ML20207E597
| ML20207E597 | |
| Person / Time | |
|---|---|
| Issue date: | 08/01/1988 |
| From: | Bagchi G Office of Nuclear Reactor Regulation |
| To: | Shao L Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8808180101 | |
| Download: ML20207E597 (6) | |
Text
T AUG 01 tggg MEMORANDUM FOR:
Lawrence C. Shao, Director Division of Engineering and Systems Technology, NRR THRU:
James E. Richardson, Assistant Director for Engineering Division of Engineering and Systems Technology, NRR FROM:
Goutam Bagchi, Chief Structural and Geosciences Branch Division of Engineering and Systems Technology, NRR
SUBJECT:
MEETING WITH SQUG/SSRAP ON ANCHOR BOLT ISSUES DATE AND TIME:
August 25, 1988, 9:00 a.m - 4:30 p.m LOCATION:
One White Flint North, 11555, Rockville Pike, Rockville, Md. Room 2F17 PURPOSE:
To discuss data and staff concerns on Anchor Bolts issues PARTICIPANTS:
NRC SQUG/SSRAP/NUMARC 1
G. Bagchi N. Smith, et. al D. Jeng R. P. Kennedy J. Ma L. A. Wyllie, Jr.
R. Lipinski P. Schiff H. Ashar M. Czarnecki P. T. Kuo A. Marion P. Y. Chen R. Schaffstall T. Y. Cheng N. Anderson 9! 01::
1 01 si ::cHT C
Goutam Baschi, Chief Structural and Geosciences Branch Division of Engineering and System Technology
Enclosures:
1.
Agenda for SQUG/SSRAP Mtg. on Anchor Bolt Issues 2.
Embeded Anchor Issues cc:
J. Sniezek Dfd b
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AGENDA FOR 8/25/88 ESGB/SQUG/SSRAP i
Meeting on Anchor Bolt Issues G. Bagchi 1.
Purpose 2.
SQUG/SSRAP SQUG/SSRAP assessment of i
expansion anchor edge distance issue and bases for conclusions 3.
ESGB technical concerns on anchor bolt issues G. Bagchi/D.Jeng J. Ma 4
4.
Action Items and Schedules for resolution r
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EMBEDDED ANCHOR ISSUES (CAST-IN BOLTS, WELDED HEADED STUDS, AND EXPANSION ANCHORS) 1.
FORTY TWO PERCENT (42%) TENSILE STRENGTH REDUCTION IN 1985 PCI DESIGN HANDBOOK OVER ITS 1978 EDITION.
(References 1and2)
This implies that anchors designed in accordance with 1978 PCI Design Handbook may be under strength.
2.
TEST DATA SHOWING 30' CONCRETE FAILURE CONES VS. 45' CONE CONCEPT USED IN U.S. METHODS (Reference 3 and 4)
This indicatos that U.S. methods that employ the 45' cone concept, such as ACI-349 code and PCI Design Handbook, may overestimate the bolt tensile strength for spacing and edge distance effects.
Based on the 30' cone concept and test results specifically designed for the effect of anchor spacings and of anchor edge distances, Reference 3 and 4 have proposed the following:
a.
Anchor Spacing Effect a.1.
For an anchorage that consists of two anchors, each anchor can assume to develop its 100% tensile strength when the anchors are being the embedment spaced equal to or greater than 3.51, with 1 d
d length of the anchor, and to develop only 50% of tensile strength whentheanchorsarelocatedadjacenttoeachother(Zerospacing) and a linear relationship between the strength and spacing of the anchor can be assumed between the two limiting values, a.2.
For an anchorage that consists of four anchors and are spaced in a square shape, each anchor can assume to develop its 100% tensile strength when the anchors are spaced equal to or greater than 3.5 ld and to develop only 25% of tensile strength when the anchors are bundled together (zero spacing) and a linear relationship between the strength and spacing of the anchor can be assumed between the two limiting values.
b.
Edae Distance Effect An anchor can assume to develop its 100% tensile strength when the anchor is located away from the free concrete edge at a distance and to develop zero tensile strength equal to or greater than 1.75 la when the anchor is located at tne free edge. A linear relationship between the tensile strength and edge distance effect can be assumed between the two limiting values.
4 Y
3.
TEST DATA HAVE g !CATED THAT THE T5NS!LE STRENGTH OF ANCHORS IS A 2
FUNCTION OF L INSTEAD OF L
, WHICH HAS BEEN ASSUMED IN U.S METHODS (E BEING THE EMBEDSENT LENGTH OF AN ANCHOR).
(References 3 D
and4).
This indicates that'ut spacing and edge distance effects.U. S. methods may overestim of bolts even witho 4.
LOW-CYCLE FATIGUE TEST DATA HAVE INDICATED SIGNIFICANT REDUCTION IN STRENGTH AND STIFFNESS OF ASTM A307 BOLTS COMPARING WITH THEIR STATIC STRENGTH AND STIFFNESS.
(Reference 5).
This implies that low-cycle fatigue phenomenon needs to be considered for bolts that are sJbjected to earthquake loadings.
5.
VARIABILITY OF PRELOAD LEVEL RANGING UP TO 6001 FOR BOTH TORQUE AND TURN-OF-THE-NUT METHODS.
(Reference 6).
THE LOSS OF PRELOAD WITH THE PASSING OF TIME.
(Reference 7).
This implies that preload in steel supports that anchored to concrete structures is substantially lost after some time and cannot be assessed with a reasonable precision. Some preload has a great influence on the stiffness of a support and the stiffness of a support may be important in the analysis of equipment, piping, and cable tray systems, a program may be needed either to verify the stiffness of supports that are important or to develop a rationale for acceptability of reduced support stiffness for 9
piping, cable trays, and equipment.
6.
ALLOWABLE LOAD LEVEL (FACTOR OF SAFETY) FOR EXPANSION ANCHORS Expansion anchor bolts have been used to transmit loads from equipment, piping, cable trays, etc., to concrete structures in nuclear power plants. Although expansion anchor bolts may experience cyclic or vibrating loading from equipment, piping, and cable trays during normal operation and will be subjected to cyclic loading during earthquake, expansion anchor bolts are usually designed for static loadings.
Expansion anchor bolt manufacturers have recommended the allowable (design)loadsoftheirboltstobeone-fourth (1/4)andone-fifth(1/5) of the average ultimate load of test values for wedge and shell types of anchor, respectively. The test values were obtained from laboratory specimens loaded with static and short term forces to individual anchors embedded in uncracked concrete. Therefore, the factor of 1/4 or 1/5 is not only intended to cover the large scattering phenomenon of expansion anchor bolt test data in the laboratory, but also to make allowances for any differences from laboratory testing conditions, as stated in Hilti anchoring manual (Reference 8).
3-In response to questions raised by the NRC staff regarding the allowable load level associated with Hilti Kwik-Bolts (wedge type of anchor) in a recent meeting between NRC and Hilti, Inc., Hilti indicated that the allowable load should be 1/4 of the ultimate test load (Reference 9).
The factor of 1/4 or 1/5 must be used in conjunction with a special inspection progran for bolt installation because proper installation is very critical to the perfomance and capacity of expansion anchor bolts.
For example, Uniform Building Code (Reference 10) pemits only a factor of 1/8 to be used for bolt tensile allowables with no special inspection. The NRC has also required the factor of 1/4 for wedge type of anchors and 1/5 for shell type of anchors with inspection in IE Bulletin 79-02:
"Pipe Support Base Plate Designs Using Concrete Expansion Anchor Bolts."
Reference 3 and 4 have reported that the Geman code takes a probabilistic approach to establish the allowable load for anchors.
Although the factor for allowable loads in the German approach will vary according to the statistical variations of test data, References 3 and 4 have shown that the factors derived from practical consideration are very close to 1/4.
Recent test results at Comanche Peak Steam Electric Station reveal that the tensile capacity of 3/4" diameter Hilit Kwik-Bolts with 9" embedment has only 53% (with masonry bit) and 37% (with diamond coredrill extraction bit) of the tensile capacity published by Hilti, Inc. in 1987, and that the tensile capacity of 3/4" diameter Hilti Kwik-Bolts with 8" embedment has only 67%
(with masonry bit) and 52% (with diamond cordrill extraction bit) of the tensile capacity published by Hilti, Inc. in 1987 (Reference 11). The staff has discussed the test data with Hilti technical staff.
Hilti has acknowledged that its staff was present during the tests and believed that the tests appeared to have been conducted properly. The reason for this significant strength reduction has not been found and Hilti is still investigating this matter. The amount of strength reduction in these tests is even greater than those at Susquehana Steam Electric Station, which led to NRC IE INFORMATION NOTICE NO. 86-94:
"Hilti Concrete Expansion Anchor Bolts."
Based on the above discussion, it appears that the NRC position regarding the allowable load level (factor of safety) stated in IE Bulletin 79-02 is still adequate, and any deviation from that should be reviewed on a case-by-case basis.
REFERENCES 1.
PCI Design Handbook - Precast and Prestressed Concrete, 3rd edition, Prestressed Concrete Institute, Chicago, Illinois, 1985.
2.
PCI Design Handbook - Precast and Prestressed Concrete. 2nd edition, Prestressed Concre,te Institute, Chicago, Illinois, 1978.
3.
Bode, H. and Roik, K., "Headed Studs - (mbeded in Concrete and Loaded in Tension." ACI SP-103-4 "Anchorage to Concrete." American Concrete Institute Detroit, 1987.
4 Eligehausen, R., "Anchorage to Concrete by Metallic Expansion Anchors."
ACI SP-103-10" "Anchorage to Concrete." American Concrete Institute.
Detroit, 1987.
5.
Klingner, R. E., Mendonca, J. A., and Malik, J.
B., "Effect of Reinforcing Details on the Shear Resistance of Anchor Bolts Under Reversed Cyclic loading," ACI Journal Proceedings V. 79 No.1, January -
February 1982.
6.
Schwarz, F. "Wedge - Type Expansion Anchor Perfomance in Tension." ACI SP-103-5 "Anchorage to Concrete." American Concrete Institute, Detroit, 1987.
7.
Burdett, E. Perry, T., and Funk, R., "Load Relaxation Tests." ACI Sp-103-15 "Anchorage to Concrete." American Concrete Institute. Detroit, 1987.
P 8.
"Hilti Anchoring Manual". Hitti Inc. 1985.
9.
"Meeting Between NRC and Hilti Inc "J. Guillen NRC to C. Rossi, NRC, May 6, 1988.
10.
"Research Report Report No. 2156 Nov.,1978 of Unifom Building Code" by International Conference of Building Officials, 5360 South Workman Mill Road, Whittier California, 90601, 11.
"Sumary of Audit th July 13, 1988 - Test Results for Concrete Anchorages" for Ccu r.che Peak Steam Electric Station, Units 1 and 2.
D.Terao,NRC, jug 15, 1988.
.