Demolition Charges brought down those 3 towers (WTC1,2,&7). All 3 came down freefalling. No airplane hit on WTC7 yet explosives brought it down in 6.5 seconds(freefall of an object is 6.0 second for a 47 story), Towers 1&2 came down in about 11 seconds(freefall of an object is 10 seconds from a 100 story building) all those 47+47+24 main support steel columns did not resist the fall at all, because the demolition charges were taken them out mili-seconds ahead of the collapses..