Inelastic Seismic Response Analysis of Piping Systems with Cyclic Hardening

We studied a method for analyzing inelastic seismic motion in piping systems. Some steel materials for pipes exhibit cyclic hardening behavior under cyclic loads. This behavior leads to higher stiffness in piping elements, and higher natural frequencies in piping systems. It is important to consider these effects in order to predict dynamic responses in piping systems. Past studies have shown that cyclic hardening is mainly dependent on two factors, (1) the number of loading cycles, and (2) strain range. Therefore, we extended the Ohno-Wang rule, which is one of the most sophisticated kinematic hardening models, so that cyclic hardening depends on strain range as well as the number of cycles. A stress-strain relationship of the extended model is dependent on the calculated strain range. We applied the extended model to a shake table test on a piping system. The results indicated the extended model exhibited a strain range dependence of cyclic hardening. Compared with the test results, the error in the calculated acceleration was 8%, and it was less than those for the results without considering cyclic hardening. As a result, we found that the extended model could simulate piping behavior with cyclic hardening, which was dependent on strain range.