Tornado damage at Blue Sea Lake and Nicabong, Quebec, July 1984

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Tornado damage at Blue Sea Lake and Nicabong, Quebec, July 1984

Allen, D. E.

BUILDING

RESEAL

ZH

NOTE

TOBNAW DAMAGE AT BLOB SEA _LAKE

Ab

D.E- Allen

Division of Building Research, Mational Research Council of Canada

National

I

+

rechmhes

TOWADO D W E AT BLUE SEA LAKE AND NLCMONG, QUEBEC, JULY 1984

by

D.E. Allen

A tornado followed a path about 150 km long from near Deep River,

Ontario, to near Mont Laurier, Quebec, causing severe damage at Nicabong (pop. 9 0 ) and Blue Sea Lake (pop. 2 8 0 ) , Quebec, and also caused damage at

LarCayamant (pop, 2 6 0 ) near Blue Sea Lake. One person died and t h i r t y were

i n j u r e d at Blue Sea Lake, eight people were injured at Nicabong and two at Laccayamant. There w a s approximately $2 million damage. Maximum wind

speeds of 160 kmlh were estimated by Environment Canada. me following

describes some impressions of a one-day v i s i t t o Blue Sea Lake and

Nicabong.

I Blue Sea Lake

As it approached the lake from the southwest, the tornado touched down

near the town of Blue Sea Lake and caused t h e following damage:

( I ) six small cottages (4 m x 4 m x 2.5 m) and a mobile home were pfcked u p

and l a n d e d in or near the lake (Fig.. I ) , with one person drowning and approximately 10 injured;

(2) three cottages (7 m x 7 m x 2.5 m) lost everything but the floor { F i g .

Z),

Figure 1. Blue Sea Lake. Only the foundatZoa s i l l s remain of small

I,I,

Figure 2. Blue Sea Lake. Only

'the

lake.

Ill

1

F i g u r e _- 3. Blue Sea Lake. Floor of a light fta* home d e p o - s i t e d 'downwind sf

(3) on t h e hill approaching the lake two light homes and their contents

w e r e p5cked up and scattered over a distance o f about 30 metres downwind

(Fig. 3), with ac least one person injured;

( 4 ) a number of cottages and a home l o s t their r00f.s and rear walls (minor

i n j u r i e s to approximately 10 people) while other cottages suffered

damage f r o m falling trees (Figs, 4 and 5);

(5) there was evidenc.e of f l y i n g debris breaking windward windows or

becoming lodged l a walls;

( 6 ) some parked cars were moved by t h e wind;

( 7 ) a truck travelling along the road overturned three times, injuring t w o

passengers;

( 8 ) a moored seaplane was l i f t e d and crashed into a hill or tree, folding in

two (Fig. 6 ) ;

( 9 ) large trees were either uprooted or broken at mid height, while smaller

trees w e r e bent aver.

The tornado created a damage area about 80 metres w i d e by 1 km l o n g .

A l l t h e d e b r i s , i n c l u d i n g f a l l e n trees, w a s strewn in the directian of the moving tornado, e x c e p t same trees at the bottom of a hill beside the lake which fell at approximately 120" windward to the tornado path.

It was not surprising to see t h a t the cottages and mobile homes were

removed or destroyed by the wind; they are l i g h t and n o t anchored to the ground, Also, standard nailing in cottage construction is often weak in

tension. One o l d e r two-storey l o g house, although badly damaged, survived

the brunt a£ th& tornado (Pig, 7 ) .

Figure 4. ELue Sea Lake. Roofs and leeward walls of cottages swept i n t o

Figure 5. Blue Sea Lake. T y p i c a l damage from f a l l l n g trees-

Figure 6 . B l u e Sea Lake, Seaplane lifted up and damaged on impact.

I

_I

What is surprising, however, is that there were not more p e o p l e

k i l l e d or seriously injured in t h e 12 buildings that either flew off or were

completely destroyed. Approximately 25 p e o p l e were i n these b u i l d i n g s when

the tornado struck. Only one died and that was from drowning, a few

suffered severe ( e - g . s p i n a l ) injuries, but most of the remainder suffered only broken bones and cuts, Apparently the woman who died w a s s w e p t away when the roof of t h e cottage took o f f and landed in the lake 25 metres away,

whereas her husband was carried i n t o the lake by the cottage flaor. In

another case, people l y i n g an the f laor ended up in the lake. In a t h i r d case the family lay an the floor while nearly all of the house and i r s

c o n t e n t s flew away. It is difficult to find out exactly what happened because most p e o p l e were ubconscious during t h e Incident.

Nicabong

The tornado approached from the west p a r a l l e l t o the road and touched down in the small v i l l a g e of Nicabong and caused the following damage:

1) the wood roof of a small church (about eight metres w f d e , 20 metres long

and three metres high) was lifted off and 200 mm block walls c o l l a p s e d ,

with only framed s m a l l rooms and the concrete foundation rema5ning (Fig.

8).

roof d i d not: appear to be anchored t o the wall. (This was not checked because visitors were forbidden to enter the immediate area.)

( 2 ) approxitnately thtee small light frame houses were s w e p t off their

foundations, with only the floors remaining ( F i g . 9);

F i g u r e 7. Blue Sea Lake. Two-storey log house survives tornado which

F i g u r e 8. Nicabang. Block wall of church collapsed inwards after roof l i f t e d o f f ,

F i g u r e 9. Nicabong. Only the f l o o r remains of a light: frame house d e s t coyed by the tornado.

( 3 ) a garage facing t h e tornado collapsed sideways, while t h e adjacent

home w a s not damaged (!Fig. 10);

( 4 ) a number of frees were b l o w over in t h e direction af the moving tornado

while some larger ones were broken off a t mid-height.

The tornado created a damage area about 30 metres wide by 1 km long.

A l l t h e d e b r i s , except f o r a f e w t r e e s , was strewn in t h e direction of the

moving tornado.

As in the case of t h e Blue Sea Lake damage, Lhe homes and garage that

were removed by the wtnd were l i g h t and not well anchored t o the floors nar

anchored to the ground. Two log houses withstood the brunt of the tornado

[ F i g . 11) and a frame s c h o o l down the road from the church w a s undamaged, apparently because the tornado was only beginning to touch down there.

E i g h t people were injured at: Nicabong, none seriously. Fa-rrunately

there were no people in t h e main hall a £ the church (one person in another

part of the church w a s injured). If the tornado

had

would have d i e d or been seriously injured when the windward bla.ck wall

c o l l a p s e d inwards (see Fig, 8).

Estimated Maximum Wind Speeds

It is useful to estimate wind s p e e d s reqaircd to overtdrn an unanchored cottage, m o b i l e home or camper or lift o f f a roof with very l i t t l e anchorage

t o the walls. Calculations given in t h e Appendix 5ndicate that the

necessary wind speeds range from 85 km/h to overturn a carnper to 130 km/h to

overturn a cottage or blow o f f a roof, whereas it would require wind s p e e d s

F i g u r e 10. Nicabong, Garage facing wind collapsed sideways; tarnado less

Figure 11. Nicabong. S m a l l log house survives tornado which destroys light frame houses nearby,

F i g u r e 12. Windsor curling rink after tornado damage.

o f approximately 170 to 180 km/h t o overturn a l o g house. Thus it appears

from the damage at Blue Sea Lake and Micabeng thaL the maximum wind speeds

were a f Lhe order of 160 h / h , which codfirms the wind speeds, obtained from Environnment Canada, reported in the newspapers.

The NBC d e s i g n 30-year return velocity pressure ( f o r wind s p e e d

averaged over one Rout) is 0.29 W a for towns near Blue Sea Lake. _Applying the N3C gust factor of 2.0 results in an NBC design gust velocity pressure

of 0.58 kPa. The valo.city pressure for a tornado wind speed of 160 km/h is

1.28 kPa, f .e., approximately twice that required by design. The tornado therefore represented an ultimate load condition that most engineered structures should be able t o survive.

Structural S a f e t y

The probability of being struck by a tornado fs small but not insignificant. Roughly three tornadoes a gear occur in the Eastern

Qntario/Western Quebec regTon. Approximately once every t w o years, these

tornadoes cause extensive property damage, i n j u r i e s and sometimes loss of

Life. Previous tornadoes in the area producing severe damage include

Winchester (19841, Messines (1980), Masson (1978), Chesterville (19731, Maniwaki (1472) and Sudbury (1970), altogether resulting in eight people being killed, approximately two hundred injured and a p p r o ~ m a t e l y

$20 million damage.

I I

Most of the p e o p l e k i l l e d by these tornadoes were tnside a light mobile home or frame cottage that became airborne, with death occurring upon impacc

with the ground. One or two qere k i l l e d outside when a light structure or

w a l l overturned, crushing them, People inside frame houses whose roofs and leeward w a l l s have disappeared have not been k i l l e d . Even p e o p l e i n s i d e

Figure 13. Tornado damage at Maniwaki 1972. Note t e n s i l e ' c r a c k in masonry

frame houses which lost everything but the floor survived although a few s u f f e r e d severe i n j u r i e s .

The Blue Sea Lake tornado damage therefore provides additional evidence

to support the requirement in CSA Standard 2240.2-1 that permanent mobile

homes be anchored to the ground. Exposed cottages would appear to be in a

similar category; however, owners are more unlikely t o t 2 e cottages down t o

the same extent as required by CSA for mobile homes. P o s s i b l y less drastic measures than a full-tie system should be used for cottages exposed in t h e westerly direction. For example, emergency planning andlor minimum

anchorage might be considered. P u r t k r studies in this area are i n d i c a t e d .

The collapse of the church in Micabong, however, strongly fndgcates t h e

need f o r improved tie-down requirements in the case of light roofs supported on unreinforced concrete block walls in b u i l d i n g s containing large open

assembly areas. A similar collapse occurred in the 1974 Wfndsor tornado,

when the roof of a c u r l i n g rink l i £ t e d off and the unsugporred block wall collapsed, killing e i g h t p e o p l e inqide (Fig, 12). Previous tornado damage

at Haaiwaki indicates that t y i n g the roof down to the top few courses of

blockwork is not s u f f i c i e n t l y reliable (Fig, 133. Therefore either the ties should extend down through the block wall i n t o the foundation or the wall

wfthout roof support should be designed t o resist NBC wind loads, e.g. by means of lateral supports.

Acknowledgements

The author would l i k e to thank Mr. Roland Mchaud, Directcur, Service

d'iacendie, V i l l e de Hull, for providing information on what happened t o the

people inside the cottages destroyed by the tornado at: Blue Sea Lake. Mr.

Michaud arrived at Blue Sea Lake 10 minutes a f t e r the tornado and d i r e c t e d

emergency measures. He was also surprised that mare people inside the

Appemdlx I Y 5 . d Speeds to Came Uplift or Overturning

Relation Between Wind Velocity (V in km/h) and Velocity Pressure (q in kPa)

Wind Pressure Coefficients (see Fig. 3-6 of Commentary t o C 1977)

These can be approximated as follows:

External Pressure

1 . 0 q

Roof uplift occurs when

Internal Pressure

Assume 2 0,5q d e p e n d i ~ g on whether openings occur

i n the windward wall

(+

(- 0.5 q ) .

Overturning occurs when wind pressure causing overturning moment about point

Estimated Wei~hts

Wood roof cottage

Building and contents camper

:cottage

I

I

I

I

wind speeds to cause 800f u p l i f t ,

Zin.

Wroof "anchor

kPa kPa

cottage church

Wind Speeds to Cause Overturning, _{Eqn, ( 3 )}

camper

cottage

log cabin log house