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Technical Note (National Research Council of Canada. Division of Building Research), 1967-04-01
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Possibilities for Large-Scale Fire Tests Employing Expo Temporary
Buildings
Stanzak, W. W.
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No.
DIVISION OF BUILDING RESEARCH
NATIONAL RESEARCH COUNCIL OF CANADA
482
NOTlE
'f
EClHI N ][CAlL
LIMITED DISTRIBUTION
PREPARED BY
w. w.
Stanzak* CHECKED BYApril 19b7
PREPARED FOR Limited distribution
SUBJECT Possibilities for Large-Scale Fire Tests
Employing Expo Temporary Buildings
At a meeting of the Subcommittee on Expo Fire Tests of the CISC Committee on Engineering and Research on 13 January 1967, the members were taken on an inspection tour of the Expo site, in order to select one or two structures suitable for large-scale fire experiments. A general discussion session following the tour indicated that additional infor mation was r equir ed befor e the subcommittee could take any further action. The author, who attended the meeting as Steel Industries' Fellow, undertook the delineation of areas useful for investigation in the light of studies completed and in hand at fire research laboratories in various countries.
To view what follows in its proper perspective, emphasis must be placed on two important questions that designers should be able to answer:
1. Under what conditions must steelwork be protected? 2. Where protection is required, how much must be
applied to keep damage within acceptable limits?
* Steel Industries Fellow, Division of Building Research. (First holder of an industrial fellowship established by
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Building Code authorities have undertaken to answer these questions in the public inter est, but it should not be for gotten that fire regulations must often be based on past experience and judgement rather than on evidence from controlled experiments supported by theory. The immediate objective of any fire test, therefore, would be to provide a more scientific basis for modern building regulations.
A broader purpose of fire experiments and research should be to simplify and generalize building regulations to permit design against the lexpected load or hazards, as is now the case in structural engineering. The ar gument most frequently entered against this is that the occupancy of a building may change during its lifetime. An extreme parallel would be to design all large buildings to withstand a live load of 600 Ib/ft 2 in case they might someday be converted to steel warehouses. A code of general rules for design would make it possible for specially trained structural engineers or competent engineers specializing in fire protection to protect buildings against fire.
A statistical evaluation of fire loads is an important fir st step in achieving realistic design methods. Projects in this area are under way in Central Europe. England and the U. S. A. DBR/NRC will co-operate with the National Bureau of Standards in making as extensive fire load surveys as staff permits. At the 13 January meeting members of the subcommittee agreed that this matter is well in hand.
The purpose of this report, therefor e, is to sketch completed work similar to that now being considered, and to discuss its implications. The final portion of the report will present a number of possibilities for additional work. with particular reference to the Pavilion of the Province of Quebec. In the opinion of the writer, this building, with
appropriate alterations, is the only one suitable for fire tests.
PART I RECENT RESEARCH INTO THE BEHAVIOUR OF ST EEL IN BUILDING FIRES
(a) Fire Tests on Exterior Steel Columns, by W. Bongard This work was carried out in a condemned school
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-were used for the test. All steel columns were placed centrally in the window openings. A fire load of 18 Ib/ft 2 (90 kg/m 2) was used in conducting the tests and temperatures on the columns were measured at 15 points, although the sections were not loaded.
The test schedule provided for variation of the following factors:
1. Type of protection, e. g. intumescent coatings versus radiation shield over exposed flange only.
2. Distance of column from wall of building.
As in many tests of this type, control was poor and the number of variables rather large. In spite of this, Bongard was able to demonstrate satisfactorily that simple radiation shielding on the flange adjacent to the wall or window, provided it projects sufficiently beyond the column flange on each side, yields adequate protection for exterior steel columns. Where a column is not in front of or adjacent to a window, radiation shielding protection is not r equir ed.
Bongard recommends measures for the protection of exterior steel columns. Although these recommendations may be correct, the results obtained do not warrant the formulation of such definite conclusions.
(b) Fire Tests on Loaded Steel Frames, by C. F. Kollbrunner A series of three fir e tests was conducted in a wood-fir ed chamber on a light, partially restrained frame and on a heavy, restrained frame. The profiles of the sections comprising the heavy frame were filled with concrete. A fire load of 5 lb/ft 2
(25 kg/m 2) was used in the first two tests, 10 lb/ft 2 (50 kg/m 2) in the third. The roof of the test chamber was an 8-in. thick (0.20 m) reinforced concrete slab resting on the cross -beams of the two frames. Loading was applied by piling steel plates on two small beams lying across the concrete slab and along the line of the cross -beam on each frame.
Kollbrunner found that both frames withstood burnout of the light fire load (5 lb/ft 2 , 25 kg/m 2) without visible damage.
In the third fire test (fire load 10 Ib/ft 2 , 50 kg/m 2) the light frame suffered slight damage and the heavy frame was still undamaged.
Kollbrunner concluded that:
I.
steel structures, comprising wide flange profiles filled with concrete, but leaving the flanges bare, are able to resistfire loads from 5 to 10 lb/ft 2 (25 to 50 kg/m 2) without damage; 2. unprotected steel structures will not collapse with a fire load
of 5 lb/ft 2 (25 kg/m 2 );
3. from the previous, it follows that steel structures with loads up to 5 lb/ft2, (25
kgJ
m 2 ) need not be protected (see (2) above); 4. investigations of the Swiss Bureau for Fire Prevention showthat fire load in office buildings varies from 2 to a maximum
of 5 lb/ft 2 , (10 to 25 kgJm 2). This does not apply to archives. The steel framework of modern office buildings need not be protected;
5. as test III demonstrated, unprotected steel columns are capable of withstanding a fire load of 10 lb/ft2 (50 kg/ m 2 ) without collapsing;
6. in steel construction one must differentiate between light and heavy members, because light sections present a greater fire hazard owing to their lesser heat capacity. These conclusions were selected from a total of nine drawn by Kollbrunner. Again it would appear that Kollbrunner has drawn many conclusions on the basis of rather limited test information.
In these tests, the control of temperatures in the fire chamber was reasonably good, but loading was not applied as it should have been. The cross-beams, because of the load resistance of the deck, were not very highly stressed; and these were the members subjected to the most severe fire exposure.
(cl Fire Tests in Typical Apartment Units: Joint Fire Research Organization, Boreham Wood, England
This series of experiments is by far the most compre-hensive yet carried out in steel-framed buildings. The first set of tests involved the burning of typically furnished flats, with the fire usually starting in a bedroom. Most members of the
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subcommittee will be familiar with these. The tests in the
furnished flats wer e of demonstrative rather than scientific value. During the second more extensive phase of testing,
wood cribs were used as fuel. These tests varied fire load and ventilation (window openings). Beams and columns were placed at various significant locations outside the building in order to study temperature rise on exterior steel elements. No live load was applied to any part of the structure during the tests.
The results are still being analysed, but the following reports have been completed:
1. The Temperature Attained by Steel in Building Fires, by E. G. Butcher, T. B. Chitty, and L. A. Ashton.
London, H. M. S. O. J. F. R. 0., Fire Research Technical Paper No. 15.
2. Parameters Which Determine the Severity of Fire, by A. J. M. Hesselden. To be published.
3. Analysis of Some Results of Experimental Fires, by Margaret Law. To be published.
4. Comparison Between Furnace Tests and Experimental Fires, by E. G. Butcher and Margaret Law. To be published.
The above reports are primarily concerned with the temperatures on steel sections. A detailed review is not necessary for present purposes. Once the analysis of the results by JFRO is completed much will be known about the behaviour of fire in compartments of relatively small size, and about the influence of air supply on the nature of fires. The work at NRC in Canada is complementary; it is leading to a better under standing of the deflection and instability of steel members in fires.
(d) Behaviour of Steel in Building Fires: National Research Council, Canada, Ohio State University, Underwriters' Laboratories of Canada
In recent years, there has been a trend toward more thorough investigation of the structural behaviour of steel elements and steel structures during fire tests or under fire conditions. Two fire test programs measured restraint and composite action in wide-flange steel beams having a steel deck with concrete fill topping; the results reported are as follows:
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-(l) Effect of Structural Restraint on the Fire Resistance of Protected Steel Beam, Floor and Roof Assemblies, by R. W. Bletzacker, Report No. EES 246/266,
Ohio State University, Columbus, Ohio, 1966.
(2) Load and Fire Test Data on Steel-Supported Floor Assemblies, by N. S. Pearce and W. W. Stanzak, ASTM Special Tech. Publ. No. 422, 1966.
The distinctive feature of these tests is that the strains developed in the principal structural member (wide -flange beam) by the live load were measured at room temperature. This is not normally done in fire tests, although it probably should be. No experimental data ar e available, however, of how the load is redistributed among elements of the assembly as the fire test progresses.
The experimental work on the creep properties of structural steels in progress at DBR/NRC makes possible not only the calculation of deflection of steel beams and trusses in fire, but also a theoretical examination of the stress distribution in the structural element(s} at any time during the fire exposure. Unfortunately, the procedures developed so far apply only to simply supported structures. Two papers describe this work:
(3) Deflection and Collapse of Steel-Supported Floors and Beams in Fire, by T. Z. Harmathy, ASTM Special Tech. Publ. No. 422, 1966.
(4) Temperature Criteria of Failure of Steel-Supported Floors and Beams in Fire, by T. Z. Harmathy and W. W. Stanzak,
presented at JFRO Symposium, Boreham Wood, January 1967. Summary to be published.
Understanding of the performance of structural elements in fir e is developing satisfactorily. The same thing cannot, however, be said for complete building structures. Controversy is developing following recent research over the validity of the standard time temperature curve and its relation to actual fire situations. Fire testing laboratories agree that it would not be practical to change the standard curve at this time, nor to introduce a number of different curves for various types of constructions. Changes, if any, should be made in the way fire test results are to be interpreted or related to conditions existing in buildings. Much work remains to be done in this area.
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Another difficult subject is the relation between different types and forms of fuel. The standard fuel in fire tests has been wood. The question is how the burning of wood cribs compares with the burning of an equivalent (calorific) amount of normal building contents. The relation between fire severity and surface area/volume ratio of ｦｵ･ｬｾ also, has not been quantitatively
investigated.
The most important and challenging ｰｲｯ｢ｬ･ｭｾ however (everyone at the JFRO Symposium agreed on this point), is the conversion of available research results to practical simplified procedures or data that can be used by the building designer. In the field of fire technology there is an extremely lar ge gap between research and practice; much information is available. but it is not being put to use. Proposed research projects. therefore, must be planned and reviewed carefully to ensure that the information sought is ｲ･｡ｬｬｹｾＬ and that it does not duplicate work which has been completed but never converted into practice.
PART II FACTORS FOR POSSIBLE INVESTIGATIONS AT EXPO Discussions were held at the Fire Research Section,
National Research ｃｯｵｮ｣ｩｬｾ Fire Research Organization, England, and the British Iron and Steel Federation regarding the need for additional research on the behaviour of steel in fire. The
following ar e offer ed as subjects for research. employing
Expo temporary buildings, but they are subject to further study as to their feasibility.
(a) Temperatures Attained by Massive Steel Members in Fire In previous fire tests, all steel members have been of relatively small cross -section. With very massive steel sections there will be a substantial temperature differ ence between the
surface of the steel and the core of the section. Temperatures considerably in excess of those considered "critical" could therefore be tolerated on the surface of such sections. No doubt
substantial savings could be achieved by applying realistic protection to massive members, and in many cases, protection is not required at all.
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(b) Fuel
Information is urgently required concerning fire behaviour using fuel cribs (wood) with different surface area/volume ratios. The effect of locations of fuel cribs in a compartment has received very limited study. Also, the previous two points have not yet been r elated to the behaviour of fir e caused by combustibles ordinarily found in buildings.
(c) Fires in Large Compartments
This is a matter not as yet investigated. (d) Behaviour of Linings in Large Compartments
At the J. F. R. O. a study of the behaviour of flames on ceiling linings has been under way for some time, and a report is soon to be issued. The effect of linings on the spread of fir e in lar ge compartments, however, has not been investigated under controlled conditions. Combustible linings present a severe hazard, even though their contribution to the total fire load is normally small.
(e) Exterior Steel Members
Temperature rise on exterior steel has been investigated reasonably thoroughly, but additional work would be of use,
for example, the use of more massive members. The previously suggested investigations would be accompanied by general interest studies such as measurement of radiation from window openings, variation of ventilation and heat balance calculations.
Lar ge scale investigations involve considerable effort and expense if they are to be carried out thoroughly. The preceding suggestions must at this time be regarded as possibilities only, but they should be studied very carefully, with specific reference to the buildings at the Expo site.
