Study on ratcheting of pipes under the combination of gravity and seismic load

After the Fukushima Daiichi nuclear accident, the mitigation of accident consequence for Beyond Design Basis Events (BDBE) becomes essential. The realistic strength evaluation is required to predict accident consequence. This study focuses on clarifying the practical ratcheting strength of piping systems against gravity and seismic loadings. For simplification, in current research, the piping component is modeled by the beam, and sinusoidal waves or their combinations represent the seismic loading. Gravity acted as primary loading and was applied in two ways - one was by the additional mass put at the free end of the beam, and the other was the self-weight of the beam. A cyclic acceleration at the base of the beam was applied as the secondary loading to provide the source of alternating dynamic loading which can be assumed as seismic loading. Equivalent loading conditions were put in the case of the experiment as in numerical analysis to validate the finite element analyses. The results showed that acceleration waves with the lower frequency components than the natural frequency is more damageable than higher frequency ones. The main reason can be explained by the phase delay between loading and response.