Evaluation of Inelastic Seismic Response of a Piping System Using a Modified Iterative Response Spectrum Method

In pressurized piping systems, strain accumulation may take place due to cyclic loading during a seismic event. This incremental plastic deformation called ratcheting may lead to failure of the piping systems. There is no numerical method available to evaluate this accumulated strain in the piping system using response spectrum as input. In the literature, incremental hinge technique is available to predict the failure level conservatively by considering static collapse as the failure mode. However, it is observed from shake table tests that failure in the piping components, especially in elbows, is due to ratcheting. Considering this failure mode and design input as a response spectrum, a modified incremental hinge technique is developed and validated with experimental results. The strain predicted by this analysis closely matches with that of experimental results which are available up to an excitation of 0.75 g ZPA (zero period acceleration). In the experiment, the pressure boundary rupture occurred at 2 g ZPA, while the analysis predicts the failure of the piping system at 2.37 g ZPA. Details of these investigations are presented in the paper.