Reply #16: Static load verses dynamic load [View All]

[LARED]

how does the weight of ten or thirty floors going down ten feet suddenly make the weight of the upper floors unbearable for the lower core structure?

The WTC structure was designed for static loads (not quite accurate if you consider wind loads) not dynamic loading from shock or impacts. The supported mass does not change but the energy of that mass changes significantly when it starts to move (dynamic). It is probably a good guess that at a minimum 15 floors impacted the noncompromised structure of the tower. I'm not going to do the math but those 15 floors falling 15 or so feet is a huge amount of energy for the structure to absorb. The structure in order not to fail must elastically absorb the energy (as strain) without failing. When the mass did hit, steel beams bent, column buckled and connections sheared or were pulled apart.

What caused the systematic and global collapse of the core?

Systematic? What do you mean?

Is there a way to mathematically prove how quickly the lower part of the building would break up as the weight of the upper building bore down on it?

Unlikely in my view. It is far to complex a problem to prove. I have done simple energy comparison based on 30% to 50% of the energy of the tower being converted into work energy (ie busted it up) and you wind up with fall time of 12 to 14 seconds. Very close to the actual time.