ML20113F632

Recommended Cable Tray Support Damping

ML20113F632
Person / Time
Site:	Hatch
Issue date:	01/31/1985
From:	GEORGIA POWER CO.
To:
Shared Package
ML20113F618	List: ML20113F616 ML20113F622 ML20113F632
References
NUDOCS 8501240082
Download: ML20113F632 (12)

Text

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RECOMMENDED CABLE TRAY SUPPORT DAMPING VALUES FOR THE E. I. HATCH NUCLEAR PLANT i.

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• UNITS 1 AND 2 JANUARY,1985 4

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B501240082 850116 PDR ADOCK 05000321 ^

.SJ .PDR 2, JJAN 16

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.-p-1.0 ~ INTRODUCTION Observations of earthquake damage at several non-nuclear power

. installations indicate that. cable tray raceway systems supported by conventional methods survived the event with little or no damage. An

example of such an observation is the Symar converter station which swas subjected to the 1971 San Fernando earthquake. These

'. observations indicate that substantial capacity exists ir. these tray

~ systems beyond that which could be identified by conventional analytical methods using previously accepted damping values. To better understand the dynamic behavior of cable tray raceway systems a detailed testing' program (Reference 1) was undertaken by Bechtel.

Power Corporation. Several utilities,-including Georgia Power

-  : Company (GPC), provided additional technical and/or financial

support. .ANC0 Engineers Inc. of Santa Monica, California was retained to design and construct a testing facility, perform dynamic testing and provide _ technical-consulting for both the implementation

~o f'the. detailed program and -interpretation of data.- The test program considered . numerous parameters that could influtince system dynamics and resulted in the conclusion that system damping is substantially

. higher than previously acknowledged.

~

. Georgia' Power Company has established a revised' position on damping

. values;for Plant Hatch (HNP) seismic analysis based on the results of

,  :.the referenced test program. . The revised. position increases the

'P1 ant Hatch safety margins on. cable tray supports for earthquake

~

I_ events, since.the cable tray support loads.are reduced and the.

support system configuration has not changed. The GPC position is

- .-described herein, along wi.th a brief summary of the technical-basis.

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1 2.0' TECHNICAL POSITION The GPC position on damping values for seismic analysis applies to

^

- seismic Catagory I cable tray supports in Plant Hatch. The position is illu'strated in Figure 1 and, as indicated, the damping values are

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. influenced by both the excitation level and cable loading.

3.0 TECHNICAL BASIS TThe basis for the HNP design damping curve for cable tray supports 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 the HNP design damping curve shown in

. Figure 1:can be conservatively used for HNP cable tray supports (Figure 2). The_use of this damping curve for analysis increases the

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safety, margins above those perceived during the initial design phase since it provides a more realistic yet lower loading onto an unchanged support system configuration. Also, several different types of tray and supports were tested.

During the test program some 2000 dynamic tests were performed on

< sever'al 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.

a IThe testing of the cable tray systems clearly demonstrated that a significant portion of_the system damping was the result of the e

JAN 16-

amount of energy absorbed between the adjacent moving cables and through friction between cables and the cable tray. Furthermore, it

.was demonstrated that the type of tray and tray support utilized did not significantly influence the system damping.

It' shou,_ be noted that while the specific HNP. type (primarily P-W

. Industries, ladder and solid bottom trough) trays and tray supports

- were not-among those tested, the damping criteria established is

. applicable to Hatch since,'as noted above, the type of tray and tray support utilized does not significantly influence the system damping.

Among'the many test cases considered to evaluate the influence of support stiffness on the tray system' damping, the test program

-included trapeze-type supports (Figure 3) in the flexible range and at the high frequency end, rigid supports, wherein the trays were directly. supported from the shake table (Figure 4). The-stiffnesses

-of the HNP. cable tray support systems fall within the range of

.stiffnesses of the flexible support systems =(trapeze type support) and the higher bound range of stiffnesses of the rigid support systems. The frequency ranges-for the tested support systems under fully loaded conditions are as follows. The flexible type support

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-systems tested had a range of system fundamental frequencies in the transverse, vertical and longitudinal directions of 2-6. cycles per second (cps).- The. rigid type support systems tested had a range of 9-25 cps.- The HNP support system fundamental frequencies fall within i the range of these frequencies.

Although the type.of tray and tray supports used in HNP have not been specifically' tested, the ability of adjacent cables to absorb energy

, through moving against each other and through friction between the l'

I I. JAN16-

A cables and the cable tray is assured by similarity to the cable tray support system dynamic characteristics employed in the test program.

.Since the HNP tray support system dynamic characteristics are within the range of the tested tray support system dynamic characteristics, the test program results, demonstrating the use of a higher damping value, can be directly used for the HNP damping for cable tray supports.

Figure 5 shows the test data collected for the trapeze type supports. The curve shown forms essentially a lower bound of the data points. Figure 6 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." For conservatism, the HNP damping curve (Figure 1) has been selected such that it falls below the

- curves shown in Figures 5 and 6, and for all practical purposes below all

.the data points shown in Figures 5 and 6.

In summary, it can be concluded that damping per Section 2.0 is a realistic yet conservative estimate of damping for cable tray supports for Plant Hatch. Since dampirg per Section 2.0 is higher than the damping used in the past, the actual seismic safety margins are actually higher for the cable tray supports that maintain their existing support

~ configuration. Also, the damping per Section 2.0, being more realistic, will maintain the intended safety margin for Plant Hatch when used for new or replacement cable tray supports and load reconciliation work.

4.0' CONCLUSION It has been demonstrated by test that the damping values of Section 2.0 care realistic and conservative estimates of damping for cable tray supports for Plant Hatch. The application of these damping values will maintain at least the intended seismic safety margins for Plant Hatch. It r

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-is concluded, th'erefore, that use of the damping values of Section 2.0 does not constitute an unreviewed safety issue. The GPC revised position is to use the damping values of Section 2.0 for new or replacement cable tray supports and load reconciliation work at Plant Hatch.

5.0 REFERENCE p

" Cable Tray and Conduit Raceway Seismic Test Program, Release 4" Report

'l .

1053-21.1-4 ANC0 Engineers, Inc. December 15, 1978.

'JAN16

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1 l

l 24 p50xTOFULLYLOADEDTRAY 20 E

e 16 /

Z g 12 / 15%

5 7

8 5%

4 0.0 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,USE DAMPING VALUES SPECIFIED IN FSAR FOR STEEL STRUCTURES. FOR TRAY LOADED LESS THAN 50%. LINEAR INTERPOLATION IS USED TO DETERMINE THE ASSOCIATED DESIGN DAMPING VALUE.

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PLANT HATCH DESIGN DAMPING CURVE FIGURE 1 i

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• TRAY SUPPORT TESTED WITH AND WITHOUT BRACE.

TYPICAL TESTED TRAPEZE TYPE TRAY SUPPORT FIGURE 3 JAN16

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TEST SET-UP FOR RIGIDLY SUPPORTED TRAYS FIGURE 4 JAN16

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DAMPING VS. INPUT LEVEL FOR HANGER SYSTEMS FIGURE 5 JANi6

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1 0.0 0.2 0.4 0.6 0.8 1.0 1.2 14 1.6 1.8 2.0 2.2 INPUT ACCELERATION ( g)

CONFIDENTIAL a CABLE TRAY DAMPING VALUES FOR PROPRIETARY EARTHQUAKE EXClTATION FIGURE 6