I remember sitting in my fourth-grade class when there was an announcement directing the staff and students into the gymnasium, that is where we found out that one of the twin towers were hit. As a kid, I did not truly understand the significance of this tower being hit, then the second tower was struck. I would never forget how quick the atmosphere changed in that gym, the look on the adult's face.. the murmurs. I don't think things have ever been the same since.
Pfatteicher has truly given me a whole new perspective on 9/11. Setting emotions aside, and get to the technical aspect of things. It was a combination of failures, which inevitably lead to material failure; that cost us the lives of nearly 3000 people.
A material can change due to temperature; as we have heard about time and time again in this course (Titanic, Challenger) those were examples of lower temperature. The twin towers were exposed to temperatures of 700-800°C, which softened the steel, allowing each floor to pancake on top each other. As Professor Halada explained this alone was not sufficient for the collapse. The difference in temperature from one side of the building to the next caused yield-level residual stress causing the steel to buckle.
I never took the time out to look at it from a material failure aspect, and if it wasn't for this class and this specific lesson; I would have probably never taken the time to do so. In a way, there is a sense of closure.