Fledermaus
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Re: MIT Prof Kausel - Structures Like WTC do not Collapse into its own Footprint Rnd
In addition, the towers did not fail from the bottom up, but from the top down. For a portion of the tower to roll to either side, it must first acquire angular momentum, which can only occur if the structure can pivot long enough about a stable plane (e.g. the stump in a tree). However, the forces concentrated near the pivoting area would have been so large that the columns and beams in the vicinity of that area would simply have crushed and offered no serious support permitting rolling. Also, both building sections above the crash site were not tall enough to significantly activate an inverted pendulum effect. Thus, the upper part could do nothing but simply fall down onto the lower part, crushing it. While photographic evidence shows the upper part of the South Tower to be inclined just as it began to collapse, it may not necessarily have rolled to the side, but instead fallen down onto the lower floors in a tilted position. (A careful review of collapse videos and additional photos should help clarify this contention.) Indirect evidence points to minimal vertical resistance to telescoping or pancaking of either tower: the duration of the collapses was nearly the same as that of an object in free fall, while any serious resistance would have slowed down the collapse. In essence then, the towers did not collapse like trees because the structures, despite their strength, were too fragile to sustain such motions.
In addition, the towers did not fail from the bottom up, but from the top down. For a portion of the tower to roll to either side, it must first acquire angular momentum, which can only occur if the structure can pivot long enough about a stable plane (e.g. the stump in a tree). However, the forces concentrated near the pivoting area would have been so large that the columns and beams in the vicinity of that area would simply have crushed and offered no serious support permitting rolling. Also, both building sections above the crash site were not tall enough to significantly activate an inverted pendulum effect. Thus, the upper part could do nothing but simply fall down onto the lower part, crushing it. While photographic evidence shows the upper part of the South Tower to be inclined just as it began to collapse, it may not necessarily have rolled to the side, but instead fallen down onto the lower floors in a tilted position. (A careful review of collapse videos and additional photos should help clarify this contention.) Indirect evidence points to minimal vertical resistance to telescoping or pancaking of either tower: the duration of the collapses was nearly the same as that of an object in free fall, while any serious resistance would have slowed down the collapse. In essence then, the towers did not collapse like trees because the structures, despite their strength, were too fragile to sustain such motions.
