Debunk This

[The Almond]

Here's my question: Wouldn't a vaccuum pull the floor up at the same time it's pulling the ceiling down? Whatever increase in speed of the ceiling that is caused by a vaccuum pulling it towards the ground would be offset by the decrease in speed of the floor caused by the vaccuum pulling it away from the ground, right?

I mean it's just so ... stupid.

That's basically true, but you would have to remember that there is no such thing as the great "suck." Vacuums don't suck things, the positive pressure differential pushes things. Thus, in a vacuum, the building remaining attached to the ground would simply not have the force of air pressure pushing back down on it. I doubt this would do any damage to the building, but the rush of air back into the vacuum certainly might.

For the record, the vacuum assisted faster-than-freefall-collapse is the stupidest thing I've heard this week, and it's already Thursday.

 

[Z]

But the aluminum part was a facade, not weight bearing. The facade covered up the steel perimeter columns, which did bear a large amount of the weight of the building.

Yes, and I think I see where I misinterpreted his statement. My apologies... carry on.

 

[Minadin]

The premise is that even if the steel was weakened 60-80% of its strength due to the fire it would have still been strong enough to support the weight of the structure given that it was designed to support the weight of a structure 2 times its actual weight. I'm not sure how else to interpret such figures. Now as to whether the safety factor was actually 2 is another matter.

Wow. Bad math coupled with poor understanding of what you talking about leads to a very flawed premise. Here is an extremely simplified explaination of why your above assumption is so flawed:

Let's assume, for simplicity's sake, that the steel in question is your normal, run of the mill, 36 Ksi steel. With a "safety factor" of 2, that means that it would be loaded up to 18 Ksi, half of its maximum capacity. If that steel was weakened by 60%, it would only be able to support 14.4 Ksi of load. However, it would still be loaded, at minimum, with 18Ksi of force - even if we ignore things like damage to the other structural members increasing the load, and the added forces caused by the deflection, torsion, and other deforming forces on these steel members. If it were weakened by 80%, its load bearing capacity sinks further, down as low as 7.2 Ksi, clearly nowhere near enough to support an 18 Ksi load.

Now, if I have mis-read your statement, please clarify.

 

[Dave Rogers]

Yes, good point. Except for one thing - at the lowest floor, the vacuum wouldn't accomplish anything there, but it still would at the very top ceiling. So you'd get the speed benefit of one floor's worth.

You need to stop thinking about vacuums sucking things down, and start thinking about air pressure pushing them down - one floor's worth of vacuum below the falling block is as good as a hundred, as long as there's some vacuum there still. That assumes a near-perfect vacuum, of course, but we're looking at maximum figures here so let's look at the ideal case. Air pressure on the roof of a WTC tower would be about 40,000 tons by my reckoning (I hope I haven't committed a Stundie here), so it would be comparable with the weight of the falling block, and could result in a fall at about twice gravitational acceleration.

Of course, none of this is even vaguely realistic. Explosives generate very large overpressures, followed by much smaller underpressures, then a smaller overpressure which decays. An explosion big enough to cause a significant amount of vacuum below the falling block would therefore also be big enough that the initial trajectory of the falling block would be upwards.

Dave

 

[R.Mackey]

Of course, none of this is even vaguely realistic. Explosives generate very large overpressures, followed by much smaller underpressures, then a smaller overpressure which decays. An explosion big enough to cause a significant amount of vacuum below the falling block would therefore also be big enough that the initial trajectory of the falling block would be upwards.

Bingo.

The "underpressure" is generally a net underpressure only, as the blast wave exits your structure and creates an overpressure outside, compared to relative ambient inside.

Gases don't oscillate (except in rare instances like superfluids). If I have high pressure at one spot, it won't "overshoot" the average, leaving a relative vacuum, then return to where it was before. Gas dynamics just don't work that way. Gas density may drop below the average, but it will be balanced by temperature, which in turn gives you higher pressures.

If you wanted to shove a building into the ground "faster than freefall," though I can't imagine why you would, you wouldn't do it by setting off explosives in the building. You'd do it by setting off explosives above the building. Former residents of Hiroshima and Nagasaki could tell you all about this. This gives you a net higher pressure above the roof than inside the structure, at least for a few milliseconds, and that will accelerate the building downward. Enough overpressure and you can crush a building like a soda can. Obviously, the amount of explosives required is tremendous, and there is no way this happened at the WTC.

The only other way to create a sudden partial vacuum inside a structure would be to rapidly consume a large volume of air, but to do so without generating a lot of heat. If the building was absolutely air-tight, you could simply combust all of the oxygen, and then wait a long time for the remaining lower density air to cool. Naturally, buildings aren't air-tight enough for this effect to be significant; what happens instead is fresh air is drawn into the building and continues feeding the fire. With the exception of fuel-air explosives, which generate enormous amounts of heat, explosives contain their own oxidizers and will not exhibit this effect at all.

Theoretically you could also do it with the "Cold Bomb," an imaginary device that suddenly lowers the temperature of everything nearby. This would reduce the pressure of the air inside the building by cooling it, perhaps even liquifying it. However, the "Cold Bomb" is pure fiction.

The OP is severely mistaken in his apprehension of the term "implosion."

 

[~enigma~]

. Perhaps you might tell me where such substances can be obtained, and how they manage to get around the laws of thermodynamics?

Forgive me for "helping" the resident CD but thermobaric devices can and do cause vacuums. For example look at the russian vacuum bomb here.

 

[R.Mackey]

Yup, I specifically mentioned FAE's above.

However, the vacuum effect on structures is miniscule compared to the blast that happens first. This initial blast is also certain to create leaks everywhere in the structure... Detonated in a deep cave, however, with walls many meters thick that would prevent leaks, you might get a significant vacuum effect.

Still, by that standard, a flamethrower could be considered a "vacuum weapon." See the Wikipedia article for an example.

 

[Belz...]

"It's typical truther cherry-picking of data"
what did he leave out?

All the stuff they didn't like.

"invented safety factors"
what are the real safety factors?

Well it sure isn't this:

However, it does not matter what temperature the columns heated. It could have been 1100 C, 1500 C, pick a temperature. It also does not matter if the columns bowed. They could have twisted, bent, fatigued, expanded, shortened, changed properties, or whatever. The columns could have lost their safety factor. They could have lost ALL their fire-proofing. It does not matter. The fact is those columns were able to handle the FULL building load during fire when they were at their weakest state.

After invisicrete^tm, invincisteel^tm, .

Do you think the investigation was conducted in a scientifically sound manner regardless of the real cause?

Uh-huh. What do you think ? And why ?

All properly designed building implosions fall faster than gravity because they are "pulled" downward by vacuum.

No, they're not. Stop skipping school.

The president of Uganda, a engineer with 25 years experience, a person who was running out of the world trade center, a member of the demo crew who planted the bombs. Who cares who he is, what does that have to do with his arguments? Just because your a structural engineer or governmental researcher doesn't make what you say true

No but beign an ignorant layman increases the chances of you not knowing what you're talking about.

Like I said, all properly designed building implosions fall faster than freefall. Can you refute this?

No, because it simply isn't true. You're making this up as you go. Controlled demolitions blow up the building's support and lets gravity "pull it" downwards. Why the **** would they want to pull it faster than gravity, anyway ?

Don't forget what Redtail said, by the way: the other debris fell faster than it; so it couldn't possibly have been falling faster than "gravity" unless the falling pieces had rocket boosters.

All I said was that for building implosions they fall faster than freefall

That's a lie. You implied quite clearly that this was the case for the World Trade Center.

Like he said, you are looking at the aluminum facade, not the steel columns, In places where the facade is completely gone and you can see the steel columns, the columns are perfectly vertical and not bent.

Now you're just being ridiculous. If the aluminum FACADE, which is on the OUTER face of the columns, is bowing INWARDS, then the columns are no longer perfectly vertical.

 

[Gravy]

Still, by that standard, a flamethrower could be considered a "vacuum weapon." See the Wikipedia article for an example.

And let's not forget the controlled demolition of earwax by ear candling.

 

[~enigma~]

Yup, I specifically mentioned FAE's above.

However, the vacuum effect on structures is miniscule compared to the blast that happens first. This initial blast is also certain to create leaks everywhere in the structure... Detonated in a deep cave, however, with walls many meters thick that would prevent leaks, you might get a significant vacuum effect.

Still, by that standard, a flamethrower could be considered a "vacuum weapon." See the Wikipedia article for an example.

Isn't it odd (at least to me) that an FAE's work is done when a charge disperses a cloud of flammable fuel (sort of like the jet fuel from flights 11 and 175) and a second charge ignites the cloud (like the fireball). Really is strange how CT's dumb ideas have perfectly normal reasons behind their mysteries.

 

[Belz...]

Anyways....as is with every attempt to debunk these theories the focus has been completely brought of what was originally asked and instead some other random point has been discussed. This whole free-fall vacuum building implosion thing was just a response to one of the posters not even reading the article because of one of the comments about something falling faster than freefall being nonsense (which it isnt).

Of course it's nonsense. How can it fall faster than freefall unless it's propelled ? Do you concede that demolition charges do not create a significant downwards force ?

We are all critical thinkers here right?

No. Some of "us" clearly aren't.

From what I have heard, building implosions fall faster than free-fall. I know at the very least:

1. It falls faster than free fall with air resistance because the air is blown out of the floors.

Semantics. Also, wrong.

What is the consensus on this board for the time it took for WTC7 to collapse?

As far as I'm concerned, hard to determine. The collapse had begun a while before we can actually see visual evidence of it happening. Also, much of the lower floors can't be seen, so we can't tell precisely when it hits the ground.

Be careful with internet videos who try to time it. Often they will purposely make it seem like it is shorter than it really is by either cutting the initial part of the collapse, or starting and ending the count-up too late or too soon, respectively.

The premise is that even if the steel was weakened 60-80% of its strength due to the fire it would have still been strong enough to support the weight of the structure given that it was designed to support the weight of a structure 2 times its actual weight.

...So.. if only 20% of its bearing capacity remains, and the building represents 100% of that... but it was able to withstand 200% normally, doesn't that mean it was still 60% short of holding the building ? How did you calculate this, exactly ?

So your entire theory now rests on the speculation that fireproofing was removed.

So you think you can ram a 767 at full speed into a building and everything'll be dandy ?

Reading the NIST bible its clear that the conclusion "Therefore, the buildings collapsed due to fire" was known beforehand and the evidence was used to work backwards back to the hypothesis

"Clear" ? How is it clear ?

Like all the other CTers who came here before you, your initial post, in which you seemed to imply you were somewhat "on the fence" was a deliberate misdirection. Dare I say, a lie.

 

[Architect]

Right, time to deal with Safety Factors a bit more:

First of all, let's look at how the towers worked structurally.

The WTC structural frame comprised three interlinked elements; an outer loadbearing facade, the floor structure, and the inner core. These three elements acted together in order to provide overall structural stability.

The outer structure resists the force of the wind, however the external envelope also carries part (around half) of the floor loadings - the big give away is the fact that the floors rested on the exterior steelwork, which I assume you will have noticed in photographs.

Now under the effect of wind alone, columns on the windward face are in tension whilst those in the lee are in compression. In reality, however, the dead load of the structure serves to minimise the tensile loads on the windward face. However for this to work, the various parts of the structure have to be adequately tied together - the girder or space frame analogy.

Now in a normal tall building, this is carried out by columns. WTC used a different, composite system comprising lightweight trussed girders and an a reinforced concrete deck on permanent steel shuttering.

The core carried the remaining half (or so) of the gravity loads. The reason that the columns appear to be larger than the exterior facade is because they have to carry more load within a smaller cross-sectional floor (or perimeter) area.

The next thing we have to understand is what we mean by safety factor: the ratio of the breaking stress of a structure to the estimated maximum stress in ordinary use.

However it is important to understand that the loads/forces found on a complex structure such as WTC may be acting in any number of ways; for example horizontal bending or overturning moments, or gravity loads.

In the same vein, there is a difference between the safety factor of an individual part of a structure and the structure as a whole. It is perfectly possible for a steel beam to have a high factor of safety against (say) buckling under vertical (gravity) loads but a different figure for other forces.

Or another way: A beam may will have been designed to deal with certain loads, and hence (say) a transverse bending moment on a beam designed to primarily deal with vertical loadings will be a completely different kettle of fish.

To claim a figure of 600%, or 200%, or 50% as a global safety factor therefore just betrays how little you understand the subject. 600% against what? Which kind of forces? How are they acting? We can therefore only really understand the performance of the structure through global modelling.

Unlike most Cters, NIST actually do this - and not once, but three times. They look at the original design calculations, modern design calculations, and then a more forgiving global model of their own. The latter tells us that:

- Core columns in WTC typically had a Demand to Capacity Ratio (DCR) of 0.83 with around 10.6% of components exceeding design capacity under normal conditions.

- Hat Truss Columns had a typical DCR of 0.59, with 14.3% exceeding design capacity (some by DCRs of up to 1.95).

Other elements of the trusses had lower DCRs, however a truss is only as strong as the weakest member so we can set these to one side.

So where does this take us:

Well, we know that the failure was initiated by collapse of floor trusses resulting in significant buckling and eventually failure of the external load bearing envelope on the impact facades. At this point, the building was doomed to failure. The load would have been redistributed to adjacent areas and to a certain extent the hat trusses.

Now the Hat Trusses may have had up to 0.4 "spare DCR" however this is in respect of design loads. The purpose of the hat trusses was not to cantilever significant loads from envelope to core, but even if it was then it certainly wasn't capable of taking double the design load.

But even if it had been, the INTACT core only had some 0.17 "spare" DCR. that's only about 20%, and we need to bear in mind that some of the core structure already exceeded calculated capacity.

Does this debunk the alternative theory on safety factors enough for you?

 

[azazal]

PE joules= xx kg * 9.8 m/s2 * xx m


energy is force over distance
force is mass times acceleration
therefore energy = mass * acceleration * distance

Just have to chime in here and say WRONG

Ke = 1/2M * V^2

OR

Kinetic Energy = one half mass times velocity squared

1kg moving a 1meter per second = .5j, distance traveled is irrelevant


Please return to basic physics

 

[Belz...]

NIST admits that the buildings fell essentially in freefall.

Uh-huh. What part of "essentially in freefall" makes you snap "faster than freefall" ?

How does that help you ?

Greening is agnostic and his distaste for this forum is clearly well placed.

Irrelevant.

He is absolutely right. Within a few posts of his opening post he was trold to submit his theory for peer review and also told that 99.9999% of the worlds structural engineers agree with the NIST report.

Unfortunately for Apollo his opening post was, shall we say, slightly belligerent. Plus, his rather subtle parody of a CT didn't go ignored, until he cleared it up.

 

[R.Mackey]

I refuted Dr. Greening's opening post with his own words.

Later on when the conversation settled a bit, I pointed out the flaws in his reasoning. I'm sure he's working on a better version now, like any good scientist.

Unsurprisingly, the CT cheerleaders missed the entire point and substance of that thread...

 

[Arus808]

Below we have a classic example of a wiki page being corrupted by the edit of a twoofer

http://en.wikipedia.org/w/index.php?title=Building_implosion&diff=next&oldid=94680837

An annonomous twoofer on jan 30th using RoadRunner as their isp.

and starting with this one (and for each newer edit):
http://en.wikipedia.org/w/index.php?title=Building_implosion&diff=next&oldid=110597282

more vandalism by a truther to link to WTC


and
http://en.wikipedia.org/w/index.php?title=Building_implosion&diff=next&oldid=122079624

clears up the disambiguation

 

[T.A.M.]

is "disambiguation" a word?

TAM

Edit: apparently so...I need to read the dictionary more often.

TAM

 

[CurtC]

Just have to chime in here and say WRONG

Ke = 1/2M * V^2

OR

Kinetic Energy = one half mass times velocity squared

But wasn't that the equation for gravitational potential energy that he was asked about? E = mgh.

 

[Matthew Best]

Can I just interject briefly to commend Architect on his posts, which are a pleasure to read conveying, as they do, technical information in a way which a comparative simpleton such as myself can understand.

Now please return to your regularly scheduled conversation.

 

[qarnos]

If you wanted to shove a building into the ground "faster than freefall," though I can't imagine why you would, you wouldn't do it by setting off explosives in the building. You'd do it by setting off explosives above the building. Former residents of Hiroshima and Nagasaki could tell you all about this. This gives you a net higher pressure above the roof than inside the structure, at least for a few milliseconds, and that will accelerate the building downward. Enough overpressure and you can crush a building like a soda can. Obviously, the amount of explosives required is tremendous, and there is no way this happened at the WTC.

Some of you guys really know your stuff! It makes me realise how much I don't know.

But it seems to me that the only way the WTC buildings could fall at or faster than free-fall is if "they" deliberately went out of their way to make it happen that way. Which would kinda defeat the purpose of making it look realistice.

Perhaps this is one of the "clues" they were leaving for all the super-intelligent 16 year-olds out there.