I really get tired of all the conspiracy theories about the Twin Towers and how some of our government officials somehow blew up the buildings. When I learned about the construction technique used, I wondered how they passed New York city building codes. Then I found out that government buildings don't need to meet city building codes. So some egotistical building architect decided that his
building should be completely open with no interior walls. So they used floor trusses. These thing will not support much weight. You have seen in the news where big box store roofs fail when the roof drains get plugged or have a heavy snow load. These trusses are made of tubing with plywood for the floor. When the planes hit the buildings, the load from the plane and the water from the sprinkler system were too much for the trusses to hold. Once one failed, it just compounded the problem. The more weight (that dropped) each floor the faster the whole building collapsed.
Anyone that has worked in the fire service (I did for 25 years with the Bend Fire Dept.) and anyone that has worked in construction (I did for 35 years) knows about these type of trusses and understands how dangerous they can be.