How many steel framed buildings ever collapsed before 9/11?

Question

Why wouldnt a pancake collapse take longer than freefall speed?

Answer 1

Lots of them suffering similar damage...

Answer 2

The most recent answer is correct in general, but here is some additional information on the 9/11 collapse:

The belief is that the fire is what caused building to collapse, combined with several factors.

The floor trusses were more than strong enough to support the building, but steel weakens as it gets hotter, particularly as it nears its melting point. To prevent the trusses from receiving excessive heat, an insulating (and fireproof) foam was sprayed onto the truss structure.

Running a plane into the building did several things according to my understanding:
1) It removed several load bearing supports (and trusses) causing the rest of the building's load above the hole to bear the rest of the weight.

2) It weakened several other members and unbalanced the loads the building had to carry

3) The impact blew off the fireproof foam that insulated the steel from excessive heat

4) The heat from the fire from thousands of gallons of jet fuel ignited all of the flamable material in the building (desks, chairs, carpet, etc) which burned long after the fuel was gone.

5) The heat softened the steel trusses to the point where they started to fall apart.

6) Once the trusses started comming apart, each remaining member had the rest of the load of the building above it.

7) The building "pancaked" - the top floor fell onto the one below, which overloaded that floor, which fell to the next, etc, etc.

Collapsing buildings in the modern era are rare. The twin towers were actually designed to withstand the crash of a commerial airplane of the time, but the fire damage, and damage to the fireproofing was not accounted for. The result was a terrible catastrophe. The buildings would still be standing if it weren't for such extreme conditions (and extreme people).

I recommend you check out some documentaries, such as Nova's "Why the tower's fell"

Answer 3

The twin towers were not a steel framed building in the classic sense. You need to do some investigation of how steel framed buildings are constructed and how the world trade center was built.

There are some significant differences.

Answer 4

Oil Field has it correct. Some of you need to do some research and find analyses done by recognized structural engineers. The 'shell framing' is not what failed. Each floor had 4" concrete slabs supported by steel trusses which connected to the 'shell framing'. The connection of the trusses to the 'shell framing' is what failed due to heat and faulty insulation.

Answer 5

There has never been a building to collapse before 9/11. There are hundreds and hundreds of other examples of other buildings that were even bigger than the WTC and they were subjected to forces even greater than 9/11 and they weren't even built as well as WTC and none of them ever fell down.
Of course must of us don't know about these since our government has kept all that info from us. Several occurred in Texas when W was gov and of course we never heard about those either.

Answer 6

NONE