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Similarly, in seismic zones, design results using a static seismic acceleration load approach are not usually compared with results using time history dynamic analysis. However, unlike the use of DLF in waterhammer and slug flow applications, at least the static seismic loads are usually based on codified values which have some justification. Time history analysis would offer a more realistic distribution of seismic loads because mass is typically not evenly distributed in a piperack structure, particularly rack structures supporting heavy equipment with piping. Seismic ground motion acceleration records are becoming increasingly more available through organizations like PEER. CSiPlant can easily import these ground motion time vs acceleration record for nonlinear time history analysis.
Most piping stress models have nonlinear boundary conditions (gaps, friction, one-way supports, etc.) for nonlinear static analysis, yet most legacy piping stress programs are incapable of nonlinear time history analysis. That means that in order to run time history cases, engineers would have to linearize all nonlinear supports for all dynamic analysis cases, which is a dubious approach. This limitation likely helped push engineers toward the DLF static analysis alternative. CSiPlant can easily account for nonlinear boundary conditions in nonlinear time history cases.
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