09-28-09, 10:59 AM
Donít trust the truss, this is an expression I heard fire fighters use in relation to the World Trade Centre, apparently it was one of the main reasons why it collapsed so quickly.
Was the WTC a one off or is this sort of structure naturally prone to failing if faced with a fire of considerable force. If the WTC had have been a re -enforced concrete structure would it have survived any better?
Most modern building are made with steel channels or I-Beams while older buildings like empire state buildings are made with both I-Beams and Re-enforced concrete that can withstand a lot of shock and load. I think I saw a History Channel program on the Empire State Building where it was designed way over the safety margin.
09-28-09, 05:24 PM
The WTC had a unique "box within a box" design to maximize the amount of rentable space, without the restrictions of inner columns within that space. It was a very elegant design. However this meant you had floor trusses that extended from the perimeter columns, all the way to the core columns without any additional support. When the debris from the plane knocked off the blown on fireproofing, it left them susecptable to sagging from heat, and then eventually collapse.
Here is a image of the trusses to show you just how delicate of a structure they were:
09-28-09, 08:26 PM
the empire state building and WTC 1 & 2 are two entirely different designs.
the outer shell of the empire state building supported the entire load of the building whereas WTC 1 & 2 the load was shared between the outer shell and the interior columns.
the floors themselves aided in keeping the building from buckling and twisting.
in effect WTC had 3 elements that kept those buildings upright, the empire state building had only one.
09-29-09, 11:29 AM