Vibration amplitudes in the Inuvik powerhouse

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Vibration amplitudes in the Inuvik powerhouse

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NATIONAL RESEARCH COUNCIL O F CANADA D I V I S I O N O F B U I L D I N G RESEARCH

V I B R A T I O N AMPLITUDES I N THE I N U V I K POWERHOUSE by G. P e r n i c a , V.R. P a r a m e s w a r a n and G.H. J o h n s t o n DBR P a p e r No. 1283 of t h e D i v i s i o n of B u i l d i n g R e s e a r c h O t t a w a , M a y 1985

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TABLE OF CONTENTS

ABSTRACT INTRODUCTION

LAYOUT OF THE POWERHOUSE TEST PROCEDURE

ANALYSIS OF RECORDS RESULTS

Narrow Band A n a l y s i s

One-Third Octave Band A n a l y s i s G e n e r a t o r G e n e r a t o r c r a d l e - p i l e s y s t e m G e n e r a t o r c r a d l e P i l e s s u p p o r t i n g t h e g e n e r a t o r c r a d l e Comparison of c r a d l e and p i l e r e s p o n s e Western s e c t i o n of powerhouse F l o o r P i l e s s u p p o r t i n g f l o o r Comparison of f l o o r and p i l e r e s p o n s e E a s t e r n s e c t i o n of powerhouse F l o o r P i l e s s u p p o r t i n g f l o o r Comparison of f l o o r and p i l e r e s p o n s e F r e e s t a n d i n g (unloaded) p i l e Ambient a c c e l e r a t i o n a m p l i t u d e s : g e n e r a t o r o f f SUMMARY AND CONCLUSIONS

ACKNOWLEDGEMENTS REFERENCES TABLES FIGURES PAGE 1 1 2 3 5 5

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6 6 6 6 7 7 8

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8 8 9 9 9 10 10 11 11 12 12 1 3 2 9

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ABSTRACT

V i b r a t i o n measurements i n t h e main powerhouse a t I n u v i k , NWT, were t a k e n t o d e t e r m i n e t h e a m p l i t u d e s of v i b r a t i o n p r e s e n t i n a s t r u c t u r e s u p p o r t e d on p i l e f o u n d a t i o n s i n p e r m a f r o s t and s u b j e c t e d t o l a r g e dynamic p e r i o d i c f o r c e s . A c c e l e r o m e t e r s were p l a c e d on t h e s u p p o r t s y s t e m f o r t h e main d i e s e l g e n e r a t o r and on t h e f l o o r and p i l e f o u n d a t i o n of t h e o n e s t o r e y

i n d u s t r i a l b u i l d i n g . One-third o c t a v e band RMS a c c e l e r a t i o n a m p l i t u d e s produced by t h e g e n e r a t o r , a 5.2

MW

s y s t e m , a r e p r e s e n t e d . I n comparison t o ambient a c c e l e r a t i o n a m p l i t u d e s ( g e n e r a t o r o f f ) , a m p l i t u d e s produced by t h e g e n e r a t o r were a p p r o x i m a t e l y 430 t i m e s l a r g e r on t h e s t r u c t u r a l s y s t e m s u p p o r t i n g t h e g e n e r a t o r and f i v e t o t e n times l a r g e r t h r o u g h o u t t h e remainder of t h e powerhouse. INTRODUCTION Foundations s u p p o r t i n g b u i l d i n g s i n p e r m a f r o s t a r e a s a r e s u b j e c t e d t o s t a t i c and a v a r i e t y of dynamic l o a d s . S t a t i c l o a d s i n c l u d e t h e weight and c o n t e n t s of t h e b u i l d i n g . P e r i o d i c dynamic l o a d s r e s u l t from v i b r a t i n g machinery (e.g., t u r b i n e s , power g e n e r a t o r s , c o m p r e s s o r s ) , moving dynamic l o a d s from c r a n e s , f o r k l i f t t r u c k s , e t c . , and shock and t r a n s i e n t dynamic l o a d s from such s o u r c e s a s s t a m p s , f o r g e s , p i l e d r i v e r s , heavy v e h i c l e s , n e a r b y b l a s t i n g o p e r a t i o n s and e a r t h q u a k e s .

P i l e f o u n d a t i o n s i n p e r m a f r o s t a r e u s u a l l y d e s i g n e d f o r s t a t i c l o a d s o n l y , because i n f o r m a t i o n i s l a c k i n g on t h e behaviour of f r o z e n s o i l s under dynamic l o a d s . The d e s i g n e r g e n e r a l l y u s e s e m p i r i c a l l y d e r i v e d p a r a m e t e r s and a c c e p t e d d e s i g n p r a c t i c e s , a s t h e r e a r e n o e s t a b l i s h e d o r s t a n d a r d i z e d d e s i g n c r i t e r i a o r codes. P i l e s a r e d e s i g n e d t o s u p p o r t t h e v e r t i c a l s t a t i c l o a d of t h e s u p e r s t r u c t u r e w i t h o u t e x c e e d i n g an a l l o w a b l e s e t t l e m e n t d u r i n g t h e a n t i c i p a t e d s e r v i c e l i f e of t h e s t r u c t u r e . When end b e a r i n g i s n o t p o s s i b l e , a s i n i c e - r i c h s o i l s , t h e b e a r i n g c a p a c i t y of a p i l e i s a s s e s s e d f r o m t h e a d f r e e z e bond s t r e n g t h between t h e p i l e and t h e s o i l . This

s t r e n g t h h a s been e x p e r i m e n t a l l y d e t e r m i n e d from s h o r t - t e r m l a b o r a t o r y t e s t s and a f e w long-term p i l e l o a d t e s t s i n t h e f i e l d . U n f o r t u n a t e l y , t h e r e i s c o n s i d e r a b l e u n c e r t a i n t y i n t h i s p r o c e d u r e , due t o v a r i a b i l i t i e s i n t h e t y p e , t e m p e r a t u r e and m o i s t u r e ( i c e ) c o n t e n t of t h e s o i l s and t h e s u r f a c e c h a r a c t e r i s t i c s of wood, c o n c r e t e and s t e e l p i l e s . Hence a l a r g e f a c t o r of s a f e t y i s i n c o r p o r a t e d i n t o t h e d e s i g n . The i m p o r t a n c e of p i l e c r e e p i n i c e - r i c h s o i l s h a s been r e c o g n i z e d . A s a r e s u l t , p i l e d e s i g n i n i c e - r i c h s o i l s i s p r e s e n t l y based on l i m i t i n g c r e e p d e f o r m a t i o n ; i n i c e - p o o r s o i l s i t

i s based on a l l o w a b l e a d f r e e z e s t r e n g t h s (Weaver and M o r g e n s t e r n , 1981). Although t h e e f f e c t s of dynamic s t r e s s e s on t h e l i f e of a p i l e f o u n d a t i o n a r e n o t t a k e n d i r e c t l y i n t o c o n s i d e r a t i q n , t h e l a r g e f a c t o r of s a f e t y i n d e s i g n a p p e a r s t o compensate f o r t h e s e e f f e c t s . S t u d i e s have shown t h a t t h e dynamic Young's modulus d e c r e a s e s w i t h i n c r e a s i n g s t r a i n a m p l i t u d e i n i c e and f r o z e n s o i l s . However, f i e l d s t u d i e s of t h e e f f e c t s of dynamic l o a d s on t h e r a t e of s e t t l e m e n t of p i l e s i n f r o z e n s o i l s have y e t t o be u n d e r t a k e n .

L a b o r a t o r y model s t u d i e s a r e underway a t t h e D i v i s i o n of B u i l d i n g R e s e a r c h (DBR), N a t i o n a l Research Council Canada (NRCC) t o o b t a i n i n f o r m a t i o n on t h e b e h a v i o u r of p i l e s i n f r o z e n s o i l s under v a r i o u s

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c o n d i t i o n s of l o a d and s o i l t e m p e r a t u r e . P r e l i m i n a r y r e s u l t s of t h e s e i n v e s t i g a t i o n s showed t h a t under c r e e p c o n d i t i o n s , an a l t e r n a t i n g s t r e s s a s s m a l l a s 5% of t h e s t a t i c s t r e s s i n c r e a s e d t h e d i s p l a c e m e n t r a t e of wood and c o n c r e t e p i l e s i n f r o z e n sand and s o i l s a t about -2.5OC by a f a c t o r of 2 t o 4 (Parameswaran, 1981 and 1984). T h i s means, based on l i m i t i n g c r e e p d i s p l a c e m e n t s , t h a t t h e s e r v i c e l i f e of a s t r u c t u r e can be reduced t o one-half of t h a t a n t i c i p a t e d . One way of m a i n t a i n i n g t h e d e s i r e d s e r v i c e l i f e of a s t r u c t u r e and a v o i d i n g p r e m a t u r e f o u n d a t i o n f a i l u r e , i s t o r e d u c e t h e a l l o w a b l e s t a t i c stress a t t h e p i l e l s o i l i n t e r f a c e .

I n o r d e r t h a t f i e l d c o n d i t i o n s c o u l d be s i m u l a t e d i n t h e l a b o r a t o r y e x p e r i m e n t s on p i l e s , a f i e l d i n v e s t i g a t i o n of v i b r a t i o n s w i t h i n an a c t u a l s t r u c t u r e s u p p o r t e d on p i l e f o u n d a t i o n s i n p e r m a f r o s t had t o be conducted. With t h e p e r m i s s i o n of t h e Northern Canada Power Commission (NCPC), t h e a u t h o r s i n v e s t i g a t e d t h e v i b r a t i o n s i n t h e newer (1970) of two powerhouses i n I n u v i k , Northwest T e r r i t o r i e s , which i s l o c a t e d i n t h e c o n t i n u o u s

p e r m a f r o s t zone. The newer powerhouse was s e l e c t e d b e c a u s e i t c o n t a i n e d t h e main d i e s e l g e n e r a t o r f o r t h e town. E x t e n s i v e measurements were c a r r i e d o u t on t h e c o n c r e t e f l o o r of t h e powerhouse and on t h e wood f o u n d a t i o n p i l e s . The r e s u l t s of t h e s e measurements a r e p r e s e n t e d i n t h i s p a p e r . Measurements t o d e t e r m i n e t h e dynamic p r o p e r t i e s of wood p i l e s i n p e r m a f r o s t were a l s o conducted on f r e e s t a n d i n g ( u n l o a d e d ) p i l e s a t two s i t e s i n I n u v i k . R e s u l t s of t h e s e measurements w i l l be p r e s e n t e d i n a s e p a r a t e paper.

Before measurements were t a k e n a t t h e powerhouse, t h e a u t h o r s were informed by Northern Canada Power Commission s t a f f t h a t t h e main d i e s e l g e n e r a t o r i n t h e powerhouse d i d n o t o p e r a t e a s smoothly a s s i m i l a r d i e s e l g e n e r a t o r s l o c a t e d i n o t h e r n o r t h e r n communities. V i b r a t i o n measurements t a k e n on t h e g e n e r a t o r by NCPC s t a f f u s i n g hand-held p r o b e s i n d i c a t e d t h a t t h e v i b r a t i o n s on t h e g e n e r a t o r were a p p r o a c h i n g t h e upper end of t h e m a n u f a c t u r e r ' s s a t i s f a c t o r y o p e r a t i n g range. A s t h e main d i e s e l g e n e r a t o r was t h e o n l y g e n e r a t o r o p e r a t i n g d u r i n g t h e measurement p e r i o d , t h e

a m p l i t u d e s of v i b r a t i o n c o n t a i n e d i n t h i s paper a r e p r o b a b l y l a r g e r t h a n t h o s e n o r m a l l y found f o r comparable g e n e r a t o r s e l s e w h e r e .

LAYOUT OF THE POWERHOUSE

The newer powerhouse i n I n u v i k ( F i g s . 1 and 2) i s l o c a t e d a d j a c e n t t o t h e E a s t Channel of t h e Mackenzie R i v e r D e l t a . The r e c t a n g u l a r one-storey i n d u s t r i a l b u i l d i n g i s a p p r o x i m a t e l y 55.8 m l o n g and 22.1 m wide, w i t h t h e l o n g i t u d i n a l a x i s p a r a l l e l t o t h e r i v e r channel. The powerhouse i s

c o m p l e t e l y s u p p o r t e d on wood p i l e s ( F i g . 3 ) .

The b u i l d i n g was c o n s t r u c t e d i n t h r e e s t a g e s : t h e w e s t e r n s e c t i o n , which c o n t a i n s the main d e s e l g e n e r a t o r , was completed i n 1970; t h e e a s t e r n s e c t i o n , which c o n t a i n s a s m a l l e r d i e s e l g e n e r a t o r f o r p e r i o d s of peak l o a d , was completed i n 1975; and a s m a l l a d d i t i o n t o t h e w e s t e r n s e c t i o n t h a t c o n t a i n s a n c i l l a r y equipment f o r t h e main d i e s e l g e n e r a t o r was completed i n 1972 ( F i g . 4). There a r e seven f l o o r c o n s t r u c t i o n j o i n t s i n t h e powerhouse b u i l d i n g ; t h e f i r s t s e p a r a t e s t h e e a s t e r n and w e s t e r n s e c t i o n s of t h e

b u i l d i n g ; t h e second s e p a r a t e s t h e s m a l l a d d i t i o n and t h e w e s t e r n s e c t i o n ; t h e t h i r d and f o u r t h i s o l a t e t h e two d i e s e l g e n e r a t o r s f r o m t h e powerhouse f l o o r ; t h e f i f t h i s o l a t e s a f l o o r a r e a i n t h e w e s t e r n s e c t i o n t h a t c o n t a i n s mechanical equipment (pumps and b o i l e r s ) ; t h e s i x t h i s o l a t e s a f l o o r a r e a i n

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t h e a d d i t i o n ; and t h e s e v e n t h i s o l a t e s a f l o o r a r e a i n t h e e a s t e r n s e c t i o n t h a t w i l l u l t i m a t e l y b e used f o r a f u t u r e b o i l e r . The dimensions of t h e t h r e e s e c t i o n s of t h e powerhouse and t h e l o c a t i o n of e a c h of t h e f i v e i s o l a t e d f l o o r a r e a s i n t h e powerhouse a r e shown i n Fig. 4.

The s u p e r s t r u c t u r e of t h e powerhouse c o n s i s t s of p o r t a l s t e e l f r a m e s a t 7.3 m s p a c i n g s . The e x t e r i o r w a l l s and c l a d d i n g of t h e s u p e r s t r u c t u r e a r e c o n s t r u c t e d f r o m s h e e t s of c o r r u g a t e d s t e e l . The f l o o r of t h e powerhouse, e x c l u d i n g t h e f i v e i s o l a t e d f l o o r a r e a s , i s a one-way r e i n f o r c e d c o n c r e t e s l a b a p p r o x i m a t e l y 200 mm t h i c k . The s l a b i s s u p p o r t e d e v e r y 2.4 m by 610 mm wide x 460 mm deep r e i n f o r c e d c o n c r e t e beams. The beams i n t u r n a r e s u p p o r t e d e v e r y 2.4 t o 3.4 m by c y l i n d r i c a l wood p i l e s ( e i t h e r Mackenzie V a l l e y s p r u c e o r Douglas f i r ) t h a t a r e embedded a t l e a s t 150 mm i n t o t h e u n d e r s i d e of t h e c o n c r e t e beams. I n t h e w e s t e r n s e c t i o n of t h e powerhouse, t h e p i l e s were from 250 t o 300 mm i n d i a m e t e r and were embedded a minimum of 4.6 m i n p e r m a f r o s t . I n t h e e a s t e r n s e c t i o n , t h e p i l e d i a m e t e r was 200 t o 250 mm and t h e minimum embedment l e n g t h was 6.1 m. The p i l e l a y o u t f o r t h e powerhouse i s shown i n Fig. 4. D e t a i l s of p i l e s i n t h e w e s t e r n a d d i t i o n were n o t a v a i l a b l e .

P r i o r t o c o n s t r u c t i o n of t h e c o n c r e t e f l o o r s l a b s , a g r a v e l l y f i l l was p l a c e d on t h e o r i g i n a l ground s u r f a c e , which s l o p e s downward from t h e n o r t h s i d e of t h e powerhouse t o t h e s o u t h ( r i v e r ) s i d e . The ground s u r f a c e on t h e s o u t h s i d e i s a p p r o x i m a t e l y 2.5 m lower t h a n t h a t on t h e n o r t h s i d e

( F i g . 5). F i g u r e 6 shows a c r o s s - s e c t i o n t h r o u g h t h e w e s t e r n s e c t i o n of t h e b u i l d i n g p r i o r t o c o n s t r u c t i o n . The p e r m a f r o s t t a b l e shown i n Fig. 6 s l o p e s i n a comparable manner f r o m t h e n o r t h s i d e of t h e powerhouse towards t h e r i v e r . A t t h e t i m e of t h e measurements (September 1 9 8 0 ) , hand p r o b i n g i n d i c a t e d t h a t t h e d e p t h of thaw was a b o u t 2.6 m on t h e s o u t h s i d e of t h e b u i l d i n g .

The two d i e s e l g e n e r a t o r s housed i n t h e powerhouse a r e s u p p o r t e d on c r a d l e - p i l e systems t h a t a r e i s o l a t e d from t h e f l o o r of t h e powerhouse. Each g e n e r a t o r c o m p r i s e s a d i e s e l e n g i n e , a f l y w h e e l and an a l t e r n a t o r

( F i g . 7). The main g e n e r a t o r , which was o p e r a t i n g d u r i n g t h e measurement p e r i o d , i s powered by a KV 1 6 Mirrlees B l a c k s t o n e d i e s e l e n g i n e manufactured by Hawker-Siddley of England. The 1 6 c y l i n d e r f o u r - s t r o k e e n g i n e o p e r a t e s a t 514 rpm and h a s a r a t e d peak l o a d c a p a c i t y of 5.2

MW.

The g e n e r a t o r i s mounted on a 12.19 x 4.55 x 1.15 m r e i n f o r c e d c o n c r e t e c r a d l e ( F i g . 8 ) . The g e n e r a t o r and c r a d l e , which weigh a p p r o x i m a t e l y 300 t o n n e s , a r e s u p p o r t e d by 28 wood p i l e s . The p i l e s a r e a p p r o x i m a t e l y 300 mm i n d i a m e t e r and a r e embedded a t l e a s t 150 mm i n t o t h e c o n c r e t e c r a d l e and a b o u t 5.6 m i n t o p e r m a f r o s t . The p i l e l a y o u t i s shown i n F i g . 4 and a c r o s s - s e c t i o n a l view t h r o u g h t h e c o n c r e t e c r a d l e i s g i v e n i n Fig. 9.

No i n f o r m a t i o n i s g i v e n i n t h i s p a p e r on t h e s m a l l e r d i e s e l g e n e r a t o r , s i n c e i t was n o t i n o p e r a t i o n d u r i n g t h e measurement p e r i o d and s i n c e n o v i b r a t i o n measurements were t a k e n on t h e u n i t o r on i t s s u p p o r t i n g

c r a d l e - p i l e system.

TEST PROCEDURE

V i b r a t i o n a m p l i t u d e s produced by t h e KV 1 6 d i e s e l e n g i n e were r e c o r d e d u s i n g a c c e l e r o m e t e r s p l a c e d a t 35 l o c a t i o n s a t t h e I n u v i k powerhouse. The

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l o c a t i o n s a t t h e powerhouse a r e d i v i d e d i n t o t h e f o l l o w i n g t h r e e g r o u p s : n i n e on t h e main d i e s e l g e n e r a t o r and i t s s u p p o r t i n g s t r u c t u r e ; 11 i n t h e w e s t e r n s e c t i o n ; and 1 5 i n t h e e a s t e r n s e c t i o n ( F i g . 4). No measurements were t a k e n on t h e s u p e r s t r u c t u r e of t h e powerhouse. I n t h e e a s t e r n s e c t i o n , t r a n s d u c e r s p l a c e d on t h e p i l e s were l o c a t e d d i r e c t l y below t r a n s d u c e r l o c a t i o n s on t h e f l o o r s l a b and a p p r o x i m a t e l y 300 mm below t h e u n d e r s i d e of t h e c o n c r e t e beam. L o c a t i o n s on p i l e s and f l o o r s l a b were chosen i n p a i r s i n o r d e r t o d e t e r m i n e t h e r e l a t i v e motion between t h e c o n c r e t e f l o o r and t h e s u p p o r t i n g p i l e . For t h e main g e n e r a t o r and t h e w e s t e r n s e c t i o n of t h e powerhouse i t was n o t p o s s i b l e t o p a i r a l l p i l e and f l o o r l o c a t i o n s because most of t h e s e p i l e s were n o t r e a d i l y a c c e s s i b l e .

V i b r a t i o n measurements were a l s o t a k e n on a f r e e s t a n d i n g ( u n l o a d e d ) wooden p i l e s i t u a t e d a p p r o x i m a t e l y 2 m from t h e s o u t h s i d e of t h e powerhouse

(Fig. 4). The s p r u c e p i l e was 230 mm i n d i a m e t e r and had an above-ground h e i g h t of 330 mm. It was assumed t o be a b o u t 7 m l o n g , based on t h e

4

m p e r m a f r o s t embedment l e n g t h s p e c i f i e d i n t h e o r i g i n a l d e s i g n drawings f o r a d j a c e n t p i l e s . T h i s p i l e was monitored i n o r d e r t o d e t e r m i n e t h e a m p l i t u d e s of v i b r a t i o n of a s i n g l e p i l e a t some d i s t a n c e f r o m a s i z e a b l e s o u r c e of e x c i t a t i o n . A t e a c h a c c e l e r o m e t e r l o c a t i o n , measurements were t a k e n i n t h e v e r t i c a l d i r e c t i o n . Except f o r a few l o c a t i o n s , h o r i z o n t a l ( p e r p e n d i c u l a r t o t h e e n g i n e c r a n k s h a f t and p a r a l l e l t o t h e l o n g a x i s of t h e powerhouse) and a x i a l

( p a r a l l e l t o t h e e n g i n e c r a n k s h a f t and t h e s h o r t a x i s of t h e powerhouse) d i r e c t i o n s were a l s o monitored (Fig. 4). On t h e main g e n e r a t o r , Bruel and K j a e r ( 8 & K) 4332 p i e z o - e l e c t r i c a c c e l e r o m e t e r s were used. These

t r a n s d u c e r s h a v e a f l a t r e s p o n s e from 2 t o 15000 Hz and a maximum o p e r a t i n g t e m p e r a t u r e of 260°C. The a c c e l e r o m e t e r s were a t t a c h e d t o t h e g e n e r a t o r u s i n g magnetic b a s e s a t t h e t h r e e l o c a t i o n s recommended by t h e m a n u f a c t u r e r f o r m o n i t o r i n g t h e u n i t ' s performance. A t a l l o t h e r l o c a t i o n s i n t h e

powerhouse, Q - f l e x QA 1100 s e r v o - a c c e l e r o m e t e r s ( S u n d s t r a n d Data C o n t r o l ) w i t h a s e n s i t i v i t y of 5 _{V/g f r o m 0 t o 500 Hz were used.} The Q-flex

a c c e l e r o m e t e r s were a t t a c h e d t o t h e c o n c r e t e c r a d l e and f l o o r s l a b of t h e powerhouse u s i n g two-sided t a p e and t o t h e wood p i l e s u s i n g aluminum f r a m e s screwed t o t h e p i l e s (Fig. 1 0 ) . Two-sided t a p e s e c u r e d t h e a c c e l e r o m e t e r s t o t h e aluminum frame.

The o u t p u t s from t h e B & K and Q-flex a c c e l e r o m e t e r s were a m p l i f i e d and low-pass f i l t e r e d a t a p p r o x i m a t e l y 630 Hz u s i n g a 6 dB/octave f i l t e r b e f o r e b e i n g r e c o r d e d on two FM t a p e r e c o r d e r s ; a seven-channel S t o r e 7D Racal and a four-channel 7003 B r u e l and K j a e r . Twenty-eight r u n s , e a c h a p p r o x i m a t e l y 20 minutes l o n g , were made t o r e c o r d t h e v i b r a t i o n s produced by t h e main d i e s e l g e n e r a t o r a t t h e 36 l o c a t i o n s a t t h e powerhouse s i t e . Three r u n s were a l s o made w i t h t h e main g e n e r a t o r t u r n e d o f f i n o r d e r t o measure t h e ambient v i b r a t i o n a m p l i t u d e s a t t h e powerhouse. For e a c h r u n , o n l y n i n e a c c e l e r o m e t e r o u t p u t s were r e c o r d e d , a s two a c c e l e r o m e t e r o u t p u t s were

d u p l i c a t e d on e a c h t a p e r e c o r d e r . For r u n s 1 t o 1 8 , t h e f r e q u e n c y bandwidth of t h e r e c o r d e d s i g n a l s on t h e Racal was o n l y 0 t o 315 Hz, a s t h e r e c o r d i n g s p e e d was s e t a t 1 5 / 1 6 i p s (24 mm/sec). The r e m a i n i n g r u n s were r e c o r d e d on t h e Racal a t 1 718 i p s (48 mm/s,ec), which e x t e n d e d t h e f r e q u e n c y bandwidth t o 630 Hz ( t h e same a s t h e low-pass f i l t e r ) .

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ANALYSIS OF RECORDS

The r e c o r d e d a c c e l e r o m e t e r s i g n a l s were a n a l y z e d on a General Radio o n e - t h i r d o c t a v e band r e a l time a n a l y z e r . The a n a l y z e r produces RMS l e v e l s i n dB f o r t h e 30 o n e - t h i r d o c t a v e bands from 12.5 Hz t o 1 0 kHz. One-third o c t a v e l e v e l s f o r f r e q u e n c y bands below 12.5 Hz were o b t a i n e d from t h e

r e c o r d e d d a t a by u s i n g playback t o r e c o r d s p e e d r a t i o s of e i g h t on t h e Racal t a p e r e c o r d e r and t e n on t h e B & K. I d e n t i c a l r a t i o s f o r t h e two t a p e

r e c o r d e r s were i m p o s s i b l e t o a c h i e v e because of d i f f e r e n c e s i n t a p e r e c o r d e r d e s i g n . The above speed r a t i o s s h i f t e d t h e e f f e c t i v e f r e q u e n c y r a n g e of t h e a n a l y z e r ; 1.6 Hz t o 1.25 kHz f o r d a t a s t o r e d on t h e Racal and 1.25 Hz t o 1 kHz f o r d a t a on t h e B & K.

T a b l e s 1 t o 11 c o n t a i n o n e - t h i r d o c t a v e band a c c e l e r a t i o n a m p l i t u d e s i n p e r c e n t g r a v i t y b e g i n n i n g a t 2.5 Hz. Amplitudes f o r band f r e q u e n c i e s below 2.5 Hz were o m i t t e d , s i n c e t h e lower f r e q u e n c y l i m i t f o r t h e B & K

a c c e l e r o m e t e r s was 2 Hz. One-third o c t a v e band a c c e l e r a t i o n a m p l i t u d e s were o b t a i n e d from RMS l e v e l s i n dB by c a l i b r a t i n g t h e r e a l t i m e a n a l y z e r w i t h a known i n p u t s i g n a l .

A one-second i n t e g r a t i o n t i m e was s e l e c t e d f o r t h e a n a l y z e r .

I n t e g r a t i o n times f o r r e c o r d e d d a t a were e i g h t seconds on t h e Racal and t e n seconds on t h e B & K. Approximately 100 t i m e a v e r a g e s (100 RMS l e v e l s p e r band) were o b t a i n e d f o r e a c h a c c e l e r o m e t e r r e c o r d . The RMS a c c e l e r a t i o n a m p l i t u d e s g i v e n i n T a b l e s 1 t o 11 f o r e a c h o n e - t h i r d o c t a v e band a r e 9 0 t h p e r c e n t i l e v a l u e s , i . e . , 90% of t h e RMS a m p l i t u d e s f o r

a

band a r e less t h a n o r e q u a l t o t h e 9 0 t h p e r c e n t i l e a m p l i t u d e . The 9 0 t h p e r c e n t i l e was

a r b i t r a r i l y chosen a s an upper bound f o r r e p o r t i n g purposes. For most of t h e a c c e l e r o m e t e r r e c o r d s , however, t h e r e was l e s s t h a n a 10% d i f f e r e n c e between t h e 9 0 t h and 5 0 t h p e r c e n t i l e s i n e a c h band ( s m a l l s t a n d a r d

d e v i a t i o n s ) .

Accelerometer s i g n a l s a t t h e t h r e e l o c a t i o n s on t h e main d i e s e l g e n e r a t o r were a l s o a n a l y z e d on a narrow band s p e c t r u m a n a l y z e r ( F o u r i e r Transform) t o o b t a i n t h e f r e q u e n c y s p e c t r u m of t h e f o r c i n g f u n c t i o n w i t h i n , t h e powerhouse. RESULTS Narrow Band A n a l v s i s F i g u r e s 11 t o 1 3 c o n t a i n t h e f r e q u e n c y s p e c t r a i n t h e v e r t i c a l d i r e c t i o n a t t h e t h r e e l o c a t i o n s on t h e g e n e r a t o r . S i m i l a r s p e c t r a l d i s t r i b u t i o n s and c o n t e n t were o b t a i n e d a t e a c h of t h e g e n e r a t o r l o c a t i o n s i n t h e two l a t e r a l d i r e c t i o n s . The f r e q u e n c y c o n t e n t of v i b r a t i o n s on t h e

KV

16 e n g i n e and on t h e a l t e r n a t o r d i f f e r . Those on t h e d i e s e l e n g i n e ( l o c a t i o n s 1 and 11; F i g s . 11 and 1 2 ) a r e s i m i l a r and c o n t a i n many

s i g n i f i c a n t s p e c t r a l peaks a t f r e q u e n c i e s above 100 Hz,, w h i l e t h e v i b r a t i o n s on t h e a l t e r n a t o r ( l o c a t i o n 1 3 ; Fig. 1 3 ) a r e composed p r i m a r i l y of

f r e q u e n c i e s below 100 Hz. The s p a c i n g between peaks i n g e n e r a t o r s p e c t r a i s 4.28 Hz, which c o r r e s p o n d s t o t h e f i r i n g f r e q u e n c y of e a c h c y l i n d e r .

However, t h e r e i s no v i s i b l e peak a t 4.28 Hz i n any of t h e f r e q u e n c y

s p e c t r a . The f i r s t n o t i c e a b l e peak o c c u r s a t 8.56 Hz, which c o r r e s p o n d s t o t h e f r e q u e n c y of r o t a t i o n of t h e c r a n k s h a f t .

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One-Third Octave Band A n a l y s i s

The r e s u l t s of t h e o n e - t h i r d o c t a v e band a n a l y s i s on a c c e l e r o m e t e r s i g n a l s , grouped by s t r u c t u r a l l o c a t i o n w i t h i n t h e powerhouse, a r e p r e s e n t e d i n T a b l e s 1 t o 11. For a c c e l e r o m e t e r p o s i t i o n s t h a t were r e c o r d e d on more t h a n one run (e.g., g e n e r a t o r l o c a t i o n 1 3 , v e r t i c a l d i r e c t i o n ) one r u n was a r b i t r a r i l y s e l e c t e d f o r p r e s e n t a t i o n of t h e o n e - t h i r d o c t a v e band r e s u l t s , a s t h e v a r i o u s r u n s produced s i m i l a r a m p l i t u d e s i n most bands ( F i g . 14). In

bands w i t h n o t i c e a b l e d i f f e r e n c e s , a m p l i t u d e s were a t o r n e a r t h e n o i s e f l o o r of t h e r e c o r d i n g - a n a l y s i s system.

Generator

Table 1 c o n t a i n s t h e broadband and o n e - t h i r d o c t a v e band RMS

a c c e l e r a t i o n a m p l i t u d e s measured a t t h e t h r e e l o c a t i o n s on t h e main d i e s e l g e n e r a t o r ( F i g . 4). No measurements were t a k e n i n t h e a x i a l d i r e c t i o n a t l o c a t i o n 11, s i n c e t h e a c c e l e r o m e t e r c o u l d n o t be p r o p e r l y s e c u r e d t o t h e d i e s e l e n g i n e i n t h i s d i r e c t i o n .

The f o l l o w i n g g e n e r a l o b s e r v a t i o n s were o b t a i n e d from t h e r e s u l t s : ( 1 ) o n e - t h i r d o c t a v e band a m p l i t u d e s i n e a c h d i r e c t i o n on t h e a l t e r n a t o r were s i g n i f i c a n t l y l a r g e r i n t h e mid-frequency r a n g e (16 t o 6 3 Hz) t h a n c o r r e s p o n d i n g a m p l i t u d e s on t h e

KV

16 e n g i n e ( F i g . 1 5 ) ; ( 2 ) minimum

broadband a m p l i t u d e s on t h e g e n e r a t o r were o b t a i n e d i n t h e h o r i z o n t a l and a x i a l d i r e c t i o n s a t t h e s o u t h ( f r e e ) end of t h e e n g i n e and i n t h e v e r t i c a l d i r e c t i o n on t h e a l t e r n a t o r ( F i g . 1 6 ) ; and

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broadband and o n e - t h i r d o c t a v e band a m p l i t u d e s i n t h e two l a t e r a l d i r e c t i o n s on t h e

KV

16 e n g i n e were l a r g e r a t t h e f l y w h e e l end t h a n a t t h e f r e e end ( F i g s . 1 5 and 1 6 ) . Generator c r a d l e - p i l e s y s t e m

G e n e r a t o r c r a d l e : Table 2 c o n t a i n s t h e broadband and o n e - t h i r d o c t a v e band RMS a c c e l e r a t i o n a m p l i t u d e s r e c o r d e d a t t h e f o u r c o r n e r s of t h e

r e c t a n g u l a r c o n c r e t e c r a d l e s u p p o r t i n g t h e g e n e r a t o r (Fig. 4). No

measurements were t a k e n i n t h e h o r i z o n t a l and a x i a l d i r e c t i o n s

a t

l o c a t i o n 3 s i n c e a t t h e t i m e of t h e measurements i t w a s f e l t t h a t i n t h e s e d i r e c t i o n s t h e r e would be v e r y l i t t l e d i f f e r e n c e i n a c c e l e r a t i o n a m p l i t u d e s between l o c a t i o n s 3 and 4.

Broadband and most o n e - t h i r d o c t a v e band a m p l i t u d e s a t l o c a t i o n s 1, 2 and 4 were maximum i n t h e v e r t i c a l d i r e c t i o n and minimum i n t h e h o r i z o n t a l d i r e c t i o n . A s t h e g e n e r a t o r c r a d l e - p i l e s y s t e m r e s e m b l e s an i n v e r t e d

pendulum, t h e l a t e r a l m o t i o n s , p a r t i c u l a r l y t h e h o r i z o n t a l , might have been e x p e c t e d t o be l a r g e r t h a n t h e v e r t i c a l , e s p e c i a l l y i n o n e - t h i r d o c t a v e bands c o n t a i n i n g l a t e r a l n a t u r a l f r e q u e n c i e s . S i n c e t h e e x a c t o p p o s i t e o c c u r r e d i n n e a r l y e v e r y band, t h e g e n e r a t o r c r a d l e - p i l e s y s t e m may be s o f t e r i n t h e v e r t i c a l d i r e c t i o n t h a n i n t h e l a t e r a l d i r e c t i o n s f o r f r e q u e n c i e s below 315 Hz o r t h e f o r c i n g f u n c t i o n produced by t h e g e n e r a t o r may be more i n t u n e w i t h v e r t i c a l r e s p o n s e s t h a n w i t h l a t e r a l r e s p o n s e s . Amplitudes i n a l l t h r e e c o o r d i n a t e d i r e c t i o n s were l a r g e r a t t h e s o u t h end of t h e c r a d l e , l o c a t i o n s 1 and 2, t h a n a t t h e n o r t h end, l o c a t i o n s 3 and 4 ( F i g s . 17 and 18). T h i s d i f f e r e n c e might be p r i m a r i l y due t o t h e dynamic e c c e n t r i c i t y p r e s e n t i n t h e g e n e r a t o r c r a d l e - p i l e system. Although t h e c e n t r e of mass and c e n t r e of s t i f f n e s s f o r t h e c o n c r e t e c r a d l e a r e

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c o i n c i d e n t a l (no e c c e n t r i c i t y ) a t t h e g e o m e t r i c c e n t r e of t h e c r a d l e , t h e y a r e n e i t h e r c o i n c i d e n t a l n o r a t t h e g e o m e t r i c c e n t r e f o r t h e c r a d l e - p i l e system. The mass c e n t r e of t h e s y s t e m i s l o c a t e d i n t h e s o u t h e r n p o r t i o n of t h e c r a d l e , a s t h e

KV

1 6 d i e s e l e n g i n e i s c o n s i d e r a b l y more massive t h a n t h e a l t e r n a t o r . The s t i f f n e s s c e n t r e , on t h e o t h e r hand, i s s i t u a t e d i n t h e n o r t h e r n p o r t i o n , a s t h e t o t a l l e n g t h and h e i g h t above t h e ground s u r f a c e of t h e f o u n d a t i o n p i l e s s u p p o r t i n g t h e c r a d l e i n c r e a s e s from t h e n o r t h t o t h e s o u t h end ( F i g . 8 ) . A s a r e s u l t of t h i s dynamic e c c e n t r i c i t y , t h e

c r a d l e - p i l e s y s t e m would h a v e a tendency ( f o r most dynamic l o a d s ) t o r o t a t e about t h e s t i f f n e s s c e n t r e , p r o d u c i n g l a r g e r a m p l i t u d e s a t t h e s o u t h end t h a n a t t h e n o r t h end of t h e c r a d l e .

Amplitudes i n t h e two l a t e r a l d i r e c t i o n s on t h e a l t e r n a t o r motor

( F i g . 1 6 ) were s u b s t a n t i a l l y l a r g e r t h a n t h e c o r r e s p o n d i n g a m p l i t u d e s a t t h e n o r t h end of t h e c r a d l e (Fig. 1 8 ) . T h i s perhaps i n d i c a t e s a need f o r a s t i f f e r s u p p o r t i n g s t r u c t u r e f o r t h e a l t e r n a t o r motor, which i s a t t a c h e d t o t h e t o p of a c o n c r e t e p e d e s t a l ( F i g . 7 ) .

P i l e s s u p p o r t i n g t h e g e n e r a t o r c r a d l e : R e s u l t s of measurements t a k e n on two p i l e s a t t h e s o u t h e r n end of t h e c r a d l e a r e g i v e n i n T a b l e 3.

Broadband and most o n e - t h i r d o c t a v e band a m p l i t u d e s i n e a c h c o o r d i n a t e d i r e c t i o n on p i l e 5 were s l i g h t l y l a r g e r t h a n c o r r e s p o n d i n g a m p l i t u d e s on p i l e 6 (Fig. 19). P i l e 5 a l s o r e c o r d e d t h e maximum broadband and o n e - t h i r d o c t a v e band a m p l i t u d e s i n t h e two l a t e r a l d i r e c t i o n s a t t h e powerhouse; 69% g broadband, 55% g a t 315 Hz i n t h e h o r i z o n t a l d i r e c t i o n and 55% g broadband, 39% g a t 400 Hz i n t h e a x i a l d i r e c t i o n . For broadband and o n e - t h i r d o c t a v e bands below 31.5 Hz and above 125 Hz, maximum RMS

a m p l i t u d e s on p i l e s 5 and 6 were o b t a i n e d i n t h e h o r i z o n t a l d i r e c t i o n and minimum i n t h e v e r t i c a l d i r e c t i o n ( t h e o p p o s i t e occured oo t h e c r a d l e ) . For

t h e remaining bands (31.5 Hz t o 1 2 5 Hz), t h e o r d e r was r e v e r s e d ; t h e v e r t i c a l d i r e c t i o n had t h e maximum and e i t h e r t h e h o r i z o n t a l o r a x i a l d i r e c t i o n , t h e minimum. T h i s r e v e r s a l may i n d i c a t e t h e o n e - t h i r d o c t a v e band l o c a t i o n s of c r a d l e - p i l e n a t u r a l f r e q u e n c i e s ; fundamental l a t e r a l modes below 31.5 Hz and t h e fundamental v e r t i c a l mode between 31.5 Hz and 1 2 5 Hz.

Comparison of c r a d l e and p i l e r e s p o n s e : During s e v e r a l r u n s , l o c a t i o n s on t h e c r a d l e p i l e s and on t h e c r a d l e were monitored s i m u l t a n e o u s l y .

F i g u r e s 20 t o 22 p l o t t h e o n e - t h i r d o c t a v e band s p e c t r a o b t a i n e d d u r i n g Runs 24 t o 26 a t p i l e l o c a t i o n 5 and c r a d l e l o c a t i o n 2. The c r a d l e l o c a t i o n i s a l m o s t d i r e c t l y above t h e p i l e .

S p e c t r a l r e s u l t s i n d i c a t e t h a t i n t h e v e r t i c a l and a x i a l d i r e c t i o n s ( F i g s . 20 and 2 1 ) , t h e c r a d l e - p i l e system behaves a s a c a n t i l e v e r w i t h a l a r g e t i p mass h a v i n g t h e f o l l o w i n g dynamic c h a r a c t e r i s t i c s ; 1 ) f o r n a t u r a l f r e q u e n c i e s below 250 Hz, modal r e s p o n s e s a r e l a r g e r a t t h e t o p of t h e c r a d l e t h a n n e a r t h e t o p of t h e p i l e s ; and 2) between 250 and 500 Hz, t h e modal r e s p o n s e of one o r more n a t u r a l f r e q u e n c i e s i s p r i m a r i l y p i l e

r e s p o n s e .

I n t h e h o r i z o n t a l d i r e c t i o n , t h e s y s t e m a p p e a r s t o behave i n a s i m i l a r way b u t w i t h some r e s t r a i n t a t o r n e a r t h e t o p of t h e c r a d l e f o r n a t u r a l f r e q u e n c i e s below 63 Hz. The s l i g h t l y l a r g e r p i l e a m p l i t u d e s below 6 3 Hz

( F i g . 22) s u g g e s t t h a t t h e c o n c r e t e c r a d l e irs r e s t r a i n e d t o s o m e , d e g r e e by t h e c o n c r e t e f l o o r s l a b of t h e w e s t e r n s e c t i o n of t h e powerhouse. The

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o r i g i n a l 1 3 mm c o n s t r u c t i o n j o i n t s e p a r a t i n g t h e c r a d l e - p i l e s y s t e m from t h e f l o o r s y s t e m may have c l o s e d a t one o r more p o i n t s a l o n g one of t h e

n o r t h - s o u t h s i d e s . The s u b s t a n t i a l l y l a r g e r p i l e a m p l i t u d e s between 250 Hz and 500 Hz a g a i n i n d i c a t e n a t u r a l f r e q u e n c i e s w i t h modes c o n t a i n i n g

p r i m a r i l y p i l e r e s p o n s e s . Western s e c t i o n of powerhouse

F l o o r : Broadband and o n e - t h i r d o c t a v e band RMS a m p l i t u d e s a t t h e s e v e n l o c a t i o n s t h a t were monitored on t h e f l o o r of t h e w e s t e r n s e c t i o n of t h e powerhouse ( F i g . 4 ) a r e g i v e n i n Table 4. I n g e n e r a l , RMS a m p l i t u d e s d e c r e a s e d w i t h i n c r e a s i n g d i s t a n c e from t h e g e n e r a t o r . The maximum broadband and o n e - t h i r d o c t a v e band a m p l i t u d e s i n e a c h d i r e c t i o n u s u a l l y

o c c u r r e d on t h e f l o o r a t t h e a l t e r n a t o r end of t h e c r a d l e ( l o c a t i o n 4 o r 5 ) and t h e minimum a t l o c a t i o n 7, which was t h e f a r t h e s t from t h e g e n e r a t o r ( F i g s . 23 and 24). Except a t l o c a t i o n 7, t h e maximum broadband a m p l i t u d e a t e a c h f l o o r l o c a t i o n o c c u r r e d i n t h e v e r t i c a l d i r e c t i o n ( F i g . 24). Axial broadband a m p l i t u d e s were minimal a t l o c a t i o n s on e i t h e r s i d e of t h e g e n e r a t o r ( l o c a t i o n s 1 and 6 ) and h o r i z o n t a l a m p l i t u d e s were minimal a t l o c a t i o n s d i r e c t l y i n f r o n t of o r d i r e c t l y behind t h e g e n e r a t o r

( l o c a t i o n s 2, 3, 4 and

5).

Broadband and o n e - t h i r d o c t a v e band a m p l i t u d e s on t h e f l o o r b e s i d e t h e c r a d l e v a r i e d w i t h l o c a t i o n . L o c a t i o n s 4 and 5 a l o n g t h e a l t e r n a t o r end of t h e c r a d l e r e g i s t e r e d l a r g e r a m p l i t u d e s i n a l l t h r e e d i r e c t i o n s t h a n t h o s e a t l o c a t i o n s 1 and 6 s i t u a t e d midway a l o n g e i t h e r s i d e of t h e c r a d l e . The l a r g e s t d i f f e r e n c e s between t h e two g r o u p s o c c u r r e d i n t h e v e r t i c a l

d i r e c t i o n and t h e s m a l l e s t i n t h e h o r i z o n t a l .

P i l e s s u p p o r t i n g f l o o r : R e s u l t s of t h e measurements on f o u r p i l e s s u p p o r t i n g t h e w e s t e r n s e c t i o n of t h e powerhouse ( F i g . 4 ) a r e g i v e n i n T a b l e 5. The t h r e e p i l e s l o c a t e d on t h e s o u t h s i d e of t h e powerhouse

( p i l e s 2 , 3 and 7 ) have above ground h e i g h t s of a p p r o x i m a t e l y 3 m. P i l e 4, l o c a t e d on t h e o p p o s i t e s i d e of t h e powerhouse, h a s a t most 0.5 m exposed above t h e s u r f a c e of t h e ground.

The maximum broadband a m p l i t u d e s i n t h e t h r e e c o o r d i n a t e d i r e c t i o n s were o b t a i n e d on p i l e 3, t h e p i l e c l o s e s t t o t h e c r a d l e , and t h e minimum on p i l e 7 , t h e p i l e f a r t h e s t f r o m t h e c r a d l e (Fig. 25). V e r t i c a l broadband a m p l i t u d e s e x h i b i t e d t h e most c o n s i s t e n t d e c r e a s e w i t h d i s t a n c e from t h e c r a d l e . I n t h e two l a t e r a l d i r e c t i o n s t h e d e c r e a s e s w i t h d i s t a n c e were o n l y a p p a r e n t when a m p l i t u d e s on p i l e 7 were compared w i t h t h o s e on t h e o t h e r t h r e e p i l e s .

Except f o r p i l e 4, t h e maximum broadband RMS a m p l i t u d e s a t e a c h p i l e l o c a t i o n were o b t a i n e d i n t h e h o r i z o n t a l d i r e c t i o n and t h e minimum i n t h e v e r t i c a l . On p i l e

4

t h e maximum o c c u r r e d i n t h e a x i a l d i r e c t i o n and t h e minimum i n t h e h o r i z o n t a l .

Comparison of f l o o r and p i l e r e s p o n s e : A t t h r e e l o c a t i o n s i n t h e w e s t e r n s e c t i o n of t h e powerhouse ( l o c a t i o n s 2, 3 and 7 ) , measurements were t a k e n on t h e c o n c r e t e f l o o r s l a b and on t h e p i l e f o u n d a t i o n d i r e c t l y below. I n t h e h o r i z o n t a l and a x i a l d i r e c t i o n s , o n e - t h i r d o c t a v e band a m p l i t u d e s on t h e p i l e s were l a r g e r t h a n t h o s e on t h e f l o o r s f o r n e a r l y a l l bands

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f l o o r l o c a t i o n s c o u l d be c o n s i d e r e d t o have i d e n t i c a l r e s p o n s e s . Above 31.5 Hz, p i l e a m p l i t u d e s were s i g n i f i c a n t l y l a r g e r t h a n f l o o r a m p l i t u d e s . The o r d e r of magnitude d i f f e r e n c e above 160 Hz p r o b a b l y i n d i c a t e s h i g h e r modes, w i t h mode s h a p e s c o n s i s t i n g p r i m a r i l y of p i l e r e s p o n s e s .

I n t h e v e r t i c a l d i r e c t i o n , n e i t h e r t h e p i l e s n o r t h e f l o o r s had

c o n s i s t e n t l y l a r g e r a m p l i t u d e s f o r o n e - t h i r d o c t a v e bands below 160 Hz, even though p i l e / f l o o r o r f l o o r / p i l e r a t i o s a t e a c h l o c a t i o n were a s l a r g e a s t h r e e t h r o u g h o u t t h i s f r e q u e n c y r a n g e ( F i g . 28). Above 160 Hz, t h e e f f e c t of p r o b a b l e modal f r e q u e n c i e s , w i t h mode s h a p e s c o n s i s t i n g p r i m a r i l y of p i l e r e s p o n s e , was a g a i n e v i d e n t a s a m p l i t u d e s on t h e p i l e s were s i g n i f i c a n t l y l a r g e r t h a n t h o s e on t h e f l o o r . E a s t e r n s e c t i o n of powerhouse

F l o o r : Broadband and o n e - t h i r d o c t a v e band a m p l i t u d e s a t s e v e n

-

l o c a t i o n s on t h e f l o o r of t h e e a s t e r n s e c t i o n of t h e powerhouse a r e g i v e n i n T a b l e 6. Measurements a t l o c a t i o n 6 were o m i t t e d b e c a u s e of t i m e

c o n s t r a i n t s .

I n g e n e r a l , broadband and o n e - t h i r d o c t a v e band a m p l i t u d e s on t h e f l o o r of t h e e a s t e r n s e c t i o n of t h e powerhouse d e c r e a s e d w i t h i n c r e a s i n g d i s t a n c e f r o m t h e g e n e r a t o r . Of t h e t h r e e d i r e c t i o n s , t h e v e r t i c a l s u s t a i n e d t h e l a r g e s t and most c o n s i s t e n t d e c r e a s e w i t h d i s t a n c e and t h e h o r i z o n t a l t h e s m a l l e s t and t h e l e a s t c o n s i s t e n t d e c r e a s e ( F i g . 29).

In

t h e v e r t i c a l d i r e c t i o n , broadband a m p l i t u d e s d e c r e a s e d m o n o t o n i c a l l y from an a v e r a g e of 2.2% g r a v i t y a t t h e two l o c a t i o n s n e a r e s t t h e g e n e r a t o r ( l o c a t i o n s 7 and 8 ) t o 0.29% g r a v i t y a t t h e two l o c a t i o n s f a r t h e s t from t h e g e n e r a t o r

( l o c a t i o n s 1 and 2). I n t h e a x i a l d i r e c t i o n minimum broadband a m p l i t u d e s o c c u r r e d i n t h e c e n t r e of t h e e a s t e r n s e c t i o n of t h e powerhouse ( l o c a t i o n s 3

and 4 ) r a t h e r t h a n a t t h e e a s t e r n end ( l o c a t i o n s 1 and 2).

Except f o r l o c a t i o n 8, broadband a m p l i t u d e s on t h e e a s t e r n f l o o r were l e s s t h a n 1% g r a v i t y . A t l o c a t i o n 8 , which was t h e c l o s e s t t o t h e c r a d l e , broadband a m p l i t u d e s i n t h e v e r t i c a l , a x i a l and h o r i z o n t a l d i r e c t i o n s were 3.5, 1.6 and 1.2% g r a v i t y , r e s p e c t i v e l y . L o c a t i o n 7, which i s o n l y 1 m f a r t h e r f r o m t h e c r a d l e , had broadband a m p l i t u d e s which were less t h a n h a l f t h o s e a t l o c a t i o n 8. It a p p e a r s t h a t more e n e r g y i s t r a n s m i t t e d i n t o t h e powerhouse f l o o r ( e a s t e r n and w e s t e r n s e c t i o n s ) a t t h e a l t e r n a t o r end t h a n a t t h e f r e e end of t h e g e n e r a t o r .

P i l e s s u p p o r t i n g f l o o r : Broadband and o n e - t h i r d o c t a v e band a m p l i t u d e s a t t h e seven p i l e l o c a t i o n s under t h e f l o o r of t h e e a s t e r n s e c t i o n of t h e powerhouse a r e g i v e n i n T a b l e 7. A t most of t h e s e p i l e l o c a t i o n s , broadband a m p l i t u d e s i n t h e h o r i z o n t a l d i r e c t i o n were t h e l a r g e s t and t h o s e i n t h e v e r t i c a l d i r e c t i o n t h e s m a l l e s t .

Amplitudes on t h e p i l e s g e n e r a l l y d e c r e a s e d w i t h i n c r e a s i n g d i s t a n c e f r o m t h e g e n e r a t o r ( F i g s . 30 and 31). The d e c r e a s e was q u i t e s i m i l a r t o t h a t e x h i b i t e d by t h e f l o o r a m p l i t u d e s . I n t h e v e r t i c a l d i r e c t i o n broadband a m p l i t u d e s d e c r e a s e d m o n o t o n i c a l l y w i t h d i s t a n c e , from 0.97% g r a v i t y a t l o c a t i o n 7 t o 0.27% g r a v i t y a t l o c a t i o n 1. I n t h e a x i a l d i r e c t i o n , minimum broadband a m p l i t u d e s o c c u r r e d ( a s was t h e c a s e f o r t h e f l o o r ) i n t h e c e n t r e of t h e e a s t e r n s e c t i o n of t h e powerhouse ( l o c a t i o n s 3 and 4 ) r a t h e r t h a n a t t h e e a s t e r n end ( l o c a t i o n s 1 and 2).

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The minimum broadband p i l e a m p l i t u d e s measured a t t h e powerhouse were o b t a i n e d on p i l e s i n t h i s s e c t i o n of t h e powerhouse. These were 0.27% g r a v i t y i n t h e v e r t i c a l d i r e c t i o n on p i l e s 1 and 2, 0.49% g r a v i t y i n t h e h o r i z o n t a l d i r e c t i o n on p i l e s 1, 3 and 4, and 0.39% g r a v i t y i n t h e a x i a l d i r e c t i o n on p i l e 4.

Comparison of f l o o r and p i l e r e s p o n s e : A t s i x of t h e e i g h t l o c a t i o n s i n t h e e a s t e r n s e c t i o n of t h e powerhouse, measurements were t a k e n on t h e c o n c r e t e f l o o r s l a b and on t h e p i l e d i r e c t l y b e n e a t h t h e f l o o r ( F i g . 4 ) . I n t h e h o r i z o n t a l and a x i a l d i r e c t i o n s , n o t i c e a b l e a m p l i t u d e d i f f e r e n c e s

between t h e p i l e and t h e f l o o r o c c u r r e d a t a l l l o c a t i o n s f o r o n e - t h i r d o c t a v e band f r e q u e n c i e s g r e a t e r t h a n 160 Hz. A t some l o c a t i o n s , s u c h a s 7 , t h e d i f f e r e n c e s began a t band f r e q u e n c i e s a s low a s 50 Hz ( F i g . 32).

R e g a r d l e s s of where t h e d i f f e r e n c e s commenced, t h e p i l e r e s p o n s e above t h i s f r e q u e n c y was l a r g e r t h a n t h e f l o o r r e s p o n s e and, s i m i l a r t o t h e o t h e r two monitored s t r u c t u r e - p i l e systems a t t h e powerhouse ( i . e . , c r a d l e - p i l e s y s t e m and w e s t e r n s e c t i o n of powerhouse), was i n d i c a t i v e of l a t e r a l modes w i t h mode s h a p e s c o n s i s t i n g p r i m a r i l y of p i l e r e s p o n s e . On t h e o t h e r hand, o n e - t h i r d o c t a v e band f l o o r and p i l e s p e c t r a i n t h e v e r t i c a l d i r e c t i o n a t e a c h l o c a t i o n were q u i t e s i m i l a r i n s h a p e and a m p l i t u d e t h r o u g h o u t most of t h e f r e q u e n c y bandwidth (0-315 Hz).

A s a r e s u l t of t h e s p e c t r a l d i f f e r e n c e s i n t h e h o r i z o n t a l and a x i a l d i r e c t i o n s , broadband a m p l i t u d e s i n t h e two l a t e r a l d i r e c t i o n s were

g e n e r a l l y l a r g e r on t h e p i l e s t h a n on t h e f l o o r ( T a b l e 8). However, i n t h e v e r t i c a l d i r e c t i o n s i m i l a r s p e c t r a l s h a p e s produced broadband a m p l i t u d e s on t h e f l o o r t h a t were s l i g h t l y l a r g e r t h a n p i l e a m p l i t u d e s a t a l l l o c a t i o n s . Except f o r t h e h o r i z o n t a l d i r e c t i o n a t l o c a t i o n

7 ,

p i l e / f l o o r broadband a m p l i t u d e r a t i o s i n t h e two l a t e r a l d i r e c t i o n s and f l o o r / p i l e a m p l i t u d e r a t i o s i n t h e v e r t i c a l d i r e c t i o n were between 0.9 and 1.5. I n t h e

h o r i z o n t a l d i r e c t i o n a t l o c a t i o n 7 , t h e p i l e / f l o o r a m p l i t u d e r a t i o was 3.7. F r e e s t a n d i n g ( u n l o a d e d ) p i l e R e s u l t s of t h e measurements t a k e n on t h e f r e e s t a n d i n g p i l e l o c a t e d on t h e s o u t h s i d e of t h e powerhouse a p p r o x i m a t e l y 11 m from t h e g e n e r a t o r , c r a d l e and 2 m from t h e n e a r e s t p i l e s u p p o r t i n g t h e e a s t e r n s e c t i o n of t h e powerhouse ( F i g . 4 ) a r e g i v e n i n T a b l e 9. Broadband a m p l i t u d e s on t h e f r e e s t a n d i n g p i l e were s m a l l e r t h a n t h e minimum broadband p i l e a m p l i t u d e s r e c o r d e d a t t h e powerhouse w i t h t h e

g e n e r a t o r on ( T a b l e 1 0 ) . I n c ~ m p a r i s o n to t h e n e a r e s t monitored p i l e under e a c h of t h e t h r e e s t r u c t u r e - p i l e systems i n v e s t i g a t e d a t t h e powerhouse, t h e broadband a m p l i t u d e s on t h e f r e e s t a n d i n g p i l e were f r o m 5 t o 250 times

s m a l l e r i n t h e two l a t e r a l d i r e c t i o n s and from 5 t o 1 2 5 t i m e s s m a l l e r i n t h e v e r t i c a l d i r e c t i o n ( T a b l e 1 0 ) . It i s a l s o e v i d e n t f r o m T a b l e 1 0 t h a t f o r

t h e powerhouse t h e d e g r e e of s t r u c t u r a l i s o l a t i o n of a s t r u c t u r e - p i l e s y s t e m f r o m a s o u r c e of v i b r a t i o n ( o r t h e d e g r e e of c o n n e c t i v i t y t o i t ) was more

i m p o r t a n t i n d e t e r m i n i n g t h e a m p l i t u d e s of p i l e v i b r a t i o n t h a n was t h e d i s t a n c e of t h e p i l e from t h e s o u r c e . P i l e l o c a t i o n 7 i n t h e e a s t e r n s e c t i o n of t h e powerhouse, which was more s t r u c t u r a l l y i s o l a t e d (no d i r e c t structural l i n k s ) f r o m t h e g e n e r a t o r t h a n p i l e l o c a t i o n 2 i n t h e w e s t e r n s e c t i o n , had s u b s t a n t i a l l y s m a l l e r a m p l i t u d e s even though p i l e

7

was c l o s e r t o t h e g e n e r a t o r . The same can be s a i d f o r t h e f r e e s t a n d i n g p i l e when

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compared t o e i t h e r p i l e l o c a t i o n 1 o r 4 i n t h e e a s t e r n s e c t i o n of t h e powerhouse. Ambient a c c e l e r a t i o n a m p l i t u d e s : g e n e r a t o r o f f V i b r a t i o n measurements a t e i g h t l o c a t i o n s ( n i n e a c c e l e r o m e t e r s ) were t a k e n w i t h t h e g e n e r a t o r t u r n e d o f f i n o r d e r t o a s c e r t a i n ambient a c c e l e r a t i o n a m p l i t u d e s t h r o u g h o u t t h e powerhouse. U n f o r t u n a t e l y , n o t a l l t h e mechanical equipment a n c i l l a r y t o t h e g e n e r a t o r c o u l d be t u r n e d o f f w i t h t h e g e n e r a t o r . S e v e r a l pumps and compressors a s s o c i a t e d w i t h c o o l i n g t h e KV 16 e n g i n e a f t e r shut-down, and l o c a t e d i n t h e w e s t e r n s e c t i o n of t h e powerhouse a t t h e s o u t h end of t h e g e n e r a t o r , c o n t i n u e d t o o p e r a t e d u r i n g t h e s h o r t t i m e i n t e r v a l t h a t t h e g e n e r a t o r was o f f . The ambient v i b r a t i o n measurements, t h e r e f o r e , c o n t a i n t h e e f f e c t s of t h i s mechanical equipment.

Broadband and o n e - t h i r d o c t a v e band a m p l i t u d e s f o r t h e n i n e ambient a c c e l e r o m e t e r r e c o r d s a r e g i v e n i n T a b l e 11. Of t h e s e , f i v e were on t h e c r a d l e - - p i l e s y s t e m s u p p o r t i n g t h e g e n e r a t o r , two on p i l e s s u p p o r t i n g t h e w e s t e r n s e c t i o n and two on p i l e s s u p p o r t i n g t h e e a s t e r n s e c t i o n of t h e powerhouse. Broadband a m p l i t u d e s a t a l l l o c a t i o n s were q u i t e low, between 0.062% and 0.83% g r a v i t y , w i t h t h e lower a m p l i t u d e s o b t a i n e d p r i m a r i l y on t h e p i l e s s u p p o r t i n g t h e g e n e r a t o r c r a d l e .

Broadband a m p l i t u d e s o b t a i n e d a t t h e same a c c e l e r o m e t e r l o c a t i o n s w i t h t h e g e n e r a t o r o p e r a t i n g a r e a l s o g i v e n i n T a b l e 11. Average on/off

a m p l i t u d e r a t i o s were 430 f o r p i l e s under t h e g e n e r a t o r c r a d l e and 1 0 and 5 r e s p e c t i v e l y f o r p i l e s s u p p o r t i n g t h e w e s t e r n and e a s t e r n s e c t i o n s of t h e powerhouse. Obviously, t h e g e n e r a t o r produced s i z e a b l e v i b r a t i o n a m p l i t u d e s w i t h i n i t s s u p p o r t i n g c r a d l e - p i l e system. On t h e o t h e r hand, v i b r a t i o n a m p l i t u d e s i n t h e e a s t e r n s e c t i o n w i t h no d i r e c t s t r u c t u r a l t i e s t o t h e c r a d l e - p i l e s y s t e m and l i n k e d o n l y t o t h e w e s t e r n s e c t i o n of t h e powerhouse v i a t h e s t e e l s u p e r s t r u c t u r e , were c o n s i d e r a b l y l e s s a f f e c t e d by t h e

p r e s e n c e of t h e g e n e r a t o r . The s l i g h t l y l a r g e r i n c r e a s e i n t h e v i b r a t i o n environment of t h e w e s t e r n s e c t i o n of t h e powerhouse a p p e a r s t o have been caused by d i r e c t c o n t a c t of t h i s s e c t i o n w i t h t h e c r a d l e - p i l e s y s t e m r a t h e r t h a n by ground t r a n s m i s s i o n of t h e v i b r a t i o n s between t h e two s y s t e m s .

SUMMARY AND CONCLUSIONS

( 1 ) A c c e l e r a t i o n measurements a t v a r i o u s l o c a t i o n s i n t h e I n u v i k powerhouse showed t h a t t h e v i b r a t i o n environment a t t h e powerhouse was c o n s i d e r a b l y a f f e c t e d by t h e o p e r a t i o n of t h e main d i e s e l g e n e r a t o r .

( 2 ) The a m p l i t u d e of t h e f o r c e d v i b r a t i o n s a t a monitored l o c a t i o n was dependent on t h e s t r u c t u r a l c o n n e c t i v i t y of t h a t l o c a t i o n t o t h e

g e n e r a t o r - c r a d l e s y s t e m and i t s d i s t a n c e from t h a t system. D e c r e a s i n g t h e d e g r e e of c o n n e c t i v i t y o r i n c r e a s i n g t h e d i s t a n c e d e c r e a s e d t h e amplitude.

( 3 ) P i l e s underwent comparable a c c e l e r a t i o n a m p l i t u d e s i n a l l t h r e e t r a r l s l a t i o n a l d i r e c t i o n s , i n d i c a t i n g t h a t l a t e r a l a s w e l l a s a x i a l v i b r a t i o n s s h o u l d be c o n s i d e r e d i n t h e d e s i g n of p i l e s i n p e r m a f r o s t .

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( 4 ) Although n o i n f o r m a t i o n i s a v a i l a b l e c o n c e r n i n g t h e performance of t h e p i l e f o u n d a t i o n s of t h e powerhouse, l a b o r a t o r y s t u d i e s i n d i c a t e t h a t t h e dynamic stresses t r a n s m i t t e d t o t h e a d f r e e z i n g i n t e r f a c e between a p i l e and f r o z e n s o i l c o u l d enhance t h e d i s p l a c e m e n t r a t e of t h e p i l e i n s o i l , and t h e r e b y s h o r t e n t h e s e r v i c e l i f e of a s t r u c t u r e b a s e d on a s p e c i f i e d a l l o w a b l e s e t t l e m e n t . A knowledge of t h e a m p l i t u d e s and f r e q u e n c i e s of v i b r a t i o n s l i k e l y t o r e s u l t f r o m o p e r a t i o n of l a r g e v i b r a t i n g o r r o t a t i n g machinery i s e s s e n t i a l f o r t h e s a f e d e s i g n of p i l e f o u n d a t i o n s i n p e r m a f r o s t

.

ACKNOWLEDGEMENTS

Before measurements were conducted a t t h e I n u v i k powerhouse,

d i s c u s s i o n s were h e l d a t t h e Edmonton o f f i c e s of t h e Northern Canada Power Commission w i t h t h e l a t e M r . J. Long, General Manager, M r . J.D. A l l a n , A s s i s t a n t General Manager, O p e r a t i o n s and E n g i n e e r i n g , and

M r . D.I. McGuinness, E n g i n e e r i n g Manager. The a u t h o r s wish t o t h a n k t h e s e gentlemen f o r p r o v i d i n g t h e n e c e s s a r y background i n f o r m a t i o n and t e c h n i c a l drawings. A t t h e I n u v i k powerhouse, Mr. J.H. Greenwood, Area

S u p e r i n t e n d e n t , and M r . D.H. Musselwhite, A s s i s t a n t S u p e r i n t e n d e n t , were most h e l p f u l i n making t h e n e c e s s a r y a r r a n g e m e n t s f o r c o n d u c t i n g t h e s t u d y . The a s s i s t a n c e and c o o p e r a t i o n r e c e i v e d from a l l NCPC s t a f f i s g r a t e f u l l y acknowledged. The a u t h o r s would a l s o l i k e t o t h a n k Mr. J.C. P l u n k e t t , G e o t e c h n i c a l S e c t i o n , D i v i s i o n of B u i l d i n g R e s e a r c h , N a t i o n a l R e s e a r c h C o u n c i l Canada, f o r h i s i n v a l u a b l e t e c h n i c a l a s s i s t a n c e d u r i n g t h e measurement program a t t h e I n u v i k powerhouse. REFERENCES

( 1 ) Weaver, J.S. and Morgenstern, N.R. (1981) " P i l e Design i n P e r m a f r o s t . " Canadian G e o t e c h n i c a l J o u r n a l , Vol. 18, No. 3 , p. 357-370.

( 2 ) Parameswaran, V.R. (1982) "Displacement of P i l e s Under Dynamic Loads i n Frozen S o i l s . " The Roger J.E. Brown Memorial Volume, P r o c e e d i n g s F o u r t h Canadian P e r m a f r o s t Conference, C a l g a r y , A l b e r t a , March 2-6, 1981,

p. 555-559.

( 3 ) Parameswaran, V.R. (1984) " E f f e c t of Dynamic Loads on P i l e s i n Frozen S o i l s . " P r o c e e d i n g s of t h e T h i r d I n t e r n a t i o n a l S p e c i a l t y Conference on Cold Regions E n g i n e e r i n g , Edmonton, A l b e r t a , A p r i l 1984, Vol. I ,

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TABLE 1

One-Third Octave Band RMS Acceleration Amplitudes on the Generator, % Gravity, 90th P e r c e n t i l e

Generator Location

B & K RACAL B & K

Tape Recorder Run No. 1 1 3 1 6 1 1 3 Direction* Frequency V H A V H V

H

A Broadband 2.5 3.15 4.0 5.0 6.3 8.0 10.0 12.5 16 20 2 5 31.5 4 0 50 6 3 80 100 125 160 200 2 50 315 400 500 630

*Measurements were not taken i n the a x i a l d i r e c t i o n a t l o c a t i o n 11, s i n c e the accelerometer could not be properly secured t o generator.

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TABLE 2

One-Third Octave Band RMS A c c e l e r a t i o n Amplitudes on t h e C o n c r e t e C r a d l e of t h e G e n e r a t o r , % G r a v i t y , 9 0 t h P e r c e n t i l e

G e n e r a t o r C r a d l e L o c a t i o n

RACAL RACAL RACAL RACAL

Tape Recorder Run No. 1 6 3 1 2 6 25 1 1 6 3 D i r e c t i o n * Frequency V H A V H A V V H A Broadband 30 7.6 12 3 0 18 2 0 17 11 4.2 8.6 2.5 0.039 0.022 0.019 0.039 0.044 0.039 0.039 0.039 0.022 0.019 3.15 0.039 0.022 0.019 0.039 0.039 0.039 0.039 0.039 0,022 0.019 4.0 0.055 0.043 0.11 0.039 0.069 0.087 0.039 0.039 0.022 0.069 5.0 0.039 0.027 0.069 0.039 0.044 0.062 0.039 0.039 0.022 0.043 6.3 0.049 0.027 0.043 0.055 0.039 0.039 0.039 0.039 0.022 0.027 r 0.98 0.49 0.44 C- 8.0 0.77 0.35 0.55 0.22 0.31 0.22 0.11 10.0 0.39 0.15 0.31 0.49 0.22 0.22 0.11 0.16 0.097 0.087 12.5 0.28 0.15 0.14 0.39 0.11 0.39 0.077 0.077 0.11 0.17 16 0.78 0.39 0.39 0.35 0.20 0.77 0.44 0.35 0.11 0.35 I 2 0 0.62 0.69 0.55 0.62 0.55 0.98 1.4 1.2 0.22 0.35 25 2.5 1.2 2.2 1.4 1.4 3.9 3.5 2.2 0.35 0.49 31.5 4.9 0.69 0.97 7.8 1.5 14 4.4 2.5 1.2 1.1 40 4.4 1.7 1.1 4.9 3.1 2.7 6.2 3.1 1.7 0.87 50 4.4 1.9 1.5 6.9 2.7 1.7 8.7 6.9 1.2 1.5 6 3 6.9 1.9 2.7 12 3.9 4.9 7.7 4.9 1.4 3.1 8 0 12 1.9 4.3 12 4.4 5.5 6.9 3.5 1.1 2.7 100 19 2.4 6.1 19 6.2 6.2 4.9 3.9 1.2 4.3 125 1 1 1.7 3.9 9.8 5.5 3.5 3.9 2,7 1.9 3.1 160 8.7 1.9 5.5 6.2 4.4 5.5 1.9 1.5 1.1 3.5 200 8.7 3.1 4.3 6.2 7.7 3.5 2.2 0.77 0.69 2.4 2 50 3.9 2.2 3.5 7.7 6.9 3.5 3.5 0.77 0.97 2.7 315 2.5 3.5 2.7 6.9 6.9 2.7 1.4 0.77 1.7 3.1

*No measurements were t a k e n i n t h e h o r i z o n t a l and a x i a l d i r e c t i o n s a t l o c a t i o n 3 s i n c e i t was f e l t t h a t t h e r e s u l t s would be s i m i l a r t o t h o s e o b t a i n e d a t l o c a t i o n 4.

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TABLE 3

One-Third Octave Band RMS Acceleration Amplitudes on P i l e s Supporting the Generator Cradle,

X Gravity, 90th Percentile P i l e Location 5 6 RACAL RACAL Tape Recorder Run No. 2 4 26 2 5 2 4 2 6 2 5 Direction Frequency V H A