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For any of two earthquake directions perpendicular to each other, stiffness–soft story irregularity should be checked. Stiffness–extreme soft story irregularity is defined as there is a story in which the lateral stiffness is less than 60% of that in the story above or less than 70% of the average stiffness of the three stories above.
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According to Table 12.6-1 - 1a and 1b type irregularities are the irregularities that are effective in the selection of the analysis procedure selection.
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