## 5 Conclusions  
We focused on an actual pile-supported spherical gas holder on alternating layers of soft sand and clay by conducting a three-dimensional seismic response analysis on an interacting holder-pile-ground system and evaluated the seismic resistance of the gas holder in the event of strong ground motion that would damage the pile during an  
Figure 24: Changes in the axial force distribution of pile over time: seismic motion (B). Figure 25: Shear strain distribution (maximum value until the end of an earthquake) of (**a**) with-piles and (**b**) without-piles models: seismic motion (B). earthquake. Here, we determined the effect that strong ground motions with the same acceleration response spectra but significantly different durations would have on the support function of the pile. When the acceleration response spectrum is identical, the maximum acceleration increases as the duration of the main motion decreases. The main conclusions of this study are as follows:  
* With regard to the characteristics of the mechanical response of the target alternating ground, when the duration of the input seismic motions was different despite the response spectrum being identical, the long-duration seismic motion (seismic motion (A)) had larger ground vibrations relative to the bottom of the ground (horizontal displacement) (i.e., larger shear displacement) and greater disturbance in the ground relative to the short-duration seismic motion (seismic motion (B)). As a result, the ground settlement amount in the former was larger than that in the latter. * The long-duration seismic motion (seismic motion (A)) exhibited a large settlement suppression effect due to the pile. This was because the axial force of the pile, as well as the positive pore water pressure, increased owing to the stress redistribution caused by the decrease in the effective confining pressure of the sand and clay layers during the earthquake, which increased the pile resistance (i.e., allowable bending moment). Consequently, when the pile damage gradually progressed with seismic motion (A), the pile could maintain support functions for a certain period of time, even if the pile was ultimately damaged in all sections. * Furthermore, the short-duration seismic motion (seismic motion (B)) exhibited almost no settlement suppression effect due to the pile. In the case of seismic motion (B), an extremely high maximum acceleration acted on the ground in a very short period of time, and the piles were suddenly damaged in almost all sections. This was because the support function of the pile was lost almost instantaneously without the increased resistance of the pile, which was generated by the decreased ground rigidity, having had no time to appear, in contrast to the case of seismic motion (A). * These results show that the ground response and pile failure modes can differ if the duration differs, even if the input ground motion has the same acceleration response spectrum. The results suggest that duration will need to be considered in the future when selecting seismic motions to be used in evaluations. * In this study, we were able to verify the possibility of the collapse of the holder during strong L2 class ground motions, including those with long durations. As a result, we will take all possible safety measures to prevent the holders from malfunctioning even after a large-scale natural disaster occurs. In order to further improve this research, it is necessary to evaluate the effects of geological composition (such as different soil conditions, geological irregularities, and so on) and the input seismic motion (in the case of seismic response spectra containing more short-period components, and the influence of consecutive earthquakes). Therefore, we will increase the number of analysis cases to deal with these issues in the future. Conceptualization, M.K. ; methodology, M.K. and T.N. ; software, T.T. ; validation, T.N. and K.N. ; formal analysis, T.T. ; investigation, M.K. and T.N. ; resources, M.K. ; data curation, M.K. and T.T.