Publisher’s version / Version de l'éditeur:
Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.
Questions? Contact the NRC Publications Archive team at
PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.
https://publications-cnrc.canada.ca/fra/droits
L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.
Fire Study (National Research Council of Canada. Division of Building Research), 1972-02
READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. https://nrc-publications.canada.ca/eng/copyright
NRC Publications Archive Record / Notice des Archives des publications du CNRC : https://nrc-publications.canada.ca/eng/view/object/?id=39d3840a-289e-408f-924b-e77c6df86b22 https://publications-cnrc.canada.ca/fra/voir/objet/?id=39d3840a-289e-408f-924b-e77c6df86b22
NRC Publications Archive
Archives des publications du CNRC
For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.
https://doi.org/10.4224/40001331
Access and use of this website and the material on it are subject to the Terms and Conditions set forth at
Column covers: a practical application of sheet steel as a protective
membrane
NATIONAL RESEARCH COUNCIL OF CANADA DIVISION O F BUILDING RESEARCH
COLUMN COVERS : A PRACTICAL APPLICATION
O F SHEET S T E E L AS A PROTECTIVE MEMBRANE
W. W. Stanzak F i r e Study No. 27 of t h e D i v i s i o n of Building R e s e a r c h OTTAWA F e b r u a r y 1972
COLUMN COVERS: A PRACTICAL APPLICATION O F SHEET S T E E L AS A PROTECTIVE MEMBRANE
by
W. W. Stanzak ABSTRACT
Two f i r e t e s t s on structural steel columns protected by stand- ard gypsum, wallboard held in place with sheet steel column covers a r e described. The t e s t s showed that sheet steel column covers a r e able t o retain the gypsum board for much longer periods of f i r e expo- eur e than other mechanical fastening methods. The f i r e endurance classifications developed were 1 i h r and 2 hr, for two layers of $-in. and two layers of 5/8-in. standard wallboard, respectively.
COLUMN COVERS: A PRACTICAL A P P LIGATION OF SHEET STEEL AS A PROTECTIVE MEMBRANE
W. W. Stanzak*
An e a r l i e r study by the author demonstrated the ability of sheet s t e e l protective membranes t o hold weak and dimensionally unstable m a t e r i a l s in place during f i r e exposure (1). It pointed out that m o s t m a t e r i a l s possessing the desirable t h e r m a l properties of low conductivity and high heat storage capacity lack the most vital c h a r a c t e r i s t i c required for a protective membrane, the ability t o remain in place. While s o m e m a t e r i a l s a r e readily damaged o r removed even at n o r m a l s e r v i c e temperatures, thin sheet s t e e l was shown t o r e m a i n i n place and retain its backup insulation for periods of over two hours under standard f i r e exposure. No attempt was m a d e in t h e previous study t o develop a prototype system, but the r e s u l t s indicated that a practical sheet s t e e l column cover with back- up insulation could be developed.
The p r e s e n t r e p o r t d e s c r i b e s f i r e t e s t s on two s t e e l wide-flange column sections protected with a sheet s t e e l membrane backed by
standard gypsum wallboard**. The covers w e r e designed t o be adaptable t o a variety of applications, joinery methods, and finishing. The
particular covers, joinery methods and finishing used in the f i r e t e s t s should be regarded only a s examples of the general design concept.
*
Steel Industries Fellow, Division of Building Research.+* Standard gypsum wallboard is manufactured by s e v e r a l f i r m s in Canada. The individual products of each f i r m a r e sufficiently s i m i l a r t o yield almost identical f i r e performance, i. e. they generally remain in place f o r a v e r y s h o r t t i m e (twenty minutes o r l e s s ) . To improve the performance, m o s t manufacturers provide a variety of "Type X" wallboards, whose ability t o r e m a i n in place during f i r e exposure is
improved by certain additives, including fibre reinforcement. No satisfactory t e s t (other than the standard f i r e test) h a s been developed, however, t o a s s e s s the quality of these special products (2). Use of
standard wallboard, made possible by combination with the sheet steel, eliminates the difficult m a t e r i a l identification problem involved with the p r o p r i e t a r y products.
A number of backup insulations can be used. In the e a r l i e r feasibility studies (1) m i n e r a l wool was used alone and in combina- tion with gypsum wallboard t o provide f i r e ratings in s t e e l columns and beams ranging from 3/4 h r to 2 h r . One application of such a combination (fire-tested in Holland by the h s t i t u u t T. N. 0. voor Bouwmaterialen en Bouwconstructies) was reported recently (3) in which rock wool batts and 1 mm (0. 0254-in.) sheet s t e e l w e r e used to provide beams and columns with 1
-
and 2-hr f i r e resistance ratings ( s e e Figure 1).The main function of a sheet s t e e l membrane should be to retain insulating m a t e r i a l s that would fall away under f i r e exposure if unenclosed. (In comparison with t h e backup material, sheet s t e e l i s not a good insulator and, f r o m a heat t r a n s f e r point of view, its u s e on the exposed surface contravenes a basic rule of f i r e endurance
rating (4)
-
that m a t e r i a l s with relatively high conductivity should be placed away from the f i r e exposed surface). To be effective, the sheet s t e e l cover must be adequately mechanically joined and backed by sufficient insulation t o provide the desired f i r e endurance. In addition, i t must be thick enough s o that it will not oxidizeexcessively during the anticipated f i r e exposure. Provided that t h e s e requirements a r e met, details can be allowed to vary from one
design t o another a s i s demonstrated in References 1 and 3 and in this paper. A satisfactory column protection does, however, have the following
general requirements :
(1) the protection should be difficult to remove after construction and during normal service,
(2) the protection should be amenable to various degrees of p r e - fabrication,
(3) the system should be capable of rapid and simple assembly by semi-skilled o r unskilled personnel,
(4) the system should fit in readily with the protective s y s t e m s of other key s t r u c t u r a l components,
(5) the aystem should preferably comprise only generic m a t e r i a l s . (6) the system should be economical in comparison with other s y s t e m s
offering s i m i l a r quality and protection,
(7) the finished protection should be aesthetically pleasing o r a t l e a s t unobtrusive.
Cognisance of these general requirements was taken in the design of the t e s t specimens.
DESCRIPTION OF TEST SPECIMENS
Two identical column sections w e r e similarly protected with a sheet s t e e l membrane backed by a double layer of gypsum wallboard. Two thicknesses of board w e r e used and the s t e e l seam details differed in the two specimens. The general design i s illustrated in Figure 2. A gypsum insulating backup material, a sheet s t e e l cover with a
mechanically fastened seam and a s e a m cover a r e the essential design features.
A description of the individual t e s t specimens follows. The item numbers correspond with the p a r t numbers in Figure $.
Specimen No. 1
1. Wide-flange s t e e l column section: 10 W F 49, 8 ft 1 in. long, s t e e l specification CSA G40. 12, supplied with welded end plates,
$
in. thick by 12 in. square.2. Regular gypsum wallboard, nominally
Q
in. thick (measured 0. 510 in. ), 8 ft long, conforming t o CSA A82. 27, density approx. 50 lb/ft3.3. 0.023 in. thick cold rolled steel, 8 ft 1 in. long, prepainted s e m i - gloss white, brake formed into top -hat section.
4. 1 in. by 2 in. (nominal) wood s t r i p (measured
$
x 1 5/8 in.) joint cover, painted semi-gloss black.1
5. Self -threading s t e e l s c r e w (8-32, 7 in. long), attached 24 in. o. c.
S ~ e c i m e n No, 2
1. Wide-flange s t e e l column section: 10 W F 49, 8 f t 1 in. long, s t e e l specification CSA G40. 12, supplied with welded end plates,
p
in. thick by 12 in. square.2 . Regular gypsum wallboard, nominally 5/8 in. thick (measured 0. 650 in.), 8 ft long, conforming to CSA A82. 27, density approx. 50 lb/ft3.
3. 0. 032 in. thick cold rolled, wiped zinc coated (galvanized) steel, 8 f t 1 in. long, brake formed into top -hat section.
(On specimen no. 2 the joint was crimped with a standard crimping tool, 1 2 in. o. c. The wood t r i m o r joint cover was omitted.)
CONSTRUCTION O F TEST SPECIMENS
All construction was c a r r i e d out by m e m b e r s of the staff of the Division of Building Research. The basic procedure was s i m i l a r for the two specimens, and the illustrative photographs w e r e taken during the assembly of specimen no. 1.
Gypsum wallboard, supplied in 4 ft by 8 ft sheets was pre-cut t o s i z e with a standard cutting knife. Two pieces, sized t o fit over the flanges, w e r e placed and each was temporarily held with two s t r i p s of masking tape (Figure 3). Figure 4 shows completion of the f i r s t layer, with two pieces of masking tape holding each board temporarily in position. The second layer was applied in a s i m i l a r manner and the sheet s t e e l column cover was positioned (Figure 5), closed, 1/8-in. holes punched with a Whitney punch, and the s e a m s fastened with sheet metal screws, approximately 2 f t o. c., with one s c r e w being about
1 ft on either s i d e of the mid-height of the column. The self-nailing wood s t r i p was centre-grooved t o a depth of about
$
in. and p r e s s e donto the seam. The completed specimen is shown in Figure 6.
F o r specimen 2, the procedure was identical up t o the stage illustrated by Figure 5. Then the seam was crimped at approximately 1 ft o. c. with a mechanical crimping tool commonly employed i n the drywall t r a d e for fastening s t e e l studs to floor and ceiling runners. Figure 7 shows a close-up of the type of joint produced. The wood finish was omitted a s it i s m e r e l y decorative and does not contribute to the f i r e performance of t h e specimen.
It should be noted that the covers on both specimens w e r e left f r e e to expand on heating, thus anticipating a floor to underfloor clearance of t o 1 in. in practical applications (5).
TEST METHOD
The f i r e endurance t e s t s w e r e c a r r i e d out in accordance with CSA Standard B54. 3-1964 (6) : Alternate test of protection for steel columns.
The upper and lower ends of the specimen w e r e insulated with c e r a m i c fibre to prevent appreciable longitudinal heat transfer. Temperatures on the s t e e l cross-section w e r e measured by fifteen chrome1 -alumel thermocouples peened into the s t e e l a t five levels ( F i g u r e 8). To demonstrate the degree of protection afforded by the sheet s t e e l cover, two thermocouples w e r e located a t mid-height between t h e s t e e l and outer layer of wallboard (specimen no. 2 only).
The furnace temperature was measured by nine thermocouples positioned symmetrically about the column ( F i g u r e 9). All thermo-
1
couples w e r e enclosed in
in.
black iron pipe with a carbon s t e e l cap a t the tip. The junction of the thermocouples was placed 12 in. away from the surface of the specimen. Both the individual t e m p e r a - t u r e s a t the nine points and the average of the nine thermocouplesw e r e recorded during the test. Fuel input t o the furnace was controlled automatically to make the aver age t e m p e r a t u r e follow the course
specified by CSA B54.3.
Figure 10 shows column no. 2 installed in the furnace immediately before the f i r e test.
OBSERVATIONS
DURING
FIRE TESTS T e s t No. 1At 1 min the wood t r i m ignited, flaming brightly in the dark furnace. Thirty seconds l a t e r the s t e e l began t o bulge slightly n e a r mid-height and the white paint on the s t e e l cover was blackening. The wood t r i m continued flaming until about 8 min, when i t s c h a r r e d remains began to fall from the column. The vertical s e a m was observed t o have opened about in. n e a r the c e n t r e a t 35 min. By 45 min this opening had increased t o 2 in. o r more, however, the wallboard behind was s t i l l intact. No further significant change was observed until 110 min, when the bulging of the s t e e l at mid-height began increasing at a noticeable rate. At 1 1 3 min the cover split open and much of t h e protective m a t e r i a l fell away. The t e s t was terminated a t 1 h r , 55 min.
Figure 11 shows the condition of the specimen in the furnace after it had cooled. Note the bulging on the right side of the seam;
it i s s i m i l a r t o the appearance of the left side, just before the cover split.
T e s t No, 2
Flames began t o i s s u e from the seam joint at about 3 rnin and continued for about 2 min before dying down. At 25 min some
buckling was observed along the lower half of one s e a m but the seam was not open. By this time the zinc coating had begun to blister off the s t e e l in l a r g e bubbles. No significant changes w e r e observed during the remainder of the t e s t with the cover and s e a m joint being relatively intact a t 143 min, when t h e t e s t was terminated.
Figure 12, showing the specimen in the furnace after cooling, indicates the condition of the seam joints and the cover. The opening on one of the joints shown in the photograph was not observed during the f i r e test. It should be noted that the wallboard behind is s t i l l in place.
RESULTS
The average furnace temperature during the f i r e t e s t s was always within the allowable limits, and a computation indicated that no time correction needed to be applied to the results. Figures 13 and 14 a r e plots showing t h e average furnace t e m p e r a t u r e s and t h e temperature r i s e of the columns at the cross-section causing t h e r m a l failure. Specimen No. 1 failed at level 1 (top, Figure 8) at 110 min. Specimen No. 2 exceeded the 1000" F allowable average t e m p e r a t u r e at level 1 at 139 min.
Accordingly the column specimens would receive f i r e endurance classifications of 1$ h r and 2 h r respectively.
COMMENTS
1. The fact that both failures occurred at level 1 is interesting. In most s t e e l column t e s t s conducted in the DBR/NRC floor furnace the failure h a s occurred at level 5, which coincides approximately
with the level of the propane burners (7). The exceptions have normally involved protective m a t e r i a l s containing considerable quantities of f r e e o r combined moisture.
*
*
The gypsum used in f i r e protective m a t e r i a l s i s calcium sulphatedihydrate, of which about 20 p e r cent by weight i s water of crystallization. When the product is exposed t o f i r e this water is released and finally driven off a s steam.
Harmathy (8) has found that moisture migrates away from the f i r e exposed surface towards the coolest p a r t of the construction. Because of the effect of gravity on migrating water the opportunity for re-condensation of moisture is obviously g r e a t e r in t h e lower cooler portions, and this in p a r t explains the temperature differences between t h e t h r e e cross-sections plotted in Figure 15.
Also, except at the burner level, furnace temperatures tend t o be higher near the top of the furnace, and i t is m o r e difficult t o
insulate t h e top of the specimen against longitudinal heat t r a n s f e r than i t is the bottom.
2. The ability of the sheet s t e e l membrane to remain in place and t h e result of a protective membrane suddenly failing h a s again been clearly demonstrated. F o r specimen 1 the membrane burst about
3 min after t h e r m a l failure had occurred at level 1. Note the rapid r i s e of t e m p e r a t u r e a t 113 min (Figure 13), after the column suddenly became unprotected.
It should be recognized that while s t e e l is not a good insulator, i t does afford some protection from the exposing f i r e a s may be seen from Figure 16. The interface between the back of the sheet s t e e l and the f i r s t layer of insulating m a t e r i a l was about 1 5 0 ° F cooler than the furnace and 80 -1 00" cooler than the calculated surface t e m p e r a t u r e of t h e s t e e l throughout most of the f i r e test.
3. In these and many other t e s t s , s t e e l has been observed to oxidize quite rapidly when a t o r near the furnace temperatures, and t h e oxide h a s a s i m i l a r appearance to the "mill scalett found on hot rolled plate. The thickness of s t e e l required depends to some extent on the p r e s s u r e the deteriorating insulating m a t e r i a l s exert on it, but to a g r e a t e r extent on the temperature it attains and at which i t must function.
In a previous t e s t (1) the 0.022 in. thick s t e e l cover burst at 120 min; in the current t e s t no. 1 the 0. 023 in. thick cover burst at 113 min. The residual thickness (i. e. thickness of s t e e l not oxidized) i n the l a t t e r t e s t was approximately 0. 018 in., and thinner in local a r e a s ; in the former, it was about 0.012 in. G r e a t e r p r e s s u r e exerted by the weight of a double layer of gypsum board (as opposed t o a single layer) explains t h e e a r l i e r failure of the second cover.
4. The s e a m s opened considerably during the f i r s t test, but t h e wallboard remained in place. This indicates that local distortions
and openings in the cover a r e unimportant, a s long a s it remains in place on the column.
C ONC LUSIONS
1. The sheet s t e e l membrane column cover was shown to hold standard gypsum wallboard in place for much longer periods than other fastening methods, and t o provide:
(a) a f i r e endurance classification of I+-hr using two l a y e r s of *-in. board ;
(b) a f i r e endurance classification of 2 h r using two l a y e r s of 5/8 -in. board.
2. A sheet s t e e l column cover for a 2-hr design should have a minimum gauge of 0. 025 in.
3. A sheet s t e e l cover will remain in place provided the s e a m s o r joints a r e fastened by some positive mechanical method. 4. Small local distortions o r openings in the cover do not
significantly impair i t s effectiveness.
5 . A sheet s t e e l membrane is effective in reducing the severity
of t h e furnace exposure, even though it is not a good insulating material.
REFERENCES
1. Stanzak, W. W. Sheet s t e e l a s a protective membrane for steel beams and columns. F i r e Study No. 23, Division of Building Research, NRC 10865, November 1969.
2. Harmathy, T. Z. Testing of Type ltXu gypsum boards and laths. Technical Note No. 508, Division of Building Research, NRC, Nov. 1967.
3. Thomsen, Kjeld. New steel-framed office building in Copenhagen (Denmark). Acier-Stahl-Steel, 1/1971, pp. 6-1 1.
4. Harmathy, T. Z. Ten r u l e s of f i r e endurance rating. Building Research Note No. 46, Division of Building Research, NRC, July 1 96 4.
5. Stanzak, W. W. F i r e endurance--some design considerations. Engineering Digest, Vol. 16, No. 4, April 1970.
6. Canadian Standards Association. Methods of f i r e t e s t s of walls, partitions, floors, roofs, ceilings, columns, beams
and girders. CSA Standard B54.3-1964, Ottawa.
7. Stanzak, W. W. Temperature measurement: alternate t e s t of f i r e protection for s t r u c t u r a l s t e e l columns. Technical Note No. 538, Division of Building Research, NRC, June
1969.
8. Harmathy, T. Z. Effect of moisture on the f i r e endurance of building elements. ASTM Special Technical Publication No. 385, May 1965.
Fig. l a : F i r e Protection of Column. 1. 2 m m cold bent s t e e l sheet.
2. 2 l a y e r s of 2. 5 cm-3. 5 c m Rockwool firebatts, density
1 10/kg/m3.
3. Rockwool batts with density 30 kg/m3.
4. 3 m m round b a r f a s t e n e r s welded to beam.
(Reproduced from Thoms en, Acier-Stahl-Steel, 1/1971)
Fig. lb: F i r e Protection of an Interior Beam.
1. Tentor reinforcement. 7. L a y e r s of 2. 5-3. 5 c m 2. Lightweight tile-concrete slabs. Rockwool firebatts.
3. 3 c m in situ c a s t concrete. 8. 1 m m cold bent s t e e l sheet fastened 4. Dowels cp 8/30 c m . t o deck.
5. 3 c m asphalt. 9. Rockwool batts.
6 . 10 mm gypsum plate. 10. 3 mm round b a r f a s t e n e r s welded to beam. (Reproduced f r o m Thomsen, Acier-Stahl-Steel, 1/1971).
F i g . l c : F i r e P r o t e c t i o n of a F a c a d e G i r d e r
Gypsum plate. 8. 1 m m cold bent s t e e l sheet
T e n t o r r e i n f o r c e m e n t . 9. 2 l a y e r s of 2. 5-3. 5 c m thick
Dowels cp 8/30 c m . Rockwool batt s.
In s i t u c o n c r e t e . 10. 3 m m round b a r f a s t e n e r s . Lightweight t i l e - c o n c r e t e 11. Rockwool batts.
s l a b s . 12. C o r r u g a t e d s t e e l s h e e t .
3 c m asphalt. 13. 10 c m Rockwool insulation.
10 m m gypsum plate. 14. T i m b e r piece. .eproduced f r o m Thomsen, A c i e r -Stahl-Steel, 11197 1).
Figure 5 : Sheet Steel Cover Positioned Adjacent
L E V E L 2
1
L E V E L 3 , - , L E V E L 4 L E V E L 5 F I G U R E 8 D I S T A N C E F R O M THE B O T T O M L E V E L 1 - 6 ' L E V E L 2-
5 ' L E V E L 3-
4 ' L E V E L 4-
3'
L E V E L 5-
2 ' T H E R M O C O U P L E 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 W I D E - F L A N G E C O L U M N S . D R +77u - 3TOTAL OF 9 THERMOCOUPLES r3/4"B L A C K I R O N P l P E U N I N S U L A T E D 3 " B L A C K IRON COLUMN
u
P l P E I N S U L A T E D FIGURE 9LOCATION OF FURNACE THERMOCOUPLES I N
PRESCRIBED FURNACE TEMPERATURE TIME OF FAILUR
AVERAGE FURNACE TEMPERATURE
VERAGE TEMPERATURE LEVEL 1
TIME, MINUTES
AVERAGE FURNACE TEMPERATURE
TIME OF FAlLU
AVERAGE TEMPERATURE LEVEL 1
-
TIME, MINUTES
60
TIME, MINUTES
FIGURE 15 TEMPERATURE DISTRIBUTION COLUMN N o . 2
( C A L C U L A T E D )
-
2 T C ' S U N D E R STEEL-
- --
-
-
-
-
-
- --
- I-
-
I 0I
I
I 1
I
I
I
I I I I
I
0 2 0 4 0 6 0 8 0 I00 1 2 0 I40 T I M E , M I N U T E SF I G U R E 16 C O L U M N TEST N o . 2 , SEPT. 1 3 / 7 2 , 2 LAYERS 5/8
![Risiko- & [und] Schutzfaktoren der psychischen Gesundheit humanitärer Einsatzhelfer : eine systematische Literaturübersicht](data:image/gif;base64,R0lGODlhAQABAIAAAP///wAAACH5BAEAAAAALAAAAAABAAEAAAICRAEAOw==)