exactly. The planes took out several of the lessor supports immediately on impact, the heat from the fire weakened the remaining pillars. Lets not forget how buildings are built. Pillars are arranged in a way which uses each slab to dissapate the load from the level above it, that way pillars don't have the weight of the entire building on them. It's kind of hard to explain, but that's about as simple as I can without diagrams.
Anyways, once those first main remaining supports heated, they collapsed, bringing the entire weight of the 20 or so floors above it onto the floor below. Millions of tons falling 10 feet onto a design meant only to hold the weight of one floor above. The rest was chain reaction all the way down.
Air gets compressed as this happens, which blew out windows, making it look like little explosions just before the floors above pancaked into the next one below, and so on.
>>>>Air gets compressed as this happens, which blew out windows, making it look like little explosions just before the floors above pancaked into the next one below, and so on.
Now that understood! THIS is why explosions were heard before the buildings collasped??!!