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Fire Study (National Research Council of Canada. Division of Building Research),
1967-06
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Fire tests on wide-flange steel beams protected with gypsum-sanded
plaster
NATIONAL RESEARCH COUNCIL CANADA
DIVISION O F BUILDING RESEARCH
F I R E T E S T S O N WIDE-FLANGE S T E E L BEAMS P R O T E C T E D WITH GYPSUM-SANDED P L A S T E R W. W. Stanzak F i r e Study No. 16 of the D i v i s i o n of Building R e s e a r c h OTTAWA June 1967
FLRE
TESTS ON WIDE-FLANGE S T E E L BEAMSPROTECTED WITH GYPSUM -SANDED PLASTER
by
W. W. Stanzak*
T h i s r e p o r t d e s c r i b e s a s e r i e s of t h r e e f i r e t e s t s on wide -flange s t e e l b e a m s p r o t e c t e d with gypsum-sanded p l a s t e r . T h e t e s t s w e r e c a r r i e d out i n a c c o r d a n c e with t h e p r o v i s i o n s of ASTM s t a n d a r d E l 19, A l t e r n a t e T e s t of P r o t e c t i o n f o r Solid S t r u c t u r a l S t e e l B e a m s and G i r d e r s ( I ) , which does not r e q u i r e a load t o b e applied during the f i r e t e s t . One of t h e b e a m s w a s loaded for information p u r p o s e s .
In o r d e r t o allow g e n e r a l application of t h e t e s t r e s u l t s , only u n r e s t r a i n e d b e a m s of s m a l l c r o s s -sectional a r e a w e r e tested. A n o n - s t r u c t u r a l top cover having a low h e a t capacity and a high insulating value w a s a l s o employed. A s a r e s u l t t h e b e a m w a s not l a t e r a l l y b r a c e d , a s i t would b e when provided with a n o r m a l floor section. C l e a r l y , n o m o r e s e v e r e condition could occur in p r a c t i c e .
DESCRIPTION O F SPECIMEN
T h e construction d e t a i l s of a typical t e s t s p e c i m e n a r e shown in F i g u r e 1. F i g u r e 2 shows a b e a m before p l a s t e r i n g , and F i g u r e 3 a completed t e s t s p e c i m e n p r i o r t o installation i n t h e furnace. F i g u r e 4 is a view of t h e t e s t s p e c i m e n
installed in t h e f u r n a c e b e f o r e t h e f i r e test. T h e i t e m n u m b e r s below c o r r e s p o n d t o t h e p a r t n u m b e r s in t h e figures.
*
S t e e l I n d u s t r i e s Fellow, Division of Building R e s e a r c h ( F i r s t holder of a n i n d u s t r i a l fellowship established by t h e s t e e l i n d u s t r y of Canada at t h e National R e s e a r c h Council).Wide-flange s t e e l b e a m section, 8 in. by 5 1/4 in. by 17 lb/ft, 16 ft
-
0 in. long, Steel Specification ASTM A36-61T. Box loops, #9SWG(O. 144) annealed s t e e l w i r e , 18 in. on c e n t r e , t a c k welded a t edges of b e a m flanges.F u r r i n g channels, 3/4 in. by 3/8 in. by 18GA(0.0478) supplied in 12 f t
-
0 in. lengths, painted with r e d lead oxide paint, *ire tied t o box loops with t h r e e t u r n s oflBGA(O.048) soft galvanized t i e wire.
2
Diamond m e s h m e t a l lath, 3.0 ~ b / ~ d
,
w i r e tied t o channels6 in. on c e n t r e with 18GA(O. 048) soft galvanized t i e wire. Expanded-wing, galvanized c o r n e r bead, 2 1/2 in. by 2 1/2 in. supplied i n 10-ft lengths.
S c r a t c h coat, 1 p a r t gypsum: 2 p a r t s sand (by weight); a v e r a g e 3
density: 105 lb/ft ; a v e r a g e c o m p r e s s i v e s t r e n g t h of 4 cylinders: 419 psi.
Brown coat, 1 p a r t gypsurn: 3 p a r t s sand (by weight); a v e r a g e 3
density: 105 lb/ft ; a v e r a g e c o m p r e s s i v e s t r e n g t h of 4 cylinders: 473 psi.
F i b r o u s a s b e s t o s cement board, 3/8 in. by 16 in., having a 3
density of 42 lb/ft
.
F i b r o u s a s b e s t o s cement board f u r n a c e c o v e r , 318 in. by 31 i n . , 3
having a density of 42 lb/ft
.
M i n e r a l wool insulating bat, approximately 4 in. thick, having 3
a density of 2.04 lb/ft
.
Stabilizer plate, 5 in. by 24 in. by 3/8 in., welded t o b e a m flush with lower flange.
12. Steel bearing plate,
6
in. b;r 24 in. by 1 in.13. Steel r o l l e r s , 1/4 in. by 8 in. long.
14. R e f r a c t o r y c o n c r e t e furnace l i d s and support b e a m s .
15. R e f r a c t o r y c o n c r e t e f r a m e .
The method u s e d i n applying p l a s t e r t o the specimens i s commonly r e f e r r e d t o a s "three coat work, " although for these t e s t s the usual finish coat was not applied. Nominal p l a s t e r t h i c k n e s s e s w e r e 314, 1, and 1 1/4 in. An attempt was made t o hold the p l a s t e r thickness constant, a s m e a s u r e d f r o m the m e t a l l a t h s u r f a c e , but variations of
*
1/8 in. w e r e not unusual; and variations of a s much a s 1/4 in. below the nominal thickness o c c u r r e d a t a few locations.Lathing and plastering was of o r d i n a r y good workmanship. C a r e was taken to apply the s c r a t c h coat s o a s 'to f o r m a good key behind the metal lath. The brown coat w a s applied a s evenly a s was p r a c t i c a l t o provide the specified p l a s t e r thickness. No c r a c k s developed during the conditioning period. T h i s was done by workmen f r o m a local contracting f i r m ; a l l othe= work
r e f e r r e d t o in this r e p o r t was c a r r i e d out by the staff of the Division of Building Re search.
F i g u r e 5 shows a photograph of a b e a m installed in the furnace immediately p r i o r to the f i r e t e s t . The t e s t s p e c i m e n s w e r e subjected to f i r e t e s t approximately t h r e e months a f t e r the p l a s t e r had been applied.
TEST METHOD
The f i r e t e s t was c a r r i e d out in accordance with the provisions of ASTM specification E-119-61: Alternate T e s t of
P r o t e c t i o n for Solid S t r u c t u r a l Steel B e a m s and G i r d e r s . F u r n a c e t e m p e r a t u r e was m e a s u r e d by nine s y m m e t r i c a l l y
disposed thermocouples enclosed in 13/16-in. OD Inconel tubes
having 0.035-in. wall thickness, the tubes tipped with a carbon s t e e l cap. The hot junction of the thermocouples was placed
1 2 in. below the plane of the b e a m under side. Both individual
t e m p e r a t u r e s a t nine points on the furnace and the a v e r a g e of the nine thermocouples w e r e recorded. The fuel input into the
.
furnace was controlled automatically in such a way that thea v e r a g e t e m p e r a t u r e closely followed the p r e s c r i b e d standard t e m p e r a t u r e / t i m e correlation.
Exposed s u r f a c e t e m p e r a t u r e s w e r e m e a s u r e d a t two points a t the c e n t r e span by m e a n s of unprotected chromel-alumel thermocouples. One was located on the under side of the p l a s t e r on the b e a m flange, the other on the under side of the a s b e s t o s board cover.
S t e e l t e m p e r a t u r e s w e r e m e a s u r e d by 17 chromel-alumel thermocouples peened into the s t e e l b e a m a t locations shown in F i g u r e 6. T e m p e r a t u r e s were m e a s u r e d a t four stations
s y m m e t r i c a l l y located along the length of the beam. T e m p e r a t u r e s on the unexposed s u r f a c e w e r e not m e a s u r e d because the f i r e
endurance of the top section was known t o exceed that of the beams. As was mentioned in the introduction, one of the b e a m s (No. 11, with 1-in. nominal p l a s t e r ) was loaded throughout the f i r e t e s t f o r information purposes. Load was applied by m e a n s of four hydraulic jacks a t two points along the span of the b e a m in
such a way that i t was s t r e s s e d t o i t s allowable limit. Additiopal d e t a i l s and load calculations a r e included in F i g u r e 7.
the beam would be s o proportioned that the t h e o r e t i c a l deflection due to the live load would not exceed 1/360 of the span. T h i s would r e s u l t in a live load e x t r e m e f i b r e s t r e s s of only 16,600 psi. Owing to the unusually light dead load on the b e a m under t e s t , however, i t was decided to apply the full live load p e r m i t t e d by maximum allowable s t r e s s design, generating an e x t r e m e f i b r e live load s t r e s s of 21, 100 p s i . Vertical deflections w e r e m e a s u r e d a t the c e n t r e - and q u a r t e r - p o i n t s of the b e a m by means of t h r e e m e a s u r i n g tapes connected to the b e a m by a mechanical s y s t e m .
The a c c u r a c y of the measurerrlents i s approximately
f
0 . 0 1 in.A detailed d e s c r i p t i o n of the f i r e t e s t facilities of the National R e s e a r c h Council i s available ( 2 ) .
RESULTS
Uniformity of the f u r n a c e t e m p e r a t u r e was v e r y good throughout the f i r e t e s t s ; maximum deviation f r o m the a v e r a g e w a s always well within that p e r m i s s i b l e and no c o r r e c t i o n f a c t o r w a s r e q u i r e d . In the two f i r e t e s t s conducted without a s u p e r - imposed load, no visible d e t e r i o r a t i o n of the p l a s t e r cover could be o b s e r v e d during the t e s t s , but a number of thin c r a c k s w e r e visible when the s p e c i m e n s had cooled.
The p l a s t e r on the b e a m with the superimposed load r e m a i n e d intact until the final s t a g e s of the t e s t , and no damage could be o b s e r v e d a t the t i m e the b e a m attained a n a v e r a g e
t e m p e r a t u r e of 1000°F. After 7 7 minutes the b e a m had deflected
downward s e v e r e l y and had buckled and twisted in a l a t e r a l direction. At this t i m e a l a r g e c r a c k w a s visible a c r o s s the width of the p l a s t e r at about the q u a r t e r - p o i n t of the beam. F i g u r e 8 shows the
collapsed beam i n the furnace a f t e r completion of the f i r e test. F i g u r e 9 i s a view of the s a m e b e a m after it had been removed f r o m the furnace.
The r e s u l t s of the three f i r e t e s t s a r e summarized in Table I . Average b e a m t e m p e r a t u r e s a t the hottest measuring station a r e plotted against exposure time in Figure 10. The station number a t which failure o c c u r r e d h a s been marked in brackets after the nominal p l a s t e r thickness.
Figure 11 i s a plot of vertical deflection and r a t e of deflection v e r s u s time for beam No. I I ; Figure 12 shows the deflection
and r a t e of deflection plotted against the average t e m p e r a t u r e of all the thermocouples located on the lower flange of the b e a m (No. 3,
4, 8,
9 ,
21, 13,14,
18, 19).After cooling, beam No. I I was removed f r o m the furnace
and examined. The p l a s t e r was found to have numerous c r a c k s ; that observed during the f i r e t e s t being over in. wide. Vertical deflections of the b e a m a r e shown in Figure 13. In addition to v e r t i c a l deflection, the b e a m was found to have a l a t e r a l deflection of 3; in. a t the c e n t r e and a twist of approximately 30 deg f r o m the original horizontal and v e r t i c a l planes of the flanges and web. COMMENTS
The p l a s t e r on the lower flange of the beam was applied in such a way that only a limited amount could be deposited behind the plane of the metal lath, i t s thickness being approximately the s a m e a s the d i a m e t e r of the w i r e used for box loops. No a i r gap existed between the protective p l a s t e r and the s t e e l of the lower flange. This indicates that heat t r a n s f e r into the beam is p r i m a r i l y through the m a t e r i a l protecting the lower flange. It may thus be expected
that f i r e endurance t i m e will v a r y l i n e a r l y with t h e thickness of p l a s t e r on the lower flange (when the r e s u l t s a r e plotted on s e m i - log paper). A s m a y b e s e e n f r o m F i g u r e 14, w h e r e this h a s been done, t h e t h r e e points do f a l l into a r e l a t i v e l y s t r a i g h t line.
Considering t h e v a r i a t i o n in p l a s t e r thickness ( e s p e c i a l l y behind t h e m e t a l lath), it would b e s u r p r i s i n g i f t h e t e s t points w e r e t o a p p r o x i m a t e
a
s t r a i g h t line m o r e c l o s e l y than they do in F i g u r e 1 4.T h e r e l a t i v e l y l a r g e s l o p e of t h e line indicates t h a t it would be i m p r a c t i c a l t o exceed a f i r e endurance t i m e of 1 1/2 hr with t h e type of p r o t e c t i o n studied. If t h e lath on t h e under s i d e of t h e b e a m w e r e f u r r e d sufficiently f r o m t h e lower flange t o p e r m i t an air gap, however, a significant reduction of p l a s t e r t h i c k n e s s f o r a given f i r e endurance t i m e might b e expected. T h e effect of a m e m b r a n e p l a s t e r protection will be d e s c r i b e d in a f u t u r e F i r e Study.
It is i n t e r e s t i n g t o note t h a t t h e deflection and r a t e of deflection c u r v e s shown in F i g u r e 1 2 begin t o r i s e v e r y steeply once the a v e r a g e t e m p e r a t u r e of t h e lower flange exceeds 1000°F. T o w a r d s t h e ends of t h e s e t e s t s t h e upper flange w a s a t a
t e m p e r a t u r e approximately 100 o r m o r e d e g r e e s below t h a t of t h e lower flange. T h e a v e r a g e of all t h e t e m p e r a t u r e s on t h e b e a m w a s usually not m o r e than 50 F d e g r e e s below that a t t h e
station causing failure.
According t o t h e Robertson-Ryan c r i t e r i a , c o l l a p s e w a s imminent when t h e a v e r a g e t e m p e r a t u r e i n the lower flange w a s 11 53" F, although i t w a s p o s s i b l e t o c a r r y on t h e t e s t until t h e a v e r a g e t e m p e r a t u r e r e a c h e d approximately 1170" F. T h i s is i n c l o s e a g r e e m e n t with other f i r e t e s t s conducted i n t h e DBR l a b o r a t o r y on s t e e l b e a m s with a r e c t a n g u l a r c r o s s -section. T h e s e b e a m s a l s o had a n o n - s t r u c t u r a l top cover having low h e a t capacity and a high insulating value.
P l a s t e r s with sand a g g r e g a t e have a somewhat higher conductivity than p l a s t e r s with light-weight aggregate. The t e s t s d e m o n s t r a t e d , however, that gypsum-sanded p l a s t e r i s a s a t i s - f a c t o r y m a t e r i a l i n that i t d o e s not d e t e r i o r a t e significantly during f i r e exposure. (The cracking and falling off of p l a s t e r on b e a m No.
II
w a s due t o the deflection of the b e a m and not t o the effects of the f i r e on the p l a s t e r . ) It h a s p r e v i o u s l y been thought that with thick p l a s t e r c o v e r s , l a y e r s of the brown coat would s e p a r a t e f r o m the s c r a t c h coat during f i r e exposure.ACKNOWLEDGEMENT
T h e s e t e s t s w e r e c a r r i e d out a s p a r t of a cooperative p r o g r a m of work in the F i r e R e s e a r c h L a b o r a t o r i e s of the Division u n d e r the S t e e l I n d u s t r i e s Fellowship a r r a n g e m e n t with the Canadian s t e e l industry.
REFERENCES
1. F i r e T e s t s o f B u i l d i n g C o n s t r u c t i o n a n d M a t e r i a l s .
A S T M
Designation: E l 19-61. A m e r i c a n Society F o r Testing and
M a t e r i a l s , Philadelphia, P a .
2. S h o r t e r , G. W. and T. Z. Harmathy. F i r e Endurance T e s t F a c i l i t i e s a t the National R e s e a r c h Council. National R e s e a r c h Council, Division of Building R e s e a r c h , F i r e Study No. 1, Ottawa, J u l y 1960, (NRC 5732).
3. Robertson, A. F. and J. V. Ryan. P r o p o s e d C r i t e r i a f o r
Defining Load F a i l u r e of B e a m s , F l o o r s and Roof Construction During F i r e Test. J o u r n a l of R e s e a r c h , National B u r e a u of S t a n d a r d s , 63C, p. 121 -124, Washington, 1959.
TABLE I
RESULTS O F FIRE TESTS
*
P l a s t e r thickness was m e a s u r e d a t 10 points on e a c h f a c e of the T e r m i n a t e d1 1/4 1 1 / 8 71 2 75
beam, spaced s y m m e t r i c a l l y in p a i r s along the length of the beam,
*:$ Load F a i l u r e (min)
-
72 1/2-
one location a t the c e n t r e span.
*
In o r d e r t h a t f i r e t e s t s might be t e r m i n a t e d before, but reasonably c l o s e to, ultimate collapse, Robertson and Ryan ( 3 ) proposed that - -42
the point a t which both 6 2
-
and 6' r-
~2c 150d should be regarded c 800d
a s a n indication of load failure. hit h e s e e x p r e s s i o n s 6 = maximum C
deflection, in.; 6' = r a t e of deflection, in./hr;
R
= c l e a r span ofC
principal s t r u c t u r a l element, in. ; d
=
distance between the upper and lower e x t r e m e f i b r e s of the principal s t r u c t u r a l element, in. The c r i t i c a l values have been m a r k e d by a r r o w s in F i g u r e s (11) and (12) and w e r e taken a s the end point of the t e s t .F I G U R E 1
T Y P I C A L T E S T S P E C I M E N
I - .
--I
F I G U R E 4 B E A M I N S T A L L E D I N F L O O R F U R N A C E B R 3 8 4 0 - 0
( E a s t )
F I G U R E
6
L O C A T I O N O F T H E R M O C O U P L E S O N STEEL C R O S S - S E C T I O N
B R 3 8 4 9 -3S t e e l b e a m : 8 W = 1 7 A = 5 sq i n .
1.
156"-
! I - 5 6 . 4 i n . ' D = 8 i n . I t BMDL , E s t i m a t e d w e i g h t o f g f i n i s h e d b e a m : 5 5 0 BM,, = 5 5 0 x 1 8 6 t 8 B MLL = 1 2 , 8 0 0 i n l l b l2 800 9 1 0 p s i = 1'4.1 P e r m i s s i b l e d e s i g n s t r e s s f o r A 3 6 s t e e l-
= 0 . 6 1 x 3 6 , 0 0 0 2 2 , 0 0 0 p s i .-.QLL = 2 1 , 1 0 0 p s i T h e o r e t i c a l d e f l e c t i o n d u e t o l i v e l o a d 186 0.5211 1 1 3 6 0 s p a n d e f l e c t i o n =-
3 6 0 0 5 2 N o r m a l d e s i g n l i v e l o a d = 5 2 2 0 x - = 4 , 1 0 0 ~ 0 . 6 6 N o r m a l d e s i g n l i v e l o a d s t r e s s = 2 1 . 1 0 0 x 0 ' 5 2 = 1 6 , 6 0 0 p s i F I G U R E 7 B E A M L O A D I N G O R 3 8 4 9 - 4>,. - ,
0 10 20 30 40 50 60 70 80 9 0 T I M E , M I N
F I G U R E 10
A V E R A G E T E M P E R A T U R E O F S T E E L A T H O T T E S T S T A T I O N V S T I M E
N o t e : D e f l e c t i o n d u e t o l i v e l o a d w a s 0 . 6 2 I n .
-
D e f l e c t i o n R a t e o f d e f l e c t i o n 10 20 30 40 50 60 70 80 90 T I M E . M I N F I G U R E 11 C E N T R A L D E F L E C T I O N A N D RATE O F D E F L E C T I O N 8 R 3 8 4 O - 6P C
-
VI 0 w
