carmen510: For anyone who says that controlled demolitions caused the towers to fall, here's a video of the beams bending due to the extreme heat caused by burning plane fuel:
http://www.youtube.com/watch?v=K8dX3foxozQ slash11: jet fuel or fire cannot melt steel. And also the fire is only on small part of the building. Also notice never in the last 100 years a steel structure building fell because of fire.
The problem always remains that you need to cut off the steel columns to get such collapses for a steel structure building. Also notice the concrete has been pulverized.
1. You're right in that jet fuel set on fire cannot melt steel. HOWEVER, at high temperatures (like those when jet fuel burns), steel deforms and loses much of its strength, which would result in the collapse. The question isn't of temperature, its of thermal conductivity. If the heat from the fire is being pumped into the steel faster than it can be conducted away, THEN THE STEEL'S TEMPERATURE RISES ABOVE THE FIRE'S TEMPERATURE, RESULTING IN DEFORMATION. At that point, the rest is simply momentum and physics.
2. You're right that a steel structure has never COMPLETELY collapsed from a fire, but that's because none of those fires were burning from such extreme temperatures. There are several of cases where steel structures partially collapsed, such as:
Parque Central Complex in Caracas, Venezuela. In 2004, a fire caused the collapse of two floors, but the temperature had dropped sufficiently to avoid a complete structural collapse.
The Windsor Building in Madrid. In 2005, a fire caused most of the top floors to collapse into the lower floors.
In 2007, A GASOLINE TANKER FIRE caused an elevated roadway (the I-580 and I-980) in Oakland, California to collapse, because UNLEADED GASOLINE BURNED AT A HIGH ENOUGH TEMPERATURE to deform and bend the steel frame of the overpass.
