Tornado damage in the Barrie/Orangeville area, Ontario, May 1985

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Tornado damage in the Barrie/Orangeville area, Ontario, May 1985

Ser

m

B82

240

National Research Consdl nafional

Council Canada de rechemhes Canada

Institute for Research in Construction

lnstitut

en

Building

Research Note

Tornado

Damage

in the BarrieIOrangeville Area,

Ontario,

May 1985

by

D.E,

Allen

TORNADO DAMAGE

IN

THE

BARRIE/ORANGEVILLE

AREA,

ONTARIO,

by

D.E.

Building Structures

Institute for Research in Construction

BRN

ISSN 0701-5232

@National

DAMAGE IN GRAND VALLEY

DAMAGE TO MONO SEOPPING PLAZA

TABLE- OF CONTENTS

DAMAGE IN BARRXE

Kesidential Buildings

Non-Residential Buildings

ESTIMATE OF HAXIHUM WIND SPEEDS

H W SAFETY IKFLICATIOHS OF THE TQIWADO DAMAGE Residential Buildings

Non-Residential Buildtngs

NATIONAL BUILDING CODE OF CANADA REFUGE AREAS

TORNADO DAMAGE IN THE BARRIE/OBAPIGEVILLE AREA, ONTARIO, MAY 1985

by

D,E, A l l e n

ABSTRACT

The b u i l d i n g damage caused by a serles of" iornadoes in the

~arrielorangeville area on 31 May 1985 is described and related to the human casualties that occurred. The damage suggests certain changes are needed in

Canadian building practice, and the National Buildfng Code of Canada. Safe refuge areas during a tornado are discussed,

Ce t e x t e dgcrit l e s dommages causgs aux bstiments p a r la s g r i e de

tornades qui s'est abattue sur la rsgion Barrie-Orangeville le 31 mat 1985

et trace le rapport entre ces domuages et l e s v&ccimes. L'elsamen des

domages occasionn€is f a l t ressortir la 116cessit6 d'apparter certains

changernents aux pratiques de construction canadiennes et au Code national du

bBtlment du Canada. k texte comprend aussi une Stude des endroits qui sont

INTRODUCTION

A series sf tornadoes followed parallel paths approximately 100 m wide for about 80 km in an Em direction (see Fig. 1) between 4:15 and 5 p.m. on

31 Hay 1985, caus3ng severe damage in the mun~cipalities of Grand Valley,

Tottenham and Barrie and fn the farm areas nearby. Thelve people d i e d ;

rhree suffered very serious i n j u r i e s (3.e. they w e r e hospitalized, but d i d n o t completely recover); approximately f i f t y suffered serious injuries ( 5 . e . they spent at least one d a y in hospital, but recovered) and approximtely one hundred fifty suffered minor i n j u r i e s

(it@.

i n hospital). More than $100 million damage occurred to more than 1000

residential and noa-residential buildings. Most of the casualties and

damage occurred in Barrie, a city w i t h a population of 45,000. A major power l i n e was knocked out during the early stages of the tornadoes

resulting I n a blackout and loss of comunicatlon fn Sarrie about

15

speeds were estimated to be of the order of 200 Icm/h.

Figure 1. Damage tracks of the Hay 31, 1985 tornadoes (courtesy Climatic

This nare briefly d e s c r i b e s t h e damage that -occurred, the associated

human casualties, and indicates what this damage .implies f a r existing

structural requirements of buildings. A more detailed study of human s a f e t y i n s - i d e the buildings damaged by the tornadoes is being carried our by t h e

Ontario Ministry of Health (HOH) with cooperation from DBK/NRCC.

DAMAGE

IN

The tornado travelled through Grand Valley along Amaranth Street (see

Fig. 2), severely damaging about 30 buildings on the north side of the

street and about ten on the south side. Two people died, one inside a house and the ather in a truck, and apptoldmarely six suffered serious injuries.

& s t of the b u i l d i n g s on Amaranth Street are relatively o l d , some dating

back t b the beginnfng of the century. The following describes t y p i c a l

damage in more detail.

One house, recently built, was completaly lifted off its basement wall,

k i l l i n g one person inside and injuring another. Figure 3 shows a front opening in the basement which allowed wind t o enter the house, helping t o

l i f t off the floor. Figure 4 shows lack of anchorage of t h e flqor in t h i s

house t o the basement foundation

w a l l .

F i p r e 2. Grand Valley. House damage on Amaranth Street (courtesy Toronto Star)

Figure 3. Grand Valley. Ebuse lifted off basement walls.

Figure 4. Grand Valley. Same house as F i g . 3. Note lack of

nailing of floor into sill plate

Figure 5 _{shows an older wood-fram house which racked as a result of}

openings in t h e front and back walls and lack of crass partitions. Must of

t h e structural damage to houses c o n s i s t e d of lift-off a£ a roof (Fig. 6 ) or

a wall (Fig. 7). No s e r i o u s injuries occurred in houses with t h i s kind of

damage.

Figure 5. Grand Valley. Racking collapse of f i r s t f l o o r of house

Figure 7. (Xand Valley. Wall b l o m off 85-year-old brick house (courtesy

FSgures 8 to i O show old brick b u i l d i n g s that were demolished: a library, t w o church buildLngs and a house. Approximately seven p e o p l e escaped from these buildings wZth a few minor i n j u r i e s at most. Ttte

buildings were heavy (three courses of brickwork In the l i b r a r y ) and

probably failed as a result of roof lift-off followed by collapse of

unsupported brick walls.

Figure 8. Grand Valley. kmolished l i b r a r y

Figure 11 shows damage t o a large church not directly in the path of

the tornado. Apparently the large front windows were initially broken fti by

missiles, which allowed the wind to enter and help blow o f f the roofing.

The damage at Grand Valley and the resulting casualties indicate the

need for anchoring light frame houses t o the foundation and for providing

Figure 20. Grand Valley. Severely damaged brick house

Figure 11. Grand Valley. Church windows on right were probably broken by missiles which allowed d u d pressure inside to help lift o f f

sufficient racking resfstance. Old brick buildtngs appear to be fafrly safe

provided p e o p l e go to places of refuge, such as a basement or a small room

~ I I the ground floor.

DAMAGE IN TOTTENRAM

The tornado followed a concession l i n e just south of Tottenham,

severely damaging approximately 20 houses, many of them recently b u i l t . Two people died, one inside a house and one i n s i d e a shed, and approximately six

suffered serious fnjurfes.

Figure 12 show the anchorage d e t a i l of a house w h i c h was lifted off

the basement foundation wall, killing one person inside. Although anchorage bolts were provided i n the foundation walls, they were not very effective

because the washers required for oversized bolt holes were not installed.

Five other ltght houses were completely l i f t e d o f f the foundations,

resulting in one very serious injury.

A number of houses were severely damaged with everything lifted o f f

except the floor and part of the walls. Most of the structural house damage

consisted of l i f t a f f of a roof or wall. A silo with no foundation, approximately one-third f u l l , overturned.

Figure 12. Tattenham. &use lifted off basement wall. Mote lack of washers below nuts of anchor b o l t s

DAMAGE

M

A large shopping plaza of block-all and steel construction, situated north of Orangeville, w a s severely damaged as the tornado travelled from

Grand Val1 ey to Tot t enham,

The south s i d e of the shopping centre, which contained a large building

s u p p l i e s store, collapsed completely {Fig. 13) whereas the north stde

suffered nonstructural damage or collapse of the front and back block walls

only (Figs. 1 4 , 15). There are two reasons for t h e difference Ln damage:

(i) the centre of the tornado, characteristically about 100 m wide, passed

through the south side of the shopping plaza;

(ii) the north s i d e of the plaza contained smaller stores w i t h Interior

steel columns anchored into the foundation p l u s infill block walls

which provided racklng resistance. The building s u p p l i e s store, on the

other hand, contained larger open areas with f m r steel columns anchored into the ground and fewer i n f i l l block walls,

None of the 40

or

low, partly because of the presence of stored goods ( F i g . 16) which

prevented the collapsing structure from reachlng the floor. Some exterior block walls, which d i d collapse inwards (Figs. 13 and 15), would have been a

serious hazard t o anyone standing nearby.

A hause near the shopping plaza lost everything except the f l o o r and a

portion of the w a l l s , but the two blind people inside escaped sertous injury. Nearby houses in the path of the tornado were undamaged.

F5gure 13. Mono Shopping Plaza. South side (bottom h a l f o f photo)

collapsed. Note inward collapse of block wall (courtesy

Figure 14. &no Shopping Plaza. East wall {leeward)* -age to block wall

near roof l i n e at north end. C o l l a p s e of south end

Figure 15,

mno

after roofing lifted oEf. Interior steel structure plus lafill

Figure 16. Mona Shopping Plaza. South sfde. Stored g w d s protected inhabitants from collapsing structure

DAMAGE IN BARRIE

The Barrie tornado followed a northeasterly path 100 to 200 m wide

through the south end of the c i t y as indicated in Fig. 17, destroying many

buildings. In all, 8 people died, approximately 33 had serious injuries and

approxlraaSely 120 had minor injuries. M the 857 buildfngs that were

damaged, 237 nust be t o t a l l y reconstructeds An aerial v i e w of typical house

damage is shown in Fig. 18. The following descrgbes the damage in more detail.

Figure 18. Barrie. &use damage on Murray Street (courtesy Toronto Globe and Mail )

R e s i d e n t i a l Buildings

Fifteen llght f r a w houses were pieked off t h e i r f oundatiods and

deposited downwind killing five persow, very seriously injuring one, and

sertously injuring s i x . As Figs, 19 and 20 show these houses were not

effectively anchored t o t h e i r foundations. A l l but one of these houses w e r e o u t s i d e the old city liaits and not subject to the building code uhen they were b u i l t -

Approximately 50 houses or apartment units s u f f e r e d heavy damage, the

tornado removing the roof and m a t of the walls; eleven serious injuries were sustained, none very s e r l w s . Typical cases are shown fn F.ig. 18,

Figure 19, Barrie. Eouse lifted o f f

foundation. Note lack of anchorage

Figure 20. hrrie. House l i f t e d off faundatlw. Note

Seven of the injuries occurred inside row houses (shown in Fig. 21).

Approximately 100 houses or apartment units lost a roof, or a roof and part

of a wall; at most, a few of the occupants suffered serious ffijuries.

Non-Residential Buildings

+proximately 10 n o n ~ e s i d e n t t a l buildings conststing of unreinforced

block walls supporting timber or steel-truss roofs collapsed, resulting in

one death and a few serious i n j u r i e s . Figure 22 shows a typical example*

Approximately five nrrn-residential large-rea buildings consisting of unreinforced exterior block walls, plus an intertar steel frame supportfng a

steel-joist roof, collapsed; a few serious fnjurles at most were sustained.

In most of these buildings the s t e e l structure collapsed w t o objects such

as storage r a c k located i n s i d e the buildings (Fig. 23). A few allateta1 buildings, although suffering considerable damage t o the cladding, did not

c o l l a p s e sufficiently to injure anyone inside* A l l the collapsed

non-resfdential b u i l d i n g s were industrial. Fortunately, most of the workers

had left before the tornado struck at 5 p .m

Figure 21. Barrie. Severely damaged row houses on A d e l a i d e Street (courtesy Canapress Photo Service)

Figure 22. Barrie. a l l a p s e d industrial building made of unreinforced

block walls supporting a truss roof

Figure 23. 8arrie. C o l l a p s e of storage b u i l d i n g consisting of exterior unrainEorced block walls and interior steel structure. Note

ESTIMATE OF HAXIMUM WIND SPEEDS

What wind speeds are necessary to cause failure of t y p i c a l small houses

and large block-wall buildings? Calculations in Appendix I i n d i c a t e t h a t ,

assuming, as often happens, that internal pressure is created by failure of windows and doors facing the tornado, roof lift-off for both types of

buildings occurs at roughly 130 h / h . This speed is usually less than that required t o overturn a small house (150 km/h, and greater if the house is anchored). Once a house roof f l i e s o f f , however, the unsupported walls will

start to collapse or pull off, making the partly demolished house lighter

and less resistant t o overturning or floor l f f t w f f ,

As

large black-all building l i f t s off (see i n c i p i e n t failure In Figure ( 1 4 ) ) , the unsupported external walls will collapse. If these block walls also

provided raclring resistance t o laterdl loads, the unsupported internal steel structure will f a i l laterally, and w i l l c o m e down where it was previously

supported by the block w a l l s .

The BarrielWangeville tornado damage indicates that:

(i) unreinforced block-wall butldiags f a i l e d , (ti) house roofs l i f t e d ,

(iii) house roofs and w a l l s flew away, and

(iv) wood-frame houses {including floors) that were

-

the foundations w e r e swept away.

This damage severity is typical for strong tornadoes In Eastern Canada (1). A review of the failure w5nd speeds in Appendix I indicates that the maximum

tornado w i n d speeds were of the order of 160 km/h, posszbly up t o 200 h l h . Also the fact that cars were overturned and became airborne, which occurs at

wind speeds of approximately 180-220 h / h , indicates that maxinnrm wind

speeds were of the order of 200 kdh.

HUHAN SAFETY IMPLICATIONS OF TIZE TORNADO DAMBGE

A survey of the damage and the human casualties indicates that htman

s a f e t y Inside buildings exposed t o tornadoes of this intensity, wRich is the strongest entensity typical for Rastern Canada, depends very much on

construction d e t a i l s , e s p e c i a l l y with regard to anchorage and t i e s , and on

the location of people i n s i d e buildings.

Table 1 glves an estimte of the human casualties and the number of b u i l d i n g u n i t s associated wlth different types o f b u i l d i n g damage. More d e t a i l e d information relatlng injuries to the location of p e o p l e and type of

damage will be obtained from the MOB survey, The following observations are, however, apparent from the information available.

Residential Buildings

Unanchored light houses without basements are a very high hazard to t h e occupants during a tornado because t h e b u i l d i n g s , including the floor,

TABLE 1. Earrie/Orangeville Tornadoes: Estimate of Casualties vs. B u i l d i n g Damage

- - - . . . - - . - - - - - - - .

Deaths and Number of

Very S e r i o u s S e r i o u s B u i l d i n g 'Injuries Injuries U n i t s (1)

Ikgree of B u i l d i n g Damage Residential buildings

Everything lifted o f f , including

floor

Roof and w a l l s l i f t e d off

Only roof or w a l l l i f t e d off

Industrial and comnercial buildings Total collapse (floor remaining) Only roof or wall collapsed

Barns, s h e d s , garages, etc.,

destroyed

Cars, trucks, cycles overturned 4 10

-

Total 15 50 550

Note: (1) A u n i t corresponds, for example, to a house, an apartment or a

store.

to be safer to s i t i n s i d e a car Gfith seatbelts on, and considerably safer t o

lie down outside, flat on the ground. Racking collapse is a l s o hazardous,

but occurs much less frequently.

If only the f l o o r remains, t h i s considerably increases t h e s a f e t y of the occupants. I£ the floor and some w a l l s rernain, the safety is increased even further. Table 1 indicates that in such cases t h e r i s k to human life is 1/10 or less, of the risk for unanchored light houses.

If only the roof or a wall i s lost, the s a f e t y for p e o p l e inside is

very high, as it is if p e o p l e go to their basements. Table I indicates that

in such cases the risk to human life is 1/100 or less, of the risk for unanchored houses.

Non-Residential Buildings

Unreinforced block walls supporting truss roofs (either steel or wood)

a l s o present a danger to the occupants. The hazard is less severe than for

unanchored light houses because the floor remains, and the structure often collapses onto objects before injuring people. Open-assembly areas,

however, do not provide such protection.

Large-span metal buildings in which the steel roof structure is tied to

the foundations through the columns are much safer than unreinforced block wall b u i l d i n g s . Those with roofs supported Tnternally by steel columns with infill b l o c k walls, and e x t e r n a l l y by unreinforced block walls, are also

Open-assembly areas would provide a s p e c i a l danger i n this regard, as noted previously.

NATIONAL BUILDING CODE OF CANADA

The p a t t e r n of damage and human casualties caused by the

~arrie/Orangeville tornadoes indicates that for residential b u i l d i n g s the

anchorage requirement of Clause 9.23.6 of the National Building .Code

of

Canada 1985 (HBCC) is necessary and, i f properly a p p l i e d , effective for human safety; a l l except p o s s i b l y one o f the deaths and very serious

injuries inside residential buildings occurred fn eases where Clause 9.23.6

was apparently n o t s a t f s f i e d . The anchorage requirements of Part 9 of the

NBCC should, nevertheless, be reviewed for small l i g h t houses without

basements. Anchorage of the floor and w a l l s to the foundation is especially

Lnportant for structures inhabited by handicapped or e l d e r l y people. Extra

tie capacity through basement walls is also desirable around large doors

(see Fig. 3).

Racking collapse is a potential hazard for houses that lack cross

partitions and have large windows or doors in exterior walls. Most houses

have s u f f i c i e n t inherent racking resistance, but the requirements of Part 9

of the ElBCC shauld be reviewed to ensure sufficient racking resistance for w e a k configurations.

The damage indicates that: the adequacy far human s a f e t y of buildings constructed of unreinforced black w a l l s supporting the roof requtres more attention. Buildings of t h i s type which do not contain Irrternal goods or

equipment t o protect the people i n s i d e , open-assembly buildings in

particular, provide a high r i s k t o the occupants during a tomado.

Preliminary calculations for tarnado u p l i f t indicate that such buildings

require minimm vertical reinforcing in the block walls extending into the

foundation, similar to that required for NBCC Seismic Zone 2.

Tornado wind speeds of 160-200 km/h exert loads that correspond approximately to the ultimate resistance of buildtng structures designed

according to Part

4

requLrementg for wind loads are satisfactory provided (1) internal pressure

is d e t e d n e d asswlng failure of windows and doors facing the wind (for

u p l i f t ) , (2) the safety factors are applied correctly using the limit-

statesdesign method (dead-load factor of 0.85 for u p l i f t and overturning). The only major deficiency with Part 4 is the application oE the empirical design rules contained in CAN3-S305+484(2) t o block-all buildings used f o r assembly occupancfes ,

REFUGE AREAS

Basements provide a safe refuge f o r people during a tornado. When a

tornado approaches, p e o p l e u p s t a i r s should go downstairs, Znto the basement,

if possible. S m a l l rooms, preferably without: exterior windows, are a l s o

good refuge areas provided the floor remains on the foundation; t h i s is

I especially important: f o r handicapped and e l d e r l y people. For people inside

have basements, lying o u t s i d e on t h e ground appears to be b e t t e r than staying inside, but advic.e on where ro go once outside is needed.

ACKNOWLEDGEMENT

The author would l i k e to thank Messrs. Chris Spanis, Ernie frord and

B i l l k f t h e a d of the C i t y

of

Mr.

Dufferin and Mr, Peter Robertson of the T m s h i p of Tecumeth f o r providing

information on the extent of building damage caused by the tornadoes.

REFERENCES

(1) Allen, D.E. Tarnado Damage at Blue Sea Iake and Nicabong, Qaebec, July 1984, Building Research Note Elo. 222, National Research Council of Canada, O t t a w a , ORtario,'November 1984.

( 2) CSA Standard CAM3-S304-M34. Masonry Design for Buildings, Canadian

APPENDIX A Wind Speeds Required to Cause U p l i f t or Overrurnfng

The fallowing equations were developed in Appendix A of Ref. (1).

where: V is the wind speed (kmJh) and q is the velocity pressure (kPa).

Roof Uplift (assumes an internal pressure coefficient of +O.5)

where: u is the weight of the roof (kPa),

P

capacity f@jm) and W is the span of roof j o i s t

r

e

%lag + 'anchor

/w

Qo =

1

+

(512

W

where: %ldg is the weight of the building (kPa) and B is the height of the

wall (m).

Estimated Minimum Weights

Roof house 0.5 kPa

block wall industrial building 0.8 W a

House whole

p a r t l y demolished

Estimated Anchorage Resistance

Toenailing

(assumes two toenails resist 0.8 kN u p l i f t ) Anchorage t o uureinforced block walls

(assumes tensile bond strength of 0.1

MPa)

House

Wind Speeds Required t o Cause Overturning

-11 house

no f oundarion anchor foundation anchor

toenails weak l i n k

block wall weak link

Partly demolished bouse 5 3 0.8

no foundation anchor foundation anchor

toenails weak l i n k b,lock w a l l weak l i n k