[Cernunnos]

Now my question is this: do structural engineers take into account burning material falling through these shafts during a fire of any kind, and is there any way to prevent the consequences?

Yes, they do. However, with buildings of that height and mass, such damage causes immense structural harmonic distortion, and you may have noticed that when the 2nd one collapsed, it imploded from the inside.

There is simply no way to account for it architecturally or on a systems basis other than not to build them nearly so high.

[TailspinJim]

Wonder if Ann Marie Smith was stewardess on any of those planes?