Seismic response of multiply supported secondary systems by a mode synthesis approach

The seismic analysis of secondary systems, like piping supported at several points of a primary structure, is of great practical interest in the nuclear and other industrial facilities. Currently, two approaches are commonly used for such analyses: (1) time history approach and (2) response spectrum approach. The time history approach provides an accurate estimate of response but only for the specified ground motion time history used in the analysis. As for a design, it is necessary to consider several possible ground motion time histories, and as the time history analysis even for a single time history is computationally expensive, this approach is clearly undesirable for seismic design of secondary systems. The response spectrum approaches are more suited for design purposes because they are computationally inexpensive and because the design response spectra used in these approaches are supposed to consider several ground motions in their definition.