Rebar is used to reinforce concrete.
The WTC's had 47 four foot thick steel colunms that ran the entire lenght of the building throught the core. Take a look at the picture I posted.
[qimg]http://i5.photobucket.com/albums/y171/karanjasjas/wtc-1.jpg[/qimg]
No, it did not.
You are incorrect.
There were either 44 or 47 columns (depending on which tower).
The outer columns (ringing the core) were about 52" by 22". But they were not solid steel. They were a box made of 5" thick steel.
The interior columns were much smaller, 36" by 16" IIRC, and were made of 2" thick steel.
Nowehere in the buildings did "4 foot thick steel" exist.
Another thing to understand is the difference between static load and dynamic load. The buildings were built to support 6 times the static load (actually, I recall hearing 8, but either way). The static load is similar to the maximun breaking weight of a piece of rope. It's the total force it can withstand, not the mass of objects.
As an example, take a rope that has a maximum breaking strength of, say, 1000 lbs. If you buy this in a store, it'll be listed as a 250 lb. working strength. But you could tie up 100 lbs. on it. However, if you tug it while it had that 1000 lbs, it'd break. Dynamic load includes not just the weigth being supported, but the force with which that weight pushes, as well.
Likewise with the towers. When the upper floors fell, That acceleration and impact was far more than 6 or 8 times the static load. Even considering static load, you had 6 to 30 (approximately) floors above the impact sites that crashed onto the floors below them. In both cases, that would go over the 6 times static load limit, causing the impacted floor to give. When it hit the next one, you get a repeat of the process all the way down.
Another thing to consider is that the core was designed for the buildings weight ot be distributed up and down. If the entire weight of the building was statically attached to the core at one point, it would fall as well.