TXX-3171, Deficiency Rept Re Use of Architectural Concrete in Floor Slabs When Determining Embedment Length of Hilti Bolts. Survey of Bolts Is Being Conducted.Bolt Installation Procedure Was Revised to Reflect Embedment Lengths
| ML19331C680 | |
| Person / Time | |
|---|---|
| Site: | Comanche Peak  |
| Issue date: | 08/08/1980 |
| From: | Gary R TEXAS UTILITIES ELECTRIC CO. (TU ELECTRIC) |
| To: | |
| References | |
| TXX-3171, NUDOCS 8008190370 | |
| Download: ML19331C680 (3) | |
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TENAS UTILITIES GENERATING COMPANY 2005 IUWAN TOWER
- DAt1AKTEXaa 78201 August 8, 1980
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TXX-3171 Mr. W. C. Seidle, Chief Reactor Construction & Engineering Support Branch U. S. Nuclear Regulatory Comission i
Office of Inspection & Enforcement 611 Ryan Plaza Dr., Suite 1000 Docket Nos. 50-445 Arlington, Texas 76012 50-446 COMANCHE PEAK STEAM ELECTRIC STATION 1982-84 2300 MW INSTALLATION USE OF ARCHITECTURAL CONCRETE IN FLOOR SLABS FILE N0:
10110
Dear Mr. Seidle:
In accordance with 10 CFR 50.55(e) we are submitting the attached report of actions taken to correct deficiencies in the design of floor slabs.
We previously made a verbal report to Mr. R. G. Taylor on July 2, 1980.
Suppwting documentation is available at the CPSES site for your inspector's review.
If we can provide any additional infonnation, please advise.
g Very truly yours, R.
. Gary Attachment RJG:dk cc: NRC Region IV (0 + 1 copy)
Director, Inspection & Enforcement (15 copies) c/o Distribution Services Branch, DDC, ADM.
V. S. Nuclear Regulatory Comission Washington, D. C.
20555 i
I 8008190S?OL
TXX-3171 Attachment August 8, 1980 USE OF ARCHITECTURAL CONCRETE IN FLOOR SLABS Descriotion of Deficiency The structural concrete drawings for Comanche Peak Steam Electric Station, as originally issued, specified the use of a 2" thick architectural topping to be placed separate from floor slabs to make easier the sloping of the finished surface to floor drains.
Due to several problems associated with the separate placement, the decision was made to delete the topping at about the time that concrete placement passed the 810'6" elevation. Structural concrete above this elevation (with a few exceptions) was placed monolithically to the finished elevation. The architectural topping utilizes 3/8" size aggregate, has a design compressive strength of 4000 psi, and utilizes welded wire fabric as a steel reinforcement. However, since the topping was not placed under the control of a quality assurance program and compressive Ltrength test cylinders were not taken in all areas that received topping, the integrity of the topping in every area with regard to compressive strength and bond between the topping and the structural slab cannot be verified. The requirement that it not be used when determining the embedment length of Hilti bolts installed in the floor was, in general, known by the architect /
engineer but the information was not available to all design groups and the presence of topping was not addressed in the Hilti bolt installation procedure CEI-20. As a result, Hilti bolts designed for floor mounted conduit cable tray, electrical equipment and pipe supports designed by one vendor may have been specified and installed 2" short of the required embedment length. The estimated number of floor mounted items that will be investigated include:
425 conduit and cable tray supports (preliminary analysis indicate none of these to be a problem), 65 instrument stands, 21 tube supports, 50 electrical panels and 125 pipe supports. The areas which have 2" topping installed are detailed on a set of drawings available for inspector review at the jobsite.
Safety Imolications Preliminary tests run in two areas having 2" topping indicate that failure of the Hilti bolt in these areas are identical to failure in structural concrete, i.e., below approximately 1-1/2" - 2" depth the failure occurs in the wedges, above this depth failure is caused by fracture of the concrete on an approximate 45 degree shear cone. This failure occurs with a factor of safety between 4 and 5 when comparing allowable working loads to ultimate failure loads. With the conditions of no documented quality of the topping compressive strength and the topping / slab interface, the design integrity could not be assured under the postulated conditions of seismic event.
TXX-3171 August 8, 1980 Corrective Action Corrective actions for the above stated deficiency include the following:
1.
All affected groups performing design functions at CPSES were notified that the 2" topping exists.
2.
Hilti bolt installation procedure CEI-20, " Installation of Hilti Drilled-In Bolts," was revised to reflect embedment lengths specified on the design drawings are defined as being into structural concrete. Additionally, specific locations where the 2" topping exists are de-tailed on drawings indicated in CEI-20.
3.
A survey of all Hilti bolts installed in areas having 2" topping is being conducted by the Civil / Structural Engineering Department. The tag number or location of the support, the bolt size, length and projection is being recorded and this information will be furnished to the various groups having responsibility for design. These groups will tvaluate each condition and will take the corrective action deemed necessary.
The action taken, whether it be confirmation of acceptability by analysis, local testing, or replacement of the existing bolts with bolts of longer embedment, will be furnished back to the Civil / Structural Department, who will ensure that all cases have been investigated and that proper documentation of the actions taken exists. The estimated completion date of this project is January 1,1981.
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