I thought Bazant meant by rigid is indestructible or at least stronger than the lower structure that apparently was not rigid. Some people think rigid means deficient in or devoid of flexibility and an object with such characteristics is indestructible. If it cannot flex, it cannot be changed. Indestructible. I agree.
Dry pasta is very flexible - it cracks immediately when a force is applied to it. Just drop it on the floor.
Rigid objects do not exist in the real world.
But doing structural analysis you always apply a rigid support to the structure you study. Reason is to ensure that it doesn't fly away, when loads are applied. If all loads balance, there is no problem - the structure doesn't fly away - balance. If loads, by mistake, do not balance, you will see that a balance force develops at the rigid support to take accout of the imbalance. If you really look at the rigid support - which has 0 m² contact surface, you will see that the stress there is infinite; force divided by 0 m² becomes infinite stress!. A rigid support evidenty can withstand infinite stress - no flexibility - but using clear thinking you know that your analysis is incorrect.
I have done plenty of structural analysises and rule 1 is to ensure that there is balance of forces. I have even been a teacher of structural analysis and rule 1b is to check that the pupils models are in balance. Very often they are not.
The beauty with structural analysis is that in every problem all forces balance ... all the time.
Bazant is cheating in his analysis. He assumes that the upper block suddenly becomes rigid , i.e. will not flex due to forces applied to it (by the lower structure) at contact. It means that infinite stresses are applied to the upper block at contact ... but that the upper block remains intact. Only the lower structure is affected - shock waves, crush fronts, etc. and such nonsense.
In the real world such nonsense does not happen. Actually the first object to get affected is the moving upper block. It may bounce, get damaged, etc. It always ends in arrest!
Look again at the videos. You do not see any impact upper block/lower structure. Before impact the upper block implodes, horizontal forces are applied to it inwards and sucks down the roof + mast. Very strange.
Later you see a lot of structural parts being ejected horizontally outwards from the lower structure all the time (through the smoke screen) + air jets. Gravity is a vertical force. The horizontal ejections are caused by some other energy - applied in another direction. Don't invent that compressed air ejected parts 200 meters sideways.
And the amount of dust!! To produce dust particles, you must produce a lot of fractures in the structures involved ... and it consumes plenty of energy. Every fracture is molecules ripped away from one another in the structure and at the tip of the fracture temperature is very high ... to permit the molecules to separate. Requires plenty of energy to produce dust.
We know the max energy applied if the upper block dropped. 1.2 GJ or 41 litres of diesel oil. To produce the dust you see on the videos I estimate you need 1000X + that energy. And I wonder where it came from;
Of course, I also wonder why Bazant becomes a con man to fool you. A retired professor. Why on earth should he put his nose into this? Maybe he has financial problems or expensive habits. Con men usually have those.
Anyway - Bazant knows little about structural (damage) analysis. That's clear.
Thanks again for starting the thread. A good opportunity to improve your arguments to debunk Bazant ... and NIST. So just carry on.
PS - Many posters are on my ignore list due to stupid posts in the past so there is no answer from me. Send PM (+ excuse) and I will remove you from the ignore list. Maybe you get an answer then.
