If the twin towers had been built a little more solidly , as the Empire State Building was, with steel beams connecting in a grid of ten-foot boxes, instead of a cage with concrete floors poured over corrugated metal, when the planes hit the towers they might have withstood the test of heat versus gravity.
The Empire State Building is solidly constructed. Within its stone and mortar skin lies a steel skeleton. It is likely to survive for the next 1,000 years, a monument unlike any other, a true wonder of the world.
Truth be told, it didn't matter. The attacker caused minimal damage, crashing into the 96th floor.
In the center, below the FBI agent and the tourists, you can see that the steel beam was bent, but was still holding.
The biggest problem with the twin towers, however, was their open format . Much of the building's support was on the outside. The steel mesh allowed the building to flex in the wind, yet still support the open floors. There were only eight main support columns on each side of the central shaft, 32 in total.
When the planes crashed into the buildings, they cut the
steel
mesh . Thus
, the integrity of both buildings was compromised.
If there had been an entire steel structure inside the building, it probably could have been repaired and still be in use today. However, when the
steel
mesh
and perhaps some of the 32 support columns were compromised , collapse became inevitable . When one floor fell , another was too heavy to bear the load, and it collapsed like a stack of pancakes.
It was a perfect accidental implosion, as the net was pulled inward as each floor collapsed. It likely saved more than a million lives by collapsing that way. Imagine if the walls had fallen outward, landing on thousands of buildings and the crowds of onlookers.
In the end, we learned a lot about the structural support and safety of an exposed city. One World Trade was built with a steel cage.