GoreNoMore, I hope you’re not maligning my intellect! :)
I’ll answer it... when steel gets hot, it expands toward the heat and gets soft. Not soft like liquid, but loses a tremendous amout of it’s yield strength. So, when you have four main columns, that are super heated, they bend toward the heat and lose their downward strentgh. The wieght above caused them to buckle and yield...give way.
If anyone was even near the building, they would hear a series of tremendous bangs. Due to the main support columns giving way, any girders or latteral support beams that were connencted to the main columns would snap and give way. All of the beams that ran horizontal between the 4 main support columns would resonate a huge bang when they were sheard, or ripped from one side to another.
The bombs people say they heard, were girders in the upper floors giving way.
Picture this... the echo in a steel and concrete stairwell. Someone pics up a 20 lb sledge hammer and whacks the floor on a landing several floors above. What do you think that would sound like? Now, picture a steel beam, not a column, a beam that runs horizontal between the vertical columns, snapping and giving way... It would be about 1000 times louder than a simple good hit with a 20 lb sledge hammer...
People who heard bombs go off, never picked up a hammer in their life...
(leaving soap box..) :)