In October 1987@ the PVRC Steering and Technical Committees on Piping Systems established a Task Group on Independent Support Motion (ISM) to evaluate the technical merits of using the ISM method of spectral analysis in the design and analysis of nuclear power plant piping systems. The results of the Task Group evaluation culminated in a unanimous Technical Position that the ISM method of spectral seismic analysis provides more accurate and generally less conservative response predictions than the commonly accepted Envelope Response Spectra (ERS) method and are reported in this WRC Bulletin. For the past ten years there has been a concern that the design of piping systems may have placed too much emphasis on seismic inertia loads. Past criteria and practices have perhaps overemphasized protection from seismic loads at the expense of providing proper support for operational thermal loads. Consequently@ this past practice has resulted in piping system designs that are stiffer than necessary@ oversupported and not as reliable as they could be. Early in1982@ the Pressure Vessel Research Committee (PVRC) established new committees to make recommendations for modifications of codes@ standards@ regulations and practices@ so that a better balance would exist between protecting piping for dynamic loads and providing flexibility for expansion.
BULLETIN 352-1990 history
1990BULLETIN 352-1990 INDEPENDENT SUPPORT MOTION (ISM) METHOD OF MODAL SPECTRA SEISMIC ANALYSIS