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Deltona Couple · 09-07-2006, 09:59 AM

Quote:

Originally Posted by willravel

Well that works in a perfect mathematical world, but it lacks many variables that were present in the wtc. There was inconsistent resistence due to the theoretical loss of strength from the fire. Some of the supports were as strong as the day they were built and would have offered a great deal of resistence. Some may have been weakened. Those aren't taken into account in the broken leg equasion. I think we should leave the legs thing alone for a while and return to the scene of the crash, as it's an odd comparison and could very easily end up getting confusing.

I think we can all agree that there was an original collapse that had nothing to do with another floor collapsing. The initial failure was attributed to mostly fire damage over time, and some impact damage, yes? Then we should look at the first collapse first.

Tis is a quote from one of many releases discussing the world trade center located at : http://www.serendipity.li/wot/wtc_ch2.htm .

... it is well known that the maximum temperature that can be reached by a non-stoichiometric hydrocarbon burn (that is, hydrocarbons like jet-fuel, burning in air) is 825 degrees Centigrade (1520 degrees Fahrenheit). ...

now if the WTC towers metal trusses were designed to retain their rigidity up to as stated in this quote:

Quote:

Now let us make a guess on the actual heat of the fire.

Fortunately, a number of studies have been done under very similar conditions. In Europe, multi-storied "car parks" are often built of steel, and the possibility of vehicle fire is a distinct possibility. A parked vehicle, loaded with gasoline, diesel, tires, engine oil, engine tar, upholstery, hydraulic fluid, etc. can cause a fire that seems very hot. A number of other vehicles could be parked close to the burning one, and they too could catch fire, with a general conflagration. Any number of cars could contain almost any household items from shopping, etc.

These materials are similar to the materials we would expect in the burning offices of the WTC: jet fuel (which is a refined kerosene, very similar to the diesel used in some European cars), oil, upholstery, etc.

A summary of the results of these studies is published on the Corus page. Go to http://www.corusconstruction.com/ and click on "Fire". Individual articles are listed across the top of the window. The fourth article, "Fire in Car Parks," discusses the temperatures of "any fires that are likely to occur" in a car park (http://www.corusconstruction.com/carparks/cp006.htm).

Presumably, one car could catch fire and inflame other cars parked closely nearby. As explained below, "The maximum temperatures reached [in actual test fires] in open sided car parks in four countries" was 360 degrees C (680 F), and structural steel has "sufficient inherent resistance to withstand the effects of any fires that are likely to occur."

Here is the relevant paragraph, complete: "Steel-framed car parks have been rigorously fire tested in a number of countries (Table 3). These tests demonstrate that most unprotected steel in open sided steel-framed car parks has sufficient inherent resistance to withstand the effects of any fires that are likely to occur. Table 3 lists the maximum temperatures reached in open sided car park tests in four countries. These can be compared with the characteristic failure temperatures for beams carrying insulating floor slabs and columns of 620 [degrees] C and 550 [degrees] C respectively."

Note that the description does not limit the duration of the fire. From this it does not appear to matter whether the fire burned all week or just for two hours. No mention is made, as some people have suggested (from erroneous interpretation of other graphs involving time), that prolonged heat brings about progressive weakening of steel.

Here is the data from Corus' Table 3 (beams are horizontal members, columns are vertical):
Full scale fire tests, Maximum measured steel temperature
Country, Beam, Column
UK, 275 C (527 F), 360 C (680 F)
Japan, 245 C (473 F), 242 C (467 F)
USA, 226 C (438 F), -
Australia, 340 C (644 F), 320 C (608 F)

A fire in a steel car park is a very imprecise event, and the heating of the steel supports varied widely in the tests. The temperature of (horizontal) beams varied from 226 C in the USA to 340 C in Australia; and the temperature of (vertical) columns varied from 242 C in Japan to 360 C in the UK. None of the steel was protected with the thermal insulation that is commonly used in office buildings, including the WTC.

To my mind, this is definitive answer: the maximum temperature in the unprotected steel supports in those test fires was 360 degrees C (680 F), and that is a long way from the first critical threshold in structural steel, 550 degrees C (1022 F).

This being said, the jet fuel temperatures could have reached 1520 deg F., which is ABOVE the 1022 deg F stated in the above quote.....this reaching higher than the required temperature for the steel trusses to exceed 80 or 90% of their load capacity.