How
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are direction factors computed during modal analysis?
The Answer: For each mode, modal direction factors identify the predominant direction predominance of excitation associated with each of the Modes. The factors are percentages associated with X- and Y- translational and Z-rotational directions. The sum of three values will always added up directions. Each factor is a percentage which relates its component (translation along X or Y, or rotation about Z) to the total displacement over all diaphragms and all stories. Direction factors therefore sum to 100.
The direction factor for of a particular mode is given by:
where,
Again all summations are overall diaphragms and overall stories.
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Example
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