Provision of fire resistance: evolution of design approaches

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Provision of fire resistance: evolution of design approaches

S e r TH1 I

National Research Conseil national

B21d

i

+

1

Council Canada _{de recherche= Canada}

no.

1529

c . 2

BLDG Institute for lnstitut de Research in recherche en

-- Construction construction

Provision of Fire Resistance

-

Evolution

of Design Approaches

by G.C. Gosselin and T.T. Lie

Appeared in Proceedings

1987 CSCE Centennial Conference Montreal, Quebec, May 19-22,1987 VOI. 1, p. 3-1 9

(IRC Paper No. 1529)

Reprinted with permission

Price $3.00 NRCC 28877

LIBRARY,

T h i s paper

i s

being d i s t r i b u t e d i n r e p r i n t form by t h e I n s t i t u t e f o r Research i n Construction. A l i s t of b u i l d i n g p r a c t i c e and r e s e a r c h p u b l i c a t i o n s a v a i l a b l e from t h e I n s t i t u t e may be o b t a i n e d by w r i t i n g t o t h e P u b l i c a t i o n s S e c t i o n , I n s t i t u t e f o r Research i n C a n s t r u c t i o n , N a t i o n a l Research C o u n c i l of Canada, Ottawa, O n t a r i o ,

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PROVISION OF FIRE RESISTANCE

-

EVOLUTION OF DESIGN APPROACHES

G.C. Gosselin and T.T. ~ i e l

ABSTRACT

The idea of making a building "fireproof" evolved late in the 19th century in an effort to cut down escalating property losses. The

concepts of compartmentalization and structural fire protection now play important roles in the building codes' approach towards the provision of a minimum level of life safety in buildings. On the other hand, property protection against fire no longer appears to be an objective pursued by designers who instead rely on listings of tested assemblies to satisfy the minimum requirements of building codes.

Notwithstanding the emergence of new calculation procedures for assessing the fire resistance of building elements and assemblies, their use as an alternative to more conventional design approaches remains rare. It is suggested that formal training in this area and the

development of user-friendly, PC-driven software would encourage the use of more scientifically-based methods and possibly lead to more

cost-effective designs.

l~esearch Officer and Senior Research Officer, Fire Research Section, Institute for Research in Construction, National Research Council of Canada, Ottawa, Ontario.

PREVOIR DE

LA

RESISTANCE AU FEU

-

EVOLUTION DES METHODES DE CONCEPTION

G.C. Gosselin et

T.T.

~ i e l

L'idee de construire les batimnts B 1'Bpreuve du feu date de la

fin du 192me si2cle alore que les propri6taires et les compagnies d'assurance d6cidSrent que les pertes materielles devenaient trop importantes. Les concepts de compartimentation et de protection de la structure contre le feu jouent maintenant des rdles importants dans la fason que les codes du Wtiment assurent un minimum de sbcuritg au public dans les bbtiments. Cependant, la protection de la structure du batiment ne semble plus paraftre parmi les objectifs des concepteurs qui se

contentent de verifier les listes d'assemblages mis B l'easai afin de

satisfaire les exigences minimales du code du batiment.

Bien que plusieurs dthodes de calcul sont maintenant disponibles pour dCterminer la r6sistance au feu des blements et assemblages de construction, leur utilisation dans le processus de conception d e m u r e l'exception plut8t que la regle. L'auteur suggsre qu'une 6ducation accrue B ce sujet ainsi que le d6veloppement de logiciel simple et support6 par les micro-ordinateurs encourageraient considerablement l'utilisation de ces dthodes scientifiques et resulteraient peut-&re

a

des i5conomies de construction.

l&ent de recherche et agent de recherche principal, Section d'etude du feu, Institut de recherche en consttuction, Conseil national de

INTRODUCTION

The i d e a of p r o t e c t i n g o u r s t r u c t u r e s a g a i n s t t h e e f f e c t s of f i r e d a t e s back o n l y a c e n t u r y , d e s p i t e man's l o n g h i s t o r y of l o s s and

s u f f e r i n g due t o f i r e ' s d e s t r u c t i v e f o r c e . F i r e p r e v e n t i o n codes have been i n e f f e c t much l o n g e r t h a n t h i s , b u t t h e y d e a l t p r i m a r i l y w i t h i n s p e c t i o n a c t i v i t i e s , t h e p r o v i s i o n of f i r e f i g h t i n g equipment and manpower,

as

w e l l a s o r d i n a n c e s aimed a t p r e v e n t i n g unwanted f i r e s . These e a r l y p r o t e c t i o n measures simply c o u l d n o t h a n d l e t h e

c o n f l a g r a t i o n s which r e p e a t e d l y s t r u c k our c i t i e s a s a r e s u l t of wars, e a r t h q u a k e s and human greed.

A s p r o p e r t y and human l o s s e s took t h e i r t o l l on s o c i e t y ' s

t o l e r a n c e , some d e s i g n e r s s t a r t e d t o make g r e a t e r u s e of f i r e r e s i s t i v e m a t e r i a l s (e.g. s t e e l , p l a s t e r ) f o r t h e c o n s t r u c t i o n of b u i l d i n g s , r e a l i z i n g t h a t i t would h e l p minimize b o t h t h e s p r e a d of f i r e and t h e amount of damage s u s t a i n e d by each s t r u c t u r e . On t h e o t h e r hand, s e l f - r e g u l a t i o n of c o n s t r u c t i o n p r a c t i c e s was f a r from b e i n g e f f e c t i v e due t o t h e l a c k of i n d i v i d u a l economic i n c e n t i v e s . The i n s i d u o u s n o t i o n t h a t " i t won't happen t o me" was a l r e a d y very much i n g r a i n e d i n p e o p l e s ' minds. Besides, i f i t were t o happen, i n s u r a n c e companies would c o v e r t h e l o s s , would t h e y n o t ?

U n f o r t u n a t e l y , i n s u r a n c e companies were n o t beyond d e s t r u c t i o n themselves. A s a r e s u l t of t h e G r e a t F i r e of Boston i n 1872, f o r i n s t a n c e , more t h a n 70 i n s u r a n c e companies had t o d e c l a r e bankruptcy ( N a t i o n a l F i r e P r o t e c t i o n A s s o c i a t i o n 1984). Needless t o s a y , t h e e v e n t u a l p u b l i c o u t c r y f o r more p r o t e c t i o n s p u r r e d t h e development of b u i l d i n g codes t h a t were a d m i n i s t e r e d l o c a l l y a s municipal bylaws. S i n c e f i r e p r o t e c t i o n e n g i n e e r i n g p r a c t i c e was i n i t s i n f a n c y (and s t i l l i s today a c c o r d i n g t o many), t h e p r i n c i p l e s of f i r e p r o t e c t i o n a p p l i e d i n t h e b u i l d i n g r e g u l a t i o n s of t h e mid-1800's were q u i t e b a s i c : provide means of e g r e s s and make maximum u s e of noncombustible c o n s t r u c t i o n m a t e r i a l s wherever you can.

EARLY EFFORTS AT PROVIDING F I R E RESISTANCE

The s t a t e - o f - t h e - a r t i n noncombustible c o n s t r u c t i o n i n t h e middle o f t h e 19th c e n t u r y c o n s i s t e d of masonry e x t e r i o r w a l l s w i t h an i n t e r i o r s t r u c t u r e of c a s t i r o n columns, g i r d e r s and f l o o r beams. The e x t e n s i v e u s e of m e t a l i n b u i l d i n g s had been made p o s s i b l e by t h e e s t a b l i s h m e n t of m i l l s c a p a b l e of r o l l i n g I-beams and o t h e r s e c t i o n s . I t was soon

r e a l i z e d , however, t h a t even t h i s t y p e of c o n s t r u c t i o n possessed very l i t t l e r e s i s t a n c e t o s e v e r e f i r e s , a s ' t h e i r o n members e l o n g a t e d and d i s t o r t e d when exposed t o e l e v a t e d t e m p e r a t u r e s , damaging t h e masonry w a l l s i n t h e process.

By t h e end of t h e n i n e t e e n t h c e n t u r y , t h e r e was a g e n e r a l

r e c o g n i t i o n of t h e n e c e s s i t y t o p r o t e c t metal b u i l d i n g elements a g a i n s t h i g h t e m p e r a t u r e s (Schoub 1961). F l a t h o l l o w - t i l e a r c h e s were i n t r o d u c e d

i n 1872 t h a t allowed attachment of p l a s t e r p r o t e c t i o n t o t h e bottom

f l a n g e s of f l o o r beams. A y e a r l a t e r , porous t e r r a c o t t a appeared on t h e market and, by 1880, was o f f e r e d i n t h e form of blocks t h a t could be used t o e n c l o s e and p r o t e c t columns. These developments, combined w i t h a n i n c r e a s i n g u s e of f i r e r e s i s t a n t p a r t i t i o n s , d o o r s and s h u t t e r s t o p r o t e c t openings and c r e a t e compartments, helped c o n t a i n f i r e t o a manageable s i z e , p r e v e n t c o n f l a g r a t i o n and minimize p r o p e r t y and l i f e l o s s e s (Shoub 1961).

NEED FOR

FIRE

RESISTANCE TESTING

A s no means e x i s t e d t o a s s e s s and compare t h e performance of t h e v a r i o u s noncombustible m a t e r i a l s b e i n g o f f e r e d i n t h e marketplace, b u i l d i n g r e g u l a t o r s were r e s t r i c t e d t o t h e development of l e n g t h y and cumbersome s p e c i f i c a t i o n - t y p e requirements.which e s s e n t i a l l y d i c t a t e d t o t h e d e s i g n e r which m a t e r i a l s could o r could n o t be used i n t h e

c o n s t r u c t i o n of a b u i l d i n g . N a t u r a l l y , t h i s was t h e s o u r c e of

c o n s i d e r a b l e f r u s t r a t i o n t o d e s i g n e r s and owners who were q u i t e l i m i t e d i n t h e i r c h o i c e of m a t e r i a l s . Concurrently, product manufacturers were c o n t i n u a l l y developing new p r o p r i e t a r y b u i l d i n g m a t e r i a l s and were p r e s s i n g t h e a u t h o r i t i e s f o r f a i r and e q u i t a b l e r e c o g n i t i o n of t h e i r products.

The need f o r f i r e t e s t i n g soon became e v i d e n t a s t h e only p o s s i b l e way of o b j e c t i v e l y e v a l u a t i n g t h e performance of new p r o d u c t s and

a s s e m b l i e s , s o t h a t t h e y could be a c c e p t e d a s e q u i v a l e n t s t o more

c o n v e n t i o n a l c o n s t r u c t i o n s . Another impetus t o c a r r y o u t f i r e t e s t s came from t h e f a c t t h a t , though new methods of c o n s t r u c t i o n and t h e

development of s m a l l passenger l i f t s and e l e v a t o r s made g r e a t e r b u i l d i n g h e i g h t s (up t o 45 m) economically a c h i e v a b l e , f i r e f i g h t i n g i n t h e e a r l y s k y s c r a p e r s p r e s e n t e d tremendous problems g i v e n t h e equipment and means a v a i l a b l e a t t h a t t i m e . Hence, i t became n e c e s s a r y t o v e r i f y t h a t t h e b u i l d i n g ' s s k e l e t o n o r s t r u c t u r e would remain s t a n d i n g even a f t e r a complete burnout of t h e combustible m a t e r i a l s c o n t a i n e d i n t h e b u i l d i n g , assuming t h a t f i r e f i g h t e r s would n o t be a b l e t o c o n t r o l and e x t i n g u i s h t h e f i r e a t a n e a r l i e r s t a g e of i t s development.

I n North America, t h e f i r s t f l o o r t e s t was conducted i n Denver i n 1890 on behalf of t h e Denver E q u i t a b l e B u i l d i n g Company (American

A r c h i t e c t and B u i l d i n g News 1891). The name of t h e company i t s e l f

suggested t h a t t h e i r b u s i n e s s c e n t e r e d around t h e o b j e c t i v e of developing and u s i n g new p r o p r i e t a r y m a t e r i a l s and p r o d u c t s i n b u i l d i n g

c o n s t r u 5 t i o n . The aim of t h i s "landmark" t e s t was t o have t h e u s e of porous hollow t i l e s o f f i c i a l l y a c c e p t e d i n l i e u of b r i c k s f o r t h e f l o o r a r c h e s spanning between i r o n beams. The f l o o r specimen was s u b j e c t e d t o s t a t i c and impact l o a d s , f i r e and water e r o s i o n t e s t s . The f i r e t e s t , conducted on a specimen w i t h no superimposed l o a d , c o n s i s t e d of a continuous exposure t o a t e m p e r a t u r e of 700°C (1300°F) f o r a 24 h r p e r i o d , a n exposure which t h e a r c h c o n s t r u c t i o n managed t o s u r v i v e w i t h l i t t l e s i g n of damage.

I n 1891, f l o o r s made up of c i n d e r c o n c r e t e a r c h e s , l a i d between I-beam and p r o t e c t e d by a f l a t c e i l i n g of t i l e s hung from i r o n b a r s , were t e s t e d i n t h e hope of o b t a i n i n g a u t h o r i z a t i o n f o r t h e i r u s e i n a new o f f i c e b u i l d i n g i n St-Louis ( F r e i t a g 1899). A f t e r having been s u b j e c t e d t o a l o a d t e s t , t h e f l o o r s were exposed t o an 815°C (1500°F) f i r e f o r a 64 h r p e r i o d and t h e n cooled. The h e a t i n g / c o o l i n g c y c l e was r e p e a t e d t h r e e times b e f o r e

a

19 mm hose s t r e a m was f i n a l l y a p p l i e d from

underneath t o v e r i f y t h e p o s t - f i r e r e s i s t a n c e of t h e f l o o r t o t h e e r o s i o n e f f e c t s of f i r e f i g h t e r s ' w a t e r sprays. With t h e e x c e p t i o n of a few minor c r a c k s , t h e f l o o r s were r e p o r t e d a s b e i n g p r a c t i c a l l y undamaged w i t h no d e f l e c t i o n .

It i s i n t e r e s t i n g t o n o t e how c o n s e r v a t i v e d e s i g n e r s and r e g u l a t o r y a u t h o r i t i e s were i n t h e absence of e x p e r i e n c e o r knowledge of what might c o n s t i t u t e a r e a l i s t i c f i r e exposure i n term of i n t e n s i t y and d u r a t i o n and what l e v e l of performance should be regarded a s s a f e and a c c e p t a b l e . It was n e v e r t h e l e s s p i o n e e r i n g work of t h i s k i n d which opened t h e door t o f i r e r e s e a r c h and, e v e n t u a l l y , t o t h e e s t a b l i s h m e n t of l e s s c o s t l y

c o n s t r u c t i o n requirements. ,

F r e i t a g (1899) a l s o r e p o r t e d on what was l i k e l y t h e most

comprehensive s e r i e s of t e s t s conducted i n t h o s e e a r l y y e a r s , t h a t i s t h e New York B u i l d i n g Department tests i n 1896. The B u i l d i n g Department c o n s t r u c t e d a number of k i l n s on v a c a n t l o t s around t h e c i t y and t e s t e d a t o t a l of 14 f l o o r / c e i l i n g a s s e m b l i e s submitted by p r i v a t e c o n s t r u c t i o n companies. Again, t h e purpose of t h e tests was t o a l l o w new and

d i f f e r e n t f l o o r s t r u c t u r e s t o be recognized a s o f f e r i n g a l e v e l of s a f e t y e q u i v a l e n t t o t h o s e s p e c i f i e d i n t h e b u i l d i n g r e g u l a t i o n s of t h e day. A l l a s s e m b l i e s were of t h e i r o n beam and a r c h form c o n s t r u c t i o n w i t h c e i l i n g s p l a s t e r e d .

The t e s t procedure employed was l a t e r i n c o r p o r a t e d i n t h e 1899 New York C i t y B u i l d i n g Code, r e p r e s e n t i n g t h e f i r s t - e v e r f i r e performance t e s t l e g a l l y recognized i n North America. Out of t h i s precedent emerged n o t h i n g l e s s t h a n

a

r e v o l u t i o n i n b u i l d i n g d e s i g n and c o n s t r u c t i o n . No l o n g e r being r e s t r i c t e d t o t h e t y p e s of m a t e r i a l s and forms of

c o n s t r u c t i o n s p e c i f i c a l l y d e s c r i b e d i n t h e r e g u l a t i o n s , d e s i g n e r s f i n a l l y had a means of a p p l y i n g t h e i r i n g e n u i t i e s t o developing more e f f i c i e n t and l e s s c o s t l y forms of c o n s t r u c t i o n , and t a k i n g advantage of t h e p o s s i b i l i t i e s a f f o r d e d by new c o n s t r u c t i o n m a t e r i a l s and products.

For t h e f i r s t t i m e , t h e procedure c a l l e d f o r l o a d i n g of t h e f l o o r system t o 7.2 kPa (150 p s f ) d u r i n g t h e f i r e t e s t s t o s i m u l a t e a more r e a l i s t i c c o n d i t i o n . With t h e u s e of wood c r i b s t e m p e r a t u r e s were

maintained a s c l o s e a s p o s s i b l e t o llOO°C (2000°F) f o r 5 h r s . A f t e r t h k t e s t , a 414 kPa (60 p s i ) hose s t r e a m was a p p l i e d t o t h e u n d e r s i d e of t h e assembly. The l o a d was t h e n removed and t h e f l o o r r e l o a d e d t o 29 kPa (600 p s f ) f o r a 48 h r p e r i o d w i t h t h e l o a d r e s t i n g e n t i r e l y on t h e

a r c h e s . No r a t i n g s were a s s i g n e d t o t h e f l o o r c o n s t r u c t i o n s t e s t e d . The m e r i t s of e a c h r e s p e c t i v e assembly were a p p a r e n t l y judged from

Although t h e r e a s o n f o r t h e p o s t - f i r e l o a d t e s t h a s n o t been

documented, i t i s s p e c u l a t e d t h a t r e - u t i l i z a t i o n of a b u i l d i n g ' s s k e l e t o n o r s t r u c t u r e i n t h e a f t e r m a t h of

a

f i r e was a d e s i g n o b j e c t i v e c o n s i d e r e d d e s i r a b l e by owners and i n s u r e r s . T h i s way f i r e l o s s e s , i n c l u d i n g

b u s i n e s s i n t e r r u p t i o n l o s s e s , could be reduced by a l l o w i n g a q u i c k e r r e f i t t i n g of t h e b u i l d i n g . A t any r a t e , t h e importance p l a c e d on

p o s t - f i r e performance c e r t a i n l y s u g g e s t s t h a t p r o p e r t y p r o t e c t i o n was t h e primary m o t i v a t i o n i n t h e c a r r y i n g o u t of e a r l y f i r e tests.

DEVELOPMENT OF A STANDARD TEST METHOD

A s a r e s u l t of t h e i n c r e a s i n g i n t e r e s t i n f i r e t e s t i n g s p u r r e d by t h e 1899 B u i l d i n g Code Amendment, a d e c i s i o n was made t o have a f i r e t e s t s t a t i o n c o n s t r u c t e d a t Columbia U n i v e r s i t y . Completed i n 1902, t h e

S t a t i o n was c a p a b l e of t e s t i n g f l o o r s measuring 5.5 m x 6.7 m and p a r t i t i o n s 3 m x 4.6 m (Woolson and Miller 1912).

While Columbia U n i v e r s i t y was conducting t e s t s under t h e d i r e c t i o n of P r o f e s s o r I r a Woolson, a committee was o r g a n i z e d by t h e American S o c i e t y f o r Standard T e s t i n g and ~ t e r i a l s i n 1905 w i t h t h e mandate t o develop a n a p p r o p r i a t e t e s t s t a n d a r d . S i n c e P r o f . Woolson a l s o c h a i r e d t h i s Committee ( t h e p r e d e c e s s o r of ASTM Committee E5 on F i r e S t a n d a r d s ) , i t i s n o t s u r p r i s i n g t o f i n d t h a t t h e t e s t procedure s u b m i t t e d f o r a d o p t i o n a s a s t a n d a r d resembled very c l o s e l y t h a t followed a t Columbia U n i v e r s i t y (Schoub 1961). The t e s t method p r e s c r i b e d t h a t a f u r n a c e t e m p e r a t u r e of 930°C be maintained f o r a l l but t h e f i r s t 30 minutes of a 4 h r t e s t , and t h a t t h e specimen c a r r y a superimposed l o a d of 7.2 kPa d u r i n g t h e t e s t and 414 kPa a f t e r cooling.

E v e n t u a l l y adopted i n 1908, t h e s t a n d a r d s p e c i f i e d t h e f o l l o w i n g a c c e p t a n c e c r i t e r i a :

( a ) no passage of smoke o r f i r e through t h e f l o o r , ( b ) no c o l l a p s e a s a r e s u l t of t h e hose s t r e a m t e s t ,

( c ) no damage t h a t would make t h e assembly i n c a p a b l e of s u s t a i n i n g l o a d s .

The f o l l o w i n g y e a r , t e s t requirements f o r p a r t i t i o n s were i n c l u d e d i n t h e s t a n d a r d . The f u r n a c e temperature was t h e same b u t t h e t e s t was of a s h o r t e r d u r a t i o n (2 h r ) , s u g g e s t i n g t h a t h o r i z o n t a l s p r e a d of f i r e by t h e c o l l a p s e of a p a r t i t i o n was n o t c o n s i d e r e d a s hazardous t o

occupants and f i r e f i g h t e r s a s v e r t i c a l s p r e a d by t h e c o l l a p s e of a

f l o o r . The c r i t e r i a f o r acceptance, o r p a s s i n g t h e t e s t , were s i m i l a r t o t h o s e f o r f l o o r s .

Although t h e s e e a r l y tests c o n t r i b u t e d s i g n i f i c a n t l y t o t h e

development of e s s e n t i a l l y noncombustible and f i r e r e s i s t a n t f l o o r s and p a r t i t i o n s , heavy l o s s e s were s t i l l s u f f e r e d due t o t h e i n a b i l i t y of noncombustible s t e e l columns t o s u p p o r t l o a d s a t e l e v a t e d t e m p e r a t u r e s - I n 1917-1918, a n e x t e n s i v e s e r i e s of column tests were conducted a t

Underwriters' L a b o r a t o r i e s i n Chicago i n c o o p e r a t i o n w i t h t h e A s s o c i a t e d F a c t o r y Mutual Companies, t h e N a t i o n a l Board of F i r e Underwriters and t h e U.S. Bureau of Standards (Ingberg e t a 1 1921). A t o t a l of 106 s t r u c t u r a l steel, c a s t i r o n and t i m b e r columns were t e s t e d . Although most columns were p r o t e c t e d w i t h e i t h e r hollow t i l e s , b r i c k , gypsum block, m e t a l l a t h and p l a s t e r , o r r e i n f o r c e d c o n c r e t e , some were l e f t b a r e t o s e r v e a s c o n t r o l specimens.

The h i s t o r i c a l s i g n i f i c a n c e of t h e s e tests l i e s i n t h e u t i l i z a t i o n of a new temperature v e r s u s time h e a t i n g exposure, which was i n c o r p o r a t e d t h e f o l l o w i n g y e a r i n t h e ASTH s t a n d a r d , and has s i n c e been adopted by o t h e r n a t i o n a l and i n t e r n a t i o n a l s t a n d a r d s w r i t i n g o r g a n i z a t i o n s around t h e world i n a s l i g h t l y r e v i s e d forms. The r a p i d l y i n c r e a s i n g

t e m p e r a t u r e curve d e p i c t i n g t h e h e a t exposure ( s e e F i g u r e 1 ) i s s t i l l t h e one used today a s s p e c i f i e d i n t h e ULC s t a n d a r d CAN4-S101, Standard

Methods of F i r e Endurance T e s t s of B u i l d i n g C o n s t r u c t i o n and M a t e r i a l s (Underwriters' L a b o r a t o r i e s of Canada 1982). The c u r v e was a p p a r e n t l y e s t a b l i s h e d on t h e b a s i s of maximum t e m p e r a t u r e s i n r e a l f i r e s , observed by u s i n g a s r e f e r e n c e s t h e f u s i o n of m a t e r i a l s of known m e l t i n g p o i n t s ( P e a r c e 1983).

Another s i g n i f i c a n t f e a t u r e of t h e 1918 e d i t i o n of t h e ASTM s t a n d a r d was t h e new p r o v i s i o n t h a t t e s t e d specimens be c l a s s i f i e d

a c c o r d i n g t o t h e i r o b t a i n e d d e g r e e of f i r e r e s i s t a n c e , i . e . t h e l e n g t h of time o r p e r i o d t h e specimen c o u l d s u s t a i n t h e p r e s c r i b e d f i r e exposure and s t i l l meet t h e performance c r i t e r i a s p e c i f i e d (Shoub 1961). We now d e n o t e t h i s c h a r a c t e r i s t i c a " f i r e - r e s i s t a n c e r a t i n g " . That

c l a s s i f i c a t i o n scheme o f f e r e d a new d e s i g n p o s s i b i l i t y whereby b u i l d i n g s could be e r e c t e d w i t h a l e v e l of f i r e p r o t e c t i o n o r f i r e endurance

j u d i c i o u s l y s e l e c t e d t o w i t h s t a n d t h e s e v e r i t y of a n unwanted f i r e i n some p a r t of t h e premises.

0

0 1 2 3 4 5

TIME OF EXPOSURE (hours)

An economical c o n s i d e r a t i o n a r o s e , however, which prevented t h e u s e of t h i s f i r e d e s i g n scheme i n p r a c t i c e : a f o r m i d a b l e number of f i r e tests, each u t i l i z i n g a d i f f e r e n t s e v e r i t y of exposure, would have been n e c e s s a r y t o d e t e r m i n e t h e a p p r o p r i a t e n e s s of u s i n g a c e r t a i n assembly of m a t e r i a l s t o c o u n t e r t h e d e s t r u c t i v e p o t e n t i a l of t h e v a r i o u s f i r e s a n t i c i p a t e d i n r e a l s i t u a t i o n s . T e s t i n g f o r t h e w o r s t c o n d i t i o n s , e s t i m a t e d t o be e q u i v a l e n t t o a 4 hour exposure t o a f i r e t h a t followed t h e s t a n d a r d temperature-time c u r v e , would c e r t a i n l y have been adequate. However, i t s u g g e s t e d c o n s i d e r a b l e wastage of m a t e r i a l s i n t h e c a s e of b u i l d i n g s i n which less s e v e r e f i r e s were expected because of s m a l l combustible c o n t e n t s . B u i l d i n g o f f i c i a l s and d e s i g n e r s l i k e l y surmised t h a t a s h o r t e r e x p o s u r e t o t h e v e r y s e v e r e f i r e s i m u l a t e d by t h e s t a n d a r d temperature-time c u r v e would l i k e l y s i m u l a t e a less s e v e r e f i r e , but no one c o u l d v e r i f y whether o r n o t t h e s e t e s t f i r e s would a c t u a l l y bear any s i m i l a r i t y f o r t h e r e a l - w o r l d f i r e s as f a r a s t h e i r e f f e c t s on b u i l d i n g a s s e m b l i e s were concerned.

ESTABLISHMENT OF FIRE RESISTANCE REQUIREMENTS

It was n o t u n t i l 1928 t h a t a means of determining a r e l a t i o n s h i p between a " s t a n d a r d " f i r e and a r e a l f i r e was proposed by S.H. Ingberg, Chief of t h e F i r e R e s i s t a n c e S e c t i o n a t t h e U.S. N a t i o n a l Bureau of S t a n d a r d s ( I n g b e r g 1928). I n g b e r g had conducted a series of f u l l - s c a l e room burns w i t h v a r i o u s amounts of combustible c o n t e n t s , o r f i r e

l o a d i n g s , s e l e c t e d s o a s t o be r e p r e s e n t a t i v e of o f f i c e , r e c o r d s t o r a g e and household occupancies. On t h e b a s i s of t h e s e t e s t s , i n which he recorded room t e m p e r a t u r e s a s a f u n c t i o n of time, h e proposed t h e e q u a l a r e a h y p o t h e s i s t o compare t h e s e v e r i t y of

a

r e a l f i r e t o t h a t of a s t a n d a r d f i r e of s p e c i f i e d d u r a t i o n . The h y p o t h e s i s e s s e n t i a l l y assumes t h a t t h e s e v e r i t i e s of t h e a c t u a l and t e s t f i r e s a r e s i m i l a r i f t h e a r e a s under t h e i r r e s p e c t i v e temperature-time curve above a b a s e l e v e l a r e e q u a l , a s i l l u s t r a t e d i n F i g u r e 2.

Although s i n c e h a v i n g been demonstrated n o t t o be s c i e n t i f i c a l l y c o r r e c t (Harmathy and L i e 1970), t h e " r u l e of thumb" r e l a t i o n s h i p

proposed by Ingberg between f i r e l o a d and e q u i v a l e n t d u r a t i o n of s t a n d a r d f i r e exposure was r e a d i l y adopted by code a u t h o r i t i e s f o r l a c k of a

b e t t e r o r more convenient way of a s s e s s i n g n e c e s s a r y l e v e l s of f i r e r e s i s t a n c e ( s e e T a b l e 1). To a s s i s t i n t h e a p p l i c a t i o n of t h e concept, numerous f i r e l o a d s u r v e y s were conducted i n t h e f o l l o w i n g y e a r s i n e x i s t i n g r e s i d e n c e s , o f f i c e s , s c h o o l s , h o s p i t a l s , as w e l l a s m e r c a n t i l e and manufacturing e s t a b l i s h m e n t s ( N a t i o n a l Bureau of S t a n d a r d s 1942;

Ingberg e t a 1 1947). The s u r v e y s i n v o l v e d t h e a c t u a l weighing of a l l movable combustible c o n t e n t s and e s t i m a t i n g t h e w e i g h t of f i x e d

f u r n i s h i n g s and combustible l i n i n g m a t e r i a l s .

Armed w i t h f i r e l o a d i n g s deemed r e p r e s e n t a t i v e of e a c h major occupancy, code w r i t i n g b o d i e s had a complete s e t of i n f o r m a t i o n which they could u s e , and indeed have used, t o s e t f i r e r e s i s t a n c e requirements f o r v a r i o u s b u i l d i n g s on t h e b a s i s of t h e i r expected t y p e s of occupancy

TEST CUWE

0

0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 TIME (minutes)

F i g u r e 2. I n g b e r g ' s h y p o t h e s i s

-

e q u a l f i r e s e v e r i t i e s i f A = B.

Table 1. R e l a t i o n s h i p between f i r e l o a d and f i r e s e v e r i t y (Ingberg 1928)

Combustible content*

Standard f i r e exposure ( l b / s q f t ) (kg/m2) d u r a t i o n ( h o u r s )

*Combustible c o n t e n t expressed a s e q u i v a l e n t weight of wood ( w i t h r e s p e c t t o c a l o r i f i c v a l u e ) p e r f l o o r s u r f a c e a r e a .

(i.e. o f f i c e , r e s i d e n t i a l , m e r c a n t i l e , e t c . ) . However, t h e committees r e s p o n s i b l e f o r w r i t i n g t h e codes recognized t h a t f i r e l o a d d a t a were based on a v e r a g e r a t h e r than extreme c o n d i t i o n s and, a l s o , t h a t o t h e r f a c t o r s , s u c h a s t h e h e i g h t and a r e a of b u i l d i n g s , t h e a b i l i t y of t h e occupants t o e v a c u a t e q u i c k l y , degree of awareness of f i r e c o n d i t i o n s , f i r e f i g h t i n g c a p a b i l i t i e s , e t c . , should i n f l u e n c e t h e i r d e c i s i o n s . Consequently, f i r e r e s i s t a n c e requirements a r e o f t e n s p e c i f i e d which i n

some cases a r e i n f l a t e d o v e r t h e l e v e l s o r r a t i n g s which would be s u g g e s t e d by a s t r i c t a p p l i c a t i o n of I n g b e r g ' s g u i d e l i n e s .

I n Canada, t h e s t r u c t u r a l f i r e p r o t e c t i o n requirements have been r e l a x e d c o n s i d e r a b l y s i n c e t h e i r i n t r o d u c t i o n i n t h e f i r s t e d i t i o n of t h e N a t i o n a l B u i l d i n g Code i n 1941 ( N a t i o n a l Research Council of Canada

1941). Now r a r e a r e requirements which c a l l f o r a f i r e - r e s i s t a n c e r a t i n g exceeding 2 h r s (some f i r e w a l l s and f l o o r l e v e l s below g r a d e a r e n o t a b l e e x c e p t i o n s ) ( A s s o c i a t e Committee on t h e N a t i o n a l B u i l d i n g Code 1985a). Although n o t w e l l documented t h e r e l a x a t i o n s may have been based on t h e

f o l l o w i n g c o n s i d e r a t i o n s :

(1) Requirements were tempered w i t h t h e e x p e r i e n c e gained r e l a t i v e t o t h e e f f e c t i v e n e s s of c e r t a i n c o n t r o l measures; f o r i n s t a n c e , evidence t h a t compartmentation r e q u i r e m e n t s , which aim t o e i t h e r i s o l a t e f i r e t o a small a r e a ( f l o o r - t o - f l o o r f i r e s e p a r a t i o n ) o r p r o t e c t a n a r e a of r e f u g e from t h e e f f e c t s of f i r e ( f i r e s e p a r a t i o n of e x i t s ) , were e f f e c t i v e . The i n c r e a s e d confidence i n t h e c o n t r o l measures s u g g e s t e d t h a t s a f e t y

f a c t o r s indeed were h i g h ' a n d c o u l d t h u s be reduced.

( 2 ) B e t t e r f i r e f i g h t i n g c a p a b i l i t i e s meant t h a t a f i r e s u p p r e s s i o n a t t a c k c o u l d be mounted e a r l i e r and more e f f e c t i v e l y , r e d u c i n g t h e need f o r p a s s i v e f i r e p r o t e c t i o n .

( 3 ) It h a s been r e a l i z e d t h a t less s t r i n g e n t requirements would s t i l l be s u f f i c i e n t t o e n s u r e s a f e t y t o l i f e , t h e primary o b j e c t i v e of t h e N a t i o n a l B u i l d i n g Code of Canada. Minimum p r o p e r t y p r o t e c t i o n i s not a n o b j e c t i v e of t h e NBCC and

t h e r e f o r e need not be completely accommodated by c u r r e n t f i r e p r o t e c t i o n requirements.

The f a c t t h a t l i t t l e and sometimes no s t r u c t u r a l f i r e p r o t e c t i o n i s r e q u i r e d f o r s m a l l e r b u i l d i n g s , which people can e v a c u a t e b e f o r e any c o l l a p s e of t h e s t r u c t u r e t a k e s p l a c e , i l l u s t r a t e s t h e t h i r d p o i n t w e l l . But a m i d s t a l l t h e s e changes, what h a s become of t h e d e s i g n p r o f e s s i o n ?

S i n c e t h e e a r l y t w e n t i e s , a tremendous amount of f i r e r e s i s t a n c e tests have been conducted a t l a b o r a t o r i e s a c r o s s North America, y i e l d i n g a w e a l t h of d a t a on t h e f i r e r e s i s t i v e p r o p e r t i e s of m a t e r i a l s and

a s s e m b l i e s . By and l a r g e , t h e s e d a t a a r e mostly a v a i l a b l e t o t h e d e s i g n p r o f e s s i o n a l . L i s t i n g s of t h e r e s u l t s of p r o p r i e t a r y t e s t s conducted on s p e c i f i c d e s i g n s a r e a v a i l a b l e i n Canada from t e s t i n g o r g a n i z a t i o n s such a s U n d e r w r i t e r s ' L a b o r a t o r i e s of Canada and Warnock Hersey (Underwriters' L a b o r a t o r i e s of Canada 1984; Warnock Hersey P r o f e s s i o n a l S e r v i c e s 1986). Furthermore, where t h e f i r e r e s i s t a n c e of an assembly depends s t r i c t l y on t h e s p e c i f i c a t i o n and arrangement of m a t e r i a l s f o r which n a t i o n a l l y - recognized s t a n d a r d s e x i s t , g e n e r i c f i r e - r e s i s t a n c ; r a t i n g s have been developed by t h e A s s o c i a t e Committee on t h e N a t i o n a l B u i l d i n g Code on t h e b a s i s of s u p p o r t i v e test r e s u l t s . These a s s i g n e d r a t i n g s a r e published i n Chapter 2 of t h e Supplement t o t h e NBCC 1985 ( A s s o c i a t e Committee on t h e N a t i o n a l Building Code 1985b).

It seems, however, t h a t t h e p r o l i f e r a t i o n of a v a i l a b l e t e s t r e s u l t s f o r c o n v e n t i o n a l c o n s t r u c t i o n a s s e m b l i e s h a s been a mixed b l e s s i n g f o r t h e d e s i g n p r o f e s s i o n . It c e r t a i n l y h a s e f f e c t e d s u b s t a n t i a l s a v i n g s i n c o n s t r u c t i o n by reducing t h e need f o r c o s t l y f i r e r e s i s t a n c e t e s t s each

time a new p r o j e c t

i s

considered. On t h e o t h e r hand, i t h a s a l s o

s e v e r e l y r e s t r i c t e d d e s i g n i n n o v a t i o n s by e n t i c i n g e n g i n e e r s t o s p e c i f y a l r e a d y t e s t e d d e s i g n s i n s t e a d of e n g i n e e r i n g new systems. It i s a f a i r l y common p r a c t i c e now f o r t h e d e s i g n p r o f e s s i o n a l s ( a r c h i t e c t s o r e n g i n e e r s ) t o d i s c h a r g e themselves of t h e i r r e s p o n s i b i l i t i e s i n meeting t h e f i r e r e s i s t a n c e requirements of t h e Code by simply v e r i f y i n g t h a t t h e i r d e s i g n i s covered by Chapter 2 of t h e NBC Supplement o r one of t h e p u b l i s h e d p r o p r i e t a r y l i s t i n g s . T h i s p r a c t i c e h a s c o n t r i b u t e d

s i g n i f i c a n t l y t o t h e s e p a r a t i o n of f i r e r e s i s t a n c e and s t r u c t u r a l d e s i g n p r o c e s s e s , w i t h some u n f o r t u n a t e consequences. For example, d e s i g n e r s

(and owners) may n o t r e a l i z e t h a t c u r r e n t code requirements do n o t g u a r a n t e e a s a t i s f a c t o r y minimm l e v e l of p r o p e r t y p r o t e c t i o n f o r

b u i l d i n g s , a n o b j e c t i v e which may s t i l l be worthwhile t o pursue s t r i c t l y from a n economic p o i n t of view.

CONTEMPORARY FIRE SAFETY DESIGN

I n r e c e n t y e a r s , c o n s i d e r a b l e r e s e a r c h h a s been undertaken a t i n s t i t u t i o n s around t h e world w i t h a view t o developing a n a l y t i c a l methods f o r c a l c u l a t i n g t h e f i r e r e s i s t a n c e of s t r u c t u r a l elements and assemblies. T h i s e f f o r t h a s produced a number of a l g o r i t h m s which r e l y on e m p i r i c a l o r semi-empirical e q u a t i o n s and a r e f a i r l y w e l l v a l i d a t e d by t e s t r e s u l t s . C a l c u l a t i o n procedures a r e a v a i l a b l e f o r a wide spectrum of primary m a t e r i a l / s t r u c t u r a l component combinations, such a s r e i n f o r c e d c o n c r e t e columns and s l a b s , p r e s t r e s s e d c o n c r e t e beams, laminated timber beams and columns, s t e e l columns p r o t e c t e d from t h e o u t s i d e by a n insu- l a t i n g membrane of gypsum w a l l b o a r d o r sprayed-on m a t e r i a l o r , from t h e i n s i d e , by p l a i n o r r e i n f o r c e d c o n c r e t e . Most c a l c u l a t i o n methods a r e r e s t r i c t e d t o r e l a t i v e l y s i m p l e l o a d i n g c a s e s s u c h a s c o n c e n t r i c l o a d s and pinned end c o n d i t i o n s , but work i s underway t o e x t e n d t h e v a l i d i t y of t h e p r e d i c t i v e a l g o r i t h m s t o a wider a r r a y of d e s i g n c o n d i t i o n s i n c l u d i n g f i x e d o r p a r t i a l l y - f i x e d end c o n d i t i o n s , e c c e n t r i c l o a d i n g , e t c .

It i s n o t t h e purpose of t h i s a r t i c l e t o o f f e r a comprehensive review of t h e c a l c u l a t i o n methods now a v a i l a b l e . E x c e l l e n t reviews, i n c l u d i n g comments on t h e l i m i t a t i o n s of each method, have been p u b l i s h e d by o t h e r s r e c e n t l y (Malhotra 1982; Milke 1985; B a r n e t t 1985). A b r i e f d e s c r i p t i o n of t h e a n a l y t i c a l t e c h n i q u e s w i l l be p r e s e n t e d , however, t o h i g h l i g h t t h e s c i e n t $ f i c p r i n c i p l e s u t i l i z e d , and t o encourage p r a c t i c i n g e n g i n e e r s t o e x p 1 o r e : t h e p o t e n t i a l of t h e s e new d e s i g n t o o l s .

The complete problem of d e s i g n i n g f o r f i r e r e s i s t a n c e can be broken down i n t o t h r e e components: c h a r a c t e r i z a t i o n of t h e e x p e c t e d f i r e

s e v e r i t y , e s t i m a t i o n . of t h e h e a t t r a n s m i s s i o n i n t h e c o n s t r u c t i o n , and knowledge of t h e e f f e c t s of e l e v a t e d temperatures on t h e performance of t h e load-bearing components of t h e c o n s t r u c t i o n .

F i r e S e v e r i t y

Of a l l t h e components of f i r e r e s i s t a n c e d e s i g n , t h e p r e d i c t i o n and a p p r o p r i a t e c h a r a c t e r i z a t i o n of t h e s e v e r i t y of t h e f i r e t o be expected i n a p a r t i c u l a r a r e a of t h e b u i l d i n g being designed i s undoubtedly t h e one a r e a which s t r u c t u r a l e n g i n e e r s a r e most i l l - p r e p a r e d t o address. F i r e i s a complex phenomenon and i t s u n d e r s t a n d i n g r e q u i r e s knowledge of chemical k i n e t i c s , f l u i d mechanics, h e a t t r a n s f e r and thermodynamics. R e a l i s t i c a l l y , one cannot e x p e c t d e s i g n e r s t o a c q u i r e a n in-depth knowledge of a l l t h e s e branches.

Only two o p t i o n s a r e t h e n a v a i l a b l e . The f i r s t i s t o r e l y on t h e v a l i d i t y and accuracy of p r e f l a s h o v e r and p o s t - f l a s h o v e r computer models developed by o t h e r s . (The term f l a s h o v e r r e f e r s t o t h e r a p i d t r a n s i t i o n from a r e l a t i v e l y s t e a d y burning, l o c a l i z e d f i r e i n a room t o a

fully-developed f i r e i n which a l l exposed combustible m a t e r i a l s burn due t o t h e i r i g n i t i o n t e m p e r a t u r e having been reached.) The development of p r e f l a s h o v e r f i r e models i s i n a n embryonic s t a g e , however, s o t h a t t h e p r e h e a t i n g e f f e c t s i n t h e e a r l y s t a g e s of a f i r e on t h e performance of a s t r u c t u r a l member can o n l y be t a k e n i n t o account by making some rough assumptions. By c o n t r a s t , t h e development' of p o s t - f l a s h o v e r o r

fully-developed f i r e modelling i s s i g n i f i c a n t l y more advanced due t o t h e p o s s i b i l i t y of making c e r t a i n s i m p l i f y i n g assumptions t h a t do n o t g r e a t l y a l t e r t h e accuracy of t h e r e s u l t s . Reasonable accuracy a p p e a r s t o be a c h i e v a b l e by some of t h e models under c e r t a i n well-defined c o n d i t i o n s w i t h r e s p e c t t o q u a n t i t y and type of combustible l o a d , t h e presence of openings f o r v e n t i l a t i o n and t h e thermal c h a r a c t e r i s t i c s of t h e f i n i s h m a t e r i a l s l i n i n g t h e room boundaries (Mehaffey and Harmathy 1985).

However, t h e l a c k of c o n t r o l t h e d e s i g n e r has i n p r a c t i c e o v e r some of t h e s e parameters d i c t a t e s t h a t they must be c a r e f u l l y s e l e c t e d s o a s t o r e f l e c t t h e w o r s t c o n d i t i o n s l i k e l y t o occur d u r i n g t h e d e s i g n l i f e of t h e b u i l d i n g . T h i s may n o t always be p r a c t i c a l , e.g. i n t h e c a s e of a s p e c u l a t i v e b u i l d i n g .

The second o p t i o n open t o d e s i g n e r s i s t o u t i l i z e a numerical d e s c r i p t i o n of t h e h e a t exposure c o n d i t i o n s p r e v a i l i n g d u r i n g a s t a n d a r d f i r e t e s t i n s t e a d of one d e s c r i b i n g t h e expected s e v e r i t y of t h e

real-world f i r e . C l e a r l y , t h i s i s n o t o p t i m a l because a n a c t u a l f i r e can f o l l o w a t e m p e r a t u r e v e r s u s time h i s t o r y q u i t e d i E f e r e n t from t h a t

s p e c i f i e d i n t h e s t a n d a r d . Nevertheless, t h i s d e s i g n approach has t h e convenience of a l l o w i n g a p r e d i c t i o n of t h e f i r e - r e s i s t a n c e r a t i n g t h e s t r u c t u r a l assembly would a c h i e v e i f s u b j e c t e d t o a s t a n d a r d f i r e t e s t , a performance measure which a u t h o r i t i e s r e a d i l y recognize.

Heat Transmission A n a l y s i s

Given a s a t i s f a c t o r y c h a r a c t e r i z a t i o n of t h e h e a t exposure, t h e d e s i g n e r may t u r n h i s l h e r a t t e n t i o n t o computing how q u i c k l y temperature w i l l i n c r e a s e a t v a r i o u s s e c t i o n s w i t h i n t h e s t r u c t u r a l components.

i n s t a n t a n e o u s p i c t u r e of t h e temperature d i s t r i b u t i o n w i t h i n t h e member a t any g i v e n time i n t h e c o u r s e of t h e f i r e .

Here, t h e d e s i g n e r can b e n e f i t from t h e numerical h e l p provided by c a l c u l a t i o n a l t o o l s s p e c i f i c a l l y developed f o r t h i s purpose. For

example, TASEF-2 and FIRES-T3 a r e two computer programs f o r c a l c u l a t i n g h e a t t r a n s f e r from f i r e s t o s t r u c t u r e s (Wickstrom 1979; I d i n g e t a 1

1977). Both r e l y on t h e f i n i t e element t e c h n i q u e , one i n two dimensions (TASEF-2), t h e o t h e r i n t h r e e dimensions (FIRES-T3). Computer r o u t i n e s have a l s o been developed based on a f i n i t e d i f f e r e n c e numerical technique

( L i e 1984). The main d i f f i c u l t y u n d e r l y i n g t h e s e approaches i s t h e i n a d e q u a t e knowledge of t h e temperature-dependence of m a t e r i a l p r o p e r t i e s . S t i l l , i n s i m p l e c a s e s where t h e s t r u c t u r a l element i s r e l a t i v e l y homogeneous (e.g. s t e e l ) , a g r e a t d e a l of accuracy i s p o s s i b l e .

Although d i f f e r e n t f i r e exposures can be used, most c a l c u l a t i o n methods u t i l i z e t h e s t a n d a r d temperature-time curve t o d e s c r i b e t h e h e a t exposure environment ( f o r t h e reasons s t a t e d above). This approach

normally e n t a i l s a d o p t i n g t h e temperature end-point c r i t e r i a s p e c i f i e d i n t h e t e s t s t a n d a r d a s t h e f a i l u r e c r i t e r i a d e f i n i n g t h e f i r e r e s i s t a n c e of t h e assembly.

S t r u c t u r a l Response t o Elevated Temperatures

The s e l e c t i o n of t h e s t a n d a r d temperature end-point c r i t e r i a i m p l i e s t h a t t h e temperature-dependent m a t e r i a l p r o p e r t i e s w i l l have undergone changes t h a t reduce t h e load-carrying c a p a c i t y of t h e s t r u c t u r a l component t o a p o i n t where f a i l u r e i s imminent. This

c o n d i t i o n can be c a l c u l a t e d u s i n g a s t r u c t u r a l e n g i n e e r i n g a n a l y s i s , i f s u f f i c i e n t d a t a e x i s t t o c h a r a c t e r i z e t h e temperature dependency of t h e m a t e r i a l p r o p e r t i e s of c r i t i c a l i n t e r e s t .

For example, t h e important mechanical p r o p e r t i e s f o r a s t e e l member a r e y i e l d s t r e s s , u l t i m a t e s t r e s s , modulus of e l a s t i c i t y , p r o p o r t i o n a l

l i m i t and c r e e p parameters. A knowledge of t h e s e p r o p e r t i e s a t e l e v a t e d t e m p e r a t u r e s could e n a b l e t h e d e s i g n e r t o perform a s t r e s s , s t a b i l i t y and deformation a n a l y s e s f o r f i r e c o n d i t i o n s . Again, t h e a n a l y s e s normally r e q u i r e t h e u s e of a f i n i t e element program t o d i s c r e t i z e t h e continuum and t o account f o r t h e non-uniform temperature d i s t r i b u t i o n w i t h i n t h e s t r u c t u r a l member. Another c o n s i d e r a t i o n i s t h e e f f e c t of thermal

expansion of a member on t h e l o a d i n g c o n d i t i o n s when t h a t member i s f u l l y o r p a r t i a l l y r e s t r a i n e d . Such c o n s t r a i n t s w i l l induce normal s t r e s s e s t h a t can reduce o r i n c r e a s e t h o s e generated by t h e a p p l i e d l o a d s and u l t i m a t e l y a f f e c t t h e f i r e r e s i s t a n c e of t h e assembly.

THE FUTURE

A s w e have s e e n , d e s i g n approaches f o r p r o v i d i n g f i r e r e s i s t a n c e have evolved c o n s i d e r a b l y o v e r t h e l a s t hundred y e a r s . E a r l y r e g u l a t o r y e f f o r t s c o n c e n t r a t e d on s p e c i f y i n g noncombustible m a t e r i a l s and r e s u l t e d i n v e r y l i m i t e d d e s i g n f l e x i b i l i t y . The development of a s t a n d a r d t e s t method f o r e v a l u a t i n g t h e f i r e r e s i s t a n c e c h a r a c t e r i s t i c s of s t r u c t u r a l e l e m e n t s and a s s e m b l i e s has p e r m i t t e d a more performance-oriented d e s i g n procedure. However, f u l l - s c a l e f i r e t e s t i n g i s a n e x p e n s i v e way of

v e r i f y i n g t h a t a d e s i g n s o l u t i o n complies w i t h t h e l i f e s a f e t y o b j e c t i v e s of t h e b u i l d i n g code. Moreover, l i t t l e a t t e n t i o n i s now being p a i d t o e c o n o m i c a l l y - d e s i r a b l e p r o p e r t y p r o t e c t i o n . More r e c e n t l y , t h e emergence of c a l c u l a t i o n procedures f o r p r e d i c t i n g t h e f i r e performance of

s t r u c t u r a l members h a s a f f o r d e d a d e s i g n a l t e r n a t i v e t o t h e e n g i n e e r . Even though t h e s e numerical t o o l s n e c e s s i t a t e v a l i d a t i o n by t e s t r e s u l t s , t h e y a t l e a s t draw maximum b e n e f i t from t h e w e a l t h of d a t a accumulated o v e r t h e y e a r s .

A s e n g i n e e r s c e l e b r a t e 100 y e a r s of e x i s t e n c e i n a n o r g a n i z e d f a s h i o n i n Canada, i t may be worthwhile t o ponder what r o l e , i f any, c i v i l e n g i n e e r s should p l a y i n t h e f i e l d of f i r e p r o t e c t i o n . The p o t e n t i a l r e t u r n f o r developing a more c o s t - e f f e c t i v e way of p r o v i d i n g s t r u c t u r a l f i r e p r o t e c t i o n can be e s t i m a t e d by c o n s i d e r i n g some

newly-released s t a t i s t i c s . The American I r o n and S t e e l I n s t i t u t e and t h e B r i t i s h S t e e l C o r p o r a t i o n have e s t i m a t e d t h a t t h e p r o v i s i o n of s t r u c t u r a l f i r e p r o t e c t i o n a l o n e amounts t o between 3 and 5 p e r c e n t of t h e i n i t i a l c o n s t r u c t i o n c o s t of a steel-framed b u i l d i n g ( L i e 1986). According t o S t a t i s t i c s Canada (1986), t h e t o t a l v a l u e of new c o n s t r u c t i o n i n Canada ( l a b o u r and m a t e r i a l s ) f o r t h e y e a r 1985 amounted t o $40.7 b i l l i o n . This f i g u r e i n c l u d e s $16 b i l l i o n worth of s m a l l r e s i d e n t i a l c o n s t r u c t i o n ( 1 and 2 f a m i l y d w e l l i n g s and row housing). By s u b t r a c t i n g t h i s amount and e s t i m a t i n g t h e v a l u e of steel-framed b u i l d i n g s a t approximately 10

p e r c e n t of t h e remaining $24.7 b i l l i o n ( F r o s t 1987), one o b t a i n s a f i g u r e of $2.5 b i l l i o n t o which t h e 3 p e r c e n t s t r u c t u r a l f i r e p r o t e c t i o n c o s t can be a p p l i e d . I f t h i s c o s t could be reduced by o n l y 10 p e r c e n t through t h e u s e of a more r e f i n e d e n g i n e e r i n g a n a l y s i s , t h e s a v i n g s would be of t h e o r d e r of $7 t o 8 m i l l i o n .

The above e s t i m a t e p r o v i d e s only a rough i d e a of t h e s a v i n g s t h a t c o u l d e n s u e from d e s i g n i n g s t r u c t u r a l f i r e p r o t e c t i o n i n a more

c o s t - e f f e c t i v e manner t h a n , f a r example, s t r i c t l y conforming t o t h e c o n s e r v a t i v e p r o v i s i o n s of Chapter 2 of t h e Supplement t o t h e NBCC. Admittedly, t h a t a 10 p e r c e n t s a v i n g may be r e a l i z a b l e i s s p e c u l a t i v e , but s u r e l y some a t t e m p t should be made t o i n v e s t i g a t e what s a v i n g s t h e new technology can a f f o r d . Designers may haye been r e l u c t a n t t o use t h e new c a l c u l a t i o n procedures f o r a number of reasons.

F i r s t , t h e a b i l i t y of s t r u c t u r a l e n g i n e e r s t o assume a l e a d i n g r o l e i n t h e development and a p p l i c a t i o n of new s t r u c t u r a l f i r e p r o t e c t i o n d e s i g n methods i s c u r r e n t l y l i m i t e d by t h e i r l a c k of e d u c a t i o n and

t r a i n i n g i n t h e a r e a of f i r e p r o t e c t i o n . A t p r e s e n t , no Canadian

n o t even a d d r e s s t h e r a t i o n a l e behind t h e r e q u i r e m e n t s of b u i l d i n g codes w i t h r e s p e c t t o f i r e p r o t e c t i o n . The knowledge of h e a t t r a n s m i s s i o n fundamentals would a l s o h e l p t h e d e s i g n e r a p p r e c i a t e t h e a p p l i c a b i l i t y and accuracy of t h e new a l g o r i t h m s f o r c a l c u l a t i n g t h e f i r e r e s i s t a n c e of s t r u c t u r a l e l e m e n t s , a l l o w i n g him o r h e r t o select t h e a p p r o p r i a t e

c o n f i d e n c e l e v e l ( s a f e t y f a c t o r ) t h a t s h o u l d b e a p p l i e d . Courses on h e a t t r a n s m i s s i o n , however, are n o t normally p a r t of t h e u n d e r g r a d u a t e

c u r r i c u l u m f o r c i v i l e n g i n e e r s , who w i l l l i k e l y shun h e a t t r a n s m i s s i o n c a l c u l a t i o n s l a t e r i n p r a c t i c e . Y e t , some l e v e l of f a m i l i a r i t y w i t h h e a t t r a n s m i s s i o n p r i n c i p l e s i s e s s e n t i a l i f o n l y t o a p p r e c i a t e t h e

assumptions u n d e r l y i n g t h e c a l c u l a t i o n methods t h a t a r e becoming

a v a i l a b l e and, t h e r e b y , t h e l i m i t a t i o n s a s r e g a r d s t h e i r a p p l i c a b i l i t y i n a p a r t i c u l a r d e s i g n s i t u a t i o n .

It i s a l s o commonly h e l d t h a t a t o o l i s o n l y a s u s e f u l a s i t s e a s e of o p e r a t i o n . Many f i r e r e s i s t a n c e c a l c u l a t i o n s o f t w a r e can now only be supported by l a r g e mainframes and do n o t come w i t h a n e l a b o r a t e

documentation manual. The development of more u s e r f r i e n d l y , PC-driven s o f t w a r e could encourage t h e u s e of t h e new numerical t e c h n i q u e s ,

provided t h e u s e r u n d e r s t a n d s t h e technology.

I n c o n c l u s i o n , i t would appear t h a t t h e implementation of more c o s t - e f f e c t i v e ways of d e s i g n i n g f o r s t r u c t u r a l f i r e p r o t e c t i o n could be f a c i l i t a t e d through e d u c a t i o n and t r a i n i n g . C e r t a i n l y , i t can be argued t h a t i t behooves t h e s t r u c t u r a l e n g i n e e r t o c o n s i d e r t h e p r o v i s i o n of f i r e p r o t e c t i o n a s a key element of s t r u c t u r a l d e s i g n . A f t e r a l l , f i r e i s an e x t e r n a l phenomenon t h a t a c t s on t h e s t r u c t u r e i n a way n o t

d i s s i m i l a r t o o t h e r elements (wind, snow and e a r t h q u a k e s )

.

H i s t o r i c a l l y

,

e n g i n e e r s have i g n o r e d t h i s d e s i g n component due t o t h e poor

p r e d i c t a b i l i t y of t h e e f f e c t s of f i r e on t h e s t r u c t u r e . However, t h i s excuse i s less t e n a b l e today w i t h t h e r e c e n t i n r o a d s made i n t o

q u a n t i f y i n g f i r e and i t s impact on t h e i n t e n d e d performance of s t r u c t u r a l members.

REFERENCES

ASSOCIATE COMMITTEE ON THE NATIONAL BUILDING CODE. 1985a. National B u i l d i n g Code of Canada 1985. N a t i o n a l Research Council of Canada, Ottawa, Ontario. NRCC No. 23174.

1985b. The Supplement t o t h e N a t i o n a l B u i l d i n g Code of Canada 1985. N a t i o n a l Research Council of Canada, Ottawa, Ontario. NRCC No. 23178.

BARNETT, J.R. 1985. Uses and l i m i t a t i o n s of computer models i n

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