ML20115A519

Masonry Wall Design for Millstone Point Unit 2, Technical Evaluation Rept

ML20115A519
Person / Time
Site:	Millstone
Issue date:	03/22/1985
From:	Con V, Triolo S CALSPAN CORP.
To:	Nilesh Chokshi NRC
Shared Package
ML20115A521	List: ML20115A519
References
CON-NRC-03-81-130, CON-NRC-3-81-130 TAC-42894, TER-C5506-250, NUDOCS 8503260410
Download: ML20115A519 (51)

Text

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. TECHNICAL EVALUATION REPORT MASONRY WALL DESIGN NORTHEAST NUCLEAR ENERGY COMPANY MILLSTONE POINT NUCLEAR POWER STAT,10N UNIT 2 -

NRC DOCKET NO. 50-336 FRC PROJECT C5506 NRC TAC NO. 42894 FRC ASSIGNMENT 6 NRC CONTRACT NO. NRC 03 81 130 F'CTASK 250 Preparedby Franklin Research Center Author: S. Triolo, V. N. Con 20th and Race Street Philadelphia, PA 19103 FRC Group Leader: V. N. Con Prepared for Nuclear Regulatory Commission Washington, D.C. 20555 Lead NRC Engineer: N. C. Chokshi C. _ . . ,

March 22, 1985 This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, or any of their -

employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third party's use, or the results of such use, of any information, appa-ratus, product or process disclosed in this report, or represents that its use by such third party would not infringe privately owned rights.

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FRANKLIN RESEARCH CENTER DIVISION OF ARVIN/CALSPAN 20th & RACE STREETS, PHILADELPHIA,PA 19103

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l TECHNICAL EVALUATION REPORT l l

MASONRY WALL DESIGN NORTHEAST NUCLEAR ENERGY COMPANY

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MILLSTONE POINT NUCLEAR POWER STATION UNIT 2 NRC DOCKET NO. 50-336 FRC PROJECT C5606 NRC TAC NO. 42894 FRC ASSIGNMENT 6 NRC CONTRACT NO. NRC-03-81 130 FRC TASK 250 Preparedby Franklin Research Center Author: S. Triolo, V. N. Con 20th and Race Street Philadelphia, PA 19103 FRC Group Leader: V. N. Con Preparedfor Nuclear Regulatory Commission Washington, D.C. 20555 Lead NRC Engineer: N. C. Chokshi ec _ _.,

March 22, 1985 This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, or any of their -

employees, makes any warranty, expressed or impiled, or assumes any legal liability or responsibility for any third party's use, or the results of such use, of any information, appa-ratus, product or procesa disclosed in this report, or represents that its use by such third party would not infringe prfvetely owned rights.

Prepared by: Reviewed by: Approved by:

A2Awfd Prindpal Author:

V An in Group Leader SW Department D[ectc8 Date: J,/82/83 Date: $f21 d Date: 5-2 2-Pr P

$6psff, ops /f FRANKLIN RESEARCH CENTER DMS10N OF ARVIN/ CAL 5 PAN 20th & RACE STREETS,PHILADEJHIA.PA 19103

TER-C5506-250

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CONTENTS Section Title Page 1 INTRODUCTION . . .

. . . . . . . . . . 1 1.1 Purpose of Review . . . . . . . . . . . 1 1.2 Generic Issue Background . . . . . . . . . I 1.3 Plant-Specific Background . . . . . . . . . 1 2 EVALUATION CRITERIA. . . . . . . . . . . . 5 3 TECHNICAL EVALUATION . . . . . . . . . . . 6 3.1 Evaluation of Licensee's Criteria . . . . . . . 6 3.2 Evaluation of Licensee's Approach to Wall Modifications . 19 4 CONCLUSIONS. . . . . . . . . . . . . . 20 5 REFERENCES . . . . . . . . . . . . . . 22 APPENDIX A - SGEB CRITERIA FOR SAFETY-RELATED MASONRY WALL EVALUATION g' ,"- -,-

(DEVELOPED BY THE STRUCTURAL AND GEOTECHNICAL ENGINEERINC BRANCH [SGEB] OF THE NRC)

APPENDIX B - SKETCHES OF WALL MODIFICATIONS iii

TER-C5506-250 FOREWORD j This Technical Evaluation Report was prepared by Franklin Research Center under a contract with the U.S. Nuclear Regulatory Cossaission (Office of Nuclear Reactor Regulation, Division of Operating Reactors) for technical assistance in support of NRC operating reactor licensing actions. The technical evaluation was conducted in accordance with criteria established by the NRC.

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TER-C5506-250

1. INTRODUCTION 1.1 PURPOSE OF REVIEW The purpose'of this review is to provide technical evaluations o'f licensee responses to IE Bulletin 80-11 [1]* with respect to compliance with the Nuclear Regulatory Comunission (NRC) masonry wall criteria. In addition, if a licensee has planned repair work on masonry walls, the planned methods and procedures are to be reviewed for acceptability.

1.2 GENERIC ISSUE BACKGROUND In the course of conducting inspections at the Trojan Nuclear Plant, '

Portland General Electric Company. determined that some concrete masonry walls did not have adequate structural strength. Further investigation indicated that the problem resulted from errors in engineering judgment, a lack of established procedures and procedural details, and inadequate design criteria.

Because of the implication of similar deficiencies at other operating plants, the NRC issued IE Bulletin 80-11 on May 8, 1980.

IE Bulletin 80-11 required licensees to identify plant masonry walls and their intended functions. Licensees were also required to present reevaluation criteria for the masonry walls with the analyses to justify those criteria.

a T ~ 1f-modifications were proposed, licensees were to state the methods and schedules for the modifications.

1.3 PLArr-SPECIFIC BACKGROUND In response to IE Bulletin 80-11, Northeast Utilities Company provided the NRC with letters plus attachments dated November 4, 1980 [2] describing

the status of masonry walls at Millstone Nuclear Power Station Unit 2. This document was reviewed, and a request for additional information was sent to the Licensee on September 28, 1982, to which the Licensee responded (3].

Another request for additional information was sent to the Licensee on

• Numbers in brackets indicate references, which are cited in Section 5.

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1 TER-C5506-250 February 24, 1984, to which the Licensee partially responded [4]. On September 27, 1984, the NRC and FRC staff met with the Licensee to discuss the

! issues raised in the February 24, 1984 request for additional information.

Subsequently, the Licensee provided submittals [5, 6] completing its response to the NRC's request for additional information.

According to the Licensee's final report on the evaluation of masonry walls (Attachment 3 in Reference 3), 312 masonry walls were surveyed, of which

, 155 were found to be safety-related. The safety-related walls serve one of j the following functions:

a. partitions -

b. partitions / fire walls

c. shielding

d. support of safety-related attachments

e. resistance of pipe break loads

, *f. resistance of pressurization loads

g. resistance of tornado wind loads

h. resistance of tornado missiles.

4 The non-shielding walls in the auxiliary building are 8 in or 12 in thick with vertical reinforcing. The shielding walls in the auxiliary building are 12 to 56 in thick and are either solid block or reinforced horizontally and vertically. The walls in the turbine building are 4 to 12 in thick and dC; - .;yertically reinforced. All safety-related reinforced walls at the Millstone Unit 2 plant are completely filled with grout.

The construction materials used are as follows: ,

Masonry Units Normal weight and lightweight hollow units - ASTM C-129 Heavyweight hollow units - ASTM C-90, Type 1, Grade P-1 i -

Solid units - ASTM C-145, Type 1, Grade P-1 Comentitious Materials i

Portland Cement - ASTM C-150, Type 1 i

Lime - ASTM C-207, Type S 4

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TER-C5506-250 Mortar Sand ASTM C-144 Agg r egate ,

ASTM C-33 for concrete blocks Reinforcement ASTM A-615-68, Grade 60 Mortar ASTM C-270, Type S (except in fire walls) i .

Fire Walls - 3 parts clean sharp sand, 1 part Portland cement, and 154 hydrated line (by cement volume) .

. In its final report (Attachment 3, Reference 3), the Licensee reported that 57 walls required structural modification. Of these walls, 43 were originally modified to satisfy elastic criteria and the remainder were modified to meet inelastic criteria, including " arching action" and " energy balance." However, all walls at this plant using the arching criteria have since been reevaluated using elastic working stress techniques. By eliminating some conservatisms found in the original elastic criteria, the

, il ~~ : Licensee has determined that these walls (18 total) meet the SGEB requirements. See Section 3.1 for further discussion of this subject.

The Licensee has relied upon the energy balance technique to qualify ,

three masonry walls. NRC, FRC, and FRC's consultants (Drs. H. Harris and A.

Basid of Drexel University) have conducted an exhaustive review of this subject based on submittals provided by the Licensee and published literature

! and have concluded that the available data in the literature do not give enough insight for understanding the mechanics and performance of reinforced masonry walls under cyclic, fully reversed dynamic loading. As a result, a meeting with representatives of the affected plants was held at the NRC on November 3,1982 so that the NRC and FRC's staff and consultants could explain why the applicability of the energy balance technique to masonry walls in l

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TER-C5506-250 nuclear power plants is questionable (9). In a subsequent meeting on January 20, 1983, consultants of utility companies presented their rebuttals [10) and requested that they be treated on a plant-by-plant basis. ,

In accordance with the above request, NRC, FRC, and consultants visited several nuclear power plants to examine the field conditions of masonry walls in the plants and to gain first-hand knowledge of how the energy balance technique is applied to actual walls. Further discussion on this subject is provided in Section 3.1.

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TER-C5506-250

2. EVALUATION CRITERIA The basic documents used for guidance in this review were the griteria developed by the Structural and Geotechnical Engineering Branch (SGEB) of the NRC (attached as Appendix A to this report), the Uniform Building Code [7],

and ACI 531-79 [8].

The materials, testing, analysis, design, construction, and inspection of safety-related concrete masonry structure should conform to the SGEB criteria.

For operating plants, the loads and load combinations for qualifying the masonry walls should conform t'o the appropriate specifications in the Final Safety Analysis Report (FSAR) for the plant. Allowable stresses are specified in Reference 8 and the appropriate increase factors for abnormal and extreme ,

environmental loads are given in the SGEB criteria (Appendix A).

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a TER-C5506-250

3. TECHNICAL EVALUATION This evaluation is based on the Licensee's earlier response [3]- and subsequent responses [4, 5, 6) to the NRC request for additional information.

The Licensee's criteria were evaluated with regard to design and analysis methods, loads and load combinations, allowable stresses, construction specifications, materials, and any relevant test data.

3.1 EVALUATION OF LICENSEE'S CRITERIA The Licensee is performing a reevaluation of the masonry walls using the ,

following criteria (2):

o The design allowables are based on the Uniform Building Code (1967 Edition) .

o Loads and load combinations are consistent with the final safety analysis report (FSAR) specifications.

o The following damping values are used:

a. for uncracked sections - 2% damping for both operating basis earthquake (OBE) and safe shutdown earthquake (SSE)

b. for cracked reinforced sections - 4% damping for OBE and 7%

damping for SSE.

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o The working stress method of analysis is used, except in 3 cases in which the energy balance technique was used.

, o Construction practices were based on the provisions of the Uniform Building Code (1967 edition) .

o A typical analytical procedure used in the working stress design method is summarized below.

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- determine wall boundary conditions (pinned or f ree)

- calculate the wall's fundamental frequency using either a one-way vertical or one-way horizontal action assumption

- obtain inertial loading from average floor response spectrum (If the fundamental frequency of the wall is on the lower side of the peak floor response spectra, the peak value was selected to obtain the inertial loading.)

- compare computed stresses with the allowable values.

O TER-C5506-250 The Licensee's criteria [2] and all responses [3, 4, 5, 6] have been reviewed. Other than those areas identified in Section 4, the Licensee's criteria have been found to be adequate and in compliance with the SGEB criteria (Appendix A) .

Following is a review of the Licensee's response [3] to the NRC's original questions as well as responses to subsequent questions [4, 5, 6] .

Question 1 Indicate whether the walls are stack or running bond. If any stack bond walls exist, provide sample calculations used to obtain stresses of a '

typical wall.

Response 1 The Licensee stated that all masonry walls at the Millstone Unit 2 plant were running bond. This response has resolved concerns about stack bond construction.

This response is satisfactory.

Question 2 Ib ~~ - . a . Section 3 of the SGEB criteria specifies ACI 531-79 [8] as the governing code for allowable stresses in masonry walls. In Section 5.1.1.3 of Reference 2, the Licensee has listed allowable shear

( stresses which exceed some allowables listed in ACI $31-79. Justify the following allowable shear stresses (the allowable stresses f rom the ACI 531-79 "Special Inspection" category are shown in parentheses and based on an f', of 1350 psi) .

No Shear Reinforcement l

Flexural members 50 psi (40 psi = 1.1 m)

Shear walls I

50 psi (33 psi = 0.91t's, M/VD ll)

Reinforcing Taking Entire Shear Flexural members 120 psi (110 psi = 3.0 % )

Shear walls 75 pai (55 psi = 1.5jfI n, M/VD 11) 1 TER-C5506-250 The Licensee should indicate whether construction practices were i in conformance with the provisions specified in ACI 531-79.

b. Provide allowable stresses for unreinforced masonry. J,ustify these values if they exceed those given in ACI 531-79 or Unc-79.

Response 2a In this response, the Licensee indicated that its construction practices and its allowable shear values were based on in the Uniform Building Code (UBC),1967 edition and that the actual construction practices met the intent t

of ACI 531-79. The masonry walls were constructed under a specification that covered the standards for all cementitious materials, reinforcement, and all -

r operations necessary for the erection of these walls. Manufacturers were required to provide a signed certificate stating that all concrete masonry units conformed to the specifications.

The Licensee's use of flexural shear allowables that exceed the values

. t recommended by ACI 531-79 is considered inconsequential for the following  ;

reasons: (a) as mentioned by the Licensee in this response, shear does not {

govern in the design of masonry walls; the primary mode of failure in masonry walls is tension and (b) the method of analysis contains enough conservatisms, such as the use of one-way spans and the use of the peak response spectrum rseeeleration for wall frequencies on the low frequency side of the peak, to ensure that actual shear stresses remain within acceptable limits.

Regarding the in-plane shear allowables for shear walls, the masonry

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! walls at this plant do not resist any major building loads (see Re,sponse 7 in

this section); therefore, the allowable values for shear walls are of no consequence.

The Licensee's response complies with the SGER criteria. ,

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i Response 2b l In this response, the Licensee provided the allowable stresses for l

i unreinforced walls as follows:

! Axial Cospression = 175 psi Flexural compression = 175 psi i

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TER-C5506-250 Bearing = 263 psi Flexural Tension = 24 psi (Spanning horizontally .

running bond)

Flexural Tension = 12 psi (Spanning vertically running bond)

Shear Stress = 12 psi These values are based on Type S mortar and having inspection provided.

They have been reviewed and compared to the values given in ACI 531-79 for solid block, since all unreinforc'ed walls at this plant are made of solid blocks. The Licensee's values are conservative.

This response satisfies the SGES criteria.

Question 3 With respect to multiple wythes, clarify whether collar joint strength was used in the analysis. If so, justify by any existing test data tne values used for allowable shear and tension of collar joints. Provide sample calculations illustrating the analysis of multi-wythe walls.

Response 3 In this response, the Licensee stated that the collar joint strength was ,

assumed to be zero. No multi-wythe walls were analysed compositely unless they were through-bolted with prestressed bolts. A sample calculation illustrating the anal sis

/ of a multiple wythe wall was provided and reviewed.

This is a calculation for a 24-in-thick, 4-wythe, solid block wall. The well was modeled as a beam spanning horizontally, with a cross section based on the composite wall section. The maximum compressive stress was 0.043 ksi, compred with an allowable of 0.438 kai. The maximum shear was 0.006 ksi, compared with an allowable of 0.020 kai. The maximum axial stress was 0.016 ksi, compared with an allowable of 0.350 ksi. The maximum tensile stress was 0.043 kai, which was slightly greater than the allowable of 0.040 kai.

TER-C5506-250 However, because of the conservatisms in this analysis, such as applying a factor of 1.5 to the peak response spectrum acceleration to account for higher modes and using a 24 damping value for SSE,'the tensile overstress is considered insignificant.

The Licensee's response satisfies the SGEB criteria.

Question 4 (from Reference 5)

. Regarding Responses 3 and 4 of Reference 3, identify walls that would not be qualified if the SGEB increase factors for allowable stresses were to be used. It should be noted that for the OBE loading case, the SGEB criteria do not allow any increase factor, whereas the Licensee used a -

factor of 1.33. Also, specify the percentage of exceedance for OBE, SSE, and other accident load cases. Explain all conservative measures (if any) used in the analysis to justify a higher increase factor.

Response 4 (from Reference 5)

In this response, the Licensee indicated that it compared the actual calculated stresses of the masonry walls evaluated under IE Bulletin 80-11 to the SGEB allowables for OBE and SSE conditions. The SGEB allowables for OBE are given in Section 10 of ACI 531-79 (no increase factor is permitted). The SGEB allowables for SSE are the OBE allowables increased by the following fh ~~-rfectors for each type of stress:

SGEB Type of Stress Factor Axial or flexural compression 2.5 Bearing 2.5 Reinforcement stress 2.0 not to except shear exceed 0.9 fy Shear reinforcement .

1.5 and/or bolts Masonry tension parallel 1.5 to bed joint Shear carried by masonry 1.3 Masonry tension perpendicular to bed joint For reinforced masonry 0 For unreinforced masonry 1.3

TER-C5506-250 The Licensee found that the calculated stresses for all unreinforced walls meet the SGES criteria for both OBE and SSE. All reinforced walls meet the SGER criteria except wall 1.23 for OBE and wall 10.3 for SSE.

The calculated compressive stress for wall 1.23 exceeds the SGEB allowable for OBE by 184; however, the wall meets all criteria for SSE conditions. Because wall 1.23 meets the SGES criteria for SSE loadings, which is the governing condition, it is assured that the wall will not fail under

, OBE conditions. Also, the conservatisms in the analysis method, such as the use of one-way spans, the use of the peak response for wall frequencies which fall on the low frequency side of the peak, and the application of a factor of '

1.5 to the peak response to account for higher modes of vibration, account for much of the difference between the calculated and allowable stress. After

, these considerations, wall 1.23 is considered adequate.

The calculated steel stress for wall 10.3 exceeds the SGER allowable by

. only 1.254. Considering the conservatisms in the analysis, this overstress is insignificant.

This response satisfies the SGES criteria.

Q g7 ,,n.uestion

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. In Reference 2, the Licensee indicated that the energy balance and arching action techniques have been used to qualify some of the masonry ,

walls. The NRC does not accept the application of those methods to masonry walls in nuclear power plants without conclusive evidence to justify this

. application. The Licensee is requested to indicate the number of walls analysed by each of these techniques and to provide sample calculations to illustrate the analysis by each technique. The Licensee is also requested to identify the types of structures (grouted, ungrouted, distribution of reinforcement) involved in these analyses. In addition, the following areas need technical verification before any conclusions can be made:

'a. Energy Balance Technique o Provide a technical basis to ensure that the ductile mode of failure will occur (if the wall fails) .

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TER-C5506-250 o Provide justification for and test data (if available) to validate the applicability of the energy balance technique to the masonry structures at Millstone Unit 2, with particular emphasis on the fol'owing: ,

'a. nature of the load 5

b. boundary conditions

c. material strengths

d. size of test walls.

b. Arching Action o Explain how the arcLihg action theory handles cyclic loading, i'

.'especially when the l'oad is reversed.

o Provide' justification for and test data (if available) to '

validate the applicability of the arching action theory to the masonry structures at Millstone Unit 2, with particular emphasis on the following areas:

j a. nature of the load

b. boundary conditions

c. material strengths

d. size of test walls, o If hinges are formed in the walls, the capability of the structures to resist in-plane shear force would be diminished, and shear failure might occur. This in-plane-shear force would also reduce the out-of-plane stiffness.

Explain how the effect of this phenomenon can be accurately gt _ _. , _ _ -

. determined. .

i Response 5 i

The Licensee reported that 21 walls were initially qualified by inelastic techniques including the arching action and energy balance techniques.

l " Fourteen of these walls were modified prior to qualification. The Licensee l

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has since reevaluated and qualified 18 of the 21 walls using elastic working stress criteria. These are the 18 walls originally qualified by arching j action.

The new elastic criteria for the reevaluation of the 18 solid block walls j initially qualified by arching action are outlined in References 5 and 6.

Basically, the criteria are the same as the Licensee's original working stress criteria used to qualify other walls at the plant., except that certain conservatisms have been eliminated. For instance, the allowable stresses i

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• TER-C5506-250 originally used for unreinforced walls (Response 2 in this section) were conservative in comparison with the SGEB allowables. The new evaluation was

based on SGEB allowables found in ACI 531-79, with the exception of 4 hear.

{ ACI531-79specifiesavalueforflexuralshearof1.impf'm,whereasthe Licensee specifies the out-of-plane shear allowable as 1.5 jf's however, in i unreinforced, solid block walls, the maximum shear stress is typically insignificant due to the limitations placed on masonry tension, which governs the design. The boundary connections for these walls have been reviewed and are adequate to transmit the shear to the surrounding structure. A typical boundary connection consists of a pair of parallel steel angles bolted to the adjacent concrete, with one leg of each angle embedded in a collar joint.

This connection occurs at the top and bottom of the wall. Another conservatism that was eliminated in the reevaluation was the one-way beam l model. In the reevaluation, the Licensee used a finite element model and j computer program to analyse the walls.

, The Licensee has relied on the energy balance tecnique to qualify three j walls. NRC staff, FRC, and FRC's consultants have conducted an exhaustive review of available information on the energy balance technique and of the i Licensee's responses to determine the technical adequacy of the methodology.

l In addition, FRC and its consultants have issued their evaluation and i

et' _ 'iisnsament of the use of the energy balance technique for masonry walls [9, 11). The SGEB has issued a position statement regarding this subject which I will be addressed in its Safety Evaluation Report. .

The Licensee's response is in compliance with the SGER criteria.

i' Question 6

! Section 3.7.2 of the Standard Review Plan requires that unless a dynamic  !

analysis is performed, the effect of higher modes of vibration shall be accounted for by multiplying the peak acceleration of the floor response j

spectrum by a factor of 1.5. The Licensee is requestea to explain how higher modes of vibration were accounted for in the analysis.

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Response 6 The Licensee indicated that in some cases the walls'were analyzed by a '

computer program ("BLOCRWALL") that used a response spectrum analysis which included the effect of higher modes of vibration. In those cases in which the wall was analyzed by hand calculations, the factor of 1.5 was applied to the peak acceleration of the response spectrum to account for higher modes of vibration. This method is considered conservative because it has been found in many cases at other plants that the first mode usually contributes 95% or more to the total response.

This response satisfies the SGEB criteria. '

Question 7 Indicate how earthquake forces in three directions were considered in the analysis.

Response 7 The Licensee stated that vertical and in-plane loading were negligible for the walls evaluated under IE Bulletin 80-11 and therefore were not considered.

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This is a valid assumption for masonry walls other than shear walls.

Because the Licensee's evaluation did not include any shear walls, this response is satisfactory and complies with the SGEB criteria.

• Question 8 Indicate how out-of-plane drif t effects are considered in the analysis.

Response 8 The Licensee responded that all masonry walls were determined to have pinned boundaries. Therefore, out-of-plane drif t effects were not a major concern in this evaluation. Boundary connections are typically stud anchors coinciding with vertical reinforcement. In unreinforced walls, steel angles anchored to surrounding concrete restrain the wall at the edges.

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TER-C5506-250 The Licensee's response satisfies the SGEB criteria.

Question 9 ~

Indicate if' block pullout was considered in the evaluation. If yes, provide sample calculations of block pullout analysis.

Response 9 A sample calculation was provided containing an example of block pullout analysis. The example was reviewed and found to be adequate. This is basically a calculation of the shear stress on the mortared area of the block, -

based on the maximum concentrated load on the wall. The calculated shear stress is 0.022 kai compared with an allowable of 0.020 kai. This overstress is insignificant because the allowable is conservative. According to ACI 531-79, an allowable shear of 0.040 kai is acceptable for normal loads.

The response is satisfactory.

4 Question 10 Specify the number of masonry walls analyzed for impact and suddenly applied loads. Provide the results (stresses, displacements) of these analyses. In addition, provide a sample calculation illustrating the gt __~ ';.

'~ " analysis for impact and suddenly applied loads.

Response 10 .

The Licensee responded that all walls that were subject to substantial impact or suddenly applied loads were analyzed for these loads. Sample calculations were provided containing examples of jet impingement analysis.

This analysis consists of multiplying the jet impingement load by a dynamic load factor (2), applying the results at the center of the beam model of the ,

wall, and combining the effects with the effects of dead, live, and seismic loads. Response 3 contains the results of a wall analysis involving jet impingement loads. The analysis technique is considered adequate to account for jet impingement effects on these walls. According to the responses in References 4 and 5, tornado missiles were evaluated in accordance with

k TER-C5506-250 Appendix 5.D of the Millstone Unit 2 FSAR. Localized impact and penetration effects of missiles were evaluated as part of the original design; however, because of the arrangement and elevations of the affected walls, the Licensee has determined that the probability of impact by tornado-borne missiles is extremely low. All walls are either shielded by other structures or too high for missiles to reach with much force.

This response is adequate and satisfies the SGEB criteria, Question 11 Provide the final report on the reevaluation and modifications to masonry-walls which was scheduled to be submitted by May 1, 1981.

Response 11 The final report on the reevaluation and modifications to masonry walls was provided. The final report is a summary of the Licensee's response to IE Bulletin 80-11. Included are general discussians of the methods used to analyze and modify the masonry walls at the Millstone Unit 2 plant (see Section 3.2 for a description and evaluation of the modification methods) .

Also provided in the final report are wall lccation plans and a summary of the

,7 __ safety-related masonry walls at the plant.

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Question 12 (from References 4 and 5)

O With reference to the reinforcement in masonry walls, the ACI 531-79 Code specifies that the minimum area of reinforcement in a wall in each direction, vertical or horizontal, shall be 0.0007 (0.07%) times the gross cross-sectional area of the wall and that the minimum total area of steel, combined vertical and horizontal, shall not be less than 0.002 (0.2%) times the gross cross-sec,tional area. Clarify whether the reinforced walls at this plant meet the above requirements. It should be noted that the horizontal reinforcement is installed to satisfy the minimum reinforcement requirement for a reinforced wall.

If the joint reinforcement is used to resist tension in the walls meeting the above minimum requirements, it should follow the working stress design method which limits its (Code) allowable to 30 ksi. Please clarify whether this requirement has been satisfied. If this requirement is not satisfied, identify all affected walls along with the calculated stress value for each wall and indicate specific actions planned to correct this situation.

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Indicate if there are any walls that may have been qualified using the tensile resistance of the joint reinforcement but not satisfying the i

minimum steel requirements. It should be noted that the NBC, at present, does not approve the use of joint reinforcement to qualify this type of wall. (See attached staff position.) In view of this, indicate all walls belonging to this category and your intended specific actions to bring these walls in compliance with the staff position.

Response 12 In this response, the Licensee indicated that 55 walls at the Millstone i

Unit 2 plant are reinforced. All the reinforced walls are filled with grout and contain at least the minimum area of reinforcement in the vertical direction (0.0007 times the gross cross-sectional area of the wall) as required by ACI 531-79. Some walls, however, do not meet the requirements for combined (horizontal plus vertical) reinforcement or horizontal reinforce-ment. Horizontal reinforcement occurs in the form of extra heavyweight Dur-o-Wal in every other course. The 8-in-thick walls have 80% of the minimum

. i ACI 531-79 requirements for horizontal reinforcement and the 12-in-thick walls have 51% of the minimum requirements. Fourteen walls contain less than the minimum requirement of 0.002 times the gross cross-sectional area of the wall for combined (horizontal plus vertical) reinforcement.

Although some walls do not meet the minimum requirements for combined C.

....Kforcement

.rei or horizontal reinforcement, only the vertical reinforcement was considered as a structural element; the Dur-o-Wal was intended only to control cracking, not to add to the strength of the wall. The highest calculated -

! vertical steel stress was reported to be 48.6 kai in wall 10.3, compared with an allowable of 48 kai (SGEB permits a maximum allowable of 0.9 fy = 54 kai l

for Grade 60 steel) . This 1.25% overstress is not considered significant because of conservatisms in the analysis. Because of these circumstances, and because all walls meet the minimum requirements for vertical reinforcing, these walls are considered to have sufficient strength to satisfy the SGEB criteria.

Question 13 (from References 4 and 5)

With respect to tornado load, specify all walls subject to tornado load (if applicable) and provide a sample calculation (with any explanation

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I TER-C5506-250  !

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necessary to make it understandable) . Also indicate how the penetration depth, perforation, and spalling along with the overall structural behavior of the wall were evaluated for a tornado missile impact.

Response 13 The Licensee indicated 10 walls that were subject to tornado loads:

1.32, 6.1, 6.2, 7. 5, 7.12, 8.22, 8.2 9, 8. 31, 10. 5, and 10.12. The design wind speed was 360 mph. See Response 10 in this section for the way in which tornado-borne missiles were considered. The Licensee provided calculations for walls 6.1 (an exterior wall partially blocked by Unit 1) , 10.5, and 10.12 (interior walls). These walls were analyzed for the dynamic wind pressure '

associated with a wind speed of 360 mph. They were also checked for an atmospheric depressurization of 3 psi. The controlling load was depressuriza-tion, which was applied as a uniform load to a simply supported beam model of the wall. The effects of this loading were combined with those of the dead and live loads. For wall 6.1, the tornado analysis yielded a maximum reinforcement tensile stress of 41.8 kai, compared with an allowable of 48 ksi, and a masonry compression stress of 1.346 kai, compared with an allowable of 1.11 kai (based on ACI 531-79 code and the SGEB allowables) . Although the wall is overstressed in compression, the Licensee concluded that

yt .3 safety-related equipment would not be jeopardized. This is reasonable because atmospheric depressurization would tend to blow the wall outward, away from equipment inside the building. Also, much of the overstress, which is on the order of 20% of the allowable, can be attributed to conservatisms in the analysis method, such as the one-way span assumption. Stress levels are within allowables for dynamic wind pressure and seismic loads. For these reasons, wall 6.1 is not considered a threat to safety-related equipment.

The Licensee's approach for tornado analysis of masonry walls is considered adequate and in compliance with the SGEB criteria.

TER-C5506-250 3.2 EVALUATION OF LICENSEE'S APPROACH TO 10LLL MODIFICATIONS In its final report on concrete masonry wall evaluation, the Licensee reported that 57 walls did not meet the acceptance criteria and required modification. The modifications includes

a. The addition of structural steel to reduce the wall span,

b. The addition of structural steel at the top and free edges to reinforce boundary conditions.

c. Through bolting multiple-wythe walls so that they may be analyzed compositely, without taking advantage of the collar joint strength. ,

d. The removal of pipe supports,

e. Through bolting pipe support base plates to distribute the load to all wythes.

f. The installation of structural shields to protect equipment in the vicinity of masonry walls.

Of the 57 modified walls, 43 were modified to satisfy elastic criteria and the rest were initially modified to satisfy inelastic criteria including the " arching action" and " energy balance" techniques. However, all walls at gt ,_- :-this

. ~~~.

plant that were originally qualified on the basis of arching action have since been reevaluated and requalified using elastic working stress methods.

The sample calculations for walls 10.5 and 10.12 provided in Reference 4 ,

contain an example of a modification involving the addition of structural steel to reinforce boundary connections and reduce wall span (see Appendix B for sketches of this modification) . The Licensee's methods of wall modification have been reviewed and found to be adequate and consistent with the SGEB criteria.

5

TE R-C 5506-250

4. CONCLUSIONS A detailed study was performed to provide a technical evaluation of the masonry walls at.the Millstone Point Nuclear Power Station Unit 2. Review of the Licensee's criteria and additional information provided by the Licensee led to the conclusions given below.

The Licensee's criteria have been found technically adequate and in compliance with the SGEB criteria except for the following areas o A flexural shear allowable stress of 50 psi was used instead of the value recommended by ACI 531-79 (40 psi = 1.1 jf's) . This discrepancy, however, is considered inconsequential because shear does '

not govern the design of masonry walls; the primary mode of failure is tension. Also, there are'conservatisms in the analysis, such as the use of one-way spans, the use of the peak response spectrum

, acceleration when the lower bound wall frequency falls on the low frequency side of the peak, and the application of a factor of 1.5 to the peak response to account for higher modes of vibration, which ensure that the actual shear stresses remain within acceptable limits.

o The Licensee used an increase factor of 1.67 for allowable masonry stresses in tension and shear in extreme loading conditions, whereas the SGEB criteria allow only 1.3 for shear and tension normal to the bed joint and 1.5 for tension parallel to the bed joint. Also, an increase in allowables of 334, not permitted by the SGEB criteria, was originally used for load combinations involving OBE and wind loads.

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The Licensee has since compared the calculated wall stresses with the SGEB allowables for both OBE and SSE. All walls, with the exception of walls 1.23 and 10.3, were found to meet the SGEB criteria. Wall 1.23 is overstressed in masonry compression for OBE by 184. But because wall 1.23 qualifies for SSE, which is the controlling

• condition, and because there are conservatisms in the analysis method (see previous item) , wall 1.23 is considered adequate. Wall 10.3 is only overstressed in steel tension by 1.254, which is not significant. Therefore, all masonry walls are considered to satisfy the SGEB criteria with respect to allowable stresses and increase factors. .

o Originally, 21 walls at the Millstone Unit 2 plant were qualified on the basis of inelastic criteria including the arching action (18 walls) and energy balance techniques (3 walls) . The 18 arching action walls have since been requalified using elastic working stress techniques and less conservative criteria. These new criteria are consistent with the SGEB criteria except for the allowable stress for i flexural or out-of-plane shear in solid block walls. The Licensee j used a value of 1.5 -ff'm , whereas ACI 531-79 specifies a value of l 1.11f's. In unreinforced, solid block walls, however, significant i l

l

TER-C5506-250 shear stress is typically prevented by the limitations on masonry tension, which governs the design. The boundary connections for these walls have been reviewed and found adequate to transmit the shear to the surrounding structure. For these reasons, these walls are considered adequate in out-of-plane shear.

o With regard to the energy balance technique, three walls were affected. As stated in the review of Response 5, FRC and its consultants have issued their assessment of the use of the energy balance technique in the analysis of masonry walls in nuclear power plants.- The Structural and Geotechnical Engineering Branch (SGEB) has also issued a position statement on this subject, which will be addressed in its Safety Evaluation Report.

o Not every reinforced wall meets the minimum area requirements of ACI 531-79 for horizontal reinforcement (0.0007 times the gross '

cross-sectional area of ,the wall) or combined (horizontal plus vertical) reinforcement (0.002 times the gross cross-sectional area of the wall) . However, the horizontal reinforcement, which is Dur-O-Wal

. joint reinforcement, was never intended to be a structural element; it  ;

was meant only to control cracking. Only vertical reinforcement ~was {

used in the structural analysis of the walls, and vertical reinforcement does meet the minimum area requirements (0.0007 times gross cross-sectional wall area) in all reinforced walls. The highest ,

calculated vertical steel stress was reported to be 48.6 ksi in wall l 10.3, compared with an allowable of 48 kai (SGEB permits a maximum l allowable of 0.9 fy = S4 kai for Grade 60 steel) . This 1.254 overstress is not considered significant because of conservatisms in the analysis, such as the use of one-way spans, the use of the peak response spectrum acceleration when the lower bound wall frequency C

.s,. s,_ falls on the low frequency side of the peak, and the application of a factor of 1.5 to the peak response to account for higher modes of vibration. Therefore, it is concluded that all reinforced walls contain sufficient reinforcement to satisfy the SGEB criteria.

o Wall 6.1 (an exterior wall) is overstressed by about 20% in masonry compression due to tornado depressurization. But much of this j overstress can be attributed to conservatisms in the analysis method, j such as the one-way span assumption. Also, the depressurization load I tends to blow the wall outward, away from equipment inside the  !

building. Af ter these considerations, it is concluded that wall 6.1 is not a threat to safety-related equipment.

)

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,. TER-C5506-250

5. REFERENCES

l. IE Bulletin 80-11 Masonry Wall Design ,

NRC, 08-May-81

2. W. G. Counsil Letter to B. H. Grier, NRC

Subject:

Millstone Nuclear Power Station Unit 2 - IE Bulletin 80-11, Masonry Wall Design Northeast Utilties, 04-Nov-80 A01021

3. W. G. Counsil -

Letter with Attachments to R. A. Clark and D. M. Crutchfield (NRC)

Subject:

Request for Additional Information on IE Bulletin 80-11, Masonry Wall Design Northeast Utilities, 03-Dec-82 B10624 Enclosure III

4. W. G. Counsil

, Letter with Attachments to J. R. Miller (NRC)

Subject:

Request for Additional Information on IE Bulletin 80-11, Masonry Wall Design Northeast Utilities, ll-May-84 A03831 C.

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. .. _ _ 5 .

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W. G. Counsil Letter with Attachments to J. R. Miller (NRC)

Subject:

Request for Additional Information on IE Bulletin 80-11, Masonry Wall Design Northeast Utilities, 2-Nov-84 -

A03831

6. W. G. Counsil Letter with Attachments to J. R. Miller (NRC)

Subject:

Request for Additional Information on IE Bulletin 80-11, Masonry Wall Design .

Northeast Utilities, 4-Jan-85 Bil418

7. Uniform Building Code International Conference of Building Officials, 1979

8. Building Code Requirements for Concrete Masonry Structures Detroit: American Concrete Institute,1979 ACI 531-79 and ACI 531-R-79 .

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TER-C5506-250

9. H. G. Harris and A. A. Hamid

" Applicability of Energy Balance Technique to Reinforced Masonry Walls" Dept. of Civil Engineering, Drexel University _

August 1982

10. Computech Engineering Services Inc., URS/ John Blume and Associates, and Bechtel Power Corporation

" Rebuttal to ' Applicability of Energy Balance Technique to Reinforced Masonry Walls' by Harris and Hamid,"

February 1983

11. A. A. Hamid, H. G. Harris, and V. Con

" Evaluation of the Applicability of Energy Balance Technique to Masonry Walls in Nuclear Power Plants" Franklin Research Center '

July 1983

• M .g e

1 1

f APPENDIX A SGEB CRITERIA FOR SAFETY-RELATED MASONRY WALL EVALUATION (DEVELOPED BY THE STRUCTURAL AND GEOTECHNICAL ENGINEERING BRANCH

[SGEB] OF THE NRC) f - . ..

FRANKLIN RESEARCH CENTER DM90N OF ARVIN/CALSPAN 20th & RACE STREETS, PHILADELPHIA,PA 19103

CONTENTS Section Title Page 1 GENERAL REQUIREMENTS .. . . . . . . . . . . A-1 2 LOADS AND LOAD COMBINATIONS. . . . . . . . . . A-1

a. Service Load Combinations . . . . . . . . . A-1

, b. Extreme Environmental, Abnormal, Abnormal / Severe Environmental, and Abnormal / Extreme Environmental Conditions . . . . . . . . . . . . . A-2 3 ALLOWABLE STRESSES . . . . . . . . . . . . A 4 DESIGN AND ANALYSIS CONSIDERATIONS . . . . . . . . A-3 5 REFERENCES . . . . . . . . . . . . . . A-4 O

e C........

iii

1 1. General Requirements The materials, testing, analysis, design, construction, and inspection related to the design and construction of safety-related concrete masonry walls should conform to the applicable requirements contained in Uniform Building Code - 1979, unless specified otherwise, by the provisions in this criteria. -

The use of other standards or codes, such as ACI-531, ATC-3, or NCMA, is also acceptable. However, when the provisions of these codes are less conservative than the corresponding provisions of the criteria, their use should be justified on a case-by-case basis.

In new construction, no unreinforced masonry walls will be permitted. For operating plants, existing utteinforced walls will be evaluated by the provisions of these criteria. Plants which are applying for an operating license and which have already built unreinforced masonry walls will be evaluated on a case-by-case basis. ,

2. Loads and Load Combinations The loads and load combinations shall include consideration of normal

, loads, severe environmental loads, extreme environmental loads, and abnormal loads. Specifically, for operating plants, the load combinations provided in the plant's FSAR shall govern. For operating license

~

applications, the following load corbinations shall apply (for definition of load terms, see SRP Section 3.8.4II-3) .

(a) Service Load Conditions (1) D + L eC. _ ,,, _ _

(3) D + L + W If thermal stresses due to T o and Ro are present, they should be included in the above combinations as follows: *

(la) D + L + To + Ro (2a) D+L+To+Ro+E (3a) D+L+To+Ro+W '

Check load combination for controlling condition fcr maximum 'L' and for no 'L'.

f A-1

t (b) Extreme Environmental, Abnormal, Abnormal / Severe Environmental, and Abnormal / Extreme Environmental Conditions (4) D + L + To+Ro+E (5) D+L+To + Ro + Wt (6) D + L + Ta+Ra + 1. 5 Pa (7) D + L + Ta + Ra + 1.25 Pa + 1.0 (Yr + Yj + Ym) + 1.25 E (8) D+L+Ta+Ra + 1.0 Pa + 1.0 (Yr + Yj + Ym) + 1. 0 E '

In combinations (6) , (7) , and (8) the maximum values of Pa , T ae Ra , Yj, Y ,r and Y ,m including an appropriate dynamic load factor, should be used unless a time-history analysis is performed to justify otherwise. Combinations (5) , (7) , and (8) and the corresponding structural acceptance criteria should be satisfied first without the tornado missile load in (5) and without Y rs Yje and Ya in (7) and (8) . , When considering these loads, local section strength capacities may be exceeded under these concentrated loads, provided there will be no loss of function of any safety-related

, system.

Both cases of L having its full value or being completely absent should be checked. -

3. Allowable Stresses Allowable stresses provided in ACI-531-79, as supplemented by the following modifications / exceptions, shall apply.

( a) When wind or seismic loads (OBE) are considered in the loading eC. . ... .

combinations, no increase in the allowable stresses is permitted.

(b) Use of allowable stresses corresponding to special inspection category shall be substantiated by demonstration of compliance with the inspection requirements of the SEB criteria. *

(c) When tension perpendicular to bed joints is used in qualifying the unreinforced masonry walls, the allowable value will be justified by test program or other means pertinent to the plant and loading conditions. For reinforced masonry walls, all the tensile stresses will be resisted by reinforcement.

(d) For load conditions which represent extreme environmental, abnormal, abnormal / severe environmental, and abnormal / extreme environmental conditions, the allowable working stress may be multiplied by the factors shown in the following table:

A-2

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, w g-,<+ . ...,- w,-- , - , , ,,w-

Type of Stress Factor Axial or Flexural Compression 2.5 Bearing 2.5 Reinforcement stress except shear 2.0 but not to exceed 0.9 fy Shear reinforcement and/or bolts 1.5 Masonry tension parallel to bed joint 1.5 Shear carried by masonry 1.3 Masonry tension perpendicular to bed joint for reinforced masonry 0 .

for unreinforced masonry 2 1,3 Notes (1) When anchor bolts are used, design should prevent facial spalling of masonry unit.

, (2) See 3(c).

'4 . Design and Analysis Considerations

( a) The analysis should follow established principles of engineering mechanics and take into account sound engineering practices.

C ~~~ -t b) Assumptions and modeling techniques used shall give proper considerations to boundary conditions, cracking of sections, if any, and the dynamic behavior of masonry walls.

(c) Damping values to be used for dynamic analysis shall be those for reinforced concrete given in Regulatory Guide 1.61.

(d) In general, for operating plants, the seismic analysis and Category I structural requirements of FSAR shall apply. For other plants, corresponding SRP requirements shall apply. The seismic analysis shall account for the variations and uncertainties in mass, materials, and other pertinent parameters used.

( e) The analysis should consider both in-plane and out-of-plane loads.

(f) Interstory drift effects should be considered.

A-3

(g) In new construction, grout in concrete masonry walls, whenever used, shall be compacted by vibration.

(h) For masonry shear walls, the minimum reinforcement requirements of ACI-531 shall apply.

( i) Special constructions (e.g. , multiwythe, composite) or other items not covered by the code shall be reviewed on a case-by-case basis for their acceptance.

(j) Licensees or applicants shall submit QA/QC information, if available, for staff's review.

In the event QA/QC information is not available, a field survey and a test program reviewed and approved by the staff shall te implemented to ascertain the conformance of masonry construction to design drawings and specifications (e.g., rebar and grouting) .

(k) For masonry walls requiring protection from spalling and scabbing due' to accident pipe reaction (Y r) , jet impingement (Y 3) , and missile impact (Ym) , the requirements similar to those of SRP 3.5.3 shall apply. However, actual review will be conducted on a case-by-case basis.

5. References

.( a) Uniform Building Code - 1979 Edition.

(b) Building Code Requirements for Concrete Masonry Structures ACI-531-79 and Commentary ACI-531R-79.

4 (c) Tentative Provisions for the Development of Seismic Regulations for Buildings - Applied Technology Council ATC 3-06.

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(d) Specification for the Design and Construction of Load-Bearing Concrete Masonry - NCMA August,1979.

( e) Trojan Nuclear Plant Concrete Masonry Design Criteria Safety

• Evaluation Report Supplement - November, 1980.

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APPENDIX B SKETCHES OF WALL MODIFICATIONS

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FRANKUN RESEARCH CENTER DMSION OF ARVIN/CALSPAN 20tt1 A RACE STREETS. PHILADELPHIA.PA 19103

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ATTACHMENT 2 SGEB STAFF POSIT 0N ON USE OF ENERGY BALANCE TECHNIQUE TO QUALIFY REINFORCED MASONRY WALLS IN NUCLEAR POWER PLANTS INTRODUCTION Under seismic loads, strain energy transfer through elastic response is very small compared to the inelastic response for energy dissipation. Therefore, inelastic non-linear analysis of reinforced masonry walls is an attractive approach. Some of the licensees have relied on a non-linear analysis approach .

known as " energy-balance technique" to qualify some of the reinforced masonry walls in their plants.

The staff and their consultants have reviewed the basis provided by licensees to justify the use of energ9;balanc'e technique to qualify the reinfored masonry walls. The staff met with a group of licesees representing approximately ten utilities on November 3, 1982 and January 20, 1983 to discuss this issue.

Further, site visits and detailed review of design calculations were conducted by the staff and their consultants to gain first-hand knowledge of field C. -pronditions and the application of energy-balance technique in. qualifying "'

in place masonry walls. Based on the information gained through the above activities, the staff has formulated the following position on the accept-

• ability of the use of energy-balance technique to qualify reinforced masonry walls in operating nuclear power plants. The staff's technical basis for the position is discussed in the attached report.

POSITION The use of energy-belance technique or any other non-linear analysis approach is not acceptable to the staff without further confirmation by an adequate test

program. Therefore, the staff position consists of the following three options.

Adoption of any one of the option and successful implementation will constitute a resolution of the issue regarding the qualification of reinforced masonry walls by energy balance technique or other non-linear techniques.

1. Reanalyse walls qualified by the energy-balance technique by linear elastic working stress approach as recommended in the staff acceptance criteria (SRP Section 3.8.4, Appendix A) and implement modifications '

to walls as needed.

2. Develop rigorous non-linear time-history analysis techniques capable of capturing the mechanism of the wall's under cyclic loads. Different stages of behavior should be accurately modeled; elastic uncracked, elastic cracked and inelastic cracked with yielding of the celtral rebars. Then, a limited number of dynamic tests (realistic design eirthquake motion.,_,

C .c. _ ,

inputs at top and bottom of the wall) should be conduct ,' to demonstate the overall conservatism of the analysis results. In this case, "as built" walls should be constructed to duplicate the construction details of a specific plant.

3. For walls qualified by energy-balance technique, conduct a comprehensive test program to establish the basic non-linear behavioral characteristics of masonry walls (i.e. lodd-deflection hysteretic behavior, ductility ratios, energy absorption and post yield envelopes) for material properties and construction details pertaining to masonry walls in question. The

/

behavior revealed from tests should then be compared with that of elastic-perfectly plastic materials for which the energy balance technjque was originally developed. If there are significant differences, then the energy

balance technique should be modified to reflect the actual wall behavior.

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EVALUATION OF THE APPL'ICABILITY OF NONLINEAR ANALYSIS TECHNIQUES TO REINFORCED MASONRY WALLS IN NUCLEAR POWER PLANTS Prepared by Harry G. Harris (1)

Ahmad A. Hamid (1) '

Vu Con (2)

1. - e -. . .

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. August 1984

.J,eAtcGVA Q 4gunws-g~> .

(1) Department of Civil Engineering, Drexel University, Philadelphia, Pennsylvania (2) Nuclear Engineering Department, Franklin Research Center.

Philadelphia, Pennsylvania .

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• INTRODUCTION

• In response to IE Bulletin 80-11, a total of 10 nuclear power plants have indicated that the energy balance technique has been employed to qualify some reinforced masonry walls in out-of-plane bending. Based on the review of submittals provided by the licensees and all available literature, the Franklin Research Center (FRC) staff and FRC consultants have concluded that the available data in the literature is not sufficient to warrant the use of nonlinear analysis techniques to predict the response of masonry walls under cyclic, full,y reversed dynamic loading. As a result, a meeting with representatives of the affected plants was held at the NRC on November 3, 1982 so that the NRC, FRC staff and 'FRC consultants ko'uld explain their concern regarding the applicability of the energy balance technique to masonry walls in nuclear power plants [13. In a subsequent meeting on January 20, 1983, consultants of utility companies presented their rebuttals

[2] and requested that they should be treated on a plant-by plant

1. ~~ r--basis. In accordance with their requests, the NRC staff st hted

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the process of evaluating each plant on an individual basis. In this process, the NRC, FRC staff and consultants visited a few nuclear power plants to examine the field conditions of reinforced masonry walls in the plants and to gain first-hand knowledge of how the energy balance technique is applied to actual walls. Key calculations were reviewed with regard to the energy balance technique.

1

EVALUATION OF ENERGY BALANCE ' TECHNIQUE Based on a review of the submittals provided by the licensees, specific plant visits, evaluation of typical design computations and review of all available literature, it is concluded that the concerns raised by the Franklin Research Center (FRC) staff and consultants pertaining to the use of energy balance technique have not been resolved. A summary of these concerns are listed below:

1. Only a f ew isolated tests have been reported on the lateral resistance of reinforced concrete block and brick masonry walls in out-of-plane bending. These tests can be summari:ed as follows:

(i) Tests 'havs be~en conducted on 20' high reinforced concrete block walls 8" thick in running bond and stack bond configurations by Dickey and Mackintosh C3]. .

These tests, although limited, revealed that, under monotonically increasing load, some of the panels failed in a brittle mode prior to reaching yield and that the stack bond was less effective than the running bond.

(ii) More recent tests conducted by the ACI-SEASC Task Committee on Slender Walls C43 on face loaded 24' high c' __"#' "

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reinforced masonry walls under monotonically increasing

_ load showed relatively low ductility ratios in the 3 panels -that attained failure. Two 6" nominal fully grouted concrete masonry walls attained ductility ratios of approximately 2 when they failed inadvertently in compression. One 6" hollow brick wall tested to failure also attained a ductility ratio of approximately 2. It has been noted that walls tested were fully grouted and have high steel percentages (0.22% to 0.37%).

(iii) Tests conducted by Scrivener C5,63 on face loaded reinforced masonry walls made of 4 1/4" reinforcing brick revealed high ductilities. The one cyclical 11y loaded panel whose load-deflection results are reported C5]

revealed very peculiar hysteretic behavior unlike the required elasto plastic behavior needed for application of the energy balance technique.

(iv) Tests on small masonry structures resulting fr,om an assembly of various components to form single story masonry homes have been carried out at the UC, Berkeley 2

earthquake simulator 'E73-E9]. The main objective was to provide design recommendations on the minimum reinforcement required for masonry housing in seismic zone 2. These are the only tests of reinforced masonry walls under realisite earthquake loads. The reinforced walls tested under out-of plane bending in this program i did not yield under the applied loads. In addition, these walls did not have the boundary conditions of typical applications of masonry walls in nuclear power plants.- -

(v) Dynamic tests on slender reinforced' block masonry walls have been conducted at the EERC, University of California, Berkeley for Bechtel Power Corporation. The program has been conducted to demonstrate the conservatism of the nonlinear dynamic analysis performed by Computech Engineering Services for the masonry walls in the San Onofre Nuclear Generating Station, Unit 1 (SONGS-1). The FRC staff and consultants witnessed one of the tests. It was shown that the wall was capable of resisting significant inelastic deformations when subjected to earthquake input motion. It has to be mentioned, however, that the few tests performed were i

plant specif,ig_and_aime,d at verifying the conservatism of the nonlinear dynamic analysis technique developed by i Computech Engineering Services. Consequently, the -

parameters included in the program were limited to "as built" condition of the walls in SONGS-1. The program objective was not to verify the use of the energy balance technique.

The above tests that have been conducted on reinforced masonry walls and which are relevant to the evaluation of concrete ~

C. 5._ ;_

masonry walls in nuclear power plants do not form a sufficient data base to warrant the use of the energy balance technique.

2. A Technical Coordinating Committee for Masonry Research (TCCMAR) has been formed under the auspises of the US-Japan Cooperative Research Program. - It is a recognition of the urgent I

need for research in the area of seismic resistance of masonry.

The committee met in Pasadena in February 1984 to assess the current state of knowledge and to outline an experimental program to provide the necessary data. It has been concluded that the current state-of-the-art of masonry has not progressed enough to i

3

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warrant ' inelastic analysis methodology of masonry structures

[113. A comprehensive- test program was recommended. This significant undertaking is a clear indication of the lack of test data available for masonry. (Note: Dr. Hamid serves as a member 1

of TCCMAR.)

3. A large number of variables exist in the construction of concrete block walls used in nuclear power plants. For example, the walls can be fully grouted, partially grouted, stack bond, running bond, single and multiple wythes with different bicch sires ranging from 4" to 12" in width. No adequate test data exist in the literature to enable a clear understanding of the

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of these v'~riab1e's on the dynamic fully revdrsed

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effects a cyclic behavior of masonry walls.

4. Eff ects of cut-outs and $c entric loads due to attachments on reinforced concrete masonry walls of the type used in nuclear .

power plants have not been evaluated experimentally. This .Jype L --c

~ of information, whe,n a,vai l ab l e, will help to substantiate the various assumptions made in the analysis of such safety related walls.

i y .

5. The limited tests that have been conducted and summarized in item 1 above have pointed out to the inability to preclude brittle type failures with low ductility ratios on face loaded panels under monotenically increasing load. A lack of knowledge e::ists on the ma::imum attainable compressive strains in the face shell of reinfcrced concrete masonry walls under out-ot-plane bending. This is particularly true under cyclic dynamic loading.

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6. In examining the available test data, it is also obvious that t,here is a significant lack of information about the post yield envelope and established cyclic load characteristics for reinforced concrete masonry walls under out-of plane bending which is essential to demonstrate the stable ductile behavior required for the applicability of the energy balance technique.

This is attributed to the fact that most tests were not conducted to ultimate failure which is essential for the determination of the post yield envelope. This deficiency exists for all of th,e types of masonry construction used in nuclear power plants [103.

7. _Some walls are- quaLif-ied based on one-way bending in the hori=ontal direction or two-way plate action. These walls are horizontally reinforced with joint reinforcement embedded in the mortar joints every course or every other course. This type of steel is a high tensile steel with a yield stress as high as g __ w 100,000 psi indicating a very limited ductility. Masonry codes are noE specific about the usefullness of joint reinforcement, particularly in seismic areas [12,13]. If joint reinforcement is to be used to resist tensile stresses, the WSD method should be employed with an allowable steel stress limited to 30,000 psi.

The only code E143 that addr, esses the use of joint reinforcement in seismic areas for categoriees C and D structures was developed by the Applied Technology Council. This code does not allow the use of joint reinforcement es a load carrying element for these two categories.. Saf ety-related masonry walls in nuclear power plants would fit into these categories. Information about the 5

cyclic behavior of joint ' reinforced masonry walls is not available in the masonry literature at the present time [12,133.

B. The energy balance technique has been originally developed as )

an approximate design tool to check the resistance of ductile concrete and steel frame buildings subjected to seismic loads.

!, i With the fast development in computers in recent years, more

. rigorous nonlinear dynamic analyses of ductile structures have also been made possible.

NONLINEAR ANALYSIS'OF MASONRY WALLS -

Under seismic loads, strain energy transfer through elastic l'

reponse is very small. compared to the inelastic response for energy dissipation. With regard to inelastic behavior, two

. methods have been used to investigate the dynamic -

response of l concrete and steel structures to a strong motion earthquake. One l of the methods requires the formulation of an inelastic model of l

the structure utilizing the finite element technique. The model C ~~ e .

is then subjected to time-history ground motion and the dynamic response is determined. The results of this approach, which is time consuming and costly, depends on how accurately the structure is represented by the inelasttic model and how well the

/

material properties are defined. Therefore, a limited'

/

confirmatory dynamic test program should be conducted to check the conservatism of the assumptions used.

The other method, whi ch is easier to apply in a design office, separates the properties of the structure from those of the earthquake. The earthquake is represented by a response 6

o spectrum which is then modified to accomodate the inelastic or ductile response of the wall [153. This method which relies on the energy balance technique requires information about ductility and energy absorbtion capability of masonry wall's which, as discussed previously, have not been demonstrated experimentally for general applications. A ductility f actor of 1 or 1.5 is suggested C163 for damage-level earthquake intensities where as ductilities of 2 to 3 is recommended [163 for use with collapse-level response spectra. Because the energy balance technique is an approximate simplified method, an adequate and more comprehensive data base should be generated to check this design methodology.

TEST PROGRAM RELATED TO ENERGY BALANCE TECHNIQUE If a confirmatory test program is elected to justify the use of the energy balance technique, it is expected that the test panels should represent the actual configuration, construction C -rg. details and boundary conditions of masonry walls in nuclear p'ower plants.

The test program should cover the different parameters that would affect wall performance such as steel percentage, bond type, partial grouting and block size.

The test objectives should be centered upon the following:

1. To demonstrate that the masonry walls would maintain their structural and functional integrity when subjected to SSE and other applied loads.

2. To demonstrate that a stable ductile behavior characterized by steel yielding is guaranteed and that any 7

brittle failure (e.g. crushing) is precluded.

3. To develop necessary information ,to veri.fy the energy balance technique as a methodology for the qualification of a

reinforced masonry walls in nuclear power plants..

4. To demonstrate that adequate margins of safety exist for walls subjected to design lateral loads.

1

SUMMARY

, CONCLUSIONS AND RECOMMENDATIONS A review and evaluation of the available information on the nonlinear behavior of block masonry walls under out-of-plane loading has been presented. It is concluded that test data are j

needed to substanti* ate ~the use'of nonlinear analysis techniques to qualify reinforced block walls in nuclear power plants. .

4 To qualify masonry walls based on nonlinear analysis, two alternatives are recommended:

1- Develop rigorous nonlinear time-history analysis CL .g_ ,

techniques capable of capturing the mechanism of the WW11s

~

under cyclic loads. Different stages of behavior should be accurately modeled: elastic uncracked, elastic cracked and s

inelastic cracked with yielding of the central rebars.

Then, a limited number of dynamic tests (realistic design earthquake motion inputs at top and bottom of the wall) should be conducted to demonstrate the overall conservatism of the analysis results. In this case, "as built" walls should b'e constructed to duplicate the construction details of a specific plant. ,

2- Conduct a comprehensive test program to establish the 8

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.s. - _

basic nonlinear behavioral characteristics of masonry walls (i e. load-deflection hysteretic behavior, ductility ratios, energy absorbtion and post-yield envelopes) for material properties and construction details pertaining to masonry walls in question. The behavior revealed from 'the tests should then be compared with that of elastic-perfectly-plastic materials for which the energy balance. technique was originally developed. If there are significant differences, then the energy balance technique should be' modified to reflect the actual wall ~ behavior.

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4 REFERENCES

1. Hamid, A.A. and Harris, H.G., " Applicability of Energy Balance Technique to Reinforced Masonry Walls," Franklin Research Center, i

Philadelphia, PA, June 1982.

2. " Rebuttal to Applicability of Energy Balance Technique to Reinforced Masonry Walls," URS/ John A. Blume Associates and Bechtel Power Corporation, January 1983.

3. Dickey, W.L. and Mackintosh, A., "Results of Variation of "b" or Effective Width in Flexeral Concrete Block Panels," Masonry Institute of America, LA, 1971.

4. Annonymous, " Test Report on Slender Walls," Report of the Task Committee on Slender Walls, Edited by J.W. Athey, ACI, Southern California Chapter, and the Structural Engineers Association of Southern California, Feb. 1980-Sept. 1982, Los Angeles, CA.

5. Scrivener, J., " Reinforced Masonry - Seismic Behavior and Design," Bulletin gi Ngw Zealand Society igC Earthguake Engineering, Vol. 5, No. 5, Dec. 1972.

6. Scrivener, J. , . ." Face _ Loa.d Tests on Reinf orced Hollow Brick Non-Load-Bearing Walls," Ngw Zealand gegineering dgurnal, July 1969.

7. Clough, R., Mayes, R. and Gulkan, P., " Shaking Table Study of Single Story Masonry Houses, Volume 3: Summary, Conclusions and Recommendations," Earthquake Engineering Research Center, Report No. UCB/EERC-79/23, College of Engineering, University of California, Berkeley, CA, September 1979.

8. Gulkan, P., Mayes, R. and Clough, R. " Shaking Table Study of g_ __TESingle Story Masonry Houses, Vol. 2: Test Structures 3 and 4,"

Earthquake Engineering Research Center, Report No. UCB/EERC-79/24, College. of Engineering, University of California, Ber kel ey, CA, September, 1979. ,

9. Manos, G., Clough, R. and Mayes, R., " Shaking Table Study of Single Story Masonry Houses- Dynamic Performance under Three Component Seismic Input and Recommendations," Report No. UCEERC-83/11, Univ. of Calif., Berkeley, July 1983.

10. Hamid, A.A., Harris, H.G., Con, V.N. and Chokshi, N.C.,

" Performance of Block Masonry Walls in Nuclear Power Plants,"

Procggdings gf the Thitd Canadian Masgnty Symggsium, Alberta, Canada, June 1983, pp. 12-1 to 12-9.

11. .Hamid, .A.A. and Harris, H.G., " State-of-the-Art Report:

Nonlinear Behavior of Reinforced Masonry Walls under Out-of-Plane Lateral Loading," Proceedings of the International Symposium on Reinforced and Prestressed Masonry, Edinburgh, Scotland,. August 1984.

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12. Hamid, A. A., Harris, H. G., and Becica, I. J., "The Use of Joint Reinforcment In Block Masonry Walls," Franklin Research Center, Philadelphia, March 1983.

13. . Harris, H.G., Hamid, A.A., Becica, I.J., Con, V.N., and Chokshi, N.C., "The Use of Joint Reinforcement in Qualifying Masonry Walls in Nuclear Power Plants," Presented at the ASCE Specialty Conference on Structural Engineering in Nuclear Facilities, Sept. 10-12, 1984, NC State University, Raleigh, North Carolina. -

14. Applied Technology Council, " Tentative Provisions for a Development of Seismic Regulations for Buildings," ATC 3-06, (NSF Publication 78-8, NBS Special Publication 510), U.S. Government Printing Office, June 1978.

15. Englekirk, R.E., Hart, G.C. and the CMA of California and Nevada, ggtthgughg pggign gi ggncretg Masonty Egildings z Mgiz 1 Besn90se Snectra Bnaixsis and General Egtthgugkg Mgdeling ggnsiderations, Prentice-Hall, Inc., Englewood Cliffs, N.J.,

1982.

16. _ Englekirk, R,E., Hart, G.C. and the CMA of California and Nevada, Earthgughg Desian gi Concrete Masanty Buildinggz Mgl z 2 SICEn9th DesiEn Qi One-to-Four-Stoty Buildings, Prentice-Hall, Inc., Englewood Cliffs, N.J., 1984.

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