The effects of copper in a steel alloy
http:// amg-v.com/copperpage.html
Designed the etc
Minoru Yamasaki
Not sure any connections to recent Japanese steel scandal?
Write about about investigation, not suppiliers.
http:// www.tms.org/pubs/journals/JOM/0711/banovic-0711.html
Not saying your wrong about motivation and intent, but my knowledge of steel a plane would take it down with alot less help.
After about 900 degrees you can throw steel ratings out the window and it's a hockey stick drop of of strength with an increase of temp. My current theory is all the thermite and det charge theory is way over kill. The unburnt jet fuel pooling on a floor below the fire would heat and vaporise. Then it would only take a broken window to cause that to act like a fuel air bomb. And that would be the "straw that broke the camel's back" causing a building chain reaction of structural failure.
That's just for the two main towers though. The other buildings not a clue