What the benefit of including different groups in different SAM cases on the Response Spectrum tab of the Dynamic Analysis dialog?
For each seismic group added in the MSRS, AutoPIPE combines each direction of the SAM displacements to the response displacements (e.g. displacements from the modal response in the X direction is absolute summed with the SAM displacements in the X direction). If you have multiple SAM groups selected, AutoPIPE combines each direction of each group with the response displacements, either through absolute sum or SRSS, depending on what the user has selected for the group combination. These displacements are all unsigned prior to combining.
The total displacement for a node using MSRS is the following
SRSS: (R^2+S_1^2+S_2^2 ) ^1/2
Abs. Sum: =|R|+|S_1 |+|S_2 |
Where R is the total modal response for the node, S_1 and S_2 are the groups 1 and 2.
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