David Chandler responds to Frank Greening

June 17, 2009
Greening vs. Chandler and Newton’s Laws:


The occasion for Frank Greening’s letter is correspondence with several physicists, chemists,
and engineers discussing arguments I made in a video posted on the Architects and Engineers
for 9/11 Truth YouTube page:

This is my response to his letter.

Chandler concludes that the block was subject to a net force of 0.64M(upper)g. Prior to the
collapse of WTC 1, the lower portion of the building was perfectly capable of holding up the
upper block which we know exerted a downward force equal to M(upper)g. So why, once the
collapse started, was the lower section of WTC 1 not able to support a load of 0.64M(upper)g?

You are confused on this point. It was the net force on the upper block which was 0.64g
downward. The net force consists of the downward force due to gravity combined with the
upwardly directed normal force. For the net force to come out 0.64g, the normal force had to
have been 0.36g. By Newton’s third law, the load on the lower section was also 0.36g.

Chandler’s answer to this question: During the collapse of WTC 1, the only way the upper
block could have accelerated at 64 % of g was for the lower section of the building to have
continuously lost its load-carrying capacity, presumably through the occurrence of column
failures ahead of the collapse front. The fact that the downward acceleration was not far
below g shows that columns failed without significant resistance. This, concludes Chandler,
proves that the destruction of WTC 1 was a controlled demolition.

Close, but you have turned my quantitative assessment based on evidence into a hand-waving
general statement. In particular, the resistance force is measurably only 36% of the weight of
the falling block. Since the lower section of the building was designed to carry 3-5 times the
weight of the upper section, the lower section appears to have lost about 90% of its load
carrying capacity. Some mechanism apart from the falling mass must have operated to
account for this failure.

The main problem with Chandler’s analysis is that he is ignoring what actually happens to a
building during collapse.

My analysis here follows the general model laid out by Bazant and Greening, which is indeed
far removed from what actually happened. The Bazant-Greening model postulates a coherent
falling block which observations show did not exist. At most there was a falling mass of
disassociated rubble from a top section of the building that largely disintegrated before the
lower section of the building even started to descend. I adopt the Bazant-Greening model to
show its internal contradictions. What I show is that EVEN IF the top block were an
indestructible pile driver, it would deliver less force to the undamaged lower section of the
building than it would if it merely remained motionless.

We no longer have two distinct masses, M(upper) and M(lower). We have M(upper) =
M(Initial upper) + dM/dt, and we have M(lower) = M(Initial lower) – dM/dt. And this is
strictly true only in the absence of mass shedding.

The equations you have written are clearly in error since the units of the terms do not even
agree. It appears that you are trying to say, in pseudo-calculus terms, that the falling mass
can be considered to grow as it sweeps up material that is crushed at the interface. I comment
on the sloppiness of your equations because what I see you doing repeatedly is using
mathematics to muddle the issue rather than clarify it. The reader shouldn’t have to come to
the rescue and infer what you probably mean by your equations. It is interesting that you do
acknowledge that there is a neglected term for mass shedding which you do not attempt to
quantify. Given that a majority of the mass of the building lands outside its footprint, this
seems like a major oversight.

Obviously this situation greatly complicates momentum transfer calculations because you
have to include a dM/dt term as well as a dv/dt (acceleration) term. I challenge
David Chandler to re-do his WTC 1 collapse analysis with inclusion of a dM/dt term.

I have already done these calculations and they are included in my paper on the downward
acceleration of WTC1 which is undergoing peer review for another journal, so cannot yet be
published here. I assume the reason you throw this down as a challenge to me is you assume,
wrongly, that turning this into a variable mass problem will “greatly complicate” the issue.
Actually, it does not greatly complicate the issue. It takes only a few extra lines to modify the
analysis. Briefly, the accreted mass is initially at rest, so it adds inertia but no momentum to
the upper block. The net result is that the accretion of mass results in a DECREASE in the
force of interaction with the lower section of the building. I might also note that the fact that
you would challenge me to demonstrate something that actually strengthens my argument is
pretty clear evidence that you have not done, and perhaps you are not able to do, the analysis
yourself. Nevertheless you “up the ante.” You brush aside adverse conclusions based on a
simple model and seek refuge in a more complex model, even though you have not followed
through and investigated the implications of the more complex model yourself. I must
emphasize again that I am using YOUR model, which requires a rigid falling block. I adopt it
to show its flaws, but it is your model nonetheless.

I note too that Chandler gives no consideration to energy transfer in the collapse of WTC 1 &
2. Energy balance requires that:

a = g – E1/3.7M(upper), ……….. where E1 is the energy needed to collapse one floor

Multiply this equation through by M and you get Ma = Mg – F, where F is the average force
of resistance. This is exactly the equation I use in my analysis. Contorting it around to
express the force in terms of energy adds nothing to the analysis. It is certainly not any kind
of “energy balance” and it does not represent something I have left out of my analysis.

The fact that a is observed to be approximately constant means E1/M is also ~ constant. That
E1/M should be more or less constant is consistent with the design of WTC 1 & 2, or indeed
any tall building.

All you are doing is agreeing with me that the acceleration is approximately constant for the
period under observation, which proves that the resistive force is approximately constant.
There is nothing profound in this. In fact it is an artifact of the Bazant/Greening assumption
that the upper block remains intact. The significant thing, as I’ve shown, is that the force of
resistance is significantly less than the weight of the falling block. If you assume the upper
block is accreting mass, as you have challenged me to consider, even the statement that the
resisting force is constant is no longer true.

FG, in a lengthy paragraph, shortened here:
When I say that E1 is “the energy to collapse one floor” please note that E1 includes all the
energy consumed during the descent of the upper block through one floor height (~ 3.7
meters). Etc. …. Thus we see that E1/M is indeed approximately constant for the floors of

You are using circular reasoning. You are not dealing with the reality. You are dealing with
consequences of your simplifying assumptions. More to the point, none of this is relevant to
the issue at hand. I have laid out a clear, coherent argument that the falling block could not
deliver the force needed to crush the bottom section of the building while it continued to
accelerate downward. None of what you say in the previous paragraph or the remainder of
your letter even addresses this issue.

On the question of energy transfer, deceleration and all that, I would say…etc.

What on earth do you mean by “energy transfer, deceleration, and all that…”? Many of the
fragments in this paragraph are true enough, but they don’t go anywhere. They don’t advance
your argument. They don’t challenge mine. They are not illuminating. There’s nothing here
to respond to.

The collapse of WTC 1 is best studied by considering how potential energy was converted to
kinetic energy and dissipated at the crush front and subsequently within the steadily growing
debris/rubble layer. This debris layer was not only a sink for potential energy, but a source of
random fluctuations in the motions of the individual debris particles. These fluctuations
cannot exert a net resultant force against the downward motion of the upper block but rather
serve to control the gravitational work rate. In fact, if this type of collapse should attain a state
of dynamic equilibrium, there will be a balance between the production of fluctuation energy
at the crush front and the conversion of this energy to heat within the debris layer through the
dissipating effects of many random collisions of debris particles. It is considerations such as
these that help to quantify the complexities of the WTC 1 collapse, not naïve applications of
Newton’s 3rd Law of motion.

You are engaging in pseudo academic obfuscation. In my video I have made the argument
that the constant acceleration of the top section of the building implies that the resistive force
is much less than the weight of the falling block. If I’m wrong, show me how. You seem to
be hoping non-technical readers will assume what you have said is profound. It is not
profound. It is incoherent.

Unsuspecting readers may not understand the significance of your last line. They should be
informed that the reason you view the application of Newton’s 3rd Law of motion as naïve, is
because, as you have clearly and repeatedly stated in both private correspondence and public
forums, that you believe Newton’s 3rd Law does not apply to falling buildings. That, of
course, is utter nonsense. Your entire letter needs to be read and understood in the light of
this concluding statement. Your argument is not with me; it is with Isaac Newton.

Off-topic comment for visibility

Has anyone noted or commented on this?


"Among the nine fatalities in yesterday's deadly subway train collision in Washington D.C. was a retired Air Force general who headed the National Guard in the nation's capital and gave the order to scramble fighter jets during the 9-11 terror attack.

At a news conference at the crash site this afternoon, Washington DC Mayor Adrian Fenty confirmed that Maj. Gen. David F. Wherley Jr. was among those killed in the crash. Also killed in the crash was his wife, Ann. Both were 62 years of age.

Prior to becoming the head of the DC Army and Air National Guard Wherley commanded the 113th Fighter Wing, based at Andrews AFB in Maryland. That Air National Guard unit provides the planes and personnel that regularly fly combat missions protecting Washington.

It was this unit that scrambled jets over Washington during the 9-11 terror attacks and received orders to shoot down any suspicious aircraft that threatened the capital."

“On the altar of God, I swear eternal hostility against all forms of tyranny over the mind of man."--Thomas Jefferson

Wherley was a key figure on 9/11

David Wherley's actions on 9/11 were in fact rather suspicious. I described these actions in my blog posting, "The Andrews Air Force Base Stand Down: How the 'Capital Guardians' Failed to Guard the Capital on 9/11":

The actions of Brigadier General David Wherley Jr. are particularly notable. As the commander of the DC Air National Guard, Wherley surely had a crucial role to play in responding to the attacks. However, although accounts are vague and sometimes contradictory, descriptions of what he did give us serious cause for concern.

Wherley was in the headquarters of the 113th Wing the morning of September 11. Yet reports indicate he only started taking action after 9:37 a.m., when the Pentagon was hit. According to the Washington Post, Wherley's "first inkling that the attacks would go beyond New York was when one of his officers, whose husband worked at the Pentagon, saw on television that the building had been hit and began shrieking." [24] After taking a moment to comfort the officer, he "raced out of his office and ran several hundred yards to the headquarters of the DC Guard's 121st Fighter Squadron." But then, upon learning that the Secret Service wanted Andrews to launch fighter jets, Wherley told squadron officers he wanted more explicit authorization, saying: "We have to get instructions. We can't just fly off half-cocked." [25]

Wherley talked over the phone with the Secret Service, which wanted the DCANG to establish a combat air patrol (CAP) over Washington. Yet he seemed reluctant to help. He told the Secret Service agent, "I would feel more comfortable receiving such an order from someone higher in the chain of command, preferably in the military." He was given the number for the Presidential Emergency Operations Center--a bunker below the White House--which he then called. The Secret Service agent who answered implored Wherley: "We want you to put a CAP up over the city. We need some fighters now." Yet Wherley was "not very comfortable taking orders from a Secret Service agent. That's just not how things are done." He asked, "Is there anybody else there from the military available to talk?" As there was not, he asked, "Is the vice president available?" The vice president was on the phone with the president. Only after further reflection did Wherley finally agree to help, saying: "Okay, then. What exactly do they want me to do?" [26]

Wherley then had to wait for the Secret Service to determine "exactly" what it wanted. According to the Washington Post, the instructions came "within a half-hour." Again, another delay. [27] The Secret Service agent who got back to Wherley said he had received instructions that came from the vice president. The guidance was "to send up the aircraft, with orders to protect the White House and take out any aircraft that threatened the Capitol." If the 9/11 Commission is correct, these instructions were not passed on to the first fighter jet that took off from Andrews, but instead only to "the pilots that launched at 10:42 and afterward." By that time, of course, the attacks were long over. [28]

Full posting:


Hmmm.... sounds like another mole.

This sounds to me like another case of a mole who knew "something big" was going down and had orders not to mess with the program. Just sit tight until you are called, then run around confused and try to make up a cover story for your sorry cowardly ass. When an insider like this claims that he first found out what was happening from CNN, you know he's a damn mole trying to act like he was out of the loop or some other crap to cover for his personal contribution to a mass murder. It's disgusting. I hope some day soon bastards like this can be rounded-up and brought before the bar of justice.

Those who make peaceful revolution impossible will make violent revolution inevitable.

John F. Kennedy, 1962

Unless I am not up-to-date

There has been NO collapse analysis of the towers done by NIST or any governmental agency. There has only been an "analysis" that ENDS at "collapse INITIATION."

Seen in this light, Greening's "challenge" to Chander to: " re-do his WTC 1 collapse analysis"
is putting the burden of analysis on the wrong party.

If Greening is deliberately presenting false arguments, then he is an accessory to the cover up of a mass murder.

Therefore, Greening is in a corner, and he MUST at least convince himself that he is sincere in his position. There is no way he can back down. He has to keep arguing - even if it means arguing against Newton's third law of motion.

Come on ...

We all saw what happened with our own eyes. The falling mass was not stopped by the floors below, and therefore no calculations are necessary to demonstrate what is clear in the videos ...


It was as clear as the 5 frame video

of the puff of smoke smashing into the Pentagon.

[wheeze, sneeze, hiccup]

Sea of Math (To zmzmzm)

There is a paper, "What Did and Did not Cause Collapse of the WTC Twin Towers in New York," by Bazant and three others, which goes into some of what you're talking about.

It's an imposing paper, with differential equations and a lot of mathematical analysis. However, it has many shortcomings. For instance, note that the very people they are claiming to debunk, are never referenced or even named within the paper. They are referred to simply as "outsiders," if memory serves me correctly.

Note as well that the model the authors construct doesn't match what we see on videos: namely, that the top section of WTC 1, on videos, gets torn and blown apart and doesn't seem to fit the block required for the complex math of Bazant and his companions.

I find it far and away the most interesting paper written by the debunkers, but the more one looks at it, the more it falls apart..

My question is: What is REALLY going on in the hearts, souls

and minds of Greening, Bazant, Sunder, Gross etc.? What kind of thoughts, fears, fantasies motivate them? Obviously, they all KNOW the towers and 7 were professionally demolished.


"Your entire letter needs to be read and understood in the light of this concluding statement. Your argument is not with me; it is with Isaac Newton."


Damn you gravity!!

Newton strikes again!!

you know...

This is brilliant work by Chandler.....

Maybe he ought to invite the debunking community for physics lessons....

Frank Greening knows the truth

One thing I can conclude by FG's arguments is that he knows the truth but is intentionally lying about what he believes.

He knows the truth but is actively trying to promote the OCT


The question is why?


There are a lot of motivations that don't involve being a paid disinformation agent (I know that's what everybody thinks, so why not just say it)

I've realized normal people will defend the indefensible for a whole spectrum of reasons.

First and foremost there is anger and indignation at the realization that "conspiracy theorists" really do have a point. This is abnormal. It's as if a psychic really is psychic. People who measure the merit of their intelligence and convictions by challenging anything "outside of the box" based on their divine "intuition" for "bullshit" will never accept what we are saying, because they think it smells like bullshit. They will be looking for holes to poke and pillars of evidence to tackle.

Ironically, the most ferocious challenges will come from those who consider themselves logical thinkers, employers of the scientific method. They simply cannot reconcile something this outrageous with their 'scientific' and 'logical' belief system, not realizing their belief system is actually ideological, not scientific.

What I see is indignant desperation and frustration. Denial of denial, and denial of cycle.

If you are a JREF member and you are used to debunking frauds looking for a million dollar reward, and you have never failed, then why would you fail now? This can't be! You were told these people were delusional, rationally challenged fools who have been debunked several times already. There can be no way some of them are actually right.

Slowly and gradually, you become part of a camp. This camp, which provides you with a sense of "belonging" is much stronger than any logic or reason. Remember that most "scientific" truths are simply considered true because we all agree upon them. Logical proof is a difficult concept. You could say gravity has been proven thus far because an enormous statistical unlikelyhood contaminated all experiments thus far. You could say this if you wanted to cling to a world view that is mutually exclusive with gravity theory.

What we are putting forth is something that is mutually exclusive with the world view of many so called skeptics. As was so profoundly described in "The Matrix", sometimes it is just too late to "wake somebody up". The shock is too great, the implications too broad. Even I have trouble accepting, but the difference is that for me truth is the authority, not vice versa. But always remember, we are in such a camp too. Never let your camp ("five monkeys"!) dictate your world view.

I have found it to be true

"Ironically, the most ferocious challenges will come from those who consider themselves logical thinkers, employers of the scientific method."

I have found this to be true. Strange world.

Agreed but one small point about the word "debunker".

The word "debunker" is a frame and is used to frame the debate. When we as truthers use the word "debunker" to describe JREFers what we are essentially saying is "these guys/gals are experts at exposing bunk claims". By doing that we frame ourselves into a position of dissadvantage painting them from the very start as experts and our claims as bunk. If we refer to them instead as "deniers" or as being "in denial" we reframe the debate to our advantage and clearly describe them as they actually are. Just my two cents. It may seem like a non-issue but if you look at it closely you will see it is important. There are many more frames we inadvertantly fall into as well such as using the word "collapse" instead of "demolished".

In the beginning

The lower block isn't yielding at all. So I wonder if Chandler has also considered that it isn't the 0.36G resistance of the lower block that is curious, but the 0.36G of the upper block...

Namely, what we are seeing is the movement of the roof relative to the failure point, you know...and below the failure point nothing is yielding yet, so the only information this gives is information about the upper block...and how it isn't really impacting the lower block to begin with.

Somebody tell me if I'm mistaken.

In other words: is the upper block being blown up first? This seems like the only possibility and it has been speculated before...IIRC.

David Continues to do Great Work

I'm a big admirer of David Chandler's work. As a former math major with 2 years of college physics, I particularly like the absolute precision of his explanations and tutorial rebukes. His accurate and concise presentations often remind me of a mathematical proof. I look forward to the peer review paper he refers to above.


David is slaying Goliath.

Six thngs Mr Greening neglects to explain

1. Samples of explosive nano thermitic particulate,
2. The witnessed to sounds of explosions,
3. The redundancy of the towers and their subsequent failure sans explosive demolition
4. 10 ton core columns from the Towers 500 ft away impaled in the Winter Garden
5. Bone fragments found on top of the Deutsche Bank building across the street from the WTC
6. The molten steel under buildings 1,2 and 7

Explain this via the pancake collapse theory and I'll go home and never ask again

I'm thinking I'll be here a while longer.

Giving Ground Unnecssarily - The Fires

This debate is allowing Greening the enormous concession that the fires somehow burned at temperatures sufficient to fatigue the steel to the point of collapse. It also concedes that the fires burned long and widely enough to create the near uniform collapse of each tower which "gives" Greening and NIST their pile driver.

This is just a section of

This is just a section of the argument. Chandler does not need to bring up the whole thing every time.

JFK on secrecy and the press


I go to the youtube site to rate Chandler's video up and to comment and guess what. Comments are disabled. Why?
Why do they do that to some videos? Anyway, rate it up and share it with all you can.

Comments are disabled. Why?

I disabled the comments on the last video I made and posted. I did it because I didn't want nay-sayers and debunkers trashing the post with their idiotic comments. IMO if a video is good, it can stand on it's own merit. If Chandler is anything like me, it's his way of saying, "If you have a comment about my video or its content, contact me directly."

Thank you for replying.

I have no particular comment now, just was wondering. I like to read what others say. The naysayers and wanna be debunkers are indeed annoying. Thanks again and KUTGW!

Exact science / empiricism

The reason is that exact science doesn't require political debate. Youtube is a place where empiricism (especially among debunkers) is an alien concept.

Youtube can also serve (although I dislike the concept of copy protection centralization anyway) as a platform for posting media without discussion. Think of it as a multimedia harddrive. There would also not be any discussion page if Chandler could host his video on his own website. Bandwidth asymmetry prevents that.

Thank you also....

for the response.

Sorry to crash this, but can

Sorry to crash this, but can anyone help me out with knowledge about research into plane impact damage from a physics or engineering perspective. I have a friend who's skeptical as hell and he says that he finds it curious that 'no one' in the 911 Truth movement is discussing plane damage. I mentioned what the architects had said about a pencil poking a screen door and said I would search further. I'll check in for a response from someone and apologize for crashing in on the comments here.

I would show your friend the "Fourteen Points" paper for a start

Fourteen Points of Agreement with Official Government Reports on the World Trade Center Destruction

The Open Civil Engineering Journal, vol 2 (1), pp.35-40
Steven E. Jones, Frank M. Legge, Kevin R. Ryan,
Anthony F. Szamboti, James R. Gourley

Linked at: http://stj911.org/

Scroll down about half way and you'll find the link to the download.

Point number two in the paper addresses the plane impact damage and the reserve capacity of the building's structure. This is a very readable paper and an excellent overview of, and introduction to, the issues regarding the Twin Towers and WTC 7.

It is my impression that even NIST's impact analysis is primarily in the form of somewhat speculative computer models, as the vast majority of the actual steel structural members were recycled before they could be examined and reassembled to forensically determine what actually happened.

Hope this helps.

The truth shall set us free. Love is the only way forward.

Start here

Start here

The WTC impacts were inelastic collisions, and I personally believe (and this is supported by sources above) that since the WTC buildings were designed to withstand the impact of a fully loaded Boeing 707, they were also designed to withstand the impact of a fully loaded Boeing 767, since the two have comparable kinetic energy. (Defined by ½mv2)

Note that "designed to withstand" doesn't mean a 707 or 767 would "bounce off" or disintegrate without entering, as would happen with some specifically designed nuclear power plant walls. It would "puncture the screen netting" as Frank DeMartini said, and that's what happened.

While theoretical models are often an incomplete and imperfect representation of what happens in the field, I think you could take the yield strength of WTC perimeter columns and use the calculated kinetic impact energy of flight 11 or flight 175 to determine what happens next, on a purely theoretical basis. However, since a plane is a difficult shape, you'll soon end up building computer models including visualizations. It comes down to this: it's normal that the planes caused the damage they did, but the extent of that damage (especially to the core columns) and the fire induced lack of remaining load bearing capacity is what is in question, just as the implausible and improbable 'collapse' that ensued in three skyscrapers.

Even if the collapses were not 'assisted', which is unlikely, then the NIST report is STILL a fraud, because the whole investigation was compromised by scientific misconduct (Bush science). In the latter case, it would STILL be important to determine why these buildings performed so poorly. The insincere praise heaped on these buildings by proponents of the OCT is fraudulent twofold: (1) to reconcile what we know what the buildings could withstand with the OCT and (2) to cover up what would otherwise be catastrophic failures of engineering and fire protection.


Just a brief comment on modelling,

We've now got a working model of the collapse, using inelastic collisions for the mass, and Bazant's column buckling Model

Its early days, but this video shows what happens if intact structure and mass is met at floor 4.


The 'collapse' is on the right and the model on the left in the video

Give Him The Word OF NIST

We're not discussing plane damage because the government collapse theory centers on the damage from the fires - Not the aircraft impact damage. The official collapse theory is based on the (alleged) loss of fireproofing and the subsequent (alleged) damage the unprotected steel suffered from the fires.

NIST says in their Executive Summary that the aircraft damage played no significant role in the collapse of the towers:


The two aircraft hit the towers at high speed and did considerable damage to principal structural components: core columns, floors, and perimeter columns. However, the towers withstood the impacts and would have remained standing were it not for the dislodged insulation (fireproofing) and the subsequent multifloor fires.


NIST's admission that the impacts' damage was largely inconsequential is supported by the claims of the towers' designers which make clear that the towers were designed to withstand jet impacts.

Give your friend this link too:



This is why Kevin Ryan neatly describes the NIST theory as a fire theory (which I never hesitate to use in public, btw).


The truth shall set us free. Love is the only way forward.


Science is perfectly, incontrovertibly... beautiful!
"Cogito ergo sum"

Work frequency increases through the 'collapse'

The fact that a (acceleration) is observed to be approximately constant means E1/M is also ~ constant. That
E1/M should be more or less constant is consistent with the design of WTC 1 & 2, or indeed
any tall building."

The problem for F.G is that as velocity increases due to a more or less constant acceleration, the amount of work being done increases, so if the crushing of the first floor requires one unit of Work = (E1/1.033s)/s, at a frequency of roughly 0.986 floors per second and a velocity of 3.58 m/s, by the end of the video observation (12 floors crushed) the block is crushing floors at a rate (frequency) of 6.67 floors per second or 6.45 units of work per second at a velocity of 24.7 m/s. Or ~ (6.45*E1) per second.

What this essentially means is that the resisting force increases by a factor >6 at the end of the sequence compared to the crushing of the first floor, this will inevitably mean an amplification of the resisting force (relative to the applied force) through the 'collapse', and if the structure is performing anywhere above 85% on every floor a terminal velocity is reached i.e. the acceleration will tend towards zero. In order for there to be constant acceleration every floor must lose an equal amount of structural integrity (>25%) that is, both 'damaged' and undamaged floors all have to have an equal amount of remaining structural integrity, otherwise there will be no constant acceleration. Accretion also plays a role, mass must accrete at 100% otherwise the applied force cannot keep up with the increased structural strength of the lower floors.

So for constant acceleration we need exactly the same structural resistance on every floor 'crushed' and we need 100% of the impacted mass to accrete to the falling block. NIST say the damage to each floor wasn't the same on every floor and a quick look at the video confirms mass is not accreting at 100%.

Greening is a squid darting away squirting ink

No_body is correct. Also you'll note that the lower section is intact and unaffected well into the collapse of the top section which loses half it's integrity to crush damage and disintegration before the lower section starts to explode downwards. This implies that the effective downward force is even less than the initial floor count, as the debris not only gets laterally ejected but the crushing action absorbs momentum.

Greenings fallaciously attempts to describe the crushed matter as a reduction in the intact resistance against the upper block which further ignores Newton's third law, the crushing pressure goes both ways and reduces the mass of the upper block due to lateral ejection and absorbs energy, the same does not go for the lower block as the structural resistance of the lower block will remain the same(actually increase) while reduction of the mass and energy of the upper block slows it down.

Greening and all other supporters of the official theory have been unable to address the impossibility of the uniform acceleration, it simply would slow down, transferring kinetic energy to gravitational potential.

Also we notice that the spire starts to topple side ways. As there is no significant pressure against the top of the building to suggest the spire is disconnected and acts of it's own accord, the top few floors, or the majority of the bock must be intact, it would have to be, after all to continue to collapse floors!
Now, that means the bulk of the top block is toppling, which means that the collapse and pressure exerted is uneven and symmetric collapse is therefore impossible, as by that stage it had not accreted enough mass to continue a symmetric collapse. The accreted mass also has no structural integrity and would exert negligible downward force anyway without the symmetric pressure of an intact block above it.

This all ignores the additional factors of plastic and elastic shortening of the steel. The propagation wave is distributed over multiple stories and further absorbs the descent, see Gordon Ross' comprehensive paper which proves it wouldn't have even reached the buckling phase!

Greening is like a squid waving it's tentacles to distract us and squirting it's ink in our faces. We have the speargun of truth but the slimy bugger just keeps swimming back under his government rock.