ML20041E295
| ML20041E295 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 03/03/1982 |
| From: | GEORGIA POWER CO. |
| To: | |
| Shared Package | |
| ML20011B385 | List: |
| References | |
| NUDOCS 8203100338 | |
| Download: ML20041E295 (43) | |
Text
C'1 V
REPORT ON CABLE TRAY SUPPORT SYSTEM DAMPING VALUES O
VOGTLE ELECTRIC GENERATING PLANT MARCH 3, 1982 82O3100338 820305 1
A
TABLE OF CONTENTS i
PAGE
1.0 INTRODUCTION
1 2.0 VEGP DESIGN DAMPING CURVE.
2 3.0 USE OF VEGP DESIGN DAMPING CURVE.
5 4.0 RESPONSES TO TECHNICAL ISSUES RAISED BY THE NRC.
7 5.0 DESIGN STATUS 22 6.0 RESPONSE TO ADDITIONAL CLARIFICATIONS ON CABLE TRAY SUPPORT SYSTEM DAMPING REQUESTED BY THE NRC ON JANUARY 28, 1982.
27 LIST OF APPENDICES APPENDIX a PROPRIETARY SAMPLE CALCULATIONS APPENDIX b PROPRIETARY TEST DAMPING CURVES APPENDIX c ADDITIONAL MATERIAL PRESENTED IN THE FEBRUARY 3, 1982 MEETING WITH THE NRC APPENDIX d TYPICAL VEGP SUPPORT DRAWINGS O
LIST OF FIGURES PAGE FIGURE 1 TYPICAL CANTILEVERED TRAY SUPPORT.
33-34 FIGURE 2 TYPICAL TRAPEZE TYPE TRAY SUPPORT.
35 FIGURE 3 TEST SETUP FOR RIGIDLY SUPPORTED TRAYS 36 FIGURE 4 DAMPING VS. INPUT LEVEL FOR BRACED HANGER SYSTEMS 37 FIGURE 5 DAMPING VS. INPUT LEVEL FOR RIGIDLY SUPPORTED CABLE TRAYS - EARTHQUAKE TYPE MOTION.
38 FIGURE 6 VEGP DESIGN DAMPING CURVE.
39 FIGURE 7 SCHEMATIC RELATIONSHIP OF SUPPORT SYSTEM FREQUENCIES TO DAMPING.
40 0
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l.0 INTRODUCTION O
On December 9, 1981, Georgia Power Company and Bechtel Power Corporation contacted the NRC by conference call to advise them of the use of a 20% damping factor for both the Operating Basis Earthquake (OBE) and the Safe Shutdown Earthquake (SSE) in the design of cable tray supports, in lieu of the PSAR commitment (for welded structures) of 2% damping for OBE and 4% damping for SSE.
The NRC raised certain issues and requested GPC to provide a response to those issues in a timely manner.
Pending review of the GPC responses to the NRC, the applicant agreed to proceed with design at their own risk with a damping value no greater O
(,j than 15% for both OBE and SSE.
It should be noted that all subsequent mention to damping of 15% or 20% applies for both the OBE and SSE conditions.
The detailed response provided in the following sections addresses the justification for using 15% damping, although 20% damping had been used in the reanalysis prior to the discussion with the NRC on December 9, 1981.
The 20% damping used was based on and supported by the test results of the Cable Tray and Conduit Raceway Seismic Test Program.I1)
In accordance with our agree-ment to not exceed 15% damping, a review of the calculations was 1.
Reference:
" Cable Tray and Conduit Raceway Seismic Test P-Program - Release 4 (Final)," Test Report (g)
- 1053-21.1-4, December 15, 1978, ANCO Ligineers, Inc.
1
conducted and it was concluded that, due to the design margins provided in the support design, the reduction from a 20% to a 15%
damping value can be accommodated, without impacting the support drawings that have already been issued for construction.
VEGP is currently proceeding with design using 15% damping.
2.0 VEGP DESIGN DAMPING CURVE The VEGP design damping curve is shown in Figure 6.
The basis for the VEGP design damping curve used in the design of the cable trays and their support systems is the Bechtel sponsored " Cable Tray and Conduit Raceway Test Program."
The evaluation of the test data obtained from the test program resulted
()
in the conclusion that for VEGP cantilevered tube steel supports (Figure 1) the VEGP design damping curve can be conservatively used.
During the test program some 2000 dynamic tests were performed on several hundred varied cable tray and conduit support systems.
The effects of numerous parameters, including support stiffness ranging from rigid to flexible, which could influence the system dynamics were investigated.
Also, several different types of tray and supports were tested.
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The testing of cable tray systems clearly demonstrated that a r"'i b
significant portion of the system damping was the result of the amount of energy absorbed between the adjacent moving cables and through friction between cables and the cable tray and that the contribution of tray and tray support to the system damping was insignificant.
It should be noted that while the specific VEGP type (P-W Industries, punched and solid bottom trough) trays and t.ny supports were not among those tested, for reasons stated above, the conclusion that system damping is not significantly affected by the tray type or the tray support types remains valid.
Among the many test cases considered, to evaluate the influence
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(,T) of support stiffness on the tray system damping, the test program included trapeze type supports (Figure 2) in the flexible range and at the high frequency end, rigid supports, wherein the trays were directly supported from the shake table (Figure 3).
The stiffnesses of the VEGP cable tray support systems fall within the range of stiffnesses of the flexible support systems (trapeze type support) ard the higher bound range of stiffnesses of the rigid support systems.
The frequency ranges for these support systens under fully loaded conditions are as follows.
Specifically, the flexible type supports tested had a range of system fundamental frequencies in the transverse, vertical and longitudinal directions O
3
of 2-6 cycles per second (cps).
The rigid type supports tested had
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a range of 9-25 cps.
The VEGP support system fundamental frequencies vary from a low end of about 3 cps and approaches those of the rigid type supports at the high end.
Although the type of tray and tray supports used in VEGP have not been specifically tested, it is to be noted that their influence on the ability of adjacent cables to absorb energy through moving against each other and through friction between the cables and the cable tray is through their effect on the cable tray support system stiffness.
Since the VEGP tray support system stiffr, esses are within the range of the tested tray support system stiff-nesses, the test program results demonstrating the use of a higher damping value can be directly used to form the VEGP design (G,/
basis.
Figure 4 shows the test data collected for the trapeze type supports.
The curve shown forms essentially a lower bound of the data points.
Figure 5 presents the data collected for rigid type supports using earthquake type motions.
Also shown therein are the "Least Squared Errors Best Fit Curve" and "15% non-exceedance Probability Curve."
Figure 6 shows the VEGP Design Damping Curve.
To form a conservative design basis for VEGP, the VEGP damping curve has been selected such that it falls below the curves shown in Figures 4 and 5, and for all practical purposes below all the data pointe shown in Figures 4 and 5.
4
3.0 USE OF VEGP DESIGN DAMPING CURVE O
As shown in Figure 6, the VEGP design damping curve is dependent only on:
1) the amount of cable in the trays and 2) the floor design acceleration (input floor response spectrum ZPA), and therefore is applicable to both the OBE and SSE design conditions.
For the 50% to fully loaded condition, the damping values range from 5% to 15% depending on the input floor acceleration level.
For empty trays, damping values of 2% for OBE and 4% for SSE, t
consistent with U.S. N.R.C. Regulatory Guide 1.61, are applicable.
For partial loading less than 50% loading, linear interpolation is to be used to arrive at the applicable damping values.
To use the maximum value of 15% damping, the floor design acceleration must have at least a ZPA value of 0.30g and the tray must be at least 50% full by weight of cable.
However, for a conservative design, 100% full by weight of cable and the damping value associated with the appropriate input floor spectrum ZPA is used as a standard design practice.
Calculations have shown tnat the design of supports using 100% loaded tray with D
5
the applicable design damping value for this load condition pro-('
duces higher stress levels and hence governs the design over partially loaded trays with applicable lower damping values.
When conditions warrant, i.e., design or construction constraints, the design will be done considering the actual cable weight and appropriate damping values rather than designing for the 100%
loaded condition.
It sho'uld be noted that 100% full by weight of cables is equivalent to 40% tray fill by area of cross section of the tray for control and instrumentation circuits and 30% tray fill by area of cross section of the tray for power circuits.
This is consistent with our PSAR commitment.
O It is also to be noted that in the VEGP design, both OBE and SSE loadings with their associated stress criteria are used.
6
4.0 RESPONSES TO TECHNICAL ISSUES RAISED BY THE NRC O
QUESTION 1:
Provide a discussion on how major cable tray test results were used in arriving at the 15 percent modal damping for VEGP.
The discussion should assure consistency of observed data and calculations used.
RESPONSE
In a linear dynamic analysis, velocity dependent forces (i.e.
viscous damping) are introduced to account for various mechanisms of energy dissipation.
These mechanisms include such things as:
friction and slip in bolted connections, hysterisis, radiation of energy away from a foundation, the effects of fluids, and no doubt other mechanisms as well.
Since these various mechanisms cannot be accounted for explicity in a linear analysis, their effect is lumped in a single viscous damping.
Dynamic testing is used to determine an effective viscous damping, appropriate for seismic response.
This procedure is common to all structural dynamic analysis.
l During the cable tray and conduit raceway test program the random vibration of cables was identified as the most significant energy dissipating mechanism.
This occurred because the cables 7
represent most of the mass of the system, are able to move relative to each other, and were not rigidly attached to the supporting tray.
During the tests, this phenomenon manifested itself as a noticeable relative movement and impact of the cables within the tray.
As is the case with other energy dissipating mechanisms, this effect is quantified in terms of an equivalent viscous damping based upon the relationship between the recorded response and the applied input to each test specimen.
The test report entitled " Cable Tray and Conduit Raceway Seismic Test Program" provides a detailed discussion of the methods used to compute an equivalent viscous damping from the recorded results of the dynamic tests.
This discussion can be found in section 5 of the test report with supplementary information in appendices G, H, and I.
O The computed damping values from the various tests are tabulated in appendix K of the test report.
Data was taken from these tables and plotted as shown in Figure 4.
On this figure the data points of computed equivalent viscous damping are plotted as a function of input acceleration (floor spectrum ZPA) for over 100 tests of various braced strut hanger tray systems.
These results represent all the data from simulated earthquake inputs.
Low level sinusoidal and snap back test data are not included since they are not directly applicable.
Since these tests represented a wide variety of tray type, connection details, struts, and cable configuration there is a broad scatter in the OV 8
data.
These data, however, do clearly show that the recorded responses of the tested tray systems is best described by a dynamic system with an equivalent viscous damping.
It should be noted that the data realistically can be utilized with accepted curve fitting techniques to obtain a "best-fit" curve which reflects the statistical average of the test data.
Such an approach would result in a maximum damping value far in excess of a conservative 20% value.
However, in the interest of conser-vatism, a bilinear curve, which effectively bounds the lower end of nearly all the points, was utilized.
This curve is given in Figure 4.
Similarly, the computed damping values from the various tests performed on the rigid type supports using earthquake type input
()
motions are plotted as a function of the input ZPA and is provided in Figure S.
Also shown therein are the "Least Squared Errors Best Fit Curve" and"15% Non-exceedance Probability Curve."
In addition to the determination of equivalent viscous damping, I
as described in the test report, for braced hanger systems (trapeze type supports) linear analysis was performed on finite element models of several of the tray system test setups.
These analyses confirmed that a very high viscous damping was required in order I
l to predict responses similar to those recorded during the dynamic testing. These analyses confirmed that the application of the damping values recommended for design in a linear analysis was O
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consistent with the results of the test program and therefore l
would result in a conservative design of support systems.
As stated previously in Section 2.0, the VEGP design damping curve (Figure 6) falls below both the curves shown in Figure 4 and Figure 5, with the highest value being 15%.
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QUESTION 2:
C Why was cable tray test input loading applied at a 45* angle instead of simultaneous horizontal and vertical load input?
What are the implications of this testing method upon the validity of the recommended 15% damping for VEGP (e.g. with respect to statistical independency requir.ements of different directional inputs)?
4
RESPONSE
The cable tray and conduit raceway test input loading was applied at 45* (vector biar.ial) because the shake table used was limited to vector biaxial motion.
In choosing the 45 relationship (i.e. horizontal equals vertical) the floor response spectra of many Containment and Auxiliary buildings were reviewed and this equality of horizontal and vertical motion was deemed most appropriate.
IEEE-344 and NRC regulatory guides recommend, but do not require, independent biaxial input.
In the case of raceways, the modes of vibration are symmetrical and are dominantly either horizontal or vertical, and therefore would be adequately excited by vector biaxial motion.
As the different modes of a given raceway gener-ally have quite distinct resonant frequencies, there is no problem introduced by the zero phase between horizontal and vertical loading bu 11 1
(i.e. vertical and horizontal responses will be randomly varying
()
in and out of phese even though the vertical and horizontal inputs are in phase).
Independent biaxial input is preferred in non-symmetrical cases and in the possible but unusual case of testing a structure with a mode whose axis of sensitivity would be at 90' to the vector biaxial input, and hence not excited.
The raceways are simple structural systems with distinct vertical, transverse, and longitudinal modes.
This was confirmed during testing.
Therefore, the test results are not affected by the use of vector biaxial input.
As described above, widely spaced modes of vibration with little cross coupling were observed during the testing.
Specifically, for the trapeze type supports, longitudinal swaying modes were b
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quite low (2 Hz), transverse modes followed (3 Hz), with tray modes following at 6 and 15 Hz for a typical 4'6" single tier unbraced raceway.
This data is illustrated in Figures 7.8 and 7.13 of Volume 1 for a 100% cable loaded raceway of 0.10g peak response.
Similar frequency ratios for raceways with longer struts are illustrated in relevant data.
Due to the reasons stated above, test results obtained from input i
loading applied at a 45' angle can be used as the basis for VEGP I
design damping curve.
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QUESTION 3:
O Will sprayed-on fireproofing affect cable friction and thus the damping ratios used in VEGP design?
RESPONSE
Yes.
The present VEGP position, however, is that sprayed-on fireproofing will not be used.
Exception to this position will be handled on a case-by-case basis.
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QUESTION 4:
L The cable tray test conditions do not reflect the actual physical site situation.
Provide the rationale for extending the test results to the actual VEGP design which is different from the test configuration.
RESPONSE
The test fixture used to test cable trays was specifically designed for this test program.
Its inverted pendulum design permitted seismic input to suspended tray support systems.
Additionally, the fixture was designed to accom-modate a 40 foot long tray system segment of up to S tiers
}
and a hanger of up to 13 feet in length.
Sufficient width was provided in the test bay to accommodate two parallel runs, including cross connections and attached conduit.
This facility allowed for testing of long multitiered tray systems with various bracing arrangements.
The test program included tests of a large number of varied tray type and support types in various configurations.
These test configurations were used during the testing program in order to simulate the actual field installed conditions.
Supports with or without bracing and with multitier cable trays were tested.
In addition, a combined 14
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system configuration comprised of various tray fittings such
()
as tees, elbows, vertical bends, and multitiers of straight
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cable tray runs was tested.
In view of the scope of the
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testing and the various test set-ups it was concluded that j
these tests do actually simulate conditions encountered in the field and, therefore, the results of the testing would l
l be applicable to the design of cable trays on the VEGP.
Detailed discussions on how the test program results were l
conservatively extended to the damping values used in the actual VEGP design is presented in Section 2.0.
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i QUESTION 5:
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i' Specify different conditions under which different modal damping ratios ranging from 5-15% are used for VEGP cable tray support system design.
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RESPONSE
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Refer to Section 3.0 for complete response, i
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QUESTION 6:
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It appears that the scope of the cable tray test and the number of tests may not support direct extension to VEGP cable tray design.
Justify that the scope of test conducted is adequate for direct design application.
RESPONSE
The scope of the cable tray and conduit raceway test program included the evaluation of a large numbcr of variables in the design of cable trays.
Included in the test report are dis-cussions of the following variables:
o Type of tray o
Type and length of hanger o
Location of splices o
Number of tiers o
Type of support systems D
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o Type and location of bracing N
3 o
Amount of cable fill o
Size and distribution of cables o
Cable ties combined conduit and tray systems o
o Sprayed fire protection material In order, to evaluate the effect of these and other variables over 2000 individual dynamic vibration tests were performed over a period of 11 months of testing.
As a result of these tests over 50 volumes of raw data were generated and evaluated.
The results of the evaluation of these data form the basis for the conclusion contained in the test report and the design recommendations for the VEGP design.
Although the type of tray and tray supports used in VEGP have not been specifically tested, the test program results demonstrated that the use of a higher damping value can be directly used to form the VEGP design basis, as disucssed in detail in Section 2.0.
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j The present position of VEGP regarding combined conduit and tray j
systems is that the conduit support system will remain independent from the cable tray system.
Exception to this position will be
)i handled on a case-by-case basis.
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l QUESTION 7:
O Identify the material, the configuration, the loading values used on VEGP and provide justification that the test results obtained are applicable on VEGP design.
This should include a comparison of the seismic responses obtained from the test results with those calculated for VEGP.
RESPONSE
The materials, the configuration and the loading values used in the support C-cign are provided in Figure 1.
Justification that the test results obtained are applicable on VEGP design is pro-vided in Section 2.0.
Sample calculations are provided in appendix "a."
In the testing program, different types of input motions including real and synthetic earthquake time histories were used with a wide range of acceleration values.
As a result, the damping curves generated from the test program data is applicable to VEGP, since the damping curve is dependent only on the amount of cables in the trays and the input design floor acceleration (spectrum ZPA),
and not on the VEGP response spectra.
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i QUESTION 8:
'O Prepare sample VEGP calculations giving the support specifics, such as geometry and loading conditions.
Make sure that the results of these calculations are equal to the results obtained i
from the test.
RESPONSE
Sample VEGP calculations are provided in appendix "a."
It is to be noted that, for VEGP, the testing program is used as I
the basis only to justify the proposed damping curve and not as a means of qualifying the cable tray support system by testing.
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k 5.0 DESIGN STATUS QUESTION 1:
Provide the extent and status of VEGP design engineering and construction using damping values of 20% for OBE and SSE, and using damping values of 2% for OBE and 4% for SSE.
What is the justification for switching from 2% OBE and 4% SSE damping values to 20% damping value for both OBE and SSE?
What will be the engineering and construction cost schedule impact if the project is reverted to using damping values of 2% for OBE and 4% for SSE?
RESPONSE
()
Calculations on the VEGP cable tray supports were formalized in late 1977 using cantilevered tube steel supports and a set of support types was developed.
(Refer to Figure 1 for a typical support.)
These calculations were completed using the following design criteria:
1)
March, 1977 Response Spectrum Curves.
2)
Combining stresses from seismic events considering two components of earthquake simultaneously.
OV 22
3)
Damping values of 2% for OBE and 5% for SSE (from PSAR amendment 13, dated December 10, 1973, using values for welded structures).
Acceptance of PSAR supplements 3 and 4, (issued November 15, 1977 t
and January 25, 1978) resulted in the following design criteria:
1)
January 29, 1979 Response Spectrum Curves.
2)
Damping ratios of 2% for OBE and 4% for SSE.
3)
Combining stresses from seismic events considering three components of earthquake simultaneously.
An integral part of a cantilevered tube steel support is a hori-zontal cantilever arm.
The new response spectra coupled with the change from two component earthquake to three component earthquake design criteria would have required VEGP to discontinue use of the cantilevered tube steel support due to the following limita-tions:
The arm could not be designed to an acceptable length for a.
higher acceleration values.
b.
For lower acceleration values, the arms could be designed for various support spacings up to a maximum allowable of v
23
8'3", but would allow no construction tollerance for support O'
spacings of 6'-0" or more.
This was discovered only recently because the design progressed upwards from the lower levels in accordance with the construction schedule.
At the lower levels, lower acceleration values per-mitted the design of the cantilever support system.
In order to design the cable tray supports for the higher accelera-tion values it would have been necessary to develop a new set of standards utilizing alternate methods of support or significant modifications to the current support types.
This would have halted the construction installation effort until the new design was completed and subsequent material lead times were overcome.
Additional fabrication costs would be incurred from having to revise or replace supports already fabricated or with material already ordered.
In order to continue using the cantilever arm and maintain flexi-bility of spacing, it was decided to utilize those results of the
" Cable Tray and Conduit Raceway Seismic Test Program" that are applicable to VEGP.
This test program was developed by Bechtel Power Corporation with participation from 11 organizations including Georgia Power Company.
The test program and results have been 24
discussed with the NRC on a generic basis. (2)
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The test program results confirmed that higher damping values could be used to determine the appropriate acceleration values for use in the design.
Technical justification for using these higher damping values for VEGP is provided in Sections 2.0, 3.0, and 4.0.
Reanalysis of the cantilever arm utilizing the increased damping values has been completed.
It has provided a design that can be utilized throughout the power plant and will also provide for reasonable construction tolerances.
Drawings have been issued for construction based on the new design.
These drawings represent approximately 50% of the total supports required for the plant.
Fabrication has proceeded for virtually all the drawings issued and construction installation has proceeded only on a portion of those supports in the lower levels of the plant.
As stated previously, the impact of reverting to the use of l
damping values of 2% for OBE and 4% for SSE is that a significant portion of the power plant will not be able to utilize the current supports.
(2)
The test reports were informally provided by Bechtel to the NRC on a generic basis during the NRC meeting held on January 8, 1980 at Bethesda, Maryland.
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l For reference purposes, typical VEGP support details are given in three representative drawings included as appendix "d."
To date, there is a total of 22 typical cable tray supports drawings.
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6.0 RESPONSES TO ADDITIONAL CLARIFICATIONS REQUESTED BY NRC QUESTION 1:
i sample calculations are for cantilevered type of cable tray supports only.
Does this mean that VEGP uses no other types of supports as braced hanger systems (trapeze-type supports) as described in response to Question #1.
RESPONSE
VEGP does not use the strut type braced hanger systems.
- However, for special circumstances representing approximately 150 supports, similar configurations made up of conventional structural shapes
)
and connections in lieu of struts have been used.
Fundamental system frequencies for these limited number of supports are bounded by the frequency range for the standard VEGP tray supports.
)
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QUESTION 2:
There is no dynamic analysis in sample calculations.
It is not known how the seismic loads and stresses are obtained, nor the damping values required for design.
RESPONSE
The seismic loads and stresses are obtained using an equivalent static analysis method.
From the appropriate response spectra curves, using the applicable damping value, the peak acceleration value is obtained.
The selection of the applicable damping value is based on the amount of cable in the trays and the floor design acceleration, and is described in detail in Section 3.0.
Using the
[~3 peak acceleration value and the mass values, the seismic loads V
on the structural system are computed and the design is carried out using standard procedures for structural steel design with conventional structural shapes and connections.
It should be noted that the design considers both the OBE and SSE conditions with the associated allowable stresses criteria.
b 28
QUESTION 3:
b The applicant still does not show us the correlation between the ANCO/Bechtel test results and the cable tray support systems that are to be used in VEGP.
The best way to demonstrate the correlation is to identify the typical systems used in VEGP and show in working drawings with the type and series number of those systems tested and reported in the ANCO/Bechtel report.
RESPONSE
As stated in Section 2.0, the type of tray and tray supports used in VEGP have not been specifically tested in the testing program.
N's The testing of cable tray systems clearly demonstrated that a V
significant portion of the system damping was the result of the amount of energy absorbed between the adjacent moving cables and partly through friction between cables.
Among the many test cases considered in the evaluation of the influence of tray support stiffness on the tray support system damping, the test program included flexible supports (strut trapeze type bracing system) and i
rigid supports, wherein the trays were directly supported from the shake table.
The frequency ranges for these support systems under fully loaded condition are as follows.
Specifically, the flexible type supports tested had a range of system fundamental frequencies in the transverse, vertical and longitudinal directions of 2-6 cycles J
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per second (cps).
The rigid type supports tested had a range of
(
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9-25 cps.
The VEGP support system fundamental frequencies vary from a low end of about 3 cps and approaches those of the tested rigid type supports at the high end.
Since the stiffnesses of the VEGP tray support systems fall within the tested range of stiffnesses of the flexible type support systems and those of the rigid type support systems, it is evident that the VEGP system would have damping values in between those obtained for the two cases above, as shown schematically in Figure 7.
For purposes of conservatism, the VEGP design damping curve has been selected such that it falls below both the damping curves for the flexible support system and the rigid support system, even though a higher damping could be justified.
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QUESTION 4:
O The applicant should explain why it is pertinent to design such that these damping values be used.
What difficulty in design may be encountered if Regulatory Guide 1.61 values are used?
Can this be shown in sample calculations?
RESPONSE
The design problems encountered in using the damping values suggested in Regulatory Guide 1.61 for the design of VEGP tray support systems have been discussed in detail in Section 5.0.
If the Regulatory Guide 1.61 damping values are used, the span between the supports would become too close.
This would pose j
significant restrictions on construction and on maintainability of the plant during operation.
It would also necessitate virtually the elimination of construction tolerances which is not realistic i
or workable at the field.
Having to design to Regulatory Guide 1.61 damping values would require the development of a new set of standard supports or making significant modifications to the current support types.
Its impact on engineering, materials, fabrication and construction is described in Section 5.0.
The use of a higher damping value for VEGP tray support system is consistent with the Regulatory Guide 1.61 position O
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that provides for damping values higher than those recommended, when justified by test results.
O It has been recognized that the Regulatory Guide 1.61 damping values i
are conservative to the design of cable tray support systems.
It has been observed during many actual earthquakes that the cable tray support systems have maintained integrity.
The incentive for l
conducting the cable tray testing program was to confirm these field observations and to develop a design damping curve that realistically but yet conservatively addresses the behavior of the cable tray support systems.
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MN/ STRUT /CRIZ MEMBER NOTE UN/ STRUT MATER /AL ASTM A-570 GRADE C {TYP)
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ELEVATION SECTION mW TYPICAL TRAPEZE TYPE TRAY SUFFORT C
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- TEST SET-UP FOR R/G/DLY SUPPORTED TRAYS FIGURE 3 0
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0.1 0.2 0.3 0.4 0.5 0.8 OJ 0.0 0.8 8.0 8.1 1.2 1.3 INM(g) ORACEO MANGERS DAMPlNG VS. INPUT LEVEL FOR BRACED NANGER SYSTEMS FIGURE 4 O
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SEE FIGURE 1, APPENDIX b 4
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0 0.1 0.2 0.30.4 0.5 0.60.70.8 0.9 1.0 1.11.2 1.3 1.4 1.5 1.6 INPUT (g) RIGID SUPPORTS LEAST SOUARED ERRORS BEST FIT CURVE 15% NON-EXCEEDANCE PROBABILITY CURVE DAMPING VS. INPUT LEVEL FOR RIGIDLY SUPPORTED CABLE TRAYS -
1 EARTHQUAKE TYPE MOTION FIGURE 5
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< 50% TO FULLY LOADED TRAY
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(SEE NOTE BELOW) e 16 1
15%
g i2 7
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4 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 INPUT FLOOR ACCELERATION (g)
NOTE FOR UNLOADED TRAY, DAMPING VALUES OF 2% FOR OBE AND 4% FOR SSE ARE APPLICABLE.
FOR TRAY LOADED LESS THAN 50%, LINEAR INTERPOLATION IS USED TO DETERMINE THE ASSOCIATED DESIGN DAMPING VALUE.
VEGP DESIGN DAMPlNG CURVE ricuae s 39 4
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FLEXIBLE SUPPORT BRACED SYSTEM O
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V0GTLE PROJECT 25-k 5
20-RIGID SUPPORT SYSTEM S
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SYSTEM FREQUENCY-HZ SCHEMATIC RELATIONSHIP OF SUPPORT SYSTEM FREQUENCIES TO DAMPING FIGURE 7 40
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