Pyro_loe schreef:‘Niets mis met norm kanaalplaat’
TECHNIEK | 06-03-2008 00:00 | Thomas van Belzen
“TNO, de Veiligheidsregio Rotterdam-Rijnmond en Efectis weten onvoldoende wat ze hebben aangericht. Iedereen rolt nu over elkaar heen. Dit internationale vraagstuk had binnenskamers opgelost moeten worden.” Het is de stellige mening van oud TNO-adviseur Nico Scholten in reactie op rapporten van bovengenoemde partijen. Hierin staan twee normen over de brandwerendheid van kanaalplaatvloeren ter discussie.
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Duidelijk is dat de rapporten over de populaire vloersoort voor opschudding zorgen. Scholten: “Dit is een internationaal vraagstuk dat we ook zullen meenemen naar een congres in Nieuw-Zeeland volgende maand, waar alle grote brandjongens uit de hele wereld aanwezig. zijn.”
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Internationaal was het blijkbaar al bekend...
Wel iets andere constructie, maar wel de kanaalplaat die faalt in de samengestelde constructie... http://www.dbi-net.dk/media/524f8058116 ... 64ca5f.pdf
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1 Introduction and summary
1.1 The report
This document reports a fire test of concrete hollow core slab elements in a deck structure intended
for use in the strongrooms at the new National Archives in Copenhagen. In the building the
concrete elements will be protected by fire insulation, however, in the present test the concrete
elements were directly exposed to the fire.
The fire test was carried out in continuation of a successful fire test of fire protected elements performed
on February 19. 2000. The present fire test was carried out at the Danish Institute of Fire
Technology (DIFT) on February 21. 2000, re-using the same test arrangement with the fire protection
removed.
The report includes records of:
· Design of the deck assembly and test specimen
· Fabrication of deck assembly and test specimen
· Measurements during and after fire tests
· Course of the fire test
· Test results
· Estimates of failure time of test specimen made prior to the fire test.
1.2 The objective
The objective of the fire test was to determine for how long a deck structure in the strongrooms of
the new National Archives is able to resist a standard fire exposure, while carrying the design load
for the fire condition, if it is not protected by fire insulation.
The decks consist of 220mm deep pre-stressed hollow-core concrete slabs with a 80mm cast-inplace
reinforced concrete topping and partly filled hollow cores.
The decks were tested under conditions like those considered for the strongrooms, i.e. as they
would be incorporated into the building structure and carrying the design load.
1.3 Previous fire tests
Three different types of concrete hollow core slab elements have previously been tested (for another
client, i.e. not for the National Archives in Copenhagen) at the Danish Institute of Fire Technology
(DIFT) during December 1998, reference /6/. The elements - 180 mm, 220 mm and 270
mm deep - were in these tests unprotected, simply supported without top concrete, and subjected
to a standard fire exposure until failure.
All three elements failed at around 25 minutes of exposure and the failure mode for the three elements
was described as a bond/shear - failure at one end support. The failure seemed to occur at
the time when the strands reached a temperature of ca. 100°C i.e. the boiling temperature for the
water chemically bonded in the concrete.
1.4 Current fire test
In the DIFT test furnace a test assembly was set up. The burners of the furnace were controlled so
that the average temperature inside the furnace corresponded to a "Standard fire" (ISO 834).
1.5 Elapse of fire test
After about 11 minutes of fire testing the slabs started to spall on the lower surface near the front
end of the furnace, where a negative bending moment over the support of the slab had been introduced
by pre-loading and rotation restriction. The spalling progressed rapidly with longitudinal
cracks along the hollow cores near the end support and after 14 minutes an opening into a hollow
section was visible. The damage progressed towards the middle of the furnace.
After 23 minutes a 3m long rib of the lower part of the outer side of an element spalled off and an
opening to the surroundings appeared. The thermocouples of the furnace were damaged and the
test was stopped immediately.
The deflection of the elements were at the time of failure considerable, 250mm. This confirms that
failure of a deck element will not occur suddenly as large deflections over a few minutes will give
warning of the danger.
1.6 Post test examination
After the test, when the test element had been allowed to cool, the test specimen was examined.
It was confirmed by the examination, as was suspected from the visual observations during the
test, that the likely failure mode was compression failure in the bottom of the hollow core slab due
to the negative end restraint moment at the support.
It is assumed that the fact that the hollow core elements have no reinforcement, apart from the
prestressing wires, means that the concrete has low ability of plastic re-distribution of stresses.
Early cracking and spalling of concrete is then initiated, as observed during the test, due to temperature
exposure and changes in the chemical structure of the concrete caused by this exposure,
and due to compressive stresses.
Once spalling and cracking starts to progress the moment restraint of the specimen loses load carrying
capacity and a hinge starts to form at the end support. At the same time the prestressing
lines are losing bond to the concrete and sagging progresses rapidly until failure.
1.7 Conclusions
An unprotected deck consisting of:
• 220 mm deep pre-stressed hollow-core concrete slabs with a
• 80 mm cast-in-place reinforced concrete topping utilised in the design capacity,
• additional shear reinforcement ensuring integrity between hollow core elements and top concrete,
• moment continuity at the end supports utilised in the design capacity, and
• loaded as described in this report
is not likely to resist a "Standard fire" (ISO 834) for more than 23 minutes.
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In het rapport staan nog 'mooie' foto's van het falen... Als ik het goed zie zij de kanalen hier ook horizontaal gescheurd!
De foto's lijken op de foto's uit het rapport van Rotterdam- denemarken2.JPG (6.33 KiB) 522 keer bekeken
The reason lies in the faulty test set-up, neglecting completely the influence of connections and surrounding structure on the fire resistance of hollow core slabs. This paper provides a detailed analysis of the effect of fire on prestressed hollow core floors, explains the phenomenon of induced thermal stresses in the webs of the units and the principle of the interlocking effect to realise sufficient shear capacity at fire. Four full-scale fire tests were carried out at the Technical Universities of Liege and Gent in Belgium, to investigate the influence of parameters governing the shear capacity of hollow core slabs exposed to severe fire. The omission of shear reinforcement is completely compensated by correctly designed connections, which also constitute the basis for the stability of the floor at ambient temperature.
