Actually Grace, the steel in the building wasn't created to withstand fire...It was created to bend to sway with the high wind speeds that sky scrapers are assualted with every day.

In otherwords, it wasn't 'thick, durable steel'. It was actually 'thick, pliable steel' specifically designed to sway with the wind and endure wind stresses.

Furthermore, when the building was being designed, it was designed in what they call a 'drop hole'...Along with the feature of the tube design (remember, the 'hollow' center?), the frame 'hung' on the outter edges of the inner circle of the 'tube', IF the building was to somehow collasp for whatever reason, it would do so within itself instead of falling over and onto other building structures around it.

The building wasn't built to withstand damage period. It was designed in a specific manner to withstand wind stress and for as much minimal damage possible to outside buildings and pedestrians IF it was to suffer significant enough damage that brought it falling down.

And that designing actually worked as it was designed to for the buildings. They did indeed 'bend' with the stess put on them, as well as the collasp was controlled in the manner the building had been designed for. Within itself, and into it's own drop hole.

Unfortunately, the designers never thought of someone using a plane to bring the towers down...So they didn't figure in debris that a high sided impact would cause to buildings around them...Many of those buildings damaged which had been built after the towers went up in fact and by then the myth that the Towers were 'indestructable' had been born.

But just like the Titanic supposedly being unsinkable...The Towers were not indestructable.