Dynamic Analysis of the Seismic Behavior of a Base-Isolated Container Crane During the 2011 Off the Pacific Coast of Tohoku Earthquake

Abstract eng:
Earthquake-resistant technologies have improved, e.g., with the introduction of seismic base isolation, since many container cranes for loading and unloading vessels were damaged during the 1995 Southern Hyōgo Prefecture Earthquake. The developed container cranes were installed to high earthquakeresistant quays and have contributed significantly to maintaining the function of the container terminal after large earthquakes. In relation to seismic performance verification of container cranes, strong earthquake motions have been observed at some container cranes in ports in Japan. Records of strong earthquake motion at a base-isolated container crane and the underlying wharf during the 2011 off the Pacific coast of Tohoku Earthquake were examined in detail to clarify the seismic properties of the container crane. Taking account of modeling of the base isolation system, a series of dynamic response analyses were conducted to reproduce the observed seismic behavior of the crane in this study. The latter half of the acceleration time history in the traverse direction, calculated by the crane model without seismic isolation, was not consistent with the observed acceleration during the earthquake. On the other hand, the acceleration history calculated by the crane model in which seismic isolation was always operational was smaller than the observed value as a whole. In the case where the seismic isolations in the four leg portions of the crane work individually by breaking of each shear pin, the calculated acceleration showed good agreement with the observed acceleration. The importance of this precise modeling of the isolation system was recognized from these results. Comparison between the calculated and observed acceleration showed good agreement in the traveling direction of the crane, which was different from the direction of motion of seismic isolation. The observed vertical acceleration of the crane, including high-frequency components, showed less agreement with the calculated acceleration. There were differences in components higher than 2 Hz in the Fourier spectrum between the observed and calculated acceleration. The strong motion seismograph is not installed directly to the main structure of the crane but in the machine chamber. Accordingly, the installation location of the seismograph was considered to influence the high-frequency components of the acceleration wave.

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