ML20040F157

Evaluation of Auxiliary Bldg Control Tower & Electrical Penetration Areas at Midland Plant.

ML20040F157
Person / Time
Site:	Midland
Issue date:	01/31/1982
From:	Corley W, Fiorato A CONSTRUCTION TECHNOLOGY LABORATORIES, INC.
To:
Shared Package
ML20040F153	List: ML20040F152 ML20040F157
References
NUDOCS 8202080388
Download: ML20040F157 (50)

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• MCLOSLRE Report to CONSUMERS POWER COMPAN'l Jackson, Michigan >

EVALUATIOli OF AUXILIARY BUILDING CONTROL TOWER AND ELECTRICAL PENETRATION AREAS AT MIDLAND PLANT by W. G. Corley A.E. Fiorato Submitted by CONSTRUCTON TECHNOLOGY LABORATORIES A Division of the Portland Cement Association 5420 Old Orchard Road Skokie, Illinois 60077 January 1982 8202080388 820129 PDR ADOCK 0500032a A PDP

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TABLE OF CONTENTS Page INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . 1 DESCRIF? ION OF STRUCTURES . . . . . . . . . . . . . . . . . 1 Auxiliary Building Control Tower . . . . . . . . . . . . 6 Electrical Penetration Areas . , . . . . . . . . . . . , S EVALUATION OF CRACKING . . . . . . . . . . . . . . .. . . . . *1 '

Auxiliary Building Control Tower . . . . . . . . . . . . 14 Electrical Penetration Areas . . . . . . . . . . . . . . l'i Other Observations . . . . . . . . . . . . . . . . . . . 29 SIGNIFICANCE OF CRACKS . . . . . . . . . . . . . . . . . . . 31 RECOMMENDED PROGRAM FOR MONITORING STRUCTURAL INTEGRITY DURING IMPLEMENTATION OF REMEDIAL MEASURES . . . . . . . . . 35

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Displacement Monitoring . . . . . . . . . . . . . . . . 38 Crack Monitoring . . . . . . . . . . . . . . . . . . . . 40

SUMMARY

AND CONCLUSIONS . . . . . . . . . . . . . . . . . . 42 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . 44 APPENDIX A - STRENGTH OF CRACKED REINFORCED CONCRETE MEMBERS . . . . . . . . . . . . . . . . . . . . . . Al

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'c' EVALUATION OF AUXILIARY BU?T. DING CONTROL TOWER AND ELECTRICAL PENETRATION AREAS AT MIDLAIT) PLANT by W. G. Ccrley and A. E. Fiorato*

INTRODUCTION This report presents an evaluation of the significance of cracks observed in the Auxiliary Building Control Tower and Electrical Penetration Areas located at Midland Nuclear Power Plant Units 1 and 2. Observed cracks in these structures are described. Significance of cracks with widths of 0.010 in. or greater are discussed in relation to future load-carrying capacity. In addition, a program for monitoring structural

. integrity during implementation of remedial measures is described. Underpinning is being done on this structure as a remedial measure.

DESCRIPTION OF STRUCTURES A site plan for the Midland plant is shown in Fig. l. I ) **

ThG Auxiliary Building is located north of the Turbine Building between the two Reactor Buildings. The Auxiliary Building houses the control room, the access control room, cable spread-ing rooms, engineered safeguard systems, switch-gear equipment,

• Respectively, Divisional Director, Eng ineering Development Division, and Manager, Construction Methods Section, Con-struction Technolcqy Laboratories, A Division of the Portland Cement Association, 5420 Old Orchard Road, Skokie, Illinois 60077.

• • Superscript numbers in parentheses refer to references listed at the end of this report.

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main uteamlines and feedwater pipes, and facilities for handling storage and shipment of nuclear fuel. Because of its safety related functions, the Auxiliary Building is designed as a Seismic Category I structure. As such, it must maintain its integrity during and after a design basis accident including a postulated safe shutdown earthquake.III A plan of the Auxiliary Building is shown in Fig. 2. The base of the structure is 155-ft long as measured between Column Lines A and H. Width of the base structure betwr en C31umn Lines 4.55 and 8.7 is 162 ft. The structure is supported on rein-forced concrete mat foundations, with the bottom of the lowest mat at elevation 562 ft.Il}

A section through the Auxiliary Building is shown in Fig. 3.

A Railroad Bay extends 28 ft north of Column Line A and is sup-ported by backfill soil at elevation 630.5 ft. The south end i

of the Auxiliary Building consists of a Control Tower which is in line with the main part of the building, and two Electrical Penetration Areas that extend east and west 90 ft from either side of the Control Tower. The Control Tower and Electrical Penetration Areas are supported on backfill soil at elevation 609 ft.

Exterior walls, the fuel pool, and most interior walls of the Auxiliary Building are constructed of reinforced con-crete.I I Some interior walls are constructed of masonry or composite concrete and masonry. Reinforced concrete floor and roof slabs are supported by walls, steel beams, and columns.

Reinforcement details for selected areas of the Control Tower l

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and Electrical Penetration Area structures are described briefly in the following sections.

Auxiliarv Building Control Tower The Auxiliary Building Control Tower area is defined by Column Lines 5.3 through 7.8 and H through Kc. The crack inves-tigation discussed in this report also included portions of the Auxiliary Building floor slabs between Column Lines G and H.

Table 1 contains a listing of drawings that were used to obtain data on member thicknesses and on amounts and arrangement of reinforcement. Table 2 shows details of selected floor slabs in the Auxiliary Building Control Tower. Slab thicknesses and primary reinforcement are shown for Column Lines G through H and Column Lines H through Kc.

Except for the 5-f t thick slab-on-grade at elevation 614.0 ft, thicknesses for all elevated slabs range from 1.0 to 1.5 ft. Slab reinforcement ranges from No. 5 bars at 12 in. on centers to No. 11 bars at 9 in. on centers specified concrete s treng th is 4,000 psi for elevated floor slabs and 5,000 psi for foundation mats. Additional reinforcement details are shown in Bechtel drawing s listed in Table 1.

Electrical Penetration Areas Electrical Penetration Areas are located to the east and west of the Auxiliary Building Control Tower. North-south walls along Column Lines 5.3 and 7.8 are common to the Control Tower and the Electrical Penetration Areas. Electrical Penetration Areas are bounded on the south by a 3.5-ft thick wall located

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TABLE 1 - AUXILIARY BUILDING DRAWINGS Bech tel Revision Drawing No.

No.

C-140 14 2/14/81 Project Civil Standards. Rein-forced Concrete General Notes and De tails Sheet No. 1 C-154 4 4/22/81 Slab Reinforcing El. 659'-0" East Wing at Line K C-155 0 1/3/77 Reinforcing Slab Center Section East and West El. 659'-0" C-157 2 1/20/78 Control Room Floor West Side at El. 659'-0" - Cancrete Outline C-158 1 2/3/78 Control Room Floor East Side at El. 659'-0" - Concrete Outline C-159 6 2/22/79 Concrete Outline El. 659 '-0" East and West Wings at Column Line K C-167 5 11/8/79 Floor Reinforcement Plan West Side at El. 691'-0", El. 695'-6", and El. 708'-6" C-168 6 11/24/80 Floor Reinforcement Plan East Side at El. 691'-0" and El. 695'-6" C-169 2 6/13/77 Reinforcing Sections Slab El. 646'-0" C-170 5 8/10/78 Slab Reinforcing El. 659'-0" West Wing at Line K C-171 3 8/11/77 Reinforcing Sections and Details at El. 674'-6" C-172 5 12/14/79 Reinforcing Sections and Details at El. 634'-6" and El. 659'-0" C-174 4 2/22/78 Shear Wall Reinforcement at Column Line 5.3 B6 tween Lines H and Kc C-175 3 8/8/78 Shear Wall Reinforcement at Column Line 7.8 Between Lines H, Kc, and at Lines 4.1 and 9.1 construction technology laboratories

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TABLE 1 - AUXILIARY BUILDING DRAWINGS (Continued)

Bech tel Revision Date Title Drawing No.

No.

C-17 6 1 5/20/77 Shear Wall Elevation at Column Line H C-200 15 7/13/81 Concrete !?cundation Plan El. 568'-0" C-201 9 6/9/76 Concrete Foundation Plan El. 574'-0" C-202 15 3/10/81 Foundation and Floor Plan at El. 584'-0" C-203 5 9/12/77 Floor Plan at El. 599'-0" C-204 11 6/25/81 Floor Plan at El. 614'-0" C-205 12 7/26/79 Floor Plan at El. 634'-6" C-206 11 5/1/79 Floor Plan at El. 646'-0" C-207 8 7/24/81 Concrete Outlines Plan at El. 659'-0" C-208 7 9/15/81 Floor Plan at El. 674'-6" and El. 685'-0" C-213 6 5/12/77 Floor Reinforcement Plan at F1. 614'-0"

! C-214 9 8/29/78 Floor Reinforcement Plan at El. 634'-6" C-215 7 7/31/79 Floor Reinforcement Plan at i

El. 646'-0" C-216 1 12/21/76 Floor Reinforcement Key Plan at El. 659'-0",

C-217 4 8/29/78 Floor Reinforcement Plan at El. 674'-6" and El. 685'-0" l C-222 5 1/24/78 Control Room Floor Reinforcement at El. 659'-0" construction technology labr ytories L i

TABLE 1 - AUXILIARY SUILDING DRAWINGS (Continued)

Bechtel Revision Drawing Date Title No.

No.

C-269 7 5/11/79 Roof Plan at El. 704'-0" C-270 4 8/16/78 Roof Reinforcement Plan at El. 704'-0" C-271 7 8/19/77 Partial Reinforcement Plans C-277 10 10/28/77 Shear Wall Elevations at Column Lines 5.3 and 5.6 C-278 8 7/8/77 Shear Wall Elevations at Column Lines 7.4 and 7.8 C-280 7 5/6/77 Shear Wall Elevations at Column Lines H and Hk C-201 11 11/27/78 Shear Wall Elevations at Column Lines F, G, K, and Kc l

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TABLE 2 - DETAILS OF SELECTED FLOOR SLABS IN AUXILIARY BUILDING CONTROL TOWER

• N ss o umn Lines G-H Column Lines H-Kc Slab Slab Fcimary Rein forcement** Slab Primary Reinforcement **

l Slab Thickness, Thickness, Elevation ft N-S E-W ft N-S E-W 614'-0" 1.25 No. 8 0 12" No. 5@ 12" 5.00 2 - No. 17. @ No. 11 0 9" 9" Top 1 - No. 11 @

9" Bottom

• • 611'-6" 1.00 No. 8@ 12" No. 5@ 12" 1.50 No. 8@ 12" No. 8 0 12"

? r 646'-0" 1.25 No. 8@ 12" No. 5@ 12" 1.00 No. 6@ 12" No. 6@ 12" 659'-0" 1.50 No. 6@ 12" No. 6@ 18" 1.25 No. 6@ 12" No. 6@ 12" 659'-0" (Cor ridor) 1.25 No. 6@ 12 '* No. 6@ 12"

• Between Column Lines 5.3 and 7.8

• • Top and bottom rein forcement unless otherwise noted 8

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adjacent to Column Line K. The north sides of the Penetration Areas are adjacent to the Reactor Buildings.

Tables 3 and 4 list details of selected floor slabs and walls in the Electrical Penetration Areas. These details were obtained from Bechtel drawings listed in Table 1. Elevated floor slabs in the Electrical Penetration Areas generally range from 1.0 to.2.0-ft in thickness with primary slab reinforcement ranging from No. 5 bars at 12-in. on centers to No. 11 bars at 9-in. on centers. Primary structural walls in the Electrical Penetration Areas include the wall along Column Line K and walls along Column Lines 5.3 and 7.8. Details of these walls are given in Table 4.

EVALUATION OF CRACKING On November 5 and 6, 1981, personnel of the Construction Technology Laboratories (CTL) inspected selected areas of the Auxiliary Building Control Tower and Electrical Penetration Areas. The inspection included a visual survey of selected floor slabs and roof surfaces. Areas selected for inspection were based on a need to obtain data on possible effects of differential settlement between the Electrical Penetration Areas, the Auxiliary Building Control Tower Area, and remaining portions of the Au::lliary Building. Therefore, primary emphasis was given to inspection of floors and roofs near intersections of these building areas. .

It should be noted that access to most areas was difficult because of construction work in progress, and because equipment already in-place obstructed many areas. Inspection of all wall

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TABLE 3 - DETAILS OF SELECTED FLOOR SLAES IN ELECTRICAL PENETRATION AREAS

• Slab Slab Thickness, Primary Reinforcement **

Elevation ft l N-S E-W 614'-0" 5.00 (Slab-on-Ground) No. 11 @ 9" No. 11 @ 9" 1.25 (Elevated Slab) No. 6@ 12" No. 6@ 12' 628'-6" 1.00 (Lines 5.0 - 5.3 No. 5 @ 12" No. 5 @ 12" and 7.8 - 8.2) 2.00 (Elsewhere) No. 11 @ 9" No. 11 @ 9" 642'-7" 1.00 No. 5@ 12" No. 5@ 12" l

659'-0" 3.50 (Lines 4.6 - 5.3 No. 6@ 9" No. 6@ 12" and 7.8 - 8.6) Top No. 8@ 12" Bottom 1.25 (Elsewhere) No. 6@ 12" No. 6@ 12" 674'-6" 1.75 No. 6@ 12" No. 6 @ 12" 695'-6" 1.75 No. 8@ 12" No. 8@ 12"

• East and west areas symmetrical

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TABLE 4 - DETAILS OF SELECTED WALLS IN ELECTRICAL PENETRATION AREAS Wall Wall Primary Primary Thickness, Vertical Horizontal Description ft Reinforcement

• Reinforcement

• Wall @ Column Line K 3.5 No. 11 0 9" No. 11 0 9"

- Elev. 614.0' to 695.5'

- West and east elec.

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- Elev. 634.5' to 674.5' 3.0 No. 11 @ 9" No. 11 @ 12"

- Elev. 674.5' to 704.0' 3.0 No. 11 @ 9" No. 11 @ 9"

' Wall @ Column Line 5.3 From Column Line Hk to Kc

- Elev. 614.0' to 634.5' 3.0 No. 11 @ 9" No. 11 @ 12" 8 - Elev. 634.5' to 674.5' 3.0 No. 11 @ 9" No. 11 @ 12"

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areas was conducted from eye level at selected floor elevations.

General lighting in all areas of inspection was relatively poor.

Therefore, primary . light for inspection was provided by hand-held flashlights.

In addition to visual observations, widths of selected cracks were measured using a 50-power crack microscope with a manufacturer's rated sensitivity of 0.001 in.

Approximate crack locations were measured using commercial quality tape measures.

Because of difficult access to many wall and floor areas,

" exact" crack locations could not always be obtained. However, the accuracy of the measurements is well within that required to draw conclusions based on the results.

Auxiliarv Building Control Tower Figures 4 through 7 show cracks mapped cn the top surface of floor slabs in the Auxiliary Building Control Tower at eleva-tions 614.0, 634.5, 646.0, and 659.0 ft. At elevations 614.0, 634.5, and 646.0 ft only a few hairline cracks were observed.

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Widths were less than 0.010 in.

At elevation 659.0 ft numerous cracks were observed in the I

floor slab between Column Lines G and H in the vicinity of Column Line 7.4. Maximum measured crack width in this area was approximately 0.015 in. Because floor cracks were inactive and were filled with dust, only approximate crack widths could be measured. The cracks observed in this area generally ran between the exposed slab edge and nearby penetrations in the slab area. Also, the cracked portion of slab is significantly thinner than adjacent slab areas. This type of cracking can

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occur because of the ef fect of discontinuities on volume changes that occur during curing and drying of concrete.

Inspection of the Control Tower floor areas indicated that a thin topping (approximately 1/8 in.) may have been applied over the cast concrete to provide a wearing surface. At the i

time of the site inspection no information could be obtained on the nature of the topping er when it had been applied. However, the topping has no influence on structural performance.

For the inspection of the Auxiliary Building Control Tower, primary emphasis was given to those areas between Column Lines G and H, und at Column Lines 5.3 and 7.8. These areas represent the intersection of the Control Tower Area with the Electrical Penetration Areas and the remainder of the Auxilicry Building.

If differential settlement between the Auxiliary Building Con-trol Tower, the Electrical Penetration Areas, and the remainder of the Auxiliary Building ware to occur, it is reasonable to expect that cracking would occur in the areas inspected.

i Electrical Penetration Areas Results of crack mapping for the west and east Electrical Penetration Areas are presented in Figs. 8 through 24. Figures 8 through 13 show cracks observed in floors of the west Elec-trical Penetration Area. Figures 14 through 19 show cracks observed in floors of the east Electrical Penetration Areas.

Figures 20 thcough 23 show cracks observed in the wall along Column Line K in both the west and east Electrical Penetration Areas. Finally, Fig. 24 shows cracks observed in the wall at Column Line 5.3 of the west Electrical Penetration Area.

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Only cracks less than 0.010 in, were observed in the floor 4 slabs. These are the types of fine cracks that commonly occur ,

because of temperature and shrinkage related volume changes.

The cracks observed are similar to those seen in industrial floors.

i Wall cracks shown in Figs. 20 through 24 can Liso be attri-buted to volume changes caused by temperature and shrinkage of wall concrete combined with restraining effect of the floor

slabs. Cores taken at selected locations in the wall located along Column Line K indicated that several cracks did penetr&te through the wall thickness. This observation suggests that the l

cracks cannot be attributed to out-of-plane bending as a primary cause. Therefore, diaphragm action appears to be the most likely cause of cracking. Maximum measured crack width in the walls was 0.010 in.

Most of the interior surfaces (north face) of the wall along Column Line K had been painted prior to the inspection in November of 1981.

Other Observations Figure 25 shows cracks mapped by Becntel personnel in partition walls of the Ocntrcl Rcc,T. at elevation 614.0 ft.I1)

These nonstructural partition walls do not extend the full story height and are not attached to the ceiling slab. Vertical cracks were mapped at control joints loc'ated at a steel column near the center of each wall. Other intermittant cracks were recorded between Column Lines H and Kc. These were primarily construction mnncion taboratories

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located at vertical control joints on either side of the center steel column.

The nonstructural walls wer.e placed after the structure was completed. The 2-ft thick wills contain No. 8 bars at 12-in, centers for vertical reinforcement and No. 6 bars at 12-in.

centers for horizontal reinforcement. The walls were cast around and key into the columns at Line J. Cracks that formed are attributed to restrained volume changes and are not struc-turally significant. On the basis of these observations, it is concluded that the observed cracks do not change stability of the walls.

On December 4, 1981, a visual inspection of selected walls in the north end of the Auxiliari Building was made by Dr. W. G.

Corley and Dr. M. A. Sozen. Several cracks were seen in the wall at Column Line A. Measured widths of these cracks ranged up to 0.010 in. Spacing and widths were similar to those of cracks in other parts of the building. The cracks are also typical of restrained volume change cracking that normally

) would be expected.

SIGNIFICANCE OF CRACKS Cracks observed on November 5 and 6, 1981, in the Auxiliary Building Control Tower and Electrical Penetration Areas are attributed to volume changes that occur in concrete during curing and subsequent drying. No evidende of structural dis-tress was observed.

The pattern of cracks observed in the Auxiliary Building Control Tower and Electrical Penetration Areas was not con-construction technology raboratories o

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sistent with structural movements that would occur as a result of hypothesized differential settlements. Figures 2 and 3 show those areas of the Auxiliary Building that are supported on

' original cbil, and those that are supported on backfill soil.

If ittis hypothesized that those areas of the building on backfill soil'could settle relative to those areas on original soil, seve.ral types of'~ structural movement would be anticipated.

For example, it would be possible for Electrical Penetration Areas to settle relative to the Control Tower Area, or the Control Tower Area and Electrical Penetration Areas could settle reiative to~ th'ose areas of the Auxiliary Building supported on original soil.

If settlements were significant enough to cause cracking in the Auxiliary Building, it is reasonable that cracks would develop in a pattern consistent with hypothesized settlements.

Considering Fig, 20, for example, if the free end of the west

(" Electrical Penetration Area settles relative to the Auxiliary Building Control Tower, defined at Column Line 5.3, structural cracking [would initiate at the upper levels of the wall and continue tcward the base with a general inclination toward l

Column Line 5.3. This type of pattern was not evident in crac,ks , observed during the November 1981 survey.

Using similar r-easoning, the observed pattern of cracks in floor slabs of the Electrical Penetration Areas were not indi-cative,of structural movements. The same was true of floor cracks cbserved' in the Auxiliary Building Control Tower.

/

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! construction technology laboratories

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As a measure of significance of observed cracks relative to future integrity of the structure,* the tensile stress that uncracked concrete is assumed to carry was compared to available tensile capacity provided by structural reinforcement crossing the cracks. This calculation was made for sections in the vicinity of cracks that had a measured width of 0.010 in. or greater. Available structural reinforcement was determined from Bechtel drawings listed in Table 1.

Table 5 summarizes comparison of " tensile capacity" for members in which cracks larger than 0.010 in. were observed.

In the calculation concrete is assumed to carry a principle tensile stress of 4 Nbfwhereffisspecifiedconcretecompres-sive strength. This assumption is consistent with Section 11.4.2.2 of the ACI Building Code. ( } Resistance of reinforce-ment was calculated as A g f , where A equals area of reinforce-s ment and f equals specified yield stress of reinforcement.

If calculated resistance provided by reinforcement crossing thecrackexceeds4Yffthereissufficientreinforcementto carry the stress attributed to the concrete. As indicated in Table 5, resistance provided by available reinforcement in the walls and floors of the Auxiliary Building exceeds tensile stress assumed to be carried by concrete.

• A general discussion of strength of cracked reinforced concrete members is given in Appendix A.

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TABLE 5 - AVAILABLE " TENSILE CAPACITY" AT SELECTED CRACK LOCATIONS Element Location 4/f[A g (kips) Af g y (kips)

Floor Slab Control Tower Elev. 659.0' 45.5 52.8

- Between Column Lines G and II

- Adjacent to Column Line 7.4 Wall West Electrical Penetration Area 142.6 249.6

- Column Line K

- Between Column Lines 3.0 and 4.0

- Between Elevations 628.5' and 642.6' l

l t Wall East Electrical Penetration Area 142.6 249.6

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I RECOMMENDED PROGRAM FOR MONITORING STRUCTURAL INTEGRITY DURING IMPLEMENTATION OF REMEDIAL MEASURES As part of remedial measures to eliminate the possibility of unsatisfactory foundation conditions, selected areas of the 4 Auxiliary Building will be underpinned.III Figure 26 shows the underpinning construction sequence plan.ned as cutlined in public hearing testimony from Midland Plant Units 1 and 2. III As part of the underpinning construction procedure a tem-porary s/ stem of post-tensioning ties has been 3.nstalled to apply a compressive force to the upper part of the east-west walls of the Electrical Penetration Areas.I } Cetails of the post-tensioning system are shown in Fig. 27. The post-tensioning ties are to be removed when temporary supports are installed and jacking loads are applied under the Electrical Penetration Areas. The temporary post-tensioning system was in place at the time of crack inspection in November 1981.*

During underpinning operations it will be necessary to monitor movement of existing structures including selected areas of the Auxiliary Building. Monitoring operations should include continuous measurement of structural displacements and periodic visual inspection for cracking.

• Note that crack mapping undertaken by CTL personnel in November 1981 was compared to earlier surveys conducted by Becthel per-sonnel prior to installation of the temporary post-tensioning.

The similarity of observed crack patterns in both inspections indicates that application of temporary post-tensioning did not have a significant effect on existing cracks.

~35- construction technology laboratories

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T O 5 Et 1066 StrJQ E TEf! dot 1 ULTtHATE CAPACIT Y : <410 kips Fm. 27 TEMPORARY POST TENSIONING SYSTEM mL

l Disolacement Monitoring A continuous time-history of displacements of the Auxiliary Building should be maintained during underpinning operations.

It is recommended that readings be taken on a daily basis with a maximum interval of one week. Additional readings should be taken at selected construction milestones.

Displacement measurements should be made to monitor absolute movement and relative distortions of struc eural elements.

Figure 28 shows approximate locations of recommended Jisplace-ment measurement points. Designation of absolute and relative measurement points will be completed as part of the overall monitoring plan prior to start of underpinning operations.

i Displaccment measurements should be recorded as a function <

of time for the duration of underpinning operations. Signifi-cant construction milestones should be identified at appropriate time intervals. Prior to start of underpinning, limiting dis-tortion criteria should be selected so that critical deformation limits of the structure are not exceeded. In this way the dis-tortion versus time plot will provide a warning of impending structural distress. If distortion limits are reached underpin-ning operations should be stopped until remedial measures are evaluated.

It is also recommended that the time-history of distortions be submitted on a regular basis to a consultant familiar with reinforced concrete behavior and design. The consultant will provide recommendations on trends observed in the data. Prior construction technology laboratories

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to start of underpinning operations and distortion monitoring, the consultant should review details of the monitoring plan.

Crack Monitoring As a supplement to the displacement monitoring program, periodic visual inspections of the Auxiliary Building Control Tower and Electrical Penetration Areas should be made to deter-mine if new cracking has developed or if existing cracks have changed in width or length. Crack inspections should be con-ducted on a periodic basis by qualified personnel. In addition, a consultant knowledgeable in reinforced concrete design and behavior should inspect the Auxiliary Building at significant construction milestones. Personnel who monitor cracking should be instructed in cracx mapping techniques by the consultant prior to start of operations.

The following criteria should be used for evaluation of observed crack widths:

1. If a new crack develops that is wider than 0.010 in.,

a consultant should evaluate signifance of the new cracking. Within two hours af ter observation of the crack the consultant should provide a verbal report recommending whether underpinning operations should stop or continue. The verbal report should be con-firmed with a written report within five days.

2. If any crack exceeds 0.030 in. in width a consultant should evaluate significance of.the cracking. Within two hours af ter observation of the crack the consultant i

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should provide a verbal report recommending whether underpinning operations should stop or continue. The verbal report should be confirmed with a written report within five days.

3. If development of yield strain in the reinforcement is inferred from any observed crack, underpinning opera-

t. ions should be stopped immediately. Individual criteria will be recommended by the consultant for each structure. If criteria are exceeded a consultant should evaluate significance of the cracking. Within two hours af ter observation of the crack the consultant should provide a verbal report recommending whether underpinning operations should resume. The verbal report should be confirmed by a written report within five days.

The following criteria should be used in evaluation of the significance of cracks that Cavelop in the Auxiliairy Building:

1. Geometry of Member.

2. Amount and Distribution of Reinforcement in the Member.

l 3. Material Properties of the Member.

i l 4. Function of the Member.

i

5. Magnitude and Distribution of Loads on the Member.

6. Construction Technique.

7. Sequence of Construction. .

8. Crack Location and Distribution.

9. Crack Size.

10. Interaction of Multiple Cracks.

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! j

Basically these criteria define a procedure that requires the function and load carrying mechanism of the member or st ruc-ture to first be detined. Then, the influence of cracks on the path of load distribution is determined. In this way the cause of cracking is defined and the influence of cracking on future load carrying capacity of the structure can be evaluated.

In evaluating cracks in reinforced concrete structures it is not sufficient to base conclusions on a single criteria such as crack width. The overall crack pattern including location and direction of cracks, length and width of cracks, and inter-relationship between multiple cracks must be considered. The pattern of cracking provides significant clues with regards to causes of cracks and their effects on future performance.

~

SUMMARY

AND CONCLUSIONS This report presents an evaluation of the significance of cracks observed in the Auxiliary Building, Control Tower, and Electrical Penetration Areas of Midland Plant Units 1 and 2.

Cracks observed in these structures by Construction Technology Laboratories personnel on November 5 and 6, 1981, are attributed l to restrained volume changes that occur during curing and drying of concrete. No indications of structural distress were l

observed during the site visit. Calculations based on section l geometry indicate that structural reinforcement provided in l .

wells and floors at selected crack locations has a capacity in excess of the tensile cracking stress attributed to the concrete.

construction technology laboratories

A program for ronitoring structural integrity of the Auxiliary Building Control Tower and Electrical Penetration Areas during implementation of remedial measures to underpin the structure is also outlined. It is recomrar.ded that measured displacements be used as the primary means of monitoring behav-ior of the structures. It is also recommended that continuous displacement measurements be supplemented with periodic visual inspections to monitor cracking in the structures. Displacement and crack monitoring chould be reviewed by a consultant know-ledgeable in reinforced concrete behavior and design.

construction technology laboratories 4

REFERENCES

1. " Testimony of Edmund M. Burke, W. Cene Corley, James P.

Gould, Theodore E. Johnson, and Mete Sozen, on Behalf of the Applicant Regarding Remedial Measures for the Midland Plant Auxiliary Building and Feedwater Isolation Valve Pits," United States of America Nuclear Regulatory Com-mission, Atomic Safety and Licensing Board, Public Hearing Testimony, Docket Nos. 50-3290M, 50-330CM, 50-3290L, and 50-3300L, Vol. 1-Text and Vol. 2-Figures.

2. ACI Committee 318, " Building Code Requirements for Rein-forced Concrete (ACI 318-77) ," American Concrete Institute, Detroit, 1977.

~44~ Construction technology laboratories 1

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APPENDIX A STRENGTH OF CRACKED REINFORCED CONCRETE MEMBERS 1 i

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APPENDIX A TABLE OF CONTENTS Page No.

INTRODUCTION A-1 TESTS OF STRUCTURAL WALLS A-1 Tests of " Low-Rise" Structural Walls A-2 j Tests of "High-Rise" Structural Walls A-4 TESTS OF BEAMS A-13 TESTS OF CONTAINMENT ELEMENTS A-15

SUMMARY

AND CONCLUSIONS A-16 REFERENCES A-23 f

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construction technology laboratories

s APPENDIX A STRENGTH OF CRACKED REINFORCED CONCRETE MEMBERS by A. E. Fiorato and W. G. Corley*

INTRODUCTION Cracking is an inherent characteristic of reinforced con-crete structures. The existence of cracks is not necessarily indicative of structural distress. The objective of this report is to clarify the relationship between cracking and strength of reinforced concrete members. The relationship will be demon-strated by examining the response of selected structural members that have been loaded to destruction in the laboratory. To provide a cross-sec' ion of data, results from tests on struc-tural walls, beams, and containment elements will be considered.

TESTS OF STRUCTURAL WALLS Reinforced concrete structural walls are commonly used as lateral load resisting elements in buildings. Both " low-rise" walls, which act as deep beams, and "high-rise" walls, which undergo significant flexural yielding, have been tested in the

! laboratory.

l

• Respectively, Manager, Construction' Methods Section and Divisional Director, Engineering Development Division, Construction Technology Laboratories, a Division of the Portland Cement Association, 5420 Old Orchard Road, Skokie, Illinois 60077.

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• Tests of " Low-Rise" Structural Walls Figure 1 shows the test setup used to apply reversing loads to eight specimens representing " low-rise" structural walls with boundary elements. (1)

• Principal variables in this test program included amount of flexural reinforcement, amount of horizontal wall reinforcement, amount of vertical wall reinforcement, and height-to-horizontal leng th rat-io of the wall. Flexural reinforcement was varied from 1.8 to 6.4% of the boundary element area. Horizontal and vertical wall reinforcement were varied from 0 to 0.5% of the wall area. Height-to-horizontal length ratio of the wall was varied from 1:4 to 1:1. The test program was designed to deter-mine effects of load reversals. Data obtained also provided information on the relationship between cracking and strength.

Principal test results for the eight walls are shown in Table 1. For all specimens, except B5-4, the maximum nominal shear stress in the wall exceeded the stress at first observed shear cracking by a factor of at least 2.4. For Specimen B5-4, #

which contained no vertical reinforcement in the diaphram, the maximum nominal staar stress exceeded the stress at first shear cracking by a factor of 1.5. The ratio of maximum nominal shear force to first shear cracking even exceeded 2.5 for Specimen B4-3 which contained no horizontal reinforement. For each of the " low-rise" walls tested, measured capacity exceeded

• The superscript numbers in parentheses refer to references listed at the end of this report. A copy of each reference is attached. -

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i TABLE 1 - Principal Test Results (1)

, First Shear Cracking Ultimate Load End of Test Shear Shear Shear

' stress A Deflect %n d stress 1 Deflection d stress h Specimen VariableIII r cr.

psi d al in.

hw r.

u psi d at, h w rm, d in. psi B11 p = 1.8%(2) 420 6.5 0.027 0.00072 1,010 15.5 0.23 280 4.4 0.0061~

B21 p = 6.4%(2) 240 4.9 0.016 0.00043 767 15.8 0.26 0.0069 270 5.5 812 Control 330 5.2 not measured 881 14.1 0 21 0.0056 190 3.0 I

B32R R epair 100 3.3 0.020 0 00053 676 11.5 0.49 0.0130 230 4.0 i 84-3 ph = 0 320 6.1 0.015 0.00040 810 15.4 0.20 0.0053 160 3.0 t 85-4 '

on = 0 33C 5.2 0.012 0.00032 538 8.3 0.20 0.0053 280 4.3 .

B6-4 pn = 0.25% 280 5.0 0.013 0.00035 686 12.3 0.23 0 0061 190 3.5 f' B 7-5 h w,f w = 1/4 330 5.4 0.006 0.00032 906 14.8 0.16 0 0085 350 5.7 885 hwd, = 1 200 3.5 0.027 0 00036 704 12,1 0.42 0.0056 150 2.6 (II E neeot as indicated below, au specimens had the fotfowing characteristics:

hwlf, = t/2, oh

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l (2) spec, mens subsected to static load /q. All other specamens subjected to load reversals.

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Figure.2 shows crack patterns in the " low-rise" walls at the ultimate load levels listed in Table 1. The inclined cracks are indicative of shear stresses that predominate in

short cantilever members. It is apparent that the presence of cracks does not necessarily indicate loss of structural capa-city. Even with the extensive cracking shown in Fig. 2, the walls were carrying maximum applied loads. For a particular section geometry and applied loading, structural capacity is a function of the amount and distribution of reinforcement.

There was no evidence that reversing loads caused residual stresses that reduced strength of the walls. Additional data on these tests are given in Reference 1.

Tests of "Hich-Rise" Structural Walls j Tests reported in References 2, 3, and 4 were conducted to 4

obtain data on strength and deformation capacity of structural walls subjected to significant numbers of inelastic load rever sa ls . Effects of load history, section shape, vertical and horizontal reinforcement, confinement reinforcement, i^

moment-to-shear ratio, axial compressive stress, and concrete strength were considered.

Figure 3 shows the setup used for tests of "high-rise" walls. The walls were tested as vertical cantilever members with forces applied through the top slab. The behavior of one of the test specimens is described in detail in the following A-4 construction technology laboratories

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parargraphs, This behavior illustrates the influence of crackra that developed during the tests. Additional data on other specimens can be obtained in Ref erences 2, 3, and 4.

i Figure 4 shows the measured load vs deflection relationship ,

for Specimen B3. This was a barbell shaped specimen which represented a wall with column boundary elements at each end.

As can be seen in Fig. 4, the wall was subjected to increasing ,

levels of icad reversals. The test consisted of 42 complete load cycles.

Initial cracking was observed in the fourth cycle at a load of 28 kips. First yielding in the vertical flexural reinforce-

ment occurred in Cycle 10 at a load of 45 kips. Maximum 1

measured crack widths were 0.012 in. in the tension boundary element and 04 025 in. across a diagonal crack in the web.

Figure 5 is a photograph of Specimen B3 at Load stage 112.

This load stage , which is marked on Fig. 4, represents a point in the test when the specimen was unloaded. There were no applied in-plane horizontal forces. Figure 5 shows the inter-secting pattern of cracks in the lower six feet of the wall after the first 21 load cycles.

From Load S tage 112, loads were increased in a positive direction until Load S tage 117 was reached. Figure 6 shows the condition of the specimen at Load S tage 117. At Load Stage 117, maximum measured crack width in the tension boundary element was 0.07 in. and maximum measured crack width in the wall web was approximately 0.16 in. It should be noted that ,

at this load stage, the wall had been pushed to a lateral deflection of more than three times its yield deflection.

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After Load Stage 117 was reached, the wall was unloaded and pushed in the opposite direction until Lead Stage 123 was reached. Figure 7 shows the condition of Specimen B3 at Load Stage 123. At this load stage, the maximum crack width measured f r. the tension column was approximately 0.07 in. and the maximum measured crack width in the wall web was 0.16 in. When the wall was again unloaded, to Load Stage 125, the crack pattern i

shown in Fig. 8 resulted. It is clearly evident from the behavior' of Specimen B3 (and from other specimens tested) that the presence of cracks did not prevent the walls from main-taining their structural integrity and developing their nominal s treng th .

, Figure 9 shows Specimen B3 at Load Stage 196. This load stage is also indicated in Fig. 4. The cracking pattern in Fig. 9 is indicative of severe distress in the member, yet at this stage the wall carried its maximum load which corresponded to approximately 3.1/T[. For purposes of comparison, the design strength this member calculated in accordance with the - American Concrete Institute Building Code is 2.3 vi[.

A question that occurs in evaluating cracked reinforced concrete structures is whether residual stresses associated with the occurrence of cracks influence strength of the member.

It is evident from the behavior of Specimen B3 that internally balanced residual stresses, such as those existing when the specimen was unloaded, did not in fluence 's treng th .

A-10 construction technoingy laboratories

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l TESTS OF BEAMS Background data on strength of cracked reinforced concrete members can also be obtained from tests on reinforced concrete besms. Data from tests reported by Scribner and Wight are shown in Figs. 10 and ll.I$I Figure 10 shows the load vs displacement curve for a reinforced concrete beam element that contained positive and negative steel. The beam was subjected to increasing levels of fully reversed lead cycles. Yielding occurred in the first load cycle as indicated in Fig. 10.

Figure 11 illustrates crack patterns that developed during the first inelastic loading and during subsequent load rever-sals. As increasing numbers of load cycles were applied, the entire beam moment at the face of the column was carried by a force couple between the top and bottom layers of longitudinal steel. Thus, applied moments were primarily resisted by the positive and negative longitudinal reinforcement.

Under load reversals a complete crack plane, labeled A-B-C in Fig. 11, formed through the beam. This crack plane did not prevent the beam from transferring load. During the final stages of the test, increasing numbers of inelastic load rever-sals caused concrete near the face of the column to abrade and eventually disintegrate. This resulted in a " slip plane" along the beam at the face of the column. The significance of such a slip plane is related to the number of inelastic load reversals and the level of shear stress on the beam. The existence of A-13 construction technology laboratories a

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the crack plane did not become significant until repeated num-bers of inelastic cycles were applied.

Additional data on beam tests can be obtained from References 6 and 7. In addition, tests of beam-column joints reported in Reference 8 also provide useful information.

Results shown in Fig. 10 indicate that beams can transfer flexural and shear loads even with the presence of cracks through their entire depth. Tests conducted at the University of Washington have shown that the effectiveness of web rein-forcement in resisting shear in reinforced concrete beams is not affected by axial force in the beam.I9) These tests were conducted on beams subjected to combined axial tension, bending, and shear. Results indicated that effectiveness of web rein-forcement is not reduced by the presence of axial tension. In

'th' tests, applied axial load was sufficient to cause cracking prior to the application of transverse load. For all beams with web reinforcement, measured load capacity of the precracked beams exceeded values calculated in accordance with the American Concrete Institute Building Code.

TESTS OF CONTAINMENT ELEMENTS Another series of tests that can be used to demonstrate the strength of cracked reinforced concrete members is reported in an experimental program to investigate shear transfer in cracked containments without diagonal reinforcement.(10) The test setup was designed and constructed to simulate boundary conditions of a wall element of a pressurized containment sub-jected to tancential shear stresses. Forces on an element in A-15 construction technology laboratories J

i a containment wall are illustrated in Fig. 12. Figures 13 and 14 show the test setup used for the experiments. The experimental program included monotonic and r,eversing load tests on large-scale specimens subjected to biaxial tension and shear. Specimens were 5-f t square and 2-f t thick with No. 14 and No. 18 reinforcement.

This discussion includes a description of one 'f the test specimens. Additional data are available in Reference 10.

Figure 15 shows the crack pattern observed in Specimen MB1 after reinforcement in the element was loaded to obtain a ten-sion stress of 54 ksi in the steel. This stress corresponds to 90% of the yield stress of the reinforcement. Crack width measurements made on the specimen after biaxial tension was applied indicated a maximum width of approximately 0.036 in.

Figures 16 and 17 show the crack pattern and nominal shear stress vs shear distortion relationship for Specimen MBl.  !

Shear forces were applied while constant biaxial tension was main tained . It is evident from Fig. 17 that the reinforced concrete element was capable of transferring shear forces even though it was traversed by biaxial tension cracks through the complete thickness.

I

SUMMARY

AND CONCLUSIONS Test data presented in this report demonstrate that cracks in an adequately reinforced concrete member do not prevent the member from developing its expected streng th. Adequate rein-forcement for the test specimens was determined in accordance with current code provisions. Data presented also indicate the i

A-16 construction technology laboratories u

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Cracks considered to Penetrcte the Full Thicke,ess of the Specirnen.

Cracks considered to Penetrate only the Cover Layer.

Fig. 15 crack Pattern After Biaxial Tension of 54 ksi in Containment Elenent Cpecimen MB1 (10)

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b) Crack Pattern Just Prior to Maximum Shear Load .

Fig. 16 Crack Pattern in Specimen .\21 (10)

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o ,.

Nominal Shear l Stress, psi 300 200 -- MBI l l l l g-- .;;

100 --

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Fig. 17 Nominal Shear Stress versus Shear Distortions for Containment Element Specimen MB1 (After Ref. 10)

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i level or severity of cracking associated with severe stress in reinforced concrete members. Obviously the presence of cracks in a reinforced concrete structure cannot be summarily dismissed as insignificant. The pattern of cracking and crack widths should be evaluated to determine their significance. However, the mere presence of a crack does not necessarily indicate that the integrity of the structure is in jeopardy, or that its load-carrying capacity has been reduced.

t 1

l .

A-22 construction technology laboratories l

i i

L e RE FE RENCES

1. Bacda , F. , H anson , J .M . , and Corley, W.G., "S hear S trength of Low-Rise Walls with Boundary Elements ," Special Publica-tion SP-53, Reinforced Concrete Structures in Seismic Zones , American Concrete Institute, Detroit, 1977, 496 pp.

2. Corley, W.G., Fiorato, A.E., and Oesterle, R .G . , "S truc-tural Walls ," Special Publication, C.P. Siess Symposium ,

American Concrete Institute , Detroit, 1979 (to be published).

3. Oes terle , R.G . , Fior ato , A.E. , and Corley , W .G . , " Rein-forcement Details for Earthquake-Resistant Structural Walls ," Concrete International, December 1980, pp. 55-66.

4. Oest arle , R.G, Fior ato , A.E . , and Corley , W.G . , "t' f f e cts of Reinforcement Details on Seismic Performance of Walls ,"

Proceedings of a Conference on Earthquakes and Earthquake Engineering: The Eastern United S tates , Vol. 2, Ann Arbor Science Publishers, Inc., 1981, pp. 685-707.

5. Scribner, C.F. and Wight, J.K., "A Method for Delaying Shear S trength Decay of RC Deams ," Proceedings of a Workshop on Earthquake-Resistant Reinforced Concrete Building Construction, Vol. 3, University of California, Berkeley, June 1978, pp. 1215-1241.

6. Wight, J.K. and Sozen , M. A. , "S trength Decay of RC Columns Under Shear Reversals ," Journal of the Structural Division, ASCE , May 19 75, pp. 10 53-106 5.

7. Brown, R.H. .and J irs a , J .O. , " Reinforced Concrete Beams Under Load Reversals ," Journal of the American Concrete I ns ti tute , Vol . 6 8, No. 5, May 1971, pp. 380-390.

8. Hanson, N.W. and Conner , H.W., "Tes ts Of Reinforced Concrete Beam-Column Joints Under Simulated Seismic Loading ," Research and Development Bulletin RD012, Portland C ement Association ,1972, 12 pp.

9. Haddadin , M.J . , Hong , S.T . , and Mattock , A.H. , "S tirrup Effectiveness in Reinforced Concrete Beams with Axial Force ," Journal of the S tructural Division, AS CE ,

S eptember 1971, pp. 2277-2297.

10. O es terle , R .G . and Russell, H.G., " Shear Transf er in Large Scale Reinforced Concrete Containment Elements ," Report No. 1, NUREG/CR-13 7 4, Construction Technology Labor atories ,

a Division of the Portland Cement Association, prepared for U.S. Nuclear Regulatory Commission , Washington , D .C . ,

April 1980.

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