Measurements of wind induced displacements and accelerations of a 57 storey building in Toronto, Canada

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Measurements of wind induced displacements and accelerations of a

57 storey building in Toronto, Canada

Dalgliesh, W. A.; Rainer, J. H.

https://publications-cnrc.canada.ca/fra/droits

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National Research

Conseil national

I*

CoundlCanada

d e r e c m c a n a d a

i

MEASUREMENTS OF

WIND INDUCED Df SPLACEMENTS

AND ACCELERATIONS OF A

57aSTOREY BUILDING

IN

TORONTO, CANADA

by W.A. Dalgliesh and

J.H.

Rainer

Reprinted

from

Proceedings, 3rd Colloquium on Industrial Aerodynamics held in Aachen, Germany, 14

-

16 June 1978

Buildings Aerodynamics, Part 2,

P.

67

-

78

DBR

Paper

No.

822

Division of Building Research

Ce r a p p o r t p r g s e n t e d e s m e s u r e s r e p r g s e n t a t i v e s d e s mouvements c a u s k s p a r l e vent d a n s l e c a s de 116difice de l a Banque de c o m m e r c e de T o r o n t o , Canada, e t f a i t p a r t i e d'un p r o j e t long t e r m e visant

>

Cvaluer l a validit6 d e s techniques c o u r a n t e s d e s e s s a i s e n souf- f l e r i e dans l a conception de bztiments. L e s proc6di.s c o u r a n t s d e conception 6tant fondks principalement s u r l e s r k s u l t a t s d e s e x p g r i - e n c e s e n soufflerie, une c e r t a i n e v k r i f i c a t i o n d a n s l e s conditions d ' u t i l i s ation s'av'ere e s s e n t i e l l e . L e r a p p o r t s e t e r m i n e p a r une &valuation p r e l i m i n a i r e d e s c o r r k l a t i o n s qui existent e n t r e l e s mouvements m e s u r k s pour l e bztiment, ceux qui s o n t prCvus d'apr'es l e s e s s a i s e n soufflerie effectu6s e n r a p p o r t avec l a conception d u b2timent e t l e s dkplacements e n r e g i s t r k s p a r l e procCdk dktaillk contenu dans l e Supplkment no 4 d u Code national d u b s t i m e n t d u

MEASUREMENTS OF WIND INDUCED DISPLACEMENTS

AND ACCELERATIONS OF A 57-STOREY BUILDING

IN TORONTO, CANADA

b

Y

W.A. Dalgliesh* and

J.H.

Rainer*

SUMMARY

T h i s r e p o r t p r e s e n t s t y p i c a l measurements of wind-induced movements i n t h e Bank of Commerce Building i n Toronto, Canada, p a r t o f a long- term p r o j e c t t o a s s e s s t h e v a l i d i t y of c u r r e n t wind t u n n e l t e c h n i q u e s i n b u i l d i n g d e s i g n . Since c u r r e n t design procedures a r e based mainly on r e s u l t s from wi,ld t u n n e l experiments, some f u l l - s c a l e v e r i f i c a t i o n

is deemed e s s e n t i a l . The r e p o r t concludes with a p r e l i m i n a r y assessment of t h e c o r r e l a t i o n s between measured b u i l d i n g movements, t h o s e p r e d i c t e d from wind tunnel t e s t s performed f o r t h e b u i l d i n g

.

d e s i g n , and displacements computed by t h e d e t a i l e d procedure c o n t a i n e d i n Supplement No. 4 t o t h e National Building Code of Canada, 1977 E d i t i o n .

DESCRIPTION OF BUILDING AND INSTRUMENTATION

C o m e r c e Court West, a 5 7 - s t o r e y o f f i c e s t r u c t u r e ,

i s

239

m

high, and 36

m

x 70 m i n p l a n . Wind loads a r e r e s i s t e d by frame a c t i o n through moment c o n n e c t i o n s and s p a n d r e l s i n t h e long d i r e c t i o n (N-S) and by a combination of framing and c o r e b r a c i n g i n t h e s h o r t d i r e c t i o n (E-W)

.

*Division of Building Research, National Research Council of Canada, Ottawa, Canada, KIA OR6

S i n c e e a r l y 1373, wind p r e s s u r e s have been monitored on f o u r l e v e l s , 102 m,

13s m, 166 m and 202 v, a s well a s s t r a i n s on s e l e c t e d s p a n d r e l s and columns a t t h e 51 m l e v e l , where a s e c t i o n change would o p t i m i z e t h e s e n s i t i v i t y of s t r a i n

measurements. The l o c a t i o n s of e i g h t p r e s s u r e t r a n s d u c e r s a t each l e v e l and t h e s t n i n gauges a r c shown i n Fig. 1 .

I n Fhrch 1975, t h r e e accelerometers were placed a t 202 m, and i n J u l y 1977 two morc were i n s t a l l e j a t t h e 234 m l e v e l along with a n a p p a r a t u s t o measure d i s p l a c e - ments r e l a t i v e t o a l a s e r beam p r o j e c t e d from t h e bottom o f t h e e l e v a t o r s h a f t a t t h e -15 m l e v e l . F i g u r e 2 shows t h e displacement s e n s o r c o n s i s t i n g of two p a i r s of p h o t o c e l l s t h a t a r e "locked" t o t h e s t a t i o n a r y l a s e r beam by means o f servomotors while t h e r e s t o f t h e instrument moves with t h e b u i l d i n g .

A t o t a l of 48 channels, r e p r e s e n t i n g wind p r e s s u r e s , s t r a i n s , a c c e l e r a t i o n s , displacements, and wind speed and d i r e c t i o n a r e sampled 20 times p e r second t o r e c o r d , on magnetic t a p e , sums, sums of s q u a r e s and extremes f o r five-minute

p e r i o d s , a t h o u r l y i n t e r v a l s . In a d d i t i o n t o t h e s e hourly summary r e c o r d s , any mean wind speed exceeding 18.5 m / s t r i g g e r s c o n t i n u o u s r e c o r d s 3 5 min long, w i t h each channel sampled two t i m e s p e r second.

TYPICAL TIME HISTORIES

F i g u r e s 3 and 4 a r e time h i s t o r i e s taken d u r i n g a wind from

E-N-E

a t 18.4 m/s.

A weighted average of t h e n e t p r e s s u r e d i f f e r e n c e s i n t h e E-W d i r e c t i o n a t t h e 202 m l e v e l i s g i v e n i n Fig. 3a. The r e s u l t i n g E-W displacement a t t h e 234

m

l e v e l (machine room) is shown i n F i g . 3b; t h e same r e c o r d , law-pass f i l t e r e d a t ' 0.05 Hz ( t h e q u a s i - s t a t i c p o r t i o n ) , i s p r e s e n t e d i n Fig. 3c and corresponds t o t h e major p r e s s u r e . v a r i a t i o n s i n Fig. 3a. The f i l t e r e d t i m e h i s t o r i e s were o b t a i n e d by computing t h e d i s c r e t e F o u r i e r Transform of t h e s i g n a l s , r e j e c t i n g a 1 1 frequency components o u t s i d e t h e d e s i r e d frequency band, and i n v e r t i n g back t o t h e time domain. The f i n a l one f i f t h of t h e c a l c u l a t i o n r e c o r d l e n g t h was t a p e r e d o f f t o

z e r o w i t h a c o s i n e w e i g h t i n g f u n c t i o n t o p r o v i d e a n i n v e r s e d f i l t e r e d s i g n a l w i t h no d i s c e r n i b l e l e a k a g e .

The a s s o c i a t e d p l o t s o f p r e s s u r e , d i s p l a c e m e n t a n d f i l t e r e d q u a s i - s t a t i c

d i s p l a c e m e n t f o r t h e N-S d i r e c t i o n a r e p r e s e n t e d i n F i g s . 4 a , b and c , r e s p e c t i v e l y . Again t h e r e i s o v e r - a l l agreement between p r e s s u r e and q u a s i - s t a t i c d i s p l a c e m e n t s .

F i g u r e 4d shows t h e mean d i f f e r e n c e o f s t r a i n s a t l o c a t i o n s 815 and 818 on t h e s p a n d r e l beams ( F i g . 1 ) . T h i s t r a c e a g r e e s v e r y c l o s e l y w i t h t h e N-S d i s p l a c e m e n t i n F i g . 4 b . S i m i l a r c l o s e agreements were found between t h e E-W d i s p l a c e m e n t and t h e mean o f s t r a i n s a t l o c a t i o n s 809 and 814 on t h e i n t e r i o r f l a n g e s of t h e columns ( F i g . 1 ) . The N-S a c c e l e r a t i o n on t h e 5 0 t h f l o o r is p r e s e n t e d i n F i g . 4 e .

A p l o t o f t h e d i s p l a c e m e n t components i n t h e h o r i z o n t a l p l a n e f o r a 1 min p o r t i o n o f r e c o r d

HW

861 is shown i n F i g . 5 . T h i s method of p r e s e n t i n g t h e r e s u l t s d e m o n s t r a t e s t h e s p a t i a l v a r i a t i o n i n t h e b u i l d i n g movement which i s n o t r e a d i l y a p p a r e n t i n t h e d i s p l a y o f t h e s e p a r a t e d a x i a l components shown i n F i g s . 3b and 4b.

The power s p e c t r u m i n F i g . 6 was formed by a v e r a g i n g f o u r s u c c e s s i v e s p e c t r a o f N-S a c c e l e r a t i o n and shows a number o f c l o s e l y s p a c e d f r e q u e n c y components t h a t a r e a t t r i b u t e d t o a n a m p l i t u d e dependence o f t h e modal f r e q u e n c y . T h i s i s f u r t h e r s u p p o r t e d by t h e d a t a i n T a b l e 1, which g i v e s dominant f r e q u e n c i e s and

c o r r e s p o n d i n g wind s p e e d . A d e c r e a s e i n f r e q u e n c i e s f o r a l l t h r e e l o w e s t modes i s e v i d e n t f o r i n c r e a s i n g wind s p e e d s .

The v a r i a b i l i t y o f n a t u r a l f r e q u e n c i e s c a u s e d problems i n e s t i m a t i n g modal damping v a l u e s . The widening o f r e s o n a n c e p e a k s a s a r e s u l t o f f r e q u e n c y c h a n g e s would i n c r e a s e t h e computed damping v a l u e s u n j u s t i f i a b l y . C l o s e l y s p a c e d

r e s o n a n c e p e a k s produced a t y p i c a l " b e a t i n g " o f t h e e n v e l o p e of peak a m p l i t u d e s i n t h e a u t o c o r r e l a t i o n f u n c t i o n . The o n l y s a t i s f a c t o r y damping c a l c u l a t i o n s o f a r h a s y i e l d e d a v a l u e o f one p e r c e n t o f c r i t i c a l , b u t f u r t h e r i n v e s t i g a t i o n i s u n d e r way.

TABLE 1

V a r i a t i o n s o f Modal F r e q u e n c i e s w i t h Wind Speed

Frequency o f Lowest Mode, Hz

Wind Speed, m/s

Record No. (averaged o v e r 35 min) D i r e c t i o n N-S E-W T o r s i o n

I

t i W 875 8 . 2 S-W 0.139 0.139 0.180

11W 861 18.4 E-N-E 0.125 0.125 0.174

S-W

I

I I W 8 8 3 30.9 S-W 0.117 0.118 0.165

DISCUSSION OF PROTOTYPE MEASUREMENTS

I

A comparison of t h e d i s p l a c e m e n t r e s u l t s w i t h t h e p r e s s u r e s shows a q u a l i t a t i v e

I

agreement w i t h major b u i l d i n g motion i n b o t h t h e E-W and N-S a x e s . Some d i f f e r e n c e s

I

c a n b e e x p e c t e d , however, s i n c e t h e p r e s s u r e s d i s p l a y e d are t h e n e t r e s u l t a n t of t h e weighted a v e r a g e from t r a n s d u c e r s a t t h e 202 m l e v e l on1 y. A s t h e p r e s s u r e s a r e n o t f u l l y c o r r e l a t e d a c r o s s t h e w i d t h and t h e h e i g h t o f t h e b u i l d i n g , some e r r o r s are i n t r o d u c e d by t h e a v e r a g i n g scheme.

The d i s p l a c e m e n t measurements a r e t h e m s e l v e s s u b j e c t t o some e r r o r s ; among them a r e b a s e r o t a t i o n and t h e r m a l i n t e r f e r e n c e o f t h e laser beam. The amount o f b a s e r o t a t i o n is t h o u g h t t o b e v e r y small s i n c e t h e b u i l d i n g is founded on a competent s h a l e . The f i l t e r e d s i g n a l s a l s o show t h a t t h e r e s o l u t i o n o f t h e d i s p l a c e m e n t measuring d e v i c e i s b e t t e r t h a n 2 ntn, which i n c l u d e s d e v i a t i o n s of t h e l a s e r beam caused by t h e r m a l a i r c u r r e n t s .

I

The major e x c u r s i o n s a n d t h e s t a n d a r d d e v i a t i o n s o f t h e f i l t e r e d f i r s t mode

I

d i s p l a c e m e n t s and a c c e l e r a t i o n s were compared t o check t h e c o n s i s t e n c y of t h e

I

measurements a n d were found t o a g r e e w i t h i n 6 p e r c e n t . U n f o r t u n a t e l y , i n a d d i t i o n

I

t o r e g i s t e r i n g a c c e l e r a t i o n s , t h e accelerometers responded t o a sma 1 1 b u t as y e t undetermined local r o t a t i o n a b o u t a h o r i z o n t a l a x i s .

FULL-SCALE AND MODEL DISPLACEMENTS COMPARED TO BUILDING CODE PREDICTIONS

I t i s expected t h a t continuous monitoring of t h e b u i l d i n g w i l l e v e n t u a l l y p r o v i d e enough r e c o r d s of s t r o n g winds from each of s e v e r a l d i r e c t i o n s t o p e n n i t a thorough assessment o f t h e accuracy of displacements p r e d i c t e d from wind t u n n e l t e s t s and t h e a n a l y t i c a l procedures r e f e r r e d t o i n b u i l d i n g c o d e s . For example, d a t a logged from l a t e September 1977 t o t h e end of January 1978 i n c l u d e d 68 segments of f i v e - m i n u t e d u r a t i o n f o r which t h e mean r e f e r e n c e p r e s s u r e a t t h e

2

anemometer (286 m above ground) exceeded 50 N/m w i t h t h e wind d i r e c t e d

approximately p e r p e n d i c u l a r t o t h e e a s t f a c e of t h e b u i l d i n g . T h i s

set

o f 68 segments was supplemented by 16 two-minute segments t a k e n from a s i n g l e windstorm

2

from t h e e a s t when t h e mean r e f e r e n c e p r e s s u r e ranged from 250 t o 450 N/m

,

t o form t h e b a s i s f o r a f i r s t comparison with wind t u n n e l d a t a and w i t h c a l c u l a t i o n s of t h e

d e t a i l e d procedure of Supplement No. 4 t o t h e National Building Code of Canada. 1

The wind t u n n e l t e s t s f o r t h e b u i l d i n g design provided mean and f l u c t u a t i n g

displacements f o r 2 3 wind d i r e c t i o n s , a t f o u r d i f f e r e n t wind The lowest

speed, when converted t o a mean r e f e r e n c e p r e s s u r e a t 286

m

f o r t h e fundamental 2

f r e q u e n c i e s of t h e a c t u a l b u i l d i n g , r e p r e s e n t e d 360 N/m f o r along-wind and 460

L

N/m f o r across-wind motion. The d i f f e r e n c e a r i s e s because t h e r a t i o s of E-W t o N-S f r e q u e n c i e s were n o t t h e same i n model and p r o t o t y p e . No c o r r e c t i o n was made f o r e i t h e r damping o r b u i l d i n g d e n s i t y .

The d e t a i l e d procedure i n Supplement No. 4 f o r c a l c u l a t i n g along-wind and across-wind a c c e l e r a t i o n s i n c l u d e s a n e x p r e s s i o n f o r displacement i n terms of l a t e r a l loading, fundamental frequency i n bending, bui l d i n g dimensions and d e n s i t y ; moreover, t h e r a t i o of s t a n d a r d d e v i a t i o n of along-wind displacement t o mean

displacement forms p a r t o f t h e computation o f t h e g u s t e f f e c t f a c t o r . T h i s p e r m i t t e d a t h r e e - f o l d comparison between o b s e r v a t i o n s and computed displacements a s shown i n F i g s . 7a, b , c : along-wind mean, along-wind s t a n d a r d d e v i a t i o n and across-wind s t a n d a r d d e v i a t i o n of displacement.

l'hc wind t u n n e l mean and s t a n d a r d d e v i a t i o n of along-wind d i s p l a c e m e n t s l i e s l i g h t l y above t h e f u l l - s c a l e measurements ( F i g s . 7a and 7b), whereas t h e s t a n d a r d J c v i n t i o n o f a c r o s s - w i n d d i s p l a c e m e n t f o r t h e wind t u n n e l r e s u l t i s c l o s e t o t h e c c n t r a l tendency of t h e f u l l - s c a l e measurements ( F i g . 7 c ) . The d i s p l a c e m e n t s computed a c c o r d i n g t o Supplement No. 4, on t h e o t h e r hand, a g r e e well w i t h t h e

n long-wind measurements and a r e somewhat h i g h i n t h e across-wind c a s e .

CONC LUS ION

The c o n s i s t e n c y of time h i s t o r i e s r e c o r d e d by v a r i o u s t y p e s o f s e n s o r s g i v e s c o n f i d e n c e i n t h e methods employed a n d p o i n t s t o t h e p o s s i b l e u s e o f l e s s

c o m p l i c a t e d equipment f o r m o n i t o r i n g b u i l d i n g d i s p l a c e m e n t s a f t e r c a l i b r a t i o n by d i r c c t measurement. A t Commerce C o u r t , where f o r p r a c t i c a l p u r p o s e s moderate t o s t r o n g winds e x c i t e only t h e fundamental modes, t h e s t r a i n gauges a t t h e 5 2 m

l e v e l might b e c a l i b r a t e d t o g i v e an a d e q u a t e r e p r e s e n t a t i o n o f d i s p l a c e m e n t a t t h e 234 m l e v e l , p r o v i d e d t h e s t r o n g c o r r e l a t i o n between s t r a i n a n d d i s p l a c e m e n t demonstrated s o f a r i s m a i n t a i n e d f o r a wide r a n g e o f wind s p e e d s a n d d i r e c t i o n s .

Good agreement was found between o b s e r v e d d i s p l a c e m e n t s and t h o s e c a l c u l a t e d a c c o r d i n g t o Supplement No. 4 - o f t h e N a t i o n a l B u i l d i n g Code o f Canada, p r o v i d e d t h a t t h e o b s e r v e d n a t u r a l f r e q u e n c i e s of t h e b u i l d i n g were u s e d i n t h e

c a l c u l a t i o n s . Wind t u n n e l d a t a , which had been a d j u s t e d f o r b u i l d i n g f r e q u e n c y , c o r r e l a t e d w e l l w i t h t h e observed motion.

A c c u r a t e e s t i m a t e s o f f r e q u e n c y a r e e s s e n t i a l f o r t h e s u c c e s s o f any

p r o c e d u r e f o r p r e d i c t i n g b u i l d i n g r e s p o n s e , and i t is i m p o r t a n t t h a t t h e v a l u e s used b e a p p l i c a b l e t o t h e wind speed o f i n t e r e s t . I n view o f t h e o b s e r v e d dependence o f b u i l d i n g f r e q u e n c y on wind speed, i t i s concluded t h a t b u i l d i n g s must b e monitored f o r a s wide a r a n g e o f wind c o n d i t i o n s as p o s s i b l e .

ACKNOWLEDGEMENTS

The a u t h o r s wish t o e x t e n d t h e i r s i n c e r e a p p r e c i a t i o n t o t h e f o l l o w i n g o r g a n i z a t i o n s and i n d i v i d u a l s : Canadian I m p e r i a l Bank o f Commerce, owners o f t h e b u i l d i n g ; C a r r u t h e r s and Wallace, s t r u c t u r a l e n g i n e e r s ; U n i v e r s i t y o f Western O n t a r i o Boundary Layer Wind Tunnel, wind t u n n e l c o n s u l t a n t s ; J . Templin, F

.

Hummel and R . Diment, D i v i s i o n o f B u i l d i n g Research, N a t i o n a l Research Council o f Canada. T h i s p a p e r i s a c o n t r i b u t i o n from t h e D i v i s i o n o f B u i l d i n g R e s e a r c h , N a t i o n a l Research C o u n c i l o f Canada, and i s - p u b l i s h e d w i t h t h e a p p r o v a l o f t h e D i r e c t o r of t h e D i v i s i o n .

REFERENCES

1 . Canada, A s s o c i a t e Conmittee on t h e N a t i o n a l B u i l d i n g Code. Supplement No. 4

t o t h e N a t i o n a l B u i l d i n g Code o f Canada, Comnentary B

-

Wind Loads, NRCC 15558- N a t i o n a l Research Council o f Canada, Ottawa, Canada, 1977.

2. Davenport, A . G . , M . Hogan and N. Isyumov. A Study o f Wind E f f e c t s on t h e Commerce C o u r t Tower, P a r t I , BLWT-7-69. U n i v e r s i t y o f Western O n t a r i o , London, O n t a r i o , Canada, November 1969.

MWUREMEh'TS OF WIND INDUCED DISPLACEMENTS

AND ACCELERATIONS OF A 57-STOREY BUILDING

IN

IDRONTO, CANADA

W .

A. Dalgliesh and J.H. Rainer

F

I GURE CAPTIONS

Fig. 1

Planviewof InstrumentationLayout

1

Fig.

2

Laser Tracking Device for Displacement Measurements

Fig.

3

Time llistories of E-W Building Response

a) Pressure at

202

m

level

b )

Displacement at

234

m level

c) Filtered displacement at

234

m level

Fig. 4

Time Histories of N-S Building Response

a) Pressure at

202

m level

b) Displacement at

234

m level

c) Filtered displacement at

234 m

level

d) Strain on spandrel beams at 51 m level

e)

Acceleration at

202

m level

Fig. 5

One-minute Path Folloued by Centre of Building (squares at 0.5 s

interva

1

s)

Fig.

6

Power Spectrum of N-S Acceleration at

202 m

level

1

Fig. 7

Comparison of Prototype and Wind Tunnel Model with Code Calculation

a) Mean of along-wind displacements

b) Standard deviation of along-wind displacements

c) Standard deviation of across-wind displacements

a ) P R E S S U R E A T 2 0 2 m L E V E t b ) D I S P L A C E M E N T A T 2 3 4 m L E V E L 0 1 2 3 4 5 6 7 8 9 1 0 1 1 1 2 T I M E , min C ) F I L T E R E D D I S P L A C E M E N T A T 2 3 4 m L E V E L F I G . 3 : E - W B U I L D I N G R E S P O N S E F O R W I N D F R O M E - N - E A T 1 8 . 4 m l s

a ) P R E S S U R E A T 202 m LEVEL 3 0 2 0 E _{1 0} E 0 - 1 0 - 2 0 b ) D I S P L A C E M E N T A T 234 m LEVEL W

-

1 0

I

-

20 C ) F I L T E R E D D I S P L A C E M E N T A T 234 m L E V E L

z

8

5

d l

S T R A I N S O N S P A N D R E L B E A M S A T 5 1 m L E V E L 0 1 2 3 4 5 _{6 7 8 9 1 0 1 1 1 2} T I M E , m i n

e l

A C C E L E R A T I O N A T 202.111 LEVEL F I G . 4: N - S B U I L D I N G R E S P O N S E F O R W I N D F R O M E - N - E A T 1 8 . 4 m l s

8 0 7 0 6 0 5 0 4 0 3 0 E-W D I S P L A C E M E N T . m m

F I G . 5: ONE M I N U T E PATH OF B U I L D I N G CENTRE ( S Q U A R E S AT 0.5 s I N T E R V A L S )

160 I I I I

-

0 0.05 0. 1 0 0. 15 0.20 - 4 0 _{0 1 0 0} 1 _{2 0 0} I _{3 0 0} I _{4 0 0} I _{5 0 0} FREQUENCY, Hz M E A N REF P R E S S U R E AT 2 8 6 m, N l m 2 F I G . 6: POWER SPECTRUM OF N - S A C C E L E R A T I O N AT 2 0 2 m LEVEL F I G . 7 a l M E A N OF A L O N G - W I N D D I S P L A C E M E N T S I I I 1 W I N D TUNNEL

-

-

M E A N REF PRESSURE AT 2 8 6 m, N l m 2 _{M E A N REF P R E S S U R E AT 2 8 6 m, N l m 2} F I G . 7b) S T A N D A R D D E V I A T I O N OF