Notes

The missing mass calculation is valid only for single point excitation response spectrum analysis (SPOPT, SPRS) and for multiple point response spectrum analysis (SPOPT, MPRS) performed with base excitation using acceleration response spectrum loading. Missing mass is supported in a spectrum analysis only when the preceding modal analysis is performed with the Block Lanczos, PCG Lanczos, Supernode, or Subspace eigensolver (Method =LANB, LANPCG, SNODE, or SUBSP on the MODOPT command).

The velocity solution is not available (Label = VELO on the combination command: SRSS, CQC...) when the missing mass calculation is activated.

The missing mass calculation is not supported when the spectrum analysis is based on a linear perturbation modal analysis performed after a nonlinear base analysis.

The missing mass is not supported when superelements are present.

To take into account the contribution of the truncated modes, the residual vector (RESVEC) can be used in place of the missing mass response. This is of particular interest if the velocity solution is requested or if a nonlinear prestress is included in the analysis (linear perturbation), or if a superelement is present, since the missing mass cannot be used in these cases.

In a multiple point response spectrum analysis (SPOPT,MPRS), the MMASS command must precede the participation factor calculation command (PFACT).

This command is also valid in PREP7.

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