Text

Enclosure B, Bechtel Report No. 25593-000-G83-GEG-00016-000, Effect of Laminar Cracks on Splice Capacity of No. 11 Bars Based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building. Part 1 of 7
	ML15299A144
Person / Time
Site:	Davis Besse
Issue date:	07/30/2012
From:	Liano R, Munshi J, Reilly R; Bechtel Power Corp
To:	; Office of Nuclear Reactor Regulation
Shared Package
ML15299A142	List: L-15-328, Enclosure B, Bechtel Report No. 25593-000-G83-GEG-00016-000, Effect of Laminar Cracks on Splice Capacity of No. 11 Bars Based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building. Part 7 of 7; ML15299A143; ML15299A144; ML15299A146; ML15299A147; ML15299A148; ML15299A149; ML15299A150;
References
	L-15-328 25593-000-G83-GEG-00016-000
	Download: ML15299A144 (93)
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Enclosure B Davis-Besse Nuclear Power Station, Unit No. 1 (Davis-Besse)

Letter L-1 5-328 Bechtel Report No. 25593-000°G83-G EG-0001 6-000.

"Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building" (Non-Proprietary) 1114 pages follow

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Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building for FirstEnergy Nuclear Operating Company (FENOC) by Bechtel Power Corporation Prepared by Jave Munshi. PhD, SE, PE, FACl Rita Liano, PE Date 7-30-12 Reviewed by Date 7-30-12_

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Table of Contents 1

Objective.....................................................................................................

5..

2 Scope.............................................................................................................

3 Background.....................................................................................................

6 3.12 STATEMENT OF CONDITION.......................................................................... 6 3.2 SHIELD BUILDING DESCRIPTION...................................................................... 7 3.3 CURRENT LICENSING and DESIGN BASIS............................................................ 8 3.4 EXTENT OF CRACKING IN THE FLUTE SHOULDERS.................................................. B 3.5 EXTENT OF CRACKING OUTSIDE THE FLUTE SHOULDERS........................................ 10

3.6 DESCRIPTION

OF THE LAMINAR CRACK............................................................ 11 4

Technical Evaluation......................................................................................... 12 4.1 INVESTIGATION INTO THE CRACK.................................................................. 12 4.2 STRUCTU RAL INTEGRITY EVALUATION............................................................. 12 4.3 CONFINEMENT....................................................................................... 15 4.4 PROTECTION FROM ENVIRONMENT............................................................... 16 4.5 ADDITIONAL MARGINS OF SAFETY................................................................. 17 4.6

SUMMARY

OF TECHNICAL EVALUATION........................................................... 17 5

Evaluation by Outside Industry Experts.................................................................... 18 6

Testing Program.............................................................................................. 20 7

Testing at Purdue University................................................................................ 21

7.1 Purpose and Scope

.................................................................................. 21 7.2 Experimental Outline................................................................................ 22 7.3 Materials.............................................................................................. 24 7.4 Observed Relationships between Applied Load and Deflection................................. 26 7.5 Crack Development.................................................................................. 31 7.6 Maximum Reinforcement Stresses Attained...................................................... 35 7.7 Conclusions........................................................................................... 35 7.8 Relevance of the Testing to Shield Building....................................................... 37 7.9 Summary of Bechtel Review........................................................................ 46 Bcchtclaend EL affilia*tod companicwhi*.ch :hall not be u:cd, d~closcd, or rzproduccd in any/form.at by 2

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bbUg-J-UUU-U,*3-tW-UUU1U-UUU irags 3 0? 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 8

Testing at University of Kansas............................................................................. 46

8.1 Purpose and Scope

.................................................................................. 46 8.2 Test Program......................................................................................... 47 8.3 Concrete.............................................................................................. 51 8.4 Cold Joint Construction and Crack Simulation.................................................... 51 8.5 Test Results........................................................................................... 54 8.5.1 Beams 1, 2, and 3 with 79-in, splice length.................................................... 55 8.5.1.1 Beam 1.......................................................................................... 57 8.5.1.2 Beam 2.......................................................................................... 59 8.5.1.3 Beam 3.......................................................................................... 62 8.6 Beams 4, 5, and 6 with 120-in, splice length...................................................... 66 8.6.1 Concrete strength................................................................................ 66 8.6.1.1 Beam 4.......................................................................................... 66 8.6.1.2 Beam 5.......................................................................................... 70 8.6.1.3 Beam 6.......................................................................................... 75 8.7 Summary and Conclusions.......................................................................... 79 8.8 What the Testing Means to the Shield Building Situation....................................... 81 8.9 Summary of Bechtel Review........................................................................ 83 9

Summary and Recommendations.......................................................................... 83 10 Quality Assurance............................................................................................ 85 10.1 QA Surveillance at Purdue University.............................................................. 85 10.2 QA Surveillance at University of Kansas........................................................... 88 11 Quality Control...............................................................................................

89 12 References.................................................................................................... 92 Appendix A - Purdue University Test Report................................................................. A-i Appendix B - University of Kansas Test Report................................................................ B-i Appendix C - Quality Assurance Documentation............................................................. C-i Appendix C.1 - Purdue University Quality Surveillance Report......................................... C-i Appendix C.2 - Purdue University Condition Report................................................... C-il Appendix C.3 - University of Kansas Quality Surveillance Report..................................... C-55 REDACTED VERSION

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o' 1 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Appendix C.4 - University of Kansas Condition Report................................................ C-63 Appendix D - Quality Control Documentation................................................................ D-1I Appendix D.1l - Purdue University Inspection Report................................................... D-1 Appendix D.2 - University of Kansas Inspection Report............................................... D-61 REDACTED VERSION

bbWJ-UUU-U5*i-UbU-L-UUU'1bS-UUU I~age b 0? '1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 1

Objective The objective of this report is the following:

(i)

Review the splice testing programs for No. 11 bars carried out at Purdue University and University of Kansas (ii)

Provide technical interpretation of results in relation to the bond capacity of No. 11 bars in the Shield building at Davis Besse nuclear plant (iii)

Provide recommendations for residual bond capacity of No. 11 bars with a laminar cracking of the order of 0.01 inches in the plane of the bar (iv)

Provide necessary QA and QC oversight of testing carried out at Purdue and Kansas.

2 Scope The overall scope of program was to provide technical oversight and third party review of testing carried out at the Purdue University and University of Kansas and provide the necessary QA and QC under Bechtel's Quality Program. This testing is being done in order to evaluate the effect of laminar cracks on the strength of No. 11 lap splices present in the Shield building. Bechtel performed vendor oversight of the applicable activities such as batching of the concrete; placing of the concrete, concrete sample testing, and the concrete bond testing to assure compliance with Bechtel's Quality Program. The detailed scope involves the following:

(i)

Review of Background of Shield Building Design and Observed Cracking (ii)

Initial Technical Evaluation (iii)

Testing Program (iv)

Review of Test Results from Purdue University (v)

Review of Test Results from University of Kansas (vi)

Summary of Test Results (vii)

Recommendations (viii)

QA and QC including calibration of equipment Note that Bechtel Q.A/QC provided oversight of the work at Purdue and Kansas with the intent of meeting Bechtel EDPI 437 deemed to be equivalent to an "augmented quality".

It is argued that test results do not have to be "Q" as the objective is to confirm the bond capacity of reinforcement for the Shield Building using the conventional and well established test methods for bond of reinforcement (Note that tests are standard splice tests to confirm the well established industry information on bond and splice behavior). In that sense this testing is characterized as "confirmatory". Thus, although the test results are not "Q", they are deemed to be a valid input to a "Q" calculation.

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DbL-UUU-Ui*L-tLUIL-UUU1Iit-UUU r-age Ii 0? 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 3

Background

3.1 STATEMENT OF CONDITION On October 10, 2011, a laminar crack was found in the architectural flute shoulder area of the opening being cut through the Shield Building cylindrical wall for replacement of the reactor vessel closure head (RVCH) (Figure 3.1). The crack was found on the vertical side of the opening (left side, looking from the outside), generally along the main reinforcing steel of the cylinder, and extending to across the top (approx 6 feet) and across the bottom (approximately 4 feet) of the opening. After some minor manual chipping along the edges, the crack indication along the left and bottom edges essentially disappeared.

Based on the observation, the crack is considered a circumferential laminar tear and not a radial through-thickness direction crack. Condition Report 2011-03346 was initiated to identify this issue.

Further IR scanning revealed similar cracking in each flute shoulder inspected. Cracking outside of the flute shoulders at the top of the Shield Building wall and local cracking around corners of blockouts for steam line Penetrations 39 and 40 was also detected. Condition Reports 2011-04648 and 2011-04402 were initiated to identify these conditions.

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Y::>i-UUU-UdJ-LU-I--UUU~h-UUU I-age I OT 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 3.2 SHIELD BUILDING DESCRIPTION The Shield Building is a safety related free standing cylindrical shell structure with eight (8) "architectural flute areas" as identified on DBNPS Drawing C-220 (see Figure 3.2). During further discussion within this document, each "fluted area" will be addressed as two built up, or thickened "shoulders". The groove between the shoulders will be addressed as the "flute".

The Shield Building design does not consider the flute shoulder area as providing additional structural capacity beyond that provided by the cylindrical shell or dome. From a loading standpoint on the structure, the Shield Building has been evaluated considering the flute shoulder area as an additional dead load.

Reinforcing within the cylindrical shell consists of meridian (vertical) and circumferential (hoop) reinforcing bars forming a grid on both faces of the shell. On the outside face of the shell, the hoop reinforcing is located outside the vertical bars. The same arrangement is true for the inside face reinforcing (i.e. the hoop bars are the inner most reinforcing layer). Reinforcing for the shoulders consists of vertical bars and horizontal ties conforming to the profile of the shoulder. These horizontal ties are anchored into the shell at both ends. Reinforcing details for the Shield Building can be found on DBNPS Drawing C-l20.

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bbI-UUU-(.J-LiIULU-UUUIIb-UUU P'aged ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 3.3 CURRENT LICENSING and DESIGN BASIS USAR Section 3.8.2.2.2 describes the design basis of the Shield Building as:

Biological shielding Providing for the controlled release of the annulus atmosphere under accident conditions Provide environmental protection for the Containment Vessel (tornado wind &

differential pressure, missiles, etc.)

USAR Section 3.8.2.2.4 & 3.8.2.3.4 describes the load combinations for the Shield Building. Per USAR, the most severe load combination per the ultimate strength design method is (D + L+ E' + TA); while, (D +

To+ E) is the most severe load combination per the working stress design method.

Where D = dead load; L = Live load; E'= Maximum Possible Earthquake; TA=Temperature at Accident; To=temperature at Operating conditions; E=Maximum Probable Earthquake.

3.4 EXTENT OF CRACKING IN THE FLUTE SHOULDERS The hydro demolition of the Shield Building for the RVCH opening revealed a laminar crack within the shoulder of a fluted area (see Figure 3.3). Based upon inspection of this crack at the opening, further examination and investigation was carried out. Construction Technology Laboratories (CTL) was contacted to perform Impulse Response (IR) testing. This methodology has been used to investigate the condition of concrete in a non destructive manner for many years.

Impulse Response method measures the structure's frequency at a specific location and plots this frequency with adjacent reading to obtain any change in building frequency. Any change in frequency within a short span would indicate subsurface indications. IR readings were confirmed by core bores in the indicated area (cracking) and adjacent area (no cracking).

IR readings were performed on all 8 readily accessible flute areas (15 out of 16 shoulder areas, one shoulder was not accessible). Based on this information, it was apparent that the laminar cracking initially identified adjacent to the RVCH opening was not restricted to this shoulder but was a generic issue for all shoulders of the Shield Building. Condition Report 2011-03996 was initiated to identify this extent of condition on the Shield Building cracking.

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~forces on bar adhesion and friction forces along the surface of the bar Figure 3.4 Bond Force Transfer Cantdfnid*-:,!

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bbHL*-UUU-U5*L-LtUI::SUUU15-UUUJ rags 1U 0? 1114 Effect of Laminar Cracks on Spiice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 3.5 EXTENT OF CRACKING OUTSIDE THE FLUTE SHOULDERS Top of Shield Building Wall - Although cracking seemed to be essentially confined within the shoulder area for most of the Shield Building height, IR scanning between Shoulders 8-9, 6-7 and 4-5 (Ref. 21) indicated that cracking may be extending into the outer surface of the shell at the top 15 ft of the Shield Building (~'Above EL 780.) The cracking seems to be very tight (most observed crack width less than 0.01 in with one 0.013 in) and essentially following the outside reinforcement in the cover area, as confirmed by core bores. Condition Report 2011-04648 was initiated to identify this condition.

Main Steam Line Penetrations - IR testing also identified two areas of interest to the right of Shoulder 9 and the left of Shoulder 6 at an elevation of approximately 665 feet. These areas are above the Auxiliary Building roof and appear to be associated with the main steam line penetrations (blockouts) in the Main Steam Line Rooms directly below the roof. Core bores were taken and confirmed that each of these areas had cracks at a depth of approximately 5.0 inches for the area adjacent to Shoulder 9 and 6.5 inches for the area adjacent to Shoulder 6. Condition Report 2011-04402 was initiated to identify this condition.

Further lR testing was performed in the Main Steam Line Rooms in all the accessible areas around the main steam penetration blockouts. These tests identified the areas of potential cracking extended below the Auxiliary Building roof into the Main Steam Line Rooms in an area to the left of Penetration 39 and to the right of Penetration 40. These areas are below the areas identified on the Auxiliary Building roof. The indications in the Main Steam Line Rooms were confirmed with core bores that identified cracks at a depth of approximately 5.0 in the area to the left of Penetration 39 and 6.5 inches to the right of Penetration 40. The left side of Penetration 40 and the accessible areas to the right of Penetration 39 did not show indications of cracking based on the IR results.

As a further investigation of the extent of cracking, testing was performed around the containment purge outlet penetration blockout in the Main Station Exhaust Fan Equipment Room. This testing revealed no indications of cracking. Based on this information, the cracking identified in the Main Steam Line rooms is confined to the localized areas to the right of Penetration 40 and to the left of Penetration 39.

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bbU5-UUU-Ud53-ULUI-UUUlrb-UUU I-age 11 ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building

3.6 DESCRIPTION

OF THE LAMINAR CRACK Based on the IR readings and confirmatory core bores taken, the description of the laminar crack can best be described as follows.

The cracks are mostly confined within the shoulder area but extend out at the top of the Shield Building.

Additional local cracking is observed near the corners of the main steam line penetration outside the blockouts. The depth of the crack varies with the thickness of the shoulder area but generally is shallower at the narrow portions of the shoulder and deeper at the thicker portions of the shoulder.

The horizontal reinforcing bars for the shoulder area consist of #8 bars at one foot vertical spacing.

These horizontal reinforcing bars are anchored into the cylindrical wall by reinforcing bar hooks located at the shoulder ends. From the IR readings performed in this area, core bores taken in this area, and chipping on the left side of the RVCH opening, it can be concluded that these cracks terminate when approaching these reinforcing hooks except at the top of the Shield Building (~~Above EL 780.)

The width of the crack was measured using a crack comparator on as many locations as possible of the core bores that had cracks. Measurement locations within the core bore were selected in areas which appeared not to be disturbed by the boring bit. Photographs of the crack and crack comparator taken using the boroscope indicated that the cracks are very tight, and in most cases less than 0.01 inches with one reading of 0.013 in.

The cracking around main steam line Penetrations 39 and 40 is limited and located near the corner regions outside the blockouts. The crackingat Penetration 39 is localized at the left side of the penetration covering an area of approximately 175 square feet (approx 15 ft diameter). The crack at Penetration 40 is at the top right corner, covers a similar area. Cracks were measured with a crack comparator in the core bore and confirmed mostly to be less than 0.01 inches with one measured at 0.013 in.

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Technical Evaluation 4.1 INVESTIGATION INTO THE C:RACK Concrete that has been exposed to carbon dioxide from the environment can be identified by performing a carbonation test. This test can be used to assess the aging effect of the concrete as it is exposed to the environment. Concrete tests conducted so far have indicated normal carbonation on the surface of the shell and almost negligible carbonation on the interface of the cracks indicating that the concrete crack face examined must not have been exposed to significant amounts of ambient environment (e.g. air).[

]Since the cracks are tight and negligible carbonation on the cracked surface the age of the crack could not be accurately established.

There is no evidence of significant corrosion on the reinforcement.[

] Note that there is no indication of surface cracking significant enough to provide a path for air/moisture to penetrate to the crack surface of interest. Also, where reinforcement bar has been exposed by the investigation there was no evidence of excessive corrosion indicating that cracking is not exposed to the environment.

4.2 STRUCTURAL INTEGRITY EVALUATION Cracking occurs in virtually all concrete structures and because of concrete's inherently low tensile strength can never be totally eliminated. Cracks can occur due to causes such as shrinkage, thermal or other load related situations. Cracks, if sufficiently large, can indicate structural problems; provide an open path to the environment for corrosion of the reinforcing steel; and inhibit a structure from meeting its performance requirements. Control of such cracking due to loads or imposed deformations is generally addressed through the American Concrete Institute (ACI) code requirements by specifying minimum reinforcing steel size and spacing including minimum bonded steel reinforcement and distribution of steel reinforcement.

Typically, cracks need to be repaired if they reduce the strength, stiffness, or durability of the structure to an unacceptable level, or if the function of the structure is seriously impaired. In addition, repairs that improve the appearance of the surface of a concrete structure may be desired from an aesthetic standpoint. Observations such as spalling, exposed reinforcement, and rust staining can be an indication that the reinforced concrete structure has deteriorated.

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bbU-UUU-U.di-USI-U-UUUIb-UUU I--sage 1i or 11"14 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building

1.

The laminar cracks are located adjacent to the reinforcing steel (hoop and vertical steel) in the shell, potentially creating a separation between the cylindrical shell and the architectural shoulders which were poured monolithically during construction.[

2.

Only one instance of the sub-surface laminar cracks propagating to the surface of the structure has been identified which was above the construction opening. This area was affected by the demolition activity and is not thought to be representative of the general condition. No indication of bulging, spalling, or rust stains exist which would indicate surface connection and degradation of the laminar crack surface. Initial lab testing of the excavated crack surface would also indicate that the area was not subjected to the atmosphere.

3. The laminar cracks have been well identified through IR and core bores and are known to be tight and of hairline nature (mostly within 0.01 in with one crack 0.013 in).[

4.

No surface rust stains exist on the outside surface of the Shield Building,[

]The steel reinforcing was observed to have generally light corrosion or no corrosion at all with no areas of reinforcing exhibiting loss of material.

5.

The #8 reinforcing steel tie bar; spaced 12 inches on centers tie the flute shoulder to the cylindrical shell and provides substantial confinement for the outer shell reinforcement. These horizontal reinforcing tie bars "anchor" the shoulders to the cylindrical shell limiting the width of the laminar crack.[

] For #10's and #11's reinforcing steel the minimum height of the deformation needs to be 0.064" and 0.071" respectively. Since the laminar crack widths are tight (generally < 0.01"), this crack will not adversely affect the load transfer between the steel and concrete.

6.

The development length or lap splice length is a Code value (in inches) used to ensure that the tensile forces from one reinforcing steel can be adequately transferred through the concrete to the adjacent reinforcing steel. Development and splice lengths per the AC! code for ultimate strength n...ctd~-y..................... :............. p crmLz+c n. Al! rih rsczcr d.

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bbW;5-UUU-UUS*-UbU::L-UUUIU-UUU w~ags 140?T 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building design were originally developed to achieve strengths beyond bar yield. The calculated reinforcing stresses are far below code allowable values and therefore full development length or splice length of the bars is not required for actual load transfer. The maximum stress in reinforcement at the critical section due to the controlling design basis loads is only 40% (a margin of 2.5, per Calculation C-CS5-099.20-046, "Evaluation of Shield Building for Permanent Condition") which indicates that actual expected bond stress demand will be significantly less. Furthermore, strength of in-place concrete is much higher than specified strength of 4000 psi at 28-days. The 90 day concrete strength was on average greater than 6000 psi which increases with time. Since concrete strength has a direct impact on the bond strength, this adds extra margin to the available bond strength.

7.

The force transfer between the reinforcement steel and concrete is well established in ACI 408R-03 (Ref. 1). Per Ref. 1, the transfer of forces from the reinforcing steel to the surrounding concrete occurs by a combination of chemical adhesion, frictional at the interface and mechanical anchorage/bearing of deformed lugs (ribs in the reinforcement), (Figure 3.4). After the initial slip between the concrete and reinforcing steel, most of the force is transferred by mechanical bearing between the reinforcing steel ribs and the concrete. (Figure 3.4).[

Ref. i also indicates that friction also plays an important role in load transfer.[

8.

The purpose of the reinforcing steel cover is to transfer the force between reinforcement and concrete, confinement, and protection for the reinforcement from the environment. There is no appreciable effect on these functions as a result of the cracks.

9.

Cracking that has been observed near the main steam line penetrations (Penetrations 39 and 40) is local and limited. The cracking is tight and reinforcement is continuous through the cracked region and remains well anchored outside of this region.[

10. Cracking that extends approximately 20-30 ft into the shell at the top of the Shield Building ("'Above EL 780) is very tight and follows the outside rebar.[

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bbYi-UUU-U~bi5-U;--UUUIh-UUU i-'age lb ol 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 4.3 CONFINEMENT As indicated above, the architectural flute shoulders are not credited for any structural purpose but merely serve as an architectural feature and provide additional cover to the Shield Building reinforcement. With laminar cracking near the reinforcing steel mat, confinement of the shell reinforcement will be addressed. The architectural flute shoulder is connected to the main Shield Building via #8 horizontal reinforcement bars spaced every 12 inches vertically.[

]Per Refs. 3-7, the crack interface shear capacity is directly proportional to the normal force acting on the surface which is supplied by the reinforcement crossing the crack (2 - # 8) in this case.[

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_-U 3-UUUIW-UUU page m( Of 11 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building For concrete outside the shoulders, visual observations indicated no spalls, popouts or staining of concrete. The hammer sounding of concrete did not reveal any indications of loose concrete on the surface.[

4.4 PROTECTION FROM ENVIRONMENT As indicated above, flute shoulders serve as additional concrete cover to some of the main shell reinforcement. The cracks inside and outside the shoulder regions are all tight (generally < 0.01 in with one crack 0.013 in) and do not seem to have path to the surface for air/moisture migration. There is no evidence of noticeable corrosion on the reinforcement near the cracks.[

Two core bores into the Shield Building cracks were transported to an off site testing laboratory at CTL for further investigation. These tests indicated the following (Ref. 19):

CTL report indicates a carbonation depth of 5-8mm on the surface and no carbonation on the fracture surface. These tests indicate that the cracking occurred after the initial and final set of the concrete; the exact time could not be established.

Data from the CTL report indicates that chloride content of concrete in the Shield Building is insignificant. Since at least 1989, ACI 318 has limited the 'water-soluble' chloride content in severe service conditions (concrete exposed to moisture and an external source of chloride such as deicing chemicals or seawater) to 0.15% of the cement content of the concrete. The highest chloride content value measured was 0.090% (acid-soluble) and 0.037% (water-soluble). Thus, the criteria for a far more severe service condition have been met even if the weight of the coarse and fine aggregate in the concrete is ignored.

CTL laboratory test report indicates that the concrete was in good condition.

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-'age i1 a T 1114 Effect of Laminar Cracks on Spiice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 4.5 ADDITIONAL MARGINS OF SAFETY The following information details additional margins of safety NOT credited in the technical assessment described above. These additional safety margins provided further assurance that the Shield Building will perform its USAR described design basis functions.

a) The design bases analyses considered the ASTM A-615 specified minimum yield strength of the reinforcing steel of 60,000 psi. The Certified Mill Test reports (CMTR) for the reinforcing steel show minimum yield strength of 66,100 psi, which represents an 10.17% increase in the steel capacity.

b) The design compressive strength for the Shield Building concrete is 4,000 psi. Concrete Pour Test Reports document a minimum f'c = 5730 psi (below grade) and 5836 psi (above grade) respectively.

4.6

SUMMARY

OF TECHNICAL EVALUATION Condition Reports 2011-03346 and 03996 document the condition of the Shield Building due to the cracking in the architectural "flute shoulder" portions of the structure. Condition Report 2011-04648 documents cracking observed in top 20 ft of the Shield Building. Condition Report 2011-04402 documents the condition of cracking in the main steam line Penetrations 39 and 40. The extent of these conditions has been thoroughly investigated using an "Impulse Response" technique to identify potential cracks and core bores into the structure to obtain the location (depth)/extent of the cracks.

Based on this technical evaluation and detailed calculations, NRC issued a confirmatory action letter subject to root-cause evaluation and testing program to be conducted to evaluate the bond capacity of No. 11 hoop splices in cracked regions. Sections 6-8 discuss the testing program and the results in detail. Condition Report 2011-03996 documents the cause for this condition and any required corrective actions.

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i-UUU-id*;--i-U-UUUIb-UUU r'age 1li OT 1114 Effect of Laminar Cracks on Splice Capacity of No. 12 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 5

Evaluation by Outside Industry Experts Two welt known industry experts Prof. Mete Sozen of Purdue University and Prof. David Darwin of University of Kansas were retained to evaluate the structural significance of laminar cracks in the Shield building. The following presents the summary of their evaluations.

TO:

Or Javeed Munsh-e Bechtel Corporation FROM-Mete A. Sozen, S. E. (Ilinoist Mete A.

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30 MI rv, LaaeteN 470 Sozen 765-494-2186 RE:

Slhield Building,, Davis-Besse Nuclear Plant DATE:

28 October 2011 Thank you for lettmin me see and comment on yor draft report *Technicai Assessment Report No.

25539-200-COR-000G0-0001, Structural Evaluatio of Shield Building, Dalvis-Besse Nuclear Plant,"

I understand that llatmiar cracklng Wast discovered in the reinforced concrete shell buili~ng of the Davis-Bess Nuclear Plant These cralcks occurred in the shoulder regions ext*ending[ approimmately over the circumferential length corresponding to the part of the shell thickened by the presence of the shoulder.

Vertically, the cracks were sensed to extend from bottom of construction opening to approximately 40 ft above the current opening in the shieldl.

I agree with your inference that the laminar cracks must have been in existence soon after the construction of the shell and, considerqig their current widts on the ordler or 0.003 to 0.007 in,. must have been dormant throuJghout the life of the structure.

I also agree with your observton that the cracks were not randomly initiated They must have been caused by stress and strain conditions associated wit the thickening of the shell. For a structure that has been an place for four decades, there is no ned to discuss the effect of these cracks on its day-to -

day functioning. As would be concluded from the explicit architectural functio of them shoulders, the shield structudre can respond to its daily structural demands just as it was intended to do in the originl design.

The impact of your report would be strengthened b~y a detailed discussion of the circumferentmia-bar splices that coincide with the laminar cracks. A measure of the maximum deman.d on these particular splices related to rare design events such as earthquake and high-velocity impact would make your report stronger.

Pleas let me know ifvyou have any questions on the above remarks or if you would like me to comment on any special secti*ons of your report.

18 REDACTED VERSION

b*-UUU-(,dJ-ULUIL-UUU1b-UUU I-'age 19 Oa" 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Review of Tecuial As~sesient Report No: 25539-200-COR-OOO0(OOO*l Sru~ctural Evaluado of Shil Building Davi-Bees Nuclear Plant Reiw By: David Darwin In addition to reviewmng the sujc docin~ezW I had the opportunit to have two telephone conversations with Javeed Mutnsl and to study drawing C-i1 0 of the SheldBidn along. with sketches showing the location of die crack within the architectural flute shoulder.

Thsreview includes commnents on individual sections of the technical assessment report followed by overall observations.

Smummary Overall. I think that the presne of the laminar cracks has the potential to redxuce the bond strength of the bars because the cracks ae in the same plane as the renocn stel With that sai the loca redution in bond stength as of little concern unless bars are spliced within the cracu_.k region The principal pups of reinforcing bars is to provide tensile strength and that tensile strength can be pro~ided as long as th bars are anchore to the concrete. If the lap slces are located outside the crack region then., at most, there wall be a sinaI! discntnut an strain between the steel aixd the conrt. but the steel wil stall serve its intended ~xpm1os Thus, if the splices an the circumferential steel are located outside of the crack region.. I agree with and support the conclusion that "'no mode change or operating resinctions" are requir'ed for this condition Based on my. discussion with Ir Manh, at is not clear if any circimiferentral-bar splices are located within the crack regions.

I. thrfr, recommend that thi point be investgated further In addition. I recommend that the locatio of the vertical bar splices be investgted to determine the number and location of these splices wilthin the crack regions. The capacity of the vertcal-bar spies mn the crack regions should be invetigated based on aprpite assmtn tied to the location of the bars within these regions (such as low or no cover) and the degree of coanfement provide by the rcuiferetia bar crossing these splices In summary, both industry experts agreed with technical assessment presented in Section 4 that the Shield building is robust enough not to be impacted by the observed laminar cracking in any significant way. However, both experts indicated that it would be worthwhile to confirm the effect of laminar cracking on lap splices, particularly for the circumferential (hoop) reinforcement as highlighted in the above excerpts. To pursue this, a detailed test program was established as discussed in Section 6.

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bbW6-UUU-UU63-U51--UUUIU-UUU I~age ZU 0oTh1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 6

Testing Program The initial technical evaluation discussed in Section 4 and S identified that the only issue of any structural significance was the possibility of having lap splices in the areas of laminar cracking. With cracking identified in most shoulder regions, two steam line penetrations areas and in top 20 ft of the Shield Building outside the Shoulder region, it is possible to have the following lap splices in cracked regions:

1.

79 in lap splices for vertical No. 11 bars in shoulders and outside shoulders (in two steam line penetrations areas and in top 20 ft)

2.

79 in laps for the hoops below El 780 which can fall in shoulder regions or in steam line penetration areas

3.

120 in lap splices for hoop reinforcement above El 780 which can fall in shoulder regions or outside shoulder regions Note that No. 11 vertical bars are well confined by the outer hoops and additional concrete cover, especially in the shoulder regions.[

To investigate the effect of laminar cracking on force transfer capacity of No. 11 bars in splice regions, the following test program was established to cover the above mentioned worse case situations:

A: Testing of.79 in lap splice for No. 11 bars with 3-5 in cover B: Testing of 120 in lap splice for No. 11 bars with 3-S in cover In order to ensure a reliable set of results, two independent and well known industry experts, Prof. Mete Sozen of Purdue University and Prof. David Darwin of University of Kansas were engaged to carry out a series of tests independently. The test program involved the following:

Purdue test program (see Appendix A) involved 6 beams with 79 inch splices and 6 beams with 120 in lap splices. In order to simulate laminar cracking in the plane of the bars, the splices were placed at 6 in spacing with a side cover of 3 inches. The laminar crack of 0.01 inches or more was initiated with a prior loading of up to yield and subsequent unloading.

Kansas test program (see Appendix B3) involved 3 beams of 79 in splices and 3 beams of 120 in splices.

The first beam with t9 in splice was cast monolithically as a benchmark. In order to simulate laminar cracking in the plane of the bars, the remaining 5 beams were cast in two lifts one up to the center of the bars and the second pour the next day to the complete the casting to top of the beam. This process allowed formation of a standard cold joint in the plane of the bars which would serve as a weak plane and help simulate/produce a laminar crack during testing. The reinforcement cover of 3 in was maintained both on the sides and to the top surface of the beam. The laminar crack of 0.01 inches or larger was initiated in the specimen by prior loading and subsequent unloading.

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bbi*-UUU-Gbi1-UW-L-UUU1Ud-UUU I-'age Z1 ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Both Purdue and Kansas beams involved 2 splices side by side with 6 inches of spacing which presents a rather aggressive condition and likely to give lower bound capacity results. Note that splices in the Shield building are actually staggered with spacing of at least 12 to 24 inches. Also, the splices in the Shield building conform to the curvature of the building which would provide additional confinement effect not included in the straight beam tests.

In both test programs at Purdue and Kansas, an effort was made to simulate the concrete mix of the Shield building to the extent possible. Purdue used a similar mix and aggregate size. Since it was practically impossible to exactly match the concrete given the age of the plant, every effort was made to test at relatively lower (conservative) compressive strength and tensile strength values to produce conservative bond capacity values. Note that compressive and more importantly, tensile strength of concrete are recognized to be the key parameters of influence for bond strength of reinforcement in concrete. Moreover, Kansas tests were carried out at an age of only 7 days which resulted in lower bound compressive and tensile strengths thus giving very conservative or lower-bound results.

The average 28 day compressive strength from original construction of the Shield building was 5836 psi.

The average compressive strength of in-place concrete tested using cores taken during the Shield building evaluation in 2011 was 7571 psi. The corresponding tensile strength of in-place concrete was determined to be 918 psi.

7 Testing at Purdue University Bechtel provided the technical oversight and QA and O.C of tests at Purdue University. This Section provides review of the testing program and the results. Note that many of the sections here are reproduced verbatim from the relevant sections of the Purdue report (Appendix A) to avoid any misrepresentation or mischaracterization of the test program and the results. Summary of Bechtel review is presented at the end of this section.

7.1 Purpose and Scope

The object of the investigation reported was to study the effect of cracks on the strength of lapped splices of #11 Grade-60 reinforcing bars embedded in concrete. The cracks in question are laminar cracks, or cracks that lie in a plane that coincides with or is parallel and close to the axis of the spliced bars.[

The test specimens were of a type used usually for testing splices (Figure 7.1). They were large-scale girders with rectangular sections. They were simply supported at two points equidistant to the center of the specimen and loaded at two points, outside the reactions, also eqiuidistant to the center of the specimen. A total of 12 specimens were tested under static loading, test durations ranging from three to 21 REDACTED VERSION

b~bY3-UUU-Ubi-ULUIL-UUUlrb-UUU M~age 22 07 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building six hours. Six of these (Series A) had 120-in splices (nominally 85 bar diameters) and the remaining six (Series B) had 79-in splices (nominally 56 bar diameters).

In each of series A and B, loading was applied continually to failure in two test girders. In the remaining four, loading was first carried to or beyond yielding. Then the load was reduced to zero to be increased again until failure occurred.

Concrete strength was not a planned variable in the program. For the test girders with the 120-in splices concrete strength, determined using standard 6x12-in. cylinders, varied from approximately 5000 to 6000 psi. For those with 79-in, splices, it varied from approximately 4500 to 5500 psi (Table 7.1).

Yield stress and strength of the #11 bars were determined to be 66 and 103 ksi, respectively. Limiting strain, measured over a gage length including the part of the bar that fracture, range from 14 to 19 %

(Table 7.2).

In addition to load and deflection measurements, crack patterns and widths as well as longitudinal and transverse deformations of the test girders were recorded. Failure characteristics of the test girders were captured by a high-speed camera operating at 5,000 frames per second. Detailed information on those topics is provided in the appendices of this report.

The observed behavior of the test girders is described in terms of measured load-deflection relationships, recorded crack-width developments, and calculated reinforcement stresses.

7.2 Experimental Outline The test set up for the 120 in and 79 in. splices are shown in Figures 7.1 and 7.2, respectively. Each girder in series A had a total length of 39 ft.The lap splice length was 120 in. as indicated in Figure 7.1.

Ends of the splice were each at three ft from the closer support. The cantilevered portions of the girder measured 11 ft 6 in. in length. Loads were applied on each cantilever segment at 10 ft from the support.

Each girder in series B had a total length of 34 ft 4 in. Length of the lap splice was 79 in. and was located as shown in Figure 7.2. The ends of the splice were each at three ft from the closer support. The cantilevered segments of the girder were 10 ft 10 14 in. long. Loads were applied on each cantilever segment at 9 ft 8 14 in. from the supports.

The test specimen configuration was based on the following considerations:

The first was to have more than one lap splice to simulate the interaction of adjacent lap splices. Two splices were used.

The second was to have a minimum cover of 3 in. that translated to a clear distance of 6 in. between the two splices and led to a cross-sectional width of (4x3+4x1.41) in. The width of the girder section was made 17 5/8 in.

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22 REDACTED VERSION

bbJ-UUU-LbL*-LSI:U-UUUlfb-UUU I-age 2Li OT 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building The third was to produce a bursting crack in the horizontal plane that would intersect both splices. To increase the probability of a bursting crack in the horizontal plane and given that cracking tends to occur in the direction in which cover is smaller, the desired minimum side cover of 3 in. was used on the outside bars of the splices and a cover of 5 in. was used on top.

The loads were applied at each loading stage of 6, 12, 18, 24, 30, and 36 kips. Above 36 kips, load increments were determined by measured displacement. Four of the specimens in series A were subjected to loading in increments of 6 kips to yield and then to a mid-span deflection of 0.9 in, unloading, and reloading to failure. In series B, the four specimens were loaded to 36 kip in 6-kip increments, unloaded, and then loaded to failure.

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23 REDACTED VERSION

bbiL-UUU-(Ut-UI=-UUUUtIU-UUU I-'age Z4 01' 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building t r,.t se*B-8 SmA-A Figure 7.3 Cross-Sectional Dimensions of Series A and B Girders (From Appendix A)

Load and deflection measurements were obtained continuously in each test. Deflections were also measured by dial gages whenever loading was stopped. An Optotrak tracking system was used to measure deformations of the girder after each load increment until there was a threat of failure. Crack patterns and widths were recorded up to a loading stage which was considered to be safe for those making the measurements. This limit, stated in terms of applied load, varied from 30 to 41 kip. Still photographs of the test specimen were taken at all loading stages.

7.3 Materials Concrete Concrete used in the specimens was mixed and delivered to the laboratory by Irving Materials Inc. of West Lafayette, IN. Each girder and related cylinders were cast using concrete from a single truck. The mix proportions by weight were Component Weight of Component!/ Weight of Cement Cement 1

Fine Aggregate 2.4 Coarse Aggregate (max. size = 11/44 in.)

bEi3-UUU-GS*J-UWI:L-UUUI*b-UUU H~age Zb Ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Target air entrainment was 5%. As concrete was being placed, temperature, air content, and slump of the mix were measured. Air temperature was recorded. Target moist curing was seven days but the curing period was reduced for some specimens as a result of early cylinder tests that indicated high strength. Detailed information for each casting is included in Appendix A.

The opening of bursting cracks depends on the relationship between the tensile strength of the concrete and the intensity of bond stress that creates the bursting stresses. Because it was known that in the DB shell the compressive strength of the concrete exceeded 6,000 psi, the tests were designed to have a concrete strength at time of tests not exceeding 6,000 psi.

Steel All #11 reinforcing bars came from the same heat. Stress-strain properties of the bars are included in Appendix A.

Table 7.1 Concrete Concrete Concrete Test Girder Cmrsie Splitting Cast Tested CylinderiveLap Length Designation Strength Cyidrin.

Strength ppsi Al 17 April 2012 4 June 2012 5270 480 120 A2 27 April 2012 1iJune 2012 6030 500 120 A3 17 April 2012 30 May 2012 5890 480 120 A4 24 April 2012 8iJune 2012 5110 440 120 A5 24 April 2012 7iJune 2012 5240 440 120 A6 24 April 2012 5iJune 2012 5490 450 120 B1 10 April 2012 10 May 21012 4460 450 79 B2 10 April 2012 23 May 2012 4800 480 79 B3 10 April 2012 21 May 2012 4780 420 79 B4 30 April 2012 14 May 2012 5460 490 79 B5 30 April 2012 17 May 2012 5260 480 79 B6 30OApril 2012 25 May 2012 5230 450 79 Con fidrntkil ~3 2012 Rccht~E Cornorit~nn. ContnJn~ c~nfidr~rtit-jl mdA'~r nrnnricfnr-.z infnrmntinnfn La..

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-'age 2b Or 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Table 7.2 Reinforcement Bar Designation

11 Nominal Diameter, in.

1.41 Nominal Area, in2 1.56 Nominal Perimeter, in.

4.43 Unit Weight, lbf/ft 5.31 Yield Stress*, ksi 66 Strength*, ksi 103 Limiting Strain in 8 in., %

14,18,19

Note: means from tests of three coupons 7.4 Observed Relationships between Applied Load and Deflection Figures 7.4 and 7.5 contain the measured load-deflection relationships of the 12 test girders. The reported deflection is the relative movement (deflection up considered to be positive) of girder mid-span with respect to the supports. The reported load is the load applied near the end of the cantilever section.

All load-deflection curves measured had two common characteristics: (1) Yield moment of the section was developed after appearance of laminar bursting cracks at low loads and at zero load in the case of the reloaded girders, and (2) all girders tested demonstrated a definite capability to maintain strength with increase in deflection beyond yield. The latter characteristic satisfies the traditional demand of professional consensus documents for cases where the loads may be dynamic and/or not known closely.

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Yi9-UUU-U*i-UE-U-UUUlb-UUU h'age 2,' oT 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Figure 7.4 Force Deflection of A Series Specimen (120 in laps) Tested at P~urdue (From Appendix A)

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bbX;i-UUU-GdJi=-ULUIL-UUU1b-UUU I-'age 2kJ Or 11 14 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building It is of interest to note that the overall behavior of test girders A1, A4, AS, and A6 that were loaded, unloaded, and reloaded to failure differed very little from those of A2 and A3 even though the failures of these four girders were initiated by bond. In fact one could not identify easily the ones that were reloaded by studying the shapes of the envelope curves. Girders in series A all had the same yield deflection (approx. 1/2/ in.) and similar maximum mid-span deflections (ranging from 1.4 to 1.8 in.).

Inspection of Figure 7.5 yields similar conclusions for the responses of girders of series B. For this series, the yield deflection was approximately 1/3 in. and maximum deflection ranged from a little below 0.5 in.

(Girder Bi) to above 0.6 in. (Girder B6). The range in concrete strength from 4460 to 5460 psi would not be expected to have a perceptible influence on the yield deflection. The three test girders,with relatively low concrete strengths (Girders Bi, B2, and B3) did have the lower maximum deflections but the maximum recorded value of 0.47 in. for Bi with a concrete compressive strength of 4460 psi was not that much lower than that of B5 that had a concrete compressive strength of 5260 psi (0.55 in.)

Maximum applied loads for series A ranged from 42 to 44.1 kip. This range was from 39.7 to 40.6 for series B. In fact, on the basis of maximum applied load alone, it is hard to discriminate the results for series B vis-a-vis those of series A.

It is worth noting that results of both Series A and Series B tests showed remarkable repeatability and consistency of results as shown in Figure 7.6 which is very reassuring in terms of expected performance.

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bbUJ-UUU-GdJ-ULUIL-UUUIb-UUU t-age *iU Ot 1 114 Effect of Laminar Cracks on Spiice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 45 40 0.

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Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 7.5 Crack Development Changes in crack patterns and widths were recorded in detail and are reported completely in Appendix A. Observed development of flexural crack patterns and thicknesses was consistent with what is normally expected in reinforced concrete beams responding primarily to flexure. Figure 7.7 shows a typical pattern of cracking observed. The flexural cracks occurred at a spacing of approximately twice the top cover or ~20 in. It is also seen that the cracks near mid-span did not reach as far towards the compressed edge of the girder as the ones near the support. This was an indication that the lap splice was effective. All four bars were participating in load resistance. In the range of linear response to flexure, the neutral axis depth increases with increase in the reinforcement ratio. Even though the total tensile force in the reinforcement at mid-span was comparable to that at the support, the amount of reinforcement was twice as much. This was reflected in the relative lengths of the flexural cracks at mid-span and at the support Figure 7.7 Typical Pattern of Flexural Cracks and Bursting Cracks Highlighted Resulting in Laminar Cracking (From Appendix A)

Cracks of primary interest in this study are those caused by the bursting stresses related to high bond demand.

Figure 7.7 shows the effect of bursting cracks as highlighted in red that traverse the beam surface horizontally at or near the level of the reinforcement. A descriptive metaphor for their formation is provided by visualizing the bars as thin walled pressurized tubes embedded in concrete as illustrated in Appendix A. The internal pressure causes circumferential tensile stresses in the concrete around the tube that decrease with distance. The crack is initiated in the weakest plane which corresponds to the plane resulting in the minimum cover. The crack is initiated in the immediate surface of the tube and progresses out as the pressure in the tube increases. It is also relevant to note that a bursting crack can exist next to the reinforcement but not be visible on the surface of the girder.

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--age 3Z 0? V114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building The projection of this metaphor to the test girders suggests that the bursting crack would occur on a horizontal plane intersecting the reinforcement and that the surface width of the crack is likely to be smaller than its width next to the spliced bars. It also provides an introduction to develop an understanding of the bond phenomena observed in the test girders by combining three sets of measurements: (1) Longitudinal strain distribution at reinforcement level, (2) vertical deformation of the girder, and (3) distribution of widths of the bursting cracks. These are presented in Appendix A.

The longitudinal-strain data show that there was a dominant pattern in strain distribution along the splice. In the first loadings, rapid change in strain occurred primarily in the outer 20-in, segments of the splice. Optotrak measurements identify that the critical segments of the splice where most of the force transfer from bar to bar took place were the outer 20-in, lengths.

The results confirm that the regions of relatively large vertical deformation occurred in the outer 20 in.

of the splices for both the 79 and 120-in, splices.

Lacking a generally accepted index value such as the intensity scale used for earthquake damage to organize and define data susceptible to scatter, the main generalization that can be made about crack-width observations made in this study is that measurable (0.005 in. or more in thickness) bursting cracks of limited length (six to 12 in.) occurred at low loads on the order of one fourth of the maximum load resisted. Bursting cracks reached levels in excess of 0.1 in. at loads approaching the maximum load. At such levels of load, bursting cracks meandering along the level of the reinforcement covered virtually the entire test span.

Bringing together the observed data from measurements of longitudinal strain, vertical deformation, and crack-width distribution, it becomes clear that most if not all of the force transfer in the splice took place in regions with bursting cracks. With that knowledge, the mean unit bond strength evaluation on the basis of assuming the bond stress to be distributed uniformly along the splice would seem irrelevant.

However, to place the results obtained in the realm of common practice, unit bond stresses were calculated. The mean unit bond strength obtained from the tests was 3.14/ff for the 120-in splices and 4.4+,f for the 79-in splices. The decrease in mean bond strength with increase in length of splice is consistent with the observation that most of the stress transfer through bond occurred within approximately 15 bar diameters from each splice end. It is of interest to note that the ratio of the observed mean bond strength, 0.70, is close to the ratio of the splice lengths, 0.66.

Figures 7.8 and 7.9 show the magnitude of the recorded maximum crack width and vertical deformation measured with the Optotrak along the splice lengths of Specimen A and B, respectively. The results show good correlation between the crack width and the vertical deformation. The results also show that cracks well exceeded the crack width observed in the Shield Building, which is generally less than 0.01 in with one 0.013 in.

Yi-UUU-Udi-UIU-UUU1b-UUU l-~age ~.i Ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Test Girder A-i (41 kip)

Test Girder A-2 (41 kip) 0.1 5.

.6 Distance to Midspan [in.]

OSVertical Deformation [Gage Length = 26 in.]

00 Max. Measured Crack Width Distance to Midspan [in.]

SVertical Deformation [Gage Length = 26 in.]

00 Max. Measured Crack Width Test Girder A-3 (36 kip)

Test Girder A-4 (40 kip) 4)

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00 Max. Measured Crack Width 50 Figure 7.8 Correlation of Vertical Deformation with Crack Width for Specimen A (120 in splices)

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00 Max. Measured Crack Width Figure 7.9 Correlation of Vertical Deformation with Crack Width for Specimen B (79 in splices)

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bb;-UUU-US.,-ULUI*-UUUlrb-UUU H'age i*b ot 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 7.6 Maximum Reinforcement Stresses Attained As documented in detail in Appendix A maximum tensile stresses achieved at the ends of the splice were computed based on the moment at the end of the splice and cross-sectional properties of the test girder. The calculated stresses are shown in Table 7.3.

The minimum tensile stress attained in the reinforcement at the end of the splice was 69 ksi (Test Girder B2) and the maximum was 80 ksi (Test Girders A2 and A3)

Table 7.3 Summary of Results Test Girder Concrete Concrete Lap Maximum Maximum Maximum Calc.

Calc.

Designation Splitting Compressive Length Applied Moment Moment Reinf.

Reinf.

Strength Strength Load at at Stress Stress (Tensile)

Support Splice at at End Support Splice End psi psi in.

kip kip*ft kip*ft ksi ksi Al 480 5270 120 43.5 481 470 81 79 A2 500 6030 120 44.1 487 476 82 80 A3 480 5890 120 44.1 487 476 82 80 A4 440 5110 120 43.3 479 468 81 79 A5 440 5240 120 43.4 480 469 81 79 A6 450 5490 120 42.0 466 455 78 77 B1 450 4460 79 39.5 425 417 72 71 B2 480 4800 79 38.9 419 419 71 69 B3 420 4780 79 39.7 427 419 72 70 B4 490 5460 79 39.7 427 419 71 70 B5 480 5260 79 40.6 436 428 73 72 B6 450 5230 79 40.6 436 428 73 72 7.7 Conclusions Two girders in each of Series A and B were loaded monotonically to failure.

Four girders of series A were loaded to a deflection of 0.9 in. (approximately twice the yield deflection) and the unloaded to be reloaded to failure. Four girders of series B were loaded to yield, unloaded and reloaded to failure.

Strain measurements and observed distribution of bursting (laminar) cracks confirmed that most, if not all, of the force transfer from one bar to another occurred in the end of the splice over a length of I

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b~ti;-UUU-*Udi-ULGI-UUUlrb-UUU Irage 3r5 oT 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building approximately 20 in.(<15 bar diameters). In this region of high bond-stress demand, cracks paralleling the spliced bars opened at as low as one fourth of the maximum load in all girders tested. In the four specimens that were unloaded and reloaded, the measured maximum residual widths of these cracks at zero load were 0.08 in for series A and 0.015 for series B.

In both series, laminar bursting cracks formed at a fraction of the yield load in all test girders. The difference between the strength and behavior of the girders loaded directly to failure and those unloaded after reaching or exceeding yield and reloaded was negligible. The existence of laminar cracks at the beginning of loading did not change the strength of the splices. The ratio of the limiting deflection to the yield deflection was approximately three in Series A with 120-in, splices and two in Series B with 79-in, splices.

As listed below and illustrated in Figure 7.10, maximum reinforcement stresses in the test girders loaded to failure after having been loaded to develop bursting (laminar) cracks and reloaded differed negligibly from those in girders loaded monotonically to failure.

Reinforcement Stress Developed by Splice, ksi 9O 80 70 60

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36 REDACTED VERSION

bb*-UUU-(idL-*5-ULU-UUUIb-UUU l-age ;i1 ot 11 14 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 7.8 Relevance of the Testing to Shield Building The following presents the memorandum from Prof. Sozen on the application of the testing to Shield building.

TO:

Dr. Javeed Munshi FROM: Mete Sozen RE:

Relevance of The Lap-Splice Tests at Bowen Laboratory to The DB Shell DATE:

22 July 2012 In response to your request, please find below my interpretation of the relevance of the conditions of the splices in the Test Girders Al-A6 and B1-B6 to those of the lap splices in the DB shell. The test results have been described in the Bowen Laboratory report submitted to First Energy Nuclear Operating Company on 12 July 20121. This note has been prepared to provide more detail on some aspects of the design of the test specimens and to summarize the results most relevant to the safety of the DB Shell.

On the basis of results obtained in Bowen Laboratory and the observations of the cracks in the DB Shell, it is certain that the lap splices in the DB shell are as good today as they were intended to be at the time of their design. In my opinion, their most important positive property with respect to the design demands is that there is every indication that they are capable of sustaining their maximum-load capacity after yielding. The tests results show that the lap splices in the DB Shell with the observed laminar cracks have requisite toughness as well as strength.

Selection of Properties of Test Specimen The splice tests carried out in Bowen Laboratory were designed to investigate the strength and toughness of lap splices of #11 bars in a reinforced concrete cylindrical shell containing laminar cracks with a maximum width of 0.01 in. running along the axis of the spliced bars. The splices in the structure, connecting the outer ring reinforcementS, were staggered and the cracks did not extend along the entire length of every splice. Two different lengths of lap splices were used in the structure: 79 in. and 120 in.

The selected target for concrete strength in the test girders was 6000 psi or below.

The overall experimental plan included six specimens for each length of splice. It was also decided during the initiation of the experiments to load two of each type of specimen continually to failure and to load four specimens in each set first to yield, unload, and then reload to failure.

1 M. A. Sozen and S. Pujol, "An Investigation of The Effect of Laminar Cracks on Strength of Unconfined Lap Splices of #11 Reinforcing Bars," A Report Submitted to First Energy Nuclear Operating Company, Oak Harbor, OH, 12 July 2012.

37 REDACTED VERSION

bD*-UUU-UJSJ-(,tc:5-uUUUIh-UUU l'age ib* Ot 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Factors considered in determining the properties of the test specimens are summarized below.

The Test Specimen In keeping with engineering tradition for determining capacity of lap splices, the selected test specimen was patterned after the one used by Kluge and Tuma (1945) and adopted in most engineering investigations of lap splices (Figure 7.11). Each test specimen comprised a central test span where the lap splice was located and two cantilever spans for applying the desired moment at the interior supports. The dimensions shown in Figure 7.11 refer to those in the Kluge-Tuma specimens. Because the splices in the DB Shell involved #11 bars, the overall dimensions of the Bowen Laboratory tests were as shown in Figures 7.12 and 7.13.

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-- I Figure 7.12 The radius of the shell in question is 72 ft. The longer splice used was l0oft. Over a circumferential distance of 10 ft, the offset of the arc from the chord would be less than 3 in. The effect of the curvature radius on the response of the splice was considered to be positive but of a magnitude that could be ignored. The test specimen was designed to be the commonly used straight beam specimen. Because a

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bbiL-UUU-i5J-51Ci.-uUU~th-UUU I-'age 3*J Ot 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building total of 12 specimens were to be built and tested, the transverse reinforcement in the shear spans was provided by external stirrups that could be reused.

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Test Saris B Figure 7.13 Staggered Splices To determine a reasonable lower bound to the capacity of the splices, the first decision in designing the experimental study was to ignore the expected positive effect of the stagger in the splices. The second decision was not to use continuous bars paralleling the spliced bars.

Crack Traiectory The third decision involved the expected trajectory of the laminar crack.

Figure 7.14 Figure 7.14 shows a representative reinforcing bar with surface deformations to enhance its ability in transferring force from the bar to the concrete and vice versa. As such a bar is pulled to one side concrete wedges form at each lug as shown in an exaggerated manner in Figure 7.15.

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bbJL-UUU-Ud.i-ULLI-LSUUUI*h-UUU I-'age 4U Ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Concrete DV Reinforcing Bar DDH Figure 7.15 As the bar moves a distance DH with respect to the surrounding concrete, concrete moves radially a distance DV as shown. This process is not expected to occur uniformly. The movement of the lugs varies from lug to lug, the shapes of the wedge vary depending on the tensile strength and aggregate distribution in the concrete. But there is a general tendency to set up radial "bursting" tensile stresses that are eventually seen as splitting cracks on the surface of the concrete as illustrated in Figure 7.16.

Typically the splitting crack has a zigzag or irregular undulating appearance on the surface. The nonuniform trajectory of the splitting crack within the body of the concrete as well as on the surface is an inherent natural characteristic of cracking in concrete. Even under ideal circumstances and even in the case of flexure it is highly unlikely for the surfaces bounding the crack to be predictable.

Figure 7.16 Splitting Cracks Observed in Tests of Lap Splices (Chinn et al, 1951)

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b.j-uu-U~jUtU-*-G.-UUUtI5-UUU I-'age 41 0? 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building The nonuniform/random trajectory of the splitting crack is of import in determining the strength and toughness of a lap splice without any confinement as it can be inferred from thinking of the phenomenon as coarse friction. It was, therefore, decided to have the test specimens develop their own cracks. From experience with similar specimens, it was known that the splitting cracks would develop at loads below half of the maximum load2.

Specimen Width Experimental studies of lap splices have shown that two critical parameters (in addition to concrete properties) affecting the strength of lap splices are the distances to the surface of the specimen from the edge of the spliced bar (or minimum cover) and the distance between the surfaces of bars in adjacent splices. Because the minimum cover in the shell was set at 3 in. and because two parallel splices were to be used in the test specimens (to provide balance or symmetry about the vertical axis),

the width of the specimen was set at 17-5/8 in. (Figure 7.17).

In order to set up the conditions for having the splitting crack in the horizontal plane intersecting both splices, top cover was made more than the side cover (Figure 7.17).

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30 in.

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bbYi-UUU-Udi*-UW-'-UUUllb-UUU I-'age 42 o1T 1 1"14 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Specimen Depth Effective depth of the specimen was set so that the reinforcement ratio would be moderate or approximately 1.5 %. This decision was driven by the concern not to have to use extremely long cantilever spans or heavy transverse reinforcement in those spans as well as by the desire not to have an over-reinforced mid-span segment.

It is important to note that the resulting test specimens for the 79-in and 120-in splices were not perfect replicas of the splices in the actual structure. But they are as close or closer to the conditions in the structure as the result of a compressive test of a cylinder is close to the compressive strength of the concrete in the structure or the result of a tensile test of a reinforcing bar is close to the tensile strength of a particular reinforcing bar in the structure. The experimental model of the splice is as good if not better than an analytical model assembled for the same purpose.

Dominant Results Two aspects of the test results described in the main report deserve special mention.

(a) Load-Deflection Curves.

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42 REDACTED VERSION

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-'age 4: 50or 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University arid University of Kansas for Davis-Besse Shield Building Test Girder 1B2 45 40 35 20.

a1 5 10 15 10 0.

0.1 0.2 0.3 0.4

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0.6 0.7 0.8 Figure 7.19 Figures 7.18 and 7.19 show typical examples of the response of specimens with 120-in. (A series) and 79-in. (B series) lap splices. All load-deflection curves are reproduced in the main report. In each series, the load-deflection curves measured were almost identical with others in the same series indicating that the results could be projected to the shell confidently. The actual yield stress of the reinforcement (66 ksi) was reached and exceeded in each test (Table 7.4). In each case, failure occurred at a deflection exceeding the yield deflection. Capability of the structural system to sustain its load-carrying capacity beyond yield is a measure of its toughness and is a critical property for impact loading. For the A series, the total energy absorption capacity ranged from approximately S to 6 times that at yield. For the B series, these ratios ranged from approximately 2 to 3.

The test results indicated consistently that the splices in the in the shell with laminar cracks were as good as they would have been without the laminar cracks.

(b) Reinforcement Stresses Developed by Splices after Laminar Cracking The reinforcement stresses reached are shown In Figure 7.20. In each case the reinforcement stress reached was more than the nominal design yield stress of 60 ksi and the actual yield stress in the test specimens of 66 ksi.

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43 REDACTED VERSION

bbi3-UUU-U*i-U5LU-UUUlrb-UUU h'age 44 01" 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Another important result of the tests was to show that the the transfer by bond forces of the main part of the tensile force took place in a length of approximately 15 bar diameters (approx. 20 in.) from each end of the splice.This fact had been observed by Kluge and Tuma in 1945 but evidently forgotten by the profession.

Reinforcement Stress Developed by Splice, ksi 90 80 70 60

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A2 A3 A1 A4 ASA6 81 B4 8283 B5 B6 Test Girder ID's Figure 7.20 Lower-Bound Determnations of Maximum Reinforcement Stress Developed (Girders A2, A3, B1, B4 were loaded continually to failure while the others were loaded to yield or beyond yield, unloaded, and the reloaded to failure.)

Table 7.4 Reinforcement Stresses Reached Test Girder A2 A3 Bi B4 Al A4 A5 A6 B2 B3 B5 B6 Type of Loading Mo noton ic Mo noto nic Monotonic Mo notonic Maximum Reinforcement Stress at Splice End 79 ksi 80 ksi 71 ksi 70 ksi Reloaded after Laminar Cracking Reloaded after Laminar Cracking Reloaded after Laminar Cracking Reloaded after Laminar Cracking Reloaded after Laminar Cracking Reloaded after Laminar Cracking Reloaded after Laminar Cracking Reloaded after Laminar Cracking 79 ksi 79 ksi 79 ksi 77 ksi 69 ksi 70 ksi 72 ksi 72 ksi E q E A Cnntidt~ntufl ~C3 2012 B~cflWI LorDor~2tcon. Lorfl3ln: conitocnmn~ anci!or oro~rcct~r': c ormrn~on to j..........

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bkS3-UUU-U*.i-U-I-UUUltb-UUU I-sage 4b ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Results of The Specimens Tested at Bowen Laboratory vis-a-vis ACI 318 ACI 318 strives to enable the structural engineer to produce a structure with acceptable strength and ductility. The latter is measured in different ways but the general understanding is that a section that serves as part of a girder subjected to flexure or of an element resisting axial tension should be proportioned and detailed to reach its yield load and maintain it under further extension or bending.

Results of the test girders satisfied that requirement.

Not everything has been anticipated by ACI 318, but the current ACI 318-11 does consider the "unconsidered" as follows.

1.4-- Approval of special systems of design or construction Sponsors of any system of design or construction within the scope of this Code, the adequacy of which has been shown by successful use or by analysis or test, but which does not conform to or is not covered by this Code, shall have the right to present the data on which their design is based to the building official or to a board of examiners appointed by the building official. This board shall be composed of competent engineers and shall have authority to investigate the data so submitted, to require tests, and to formulate rules governing design and construction of such systems to meet the intent of this Code. These rules, when approved by the building official and promulgated, shall be of the same force and effect as the provisions of this Code.

It is not unreasonable to assume that in the case of the DB Shell there has been sufficient analysis and experimental work to justify presentation to a board of examiners (NRC).

We may also invoke Chapter 20 of ACI 318.

2.01.2-- If the effect of the strength deficiency is well understood and if it is feasible to measure the dimensions and material properties required for analysis, analytical evaluations of strength based on those measurements shall suffice. Required data shall be determined in accordance with 20.2.

It is not impossible for us to argue that we can qualify under the "analytical" evaluation clause. We have done enough thinking and any experienced structural engineer would accept that the effect of the laminar crack has to be determined by proper testing.

Capacity of The Lap Splices with Laminar Cracks The tests at Bowen Laboratory have confirmed the adequacy of the DB-Shell splices on the circumferential reinforcement in their reported existing condition with respect to the general requirements for strength and toughness of (a) static Ioadsrelated to wind and thermal demands and (b) impact loads related to the expected tornado and wind demands.

45 REDACTED VERSION

Y~-UUU-U~iJ-ULU-UUU1b-UUU I-'age 4b oT 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building bbU3-UUUItS*3-*I::LS-UUU'I*-UUU P'age 4* ot 1 114 8

Testing at University of Kansas Bechtel provided the technical oversight and QA and O.C of tests at University of Kansas. This Section provides review of the testing program and the results. Note that many of the sections here are reproduced verbatim from the relevant sections of the Kansas report (Appendix B) to avoid any misrepresentation or mischaracterization of the test program and the results. Summary of Bechtel review is presented at the end of this section.

8.1 Purpose and Scope

Past research on the strength of lapped bar splices in reinforced concrete has focused on investigating the performance of various lap splice configurations in monolithic members. The research program described in this report investigates the effect of preexisting cracks, oriented in the plane of and parallel to the reinforcing steel, on the strength of lapped bar splices. The research program was conducted in two phases, a pilot study investigating various methods to simulate the preexisting cracks that is r

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-UUU rage 41 ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building described in Appendix B of this report, and a series of beam tests described in the main body of the report.

Beams in the main study had cold joints in the splice region, along the plane of the reinforcement, to facilitate the initiation of a crack prior to failure. Two No. 3-bar hoops (one on each side) crossing the plane of the cold joint, in the center of the specimen and on the exterior of the lap splices, were used to simulate the effects of the continuity of concrete in an actual structure.

The beams contained two spliced No. 11 bars with 79 or 120-in, long lap splices. Some of the beams were loaded until horizontal cracks had developed along the plane of the cold joint with a minimum width of 10 mils (0.01 in.); they were then unloaded and subsequently reloaded to failure. The remainder of the beams were loaded monotonically to failure.

8.2 Test Program A total of six beam-splice specimens were tested in the main study - three specimens with a splice length of 79 in. and three with a splice length of 120 in. For the three specimens with a 79-in, splice length, one was cast with monolithic concrete and the other two were cast with a cold joint in the plane of reinforcing steel. All three specimens with a 120 in. splice length were cast with a cold joint in the plane of reinforcing steel. All specimens with cold joints had two No. 3-bar hoops crossing the plane of the cold joint, outside the spliced bars, at the center of the specimen.

The beams were subjected to four-point loading to provide a constant moment (excluding dead load) in the middle portion of the member, where the splice was located, as shown in Figure 8.1.

The specimen was configured to have a constant moment in the splice region to eliminate the effect of shear forces on splice strength, and also to eliminate the need for shear reinforcement within the splice region. The spacing of the supports was chosen so that the distance from either end of the splice to the central pin and roller supports was equal to or greater than the effective depth of the beam. The span lengths were selected in increments of 3 ft based on the spacing of load points in the Structural Testing Laboratory of University of Kansas.

47 REDACTED VERSION

bM-UUU-U~iUL.-*-UUU1t,-UUU I-'age 4*5 OT 11 14 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building I

I fly/I Shear Diagram Moment Diagram Figure 8.1 Configuration and shear and moment diagrams for the testing fixture The reinforcement diagrams for the specimens in the study are shown in Appendix B. The top reinforcement layer of the beams consisted of two No. 11 reinforcing bars, which were spliced at the center of the beam, as shown in Figure 8.1. The No. 11 bars used in all the specimens were from a single heat of reinforcement. The bottom layer of reinforcement, placed to maintain the integrity of the beam after failure of the splice and to facilitate placement of shear reinforcement in the constant shear regions, consisted of two Grade 60 No. 3 bars. Beam dimensions and effective depths are summarized in Table 8.1.

The specimens were proportioned to have two splices, each with a nominal side concrete cover of 3 in.

to the outermost No. 11 bars and a top concrete cover of 3 in.

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(-'age 4* or 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Table 8.1 Summary of Design Beam Dimensions for Beam-Splice Specimens Bi 79None B2 79 Codjit 11 25 18 24 20.3 2.8 B3 79 C~(oldnolinthic2)8 403.

B4 120 Cold joint 14 28 18 24 20.3 2.8 B3 120 Cold joint 14 28 18 24 20.3 2.8 B6 120 Cold joint 14 28 18 24 20.3 2.8 Figure 8.2 Four-Point Loading Configuration Loads were applied at the ends of the specimen using two loading frames, as shown in Figure 8.2. Each loading frame consisted of two load rods attached to a loading beam that was placed above the specimen. The following data were recorded and continuously transferred to disk throughout each test:

-Force applied to each load rod

-Displacement at midspan and each load application point

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J-uUU-Ud-C*L-.U-UUU 1 ti-UUU I-"age *U Or 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Table 8.2 Detailed Loading Protocol for Each Beam Beam Loading Protocol Bi (1)Monotonically-increasing load up to an average end load of 40 kips in increments of S kips.

At the end of the each increment, the beam was inspected for cracks and dial-gage displacement measurements were recorded.

_______(2)

Loading resumed with increasing displacement until failure occurred.

B2 (1)Monotonically-increasing load up to an average end load of 25 kips in increments of 5 kips.

At the end of the each increment, the beam was inspected for cracks and dial-gage displacement measurements were recorded.

(2) Dial-gage measurements were recorded at an average end load of 30 kips.

(3) Loading resumed with increasing displacement until failure occurred.

B3 (1)Monotonically-increasing load up to an average end load of 30 kips in increments of 5 kips.

At the end of the each increment, the beam was inspected for cracks and dial-gage displacement measurements were recorded.

(2) The beam was fully unloaded and dial-gage displacement measurements were recorded.

(3) The beam was loaded a second time up to an average end load of 35 kips in load increments of 5 kips. At the end of the each increment, dial-gage displacement measurements were recorded. The beam was inspected for cracks at an average end load of 30 kips.

(4) Loading resumed with increasing displacement until failure occurred.

B4 (1)Monotonically-increasing load up to an average end load of 35 kips in increments of 5 kips.

At the end of the each increment, the beam was inspected for cracks and dial-gage displacement measurements were recorded.

(2) Loading resumed with increasing displacement until failure occurred.

B5 (1)Monotonically-increasing load up to an average end load of 40 kips in increments of 5 kips.

The beam was inspected for cracks and dial-gage displacement measurements were recorded at the end of each increment.

(2) The beam was fully unloaded and dial-gage displacement measurements were recorded.

(3) The beam was loaded a second time up to an average end load of 40 kips in increments of 5 kips. Dial-gage displacement measurements were recorded at the end of each increment.

The beam was inspected for cracks at average end loads of 20, 30, 35 and 40 kips.

(4) Loading resumed with increasing displacement until failure occurred.

B6 (1)Monotonically-increasing load up to an average end load of 40 kips in increments of 5 kips.

The beam was inspected for cracks and dial-gage displacement measurements were recorded at the end of the each increment.

(2) The beam was fully unloaded and dial-gage displacement measurements were recorded.

(3) The beam was loaded a second time. The beam was inspected for cracks and dial-gage displacement measurements were recorded at average end loads of 10, 20, 30, 35, and 40 kips.

(4) Loading resumed with increasing displacement until failure occurred.

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bbJL-UUU-(UdJ-(3P-W-UUUIb-UUU I-'age bl Or 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 8.3 Concrete The concrete used to fabricate the test specimens was supplied by a local ready mix plant. The concrete was non-air-entrained with Type I portland cement, 11/2-in, nominal maximum-size crushed coarse aggregate, and a water-cement ratio of 0.42. A trial batch was prepared at the concrete laboratory of the University of Kansas prior to casting the first three beams. The aggregate gradation, mixture proportions, and concrete properties for the trial batch and each of the placements are presented in Appendix B. The dosage of high-range water reducer was adjusted on site when considered necessary to obtain adequate slump for placement.

8.4 Cold Joint Construction and Crack Simulation The specimens with cold joints were cast using two placements, with a cold joint at the mid-height of the top layer of reinforcement, to ensure that a longitudinal crack would develop in the plane of the reinforcing steel before the beam failed. The cold joints spanned the entire length of the spliced region and extended approximately 6.5 ft outside of the spliced region.

In the first placement, concrete was cast up to the center of the top layer of reinforcement (Figure 8.3).

After the concrete was placed, a roughened surface was created to simulate the roughness of a natural crack by introducing indentations in the concrete while it remained plastic (Figure 8.4). The exposed reinforcing steel was cleaned using sponges to facilitate adequate bond between the exposed bars and the concrete cast during the second casting stage. The specimens were moist cured for a day, and the remainder of the concrete was placed no later than 26 hours3.009259e-4 days 0.00722 hours 4.298942e-5 weeks 9.893e-6 months after the original placement. The concrete for the second placement had the same mixture proportions and was supplied by the same ready-mix plant as the first. Before the second placement, the concrete surface was cleaned using compressed air to remove debris and loose concrete, and maintained in a wet condition until the second placement started (Figures 8.5 and 8.6). After casting, the specimens were moist-cured until the compressive strength of the concrete from the first placement exceeded 3500 psi.

Some beams were loaded in two stages to ensure that the preexisting crack of minimum width had formed in the plane of the reinforcing steel. To do this, beams were loaded monotonically until the width of the horizontal cracks at the cold joint exceeded 10 mils (0.01 in.). After initial loading, the specimens were unloaded and subsequently reloaded monotonically to failure.

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-UUUlb-UUU I-sage b2i 01 1 1t4 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Concrete cast monolithically at the ends of the beam specimen.

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bbJ-UUU-UtIJ-ULIU.-UUU~tb-UUU r-age b~J Ot 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building (a)

(b)

Figure 8.4 Roughening of the Concrete Surface at the Cold Joint. (a) roughening of the concrete surface while the concrete remains plastic. (b) roughened surface after concrete had set.

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bOi:I-UUU-J-UI:L-IU-UUUrI(-UUU 1-'age b40ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Figure 8.6 Wetting of Concrete Surface Prior to Concrete Placement 8.5 Test Results The testing program consisted of six beam-splice specimens. Three of the specimens had a lap splice length of 79 in., and three had a lap splice length of 120 in. The measured loads and calculated bar stresses at failure are presented in Table 8.3. In addition to failure loads, Table 8.3 includes measured material properties and bar cover dimensions. Bar stresses at failure listed in Table 8.3 include those calculated using the equivalent rectangular stress block and moment-curvature analysis.

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I1"1, (monolithic) 2 -79 in.

(cold joint, loaded monotonically) 3 -79 in.

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(cold joint, loaded monotonically) 5 - 120 in.

(cold joint, unloaded and reloaded) 6 - 120 in.

(cold joint, unloaded and reloaded) 3/2.8/3.4 105 350 71 72 Splice failure and secondary flexural failure 5 230/

5490 +

Splice failure and 3.15/3/15/3.15 96 325 66 67 secondary flexural failure 3.15/3.15/2.9 100 338 69 69 Splice failure and secondary flexural failure aTop cover/north side cover/south side cover

Compressive strength of concrete below and above the cold joint.

Test was stopped after reinforcing steel yielded, when crushing of the concrete in the compression zone was observed.

Splice failed prior to yielding of the flexure reinforcement.

- Splice failed after yielding of the flexure reinforcement 8.5.1 Beams 1, 2, and 3 with 79-in, splice length The concrete strengths for Beams 1, 2 and 3 are summarized in Table 8.4. Beam 1 was cast monolithically, while Beams 2 and 3 were cast in two stages to accommodate the presence of a cold joint at the level of the flexure reinforcement. Beam 1 and the concrete below the cold joint for Beams 2 and 3 were placed on May 24, 2012 and the concrete above the cold joint was placed on May 25, 2012.

The forms were removed on May 28, 2012, when the average concrete compressive strength for both placements exceeded 3500 psi. All three beams were tested on May 31, 2012. On that date the concrete Conidcti! © 2012 B cchtel Ccrporat÷on. "^nt*in..... idcnti l

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bbJL-UUU-GdtJ-uLUL-UUUltb-UUU Page ~b 0?" 11ll4 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building from the first placement had an average compressive strength of 5330 psi, and the concrete from the second placement had an average compressive strength of 4330 psi (Table 8.4). The average split cylinder strength and the average modulus rupture were 435 and 570 psi for the concrete below the cold joint in accordance with ASTM C496 and ASTM C78, respectively. The tensile strength for the concrete above the cold joint was not recorded for the first three beams. The flexural beam specimens with cold joints were also tested and had an average modulus of rupture of 140 psi, significantly lower than that of specimens cast monolithically. The fact that the tensile strength of the flexural beam specimens with cold joints was significantly lower than the strength of monolithic specimens indicates that the presence of a cold joint did in fact introduce a weak plane at the level of reinforcing steel. The proportions of the concrete mixture and the properties of the concrete for each placement are reported in Appendix B.

Table 8.4 Concrete Strengths for Beams B1, B2 and B3 Concrete below cold joint Concrete above cold joint Average Compressive Strength when 4010a360 forms were removed Average Compressive Strength at test 5330c430 date, psi Split Cylinder Strength (ASTM C496),

435c psi Modulus of Rupture (ASTM C78), psi 570C Modulus of Rupture for specimens 240 with cold joint,_psi_____________

aTested at 4 days; btested at 3 days; ctested at 7 days; dtested at 6 days A segment of the No. 11 bars used in the splice-beam specimens was tested in tension and the bar strains were recorded using an LVDT used as the extensometer (gage length = 8.0 in.). The measured stress-strain curve for the No. 21 bar is shown in Figure 8.7. The yield stress calculated using the 0.2%

offset method was 67 ksi and the measured elastic modulus was 28,990 ksi. The maximum measured steel stress was 105 ksi.

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0.2% offset Yield (0.2% offset): 67.1 ksi

______________________Ultimate:

104.7 ksi Elastic Modulus:28990 ksi 0

0.05 0.1 0.15 Strain Figure 8.7 Measured Stress-Strain Curve for No. 11 Bar 8.5.1.1 Beam 1 Beam 1 was cast monolithically with a splice length of 79 in. It was loaded monotonically to failure (the load protocol is presented in Table 8.2). The load-deflection curve for Beam 1 is shown in Figure 8.8. The displacement shown in the figure was calculated by adding the average of the displacement at the two load points to the displacement at the beam centerline. The load shown in the figure corresponds to the total load applied to the beam (the sum of the two end loads). The load-deflection relationship shows that there was a significant reduction in the stiffness of the beam at a total load of approximately 20 kips, which coincided with the first observation of flexural cracks. Another significant reduction in flexural stiffness was observed at a total load of 94 kips and a total displacement of approximately 2.8 in. In this case the reduction in stiffness is attributed to the yielding of the flexural reinforcement. The calculated bar stress corresponding to the total load of 94 kips is 68 ksi based on moment-curvature analysis (Table 8.3). The positive slope of the load-deflection relationship after a total load of 94 kips is attributed to the strain hardening of the reinforcing steel. Loading continued until a flexural failure occurred, which was accompanied by crushing of the concrete in the compression zone, near the supports, at a total load of 103 kips, corresponding to a bar stress of 70 ksi, and a total deflection of approximately 5 in. (Figure 8.9).

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Figure 8.8 Total Load vs. Total Deflection for Beam 1 (cast monolithically) (Total load calculated as the summation of the two end loads and total deflection calculated defined by adding the average deflection at two ends and the deflection in the beam centerline)

Figure 8.9 Flexural Failure in the Compression Region for Beam 1

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i-UUU-*UJ-LILU-UUU i*-UUU I-"age *Y Ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 8.5.1.2 Beam 2 Beam 2 was cast with a cold joint in the plane of reinforcing steel. It was monotonically loaded with a load increment of approximately 5 kips (average end load, the load protocol is presented in Table 8.2).

The load-deflection curve for Beam 2 is shown in Figure 8.10. The total displacement and total load shown in the figure were calculated in the same manner as for Beam 1. The total load corresponding to cracking was very similar to that of Beam 1, approximately 20 kips. The beam was loaded to a maximum total load of 85 kips, with a corresponding total displacement of 2.25 in. At this point the beam failed with a sudden splitting of the concrete along the cold joint. Wide horizontal cracks were observed in the plane of the cold joint within the splice region (Figure 8.11). The widest horizontal crack was measured to be 1/2, in. wide after failure. It is concluded that the beam failed due to failure of the splice at a total load of 85 kips. The mode of failure (splice failure) was confirmed by the measurements of bar slip at the edges of the lap splice performed after testing. The calculated bar stress corresponding to the total load of 85 kips is 62 ksi based on moment-curvature analysis (Table 8.3), above the minimum specified yield strength of 60 ksi for Grade 60 reinforcement but 5 ksi below the actual yield strength of 67 ksi.

Beam #2 Total load vs. Total deflection 90 8 0 20 1

Total Deflection, in.

Figure 8.10 Total Load vs. Total Deflection for Beam 2 (with a cold joint)

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-'age tiU OT 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Figure 8.11 Beam 2 (with a cold joint) Failed with Wide Horizontal Crack Maximum measured crack width versus load for Beam 2 is shown in Figure 8.12; the crack map for Beam 2 is presented in Figure 8.13. The first flexural cracks formed near the supports and ends of both splice regions at an average end load of 15 kips (total load of 30 kips). Horizontal cracks first formed at an average end load of 20 kips at both ends of the splice region along the cold joint (Figure 8.14). Both longitudinal and flexural cracks continued to increase in width and number as the load increased, with horizontal cracks propagating along the cold joint. When the last cracks were marked prior to failure (conducted at an average end load of 30 kips), the widest flexural crack had a width of 20 mils (0.02 in.)

and the widest horizontal crack had a width of 13 mils (0.013 in.).

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~40 u 3 010 20 30 40 50 Average End Load, Kips

-- e-- Flexural Crack

- Horizontal Crack Figure 8.12 Maximum Crack Width vs. Average End Load for Beam 2 R I J

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-UUU-tJ-(*tU-UUUIb-UUU wage *I OT 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building North Face E

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Top Face Loading Point Pedestal Splice Center Support Region Line Splice Region Pedestal Loading Support Point Figure 8.13 Crack Map for Beam 2. Numbers indicate maximum average end load when cracks marked.

Figure 8.14 Beam 2, Northeast Support with Horizontal Crack, 20 Kips End Load Failure occurred at an average end load of approximately 43 kips (total load of 85 kips). At failure, the concrete above the cold joint separated from the remainder of the beam (Figure 8.15).

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bbILS-UUU-Udi*-ULUI--UUUIIb-UUU I-'age (5; OT 1 114 Effect of Laminar Cracks on Splice Capacity of No. 22 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Figure 8.15 Beam 2, Southwest Splice Region Showing Separation of Concrete, 43 Kips End Load 8.5.1.3 Beam 3 Beam 3 was cast in the same manner and at the same time as Beam 2, with a cold joint in the plane of reinforcing steel. Instead of loading the beams to failure monotonically, Beam 3 was first loaded to a total load of 60 kips, unloaded to zero, and then re-loaded monotonically to failure (the load protocol is presented in Table 8.2). When the beam was first loaded to a total load of 60 kips (average end load of 30 kips), the average end load was increased in increments of approximately 5 kips. The specimen was inspected for cracks, which were marked at each load step. At a total load of 60 kips, the maximum horizontal crack width was 20 mils (0.02 in.). When the beam was loaded for the second time, it was loaded up to a total load of 60 kips without inspecting for cracks. The only visual measurement conducted during the second loading was the recording of dial gage readings at approximately 5-kip increments (average end load). The beam was inspected for cracks again when the total load reached 60 kips for the second time. At this point some of the horizontal cracks widened to a maximum width of 35 mils (0.035 in.)

The load-deflection curve for Beam 3 is shown in Figure 8.16. Overall, Beam 3 performed very similar to Beam 2, except for the peak load. The beam failed at a total load of 80 kips (compared with a total load of 85 kips for Beam 2), in the same manner as observed for Beam 2. A wide horizontal crack in the plane c3nfld~ntiaI © 2012 Bechtel Cornaration. Contains confidc~bl and/or DrODriCtar~ information to Bechte land it affiliate any non Bechtel patty wI ~l mpnic*wh;r

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62 REDACTED VERSION

bU-UUU-L,*5J-4S~U-UUUlh-UUU I-age bJ OT 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building of the cold joint, within the splice region, was observed after failure (Figure 8.17), with the widest portion of the crack being 3/8-in. It is concluded that the beam failed due to a splice failure. The calculated bar stress corresponding to the total load of 80 kips is 57 ksi based on moment-curvature analysis (Table 8.3).

Beam #3 Total load vs. Total deflection 9 0

0 1./

2 34 Totl Dfletio, in Figure 8.16 Total Load vs. Total Deflection for Beam 3 (with a cold joint)

Figure 8.17 Beam 3 Failure with Wide Maximum measured crack width versus load for Beam 3 is shown in Figure 8.18; the crack map for Beam 3 is presented in Figure 8.19. As seen in both figures, the first flexural cracks formed near end of the east splice region at an average end load of 10 kips (total load of 20 kips). At an average end load of 15 kips, Cenfldcntial ~1 2012 Bc:htcl Corporation. Cantain~ confidzntbl and,'or proprietary information to I

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v 63 REDACTED VERSION

bblJ-UUU-1Ud*i-1U1::-UUUIb-UUU I-'age b4 0? 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building flexural cracks were present at both ends of the splice region and both supports. A horizontal crack first formed at an average end load of 15 kips at the west end of the splice region along the cold joint, with additional horizontal cracks forming and reaching a 9-mil (0.009 in.) width at an average end load of 20 kips (Figure 8.20). At an average end load of 30 kips, a 40-mil (0.04-in.) width flexural crack and 20-mil width horizontal crack were recorded. At this point, the beam was unloaded. With zero load, the maximum flexural and horizontal crack widths decreased to 13 and 7 mils (0.013 and 0.007 in.),

respectively. The load was reapplied, and at the last crack mapping (average end load of 30 kips), the widest flexural crack had a width of 55 mils (0.055 in.) and the widest horizontal crack had a width of 35 mils (0.035 in.), much wider than the cracks noted at the first loading to a 30-kip average end load.

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- 40

~30 LiE 20 0

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0 10 2C Aver; Flexural Crack (1st loading)

-~Flexural Crack (2nd loading) 0 30 age End Load, Kips 40 50 Horizontal Crack (1st Loading)

-4Horizontal Crack (2nd Loading)

Figure 8.18 Maximum Crack Width vs. Average End Load for Beam 3 North Face IiI 3j

'V South Face

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Top Face Loading Pedestal Splike Point Support Region Center Splice Pedestal Line Region Support tW Loading Point Figure 8.19 Crack Map for Beam 3. Numbers indicate maximum average end load when cracks marked.

C3nJId~nfiuI ~ 2012 Bechtel Corpcratian. Cantain~ confidc ntial and/or proprietarf information to Be~htdand it affiliated ~ompanic~which shall not be u:ed, dizclozed, arr~produccd in anyformat b1 any llli nn Bechtll l

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-'age tb Ot 1 14 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Figure 8.20 Beam 3, Northwest Splice Region with Horizontal Crack, 20 Kips End Load Failure occurred at an average end load of 40 kips (total load of 80 kips), a slightly lower load than the monotonically loaded Beam 2 (total load of 85 kips). At failure, the concrete above the cold joint separated from the remainder of the beam, with the horizontal crack propagating along the cold joint in a region that was somewhat larger than the splice region.

Figure 8.21 Beam 3, Splice Region and Centerline Showing Separation of Concrete, 40 Kips End Load CVnfkknI3*II I*

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bbJL-UUU-UbJ)L-ULU--UUU1 t-UUU t-'age t~ti 0? 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 8.6 Beams 4, 5, and 6 with 120-in, splice length 8.6.1 Concrete strength The concrete strengths for Beams 4, 5 and 6 are summarized in Table 8.5. The three beams were cast in two stages to accommodate the presence of a cold joint at the level of the flexural reinforcement. The concrete below the cold joint was placed on June 13, 2012, and the concrete above the cold joint was placed on June 14, 2012. The forms were removed on June 17, 2012 when the average concrete compressive strength for both placements exceeded 3500 psi. The beams were tested on June 20, 2012.

On that date, the concrete from the first placement had an average compressive strength of 5230 psi, and the concrete from the second placement had an average compressive strength of 5490 psi (Table 8.5). The higher strength for the second placement was likely due to the slightly lower water-cement ratio of the concrete, as shown on the batch ticket in Appendix B. The average split cylinder strength and average modulus rupture were, respectively, 370 and 600 psi for the concrete below the cold joint and 470 and 700 psi for the concrete above the cold joint. The flexural beam specimens with cold joints were also tested and had an average modulus of rupture of 274 psi, significantly below that of specimens cast monolithically. The proportions of the concrete mixture and the properties of the concrete for each placement are reported in Appendix B.

Table 8.5 Concrete Strengths for Beams B4, B5, and B6 (add age of concrete when tested)

Concrete below cold joint Concrete above cold joint Average Compressive Strength when 4310a450 Forms were removed Average Compressive Strength at test 5230c540 date, psi Split Cylinder Strength (ASTM C496),

370C 40 psi Modulus of Rupture (ASTM C78), psi 600c 00 Modulus of Rupture for specimens 274-_

with cold joint, psi___________________________

aTested at 4 days; btested at 3 days; etested at 7 days; dtested at 6 days The same reinforcing steel was used for Beams 4, 5, and 6 as for Beams 1, 2, and 3.

8.6.1.1 Beam 4 Beam 4 was cast with a cold joint in the plane of reinforcing steel. It was subjected to monotonically-increasing load in increments of approximately 5 kips (average end load, the loading protocol is presented in Table 8.2). The load-deflection curve for Beam 4 is shown in Figure 8.22. The total load and deflection were determined in the same manner as for Beams 1, 2 and 3. The flexural stiffness of the Bec~lhtl and-it afl-

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iJ-UUU-L*d-(L*P_.-UUUlfb-UUU t-age tbl 0?" 11 14 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building beam decreased once the total load exceeded 20 kips, coinciding with the formation of flexural cracks. A sharp decrease in the slope of the load-deflection curve was observed at a total load of about 94 kips and corresponding deflection of approximately 2.8 in. The decrease in the slope of the load-deflection curve at a total load of 94 kips indicates that the reinforcing steel yielded. After yielding of the reinforcing steel, the total load continued to increase but at a lower rate, which is attributed to the strain hardening of the reinforcing steel. The beam was loaded to a total load of 105 kips (and a displacement of 5.5 in.) and at that point failed with the sudden splitting of the concrete along the cold joint. Wide horizontal cracks in the plane of the cold joint were observed within the splice region. Wide flexural cracks were also observed near the support (Figure 8.23). It is concluded that the reinforcing steel yielded at a total load of approximately 94 kips and beam failed at a total load of 105 kips due to failure of the splice, the latter corresponding to a bar stress of 72 ksi (Table 8.3).

110 100 90 80

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-- 40

~30 20 10 0

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Total Deflection, in.

10 Figure 8.22 Total Load vs. Total Deflection for Beam 4 (with a cold joint)

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bbJJ-UUU-Ub*J-ULUI:-UUUti*-UUU l-'age bI5 0?

1 "4 Effect of Laminar Cracks on Splice Capacity of No. 21 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Flxra l ca cks near the su ppo rt Horizontal cracks at the face of cold joint SSupport Figure 8.23 Beam 4 (with a cold joint) at Failure Maximum measured crack width versus load for Beam 4 is shown in Figure 8.24; the crack map for Beam 4 is presented in Figure 8.25. The first flexural cracks formed near end of the west support at an average end load of 10 kips (total load of 20 kips). At an average end load of 15 kips, flexural cracks were present at both ends of the splice region and both supports. Horizontal cracks first formed at an average end load of 20 kips, at the both ends of the splice region along the cold joint. Both longitudinal and flexural cracks continued to increase in width and number as the load increased, with horizontal cracks propagating along the cold joint. At the last load prior to failure at which cracks were marked (average end load of 35 kips), the widest flexural crack had a width of 30 mils and the widest horizontal crack had a width of 16 mils. At this point, the horizontal cracks extended along most of the length of the splice region (Figure 8.26), with some of the horizontal cracks that formed at earlier stages merging together.

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bb5-UUU-IUdJ-LSI-U-UUU1b-UUU r-age b* 0? 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 60

~40 S20 0

10 20 30405 Average End Load, Kips

- Flexural Crack

-a-Horizontal Crack 40 50 Figure 8.24 Maximum Crack Width vs. Average End Load for Beam 4 t

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69 REDACTED VERSION

bOJ-UUU-(*bi-£Uti-UUUIb-UUU I-age fU 0? 11 14 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Figure 8.26 Beam 4, South Side of West Splice Region with Horizontal Cracks, 35 Kips End Load 8.6.1.2 Beam 5 Beams 5 and 6 were cast in the same manner and at the same time as Beam 4, with a cold joint at the plane of reinforcing steel. Instead of monotonically loading the beams to failure, Beam 5 was first loaded to a total load of 80 kips, and subsequently unloaded to zero, and then re-loaded to failure (the load protocol is presented in Table 8.2). When the beam was first loaded to a total load of 80 kips, the average end load was increased in increments of approximately 5 kips. The specimen was inspected for cracks and marked at each load step. Horizontal cracks on the plane of the cold joint within the splice region were observed when the beam was subjected to a total load of 80 kips. The maximum horizontal crack width at this load was 35 mils (0.035 in.). It should be noted that the beam was unloaded in a rapid manner and that one of the load cells had large fluctuations after that point (load cell C in Figure 8.27).

Although there were clear problems with the load readings from load cell C for the remainder of this test, the rams were at all times subjected to uniform pressure, and load readings from the other 5 beam tests show that the load was evenly applied to the four different load rods at all times. Furthermore, the load beam remained level and the displacement readings were similar at both ends of the beam, strong indicators that although the load cell readings were not accurate, the load was uniformly applied to the four load rods. Based on these observations, the total load was calculated based on the readings from load cells A and B. When the beam was loaded for the second time, it was loaded up to a total load of 80 kips at an increment of 5 kips (average end load). At the end of the each increment, dial-gage displacement measurements were recorded. The beam was inspected for cracks at total loads of 40, 60, L~flJfUflU3I ~] 2012 Bc~htcl Corporation. Ccntain~ coniici~ntiai ana/or proprlctarj inrarmatian ta B~chtcl and it affiliatcd companic~ which :hall not bc u~cd, dizcIo~cd, or rcproduccd in anyformat by an., n... Bcchtcl pa.t';w~hout Bc chtcr= p.nocr wr;.c.n. pc ri.zia~n. All.gl rzr*

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bb.i-uUU-Ud-UtU-I:(-UUUltO-UUU I-'age (1 Ot 11 14 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 70, and 80 kips. When the beam was inspected for crack during the second loading, some of the horizontal cracks elongated or widened and some new horizontal cracks were noticed. The maximum horizontal crack width was still 35 mils (0.035 in.)

.=.

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Total Deflection, in.

Figure 8.27 Load Cell Readings for Beam 5 The load-deflection curve for Beam 5 is shown in Figure 8.28. Due to the problem documented for load cell C, the total load is calculated as twice the summation of load cells A and B, located at the West loading point. Overall, Beam 5 performed very similar to Beam 4. The slope of the load-deflection curve first decreased at a total load of 20 kips, which coincides with the first observation of flexural cracks.

Another decrease in the slope of the load-deflection curve was observed at a total load 91 kips, with a corresponding total displacement of approximately 2.7 in, which is attributed to the yielding of the flexural reinforcement. The positive slope of the load-deflection relationship after a total load of 91 kips is attributed to the strain hardening of the reinforcing steel. The beam was loaded to a total load of 96 kips, with a corresponding total displacement of 3.6 in., at which point the beam failed suddenly. Wide flexural cracks near the support and horizontal cracks in the plane of cold joint were observed within the splice region (Figure 8.29). It is concluded that the reinforcing steel yielded at a total load of 91 kips and beam failed at a total load of 96 kips due to failure of the splice, the latter corresponding to a bar stress of 67 ksi (Table 8.3).

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I 71 REDACTED VERSION

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-'age fZ O1" 11 14 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 110 100 90 S80

*70

60 S50

-- 40

~30 20 10 0246 8

10 Total Deflection, in.

Figure 8.28 Total Load vs. Total Deflection for Beam 5 (with a cold joint)

Figure 8.29 Beam 5 (with a cold joint) at Failure Maximum measured crack width versus load for Beam 5 is shown in Figure 8.30; the crack map for Beam 5 is presented in Figure 8.31. The first flexural and horizontal cracks formed at the supports at an average end load of 10 kips (total load of 20 kips). At an average end load of 15 kips, flexural and horizontal cracks were present at both ends of the splice region and both supports (Figure 8.32). At an average end load of 40 kips, a 45-mii width flexural crack and 35-mii width horizontal crack were I-f LL I I i

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bb.J-UUU-ULJ*-U t::U-UUU1bt-UUU I-'age /*i 0? 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building recorded. At this point, the beam was unloaded. The load was reapplied, and at the last load prior to failure at which cracks were marked, the maximum width of the cracks had not increased from first loading (Figure 8.30). Although the crack width was approximately the same, several cracks had increased in length.

60

.* 40 E20 0

10 20 30 40 50 Average End Load, Kips

-~-Flexural crack (1st loading) - Horizontal crack (1st Loading)

Flexural crack (2nd loading) F-Horizontal crack (2nd Loading)

Figure 8.30 Maximum Crack Width vs. Average End Load for Beam 5 North Face

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73 REDACTED VERSION

bbJ-UUU-Ud5*3-LSILU-UUU~b-UUU I-'age (40? 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Figure 8.32 Beam 5, Northeast Splice Region with Horizontal Crack, 15 Kips End Load Failure occurred at an average end load of 48 kips (total load of 96 kips), slightly lower than the failure load for Beam 4 (average end load of 52 kips, total load of 105 kips), which was subjected to monotonically-increasing load up to failure. At failure of Beam 5, the concrete above the cold joint separated from the remainder of the beam, with the horizontal crack propagating along the cold joint throughout a region that was somewhat longer than the splice region. As with the other beams, large flexural cracks were also present near both ends of the splice region (Figure 8.33).

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ki*J-UUU-UdJ-UL::-UUU1b-UUU P-age 10: Ot 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Figure 8.33 Beam 5, Splice Region, 48 Kips End Load 8.6.1.3 Beam 6 The configuration and loading protocol of Beam 6 were similar to those of Beam 5. The beams were cast using the same procedures and at the same time and were tested in the same manner, except that unloading was much slower for Beam 6 and the beam was inspected for cracks more often during the second loading. The testing protocol for Beam 6 is presented in Table 8.2.

The individual load cell readings are plotted versus total deflection in Figure 8.34. As shown in Figure 8.34, the readings for the four load cells were identical, which verifies the assumption that the load was evenly distributed on the four load rods.

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bbML-UUU-U.dJIL-ULSIz-UUUlt2-UUU I-sage (t5 0?" 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building

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-Load Cell A (west)

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",-,,,-oad Cell B (west

20

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-Load Cell C (east S15

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Figure 8.34 Individual Load Cell Readings (Beam 6)

The total load versus total deflection for Beam 6 is plotted in Figure 8.35. Overall, Beam 6 performed very similar to Beam 5. Yielding of the flexural reinforcement was observed at a total load of 92 kips and a total displacement of 2.7 in., compared with 91 kips and 2.7 in. for Beam 5. The maximum horizontal crack width at the unloading point was 30 mils (0.03 in.), compared with 35 mils (0.035 in.) for Beam 5.

Beam 6 also failed due to splice failure (Figure 8.36) at a total load of 100 kips, corresponding to a bar stress of 69 ksi, and a total deflection of 4.7 in. (versus 96 kips and 3.6 in. for Beam 5).

110 100 92 kips 90

.*70

/

50 N 40 0

2 4

6 8

10 Total Deflection, in.

Figure 8.35 Total Load vs. Total Deflection for Beam 6 (with a cold joint) 76 REDACTED VERSION

Ybgi-UUU-US*J-UtU:L-UUUtI5-UUU W-age (I" 0" 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Flxrlcracks na h

upr Figure 8.36 Beam 6 (with a cold joint) at Failure Maximum measured crack width versus load for Beam 6 is shown in Figure 8.37; the crack map for Beam 6 is presented in Figure 8.38. The first flexural cracks formed at the east splice region and support at an average end load of 10 kips. At an average end load of 25 kips, flexural and horizontal cracks were present at both ends of the splice region and both supports (Figure 8.39). At an average end load of 40 kips, a 35-mil (0.035 in.) wide flexural crack and 30-mil (0.03 in.) wide horizontal crack were recorded. At this point, the beam was unloaded. The load was reapplied, and at the last load prior to failure at which cracks were marked (average end load of 40 kips), the crack width had not increased with respect to first loading (Figure 8.37). Although the maximum crack widths remained the same, several cracks had increased in length.

60 E 50 S30 S20

"* 10 010 20 30 40 50 Average End Load, Kips

-- Flexural Crack (1st loading)

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Figure 8.37 Maximum Crack Width vs. Average End Load for Beam 6 Bcchtel and it~ affiliated zornoanic~ which shall not be u:ed. d~da~cd. or reDraduced in anytormat by i

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bbJ-UUU-LdS*-USI-U-UUUltb-UUU i-'age Ri o? 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building a

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I Top Face Peetl Splike Cefiter Une Spike Pedestal Rego Sujpport Figure 8.38 Crack Map for Beam 6. Numbers indicate maximum average end load when cracks marked.

Figure 8.39 Beam 6, Splice Region with Horizontal Crack, 25 Kips End Load Failure occurred at an average end load of 50 kips, slightly lower than for Beam 4 (average end load of 52 kips, total load of 105 kips), and higher than Beam 5 (average end load of 48 kips, total load of 96 kips). As observed in Beams 2 through 5, at failure occurred at the cold joint with the upper concrete separating from the remainder of the beam, with the horizontal crack propagating along the cold joint between the pedestal supports. As for Beam 5, a small region near the centerline was restrained by the CofdniI 2012.

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I Tr-78 REDACTED VERSION

JD-UUU-Ubi-UI-W.-UUU1t$-UUU I-'age f* O 011114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building No. 3-bar hoop and had a tighter horizontal crack and a failure surface that passed through the top of the beam in the vicinity of the hoop. As in the case of the other beams, large flexural cracks were also present near both ends of the splice region (Figure 8.40).

Figure 8.40 Beam 6, Splice Region, 50 Kips End Load 8.7 Summary and Conclusions The effect of preexisting cracks, oriented in the plane of and parallel to the reinforcing steel, on the strength of No. 11-bar lap splices was investigated by testing six beams - three with a splice length of 79 in. and three with a splice length of 120 in. One of the beams with a 79-in, splice was cast monolithically and loaded monotonically to failure. To simulate the cracks, the other five specimens were cast with a cold joint at the mid-height of the reinforcing steel. Two beams (one with a 79-in, splice and one with a 120-in, splice) were loaded monotonically to failure. The other three beams were pre-loaded to develop horizontal cracks in the face of the cold joint, unloaded and then loaded to failure; those beams developed horizontal cracks with widths of 20, 30 and 35 mils (0.02, 0.03, 0.035 in.) just prior to unloading. The test results are summarized below:

1.

For the beam with a splice length of 79 in. and cast with monolithic concrete, the reinforcing steel yielded and the beam failed in flexure.

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se~ve4 79 REDACTED VERSION

bbi-UUU-Ud*i-Ui::.U-UUUI b-UUU l-'age *U or 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building

2.

For the beam with a splice length of 79 in., cast with a cold joint, and subjected to monotonically-increasing load to failure, splice failure took place at a bar stress of 62 ksi, about 8% below the bar yield strength of 67 ksi.

3.

For the beam with a splice length of 79 in., cast with a cold joint and subjected to cyclic loading, horizontal cracks with a maximum width of 20 mils (0.02 in) developed prior to failure. Splice failure took place prior at a bar stress of 57 ksi, about 15% below the bar yield strength (67 ksi).

4.

For the beam with a splice length of 120 in., cast with a cold joint, and subjected to monotonically-increasing load, the reinforcing steel yielded prior to a splice failure, which occurred in the strain-hardening region of the stress-strain curve at a bar stress of 72 ksi.

5.

For the two beams with a splice length of 120 in., cast with a cold joint, and subjected to cyclic loading, horizontal cracks with maximum widths of 30 and 35 mils (0.03 and 0.035 in.) developed prior to splice failure, which occurred at bar stresses of 67 and 69 ksi, respectively, values that equaled or exceeded the bar yield strength.

The following conclusions are based on the test results and analyses presented in this report.

1.

The methods described in this report provide a viable means of simulating a crack in the plane of flexural reinforcement.

2.

The cyclically load beams incorporating a cold joint to simulate crack in the plane of the reinforcement exhibited slightly reduced lap splice capacity compared to the monotonically loaded beams.

3.

In the presence of a simulated crack in the plane of the reinforcing bars, the lap-spliced No. 11 bars with a 79-in, splice length achieved bar stresses of 62 and 57 ksi.

4.

In the presence of a simulated crack in the plane of the reinforcing bars, the lap-spliced No. 11 bars with a 120-in, splice length achieved bar stresses greater than or equal to the yield strength, 67 ksi.

Confid.........

2.........C rpr. i C......[.:...o................do proprietary information to Bechtel and i+t offiflated =cmpanie:z ;.hich :half not be uzed, d'*c~o~ed, or reproduced in anyiformat byi anyi non Bcchte! pa*/wt'hout Bechtel': priorw',rifen perm~ion. All right: rc*.cr'ed.

80 REDACTED VERSION

btYi-UUU-Ut$-U-LU-UUU'Hs-UUU

-'age I:;1 ot 1114.

Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 8.8 What the Testing Means to the Shield Building Situation The following presents the memorandum from Prof. Darwin on various questions from Bechtel.

MEMORANDUM TO: Javeed Munshi FROM: David Darwin DATE: July 13, 2012

SUBJECT:

Interpretation of Splice Test Results presented in SL Report 12-2

1.

How tests represent conditions in the Shield Building.

Laminar cracks have formed in the Shield Building, primarily in the plane of the outer-most reinforcing steel (vertical bars confined by outer horizontal bars). The key question involves the impact of the laminar cracks on the splice strength of the outer reinforcement, which provides confinement for the vertical bars. In the Shield Building, the outer horizontal bars have staggered lap splices so that no two adjacent bars are spliced at the same location. Staggering the splices provides an inheritently stronger condition than if the splices were adiacent by increasing the spacing between the spliced bars, which increases splice capacity. and providing a mechanism to absorb energy should the splices fail. If the loading becomes high enough to cause the splices to fail in the Shield Building, the continuous bars will initially pick up any load shed by the splices. The Shield Building itself is a curved structure, which should result in somewhat higher capacity for splices because of the stress normal to the face between the bars and the concrete. With that as background, the current tests may be viewed as a conservative representation of the conditions in the Shield Building. The tests are conservative because the beams can contain two lap-spliced bars, with no continuous reinforcement. Thus, the spacing between the spliced bars is closer than in the Shields Building, resulting in lower splice strength, and when the splices begin to fail in the beams, no continuous bars are available to absorb the energy that is released. The beams simulate laminar cracks through the construction of a cold joint along most of the length of the beam (see Figures 2.2-2.5 in SL Report 12-2). During the tests, splice failure was preceded by delamination at the cold joint interface.

Confinement in the test specimen is limited to single No. 3-bar hoops on either side of the beams at midspan, which are used to simulate the capacity of the continuous concrete on either side of lap-spliced bars in the Shield Building. Simulating continuity is important because it is highly unlikely that splice failure in the Shield Building will cause total delamination in the vicinity of the splices. Some specimens in the tests were loaded monotonically and some were subjected to a loading-unloading-reloading cycle. The specimens subjected the cyclic loading regime exhibited strength somewhat below the specimens that were loaded monotonically. During the loading of all specimens, a horizontal crack at the interface between the concrete placed above the cold joint and the concrete place below the cold joint grew as the tests progressed. The widths of the horizontal cracks, between 20 and 35 mils, were 81 REDACTED VERSION

bfL-UUU-Ud*-(I:W-UUU1 h-UUU P-age d2 01 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building significantly greater than those observed in the Shield Building (10 mils or less). The concrete in the test specimens had a nominal compressive strength of 5,000 psi, compared to the current strength in the Shield Building, which ranges from 6,000 to 7,000 psi. Overall, the tests provide a conservative measure of the capacity of the splices in the Shield Building.

2.

Relationship between tensile capacity of concrete and bond strength.

The bond strength between reinforcing steel and concrete, as measured in both development and splice tests, is governed by structural failure of the concrete and is only affected to a minor extent by interactions at the steel-concrete surface. The nature of development or splice failure is one of fracture of the concrete parallel to the reinforcing steel. Depending on the configuration of the member, cracks will form through the concrete between the reinforcing bars or through the cover between the individual bars and the exterior of the member. Because of the nature of bond failure, bond strength is a function of both the tensile strength of the concrete and the fracture energy required to open a crack once it has initiated. The similarity between the cracks observed in splice tests and the laminar cracks in the Shield Building is the reason that the question arose as to the effect of the laminar cracks on the lap-splice strength of the bars in the outer layer of reinforcement in the Shield Building.

The presence of cracks that are 10 mils or less in width (as observed in the Shield Building) should not be construed to mean that the concrete has zero tensile strength perpendicular to the cracks. In fact, when concrete fails in tension, the process involves fracture in which the concrete gradually loses its tensile capacity as the cracks open, rather than losing it all at once. The results of the current study are applicable and, in fact, conservative because the crack widths observed for the cyclically-loaded specimens exceeded those observed in the Shield Building -

meaning that the specimens subjected to cyclic load in the current test had a lower residual tensile capacity across the crack than the concrete in the Shield Building.

3.

How results meet ACI Code requirements.

There are no specific requirements in the ACI Code for testing bond in actual structures. The results, however, are intimately connected with the ACI Code because the ACI Code expressions for development and splice length are based on splice tests of monolithically-cast concrete with configurations similar to those used in the current study.

4.

Recommendations for bond strength capacity for reestablishing design basis of Shield Building for various load conditions (wind, tornado, impact, thermal, and seismic loading).

The tests presented in SL Report 12-2 indicate that in the presence of laminar cracks, it would be conservative to conclude that in the Shield Building, the lap-spliced No. 11 bars with a 79 in. splice length can achieve bar stresses on the order of 55 ksi or more and that the lap-spliced No. 11 bars with a 120 in. splice length can achieve yield with bar stresses in excess of 60 ksi. Note that because the bars are staggered in the Shield Building, actual splice capacities would be expected to be higher than these values because of the wider splice spacing in the building compared with that used in the tests. It would be appropriate to use the reinforcement capacity values determined through this testing for all design loading conditions on the Shield Building.

82 REDACTED VERSION

bbYi-UUU-UdJ-UbU-UUU1b-UUU Page Ui 011114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building bbW*-UUU-LS*-LSI-LS-UUUI ti-UUU F'age U* ot 11

4 9

Summary and Recommendations During the removal of concrete in the Shield building for RVCH replacement at Davis-Besse nuclear plant, laminar cracking was observed in the plane of the outer reinforcement mat consisting of No. 11 bars. A detailed condition assessment was carried out to determine the extent of cracking as described in Section 3. This evaluation indicated that cracking is present in most, if not all, of the architectural flute shoulders, two steam line penetration areas and in about 70% of the top 20 ft of the Shield building cylinder. A detailed technical evaluation was also carried out to determine the effect of laminar cracking on the structural capacity of the Shield building to resist its design basis loads as described in Section 4.

] Two outside experts Prof. Sozen and any non Bechtel pa~rxRhoutBechter: ~r[orwrEflen perm~ion. All right rezer:ed.

I I

83 REDACTED VERSION

bbiJ-UUU-Udi;-GS:LU-UUUlfd-UUU l-age *4 Ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Prof. Darwin were retained to provide an independent opinion on the effect of laminar cracking on the structural capacity of the Shield building. Both experts agreed with the technical assessment but recommended that the only issue to be confirmed would be the effect of laminar cracking on the splices of No. i11 bars especially for the outer hoop reinforcement (see Section 5).

The above recommendations by the outside industry experts was carried out by developing a detailed testing program as described in Section 6.

In order to ensure a reliable set of results, Prof. Mete Sozen of Purdue University and Prof. David Darwin of University of Kansas were engaged to carry out a series of tests independently. The test program involved the following:

Purdue test program (see Section 7) involved 6 beams with 79 inch splices and 6 beams with 120 in lap splices. In order to simulate laminar cracking in the plane of the bars, the splices were placed at 6 in spacing with a side cover of 3 inches. The laminar crack of 0.01 inches or more was initiated with a prior loading of up to yield and subsequent unloading.

Kansas test program (see Section 8) involved 3 beams of 79 in splices and 3 beams of 120 in splices. The first beam with 79 in splice was cast monolithically as a benchmark. In order to simulate laminar cracking in the plane of the bars, the remaining 5 beams were cast in two lifts one up to the center of the bars and the second pour the next day to the complete the casting to top of the beam. This process allowed formation of a standard cold joint in the plane of the bars which would serve as a weak plane and help simulate/produce a laminar crack during testing. The reinforcement cover of 3 in was maintained both on the sides and to the top surface of the beam. The laminar crack of 0.01 inches or larger was initiated in the specimen by prior loading and subsequent unloading.

Both Purdue and Kansas beams involved 2 splices side by side within 6 inches of spacing which presents a rather aggressive condition and likely to give lower bound capacity results. Note that splices in the Shield building are actually staggered with spacing of at least 12 inches. Also, the splices in the Shield building conform to the curvature of the building which would provide additional confinement effect not included in the straight beam tests.

In both test programs at Purdue and Kansas, an effort was made to simulate the concrete mix of the Shield building to the extent possible. Purdue used a similar mix and aggregate size. Since it was practically impossible to exactly match the concrete given the age of the plant, every effort was made to test at relatively lower (conservative) compressive strength and tensile strength values to produce conservative bond capacity values. Note that compressive and more importantly, tensile strength of concrete are recognized to be the key parameters of influence for bond strength of reinforcement in concrete. Moreover, Kansas tests were carried out at an age of only 7 days which resulted in lower bound compressive and tensile strengths thus giving very conservative or lower-bound results.

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84 REDACTED VERSION

bbYi-UUU-US*:-UW:I-UUUlrb-UUU h'age *b 0" 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building The average 28 day compressive strength from original construction of the Shield building was 5836 psi.

The average compressive strength of in-place concrete tested using cores taken during the Shield building evaluation in 2011 was 7571 psi. The corresponding tensile strength of in-place concrete was determined to be 918 psi.

The testing at Purdue confirmed that No. 11 bars with a crack in the plane of the bars will be able to develop their full yield both for 79 in splice as well as 120 in splice. This is despite the fact that beams were pre-cracked with 1st cycle loading and had splices next to each other (not staggered) at only 6 in spacing.

The testing at University of Kansas confirmed that No. 11 bars with a simulated crack (involving a cold joint that is pre-cracked) will be able to develop near yield (57 and 62 ksi) for 79 in splice and full yield for 120 in splice. But it should be noted that these results are based on a very aggressive test condition of splices next to each other at 6 in spacing compared to that of the Shield building where splices are staggered and in most cases placed at approximately 12 to 24 in apart. As indicated in Prof. Darwin's memorandum (item 1), as the spliced bar reaches its full capacity, the adjacent continuous bar with yield of 67 ksi (larger than specified 60 ksi for Shield building) is likely to pick up the remainder load and continue to carry it until yield and beyond. This will obviously increase the load capacity of the group of spliced bar and continuous bar adjacent to it to beyond 60 ksi on the average basis.

10 Quality Assurance 10.1 QA Surveillance at Purdue University Bechtel QA performed five (5) surveillances of the testing activities conducted by Purdue University.

These surveillances were performed to ensure that Purdue performed testing activities in accordance with the requirements of Bechtel Engineering Technical Specification for Concrete Specimen Testing Services, 25593-O00-3PS-SY01-O0001, Rev. 0, and Bowen Laboratory, Purdue University "Tests to Determine The Behavior of #11 Bars With Lap Splices", Rev. 0, 1 and 2.

Quality program requirements were categorized as "Augmented Quality" and were met by Purdue University for the activities specified by in 25593-O00-3PS-SY01-O0001.

9B:htcland it* affiliatcd companics:-hich shal! notbc used, d'=c~o*.d, or reproduced,En anyformat by 85 REDACTED VERSION

bbEi-UUU-U5*i-USL(S-UUU1Ib-UUU I-'age *5 ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Surveillances were performed by Bechtel O.A during the following critical activities:

Surveillance Surveillance Surveillance Details Subject No.

Date Purdue 25539-000-03/21/12 Assessed Purdue QA Program to determine if University Quality QSVS-12-001-project specific OQA requirements were met. Also Program 000 reviewed the certification and calibration of Assessment Purdue University's concrete batch plant supplier.

Purdue 25593-000-04/10/12 Verified concrete batching activities including University QSVS-12-003-verification of batch materials, testing and Concrete 000 placement of concrete into "B" series 79" rebar Batching and overlap forms. Observed Bechtel QC performing Placement inspection activities in conjunction with these Activities operations.

Purdue 25593-000-05/07/12 Observed Purdue University performing a "dry University Test QSVS-12-004-run" of the test procedure on an example test "Dry Run" 000 beam. This exercise was conducted to ensure that Activities the procedure was acceptable, and to prove that assumptions made by Purdue in the design of the concrete beams in conjunction with the requirements of the test procedure were acceptable for use with the actual test beams.

Purdue 25593-000-05/10/12 Observed and verified the testing of the 79" rebar University QSVS-12-005-overlap; Beam B-3 Testing of Series 000 "B" test beams Purdue 25593-000-05/30/12 Observed and verified the testing of the 120" University O.SVS-12-006-rebar overlap; Beam A-3 Testing of Series 000 "A" test beams flnnfidrntfrrl ~ 'nl~ Rr-r~-~tr'J flnrn'~riflnn r~nni-~,in-mnfHr-nThiF nnrqfl~~r nrnnrtrtnrxz infnrmilThn tn

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86 REDACTED VERSION

nblYJ-UUU-Ud5*J-USI'U.-UUUlfb-UUU i-'age ut Or 1114 Effect of Laminar Cracks onSplice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Surveillance Activities Surveillances performed to support the test activities included verification of the following critical characteristics associated with the testing activities:

Training Safety Calibration of Instrumentation Certification and Calibration of the Batch Plant Qualification of Personnel performing the Testing Activities Testing Set-up Activities Monitoring Bechtel QC Activities Observation of Testing Activities Reviews of Suppor'ting Test Data Sheets The five (5) surveillances conducted at Bowen Laboratory @ Purdue University are in Appendix C.1.

Condition Reports One condition report was generated as a result of the 5 surveillances. CR 23568-O0O0-GCA-GAMG-00009

- NES Core Support; 25593 - Test Procedure - Tests to Determine the Behavior of #11 Bars with Lap Splices, Section 3.0 -= "Does not address the tolerance required to determine if the roller supports are correctly installed." documents this issue. The project responded by revising test specification specifying a tolerance of 1/4/". See the condition report (CR) in Appendix C.2 for additional details.

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87 REDACTED VERSION

b*-UUU-UL*J-(I--UUUIb-UUU P'age bd ot11114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 10.2 QA Surveillance at University of Kansas Bechtel QA performed four (4) surveillances of the testing activities conducted by the University of Kansas. These surveillances were performed to ensure that the University performed testing activities in accordance with the requirements of Bechtel Engineering Technical Specification for Concrete Specimen Testing Services, 25593-O00-3PS-SY01-O0001, Rev. 0, and the University of Kansas test procedure, "Lap-Splice Beam Tests", Rev. 0 and 1. The testing activities were performed in accordance with these procedures.

Quality program requirements were categorized as "Augmented Quality" and were met by the University of Kansas for the activities specified by in 25593-000-3PS-SY01-00001.

Surveillances were performed by Bechtel QA during the following critical activities:

Surveillance Surveillance Details Surveillance Subject N.Dt The University of 25539-000-03/29/12 Assessed Purdue Q.A Program to determine if Kansas Quality QSVS-12-002-project specific OQA requirements were met.

Program 000 Also reviewed the certification and calibration Assessment of Purdue University's concrete batch plant supplier.

The University of 25593-000-05/24/12 Verified concrete batching activities including Kansas Concrete QSVS-12-007-verification of batch materials, testing and Batching and 000 placement of concrete into "B" series 79" rebar Placement Activities overlap forms. Observed Bechtel QC performing inspection activities in conjunction with these operations.

The University of 25593-000-05/31/12 Observed and verified the testing of the 79" Kansas Testing of QSVS-12-008-rebar overlap - Beams 1, 2, 3 79" splice test 000 beams The University of 25593-000-06/20/12 Observed and verified the testing of the 120" Kansas Testing of QSVS-12-009-rebar overlap - Beams 4, 5, 6 120" splice test 000 beams f-*

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88 REDACTED VERSION

bb3-UUU-U5*3-UEU-L-UUU11b-UUU W'age *U Ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Surveillance Activities Surveillances performed to support the test activities included verification of the following critical characteristics associated with the testing activities:

Training Safety Calibration of Instrumentation Certification and Calibration of the Batch Plant Qualification of Personnel performing the Testing Activities Testing Set-up Activities Monitoring Bechtel OC Activities Observation of Testing Activities Reviews of Supporting Test Data Sheets The four (4) surveillances conducted at the University of Kansas are in Appendix C.3.

Condition Reports Two condition reports were generated as a result of the 4 surveillances. CR 23568-000-GCA-GAMG-00010 -"NES Core Support; 25593 - University of Kansas Concrete Testing for Davis Besse - The current process for mapping cracks during the testing of concrete samples does not adequately document the location of cracks as they occur"; and CR 23568-000-GCA-GAMG-00011 - "NES Core Support; 25593 -

University of Kansas Concrete Testing for Davis Besse - Dial Indicators being used to measure deflection during testing did not contain identification numbers or serial numbers that correspond to calibration certifications". See the condition reports (CRs) in Appendix C.4 for additional details.

11 Quality Control Bechtel QC performed oversight inspections for testing conducted at both Purdue University and University of Kansas. The inspections performed pertained to the casting and testing of each concrete beam per specification and procedure. The tests were setup and performed in accordance to each of the universities procedure.

Bowen Laboratory, Purdue University test procedure "Tests to Determine the Behavior of #11 Bars with Lap Splices" Structural Testing Laboratory, University of Kansas test procedure, "Lap-Splice Beam Tests" 89 REDACTED VERSION

bb*L-UUU-US*i-U.b,-'-UUU1 b-UUU I-'age *U Ot 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Purdue University Inspection Report #t Inspector Date Details 2553-11-PP--O01 SauelWorty Aril 0, 012 Concrete pre-placement inspections and verifications for test beams B1, B2, and B3.

2553-11-PP--002 SauelWorty Aril 7, 012Concrete pre-placement inspections and verifications for test beams Al, A2, and A3.

2553-11-PP--003 SauelWorty Aril 4, 012 Concrete pre-placement inspections and verifications for test beams A4, AS, and A6.

2553-11-PP--004 SauelWorty Aril 0, 012 Concrete pre-placement inspections and verifications for test beams 84, 85, and 86.

2553-11-P-1000 Sauel orty Aril 0, 012 Concrete placement inspections and verifications for test beams 81, 82, and 83.

2553-11-P-1000 Sauel orty Aril 7, 012 Concrete placement inspections and verifications for test beams Al, A2, and A3.

2553-11-P-1000 Sauel orty Aril 4, 012 Concrete placement inspections and verifications for 25539-215-P-1-0003 Samuel Worthy April 30, 2012 Cnrt lcmn npcin n

eiiain o

test beams 84, 85, and 86.

25539-215-cur-1-0004 Samuel Worthy April 17, 2012Coceepsplemnisetosad vrfctosfrtest beams 81, 82, and 83.

25593-115-cure-l-0002 Samuel Worthy April 23, 2012Coceepsplemnisetosad verifications for test beams Al, A2, and A3.

2559-11-cur-1-003 Samul Wrth May7, 012 Concrete post placement inspections and verifications for test beams A4, AS, and A3.

25593-115-cure-1-0003 Samuel Worthy May 1, 2012 Coceepsplemnisetosad verifications for test beams 84, 85, and 86.

25593-115-cur-1-0004 Samuel Worthy May 10, 2012 Osre eu n etn fcnrt em81 25486-007-BT-1-0002 Samuel Worthy May 14, 2012 Observed setup and testing of concrete beam 8-4.

25486-007-BT-1-0002 Samuel Worthy May 17, 2012 Observed setup and testihg of concrete beam B-4.

25481-007-01-00 Ben Vessels Woty May 217, 2012 Observed setup and testing of concrete beam 8-3.

BT-1-0001-4 Ben Vessels May 23, 2012 Observed setup and testing of concrete beam 8-2.

BT-1-0001-5 Ben Vessels May 25, 2012 Observed setup and testing of concrete beam 8-6.

BT-2-0001-6 Ben Vessels May 30, 2012 Observed setup and testing of concrete beam A-3.

BT-1-0001-7 Ben Vessels June 10, 2012 Observed setup and testing of concrete beam A-2.

BT-1-0001-8 Ben Vessels June 4, 2012 Observed setup and testing of concrete beam A-i.

BT-1-0001-90 Ben Vessels June 5, 2012 Observed setup and testing of concrete beam A-1.

BT-1-0001-10 Ben Vessels June 7, 2012 Observed setup and testing of concrete beam A-5.

BT-1-0001-11 Ben Vessels June 8, 2012 Observed setup and testing of concrete beam A-5.

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-'age *J1 ot 11 14 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building University of Kansas Inpcin Inspector Date Details Report# #____________________

Uk-1 Gary Nickolaus May 24, 2012 Pre placement inspections of concrete test beams 1, 2, and 3.

Concrete placement inspections and verifications for test beams 1, Uk-2 Gary Nickolaus May 24, 2012 2,ad3 Concrete post placement inspections and verifications for test uk-3GaryNicklau May31, 012 beams 1, 2, and 3. Setup and testing of beams 1, 2, and 3.

Uk-4 Ben Vessels June 13, 2012 Pre placement inspections of concrete test beams 4, 5, and 6.

Concrete placement inspections and verifications for test beams 4, Uk-5 Ben Vessels June 13, 2012 5,ad6 Concrete post placement inspections and verifications for test Uk-6 Ben Vessels June 20, 2012 bas4,ad6 Uk-7 Ben Vessels June 20, 2012 Concrete testing inspections for beams 4, 5, and 6.

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91 REDACTED VERSION

bbt*-UUU-US*i-UW-L-UUU1 b-UUU P'age YZ of 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 12 References

1.

ACI 408R-03, Bond and Development of Reinforcement of Straight Bars in Tension, American Concrete Institute

2.

ASTM A615, Standard Specification for Deformed and Plain Carbon Steel Bars for Concrete Reinforcement

3.

ACI 318-08, Building Code Requirements for Structural Concrete, American Concrete Institute

4.

ACI 318-63, Building Code Requirements for Reinforced Concrete, American Concrete Institute

5.

Reineck, K. H. "Ultimate Shear Force of Structural Concrete Members without Transverse Reinforcement Derived from Mechanical Model," ACI Structural Journal, Sept-Oct, 1991

6.

Mattock, A. H. and Hawkins, N.M. "Shear Transfer in Reinforced Concrete" PCI Journal, March-April, 1972

7.

Hsu, T., Mau, S.T., Chen, B. "Theory of Shear Transfer Strength of Reinforced Concrete" ACI Structural Journal, March-April, 1987

8.

Condition Report 2011-03346

9.

Condition Report 2011-03996

10. Condition Report 2011-04648

11. Condition Report 2011-04402

12. Calculation C-CSS-099.20-045

13. Calculation C-CSS-099.20-046

14. Calculation VCO3-BO01-O01

15. Calculation VCO3-BO01-O02

16. Calculation VCO3-BOO1-008

17. Updated Safety Analysis Report (USAR) for Davis-Besse Nuclear Power Station No. 1, Rev. 28

18. Davis-Besse Nuclear Power Station Unit 1 Design Criteria Manual, Rev. 26

19. CTL Laboratory Test Report of Concrete in Shield Building, October 27, 2011

20. Shield Building Dwgs. C-100, C-l10 and C-112

21. Dwg. SKZ904, Shield Building Exterior Developed Elevation

22. Kluge and Tuma "Lapped Bar Splices in Concrete Beams," Journal of the American Concrete Institute, V.17, No.1, September 1945

23. Chinn et al "Lapped Splices in Reinforced Concrete Beams," Journal of the American Concrete Institute, V27, No. 2, October 1957

24. ACI 318-11, Building Code Requirements for Structural Concrete, American Concrete Institute Co,:fidentia © 2012 Bc chtcE Corporation. Contain: co nfid cntial on d/or proprictay i nformation to any non.. B,, c chtcl pat wh/';'h t Bechtcl': p ric rw.r~cn pcrm*fon. All right..

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92 REDACTED VERSION

Enclosure B Davis-Besse Nuclear Power Station, Unit No. 1 (Davis-Besse)

Letter L-1 5-328 Bechtel Report No. 25593-000°G83-G EG-0001 6-000.

"Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building" (Non-Proprietary) 1114 pages follow

b*-UUU-u*i:;I-ut1-u-UUUlti-UUU rage 1 or 1 114 (Non-Proprietary Redacted Version)

Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building for FirstEnergy Nuclear Operating Company (FENOC) by Bechtel Power Corporation Prepared by Jave Munshi. PhD, SE, PE, FACl Rita Liano, PE Date 7-30-12 Reviewed by Date 7-30-12_

Approved by Date 7-30-12 rnnfik-ntfril ~ 2012 Rc chtc I Coroo ration. Contains confidcntE~! ~nd,'or ~ro ~ r~ctrV rntorm~ttofl to E~chtckrnd it affi!i~t~d ~rnp~nE~:whfch:haEE notbc u:cd, cThclo:cd, orrcproduccd in ~nytormatD'~r m t'l _=__F_*I

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bbVLI-UUU-UU3-U*I=U-UUU1UJ-UUU 1IagS z o071114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building.

Table of Contents 1

Objective.....................................................................................................

5..

2 Scope.............................................................................................................

3 Background.....................................................................................................

6 3.12 STATEMENT OF CONDITION.......................................................................... 6 3.2 SHIELD BUILDING DESCRIPTION...................................................................... 7 3.3 CURRENT LICENSING and DESIGN BASIS............................................................ 8 3.4 EXTENT OF CRACKING IN THE FLUTE SHOULDERS.................................................. B 3.5 EXTENT OF CRACKING OUTSIDE THE FLUTE SHOULDERS........................................ 10

3.6 DESCRIPTION

OF THE LAMINAR CRACK............................................................ 11 4

Technical Evaluation......................................................................................... 12 4.1 INVESTIGATION INTO THE CRACK.................................................................. 12 4.2 STRUCTU RAL INTEGRITY EVALUATION............................................................. 12 4.3 CONFINEMENT....................................................................................... 15 4.4 PROTECTION FROM ENVIRONMENT............................................................... 16 4.5 ADDITIONAL MARGINS OF SAFETY................................................................. 17 4.6

SUMMARY

OF TECHNICAL EVALUATION........................................................... 17 5

Evaluation by Outside Industry Experts.................................................................... 18 6

Testing Program.............................................................................................. 20 7

Testing at Purdue University................................................................................ 21

7.1 Purpose and Scope

.................................................................................. 21 7.2 Experimental Outline................................................................................ 22 7.3 Materials.............................................................................................. 24 7.4 Observed Relationships between Applied Load and Deflection................................. 26 7.5 Crack Development.................................................................................. 31 7.6 Maximum Reinforcement Stresses Attained...................................................... 35 7.7 Conclusions........................................................................................... 35 7.8 Relevance of the Testing to Shield Building....................................................... 37 7.9 Summary of Bechtel Review........................................................................ 46 Bcchtclaend EL affilia*tod companicwhi*.ch :hall not be u:cd, d~closcd, or rzproduccd in any/form.at by 2

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bbUg-J-UUU-U,*3-tW-UUU1U-UUU irags 3 0? 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 8

Testing at University of Kansas............................................................................. 46

8.1 Purpose and Scope

.................................................................................. 46 8.2 Test Program......................................................................................... 47 8.3 Concrete.............................................................................................. 51 8.4 Cold Joint Construction and Crack Simulation.................................................... 51 8.5 Test Results........................................................................................... 54 8.5.1 Beams 1, 2, and 3 with 79-in, splice length.................................................... 55 8.5.1.1 Beam 1.......................................................................................... 57 8.5.1.2 Beam 2.......................................................................................... 59 8.5.1.3 Beam 3.......................................................................................... 62 8.6 Beams 4, 5, and 6 with 120-in, splice length...................................................... 66 8.6.1 Concrete strength................................................................................ 66 8.6.1.1 Beam 4.......................................................................................... 66 8.6.1.2 Beam 5.......................................................................................... 70 8.6.1.3 Beam 6.......................................................................................... 75 8.7 Summary and Conclusions.......................................................................... 79 8.8 What the Testing Means to the Shield Building Situation....................................... 81 8.9 Summary of Bechtel Review........................................................................ 83 9

Summary and Recommendations.......................................................................... 83 10 Quality Assurance............................................................................................ 85 10.1 QA Surveillance at Purdue University.............................................................. 85 10.2 QA Surveillance at University of Kansas........................................................... 88 11 Quality Control...............................................................................................

89 12 References.................................................................................................... 92 Appendix A - Purdue University Test Report................................................................. A-i Appendix B - University of Kansas Test Report................................................................ B-i Appendix C - Quality Assurance Documentation............................................................. C-i Appendix C.1 - Purdue University Quality Surveillance Report......................................... C-i Appendix C.2 - Purdue University Condition Report................................................... C-il Appendix C.3 - University of Kansas Quality Surveillance Report..................................... C-55 REDACTED VERSION

bb*i-UUU-UW*;.-U~i~U~-UUU1Wd-UUU Hage 40?

o' 1 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building Appendix C.4 - University of Kansas Condition Report................................................ C-63 Appendix D - Quality Control Documentation................................................................ D-1I Appendix D.1l - Purdue University Inspection Report................................................... D-1 Appendix D.2 - University of Kansas Inspection Report............................................... D-61 REDACTED VERSION

bbWJ-UUU-U5*i-UbU-L-UUU'1bS-UUU I~age b 0? '1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 1

Objective The objective of this report is the following:

(i)

Review the splice testing programs for No. 11 bars carried out at Purdue University and University of Kansas (ii)

Provide technical interpretation of results in relation to the bond capacity of No. 11 bars in the Shield building at Davis Besse nuclear plant (iii)

Provide recommendations for residual bond capacity of No. 11 bars with a laminar cracking of the order of 0.01 inches in the plane of the bar (iv)

Provide necessary QA and QC oversight of testing carried out at Purdue and Kansas.

2 Scope The overall scope of program was to provide technical oversight and third party review of testing carried out at the Purdue University and University of Kansas and provide the necessary QA and QC under Bechtel's Quality Program. This testing is being done in order to evaluate the effect of laminar cracks on the strength of No. 11 lap splices present in the Shield building. Bechtel performed vendor oversight of the applicable activities such as batching of the concrete; placing of the concrete, concrete sample testing, and the concrete bond testing to assure compliance with Bechtel's Quality Program. The detailed scope involves the following:

(i)

Review of Background of Shield Building Design and Observed Cracking (ii)

Initial Technical Evaluation (iii)

Testing Program (iv)

Review of Test Results from Purdue University (v)

Review of Test Results from University of Kansas (vi)

Summary of Test Results (vii)

Recommendations (viii)

QA and QC including calibration of equipment Note that Bechtel Q.A/QC provided oversight of the work at Purdue and Kansas with the intent of meeting Bechtel EDPI 437 deemed to be equivalent to an "augmented quality".

It is argued that test results do not have to be "Q" as the objective is to confirm the bond capacity of reinforcement for the Shield Building using the conventional and well established test methods for bond of reinforcement (Note that tests are standard splice tests to confirm the well established industry information on bond and splice behavior). In that sense this testing is characterized as "confirmatory". Thus, although the test results are not "Q", they are deemed to be a valid input to a "Q" calculation.

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5 REDACTED VERSION

DbL-UUU-Ui*L-tLUIL-UUU1Iit-UUU r-age Ii 0? 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 3

Background

3.1 STATEMENT OF CONDITION On October 10, 2011, a laminar crack was found in the architectural flute shoulder area of the opening being cut through the Shield Building cylindrical wall for replacement of the reactor vessel closure head (RVCH) (Figure 3.1). The crack was found on the vertical side of the opening (left side, looking from the outside), generally along the main reinforcing steel of the cylinder, and extending to across the top (approx 6 feet) and across the bottom (approximately 4 feet) of the opening. After some minor manual chipping along the edges, the crack indication along the left and bottom edges essentially disappeared.

Based on the observation, the crack is considered a circumferential laminar tear and not a radial through-thickness direction crack. Condition Report 2011-03346 was initiated to identify this issue.

Further IR scanning revealed similar cracking in each flute shoulder inspected. Cracking outside of the flute shoulders at the top of the Shield Building wall and local cracking around corners of blockouts for steam line Penetrations 39 and 40 was also detected. Condition Reports 2011-04648 and 2011-04402 were initiated to identify these conditions.

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Y::>i-UUU-UdJ-LU-I--UUU~h-UUU I-age I OT 1 114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 3.2 SHIELD BUILDING DESCRIPTION The Shield Building is a safety related free standing cylindrical shell structure with eight (8) "architectural flute areas" as identified on DBNPS Drawing C-220 (see Figure 3.2). During further discussion within this document, each "fluted area" will be addressed as two built up, or thickened "shoulders". The groove between the shoulders will be addressed as the "flute".

The Shield Building design does not consider the flute shoulder area as providing additional structural capacity beyond that provided by the cylindrical shell or dome. From a loading standpoint on the structure, the Shield Building has been evaluated considering the flute shoulder area as an additional dead load.

Reinforcing within the cylindrical shell consists of meridian (vertical) and circumferential (hoop) reinforcing bars forming a grid on both faces of the shell. On the outside face of the shell, the hoop reinforcing is located outside the vertical bars. The same arrangement is true for the inside face reinforcing (i.e. the hoop bars are the inner most reinforcing layer). Reinforcing for the shoulders consists of vertical bars and horizontal ties conforming to the profile of the shoulder. These horizontal ties are anchored into the shell at both ends. Reinforcing details for the Shield Building can be found on DBNPS Drawing C-l20.

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bbI-UUU-(.J-LiIULU-UUUIIb-UUU P'aged ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 3.3 CURRENT LICENSING and DESIGN BASIS USAR Section 3.8.2.2.2 describes the design basis of the Shield Building as:

Biological shielding Providing for the controlled release of the annulus atmosphere under accident conditions Provide environmental protection for the Containment Vessel (tornado wind &

differential pressure, missiles, etc.)

USAR Section 3.8.2.2.4 & 3.8.2.3.4 describes the load combinations for the Shield Building. Per USAR, the most severe load combination per the ultimate strength design method is (D + L+ E' + TA); while, (D +

To+ E) is the most severe load combination per the working stress design method.

Where D = dead load; L = Live load; E'= Maximum Possible Earthquake; TA=Temperature at Accident; To=temperature at Operating conditions; E=Maximum Probable Earthquake.

3.4 EXTENT OF CRACKING IN THE FLUTE SHOULDERS The hydro demolition of the Shield Building for the RVCH opening revealed a laminar crack within the shoulder of a fluted area (see Figure 3.3). Based upon inspection of this crack at the opening, further examination and investigation was carried out. Construction Technology Laboratories (CTL) was contacted to perform Impulse Response (IR) testing. This methodology has been used to investigate the condition of concrete in a non destructive manner for many years.

Impulse Response method measures the structure's frequency at a specific location and plots this frequency with adjacent reading to obtain any change in building frequency. Any change in frequency within a short span would indicate subsurface indications. IR readings were confirmed by core bores in the indicated area (cracking) and adjacent area (no cracking).

IR readings were performed on all 8 readily accessible flute areas (15 out of 16 shoulder areas, one shoulder was not accessible). Based on this information, it was apparent that the laminar cracking initially identified adjacent to the RVCH opening was not restricted to this shoulder but was a generic issue for all shoulders of the Shield Building. Condition Report 2011-03996 was initiated to identify this extent of condition on the Shield Building cracking.

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bbL-UUU-i~S~-LLt[-UUUlti-UUU F-age Y 0t 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building regiai of crackling left bmmiary of access opening Figure 3.3 Cracking in Flute shoulder Region to the Left of the Construction Opening bearing and friction

~forces on bar adhesion and friction forces along the surface of the bar Figure 3.4 Bond Force Transfer Cantdfnid*-:,!

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bbHL*-UUU-U5*L-LtUI::SUUU15-UUUJ rags 1U 0? 1114 Effect of Laminar Cracks on Spiice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 3.5 EXTENT OF CRACKING OUTSIDE THE FLUTE SHOULDERS Top of Shield Building Wall - Although cracking seemed to be essentially confined within the shoulder area for most of the Shield Building height, IR scanning between Shoulders 8-9, 6-7 and 4-5 (Ref. 21) indicated that cracking may be extending into the outer surface of the shell at the top 15 ft of the Shield Building (~'Above EL 780.) The cracking seems to be very tight (most observed crack width less than 0.01 in with one 0.013 in) and essentially following the outside reinforcement in the cover area, as confirmed by core bores. Condition Report 2011-04648 was initiated to identify this condition.

Main Steam Line Penetrations - IR testing also identified two areas of interest to the right of Shoulder 9 and the left of Shoulder 6 at an elevation of approximately 665 feet. These areas are above the Auxiliary Building roof and appear to be associated with the main steam line penetrations (blockouts) in the Main Steam Line Rooms directly below the roof. Core bores were taken and confirmed that each of these areas had cracks at a depth of approximately 5.0 inches for the area adjacent to Shoulder 9 and 6.5 inches for the area adjacent to Shoulder 6. Condition Report 2011-04402 was initiated to identify this condition.

Further lR testing was performed in the Main Steam Line Rooms in all the accessible areas around the main steam penetration blockouts. These tests identified the areas of potential cracking extended below the Auxiliary Building roof into the Main Steam Line Rooms in an area to the left of Penetration 39 and to the right of Penetration 40. These areas are below the areas identified on the Auxiliary Building roof. The indications in the Main Steam Line Rooms were confirmed with core bores that identified cracks at a depth of approximately 5.0 in the area to the left of Penetration 39 and 6.5 inches to the right of Penetration 40. The left side of Penetration 40 and the accessible areas to the right of Penetration 39 did not show indications of cracking based on the IR results.

As a further investigation of the extent of cracking, testing was performed around the containment purge outlet penetration blockout in the Main Station Exhaust Fan Equipment Room. This testing revealed no indications of cracking. Based on this information, the cracking identified in the Main Steam Line rooms is confined to the localized areas to the right of Penetration 40 and to the left of Penetration 39.

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bbU5-UUU-Ud53-ULUI-UUUlrb-UUU I-age 11 ot 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building

3.6 DESCRIPTION

OF THE LAMINAR CRACK Based on the IR readings and confirmatory core bores taken, the description of the laminar crack can best be described as follows.

The cracks are mostly confined within the shoulder area but extend out at the top of the Shield Building.

Additional local cracking is observed near the corners of the main steam line penetration outside the blockouts. The depth of the crack varies with the thickness of the shoulder area but generally is shallower at the narrow portions of the shoulder and deeper at the thicker portions of the shoulder.

The horizontal reinforcing bars for the shoulder area consist of #8 bars at one foot vertical spacing.

These horizontal reinforcing bars are anchored into the cylindrical wall by reinforcing bar hooks located at the shoulder ends. From the IR readings performed in this area, core bores taken in this area, and chipping on the left side of the RVCH opening, it can be concluded that these cracks terminate when approaching these reinforcing hooks except at the top of the Shield Building (~~Above EL 780.)

The width of the crack was measured using a crack comparator on as many locations as possible of the core bores that had cracks. Measurement locations within the core bore were selected in areas which appeared not to be disturbed by the boring bit. Photographs of the crack and crack comparator taken using the boroscope indicated that the cracks are very tight, and in most cases less than 0.01 inches with one reading of 0.013 in.

The cracking around main steam line Penetrations 39 and 40 is limited and located near the corner regions outside the blockouts. The crackingat Penetration 39 is localized at the left side of the penetration covering an area of approximately 175 square feet (approx 15 ft diameter). The crack at Penetration 40 is at the top right corner, covers a similar area. Cracks were measured with a crack comparator in the core bore and confirmed mostly to be less than 0.01 inches with one measured at 0.013 in.

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11 REDACTED VERSION

btB;i-UUU-Ud~3-ULUIL-UUUltb-UUU t-'age 12' OT 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 4

Technical Evaluation 4.1 INVESTIGATION INTO THE C:RACK Concrete that has been exposed to carbon dioxide from the environment can be identified by performing a carbonation test. This test can be used to assess the aging effect of the concrete as it is exposed to the environment. Concrete tests conducted so far have indicated normal carbonation on the surface of the shell and almost negligible carbonation on the interface of the cracks indicating that the concrete crack face examined must not have been exposed to significant amounts of ambient environment (e.g. air).[

]Since the cracks are tight and negligible carbonation on the cracked surface the age of the crack could not be accurately established.

There is no evidence of significant corrosion on the reinforcement.[

] Note that there is no indication of surface cracking significant enough to provide a path for air/moisture to penetrate to the crack surface of interest. Also, where reinforcement bar has been exposed by the investigation there was no evidence of excessive corrosion indicating that cracking is not exposed to the environment.

4.2 STRUCTURAL INTEGRITY EVALUATION Cracking occurs in virtually all concrete structures and because of concrete's inherently low tensile strength can never be totally eliminated. Cracks can occur due to causes such as shrinkage, thermal or other load related situations. Cracks, if sufficiently large, can indicate structural problems; provide an open path to the environment for corrosion of the reinforcing steel; and inhibit a structure from meeting its performance requirements. Control of such cracking due to loads or imposed deformations is generally addressed through the American Concrete Institute (ACI) code requirements by specifying minimum reinforcing steel size and spacing including minimum bonded steel reinforcement and distribution of steel reinforcement.

Typically, cracks need to be repaired if they reduce the strength, stiffness, or durability of the structure to an unacceptable level, or if the function of the structure is seriously impaired. In addition, repairs that improve the appearance of the surface of a concrete structure may be desired from an aesthetic standpoint. Observations such as spalling, exposed reinforcement, and rust staining can be an indication that the reinforced concrete structure has deteriorated.

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Ha 2012 Bechtel Corporation. Contain:. confidec[ia and/or proprictar; information to aynnBechtel pat/;without Bechtel': prirwrilrlen permiio.q All right reer*e.-c 12 REDACTED VERSION

bbU-UUU-U.di-USI-U-UUUIb-UUU I--sage 1i or 11"14 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building

1.

The laminar cracks are located adjacent to the reinforcing steel (hoop and vertical steel) in the shell, potentially creating a separation between the cylindrical shell and the architectural shoulders which were poured monolithically during construction.[

2.

Only one instance of the sub-surface laminar cracks propagating to the surface of the structure has been identified which was above the construction opening. This area was affected by the demolition activity and is not thought to be representative of the general condition. No indication of bulging, spalling, or rust stains exist which would indicate surface connection and degradation of the laminar crack surface. Initial lab testing of the excavated crack surface would also indicate that the area was not subjected to the atmosphere.

3. The laminar cracks have been well identified through IR and core bores and are known to be tight and of hairline nature (mostly within 0.01 in with one crack 0.013 in).[

4.

No surface rust stains exist on the outside surface of the Shield Building,[

]The steel reinforcing was observed to have generally light corrosion or no corrosion at all with no areas of reinforcing exhibiting loss of material.

5.

The #8 reinforcing steel tie bar; spaced 12 inches on centers tie the flute shoulder to the cylindrical shell and provides substantial confinement for the outer shell reinforcement. These horizontal reinforcing tie bars "anchor" the shoulders to the cylindrical shell limiting the width of the laminar crack.[

] For #10's and #11's reinforcing steel the minimum height of the deformation needs to be 0.064" and 0.071" respectively. Since the laminar crack widths are tight (generally < 0.01"), this crack will not adversely affect the load transfer between the steel and concrete.

6.

The development length or lap splice length is a Code value (in inches) used to ensure that the tensile forces from one reinforcing steel can be adequately transferred through the concrete to the adjacent reinforcing steel. Development and splice lengths per the AC! code for ultimate strength n...ctd~-y..................... :............. p crmLz+c n. Al! rih rsczcr d.

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bbW;5-UUU-UUS*-UbU::L-UUUIU-UUU w~ags 140?T 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building design were originally developed to achieve strengths beyond bar yield. The calculated reinforcing stresses are far below code allowable values and therefore full development length or splice length of the bars is not required for actual load transfer. The maximum stress in reinforcement at the critical section due to the controlling design basis loads is only 40% (a margin of 2.5, per Calculation C-CS5-099.20-046, "Evaluation of Shield Building for Permanent Condition") which indicates that actual expected bond stress demand will be significantly less. Furthermore, strength of in-place concrete is much higher than specified strength of 4000 psi at 28-days. The 90 day concrete strength was on average greater than 6000 psi which increases with time. Since concrete strength has a direct impact on the bond strength, this adds extra margin to the available bond strength.

7.

The force transfer between the reinforcement steel and concrete is well established in ACI 408R-03 (Ref. 1). Per Ref. 1, the transfer of forces from the reinforcing steel to the surrounding concrete occurs by a combination of chemical adhesion, frictional at the interface and mechanical anchorage/bearing of deformed lugs (ribs in the reinforcement), (Figure 3.4). After the initial slip between the concrete and reinforcing steel, most of the force is transferred by mechanical bearing between the reinforcing steel ribs and the concrete. (Figure 3.4).[

Ref. i also indicates that friction also plays an important role in load transfer.[

8.

The purpose of the reinforcing steel cover is to transfer the force between reinforcement and concrete, confinement, and protection for the reinforcement from the environment. There is no appreciable effect on these functions as a result of the cracks.

9.

Cracking that has been observed near the main steam line penetrations (Penetrations 39 and 40) is local and limited. The cracking is tight and reinforcement is continuous through the cracked region and remains well anchored outside of this region.[

10. Cracking that extends approximately 20-30 ft into the shell at the top of the Shield Building ("'Above EL 780) is very tight and follows the outside rebar.[

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bbYi-UUU-U~bi5-U;--UUUIh-UUU i-'age lb ol 1114 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 4.3 CONFINEMENT As indicated above, the architectural flute shoulders are not credited for any structural purpose but merely serve as an architectural feature and provide additional cover to the Shield Building reinforcement. With laminar cracking near the reinforcing steel mat, confinement of the shell reinforcement will be addressed. The architectural flute shoulder is connected to the main Shield Building via #8 horizontal reinforcement bars spaced every 12 inches vertically.[

]Per Refs. 3-7, the crack interface shear capacity is directly proportional to the normal force acting on the surface which is supplied by the reinforcement crossing the crack (2 - # 8) in this case.[

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_-U 3-UUUIW-UUU page m( Of 11 Effect of Laminar Cracks on Splice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building For concrete outside the shoulders, visual observations indicated no spalls, popouts or staining of concrete. The hammer sounding of concrete did not reveal any indications of loose concrete on the surface.[

4.4 PROTECTION FROM ENVIRONMENT As indicated above, flute shoulders serve as additional concrete cover to some of the main shell reinforcement. The cracks inside and outside the shoulder regions are all tight (generally < 0.01 in with one crack 0.013 in) and do not seem to have path to the surface for air/moisture migration. There is no evidence of noticeable corrosion on the reinforcement near the cracks.[

Two core bores into the Shield Building cracks were transported to an off site testing laboratory at CTL for further investigation. These tests indicated the following (Ref. 19):

CTL report indicates a carbonation depth of 5-8mm on the surface and no carbonation on the fracture surface. These tests indicate that the cracking occurred after the initial and final set of the concrete; the exact time could not be established.

Data from the CTL report indicates that chloride content of concrete in the Shield Building is insignificant. Since at least 1989, ACI 318 has limited the 'water-soluble' chloride content in severe service conditions (concrete exposed to moisture and an external source of chloride such as deicing chemicals or seawater) to 0.15% of the cement content of the concrete. The highest chloride content value measured was 0.090% (acid-soluble) and 0.037% (water-soluble). Thus, the criteria for a far more severe service condition have been met even if the weight of the coarse and fine aggregate in the concrete is ignored.

CTL laboratory test report indicates that the concrete was in good condition.

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-'age i1 a T 1114 Effect of Laminar Cracks on Spiice Capacity of No. 11 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 4.5 ADDITIONAL MARGINS OF SAFETY The following information details additional margins of safety NOT credited in the technical assessment described above. These additional safety margins provided further assurance that the Shield Building will perform its USAR described design basis functions.

a) The design bases analyses considered the ASTM A-615 specified minimum yield strength of the reinforcing steel of 60,000 psi. The Certified Mill Test reports (CMTR) for the reinforcing steel show minimum yield strength of 66,100 psi, which represents an 10.17% increase in the steel capacity.

b) The design compressive strength for the Shield Building concrete is 4,000 psi. Concrete Pour Test Reports document a minimum f'c = 5730 psi (below grade) and 5836 psi (above grade) respectively.

4.6

SUMMARY

OF TECHNICAL EVALUATION Condition Reports 2011-03346 and 03996 document the condition of the Shield Building due to the cracking in the architectural "flute shoulder" portions of the structure. Condition Report 2011-04648 documents cracking observed in top 20 ft of the Shield Building. Condition Report 2011-04402 documents the condition of cracking in the main steam line Penetrations 39 and 40. The extent of these conditions has been thoroughly investigated using an "Impulse Response" technique to identify potential cracks and core bores into the structure to obtain the location (depth)/extent of the cracks.

Based on this technical evaluation and detailed calculations, NRC issued a confirmatory action letter subject to root-cause evaluation and testing program to be conducted to evaluate the bond capacity of No. 11 hoop splices in cracked regions. Sections 6-8 discuss the testing program and the results in detail. Condition Report 2011-03996 documents the cause for this condition and any required corrective actions.

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i-UUU-id*;--i-U-UUUIb-UUU r'age 1li OT 1114 Effect of Laminar Cracks on Splice Capacity of No. 12 Bars based on Testing Conducted at Purdue University and University of Kansas for Davis-Besse Shield Building 5