The 9/11 Forum

David B. Benson wrote:OneWhiteEye --- What are the dimensions and mass of your bathroom tiles?

The measurements are 10.7 x 10.7 x 0.5 cm. I don't have any scale, not even a bathroom scale, so I don't know the mass. Ceramic density varies, there are all kinds. Need to get a cheap electronic scale.

Here they are. There's a box of yellow, too.

OneWhiteEye --- Thanx. Without the mass there is no way to estimate the diameter, d, of the SSS columns. But for length I suggest arund 4x0.5 + d cm, so d had better be quite small; otherwise won't buckle.

Edited to add: On further consideration, need to have intermediate length columns,
http://en.wikipedia.org/wiki/Buckling
of what ever material (and shape) is chosen. Some experimentation seems to be in order.

Well, I see you are still trying to get your crush down models together. I have just completed another kids' show why crush down models - like perpete mobile - don't work. You can see it at http://heiwaco.tripod.com/funnym.htm .

Heiwa will love this one,

I built a roughly symmetrical (strengthwise anyway) six floor structure out of lego. Then I dropped one equivalent complete floor on top of it. Here is the result:

Top part completely destroyed. Lower part 1 1/2 floors destroyed. After a statistically non-significant sample of 1, it does appear that the upper part has somewhat of an advantage.


Note: I had to run out of the room to escape the pyroclastic flow so the photo (taken later) didn't capture the "afterglow".

Issues with this test:

1. There were no CDLs, SDLs of SLLs.
2. The structure was not nearly loaded to 50% load capacity.
3. The structure was not really symmetrical (could have contributed to failure of floor 5) and should have larger spans.
4. I need to get more Lego because I don't have enough to model points #1-3.

Hambone wrote:1. There were no CDLs, SDLs of SLLs.

Neat!
What are CDLs, SDLs of SLLs?

David B. Benson wrote:

Hambone wrote:1. There were no CDLs, SDLs of SLLs.

Neat!
What are CDLs, SDLs of SLLs?

Construction Dead Load (floors, floor toppings, fire-proofing etc.)
Superimposed Dead Load (all plumbing, electrical, mechanical, HVAC, fixed partitions, ceilings, etc.)
Superimposed Live Loads (moveable stuff like people, furniture, computers, etc.)

Hambone wrote:Heiwa will love this one,

I built a roughly symmetrical (strengthwise anyway) six floor structure out of lego. Then I dropped one equivalent complete floor on top of it. Here is the result:

Top part completely destroyed. Lower part 1 1/2 floors destroyed. After a statistically non-significant sample of 1, it does appear that the upper part has somewhat of an advantage.


Note: I had to run out of the room to escape the pyroclastic flow so the photo (taken later) didn't capture the "afterglow".

Issues with this test:

1. There were no CDLs, SDLs of SLLs.
2. The structure was not nearly loaded to 50% load capacity.
3. The structure was not really symmetrical (could have contributed to failure of floor 5) and should have larger spans.
4. I need to get more Lego because I don't have enough to model points #1-3.

Just proves my point. Top part C completely destroyed, Part A just partly damaged (even if bottom part of A seems to be same strength as C - should be reinforced, e.g., if C has one lego brick as support between floors, A should have plenty more down at bottom).

A friend of mine started to build a crush-down model. It consists only of 1000 material points, each with a mass and a position relative to an origin. The model is 3-D and resting on ground. Each material point is linked to other points up/down/sideways except at the boundaries. The links are viscoelastic and will deform elastically and plastically before they break. Some energy applied to the links will thus be lost as heat during this process. The structure looks like a tower with a square base. The height of the structure is 10 times the length of the base side. The links are adjusted so they are equally stressed due to gravity forces. The total potential energy of the structure relative origin and associated deformations of the links are easy to calculate.

Now he disconnects the top 1/10th of the structure from the rest; the top part is called part C and the bottom part is called part A. Part C thus consists of 100 material points linked together. Note that part C cannot be regarded as rigid! It is as flexible as the lower part A.

Top part C is positioned a distance h above part A and is floating in the air. Part A is fixed to ground. Again the total potential energy of the structure A+C is calculated. A is less deformed as before and C is not deformed at all as it is floating in air.

And then part C is dropped on part A. The energy applied at contact is easy to calculate. Contact is when material points in C and A meet at interface C/A and dynamic forces develop that affect all the material points of the two parts and are ultimately transmitted to ground.

The dynamic forces are like pressure waves in the structure. The two parts - or their material points - osciallate until all applied energy has become heat.

One basic observation is that part C is always decelerated at contact with A. Another observation is that high forces in the links are observed at elements adjacent to the interfaces C/A and A/ground. Any 'one-way crush down' of part A cannot start without part C decelerating!

My friend is trying (the model only exists on paper at present) to arrange the material points and their links in such a way that only links between material points in part A at interface C/A fail first, i.e. material points in the top of part A become free to drop on the material points below ... or be ejected outside the structure. These free material points he calls part B (rubble)!

I have to say that to model the first step - contact C/A + producing a number of free material points to become part B - is quite difficult. Material points/links in part C adjacent to interface C/A have a tendency to become free/broken, too!

To model step 2 - free material points displacing and contacting part A below with part C pushing from above - is even more difficult.

It would appear that part A - its material points and links - offers a fair amount of resistance, while transforming the applied energy into heat. Actually a fair amount of the energy applied is also transformed into heat in part C.

I will report the progress of my friend. He is hard at work.