Hardfire: Physics of 9/11

[Furcifer]

"Unit stress"? What do you mean? Stress is already per unit area.

Since TZ doesn't know (he's just regurgitating verbatim from that link) I'll take a stab at it and say it's based on the "unit" being a column assembly. Each assembly was fabricated to handle a given stress at every level based on the wind load.

Don't quote me on that though

 

[aggle-rithm]

So what is your problem with the NIST coming up with 24 numbers. What were they paid $20,000,000 for?

Truthfully? They blew most of it on cigarettes and lottery tickets.

 

[BigAl]

Given the number of pre fabricators and the scale of the project I'm not surprised the actual grades and plate thickness of every column was not recorded. Even if they were recorded, why would they be kept for 30 years by all 15 fabricators? Without NIST having coupons from every column they wouldn't know either. As for the mass, the only one who would have been concerned with that would have been the crane operator.

One of the papers I read but forgot to bookmark calculated the kinetic energy dissipation of a 757 going through the steel/glass wall of the WTC tower.

The author said that he was unable to find records that clearly identified the dimensions of the beams at the impact floor.

I wish I could find that paper again. I've looked.

 

[Furcifer]

Truthfully? They blew most of it on cigarettes and lottery tickets.

I heard they all paid off their student loans

 

[Furcifer]

The author said that he was unable to find records that clearly identified the dimensions of the beams at the impact floor.

I'm pretty sure the outer dimensions on every box column was 14 in. The inside dimensions and the grade of steel are a mystery. Without an actual sample who is to say what was actually used by any fabricator on any given day?

It's actually an interesting quality control issue that I'm not familiar with. I've only worked on concrete buildings. You'd be lucky to find the consistency of concrete from truck to truck to be within 10% of each other. At least on most projects. Steel is different by nature, and one of the reasons it is easier to build 110 story buildings with.

 

[Newtons Bit]

Given the number of pre fabricators and the scale of the project I'm not surprised the actual grades and plate thickness of every column was not recorded. Even if they were recorded, why would they be kept for 30 years by all 15 fabricators? Without NIST having coupons from every column they wouldn't know either. As for the mass, the only one who would have been concerned with that would have been the crane operator.

A grade of steel doesn't directly relate to a yield strength. A grade of steel only tells you the minimum yield strength (and, for most grades of steel today, a maximum as well).

It's pretty common to spec A36 steel and get 50ksi+ steel instead of 36ksi.

 

[Furcifer]

A grade of steel doesn't directly relate to a yield strength. A grade of steel only tells you the minimum yield strength (and, for most grades of steel today, a maximum as well).

It's pretty common to spec A36 steel and get 50ksi+ steel instead of 36ksi.

If I get this correct, even if the grade of steel for every single piece of steel in the columns was recorded it does little for a mass calculation. As far as I know the density of A36 and A50 are the same. You still need to know the plate thickness. If I'm not mistaken the plate thickness goes up in increments of 2mm, so you could have a single column made with 2 or 3 different plates. And even then that's a nominal thickness, it can vary by +- 5%.

Trying to calculate the mass of a panel seems like a fools game to me. What I do find interesting is the process from what was spec'd by the architects to what was actually put into place.

 

[aggle-rithm]

I heard they all paid off their student loans

That's just what they told their parents.

 

[BigAl]

Trying to calculate the mass of a panel seems like a fools game to me. What I do find interesting is the process from what was spec'd by the architects to what was actually put into place.

One of the arts of engineering is to know when to not over-specify. It drives up costs unnecessarily. I imagine that current mechanical CAD systems can do sensitivity analysis that calculates where tight tolerances are justified.

Electronics design packages have been doing this for 40 years that I know of. Why pay for 5% tolerance parts in spots where 20% parts work just as well.

 

[R.Mackey]

Comedy Gold.
You quote "principles", yet are using an approximation (all FE equations are approximations--hell-all analysis mathematics of any kind is approximate)--and a linear approximation at that, for a complex, highly non-linear event.

WTF are you trying to do here? Just annoy him and waste his time?

It is entirely logical to use the actual accurate information if it exists.

Let me try to reconcile these two seemingly opposite reactions...

In engineering, we frequently run across a phenomenon known as "gold plating." This refers to unnecessary development effort or system performance that has no real impact on functionality. An example would be putting seatbelts in a car that withstand a 1,000 g deceleration without addressing the fact that the seat brackets, car itself, or passenger won't. Another example would be estimating the mass of columns in the Towers to within 1% for purpose of collapse modeling, while neglecting that other important quantities -- like the amount of descending mass as a function of time, or how long the collapses really took in the first place -- are not even known or defined to within 20%.

As Dr. Dimotakis, one of my old professors, once said in a Watson Lecture, modeling to within 1% requires a much deeper understanding of the problem. Fortunately, in this case we really don't need to do this. We don't have a measurement to within 1% that we're trying to match in the first place. This kind of detail really doesn't help us at all, and anyone who models can and should use that model to demonstrate that it doesn't matter.

That doesn't mean there aren't other reasons to attempt a better estimate of steel masses, particularly if it costs us nothing to do so. This is potentially a worthwhile endeavor in itself. But if all we're interested in is the collapse model, it's really not relevant. Close enough is close enough.

 

[psikeyhackr]

Truthfully? They blew most of it on cigarettes and lottery tickets.

What no coke?

 

[psikeyhackr]

Why don't you tell us how the known frequency of oscillation will be affected by the weight distribution of the panels or the core for that matter. Then I'll explain to you why the mass and velocity of the plane is more important.

.
I never said the frequency of the oscillation was important.

It was the amount of energy from the plane that pushed the building off center to start the oscillation that matters. That energy must be subtracted from the total kinetic energy of the plane to compute how much was left to do structural damage.

Doesn't the structural damage have something to do with the collapse? Oh, that's right! The NIST is only concerned about collapse initiation. Well doesn't the structural damage have something to do with collapse initiation?

psik

 

[aggle-rithm]

In engineering, we frequently run across a phenomenon known as "gold plating." This refers to unnecessary development effort or system performance that has no real impact on functionality. An example would be putting seatbelts in a car that withstand a 1,000 g deceleration without addressing the fact that the seat brackets, car itself, or passenger won't.

There's an interesting example of this in the Hyatt in Kansas City after the catwalk collapse there killed a lot of people...the defective supports were replaced by HUGE columns that could survive stresses that would destroy the rest of the building.

 

[aggle-rithm]

.
I never said the frequency of the oscillation was important.

It was the amount of energy from the plane that pushed the building off center to start the oscillation that matters. That energy must be subtracted from the total kinetic energy of the plane to compute how much was left to do structural damage.

Doesn't the structural damage have something to do with the collapse? Oh, that's right! The NIST is only concerned about collapse initiation. Well doesn't the structural damage have something to do with collapse initiation?

psik

Looks like you have a real mystery there. Hmmmm....

Let's look at a picture:

Yep, looks pretty damaged. I guess there was plenty of kinetic energy left over, after all.

 

[psikeyhackr]

Looks like you have a real mystery there. Hmmmm....

Yep, looks pretty damaged. I guess there was plenty of kinetic energy left over, after all.

.
But was it enough to make the building collapse?

Our world renowned EXPERTS can't even tell us the amount of steel on every level.

And in 2 1/2 months we will be celebrating the 40th anniversary of the Moon landing.

Those astronauts must have brought back some kind of stupidity inducing germ that has infected government agencies. Maybe Ryan Mackey has caught it.

psik

 

[BigAl]

.
But was it enough to make the building collapse?

Our world renowned EXPERTS can't even tell us the amount of steel on every level.

Is it possible that the information you seek is coded into the data that was fed to the simulation software and that the authors of the NIST study didn't see the need to take up pages of boring tables to satisfy some loon in 2009?

I dunno. Just asking.

 

[psikeyhackr]

Is it possible that the information you seek is coded into the data that was fed to the simulation software and that the authors of the NIST study didn't see the need to take up pages of boring tables to satisfy some loon in 2009?

I dunno. Just asking.

.
It is at least conceivable that pompous jerks assume they do not need to explain themselves with clarity.

That does not mean that their pompous jerkiness should be tolerated.

Stop the personal attacks please, and keep the discussion civil. Attack the argument, not the arguer.

Replying to this modbox in thread will be off topic  Posted By: Myriad

psik

 

[Furcifer]

.
I never said the frequency of the oscillation was important.

It was the amount of energy from the plane that pushed the building off center to start the oscillation that matters. That energy must be subtracted from the total kinetic energy of the plane to compute how much was left to do structural damage.

Doesn't the structural damage have something to do with the collapse? Oh, that's right! The NIST is only concerned about collapse initiation. Well doesn't the structural damage have something to do with collapse initiation?

psik

I never said you said that the frequency of oscillation wasn't important. But you knew that I knew you would imply that I was thinking you had said that. Unless you meant to infer that I was only implying you had said that when in fact it was I that had implied it based soley on the inference of it in your earlier posts. Whether it was implied, inferred or misread is irrelevant to your current misunderstanding.

The building wasn't pushed off center, only part of it. I'm sure you understand that but it needs to be said.

I haven't read NCSTAR from cover to cover. Only parts. And it was a while ago, but I seem to recall this being accounted for in the report. Some of the kinetic energy of the plane was absorbed in the oscillation, but most of it contributed to damaging the exterior and core.

What I don't get is your insistence the mass of the perimeter has anything to do with that calculation. The point of impact and the thickness of the plate in that specific area is the only thing of relevance. The rest of the perimeter mass has nothing to do with it. The energy absorbed in the oscillation was calculated from the known frequency of oscillation.

To put it very simple psikey, if I know that when I hit a piece of glass with a force = X it breaks, why do I need to know the mass of the glass? Same thing with a spring, if I know an applied force = X will deform the spring, who cares what the spring weighs? If it weighs a million tonnes or an ounce it doesn't matter, I know that if I pull it this hard (X) it will deform or break or whatever.

All I've seen you do here is apply the wrong math to the wrong principles to get the wrong conclusions. You need to consider for a second maybe it isn't so simple, it's not so easy and it's not so obvious.

 

[psikeyhackr]

The building wasn't pushed off center, only part of it. I'm sure you understand that but it needs to be said.

I haven't read NCSTAR from cover to cover. Only parts. And it was a while ago, but I seem to recall this being accounted for in the report. Some of the kinetic energy of the plane was absorbed in the oscillation, but most of it contributed to damaging the exterior and core.

What I don't get is your insistence the mass of the perimeter has anything to do with that calculation. The point of impact and the thickness of the plate in that specific area is the only thing of relevance. The rest of the perimeter mass has nothing to do with it. The energy absorbed in the oscillation was calculated from the known frequency of oscillation.

.
Since I built a model and demonstrated the effect of impacts I feel there is a lot I don't need to say. I showed it.

http://www.youtube.com/watch?v=z0kUICwO93Q

Obviously the base did not move. On the real building I would expect every thing above the 20th floor moved to a significant degree. Since the NIST says the 70th level moved 12 inches that means the floor slab the core columns and beams AND THE PERIMETER COLUMNS AND SPANDRELS. I have not seen anywhere that explains how the energy to produce that movement was accounted for in relation to the structural damage caused by the impact. I would be most interested in someone specifying that in the NCSTAR1 report.

I have communicated with a number of people over the years that have claimed various stuff was in the NIST report but than they didn't say where it was. Ron Wieck played that game with me once saying, "Did you look here?" And then provides a link to a 200 page report. I provide links page numbers and quotes when I say something is in the NCSTAR1.

psik

 

[e^n]

I have not seen anywhere that explains how the energy to produce that movement was accounted for in relation to the structural damage caused by the impact.

I apologise for not reading over all of the previous pages but I am unsure what you are asking for here. Other than small ejecta and fuel, all of the plane's energy was expended into the towers?

Could you be more precise?