Eli5: Why did the World Trade Center towers collapse when they were hit so high up?

Question

Was there a design flaw or would any building of that height have failed?

In: Engineering

Answer 1

Any building of any significant height (anything taller than something like 4-6 floors) fails when a significant portion of the building comes down like a hydraulic hammer ram on the rest of the building.

Basically the supports at one level breaks, then everything above it comes down like a hammer on the rest of the building, using its weight and momentum to break floor after floor.

This is the fundamental principle of any form of high-rise demolition, although in construction they tend to go for overkill to make sure that the building comes straight down (to minimize collateral damage).