Loading ...I looked at a few parts of the link. They say, the bigger the explanation, the bigger the lie. Anyway, I also have a structural mechanical engineering background. I read a lot about the way the (new fangled) buildings were constructed.
They were not built the old fashioned way. They were built the modern “cheap skate way”. Not the old expensive 1910, tried and true way, four square construction. That’s why they collapsed. Before that day, nobody ever saw a high rise collapse. That’s why the firemen and equipment were so close to the buildings. They had no idea how cheaply they were built.
Basically, two objectives before they were built was use the minimum amount of steel, and they wanted more open spaces from wall to wall with no vertical beams getting in the way. So, it was a very ingenious new fangled method.
They constructed or created an outside perimeter of vertical steel columns bottom to top. Picture a big vertical hollow square tube. In the center of the square tube, for the elevators, they also had vertical steel beams top to bottom.
Then to keep the outer walls in line and parallel with the center beams, they connected them left to right with the cheap light flooring or roofing type girders, only designed just strong enough to hold the weight of contents. Or snow if its the roof.
There was no left right stresses on the girders. All they had to do was hold all the vertical stuff in place, from moving side to side, so they did NOT have to be strong at all. However, the flooring was the weakest link in the chain.
Melt or remove the flooring and it all falls down. Now we all know why old buildings were built the old fashion way. The ingenious new way is vulnerable to a fire. The engineers should have known that. And probably they did. But probably told themselves there would never be fire in there.
They did have some spray on insulation on those left right girders, allowing for a small fire in one section, but the plane crashed into the structure and pulverized the insulation, and the floors melted and down it all went.