Hardfire: Physics of 9/11

[rwguinn]

This was my favorite machine back in the day.

http://www-03.ibm.com/ibm/history/exhibits/vintage/vintage_4506VV4024.html

My god that stuff looks primitive now. ROFL

8" floppy disk drives. They weren't even double sided. 256KBytes.

A download from Youtube wouldn't even fit on my first hard drive.

psik

And the big hole on the RH console is where you shoveled in the coal...

 

[psikeyhackr]

The original question was about mass distribution. The Urich paper uses a linear distribution from roof to base.

I'm after a more accurate distribution method.

.
WHAT!?!

Haven't you heard that accuracy isn't important?

You must be some kind of subversive.

They wouldn't let you work for NASA.

psik

 

[femr2]

.
WHAT!?!

Haven't you heard that accuracy isn't important?

You must be some kind of subversive.

They wouldn't let you work for NASA.

psik

Well until I get additional detail, I'm going to ramp the mass non-linearly placing a higher proportion towards the base. (With the ability to configure the 'curve')

I'll also set elevated mass on the external columns of each mechanical floor region.

If people then object, I'll expect specific detail as to why.

 

[Newtons Bit]

The original question was about mass distribution. The Urich paper uses a linear distribution from roof to base.

I'm after a more accurate distribution method.

I'll say it again: it's pretty dern close to being linear.

 

[GlennB]

Well until I get additional detail, I'm going to ramp the mass non-linearly placing a higher proportion towards the base. (With the ability to configure the 'curve')

I'll also set elevated mass on the external columns of each mechanical floor region.

If people then object, I'll expect specific detail as to why.

In terms of arresting collapse, I would have thought that placing more mass higher up would be the way to go - i.e. it's a more conservative approach, CT-wise. But making the distribution configurable is good.

Bottom line - it's academic. There is no feasible mechanism for organising the CD of the Towers under the circumstances of 9/11, so you're engaging in an interesting engineering study. Fine.

 

[Myriad]

I'll also set elevated mass on the external columns of each mechanical floor region.

Why?

Obviously, any additional strength in the vertical columns to handle the extra weight of the reinforced floor and of mechanical equipment would be useless unless continued all the way down to foundation level.

I could see stepping down the column masses just above each mechanical floor instead of linear tapering; or a combination of linear tapering and additional step-downs above each mechanical floor. (As well as, naturally, using appropriately higher values for the floor masses and floor loads on the mechanical floors.) But just arbitrarily adding additional external column mass on the mechanical floors themselves doesn't seem to make any sense.

Respectfully,
Myriad

 

[psikeyhackr]

Well until I get additional detail, I'm going to ramp the mass non-linearly placing a higher proportion towards the base. (With the ability to configure the 'curve')

I'll also set elevated mass on the external columns of each mechanical floor region.

If people then object, I'll expect specific detail as to why.

.
That's what I was figuring. If you start with some specific weight for one level at the top. Then as you come down you eventually get to a point where you have to make a level stronger to support the multiple levels above but that adds more steel which makes that level heavier. But that means levels below have to support it. So the distribution in weight of steel has to be some kind of curve.

But I have searched websites for skyscraper enthusiasts and I haven't found info about it.

That is why I wanted it specified in tons of steel and concrete on every level. How could there be a simpler way to express it than that? Equations may be nice but the real world ain't that smooth. They have to deal with column sections 36 feet long. But they did it in the 60s with crap for computers so why ain't this solved by now? If I didn't have to live on this planet I could find this hysterically funny.

psik

 

[beachnut]

.

... I wanted it specified in tons of steel and concrete on every level. How could there be a simpler way to express it than that? ...
psik

Have you used the weights from Greg? What did your model do? You have been given sources for estimates of weight in the WTC.

What is wrong with Greg's numbers. I think they are off on the low side but they should give you a good start. Did you try using them in your complex model?

You complain about this all over the Internet and unlike some "truthers" who have complied a model of the tower in weight, you just keep whining about you can't find the weight. Have you seen the plans for the WTC?

How are you going to change your washers? Will you use sand paper to make them weigh less?

 

[Furcifer]

How are you going to change your washers? Will you use sand paper to make them weigh less?

Floor 110- 367 000 washers
Floor 109- 363 543 washers
Floor 108- 362 243 washers



Psik new line of reasoning has nothing to do 9/11. It's more about engaging Newton and Ryan in pointless debate. As if his self professed "book learnin" can trump years of experience and education. Negative attention is still attention.

 

[tsig]

What did they use for electricity back then?

In keeping with a slower time it was static electricity.

I'll be here all week but come back anyway.

 

[ozeco41]

This was my favorite machine back in the day.

http://www-03.ibm.com/ibm/history/exhibits/vintage/vintage_4506VV4024.html

My god that stuff looks primitive now. ROFL

8" floppy disk drives. They weren't even double sided. 256KBytes.

A download from Youtube wouldn't even fit on my first hard drive.

psik

My early computer programming experiences were even earlier - same "Big Blue"

http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_PP1401.html

without the tape drives and we managed to model water supply networks in the fully extended memory.

It was 16,000 < yup 16 thousand - not 16 "K" - it was coded BCD and core memory - literally - ferrite cores woven on all those wires.

 

[tfk]

psik,

Compared progressive collapse to rock slide

Yeah, why don't you research those.

I don't have to research those. I've been up close & personal with both avalanches and rock slides, and I've got 3 1/2 decades of mechanical engineering experience.

I wasn't asking your opinion about the analogy between the two.

I generated the analogy for you to help you understand by example a critical point that you have been struggling with & misunderstanding for quite some time. Specifically, that vertical collisions in a gravitational field are NOT vertically symmetric. Unlike horizontal collisions on a flat surface. Or collisions between ships at sea. This is precisely the same error that Heiwa makes so consistently & gleefully.

Overall, the analogy between a rock slide & the collapse of the towers is not perfect. But from the perspective of this one consideration, it is perfect. Once again, I am not asking whether you think that I'm correct about this.

The factor you are leaving out is that weaker layers underneath give way because they are weakened by rain or temperature. You think you can use that simpleminded physics by analogy.

I'll bypass the "simpleminded" for the moment to ask you a question.

Why is it that you guys immediately start down this path of snarkiness? I gave you a response that was completely neutral and informative. I addressed several very specific points that you made without rancor or patronization.

And yet, in your first response, you come back with this. And your "I'm so impressed" sarcasm below.

Finally, once we (who know what we are talking about) finally get fed up with the petty insolence, we'll rip off your head and ◊◊◊◊ down your shoulders. And six months from now when it has degenerated into a snark-fest, you'll suffer a convenient case of amnesia and claim that I "started insulting you from the moment you started posting"?

Do you mind if I hold you to a higher standard, and insist that you maintain the same respectful demeanor that you'd want from me?

Those are cases where something is already on the brink of collapse and simply waiting for a trigger. That is why avalanches can be started by loud noises.

And here you are 99.99% wrong. This video explains why.
http://www.youtube.com/watch?v=ManGanavlL8&feature=related

This is a massive landslide. The huge trees, boulders and the road that were destroyed in this landslide were not "on the brink of collapse". They were solid & robust. They'd certainly weathered giant storms, probably hurricanes in their lifetimes.

Only a tiny percent of the rocks that were far above them needed to be delicately balanced. You could trace the landslide to a single rock or pebble. If that collapse hadn't occurred, then the rest of the rocks might well have stayed in place for a couple hundred years more.

And this is precisely the point. Those rocks & trees were not fragile or delicate. And yet, they were dislodged, broken free and sent sprawling by objects much smaller than themselves. Because the objects that dislodged them did not have to be bigger than they were. They simply had to have more kinetic energy than the energy absorbing capacity of the CONSTRAINTS that held them in place.

Are you starting to get the picture?

Trying to compare natural phenomenon to a man made object designed to resist the known forces. I'm so impressed.

Natural & man-made are irrelevant in this particular case: vertical collisions in a gravitational field. You need to learn the difference between an incidence and a principle. Incidences are not important. Principles are crucial.

What does that have to do with our not being told the number and weights of perimeter wall panels on that man made object?
psik

It had nothing whatsoever to do with the distribution of weights. I answered that question separately.

tom

 

[R.Mackey]

So as of this moment, I estimate psikeyhackr is responsible for 99 off-topic posts, and indirectly for 176 off-topic retorts, out of 1093 total -- that's over 25% of this entire thread. And that doesn't count the multiple splits and moderator actions already.

I have him on Ignore, and you should too. He apparently can't help himself. What's your excuse?

Don't answer that here, just try to keep the derail to Orient Express levels, please?

 

[femr2]

Why?

Obviously, any additional strength in the vertical columns to handle the extra weight of the reinforced floor and of mechanical equipment would be useless unless continued all the way down to foundation level.

I could see stepping down the column masses just above each mechanical floor instead of linear tapering; or a combination of linear tapering and additional step-downs above each mechanical floor. (As well as, naturally, using appropriately higher values for the floor masses and floor loads on the mechanical floors.) But just arbitrarily adding additional external column mass on the mechanical floors themselves doesn't seem to make any sense.

Respectfully,
Myriad

I have no issue with a step-down above each mechanical floor region. It certainly implies a less 'linear' distribution, and is hopefully more accurate.

What would be useful is detail of the physical cause of the visual difference to the external facade on the mechanical region floors.

As far as I understand, a very basic view of the construction of each tower was three 'stacked' buildings. Why would the mechanical floor regions NOT be built with stronger external columns ? (Adding 2 bands of increased rigidity)

Increased column mass for a few floors would add minimal additional requirement to the columns below IMHO. They are not designed to simply carry the mass of the columns above after all.

femr2

 

[psikeyhackr]

So as of this moment, I estimate psikeyhackr is responsible for 99 off-topic posts, and indirectly for 176 off-topic retorts, out of 1093 total -- that's over 25% of this entire thread. And that doesn't count the multiple splits and moderator actions already.

I have him on Ignore, and you should too. He apparently can't help himself. What's your excuse?

Don't answer that here, just try to keep the derail to Orient Express levels, please?

.
DAMN, I'm so upset!

The correct weights, number and of course strength of perimeter wall panels are totally irrelevant to making a SCALED MODEL of the WTC. You did talk about a scaled model in Hardfire 3 didn't you? Of course, why you brought that up when you never seemed particularly interested in accurate data on the WTC in the first place is beyond my comprehension.

psik

 

[ozeco41]

I have no issue with a step-down above each mechanical floor region. It certainly implies a less 'linear' distribution, and is hopefully more accurate.

What would be useful is detail of the physical cause of the visual difference to the external facade on the mechanical region floors.

As far as I understand, a very basic view of the construction of each tower was three 'stacked' buildings. Why would the mechanical floor regions NOT be built with stronger external columns ? (Adding 2 bands of increased rigidity)

Increased column mass for a few floors would add minimal additional requirement to the columns below IMHO. They are not designed to simply carry the mass of the columns above after all.

femr2

If the purpose in trying to define weight distribution is to answer the "demolition or not" question it is not needed.

The outer tube columns were "peeled off" and played little if any part in the collapse whether you are for or against demolition.

If you are for demolition the outer columns were disconnected and therefore gave no resistance. If you say "no demolition" (my position BTW) then the only contribution of the outer tube columns to resisting collapse was limited to the failure in shear strength of one floor (one floor at a time) even for the mech services floors that failure strength was only a few percent of the columns strength.

Similarly the core could only contribute the same floor joist disconnect failure in shear PLUS whatever "core on core" load transfer occurred. The latter by the lower core resisting the core of the falling "Top Block".

That "core on core" resistance could not be any more than a small fraction of the original strength of the core. That is the fundamental error in the Szamboti "Jolt" explanation AND the point where Bazant's original paper was wrong other than Bazant's aim (or one of them) was to show sufficient energy available under worst case. The energy was available. BUT the worst case did not happen so relying on Bazant for any other conclusions beyond the limited ones that Bazant claimed is wrong.

 

[Newtons Bit]

I have no issue with a step-down above each mechanical floor region. It certainly implies a less 'linear' distribution, and is hopefully more accurate.

What would be useful is detail of the physical cause of the visual difference to the external facade on the mechanical region floors.

As far as I understand, a very basic view of the construction of each tower was three 'stacked' buildings. Why would the mechanical floor regions NOT be built with stronger external columns ? (Adding 2 bands of increased rigidity)

Increased column mass for a few floors would add minimal additional requirement to the columns below IMHO. They are not designed to simply carry the mass of the columns above after all.

femr2

The perimeter columns for the vast majority of the building were part of a moment frames. At the mechanical floors, this was a braced frame (diagonals forming trusses in layman's terms). Braced frames are substantially stiffer and stronger by weight than a moment frame is. A designer can get a lot more "bang for the buck" as it were with a braced frame. But architects don't like them because there isn't as much room for windows.

Three things for you to think about in sizing the exterior columns:
1. The wind pressure increases as a function of height.
2. The overturning moments are resisted predominately by axial forces in the perimeter columns in a manner much like a VERY deep beam.

A perimeter column at any floor must have the strength for both the axial component of the overturning moment above and the overturning moment delivered in shear by the diaphragm of that floor. This additional shear decreases at each floor as well as the height above base decreases.

3. Moment frames are frequently controlled not by strength, but by deflection. A larger stiffness on the lower floors will reduce the rotation of the columns at that floor (more or less linearly). When trying to control deflection, it makes a lot of sense to add more steel at the bottom most floor.

This is why I say it's mostly linear.

 

[Minadin]

The perimeter columns for the vast majority of the building were part of a moment frames. At the mechanical floors, this was a braced frame (diagonals forming trusses in layman's terms). Braced frames are substantially stiffer and stronger by weight than a moment frame is. A designer can get a lot more "bang for the buck" as it were with a braced frame. But architects don't like them because there isn't as much room for windows.

<snip>

Or, doors. We once had a structural engineer try to put diagonal bracing across 2 consecutive bays along an interior corridor, because it was easier and cheaper. Never mind the fact that this completely excluded any sort of entry or exit from prospective tenant spaces on that side of the hall, rendering that half of that level of the building completely useless.

It's fine for a mechanical level, though.

3. Moment frames are frequently controlled not by strength, but by deflection. A larger stiffness on the lower floors will reduce the rotation of the columns at that floor (more or less linearly). When trying to control deflection, it makes a lot of sense to add more steel at the bottom most floor.

I think that there are a large number of people (truthers and non-) who will not understand this at all. For one thing, most people do not understand the difference, when we are speaking in structural terms, between stiffness and strength. Vernacularly, stiff things seem to be strong and vice versa. I understand the difference but perhaps you could go into greater detail.

Also, though I have limited experience with tall buildings and none with very tall ones (over 100 ft) I was under the impression that in general, taller buildings are more controlled by seismic and not wind load considerations. Perhaps that is based on where I practice, and it's certainly possible that I'm entirely wrong.

 

[Dave Rogers]

I could see stepping down the column masses just above each mechanical floor instead of linear tapering; or a combination of linear tapering and additional step-downs above each mechanical floor. (As well as, naturally, using appropriately higher values for the floor masses and floor loads on the mechanical floors.) But just arbitrarily adding additional external column mass on the mechanical floors themselves doesn't seem to make any sense.

IIRC the spacing of the mechanical floors was greater than the others, wasn't it? In that case it might be necessary to increase the column thickness in that region because the unbraced column length is greater, resulting in a more slender column. I don't know enough about structural engineering to know whether that's reasonable.

Dave

 

[tfk]

The perimeter columns for the vast majority of the building were part of a moment frames. At the mechanical floors, this was a braced frame (diagonals forming trusses in layman's terms). Braced frames are substantially stiffer and stronger by weight than a moment frame is. A designer can get a lot more "bang for the buck" as it were with a braced frame. But architects don't like them because there isn't as much room for windows.

Three things for you to think about in sizing the exterior columns:
1. The wind pressure increases as a function of height.
2. The overturning moments are resisted predominately by axial forces in the perimeter columns in a manner much like a VERY deep beam.

A perimeter column at any floor must have the strength for both the axial component of the overturning moment above and the overturning moment delivered in shear by the diaphragm of that floor. This additional shear decreases at each floor as well as the height above base decreases.

3. Moment frames are frequently controlled not by strength, but by deflection. A larger stiffness on the lower floors will reduce the rotation of the columns at that floor (more or less linearly). When trying to control deflection, it makes a lot of sense to add more steel at the bottom most floor.

This is why I say it's mostly linear.

Newton,

I really enjoy reading your posts.

You positively REEK of "knowing what you are talking about". This post is a great example.

Mackey & several others here suffer the same affliction.

Plus I get to learn a whole bunch about the ways that you guys look at the issues that are unique to your fields. It's fun.

[OK, that's all the sucking up I can stand for one day.]

I don't get this one, tho.

"A perimeter column at any floor must have the strength for both the axial component of the overturning moment above and the overturning moment delivered in shear by the diaphragm of that floor. This additional shear decreases at each floor as well as the height above base decreases."

By "this additional shear" in the 2nd sentence, I assume you mean "... the overturning moment delivered in shear ..." etc, in the first sentence.

For a first approximation, assume that each story's floor load per unit area is the same. And therefore, the total shear load is the same. And that it is shared approximately uniformly amongst all the external columns.

It seems to me that this would make the absolute value of the shear on the columns approximately the same on all stories (perhaps higher on the mech floors due to higher floor loads).

It's easy to see that the overturning moment decreases as you rise off the ground, but I'm not seeing this "moment due to membrane shear" doing the same.

thanks.

tom