OneWhiteEye wrote:When, exactly, did varying strength enter the picture in your mind? After you proclaimed my earlier simulations invalid? Why is greater connection strength below now a neccessity to produce your expected results? Do you still claim the previous sims are invalid (yes/no will suffice)?
Evidently from day one I got interested in this matter. Stronger elements in a structure always destroy weaker elements in a collision contact, e.g. horizontal stringers in the side of ship is good collision protection like a bumper on a car. But normally you don't fit them for other reasons. I have studied plenty of (ship) structures under various dynamic, short-lived impact loads (both ship/ship collisions and ship/wave contacts) and what happens due to them. The energy applied is converted into pressure/force and displace the adjacent
elements, so you have to start there. What happens to the energy? If failures occur (plenty energy consumed) and the interface changes, you have to see what happens then. In ship/wave collisions the ship structure may fail and the water will splash! In ship/ship collisions both structures fail. I just apply the same method to WTC 1.
Result is that there is too little energy available to initiate, e.g. total destruction. Read my paper! Energy applied can only elastically deform the total structure C+A and produce some local failures at contact. And one-way crush down
of big A by little C is simply not possible, as A and C have identical structures apart from A columns getting stronger lower down; Strong elements/columns in A destroy the weak elements/floors in C and vice versa and, as I see it, collapse arrest follows at once.
But subject is one-way Crush-down models
or sims. Evidently you must then consider that columns get much stronger and weaker away from the contact interface, &c. Your sims are simple solid mechanics sims - masses colliding in a gravity field - and the connections between these masses do not seem realistic.
Depending on energy input I expect the following of any model/sims:
1. Little energy input E1! Both sections A and C deform elastically and there will be a bounce.
2. A little higher energy input E2! Both sections A and C deform elastically and there are very local plastic deformations of elements in contact followed by a bounce.
3. Medium energy input E3! Both sections A and C deform elastically and strong elements destroy weak elements in both A and C. Interface changes. Arrest follows.
4. Medium energy input E4! As 3 but for some reason strong elements are affected, e.g. C columns fail! Then C may drop off, &c.
5. High energy input E5! All adjacent elements in contact (weak and strong) fail at one connection in both A and C. Interface changes. Elements get entangled into one another. Friction must be considered. C may drop off, &c.
6. Energy input E6 for Crush-down. It is not clear how that can be done!
From above it is clear that if 5 takes place, it also includes all effects of 1-4.
So any model/sims must be tested with various energy inputs E1-E6 to ensure that 1 and 3 actually takes place when 4-6 follow. You will also get a good feel how strong the model is to resist various energy inputs.
Some people will argue that in, e.g. the E6 case, the energy is applied so fast that events 1-3 do not really happen! So model is to be adjusted for, e.g. drop height 3.7 m and associated contact velocity due to gravity.