WTC7 - The fires failed Girder 44-79

[ozeco41]

Couple of simple facts to keep in mind…

• Column 79 was the largest and most heavily loaded column in the building. If you are looking for a suspect for one building member failing, and starting a total progressive collapse of the structure, column 79 has to be number one on your list.

Correct. My point was the far simpler one that Col 79 must have failed because EPH fell. But next step easy - all the rest of the support under EPH fell also. And the point you make - very strong reasons why the biggest column would be the leading suspect as villain in the piece.

• Girder 44-79 didn’t walk off its support, the connection exploded apart. The bottom 7/8” high strength bolts probably ripped a large piece of the bottom flange out of the girder. Releasing 40-60 tons of built up force, produced by the heat...

Highly likely and probably supported by detailed analysis. I've never needed to go there. However simple "slide off" OR more complicated "walk off" scenarios are plausible but not top of the probability list.

• WTC 7 (IMHO) was a poorly framed building. Shear connections between the girder and columns, not full moment connections, which would be required in a seismic zone. The overall structural frame lack redundantly and ductility.

Yes to all.

 

[Newtons Bit]

WTC 7 (IMHO) was a poorly framed building. Shear connections between the girder and columns, not full moment connections, which would be required in a seismic zone. The overall structural frame lack redundantly and ductility.

This is not true. A "seismic zone", which is a misnomer to begin with, does not trigger any code rule in the IBC or CBC that would require all connections, or even any connection, to be a full moment connection.