ML20027C595
| ML20027C595 | |
| Person / Time | |
|---|---|
| Site: | Haddam Neck File:Connecticut Yankee Atomic Power Co icon.png |
| Issue date: | 08/31/1982 |
| From: | Hamid A DREXEL UNIV., PHILADELPHIA, PA |
| To: | |
| Shared Package | |
| ML20027C596 | List: |
| References | |
| NUDOCS 8210190151 | |
| Download: ML20027C595 (7) | |
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Technical Report on APPL /CABILITY OF ENERGY BALANCE TECHNIQilE TO REINFORCED MASONRY WALLS for Franklin Research Center Philadelphia, Pennsylvania by Dr. Ahmad A. Hamid and Dr. Harry G. Harris l
l Department of Civil Engineering Drexel University f
Philadelphia, Pennsylvania 19104 o
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Aug.1982
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INTRODUCTION
'For a vibrating or moving system, the energy demands should be bal-anced'as well as the static and dynamic forces' acting on the system.- Dif-ferent forms of energy must be considered:
kinetic energy from the ground motion, strain energy stored in the system, energy dissipation through friction and damage and. energy feedback from the structure to the soil.
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At peak demands,' feed-in kinetic energy less energy feedback must equal the strain energy plus energy dissipation in damage done (1,2).
The strain energy through the elastic response-is a very small part of the total
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energy (capacity) and energy balance mostly relies on energy dissipation' through inelastic response.
This technique which assumes that the maximum'
- energy attained in an elasto-plastic system is equal to the maximum elas-tic energy attained as if the system was perfectly elastic is called the
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~ energy balance or reserve energy technique.
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The energy balance technique has been successfully applied to ductile materials that possess elasto-plastic load-deflection characteristics.
In order to allow for deterioration or softening of the resistance under re-peated cycles beyond the yield, a hump deterioration factor is introduced (1) which varies from one system to the other.
The technique has been used I-in the analysis of reinforced concrete members under seismic loading pro-v,ided that a ductile behavior is maintained.
This requires precluding any.
Pro-type of brittle failure such as ' shear compression and siip failures.
viding adequate web reinforcement and confining steel with proper detail-ing, a reinforced concrete member could behave in a ductile manner ender cyclic loading (3).
The applicability of the energy balance technique to reinforced masonry structures is discussed below.
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j' INELASTIC BEHAVIOR OF REINFORCED MASONRY WALLS l
Masonry is a brittle material having limited deformational capability.
The mortar joints are the weak links in the system and because of deforma-tion incompatibility between the mortar and the masonry units, splitting failure through the units and/or debonding failure at the interfaces are expected (4).
Providing reinforcement in masonry walls significantly con-tributes in producing desirable inelastic performance.
Extensive test _ing programs have been conducted by Wil.liams (5) and Scrivener (6,7) in New Zealand to study the behavior of masonry shear i
walls under cyclic static in-plane loading.
These investigators have found i
that, if the flexural reinforcing is provided at the wall ends, the bear-ing load is kept low, and the aspect ratio is high, masonry walls behave I
in a most ductile manner.
The limitation on the aspect ratio is essential to prevent brittle shear failure.
They also tested similar walls under dy-namic loading in which severe stiffness degradation and' load deterioration
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was evident.
In these tests, compression failure at the toe of the walls
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occurred which caused accele rated deterioration and unstable action.
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"Thus, although the static tests have shown encouraging results with re-1-
gard to the attainment of ductility, until the structural deterioration revealed in dynamic testais prevented, it is suggested that for seismic
..,.. g design using reinforced masonry the working stress approach should be re-tained" (5).
, Priestley (8,12) observed similar deterioration in his testing program
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1 of masonry walls. He used confining steel plates embedded in the lower courses of mortar joints at each end of the.vall to prevent compression failure.
These plates confine the crushing zone, thus eliminating vertical t
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tension cracks and provide restraint against buckling of,the compression steel.
With the use of these confining plates, a more stable ductile be-havior was achieved.
A more recent extensive testing program (9) has been conducted at the University of, California-Berkeley to study the dynamic behavior of rein-4 forced masonry piers under in-plane cyclic loading.
It has been sh'own that masonry walls could have inelastic capability provided that brittle 2
shear and debonding failures could be p'revented.
All the piers suffered substantial stiffness. degradation when subjected to gradually increasing J(
lateral displacement which agrees with the Scrivener (7), Williams (5),
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and Priestley (8) findings.
In their evaluation of the seismic. design f:
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. provisions for masonry in the United States, Sveinsson, et al. (10) point-ed out the inaccuracies inherent in the use of a ductility reduced elastic spectrum to represent the inelastic response of a masonry building.
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I BEHAVIOR OF MASONRY WALLS IN NUCLEAR PLANTS For safety related masonry walls, it is required that these walls withstand the seismic loading under earthquake to preserve their safety-related function.
For the walls to dissipate energy through elastic re-sponse (strain energy), high forces and stresses are created.
It is far more efficient for the wall to, dissipate energy through inelastic action and acceptable damage. A ductile stable behavior under dynamic cyclic loading is a must for the wall to have energy reserve capacity.
. Concrete masonry walls in nuclear power plants are generally not pro-vided to resist building shear or moment due to the seismic event.
The walls are designed to resist out-of-plane loading normal and/or parallel to the bed joint direction.
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Shear failure is highly unlikely for masonry walls under out-of-plane bending because of the high aspect ratio which is evident in some plants.
For this case, walls essentially behave in a flexural mode. They are, however, more susceptible to stiffness degradation and possible compress-ion failure under cyclic repeated loads.
The reinforced masonry walls used in nuclear power plants exhibit many varieties:
for example, fully grouted, partially grouted, st'acked bond, running bond, single and multiple wythes.
All the documented dynam-ic test data are only for running bond walls under in-plane loading.
Applicability of these results to the variety of masonry walls in nuclear plant structures is therefore questionable.
Partial grouting increases the degree of anisotropy of the walls and provides weak areas where fail-ure could be initiated.
Stack bond walls have less strength to resist horizontal bending because of the weak continuous mortar head. joints.
The experimental testing available (11) for out-of-plane bending of reinforced masonry walls is of a static nature where the problem of stiff-ness degradation is irrelevant.
Williams (5), as a result of his exten-sive testing program, pointed out that static tests of masonry walls can-3I not be applied to a dynamic situation.
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CONCLUSIONS AND RECOFDiENDATIONS Y,:
Based on the limited available test data, it is concluded that rein-forced masonry walls exhibit stiffness degradation and load deterioration under cyclic dynamic loading even if shear failure is precluded.
There-fore, a stable ductile response which is essential for reserve energy capacity should be demonstrated for masonry walls under dynamic load.
It is recommended that a testing program be conducted to provide data 8
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s applicable to the masonry walls in the nuclear power plants. Walls with different configurations and construction details should be tested.
hhe effect of partial grouting and stack bond pattern should be examined.
Of significant importance is the investigation of stiffness degradation and means'to prevent compression failures to achieve stable ductile response.
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REFERENCES 9
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1.
Blume,- J. A., Newmark, N.M. and Corning, L.H., Design af -Multistory Reinforced Concrete Buildings for Earthquake Motions, Portland Cement Association, Skokie, Illinois, 1961.
2.
Newmark, N.M., " Current Trends in the Seismic Analysis and Design of J
High-Rise _ Structures," Chapter 16, Earthquake-Engineering, Edited by.
R.L. Wiegel,'McGraw-Rill, 1970.
3.
MacGregor, J., "Ducpility of Structural Elements," Handbook of Con-v crete Engineering, thrk Fintel, Ed., Van Nostrand'Reinhold Co., 1974.
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Hamid, A., " Behavior Characteristics of Concrete Masonry," Ph.D.
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Thesis, McMaster University, Hamilton, Canada,1978.
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- Williams, D., " Seismic Behavior of Reinforced Masonry Shear Walls,"
Ph.D. Thesis, University of Canterbury, Christchurch, New Zealand, 1971.
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6.
Scrivener, J., " Face Load Tests on Reinforced Hollow Brick Non-Load-Bearing Walls," New Zealand Engineering Journal, July 1969.
7.
Scrivener, J., " Reinforced Masonry - Seismic Behavior and Design,n"'
Bulletin of New Zealand Society for Earthquake Engineering,. Vol. 5, No. 5, Dec. 1972.
- 8. :Priestley, M.'and Bridgeman, D.,_" Seismic Resistance of Brick Masonry
-i Walls,"
The New Zealand National Society for Earthquake Engineering, Vol. 7, No. 4,- 1974.
9.
Hidalgo, P., Mayes, R. and McNiven, H, ' " Cyclic _ Loading Tests of '
Masonry Single Piers Volume 3
. Height to Width Ratio of 0.5,"
Report No. UCB/EERC 79/12, College of Engineering, University.of California Berkeley, California, May 1979.
10.
Sveinsson, B. I., Mayes, R.L. and McNiven, H.D., " Evaluation of Seismic Design Provisions for Masonry in'the United States," Earth-quake Engineering Research Center, Report No. UCB/EERC-81/10,
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University of California, Berkeley, August 1981..
11.
- Amrhein, J.E., " Slender Walls Research Program by-California Struc-tural Engineers," The Masonry Society Journal, Vol.1, No. 2, July-December, 1981, pp. G9-G15.-
- 12. 'Priestley, M.J.N., " Ductility of Unconfined and Confined Concrete Masonry Shear Walls,", The Masonry Society Journal, _Vol.1, No. 2, July - December, 1981, pp. T28-T39.
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