as the measured site settlements. l' i (b) During compaction of the clam shell material (placed as a filter j blanket under the mat), a " mud spurt" occurred in one block of the mat when standing water existed in the excavation. According to j EBASCO engineers, this spurt occurred when a vibratory roller was Y being used to compact the shell filter blanket. Although the ground I, water table was effectively lowered, these upper silts were still saturated and would be susceptible to vibratory effects. The total j extent of this " spurt", however, covered an area of 10' x 12' (120 A li [s
*...,7-.,. ...,s... , y 7 s , ,.m .~ ,- -- - - ,
2 F - 13 square feet), while the typical block plan area is 2000 to 5000 square feet. j (c) Difficulties were noted in trying to obtain the desired compaction of the shell filter blanket in the block area mentioned above. This filter blanket is only 1 foot thick, and its state of compaction is imaterial to the behavior of the mat. The purpose of this filter
; blanket is to provide a porous path imediately under the mat to ensure that any variations in pore pressure to the sides' of the structure are immediately felt under the mat. The high porosity of the shell blanket indicates that it will consolidate imediately when subjected to the weight of the wet concrete during a pour.
(d) Any variability in the compaction of the surface silts, as indicated 3 by the mud spurt and compaction of the shell blanket mentioned above, l can at best be limited to the top several feet of the soil under the mat. Certainly, this is the effective derth to which any of the compaction methods can extend. The measured imediate settlements of all the block pours were about 0.75 inches. If there were any
^
significant differences in the upper Pleistocene compressibilities,
- there should have been some indication noted in these imediate 5
settlement values. In addition, the presence of the filter blanket ensures that the top several feet will consclidate rapidly under the
; concrete weight, certainly much more rapidly than the measured three year period associated with the deep seated settlements. The soil sample blow counts, laboratory data, etc., generally indicate a g uniform foundation condition.
ij In summary, it should be concluded that in the primary compression
~
zone under the mat, the vast majority of soil data indicates that the soil
.2 i is effectively uniform and that any differential settlements are .4 i
l Y y,,., , , . ,;.-- . -.,w,..u n .--s + ,..m. .w+ -
.-e p . p. . , - , .,y.. -73 ,3 y m.
4 , ,
F - 14 attributable to construction sequences and dead loadings, i.e., the weight of the mat and partially completed superstructure early in the construction process. 4.2 VARIABLE S0Il MODULUS ANALYSES d
', On page 25 of Dr. Ma's affidavit he. states that "... a decrease of i soil stiffness from 150 pci to 70 pci within the ring wall resulted in a positive bending moment increase ... This type of 400 percent increase in bending moments is certainly not covered in the detailed calculations recomended by BNL . . . ." . While this statement appears to be offered as an example, the magnitude of the variation cited tends to be misleading since it is far larger than any variation we believe would be shown by an appropriate analysis rather than referring to the methods of the' simple , numerical studies performed by EBASC0/HEA for design purposes.
4 In the numerical studies performed by EBASC0/HEA, the interaction of the basemat and the foundation soils are represented by a series of springs under the mat of specified stiffness (pounds per square inch of [j area per inch of mat deflection). This method of analysis is a standard 1
- 4 one often used in foundation studies to estimate the behavior of the mat i and is known as the Winkler foundation model.
A, 1 Several characteristics of this approach are known. Firstly, it l} should be pointed out that in general the method can yield only gross approximations to the actual soil-structure interaction (SSEI) effects. j For example, if one places an ideal uniformly loaded rigid mat upon a set 1 ] of uniform springs, the computed contact pressure between the bottom of the mat and the springs will obviously be uniform since the displacement 5 of the mat will be uniform. The magnitude of the contact pressure is N simply the " soil" . spring constant times the displacement. On the other ii q !i
~
.. , . - . , , . . , . = . . - - g.,-...- .
- e. . _e - , . - - -. .
F - 15 hand if, one places the same rigid uniform mat on the surface of a uniform ideal linear soil (continuous medium with both lateral extent and depth) the actual contact pressure developed under the mat is hyperbolic, being 4 very large at the edge (theoretically infinite) and less than average
; under the central portion of the mat. Thus, it is well known that the j Winkler model is only a gross simplification of the actual SSI problem.
The comparisons of the spring model with the continuous medium solution for the dynamic or seismic problem is even more tenuous. However, the Winkler model has one over-riding advantage and that is its simplicity. It serves to uncouple the mat (and superstructure) analysis from that of the foundation soils. If one can, somehow, justify the applicability to the particular problem under consideration, a great saving can be achieved. 3 h For the Waterford analysis, EBASCO decided to utilize the Winkler
~
concept. The first trial run made use of a uniform spring constant of 150 J pci. It should be noted that this value lies somewhere in the range of values typically recomended in the literature for soils similar to the
; site soils. These recommended ranges are usually very wide, with upper j and lower bounds easily differing by factors of three, four or five. It should be noted that for the Waterford mat configuration, the particular
]
; choice of spring value is relatively unimportant since in comparison with j the mat, the soil is relatively soft. The only impact of this value is merely to control the magnitude of gross rigid body displacements of the
] ' mat but not the developed stress resultants (moments and shears).
?
c1 j For this first run, the computed contact pressures under the mat (due i A to structural flexibiltiy and load distribution) were not uniform. The
? design philosophy adopted by EBASCO wes to have the average contact i pressure under the mat equal the weight of soil removed in the excavation k
M = *P . " r" % f ' N ' **P", **'W W* *"*T''. "W**" T STh N'""'T
- L
*8 7#*# '
""~'tg T'# # * #-
I* ^
O 6 F - 16 (this is the so-called floating foundation concept). This is snother typical foundation design approach used throughout the geomechanics area, whose sole function is to attempt to limit the settlements induced by the construction process. In keeping with this general philosophy, EBASCO then modified the spring values in the center of th'e NPIS to a value of 70 pci, keeping the outer spring stiffnesses at 150 pci and utilizing an intermediate zone of 110 pci. The full finite element analyses were then rerun with these revised variable values. This variable moduli model, a completely arbitrary one, had the one advantage, namely, that the computed , contact pressures under the mat were approximately uniform. This result is in keeping with the intuitive sense of the EBASCO engineers as to the long term configuration of the NPIS, after long term soil consolidation is completed. It should be clear that such a simplified foundation analysis
! approach cannot be utilized to properly assess the differential settlements that were induced in the mat due to such real construction phenomena as dewatering, recharging, excavation, dead loadings developed during construction, etc.
1 Dr. Ma appears to infer that the confinnatory calculations 3 reconinended by BNL will not adequately consider the bending moment increases due to local variations in soils. This is simply not true. The confirmatory calculations recommended by BNL would not be based on the {
] soil spring analogy, since the construction sequence loadings can not h reasonably be characterized in that approach, but rather on a study making use of the actual mat / soil interaction process, see Section 5(u) below.
5.0 DETAILED CRITIQUE OF REFERENCE 3 8 I b 2 e
***9 *4 Wg g[ ] f . N
}
- f { '?" 7 -- 'f "*g "9**1 d
M,* "Og%%f 9 *m*Fv)
- 7 *D =
' Df 4 -
F - 17 The following specific comments are presented for completeness of this report and most of the differences between the BNL conclusions and those of Reference 3 are listed. h (a) The discussion on pages 6 and 7 dealing with soil movements actually supports the BNL contention that the cracks developed during the [ construction stage when nonuniform soil movements and unaccounted dead loadings occurred.
? ! (b) It should be noted that the discussion of mat deflection profiles postulated on page 8-9 of the report (and Fig.1) are incorrect for loadings which occurred during the construction phase. In fact they do not agree with the measured mat deformations as shown in Fig. 2 of Pef. 4.
Furthermore, at the time of discovery of the cracks under the RCB, in
- midyear 1977, the fill concrete was not yet in place. Therefore only ring wall loadings (and other partially completed structural loadings) were acting on the mat. This would cause different bending patterns than those
^ shown in Fig. 1. l (c) On page 11, it should be noted that Figs. 2 and 3 cannot be compared. j] Figure 2 presents the results of dead load only while Fig. 3 presents a J moment diagram for different load combinations (dead load, live load, 7i nonnal side pressure, and buoyancy) each multiplied by different load l factors and then summed to obtain resultant moments. These data cannot be used to support the conclusions on the effect of backfill soil loadings. y (d) On page 12, it is stated "... according to the actual construction ]
- sequences, ...". It should be noted that the EBASCO computer output never
> considered construction sequence loadings or soil movements.
a. l l L' 9-F # "' '"W ##** #** '
#T#*E' ' ' " - %-
_%* , g
# 1 ) b- . i [1 I, * ' % f d g, } [ 8 ,
* ** 7
F - 18 (e) On Page 12/13 of Dr. Ma's affidavit, it states that "...in order to have a coninon deflection at the centers of both strips, the shorter E-W
, strip has to bend more than the longer N-S strip; hence, bending moments j *in the E-W direction are greater than the N-S direction." It should be ; obvious to any engineer that bending moments are related to curvature and not deflection, and that the moments in the E-W and N-S direction are d related to both applied loads and plate boundary conditions. Obviously, j if the E-W strip deflects unifonnly, the E-W moment is zero, even though i the deflections are the same at the center. Any standard text book on plate theory can attest to this fact.
9 (f) On the bottom of page 13, Dr. Ma states that "...These ccmparisons provide certain confidence as to the correctness of the computer programs used by EBASCO and.to the ability of EBASCO engineers who adequately 3 modeled the real structure for mathematical analysis..." It should be 3 noted that (a) even though the computer programs used by EBASC0/HEA may be correct, the soil model (Winkler foundation) used in these analyses are only gross simplifications of soil-structure interaction and cannot be used to predict construction stage stresses, and (b) the measured mat 'i displacements indicate inverted dish displacements (required for upper surfacecracking). i (g) Reference is made on page 13 to an analysis performed by Dr. Ma for j positive and negative bending moments within and near the ring wall. A ,- copy of that analysis was cbtained on December 13. The mat area within the ring wall was modeled as a circular plate with fixed supports at the
}'
ring walls and loaded with a uniform load of 6.29 ksf. No account was given to the fact that the soil provides support over the entire area of w the plate. It is also interesting to compare the results of Dr. Ma's i computation with the EBASCO results on Fig. 2 of Ref. 3. Dr. Ma calculated an edge moment at the ring wall of 4662 kft/ft while Fig. 2 of 4 o s
- m. . . . .p . m w . . . - - . ~ .
..q.,... ....-_.-..-,,...7
. . . . . - . . ~.,
L.
F - 19 , Ref. 3 shows a moment at the ring wall of less than 200 kft/ft. Dr. Ma's mcment at the center of the plate of 2797 kft/ft while Fig. 2 shows a moment of 800 kft/ft. In spite of these differences of 23/1 and 3/1, Dr. Ma conludes that "EBASCO bending moments were adequate for design"! (h) Dr. Ma states on page 14 that "...the stiffer the mat; the more uniform type of forces for the soils". It is assumed he means by this
' statement that the contact pressure under a stiff mat is unifom.
However, it is a well known fact in geomechanics that the actual contact l pressure developed beneath a perfectly rigid mat is hyperbolic and is not
! uniform as implied, with stresses under the outer edges being very large (theoretically infinite for an ideal soil) and less than average in the center.
He states further that "....since there is no analysis performed i incorporating the actual soil condition, the maximum is not known for the stress level that the mat actually experienced during construction. This makes later assessment on the cause of cracking more difficult." It should be apparent to Dr. Ma that the analyses performed by' EBASC0/HEA i were never intended to account for the stresses developed during j construction, as discussed in Section 4.2 of this report. As an aside, it i should be noted that Dr. Ma previously reviewed this analysis and accepted its results. In addition, the fact that the soil spring approach is only i a gross simplification to the actual soil-structure interaction process in no way prevents anyone from assessing the cause of the mat cracking. ,4 (i) BNL agrees with Dr. Ma's statement on page 16 that "...the extensive ] 4 cracking in both length and depth, as indicated by NDT, has raised a 1:: question on the validity of this assumption and a need for further a* examination." Based on all of our numerical studies, it is our considered opinion that the impact of the cracking on the dynamic response will be 1 4 e e ,-en e W s = -wsa p
- senpa 'W*% - W se 'iet P ** W: d' *. *F
- p +-g--,
. +++=w#- . % pe * + g 9y
)
l F - 20 l small and requires only confirmatory calculations. See Appendix D to Ref. 6. (j) On page 16, it is stated that "... the mat concrete alone provides a j tensiIe force of about 166 million pounds, while the top rebars can only
; provide a tensile force of 50 million pounds ....". Since the net force across the concrete is always in compression (due to the lateral soil and 1 waterforces),thesignificanceofthiscalculationisquestionable. In addition, if bottom steel is included, the tensile capacity of the steel - is 235 million pounds and not 50 million pounds. The consequence of this calculation, however, is still unclear.
(k) On page 16, a mathematical model of the cracked mat is postulated. The top spring in the proposed model only includes the reinforcement j stiffness. This model cannot be correct since the top of the slab is in j ' compression. Therefore concrete stiffness must be added to the steel stiffness in the model to obtain a realistic stiffness of the top spring. 4 9 (1) On page 18, the bridge joints mentioned refer to expansion joints, s F which are designed to allow relative movements between the two side of the ij bridge with n,o restraints. Certainly, lateral restraining forces are
'! available for the Waterford mat to prevent such relative movement and ) thus, hamering between sections will not occur.
1 (m) On page 19, Dr. Ma stated that he understood BNL's position to be that
] " dead loads (weights) were mainly responsible for producing the extensive j cracks..." It has been consistently stated by BNL (see page 11 of Ref. I and, page 4 of Ref. 2) that the cracks were most likely caused during i construction by uneven settlement of the soil due to construction h sequence and the weight of the slab.
4
, .....o
,-.. 4 m, .,,.-.n.. .% . .r ,, 7 . ... ,.s,y,,,., ,, ,,p y 7% m, . . , y y w - -- -- ~. g
. e ,
F - 21 (n) On page 19, reference is made to the analysis presented in Appendix B of Ref. 1. This analysis was performed as a result of Dr. Ma's contention that diagonal tension (shear) cracks existed in the mat. It demonstrated that diagonal tension cracks were unlikely. It showed that, if uneven 4 settlements occurred during construction, bending cracks were much more j likely than shear cracks. (o) On page 20, it is implied that BNL changed its position after learning about the NDT results. It should be noted that BNL presented the same position in the July 18 report (Ref.1) prior to the NDT results becoming available. In fact, the reason for presenting this position in
' the BNL report was simply to counter Dr. Ma's contention tha.t diagonal shear (and not bending) caused the cracks in the mat.
(p) On page 20, it should be noted that not only do the BNL results i contradict Dr. Ma's intuition, but the measured EBASCO displacement maps, available prior to the BNL report, contradict it. (q) The discussion on pages 21 through 24 of the domino theory and neutral axis location have been previously discussed on page 5 of this ft Appendix. l 4
! (r) On page 22, Dr. Ma states that ".....if concrete is cracked in the N-S l strip and the E-W strip is uncracked, then a greater portion of the total load and bending moment will be taken by the uncracked E-W strip." It is j apparent that such postulated behavior of plate action violates even the j simplest concepts of mechanics. The total load and moment that must be I 3 transferred from one side of the mat to the other side is specified by considering simple equilibrium; i.e., by considering equilibrium of a free
} body. If a moment exceeds the section capacity at one point, it cannot simply " turn around" and move in another direction, as equilibrium will is e t J 9
- ,. , . ,,.s .. ...e-m.- .m , ; p . w .e , , . ~~- n v~ m m . p e -~.~ r * ~.
- o .
F - 22 then be violated. The ACI building code (Chapt. 13) recognizes this fact in its design requirements for two way concrete slab action in that the total moment in one direction must be calculated separately from the total d moment in the other direction. - (s) Section IV. 2.5 (page 24) discusses the confirmatory analyses recommended in Ref. 1. A statement is made that "....the purpose of the i detailed calculations is striving for calculation accuracy, not for i errors, such as may result from major incorrect assumptions....." In fact, just the opposite is true, BNL's assessment of the adequacy of the basemat is based upon a review of the EBASC0/HEA analyses with special attention paid to the assumptions upon which these analyses are based. When a particular assumption was questionable, an effort was made to evaluate the sensitivity of the final results to the assumption and to assess the extent to which the assumption may be unrealistic. The judgement has been made that, in the five cases cited for confirmatory analyses, the assumptions used by EBASC0/HEA are in some cases no more than an improved set of assumptions. This is not expected to change the bottom line conclusion regarding the adequacy of the mat. BNL has recommended, however, that additicnal confirmatory work be performed to
) obtain a firmer basis for this judgement than is now available.
I (t) On page 25, Dr. Ma states that ".....this type of 400 percent increase
, in bending moments is certainly not covered in the detailed calculations recommended by BNL." BNL originally recommended 5 separate items for g
further study, later reduced to 4 at the completion of the NDT study j (cracks in the vertical walls are no longer considered a problem). The g! first two of these, as listed on page 24 of Dr. Ma's testimony, refer to 3 (a) dynamic coupling between the flexible basemat and RCB and (b) dynamic l effects of lateral soil / water loadings. It should be obvious to anyone d* . m. v.. g
# + ' M .9479 4 . e , A* 1 Syi '2 5 'sp., *=,,aw'*- "37- ;- &-* %7 * * * - * * * * * -
s . F - 23 associated with SSI calculations that the only way to properly assess these items is not to perform another study using the Winkler soil spring model, but 'rather to perform a numerical study making use of the actual mat / soil interaction process through either finite element (FLUSH)
; analysis or analytic approaches (CLASSI). In either case, the approache must include the wave propagation problem through the soils both to the sides and below the NPIS.
1 [ (u) The discussion as to " uniform" soils presented on page 27 is incorrect. Although it is our contention that soils within the primary compression zone of the mat are uniform, this does not imply that soil movements that occurred during construction are uniform. Displacements of the soil at any location are controlled by excavation and dewatering procedures, stockpiling locations, as well as mat loadings in the y vicinity, which are in turn controlled by deep seated soil behavior, and i not simply the soil properties imediately below the slab. The slab movements woul'd not be expected to be uniform. However, there is no indication that any " soft" spots exist under the slab. The differential movements noted are entirely compatible with the construction procedures j imposed at the site.
- ' (v) On page 30, reference is made to the effect that the measured crack widths are at the compression side of the mat (top) while the criteria is ll
; intended to be applied to maximum crack widths at the tension side of the mat. It should be noted that the NDT crack width measurements were made q for the entire depth of the crack and not just at the top surface. It
- i should also be noted that the existing cracks would have no impact on the width of flexural cracks which start from the bottom of the mat.
u I L p
=. e *
- Me + 6e4 - v - yp e a er. , vey .,,.- g e S
- ae g == a' # '.aary
- s
.. s.
~
~
F - 24 REFERENCES
- 1. " Review of Waterford III Basemat Analysis", BNL, July 18, 1984.
- 2. Addendum to " Review of Waterford III Basemat Analysis", BNL, August 1
s 1984.
- 3. "Waterford Unit 3 Basemat" Affidavit by John Ma, December 1984.
- 4. " Summary Evaluations Structural Significance of Basemat Nondestructive Testing Result", Rev. 2, EBASCO, November 27, 1984.
- 5. Liable, J.P. While, R.N. and Gergely, P. , " Experimental Investigation I
of Seismic Shear Transfer Across Cracks in Concrete Nuclear , ~j Containment Vessels", ACI SP-53-9, Reinforced Concrete Structures in ii Seismic Zone, 1977. t
- 6. Addendum 2 to " Review of Water III Basemat Analysis", BNL, December
- < 1984.
ii ?$ If n l 4-.i t b t 2 1 e
- a. -- +v-m,v,*,.,-,~~mw._,-,,---.n.w..r,-,. --s+ -< - - -~ ~ r-r .:- ~ , ~ - ~ ~ - - - - ~t ~
pr=
. _. _. a _._......s_. , _ . _ . , ., _
4 , ,~ ~, 7 e: e ~ :. _ . - . , . _ , _ _ _ ~ . , ._. ..
;c. ..
t 0 i t . 1 [. APPENDIX G BNL'S REVIEW OF GE0 TECHNICAL ENGINEERING EVALUATION 1
! 0F CONCRETE CRACKING IN THE BASEMAT 5
WATERFORD UNIT 3 JOHN T. CHEN, GE0 TECHNICAL ENGINEER l
-it )
M 5 e 8 e ,i i N e i
' ~ ~u ,~ ny~,;wy
~ m m ,- : 7-,-e . ,.-- : , ,- _ , ; ; .. sy y-7= .g w.7 - - .
;, -~~r_m ym - : , m-- -
---- - - w - ,,,
G-2 During the past 8-1/2 months BNL has acted as consultant to NRC and has reviewed the significance of the cracks in the Waterford basemat. The conclusions reached indicate that the cracks were most likely caused by -j loadings developed during the construction stage (dead loads and soil 1 settlements) and that the cracks should not adversely affect the capa-j bility of the mat to safely perform its intended design function, provided that the lateral soil / water loadings are sustained. A Following a site visit in connection with review of the base mat { cracking, during which the applicant's records of geotechnical matters
; related to the construction of the base mat were reviewed,' an NRC staff engineer Dr. J. Chen prepared an internal report reflecting his views of the material reviewed, Geotechnical Engineering Safety Evaluation, Waterford No. 3, Louisiana Power and Light Company. Dr. Chen's report is 4 cited as Reference 2 in the December 12, 1984 affidavit of John Ma.
~ !, Presented below are coments on the report mentioned above. These comments are placed in a simple statement / response format. The symbol "S" refers to the statement made by Dr. Chen in his evaluation while the symbol "R" refers to the BNL response to that statement. 4 g Sl. Page 3, par. 2 ... However, the control of insitu vertical i effective stresses and groundwater levels was quite difficult because the
, subsurface soil conditions were somewhat different than anticipated.
Numerous construction difficulties encountered during construction may have caused some differential settlements which may have contributed 4 directly or indirectly to the observed cracking of the foundation mat... i )a Rl. From the documents BNL has reviewed, together with discussions yj with EBASCO Site Engineers, no specific foundation problems were y encountered which were different than anticipated. The only significant problem encounted during construction concerned contractor control of the T* *-'_5 *O -M, ,# 'N* ' ' 7, # * * * *I"T
- M #
K&M 4 * * *%# 9%TT , gF .# mop *. W'*d% % ' ', 9 % *h*^A*=0 %* 7 T - M. -gi, '? F [*'-
1
- a G-3 dewatering and recharging operations. This in turn led to the settlements prior to mat placement being larger than originally planned. This l procedure would effectively preload the medium stiff grey clay between f elevations -92 and -108, which is probably the major contributor to the NPIS settlements. I ; S2. Page 3, par. 3 ... Because of the very low permeability of the upper Pleistocene clay, all the wells did not completely lower the ; groundwater level in the foundation soils to below El. -48 as evidenced by }
some of the piezometric readings (Ref. 6). Locally those high groundwater
~
conditions appear to have caused soil disturbance, mud spurt, standing water in some area of the excavation and difficulties in compaction of the shell blanket (Ref. 5)... R2. Firstly, a review of LPL's Draft Responses to NRC's Question on
- Waterford 3 Basemat (March 26,1984) does not indicate that the dewatering l wells were not effective. The only erratic behavior appears to have occurred in the piezometers located in the shallow foundation silts. In such fine-grained soils, piezometer readings can be expected to behave erratically.
i j S3. The phrdatic surface (effective groundwater surface) was j effectively lowered by the dewatering program, as evidenced by the
- measured site settlements which developed after the dewatering operation j was initiated. The measured settlements also agree with the anticipated j behavior for the uniformly bedded site soils. However, as with any silty l- clay, the water retained in the upper Pleistocene is trapped by its low
- { permeability, leaving it with a high water content. This water is il essentially bound water, retained by the soil until it is able to h dissipate by seepage into the underlying aquifer.
3 A p 1
. --m ,. . ._ . - y. -.w
. , m .7, , --,s- . ---. . .
,-._-m. . . . . ~ . .
. . 4 G-4 R3. The saturated silty clay in this wet condition is then suscep tible to vibratory effects. It should be noted that only one " mud spurt" . occurred, this in strip number 2, when standing water existed in the i filter blanket. This spurt occurred when a vibratory roller was used to I attempt to compact the shell filter. The total extent of the " spurt" covered an area of 10' by 12' (120 square feet). The total plan area of l
each block is 2000 to 5000 square feet. This single " spurt" was then cleaned, the standing water from strip no. 2 removed, and the shell filter recompacted. According to Site personnel of EBASCO, the standing water in strip no. 2 developed from the concrete pours of strip no. I as well as accumulated water ponding from weather conditions. In any case, the ease with which the ponding was removed indicates .that the shell filter was in fact porous, as desired. j S4. Page 4, par. 2 ... within the boundary of the foundation mat, .i the penneability and the compressibility of the clay layer varied significantly from one location to another as evidenced by the results of the piezometric and heave monitoring during construction (Ref. 6). The F measured heave at varicus locations was 2 to 4 times the anticipated maximum heave used in the mat design ... I j R4. The differences in measured and planned heave seems to be entirely in keeping with the fact that the dewatering program did not
- follow the excavation sequence as originally planned. For the new j situation, the measured settlements in the field correspond with the new j loading data. As stated above, the majority of the settlements are probably attributable to the lower clays with OCR's of only 1.1 to 1.4 and j not with the upper Pleistocene.
- The measured immediate settlements of all the block pours were about
," 0.75 inches. If there were any significant differences in upper i
( n y e:. =~- - ~p y~ . ,: . ... . r~: t*rm- * :n --~ , .
~
.~ ~ ~---~*~~ ~~ ~ '~r~r~v
s ,. - d G-5 Pleistocene compressibilities, one would expect to see differences in these measured valuses. The measured settlement patterns of the mat during the various stages of construction do not indicate any significant
,?
variations in compressibiliaty, but rather seem to correspond to the actual loading program on uniform soils. S5. Page 5, par 1... However, due to the variability of the [ supporting soil and groundwater conditions, despite occasional effort up l- to 40 passes, the degree of compaction achieved in these shell filter
.i j strips varied widely.... +
R5. It should be apparent that the state of compaction of the shell blanket itself is imaterial to the behavior'of the mat, for the following reasons: j
- 1. The purpose of the filter blanket is to provide a porous path
}!' imediately under the mat to ensure that any variations in pore f pressures (water levels) to the sides of the structure are I' immediately felt unifomly under the mat; no variable pore '/ pressure loads can then be applied to the NPIS.
, 2. The high porosity of the shell blanket indicates that it will 7
i- consolidate immediately when subjected to the weight of the wet ) concrete during a pour. ijf 3. The shell blanket is only 1 foot thick on the average, much less i than would ordinarily be used for a load bearing blanket. u j Certainly there cannot be any thru-thickness variations of any significance.
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r > a G-6 . Any variability in the compressibility of the supporting soil can
, only be limited to the top several feet of the silty clay. Certainly, j this is the effective depth to which any of the compaction methods can i extend. As mentioned above, if there were any major differences in ! compressibility, there would have been measured differences in immediate
] settlements of the blocks when poured. The presence of the filter blanket { ensures that the top several feet will also consolidate rapidly, certainly much more rapidly than the measured three year period associated with the i deep seated settlements. 1 l S6. Page 5, par. 2 ... These variable degrees of shell compaction reflect the condition and consolidation of the underlying foundation soils
' indicating that the subgrade moduli varied among these strips.
Settlements of the mat due to uniform structural loads would be expected
! to vary accordingly ...
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;- R6. As stated above, the measured settlements are entirely in i keeping with deep seated compression of soils of uniform compressibility.
The subgrade moduli represent this unifomity. If there were any near surface variation of compressibility, it should be noted in the measured 1 imediate settlements. It was not. b i j S7. Page 6, par.1... Subsequently, differential settlements would j be experienced by the superstructure founded over different strips with j variable soils properties and rates of consolidation ...
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R7. All measured data indicate extremely uniform rates of f.- consolidation for such a widespread structure. There is no indication of any significant foundation nonuniformity. y i sh i
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,. o G-7 S8. Page 6, par. 2 ... After the second and third blocks were poured adjacent to the first block, differential settlements between the tops of the completed blocks were observed.
4 R8. The settlements mentioned occurred immediately with the pour,
! and certainly before the concrete of the second and third pours hardened.
- 59. Page 7, par. 1 ... These changes in hydrostatic pressures changed the effective stresses in the foundation soils and caused j movements of the foundation suils and the concrete mat ...
R9. The measured movements of the mat since the completion of the NPIS structure are certainly much less than the 2 inch differential
, settlements shown by the measured mat profiles. The settlement / pore pressure relationship appears to follow the original concept of a floating I structure on a uniform horizontally bedded soil site.
S10. Page 7, par. 2 ... The differential settlements were caused
. mainly by the variable soil conditions, high groundwater levels, variable compaction of the shell filter strips, and foundation mat construction j sequence. The hydrostatic pressure changes, affecting the effective j stress state in supporting soils, may ha've aggravated the growth of the cracks after the mat was completed...
R10. As stated above, the variability of the state of compaction of the shell filter certainly has no bearing on potential differential j settlements of the mat. There is no indication of any significant $ variability of foundation soils. The differential settlements are
! entirely in keeping with NPIS construction sequence on uniform soils.
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G-8 511. Page 8, par.1... To evaluate the potential for future cracking, the effects of differential settlements during construction
, should be determined so that the current state of stresses in the base mat I can be better assessed. The soil shear moduli to be used in such an analysis should reflect more closely the soil conditions that existed during construction, when the foundation soil was in the process of being consolidated.
i R11. BNL agrees with the general intent of this comment. However, l
! several items should be made to clarify the situation. . (a) There is no significant triaxial and consolidation laboratory I
data currently available for the site soils which could be used in performing a detailed, complex numerical study of the NPIS. Certainly, j since construction is now completed, a sampling / testing program cannot now j be undertaken to develop the necessary data. (b) There is no computer code available to do the full three dimensional analysis of the site, including the effects of the initial stress and strain states of the soil, nonlinear soil and concrete behavior, seepage, time consolidation, etc. On the basis of these two concents, BNL feels that a numerical analysis should still be performed to attempt to assess the impact of the { i construction procedures on the induced stresses in the mat, which have not been evaluated by the applicant. These analyses must be performed with care since approximations will be required to carry them out. Based upon our estimates of this initial or construction stress I state, it is our opinion that these stresses are small. Therefore, we recomend that these studies be considered as confirmatory only. e G bg. .-wes eew , gga g pgeagg ++ e - .s p a-e,-m w 4m. . g e pengv e a- g = yygy m s yqppy s
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