dankie
Well-Known Member
The buildings were built with very different construction methods.
The Empire State is steel frame construction
Steel frame
The classic concept of a skyscraper is a large steel box with many small boxes inside it. The genius of the steel frame is its simplicity. By eliminating the inefficient part of a shear wall, the central portion, and consolidating support members in a much stronger material, steel, a skyscraper could be built with both horizontal and vertical supports throughout. This method though, though simple, has drawbacks. Chief among these is that as more material must be supported (as height increases), the distance between supporting members must decrease, which actually in turn, increases the amount of material that must be supported.
The World Trade Center was tube frame constructed:
Tube frame
This short section requires expansion.
After 1965 a new structural system of framed tubes appeared. Fazlur Khan and J. Rankine defined the framed tube structure as "a three dimensional space structure composed of three, four, or possibly more frames, braced frames, or shear walls, joined at or near their edges to form a vertical tube-like structural system capable of resisting lateral forces in any direction by cantilevering from the foundation."[1] Closely spaced interconnected exterior columns form the tube. Horizontal loads, for example wind, are supported by the structure as a whole. About half the exterior surface is available for windows. Framed tubes allow fewer interior columns, and so create more usable floor space. Where larger openings like garage doors are required, the tube frame must be interrupted, with transfer girders used to maintain structural integrity.
So while tube construction is stronger when lateral (horizontal) force is applied. The world trade center was brougt down by the unsupported weight (vertical force) of the 14 floors above.
When the interior steel columns of the world trade center were severed (we know this happened because the elevator shafts and stair cases were blocked) the center core of the building had nothing supporting the upper floors. The only remaining support was given by the exterior columns.
When the B25 hit the empire state building only the boxes of steel that were severed stopped supporting, but the undamaged steel boxes were able to take the strain.
We are also dealing with exponentially larger forces when a plane that weighs 10 times more and was travelling at 7 times the speed of the smaller plane hit an object.
The Empire State is steel frame construction
Steel frame
The classic concept of a skyscraper is a large steel box with many small boxes inside it. The genius of the steel frame is its simplicity. By eliminating the inefficient part of a shear wall, the central portion, and consolidating support members in a much stronger material, steel, a skyscraper could be built with both horizontal and vertical supports throughout. This method though, though simple, has drawbacks. Chief among these is that as more material must be supported (as height increases), the distance between supporting members must decrease, which actually in turn, increases the amount of material that must be supported.
The World Trade Center was tube frame constructed:
Tube frame
This short section requires expansion. After 1965 a new structural system of framed tubes appeared. Fazlur Khan and J. Rankine defined the framed tube structure as "a three dimensional space structure composed of three, four, or possibly more frames, braced frames, or shear walls, joined at or near their edges to form a vertical tube-like structural system capable of resisting lateral forces in any direction by cantilevering from the foundation."[1] Closely spaced interconnected exterior columns form the tube. Horizontal loads, for example wind, are supported by the structure as a whole. About half the exterior surface is available for windows. Framed tubes allow fewer interior columns, and so create more usable floor space. Where larger openings like garage doors are required, the tube frame must be interrupted, with transfer girders used to maintain structural integrity.
So while tube construction is stronger when lateral (horizontal) force is applied. The world trade center was brougt down by the unsupported weight (vertical force) of the 14 floors above.
When the interior steel columns of the world trade center were severed (we know this happened because the elevator shafts and stair cases were blocked) the center core of the building had nothing supporting the upper floors. The only remaining support was given by the exterior columns.
When the B25 hit the empire state building only the boxes of steel that were severed stopped supporting, but the undamaged steel boxes were able to take the strain.
We are also dealing with exponentially larger forces when a plane that weighs 10 times more and was travelling at 7 times the speed of the smaller plane hit an object.
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