ML18053A345

Tech Rept on Use of Joint Reinforcement in Block Masonry Walls.

ML18053A345
Person / Time
Site:	Palisades
Issue date:	03/31/1983
From:	Becica I, Hamid A, Harris H DREXEL UNIV., PHILADELPHIA, PA, FRANKLIN INSTITUTE
To:
Shared Package
ML18053A344	List: ML18053A345
References
IEB-80-11, TAC-42894, NUDOCS 8804280144
Download: ML18053A345 (14)

Text

Enclosure 2 TECHNICAL REPORT ON

'1'BE OSE OP' JOINT .REINFORCEMENT IN BLOCX MASON~ WALLS

• SUBMITTED TO PRANKLIN RESEABCB CENTER PHILADELPHIA, PE?.NSYLVANIA BY DR. AHMAD A. HAMID AND QR. BARBY G. BARRIS I:'EPARrMENT OP CIVIL.ENGINEERING, DREXEL UNIVERSITY PHILADELPHIA, PENNSYLVANIA 1910,4 AND IVAN J. BECICA FRANKLIN RESEARCH CENTER PHILADELPHIA, PENNSYLVANIA 19103 MAJCB 1983 J t~~:~gM:'g0~~~5\1 .. )

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l. PROBLEM STATEMENT Joint reinforcement has been used as a structural element to qualify unreinforced block masonry walls iri nuclear power plants. Joint reinforcement is commonly used for cr'ack control and to provide. continuity for multiple wythe walls (10, 14].

'l'he structural significance (resisUng of tensile stresses) of joint reinforcement in masonry walls is not well established. This is partic.ilarly true for unreinforced hollow block masonry walls under cyclic dynamic

\oading. 'l'he foilowing two sections summarize test data.and bui~ding code requirements for joint reinforcement in an attempt to evaluate i';s str1.:ctural

-significance.

' 2. EVALOATION OP TEST DATA There are few test program:a docunented in the literature addressing the function of joint reinforcement;embedded in the mortar joints of masonry walls. Table 1 summarizes. the different test data of joint ~einforced walls having material properties and cqn~truction details similar to .block walls in nuclear power plants. The available data are limited to static, normal loads applied to horizontally spanning wali segments. Analysis of the test data presented in the table"revealed the following conclusionss

1. Joint reinforcement did not affect the cracking load. oncracked wall stiffness of unreinforced walls was similar to that of walls with joint reinforcement.

2. ~e contribution .of joint reinforcement in the load carrying capacity ranges from -10' to 300\ indicating the sensitivity to variation in material properties and construction details.

3. The single test data (2] available under.cyclic loads showed a 33\.

strength reduction on the first half cycle. This indicates the possible strength degradation under earthquake loads.

4. The deflection at ultimate '1oads of reiiiforced walls was, in some cases, much higher than that for unreinforced walls which exhibited a brittle cleavage failure.

s. '!be statistical significance of the few samples tested is questionable and does* not provide confidence in the available test results.

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3. REVIEW OP. CODE PROVISIONS Table 2 presents the different code design provisions concerning the role of joint reinforcement in masonry walls. As can be noted from Table 2, these codes are rarely speci~ic about the usefulness of joint reinforcement and its function as a structural element to carry lateral loads. 'rhe codes, however, allow the use of jo~nt reinforcement as part of the required minimum reinforcement in. reinforced *masonry construction. 'l'bis implies *that the main structural function of joint reinforcement is to distribute the load to the main vertical steel. It must be noted, however, that the codes, if they allow*

wire reinforcement to be used as principal reinforcing steel, specify that the working stress design (WSD) approach should be followed. 'l'be WSD approach assumes linear elastic material properties and limits the allowable steel stress to 30,000 psi.

'l'be new edition (1982) of the Uniform Building Code (OBC) allows the use of joint reinforcement as principal horizontal steel to carry design stresses (13]. This is, however, limited to reinforced masonry walls designed using.

the WSD method.

The design provisions. of most codes apply to masonry buildings under,

• static loads. ATC-3 (3) is the only code that _specifies the structural use of joint reinforcement under earthquake loads in seismic areas. It does permit the use of joint reinforcement to resist tensile stresses for seismic Category A and B structures, but states that it cannot be used as the principal reinforcement for Categories C and D structures, except as part of the minimum reinforcing requirements.

4. DESIGN OP MASONR:C WALLS WITH JOINT REINFOH:EMENT North 1'merican codes for reinforced masonry design assign allowable flexural compressive stresses for masonry and tensile stresses for reinforcing steel. Table 3 presents calculated allowable moments/ft cf typical 8-in hollow block walls which span horizontally based on the wcrking*stress *.

design. It is assumed that the wall is cracked and that steel carries all the tension. 'l'be allowable moment <1\o> the unreinforced wall carries horizontally is calculated based on an allowable flexural stress cf l.O"'Viii;'

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Table 2. Code Design Provisions for Joint Reinforcement Code Design Provisions ACI [l) Section 6. 7 "Horizontal joint reinforcement may be used in the wall to increase the tensile resistance and.as a means to resist design tensile stresses.*

Section 8.2 *'l'be function of joint reinforcement is tQ prevent the formation of excessively .

large, unacceptable shrinkage cracks in masonry* walls.*

OBC [12) Section 2418 *The minimum diameter of reinforcement shall be 3/8 inch except that joint reinforcement may be considered as part of* the required mini.lnum reinforcement.*

N:MA [lS) Section 3.10 *Approved wire reinforcement, placed in horizontal mortar joint, may be used as part of the required reinforcement.*

ATC (3) Section 12.5.l *JOINT REINFOICEME:NT: Longitudinal masonry joint reinforcement may be used in reinforced grouted masonry and reinforced hollow unit masonry only to fulfill minimum reinforcement ratios but shall not be considered in the determination of the strength of. the member.*

CSA [6) Section 4.6.8.l "Wire reinforcement in the mortar joints may be considered as required horizontal reinforcement.*

Note: No provisions a~e given in BS 5628 [4) or TMS (16) concerning the use of joint reinforcement.

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,.. *e Table 3. Ailowable Moments Joint calculated Allowable MAR*

Reinforcement Moment, MAR, lb-in/ft (10) -MAO

• 9 gage 8 in o.c. 4880 l.42 16 in o.c. 2440 0.11 8 gage 8 in o.c. S820 l.69 16 in o.c. 2910 a.as 3/16* 8 in o.c. 7430 2.16 16 in o.c. 3720 l.08 f'm.* 2000 psi, fm

• 0.33 f'm, fs

• 30,001 psi, types-mortar,

• ratio ~f calculated moment ~f reinforced wall to unreinforced wall (MAD

• 3436 lb-in/ft).

The results presented in Table 3 show that the a1lowable moments for masonry walls spanning horizontally depend primarily on the steel ratio. It is interesting to note that joint reinforcement at lower percentages does not increase the wall resistance.

The contribution of joint reinforcement in the ultimate (failure) lateral load resistance of masonry walls was ca1culated by cajdert [SJ. Be assumed a linear bending strain with a triangular stress distribution in the compression zone. The ultimate strength is assumed to be reached when, ~fter yielding of the tensile reinforcement, the ultimate masonry strength, f ' 11 , .is reached.

It must be noted that the joint reinforcement is high tensile steel with a yield stress as high as 100,000 psi. No published data are available on its stress-strain behavior which is needed in the ultimate load analysis.

Cajdert's [SJ approach of ultimate stress design necessitates precluding any bond failure to develop yielding of the joint reinforcement.

5. CO?CLUSIONS AND RECOMMENDATIONS

'l'he structural performance of joint reinforcement is not well established *

. The qualification of masonry walls in nuclear power plants which takes into account tensile stength due to joint reinforcement is questionable. This is based on the following arguments&*

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i. 'l'he available test data are scarce. Conflicting values have been

.obtained concerning the conb:ibution of joint reinforcement. Also,

• -thestatistical. significance of so few samples of such a variable material is questionable. *

2. All the tests were performed under static loading which cannot be extrapolated to predict the performance under earthquake loads, which are dynamic and cyclic, fully reversed in nature. The only test data for* cyclic static loading showed a dramatic decrease in streng.th of 33' in half a cycle. This indicates the possibility of severe strength deterioration under multiple reversed cyclic.dynamic loading.

3. Masonry codes are not specific .about the usefulness of. joint reinforcement. Its use is allowed to satisfy the minimum steel requirements for reinforced masonry. If it is to be used to resist tensile stresses, the WSD method should be employed w~tb an allowable

• steel .stress limited to 30,000 psi. This approach limits the contribution of joint reinforcement in increasing the a~lowable

• moment over that of anreinforced walls with running bond. It must be noted tbat codes allow the use of joint reinforcement as a structural steel only in reinforced walls which satisfy the miniI!lum steel requirements in both vertical and horizontal directions. This may not be the case for the masonry walls in nuclear power plants.

4. 'l'he only code (3) that addresses the u!;e of joint reinforcement in seismic areas does r..ot allow its use a:s principal steel for categories C and D structures. Safety-related masonry walls in nuclear power plants would fit into these categories.

s. For boll.ow block walls with joint reinforcement, cracking extends to the compression face shell causing a dramatic reduction in wall stiffness. and consequently excessive deflection,. particularly under cyclic loading.

A serviceability limit state should be applied to assure proper performance of wall attachments (pipes). This limit state may restrict the performance of joint reinforcement to the linearly elastic stage. *

6. Unreinforced walls in nuclear power plants that are joint reinforced to span horizontally should have base boundary conditions which are free to allow both translation and rotation in the out-of-plane direction. 'l'his boundary condition, if it exists, forces the wall to tr~sfer its self weight by beam action to the vertical support.

'l'herefore, the wall is under in-plane and out-of-plane forces. The effect of possible interaction on the*wall performance, particularly under cyclic dynamic loads, is not known.

In conclusion, the stat~of-tbe art does not give enough insight to understand the performance of joint reinforcement under seismic loads.

Therefore,.it is the Fie consultants' opinion that 1!2. credit should be given

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to joint reinforcement to resist tensile stresses due to earthquake loads. A confirmatory test program is therefore* recommended to pr.ovide data about the structu~al performance of joint reinforcement in block masonry walls under cyclic dynamic loading.

6. REFEBENCES .

l. American Concrete Institute, *Building Code Requirements for Concrete Masonry Structures4

• ACI Standard ~31:..79, Detroit, Michigan

2. Anderson, D~ L., Nathan, N. D., Cherry~ s., and Crajer, R. B.,* Seismic Design of Reinforced concrete Masonry Walls,* Proceedings of the Second

• Canadian Masonry Symposium, Ottawa, Canada, June 1980

3. Applied Technology council, *Tentative Provisions for a Development of Seismic Regul.ations for Buildings,* ATC 3-06 (NSF Publication 78-8, NBS Special Public~tion 510), o.s. Government Printing Office, June 1978

4. British Standard Institution, *The Structural ose of Masonry,* BS 5628:

Part 2: Reinforced and Prestressed Masonry, London, 1981

5. Cajdert, A., *Laterally Loaded Masonry Walls,* Ph.D. Thesis, ctalmers cniversity of Technology, Goteberg, Sweden, 1980

6. Canadian Standard Association, *Masonry Design and Construction for Buildings,* Standard S304-M78, Rexdale, ontario, Canada,.1978

7. cox, P. w. and Ennenga, J. L., *nansverse'strength of Concrete Block Walls~* Proceedinas of American Concrete Institute, Vol. 57, 1961

8. Churchward, G. and Mattison, E. N~, *Some Tests on the Bending Strength of Concrete Masonry in Running Bond,* Division of.Building Research, Melbourne, Australia, 1969

9. Dickey, W. L. , *Joint Reinforcement and Masonry,* Proceedinas of the Second North American Conference, College Park, Maryland, August 1982

10. DUR-0-WAL Technical Bulletin No. 74-6, *noR-O-WAL Masonry Reinforcement in High-Rise Bearing Wall Buildings,* January 1974

11. Hedstrom, R.O., *Load Tests of Patterned Concrete Masonry Walls,*

Proceedinas of American Concrete Institute, Vol. 57, 1961

12. International Conference of Building Officials, *Masonry Codes a~d Specifications,* 1979 CBC, Chapter 14, whittier, california, 1979

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13. International conference Of BUilding Officials, Research Report No. 2292, January 19 82

14. National Concrete Masonry Association, *The Structural Role Qf Joint Reinforcement in concrete Masonry,* TEK-99, 1978

15. National Concrete Masonry Association, *specification for the Design and construction of LOad-Bearing concrete Masonry,* Herndon, Virginia,* 1979

16. The Masonry Society, *standard Building Code Requirements for Masonry Construction,* Boul~er, COlor ado, AUgus t 19 81

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Enclosure 3 BVALOM'IOR OP AICBING THEORY IN OHREINPOR:ED

'* MASONRY ~* IN Ntl:LEAR POWER PI.ANTS Prepared by Ahmed A. Bamia1 B~ry G. B~ria 1 2

Vu Con June 1983

1. Department of Civil Engineering, Drexel University

2. Nuclear Engineering Department, Franklin Research Center

Ill'l'RODOCTION In responae to IB Bulletin ao-11, a total of 16 nuclear pover plants ha~e

' indicated *that the arching action technique has been employed to.qualify some unreinforced masonry walls. Based on the review of submittals provided by the licensees and published literature, Pranklln Research Center (FIC) staff and FIC consultants have concluded that the available data in the literature do not give enough insight for understanding the mechanics and performance of unreinforced aasonry walls under cyclic, fully reversed dynamic loading. As a result, a meeting with representatives of the affected plants was held at the NlC on November 3, 1982 so that the NIC, FIC staff, and FIC consultants could explain vhy the applicability of arching theory to masonry walls in nuclear power plants is questionable (1). In a subsequent meeting on January 20, 1983, consultants of utility compa~ies presented their rebuttals (2) and requested that they should be treated on a plant-by-plant basis. In accordance with their requests, the NIC staff has started the process of evaluating each plant on an individual basis. In this process, the NRC, F.FC ataff, and consultants have initiated visits to various nuclear plants to examine the field conditions of unreinforced masonry walls in the plants and to gain first-hand knowledge on how the arching theory is applied to actual walls. Key calculations have been reviewed with regard to the arching theory.

EVALUATION OP AICBING 'l'BEORY Test of unreinforced concrete masonry walls were recently conducted by Agbabian Associates, s. B. Barnes and Associates, and Kariotis and Associates (3) (this joint venture vork is designated as ABK). Based on the visit to

• Oconee Nuclear Station, the results of the ABK tests, and all relevant information submitted by the licensees including the rebuttals given by the licensees in the January 20, 1983 meeting, the NIC, FRC staff, and consultants have made the following evaluations:

. l. The design methodology used at* various nuclear plants was developed*

by McDowell et al. (4) in 1956 for solid brick walls under*static monotonic loading. No test data are available to check the adequacy of hollow block masonry under cyclic, ,fully reversed dynamic loading.

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2. 'l'be only dynaaic test data for arched aasonry valls are the ORS tests (SJ for blaat loading. lfhia type of loadincJ is not a true represen-

\ tation of earthquake loading becauae it is not fully reversed and has

• a decayed nature. Under very abort-duration blast loading, masonry walls, which have much lower natural frequencies, would.not fully respond to the applied load. In addition, only two walls vere tested under cyclic blast loading at ORS for arched masonry walls.

3. EXtrapolation of test data from solid masonry to hollow block masonry is questionable. Recent test data (6) of eccentrically loaded

• masonry assemblages showed that the failure mechanism, strain

• distribution, and overall behavior of hollow masonry are quite different from those of solid or grouted masonry.

4. Hollow block masonry walls are more susceptible to premature web-shear failure or crushing compression .failure. Precluding these types of failure is neccesary for the development of the arching mechanism. No data are available at the present time to determine the safety factors against these brittle failur-es under seismic loading.

s. Recent ABK dymanic tests (3) showed that unreinforced block masonry walls did fail (collapse) under earthquake loads with ground acceleration (effective peak acceleration) of about O.Jg to 0.4g, which is typical for nuclear plants. Also, some walls experienced local crushing at the base before failure by instability, which emphasizes the possibility of premature compression failure of arched walls. It aust be noted, however, that the ABK test walls were not restrained at top to develop arching. The effect of boundary conditions could be significant and cannot be evaluated without further testincJ.

6. Unreinforced block masonry walls are extremely brittle, and flexural failure occurs without warning. The sensitivity of unreinforced masonry *to crack development due to temperature and shrinkage is evident. Also, the inherent stren9th variability indicates the necessity of different safety indexes in ultimate failure analysis.

7. Masonry walls in nuclear plants usually have openings and attachments.. Their effects on wall stability under seismic loading are unknovn and cannot be rationally evaluated without _testing.

8. No test data are available for gapped.arching block walls under cyclic loading. In some cases, restrainers are provided around the gap to prevent gross sliding; this repair measure does not necessarily Cbange t.he wall_ be~~vior from gapped arch to rigid arch.

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CON:LOSION A review and evaluation of the available information on the applicability of arching theory to unreinforced 11asonry walls in nuclear power .Plants has been presented. NR:, PR: *taff,.and consultants are firmly convinced that their original position expressed to the licensees in the November 3, 1983 aeeting is still valid. It is evident that test data are needed to quantitatively determine the effects of different wall geometries, material properties, and boundary conditions on unreinforced block masonry walls' resistance to earthquake loading. It is recommended that a confirmatory testing program be performed to investigate the applicability of arching theory to unreinforced block masonry walls in nuclear power plants.

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REFERENCES

l. Hamid, A. A. and aarri_s, 9. G., *'4pplicability of Arching Tb_eory to .. **-.

unreinforced Block Masonry Walls Under Earthquake Leading,* Franklin Research Center, Philadelphia, PA

• August 1982

2. *Rebuttal to Applicability of Arching Theory to unreinforced Block Masonry Walls Under Earthquake Leading,* Computech Engineering Services, Inc., ORS/J. A. Blume ' ASsociates and Bechtel Power Corporation, January 1983

3. *Methodol09y of Mitigation of Seismic Hazards in Existing

. Unreinforced Masonry Buildings: Wall Testing, out-of-Plane,*

ABK report, El Sequndo, CA 1981 .

4. McDowell, E. L., McKee, M. E., and Sevin, E., *Arching Action Theory of Masonry Walls,* ASCE Proceedings, Journal of the Structural Division, ST2.

March 1956

s. Gabrielsen, B., Wilton, c., and Kaplan, K., *aesponse of Arching Walls and Debris from Interior Walls Caused by Blast Leading,* Report No., 7030-23, ORS Research Company, San Mateo, CA February 1975 * *

6. Drysdale, R. G. and Hamid, A. A., *capacity- of Concrete Block Masonry Prisons Onder Eccentric Compressive Leading,* ACI Journal, Proceedings, Vol. 80 March-April 1983

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