how these three buildings collapsed due to fire, when other known high rise buildings on fire remained standing?
Please tell me how many other high rise buildings were hit by a 767 traveling over 500 mph and nearly full of fuel. To my knowledge what occurred on Sept. 11, 2001 was unprecedented. It wasn't just fire, it was also the damage done to the buildings, the necessary support structures in conjunction with the fire that weakened, not destroyed, but weakened support enough for a collapse.
Okay let's take WTC7, the 47 story building standing next to the World Trade Center. I'm attaching a few images to help explain. I wish I could paste them here where they could line up with the text but I don't want to steal bandwidth so I'm attaching them instead.
The first image is an image whereby colored lines have been overlayed on a picture of the collapsed building. The white lines indicate an area that was "scooped out" (quote by NIST) during the collapse of the twin towers. The light brown rectange is approximately where the louvers were. The light green is approximately where the third floor promenade was.
Another image is of WTC7 undamaged, before Sept. 11. As you can see if the columns (represented by the white lines in the first image) were taken out, it is not unreasonable to think the mechanical floors (behind the louvers and above the lobby) that contained heavy equipment, would fall into the open lobby. On those mechanical floors, there were transformers. According to FEMA, "WTC 7 contained 10 transformers at street level, 12 transformers on the 5th floor, and 2 dry transformers on the 7th floor."
Transformers are filled with oil and can explode. Want to see a transformer explode? Just one?
http://www.stupidcollege.com/items/Electric-Transformer-Explosion
Remember WTC7 had been in flames for hours. It is reasonable to surmise the building's condition was worsening over that time.
Additionally, there is video showing a gash on WTC7 running from the top of the building down. I'm attaching it as the third image. Why is that gash important? Because it lined up with the fuel system that I am attaching as the last image.
There is more, quite a bit more and quite a bit more detailed, that is found here:
http://www.debunking911.com/WTC7.htm
But I wanted to give you just the barest overview and to give you an answer. With all due respect, this has nothing to do with your experience, but rather simple physics, mathematics and gravity.
Chris