ML20215F963
| ML20215F963 | |
| Person / Time | |
|---|---|
| Site: | Fort Saint Vrain  |
| Issue date: | 05/29/1987 |
| From: | Warembourg D PUBLIC SERVICE CO. OF COLORADO |
| To: | Calvo J NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM), Office of Nuclear Reactor Regulation |
| References | |
| P-87170, TAC-55287, NUDOCS 8706230065 | |
| Download: ML20215F963 (16) | |
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{{#Wiki_filter::) i , j e h Public Service- mia_ l 2420 W. 26th Avenue, Suite 1000, Denver, Colorado 80211
'May 29, 1987 j Fort St, Vrain l Unit No. 1 I 1
P-87170 8
'l U. S. Nuclear Regulatory Commission 1 ATTN: Document Control Desk I Washington, D.C. 20555 l Attention: Mr. Jose A. Calvo Director, Project Directorate IV Docket No. 50-267
SUBJECT:
Request for Additional Information on FSV Building 10
REFERENCES:
'1) NRC Letter, Heitner to Williams,-dated ; 03/31/87,(G-87104) 2)Telecon,PSC.(Holmes)'. to NRC (Heitner)~and Brookhaven National Laboratory (Miller)'on
- 05/27/87. 1-
Dear Mr. Calvo:
As requested during the -telephone conversation .on May 27, 1987 l (Reference 2), PSC has prepared written ~ responses to the' requests for ; additional information on Fort' St. . Vrain' Building '10, posed in ' Reference 1. This.information is contained in Attachment'l- to- this letter. Supporting material for all; Building 10 structural analyses is- l available in our office for'your review. ' I
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P-87170 l 4 Page 2 May 290 1987 I If you have any questions concerning this subject, please contact Mr. M. H. Holmes at (303) 480-6960. l Very truly yours, 1 1 1 b /Y fY& 0 D.W. Warembourg, M l Nuclear Engineering Division DWW/MM:pa Attachment l l J
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1 Item 1 l 4 NRC REQUEST In the analysis of the Building 10 caissons, two foundation moduli ! values were considered. It should be demonstrated that these two I cases bound the actual condition, where a stiff layer is sandwiched f between two soft layers. Consideration should be given to both the equivalent interaction springs and dampers. . 1' PSC RESPONSE See next page. , I l l i I h
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s Response to Request 1 The modulus of subgrade reaction (K h ) is significant in determination of the horizontal soil springs and, to a lesser degree, the torsional l soil springs. The torsional spring has very'little significance in the ' overall building response due to the symmetry of the building. The peak of the response (especially for the upper floors) is' governed by the rocking springs, which are based primarily on the full length of the : caisson to bedrock. ! From Attachment 2 of Reference 2, the lengths of the equivalent cantilever and the horizontal and rocking soil spring values are: Kh=50 lb/in3 Kh = 170 lb/in 3 j Lb 17.3 ft 1.35 E + 01 ft 1 Horizontal sprinos 8.50 E + 04 k/ft 1.79 E + 05 k/ft E W Rockino 1.96 E + 08 ft k/ rad 1.9 9 E + 0 8 ft k/ rad N.S Rockino 1 1.57 E + 08 ft k/ rad 1.5 9 E + 08 ft-k/ rad Since the horizontal response is a function of both the rocking and-lateral: soil springs, the major difference in the response of the two soil , cases is due to the horizontal soil spring values since the rocking springs are nearly identical. Using the approach given in Reference 1, the equivalent cantilever bending length places the base of the equivalent cantilever a- short distance into the stiff soil layer. For the assumptions used in the . equivalent cantilever analysis, the stiffness of the soil near the surface is much more sf gnificant than that at the base. Therefore, the lateral stjffness of the system is most closely approximated by tpe Kh = 50 lb/in - case. The usage of soil springs based on Kh = 170 lb/in was included to provide an upper bound for the frequency of the system. A damping value of 7% for SSE and 4% for' OBE was used for all modes. These are much-lower than the values typically used in soil damping.which -could be in the range of 10 to 30%. The damping values used will .give a - conservative response of the system. In order to demonstrate that the two soil cases bound the layered soil-condition, the ' computer program . Dynamic Response of' Piles (PILAY2), developed under the direction of Professor M. Novak by Systems. Analysis Control and Design Activity - The University of Western .0ntario. wasi run for several conditions. This program is based on years of. studies by M. Novak and his associates. The . program. showed that the horizontal 1 stiffness of the pile group for, the layered soil condition is 11 percent - 1 higher than that for a condition based entirely on the lower soil' stiffness and is significantly less than that' based entirely on the higher soil' stiffness. This is well within the range of soils ' springs ' used.' for. the analysis, and shows that the response of the layered soil system will be .very close to that based on the lower soil' spring . values.1
<L Response to Request 1 (cont...) Reference 1 - Design ~of Machine Foundations on Piles, Journal of the Geotechnical Engineering Division, J. P. Singh, N. C. Donovan, A. C. Jobsis, August 1977, pages 863-877
- Reference 2 - PSC Letter Warembourg to Berkow (P-86489) dated-July 28,.
1986. Reference 3.- Systems Analysis Control and Design Activity (SACDA), User Manual, PILAY2, A' Computer Program for. Calculation. of Stiffness and Damping of Piles in Layered Media, the. University of Western Ontario, London, Ontario, Canada', January, 1981.
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l Item 2 NRC REQUEST ! The rocking interaction parameters were developed based on the l assumption that the foundation is rigid in flexure relative to the axial stiffness of the caisson. Provide information so that the ; validity of this assumption may be reviewed. PSC RESPONSE The foundation is stiffened by the vertical walls of the building. This gives a moment of inertia of the wall system of two to four { times that of the caisson stiffness. This relative stiffness was sufficient to utilize the standard practice of ~ assuming the- i foundation was rigid for the calculation of the rocking soils springs. ; 1 l i l i I I
q 1 Item 3~ ~l NRC REQUEST The seismic input ground motion used .for : Building 10 and the turbine building are different. Information describing and justifying the-use of two different inputs should be provided. )1 i PSC' RESPONSE ] Design for seismic loading conditions on_ both Building 10 and Walkover-
' Structures are accomplished by the response spectrum '(modal superposition) method, using. . appropriate response spectra curves dictated by application of Regulatory Guides 1.60 (Rev. 1, 12/73) g and 1.61 (10/73). . Curves from _ Reg. Guide 1.60 are scaled to .0.05g .i (0BE) . and 0.10g (DBE) maximum horizontal ground acceleration to be-used in structural design - for Fort St. Vrain, as specified .in FSV.-
FSAR Section 14.1.1. Both the horizontal and vertica1L component design response spectra for Building 10 and the Walkover Structure a.re derived in this manner. The FSAR; horizontal component design response spectra for 0,10g maximum
. horizontal ground acceleration are' shown in Fig. 14.1-l' of the' FSAR '
-(see attached). This is the input ground motion used _in design .of the' Turbine Building. The vertical . component is taken _as 2/3 of the horizontal (FSAR 14.1.1-1). Data for a 0.05g earthquake' is obtained i by multiplying the.0.10g accelerations by 1/2.
l Building.10 is 'a reinforced concrete structure; the Walkover Structure ~ 1 and Turbine _ Building are cross-braced bolted steel' structures. Assumed _~ damping factors-from Reg. Guide 1.61 are used in the design'of Building 10 and the Walkover Structure. . .The Reg.' Guide 1.61 '. damping values-for reinforced concrete and bolted steel structures. differ. from those outlined in FSAR Table 14.1-2, used - in the design of the o Turbine ? Building. A tabulation of these values is shown in Table 1 (in terms of percent of critical damping).. Because the design inputs -for .Buil' ingd 10 .and the. Walkover 1 Structure ' are different than FSAR seismic criteria (in terms.' of ; curve.. shape; and permissible. damping factors), a graphical comparison of appropriate - design curves was generated. Comparing Reg. Guide 1 60 0.05g earthquake horizontal component at 5% damping to FSAR 0.05g earthquake horizontal component at 2% damping (Fig.1). addresses OBE case for both structure. types. . Reg. Guide -1.60 data at 5%.was _used since the 4% curve requires interpolation ' between Reg. Guide ' information for- 5% ~.and 2%: damping (both . directly . available), and.; the 4%' curve lwould be abovef the' 5% curve. .Likewise, a plot of Reg. Guide 1.60' O.10g earthquake horizontal-
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component . spectrum at 7% damping versus FSAR 0.10g earthquake ~ horizontal component . spectrum at 5% damping (Fig. 2)Laddresses DBE: (SSE) case fori reinforced : concrete directly and _ bolted steel indirectly, since. FSAR
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curve.at 5% envelopes the'FSAR curve at 10%. CONCLUSION Response spectra curves for horizontal' component -from . Reg. Guide L1.60 envelope their FSAR counterparts, with appropriate. damping -values a
3 1 ( 2 taken into account, as shown in Figs. 1 and 2. These comparisons j adequately encompass the vertical component spectra also, because ) ratio of vertical to horizontal components is a constant 2/3 for FSAR requirements, and varies between 2/3 and 1 for Reg. Guide 1.60 l Guidelines. Therefore, seismic design response spectra input for j Building 10 and the Walkover Structure can conservatively be used 1 to fulfill seismic design criteria specified in Fort St. Vrain's FSAR. j a a I a 1 T I
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1 w - i e. H Item 4 NRC REQUEST f The license's submittal includes spectra labeled " Isolated" and~
"Cou pl ed . " It is not clear whether the " coupled" spectra are the spectra of the Turbine Building basemat motion,'or spectra of the -l response of Building 10 to an input motion due _to the Turbine- l
' Building basemat motion. If the first is the' case, then 3 information should be provided demonstrating that this solution- l bounds' the structure / soil / structure interaction situation. If the 1 latter is true, information describing the model'used and the input. j motion should be provided.. J q
PSC RESPONSE i a The " coupled" spectra referenced in PSC's submittal (Attachment 3 )j to PSC Letter P-86489, dated July 28,1986) represent the' response ' spectra of the Turbine / Reactor Building grade slab at the given. damping values. As stated in the Attachment 3 report (Sargent & i Lundy Report No. 481)', this . spectra also represents the grade : elevation motion of Building 10 resulting from the structure-soil- { structure interaction effects. The occurrence of this phenomenon is discussed in detail in the j above referenced report. In summary, this report demonstrates the j following: J
- 1. Because Building 10 is very close to and its' size and mass are-very small compared to the Turbine / Reactor Building,- th.e ;
Turbine / Reactor Building will drive the~ grade slab. (elevation 4791 feet) of Building 10 by the same horizontal motion:as:the i motion of its own grade slab. ;
- 2. In the vertical direction, the structure-soil-structure .
interaction will have an insignificant effect on Building 10. l
- 3. The presence of Building 10 will not- affect the seismic j response of the Turbine / Reactor Building. 1 The seismic response spectra at the grade slab for which Building' 10 was designed envelopes the' grade slab response _ spectra _ resulting from structure-soil-structure interation (i.e. the Turbine / Reactor- o
. Building grade . slab spectra) at all frequencies ~of- concern.
Therefore,_the_ design. of Building 10, which uses a' conservative , Reg.' Guide 1.60 input motion, bounds the structure-soil-structure lj interaction situation. .y a
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1 Item 5 NRC REQUEST The basis for the displacements of the Turbine Building and Building 10 , used to determine the relative. building displacements should be l provided. , l I PSC RESPONSE The Turbine-Reactor Building Seismic Analysis models the structure l as a three-dimensional slab-spring system. A dynamic modal. analysis l was performed on this building, using the computer program DSASS l (Ref. 1). This program calculated the maximum building displacements which were supplied to the NRC in Attachment 4 to Ref. 2. As stated in PSC's response to Request #3, contained in this letter, the seismic input motion used in the Turbine-Reactor Building design is taken from the response spectra shown on FSV FSAR Figure 14.1-1. Building 10 was analyzed using a lumped mass model as outlined in Attachment 1 of Ref. 2. A dynamic' modal analysis was performed, and seismic displacements calculated, using the STRUDL II computer program (Ref. 3) and the results verified by use of Ref. 4. As stated in PSC's Response to Request #3, the seismic input motion used in the design of Building 10 was derived from the response spectra curves of Regulatory Guide 1.60 scaled to 0.05g (0BE) and 0.10g (DBE). The Walkover Structure is a fixed base, cantilever truss building- a system, and is modeled accordingly in the dynamic modal analysis which ! was performed using the P-DELTA STRUDL computer program (Ref. 5). The seismic input motion used for this analysis is the'same as that used for Building 10. Please note that the maximum walkover displacement listed in Attachment 4 of Ref. 2 is in error. The actual peak east-west ; displacement resulting from DBE input ground motion is 0.858 inches, l not 0.6 inches as reported previously. This discrepancy results from I an error in the original computer analysis of the Walkover Structure l which incorrectly calculated the lumped mass terms representing non { structural attachments, such as building siding and bullet-proof steel. { The structure was reanalyzed using correct mass terms, resulting in the peak displacement of 0.858 inches. This error did not have a . detrimental impact on the results of the structural analysis of the building, and therefore the Walkover Structure is adequate to resist , the design basis loading, as previously concluded. A summary of peak east-west displacements, resulting from DBE loading, is shown below: Turbine Building 0.096" Buildir- 10 0.210" Walkover structure 0.858" From the above figures, the maximum probable differential displacement
i 2 > between two adjacent structures is as follows: I
- 1. Between Turbine-Reactor Buf1 ding and Wal kover Structure -
o = 0.096" + 0.858" = 0.954"
- 2. Between Walkover Structure and Building 10 -
A = 0.858" + 0.210" = 1.068" The aforementioned displacements do not present a problem with adjacent structures impacting during a seismic event, since the 2-inch clearance _ provided between structures is greater than the maximum displacements. The computed maximum relative displacements occur at the Walkover , Structure roof and are less than 1.068 inches at lower elevations. The large difference in computed displacements . between the Turbine Building and Walkover Structure / Building 10 can be best explained by the following factors:
- 1. The input ground motion used in the Building 10 and Walkover Situcture seismic analyses envelopes that used in the Turbine Bui.1 ding analysis. This fact results in a more conservative analysis and thus greater dynamic response of these two structures.
- 2. The geometry of the structures vary appreciably. The Wal kover Structure is an extremely tall, narrow building relative to the Turbine Building and thus would be expected to have a greater l response to seismic input motion. Likewise, Building 10 _is very f
tall and narrow in comparison to the Turbine Building and would j also be expected to have a greater response.
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{ References
- 1) "DSASS - Dynamic Seismic Analysis of Shear Structures", by M. Amin and S. L. Chu, Analytical & Computer Division, Sargent and Lundy Engineers, Feb., 1967. 1
- 2) PSC Letter Warembourg to Berkow (P-86489) dated July 28, 1986.
- 3) STRUDL-II, Version -10 Level-06.
- 4) GT-STRUDL-BCS, Version-2, level-04.
- 5) P-Delta STRUDL, Version 1086.}}