Shrimps

I was told a few years ago by a civil engineer the reason the towers fell the way they did was a largely due to the way they were constructed. I was wondering if the following is indeed correct / plausible explanation. It all seems logical to me.

He said they were not constructed in the 'traditional' method; instead they were a central core with the elevators/electrical/pluming with a outer 'shell' composed only steel. The core and the shell were only connected with beams designed to carry the load of the floor / occupants. He then showed us a structure composed of a bottom plate and a top plate (a fair distance apart) connected with only with small metal rods. As you can imagine it was pretty unstable, prone to torsional and compressive loads. He then added additional plates in between the top and bottom plate (think of them as floors) and voila it was very stable. Anyways, that was the his attempt to show us the basic idea of the structure of the towers.

He then went on to explain that the jet fuel (which burns at a higher temperature than normal office fires) melted the connecting beams between the outer shell and inner core (similar to removing the intermediate plates in his demo structure). He really stressed that the impact of the plane did not cause the building to fail, of course the WTC was designed to survive a plane impact, it's happened by accident with other tall towers in the past. He said that it was designed so that the connecting beams could survive a normal office fire, but no one really designed the beams that support the floors to hold up to 200k litters of jet fuel burning.

Anyways he then took out the intermediate plates form his little demo, and applied a vertical compressive force simulating the weigh of the floors on top of it. Of course the metal vertical rods buckled outwards eventually leading to failure. He said that caused an entire floor of the tower to drop down onto the next floor that was also weakened. By the time all of this hit the unawakened floors, it had enough momentum and force to buckle to next floor leading to a domino effect.

Anyways, that's how the guy described it, it sounds logical to me. I was wondering if this theory was indeed correct / plausible as to the reason the towers fell the way they did.

So why are people still pointing and screaming it's impossible for the towers to fall down the way they did naturally? I am really at a loss.

Edit: yes melt was the wrong word, I just wasn't thinking when I was typing since I had just woken up.