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I have seen building demolitions. The explosives crew worked for about two weeks drilling columns and planting charges.

I also saw a smokestack demo, and it looked like it just drifted down, until the differential acceleration broke it in half, then the last part looked pretty quick.

I've seen two burning buildings collapse. One moment they are up, then, there is flame in all the windows, then, in a great rush of sparks, the walls buckle and the roof and everything comes down WHOMP and the sound and color and sparks and the wash of flame is beautiful, awesome, and terrifying. This increased my respect for firefighters tremendously, these guys will run into a building on fire.

What speed would you expect a burning building to collapse at? Why?

Did you measure the actual speed of WTC7's fall? Everyone says "too fast!" Well, how fast was it in feet per second, or meters if you prefer. Let's put a number on how fast is too fast before we go any further.

I believe the building was 47 stories or so and it came down symetrically and totally in what looks like 7-8 seconds in a manner that suggests all the weight supporting columns failed at the same time. If interested, you can read a report on this at wtc7.net/articles/FEMA/wtc_ch5.htm