After 'Save as' with the same model without any changes, the reaction value is different every time I analyze it, why?
When the analysis model has complete symmetry in both the X and Y directions, there can be 10 modes out of the 15 modes that have identical natural vibration periods in both X and Y directions, resulting in a total of 5 pairs.
In such cases, the order of modes can change between X and Y directions during each analysis run, potentially affecting the results when modes are combined. To address this issue, it is recommended to use Combination of Quadrature Components (CQC) for analysis, which considers the correlation between modes rather than using Square Root of the Sum of Squares (SRSS). When using CQC for combination, you will not encounter this phenomenon.