The steel columns resulted in about a 1 second increase in collapse time. This number is small because any section of steel column could only resisted collapse until it broke, which happens at a relatively small compression. For the majority of the collapse, therefore, the steel columns were offering no resistance; each section only offered resistance for the brief period of time between impact and failure.
There is another component to the collapse time due to conservation of momentum in inelastic collisions between the upper block and stationary parts of the lower structure; in effect, the lower block had to accelerate debris from the lower structure as it fell, and this decelerated the upper block. This added about another three seconds to the collapse time. It didn't add any more because the upper block was very much heavier than each floor it encountered.
For some reason, Judy Wood believes the upper block had to stop dead every time it encountered any part of the structure below. This is laughably absurd and violates the law of conservation of momentum, but is the reason why her calculation suggests that the collapse time should have been a minute or more. Calculations based on an understanding of the laws of physics, rather than a deliberate attempt to misinterpret them, give collapse times of typically 12-16 seconds depending on assumptions. And, as I've said before, this agrees very well with the observed collapse time.
What's ironic is that, if the buildings had turned to dust and then fallen, they would have fallen more quickly than was observed, because then there would literally be no resistance. The 5 seconds or do by which the towers fell more slowly than freefall is disproof, not proof, of the dustification fantasy.
I prefer not to use the word "theory" for such inane trash.
Dave
