Why does the Structural Analysis Guide give a different procedure for Spectrum?
The 8.1 Dynamics course shows a 3-step process:
(1) modal analysis with expand,
(2) spectrum analysis, and
(3) postprocess including reading the .mcom file
The Structural Analysis Guide chapter on Spectrum analysis shows a 6-step method:
(1) Build the model.
(2) Obtain the modal solution (Modal analysis).
(3) Obtain the spectrum solution (Spectrum analysis).
(4) Expand the modes (Modal analysis).
(5) Combine the modes (Spectrum analysis).
(6) Review the results (/Input the jobname.mcom file).
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The Structural Analysis Guide procedure is a little more efficient in that a user can expand only the modes that were determined to be significant in step 3. Very few users take advantage of that and it makes the procedure seem very complicated, so we don`t teach it that way in the dynamics seminar. Both procedures are correct, although technically the mxpand is supposed to be done in a separate expansion pass. I haven`t experienced any problems combining it with the modal extraction myself. |
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