TR.30.2 Mode Selection
This command allows specification of a reduced set of active dynamic modes. All modes selected by this command remain selected until a new MODE SELECT is specified.
This command is used to limit the modes used in dynamic analysis to the modes listed in this command and deactivate all other modes that were calculated but not listed in this command. If this command is not entered, then all modes calculated are used in the dynamic analysis.
CUT OFF MODES 10 MODE SELECT 1 TO 3
In this example, 10 modes will be calculated but only modes 1 and 3 will be used in dynamic analysis.
- Do not enter this command within the loads data (from the first Load command in an analysis set down to the associated Analysis command).
- The advantage of this command is that you may find the amount of structural response generated from a specific mode or a set of modes. For example, if 50 modes are extracted, but the effect of just the 40th to the 50th mode in a response spectrum analysis is to be determined, you may set the active modes to be 40 through 50. The results will then be devoid of any contribution from modes 1 through 39.