No Steel-Structured Building Has Ever Collapsed Due To Fire

Originally posted by Stumpy1
did a plane crash into that building as well? Don't you think that the force of impact of the plane coupled with intense wind force and gravity could have made a the WTC buildings collapse?

As stated before structural damge is structural damage if its casued by plane impact or fire does make a difference. Other steel buildings have had worse fires and structural damge then the WTC building and did not collaspe.

As stated in reports, the buldings withstood the planes impacts and there was no intense wind force that day.

www.tms.org...

The early news reports noted how well the towers withstood the initial impact of the aircraft; however, when one recognizes that the buildings had more than 1,000 times the mass of the aircraft and had been designed to resist steady wind loads of 30 times the weight of the aircraft, this ability to withstand the initial impact is hardly surprising. Furthermore, since there was no significant wind on September 11, the outer perimeter columns were only stressed before the impact to around 1/3 of their 200 MPa design allowable.

Originally posted by ULTIMA1
As stated before structural damge is structural damage if its casued by plane impact or fire does make a difference. Other steel buildings have had worse fires and structural damge then the WTC building and did not collaspe.

The fact that the 'other steel buildings' didn't collapse just says to me that they suffered less structural damage in relation to the design strength than the WTC towers did.

You can't honestly compare wind loading to an impacting aircraft unless you believe a 201MPa wind loading would smash holes in the outer wall. What effect would you expect from a wind in excess of 200MPa loading and where would you expect a failure (if any) to occur?

Originally posted by mrRviewer
there is a little mall by me that burnt up. it had steal beams on walls and ceiling.
the walls stayed straight but all the roof and ceiling beams are bent "extremely warped". if it had too many stories it would have collapsed. i doubt it got as hot as a cement steal building that was hit by a speeding plane filled with its burning fuel. there other unusual events of that day that dont add up but i dont think the power of steal is all powerful considering the hight and power of the impacts.

Extremely warping flimsy roofing trusses do not equate to structural steel columns.

Talk about comparing apples with oranges.

[edit on 4/15/2008 by Griff]

[edit on 4/15/2008 by Griff]

Originally posted by thedman
It had a core of high strenght
concrete up to 16th floor, above that steel was used for structural
support. Steel part of building collapsed, concrete left standing. Which
shows you one thing - concrete fire resistant, steel not.

It shows more than one thing. First, I don't care how "high strength" the concrete was in the Windsor, it would still be far less strong than steel.

Compressive strength of concrete:

Concrete has relatively high compressive strength, but significantly lower tensile strength (about 10% of the compressive strength). As a result, without compensating, concrete would almost always fail from tensile stresses – even when loaded in compression. The practical implication of this is that concrete elements subjected to tensile stresses must be reinforced with materials that are strong in tension. Concrete is most often constructed with the addition of steel or fiber reinforcement. The reinforcement can be by bars (rebar), mesh, or fibres, which provide the required tensile strength to concrete producing reinforced concrete.

Even going by the "concrete is more fire proof" arguement, the untouched steel in the towers would be far stronger to stop a collapse (as the concrete in the Windsor did).

So, what softened up this untouched steel to allow global collapse?

Remember that the strength of concrete gets to about 10 KSI at most (really high strength).

There are higher strengths but those mixes use, guess what, steel fibers for their strength.

A-36 steel's strength is 36 KSI.

10 KSI < 36 KSI.

So, how do we explain a global collapse then?

Originally posted by Pilgrum
What effect would you expect from a wind in excess of 200MPa loading and where would you expect a failure (if any) to occur?

Actually, since it would act as a cantilevered beam, the maximum shear stresses would act near the anchor. Or the base in this case.

If you have exactly 1 ounce of lighter fluid and 1 gallon of water, you know exactly how hot you can get that water by the time you burn all the fuel. A very well-understood science called thermodynamics enables us to do this.

If you have exactly 1 ounce of lighter fluid and 1 pound of steel, you also can say exactly what the highest temperature the steel will ever reach.

Extend this knowledge to a mass of steel & concrete like the impact zone of the WTC, and increase the amount of fuel to what existed in the building.



Add up every BTU of energy available from everything that can burn in the area:

- the jet fuel
- the carpets
- the desks
- the drapes


Then, look at the specific heats of steel & concrete,

Then, find out how much mass of steel & concrete existed on the floors in question,

Then, see how much of a temperature rise those btus will invoke in that mass of steel & concrete.



Guess what? This has been done already.


Conclusions?


The maximum temperature the steel could have reached was 650 F. At this temperature the steel should have still retained 90% of its strength.


This was NOT taking into account the following effects:

- The steel acting like a heat sink
- Heat escaping through windows
- Imperfect transfer of energy from fuel/oxygen to structural materials
- Imperfect fuel/oxidizer ratios


What this means is that the maximum temperature possible was nowhere near high enough to even structurally weaken the steel. Considering that the factors listed above were not included, the 650F temperature would have been the MAXIMUM theoretically possible. The real-world temperatures would have been lower.

reply to post by Griff


Yes - which is why I feel it's not at all reasonable to compare what happened to wind loading capacity. An intense force was applied over a relatively small portion of a single face of the buildings unlike wind which is distributed.

My house survived winds over 100mph a couple of weeks ago but I doubt it would fare very well with a plane, whatever size.



[edit on 15/4/2008 by Pilgrum]

Originally posted by Pilgrum
Yes - which is why I feel it's not at all reasonable to compare what happened to wind loading capacity. An intense force was applied over a relatively small portion of a single face of the buildings unlike wind which is distributed.

But, in design and analysis, point load and distributed load are the same thing.

In structural engineering, we convert the distributed load to an equivalent point load.

So, yes, they would be the same from that perspective.

reply to post by Griff


Considering that 200MPa is a pressure (applied force/area), doesn't the damage to the outer walls indicate application of a pressure far in excess of the wind rating was applied quickly enough to take advantage of the building's inertia?

Seems we're getting away from the fire topic - sorry all.



[edit on 15/4/2008 by Pilgrum]

still, the architects designed these buildings with the knowledge that the just MIGHT get hit by a passenger jet because they were so tall. they had already taken this into account and had them built to withstand this exact scenario! these buildings should not have collapsed!

From what I've seen of the aftermath (post-collapse) I feel nearly all the steel came down stone cold, not hot. Only a very small portion was affected by fire before it came down but I hope we can agree that it did, fact, come down.

Originally posted by Pilgrum
Considering that 200MPa is a pressure (applied force/area), doesn't the damage to the outer walls indicate application of a pressure far in excess of the wind rating was applied quickly enough to take advantage of the building's inertia?

I'd say yes since they punched a hole in the buildings as oppossed to the towers bending and sling shoting them back. Or snapping off at the base.

BTW, KSI is also a pressure. Kilopounds/square inch. Force/area.

And yes, we structural engineers in the US still use pounds and inches. I don't know why, but we still do. Although, we do learn SI ie Pascals, Newtons, etc.

Originally posted by Pilgrum
From what I've seen of the aftermath (post-collapse) I feel nearly all the steel came down stone cold, not hot. Only a very small portion was affected by fire before it came down but I hope we can agree that it did, fact, come down.

But, then you have to think about what I was saying about the concrete in the Windsor.

If the concrete in the Windsor was strong enough to hinder a global collapse caused by the upper floors collapsing, what happened to the stronger uneffected steel in the WTC to cause a global collapse?

And why hasn't any official story come out as to why this happened? Just "it was inevitable".

You guys have brought up some interesting points that got me thinking about something...

How come in the footage of the actuall collapses we dont see burning hot / melted steel? I would think that in all the pulverized powder, we would at least see something so hot as to back up their claim, yet its absent... Ive looked frame by frame and i dont see any fire or red-hot / white hot objects in there.

Also, It seems that there are responses in this thread that have not looked in depth at the other buildings that have gone through fires hot enough to compare to their theory and have not collapsed, I will post it one more time:

www.serendipity.li...

To say apples and oranges, shows that you are not even looking at what can explain why exactly they are both bananas.

Originally posted by Griff

Originally posted by Pilgrum
From what I've seen of the aftermath (post-collapse) I feel nearly all the steel came down stone cold, not hot. Only a very small portion was affected by fire before it came down but I hope we can agree that it did, fact, come down.

But, then you have to think about what I was saying about the concrete in the Windsor.

If the concrete in the Windsor was strong enough to hinder a global collapse caused by the upper floors collapsing, what happened to the stronger uneffected steel in the WTC to cause a global collapse?

And why hasn't any official story come out as to why this happened? Just "it was inevitable".

Star for that one. Its a good question on the concrete in the Windsor Tower compared with the unaffected steel in the WTC. Especially, with the NORT TOWER since it was hit much higher up and there was much more unaffected Steel below.

Originally posted by Pilgrum
The fact that the 'other steel buildings' didn't collapse just says to me that they suffered less structural damage in relation to the design strength than the WTC towers did.

But we have photos of buildings that had worse fires and worst structrual damage and they did not collapse.

reply to post by ianr5741


Seem to think that all the steel has to be heated to failure point - all you
need is to heat one small piece to its critical temperature at which it
begins to undergo deformation and then fails. When this piece fails
loads transfer to adjacent sections which in turn fail initiating collapse.

Originally posted by thedman
Seem to think that all the steel has to be heated to failure point - all you
need is to heat one small piece to its critical temperature at which it
begins to undergo deformation and then fails. When this piece fails
loads transfer to adjacent sections which in turn fail initiating collapse.

Let me ask. Have you ever, in the line of duty as a firefighter, heard of partial collapses initiating a global collapse? Ever? Columns and all?

reply to post by thedman


Can you explain how the steel had gotten hot enough to fail? NIST claimed the air temps may have been 1800 degreesF, which is the max burn temp of jet fuel. How can the air temp be 1800 degrees if the open air burn temp of jet fuel is around 600F? Does wood and office furniture burn at 1800 in open air, or are they implying that the towers were actually big jet engines?
Do you have a link to where NIST found that the steel had been heated anywhere near the temperature they are claiming(1800)??

Thanks

reply to post by thedman


If this were true, CD teams would only have to blow one column to bring down a building. Or even all of the columns on just a few floors. This is not the case.