ML20080E252
| ML20080E252 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 03/31/1983 |
| From: | Becia I, Hamid A, Harris H DREXEL UNIV., PHILADELPHIA, PA, FRANKLIN INSTITUTE |
| To: | NRC |
| Shared Package | |
| ML20080E255 | List: |
| References | |
| CON-NRC-03-31-130, CON-NRC-3-31-130 IEB-80-11, NUDOCS 8308310512 | |
| Download: ML20080E252 (9) | |
Text
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TECHNICAL REPORT ON THE USE OF JOINT REINFOPCEMENT IN BLOCK PASONRY ELLS SUBMITTED TO FRANKLIN RESEAPCH CENTER PHILADELPHIA, PE! NSYLVANIA BY DR. AHPAD A. HAMID AND DR. AARP3 G. HARRIS DEPARTMENT OF CIVIL ENGINEEPlNG, DREXEL UNIVEPSITY PHILADELPHIA, PENNSYLVANIA 19104 AND IVAN J. BECICA FPANFl.IN RESEAPCH CENTER PHILADELPHIA, PENNSYLVANIA 19103 MAPCH 1983 A
"".a:'AffMIT" XA Copy Has Been Sent to PDR y,$0F 08/ 8/4
- i" 1.
PROBLEM STATEMI:NT Joint reinforcement has been used as a structural element to qualify unreinforced block =asonry walls in nuclear power plants. Joint reinforcement is commonly used for cr'ack control and to provide continuity for multiple wythe walls (10,14].
The structural significance (resisting of tensile stresses) of joint reinforcement in masonry walls is not well established. This is particularly true for unreinforced hollow block masonry walls under cyclic dynamic loading. The following two sections sum =arize test data and buiAding code requirements for joint reinforcement in an attempt to evaluate 1:s structural significance.
2.
EVALUATION OF TEST DATA There are few test programs documented in the literature addressing the function of joint reinforcement e= bedded in the mortar joints of masenry walls. Table 1 summarizes the different test data of joint reinforced walls
lay 1'ng mhter'iAI"pEoperties and construction details similar to block walls in nuclear power plants. The available data are limited to static, nor=al loads applied to horizontally spanning wall segments. Analysis of the test data presented in the table revealed the following conclusions:
1.
Joint reinforcement did not affect the cracking load. Uncracked wall stiffness of unreinforced walls was nimilar to that of walls with joint reinf orcement.
2.
The contribution of joint reinforcement in the load carrying capacity ranges from -10% to 3001 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 s trength degradation under earthquake loads.
4.
The deflection at ultimate loads of reinforced walls was, in some cases, much higher than that for unreinforced walls which exhibited a brittle cleavage failure.
5.
The statistical significance of the,few samples tested is questionable and does not provide confidence in the available test results.
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7 3.
REVIEW OF-CODE PRCVISIONS Tabic 2 presents the different code design provisions concerning the role of joint reinforcement in masonry walls. As can be noted from Table 2, thes e codes are rarely specific about the usefulness of joint reinforcement and its function as a structural element to carry lateral loads. The codes, however, allow the use of joint reinforcement as part of the required minimum reinforcement in reinforced ' masonry cons truction. This 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 s tress design (WSD) approach should be followed. The WSD approach assumes linear elastic material properties and limits the allowable steel stress to 30,000 psi.
The new edition (19 82) of the Uniform Building Code (UBC) allows the use of joint reinforcement as principal hori:ontal steel to carry design stresses (13]. This is, however, limited to reinforced masonry walls designed using the WSD me thod.
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 OF MASONRY WALLS WITH JOINT REINFOPCEMENT North American codes for reinforced casenry design assign allowable flexural compressive stresses for masonry and tensile stresses for reinforcing steel. Table 3 presents calculated allowable moments /f t of typical S-in hollow block walls which span horizontally based on the working stress design.
It is assumed that the wall is cracked and that steel carries all the tensien. The allowable moment (M U) the unreinforced wall carries hori:entally is calculated based on an allowable flexural stress of 1.0Im7
[1].
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Table 2.
Code Design Provisions for Joint Reinforcement Code Design Provisions ACI [1]
Section 6.7 "Hori: ental joint reinforcement may be used in the wall to increase the tensile resistance and as a means to resist design tensile stresses."
i section 8.2 "The function of joint reinforcement is to prevent the formation of excessively j
large, unacceptable shrinkage cracks in masonry walls."
USC [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 minimum reinforcement."
1CMA [15]
Section 3.10
" Approved wire reinforcement, placed in horicontal cortar joint, may be used as part of the required reinforcement."
ATC [3]
Section 12.5.1
" JOINT REINFOPCDENT: Mngitudinal masonry joint reinforcement may be used in reinforced grouted masonry and reinforced hollow unit masonry only to 3
fulfill minimum reinforcement ratios but shall not be considered in the determination of the strength of the member."
CSA [6]
Section 4.6.8.1 " Wire reinforcement in the mortar joints may be considered as required hori: ental reinf orcement. "
Note:
No provisions are given in BS 5628 [4] or 31S [16] concerning ene use of joint reinforcement.
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Allowable Moments Joint Calculated Allowable MAR
- Reinforcement Moment, MAR, lb-in/ft [10]
Mgg 9 gage 8 in o.c.
I 4880 1.42 16 in o.c.
2440 0.71 8 gage 8 in o.c.
5820 1.69 16 in o.c.
2910 0.85 3/16" 8 in o.c.
7430 2.16 16 in o.c.
3720 1.08 f'm = 2000 psi, fm = 0.33 f'mr fs = 30,000 psi, type S-=ortar,
- ratio of calculated moment of reinforced wall to unreinforced wall (M3g =
343 6 lb-in/f t).
The results presented in Table 3 show that the allowable moments for masenry walls spanning hori:entally depend primarily on the steel ratio. It is interesting to note that joint reinforcement at lower percentages does not increase the wall resistance.
......,,...Th.e, contribut.icn of_ joint reinforcement in the ultimate (f ailure) lateral load resistance of =asonry walls was calculated by Cajdert (5]. He assumed a linear bending strain with a triangular stress distribution in the compressica The ultimate strength is assumed to be reached when, ef ter yielding of ene.
the tensile reinforcement, the ultimate masonry strength, f',, is reached.
It must be noted that the joint reinforcement is high tensile steel with a yield stress as high as 10 0,0 00 ps i. No published data are available on its stress-strain behavior which is needed in the ultimate lead analysis.
Cajdert's [5] approach of ultimate stress design necessitates precluding any bond failure to develop yielding of the joint reinforcement.
5.
CO!CLUSIONS AND RECOMMENDATIONS The 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:
4.
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The available test data are scarce. Conflicting values have been obtained concerning the contribution of joint reinforcement. Also, the statistical 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 strength of 33% in half a cycle. This indicates the possibility of severe s trength 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 with an allowable steel stress limited to 30,000 psi. This approach limits the contribution of joint reinforcement in increasing the allowable moment over that of unreinforced walls with running bond. It must be noted that codes allow the use of joint reinforcement as a structural steel only in reinforced walls which satisfy the minimum steel requirements in both vertical and horizontal directions. This may not be the case for the masonry walls in nuclear power plants.
4.
The only code [3] that addresses the ute of joint reinforcement in seismic areas does not allow its use an principal steel for Categories C and D structures.
Safety-related masonry walls in nuclear power plants would fit into these categories.
5.
For hollow block walls with joint reinforcement, cracking extends to the compression face shell causing a dramatic reduction in uali stif fness and consequently excessive deflection, particularly under cyclic loading.
A serviceability limit state should be applied to assure proper performance of wall attachments (pipe s). 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.
This boundary condition, if it exists, forces the wall to transfer its self weight by beam action to the vertical support.
t Therefore, 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 state-of-the art does not give enough insight to understand the performance of joint reinforcement under seismic loads.
Therefore, it is the FRC consultants' opinion that njg credit should be given I
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.t s * =s s to joint reinforcement to resist tensile stresses due to earthquake loads. A confirmatory test program is therefore recommended to provide data about the structural performance of joint reinforcement in block masonry walls under cyclic dynamic loading.
3 6.
REFERENCES 1.
American Concrete Institute, " Building Code Requirements 'for Concrete Masonry Structures," ACI Standard 531-79, Detroit, Michigan 2.
Anderson, D. L., Nathan, N. D., Cherry, S., and Craj er, R.
B.," Seismic '
Design of Reinforced Concrete Masonry Walls," Proceedinos of the Second Canadian Masonry Symeosium, Ottawa, Canada, June 1980 3.
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 4.
British Standard Institution, "The Structural Use of Masonry," BS 5628:
Part 2: Reinforced and Prestressed Masonry, London,1981 5.
Cajdert, A., " Laterally Leaded Masonry Walls," Ph.D. Thesis, Cr almers University of Technology, Goteberg, Sweden, 1980 6.
Canadian Standard Association, "Maronry Design and constructicn for Buildings," Standard S304-M78, Rexdale, Ontario, Canada,,1973 7.
Cox, F. W. and Ennenga, J. L., " Transverse Strength of Concrete Block Walls," Proceedinos 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 4
Second North American Conf erence, College Park, Maryland, August 1982 10.
DUR-O-WAL Technical Bulletin No. 74-6, "DUR-O-WAL Masonry Reinforcement in High-Rise Bearing Wall Buildings," January 1974 11.
Hedstrom, R.O., " Load Tests of Patterned Concrete Masonry Walls,"
Peceeedines of American Cenerete Institute, Vol. 57, 1961 12.
International Conference of Building Officials, " Masonry Codes and Specifications," 1979 UBC, Chapter 14, Whittier, California,1979 2) Franklin Research Center
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International Conference of Building officials, Research Report No. 2292, January 1982 14.
National Concrete Masonry Association, "The Structural Role of Joint Reinforcement in Concrete Masonry," TEK-99, 1978 15.
National Concrete Masonry Association, " Specification for the Design and Construction of Ihad-Bearing Concrete Masonry," Herndon, Virginia,1979 16.
The Masonry Society, " Standard Building Code Requirements for Masonry Construction," Boulder, Colorado, August 1981 I
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