Ratcheting occurrence conditions of piping under sinusoidal excitations

Abstract

Ratcheting is one of the dominant failure modes under excessive earthquakes and may cause extreme failures of structures (e.g., collapse). We focused on clarifying the ratcheting mechanism of piping under sinusoidal excitations. Both finite element analyses and experiments were conducted on bent solid bars, which represented piping in this study. Seismic ratcheting occurred due to the combined effect of constant external compressive force and cyclic vibrations. The external compressive force acted as a load-controlled load. Vibrations were applied to provide the source of the dynamic load. Characteristics of vibrations between load-controlled and displacement-controlled properties were studied from the viewpoint of the frequency ratio of the forcing frequency to the natural frequency of the piping model. In addition, the influence of supports on the occurrence of ratcheting was also considered. The results showed that the resonance effect was evident in the piping model compared with the beam model due to the limited plastic area in the piping model. The vibration with a lower frequency had load-controlled characteristics. In contrast, the vibration with a higher frequency presented displacement-controlled properties. In terms of the occurrence of ratcheting, providing more supports sometimes increased the possibility of the occurrence of ratcheting under relatively higher forcing frequencies because more supports increased the natural frequency and decreased the frequency ratio.

Study on post-buckling crack propagation in thin-walled cylinders under dynamic cyclic load

“…A stable crack propagation mode is always observed, where crack growth rate declines with crack circumferential angle. It is achieved by the displacement-controlled condition of the dynamic load at high frequency ratio, which is consistent with previous studies on failure modes of piping (Kasahara et al, 2019;Lyu et al, 2020).…”

“…As a lesson learned from the Fukushima nuclear power plant accident, the nuclear industry recognized the importance of mitigating accident consequences after Beyond Design Basis Events (BDBEs), which would lead to terrible consequences despite a low likelihood of occurrence (Kasahara et al, 2019;Lyu et al, 2020). BDBEs generally occur due to extreme conditions such as excessive seismic load.…”

“…So far, the crack propagation mechanism after buckling under seismic load remains unclear, because seismic load has both load-controlled and displacement-controlled characteristics. Previous studies on the failure modes of piping revealed that seismic load acts as a load-controlled load when the frequency ratio is low, while it acts as a displacementcontrolled load with a high frequency ratio (Kasahara et al, 2019;Lyu et al, 2020). The latter is more advantageous for the safety of piping, because it causes progressive damage rather than immediate collapse.…”