Posted by JF on June 01, 2003 at 20:23:14:
In Reply to: twin towers collapse posted by Alberto on June 01, 2003 at 15:12:33:
Alberto, the key is CONTROLLED demolition. The collapse of the towers destroyed a very large collateral area, shut lower Manhattan communications, power and transportation down for several months, caused a host of health problems and killed some 3000 people.
The towers were tubular structures, so at first, the outer cage of steel held in the floors as they pancaked down. But the pancaking started partway down at the crash levels. There was an enormous load, basically 20 some stories (an entire typical building) that started moving when the fire level failed. That's a hell of a chunk of mass. Eventually the potential energy being released as kinetic energy, along with loss of internal bracing and sheer bulk of avalanching concrete, caused the outer cage to buckle and come apart.
It's a matter of scale. If the towers had been demolished professionally, there would have been a prolonged stripping and top-down disassembly phase prior to any final dramatic implosion. The amount of material and extreme height would otherwise release far too much energy in the collapse. Most likely, an implosion demolition would have been limited to the last dozen or two stories. Nobody would attempt to implode a 110 story building commercially. Probably, after disassembling 80-90 stories, the demolition project would just keep going rather than mess up the site with an implosion. Also consider that the sub-basements were seriously weakened in the collapse, threatening many surrounding buildings with collapse into the hole. Only the mass of stuff filling the hole helped prevent collapse of the retaining foundation. A demolition project would seek to preserve that subbasement structure rather than dump a jumbled load of burning steel and concrete into it.
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