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|----| top part falls in this direction--->>> then down
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|---| <----place of impact
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If the structural columns were damaged on impact, they would be more damaged on one side than the other. The weakening would not be equal on all sides. So if the building would collapse naturally, the top would tip over to the side then collapse down, most of the remaining structure would still stand but if it collapsed too a large part of the base would still be left, think of a root of a tree after it's been chopped down. Most likely the buildings would not have collapsed at all.
If the entire building would collapse, it would do so as a domino brick
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|----| -->>
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