The 9/11 Forum

The first collision is in the core and along both perimeters



Both upper and lower core columns act as spears puncturing flooring. We know that the floor sheets, 4" concrete, won't do much to stop them. We see a spearing destruction happen to both upper and lower flooring. Will core columns vs flooring create a jolt? Probably not.

Along the perimeter we see only the lower floor slammed on the left and only the upper floor smashed on the right. Notice how different the damage is, depending on whether the lower perimeter sheet slips within or outside the upper sheet. Inner position is important. Will this create a noticable jolt along the roofline of either the right or left side? Maybe.


The next collision



Floor slab against floor slab. Will this create a jolt along the roofline? Maybe and maybe not. We would assume so, but we notice the perimeter wall administered a shock to the outer flooring connections in the last collision. Wouldn't the perimeter spandrels smashing and breaking outer flooring connections send a pulse to the perimeter roofline more effectively than floor slab collisions?

In reality, it is not stubby sections of perimeter columns that are smashing against the floor connections. It is the spandrel plate. The spandrel plate acts as a powerful hammer against flooring connections.

If there are jolts detected along the WTC1 north face roofline, I suspect it is this spandrel hammering action that is responsible.

We see the overlap region in yellow. That should be the same as the roofline drop.

Evidently only half the spandrel belt around the perimeter can contact anything in the unlikely event all columns have fractured and displaced sideways. The other half will just hit nothing! That 'hammer' misses completely the target!

Yes. It is important to know which perimeter sheet manages to slip inside the other. The inside sheet always has the advantage. The other spandrel hits nothing.

If lower slips inside upper, we expect the upper perimeter wall to be stripped of it's flooring, trashing the structure of the upper block.

If upper slips inside lower the process is reversed.


In this simple model it is enlightening to observe how upper block and lower block masses make contact with each other.

Can we ever say that the entire upper block mass M is acting against columns to create buckling at the collapse front? Of course not. It's a silly idea.

Can we ever rule out upper block crush up on the basis that the upper block columns, core and perimeter, receive insufficient force to buckle upwards? God no! That is a silly idea.


Yet that is the exact reasoning given in BL to defend the claim that the upper block experiences minimal crush up. No kidding.

Using this simple visualization we can already see that BV, equation 12 treats the upper block mass wrongly. BL treats the upper block structure poorly.

Major_Tom --- Escept that you neglected the tilt

Obviously. Baby steps, David.

Your comments about the upper block perimeter ejections are way off.

Why would I try to explain perimeter kickout and the extent of it on this thread?

Many, many photos in order are posted on the other thread.

I just look at the grouped pictures. Nothing special. You could do the same. I cannot see anything in the pictures that you cannot.

The difference is I group them, look at them and notice patterns. All the info is posted there in images.

If one picture is worth a thousand words, consider the value of lists of images grouped in order recording the fall evolution of the pieces under discussion.

Using the same images, you could answer all these questions yourselves, possibly better than me.

Let's try to understand the nature of the first floor slab collision in the first simplified visual model from my last posts.



In the image slab slams against slab.

Each slab is an independent structure and is held onto the building only throughperimeter and core column connections. Were it not for these connections each slab could move freely.

So what is the nature of this collision? Neither slab has an advantage in the collision, so the destruction and connection breakage would be shared evenly. Each can be crushed.

This collision must result in the disconnection of both slabs from the larger structures.


Now please consider:

1) Is there any reason to include the entire mass of the upper block in the first collision with the slab below? No. The slab resists disconnecting from the larger structure only as the strength of the connections allow.

Were the slab strength and connection strength infinite, the building would bounce. The roofline fall would be slowed only as much as connection strength will resist breakage.

2) How does column yield strength enter into this collision? It doesn't. No connection whatsoever.

3) What collisions act to slow the fall? (What is the source of resistance force F?) Connection breakage and rubblization of slabs.

Major_Tom wrote:So what is the nature of this collision? Neither slab has an advantage in the collision, so the destruction and connection breakage would be shared evenly. Each can be crushed.

This collision must result in the disconnection of both slabs from the larger structures.

Very similar to the behaviour expressed by the asynchronous impact model I've started.




(Behavioural differences due to change in Coefficient of Restitution for partially elastic collisions.)

It is interesting to note that both traces show simultaneous *crush up* and *crush down* without affecting the roofline trace (The model does not really include the supports as yet, but a small energy expenditure to break the connections of static impacted floor, so there *cannot* be any effect on the roofline. The observation still stands of course, even in the situation more elaborate floor linkage was implemented). The only place it would be evident is within the *crush zone* itself.

Obviously not true. You found patterns where on my monitor I only see uniform dark grey.

This could be the only difference between us, the quality of our monitors. Maybe if you had a better monitor you'd understand why people are making accusations of demolition.

The devil is in the details. If you cannot watch them, you can't see.

Then please correct.

Have to verify for yourself or it's just words. Look with your own eyes.



Many people have mentioned that collisions between slabs, one that is inclined, can cause an equal amount of damage and connection breakage as a collision between 2 horizontal slabs.


The two cases involve a very different mechanics.

Consider letting the upper slab go into freefall in the two cases shown.



Consider the lower slab to be connected to a structure by breakable connections.

Instinctively, I would think the first case would have the better chance of breaking all the connections.

The falling inclined slab would make initial contact along one edge. The upper slab would be receive a torque impulse and, being made of concrete, would form major cracks and deformities from the backlash of the first strike (It's no longer a slab).

It could administer a sharp blow to only one of the four edges of the lower slab before it becomes cracked and deformed.

In the case of the two slabs being horizontal, a sharp blow can be delivered to all connections at the same time.

Breakable inclined slabs cannot be considered to have the same potential for destroying the connections of the slab below because it loses it's own structure more easily upon initial impact.


Interestingly, there is no reasom we cannot see jolts along the north roofline just because upper slabs are inclined.

If we view the source of these jolts to be a spandrel plate acting as a hammer against floor to perimeter connections (in the case the upper north wall slides over the lower wall), we can see inclined slabs, inclined downwards from north to south, will not diminish these jolts.


Hmmm.