FICTITIOUS MASS ELEMENT IN STRUCTURAL DYNAMICS

Fictitious masses are used to improve the accuracy and efficiency of m odal-based structural analyses that involve substructure synthesis, lo cal excitation, and local structural changes. New formulations, which allow easy applications in various subsequent analyses, are given for two categories of fictitious masses: regular and very large. Regular m asses are of the order of entire substructures, whereas very large one s are several orders of magnitude larger The regular fictitious masses are added to selected coordinates of the finite element model for nor mal-mode analysis, and then removed in a way that produces modes with local deformations near the selected points, in addition to the nomina l natural vibration modes. Subsequent analyses of local nature can the n be performed in the standard way. Very large masses are used to gene rate static constraint modes for fixed-boundary modal coupling, and br oken modes are used for representing rigid-body relative motion betwee n structural segments with application to loads analysis. The inclusio n of fictitious masses as optional elements in standard structural dyn amic procedures is facilitated.