## 3 Earthquake Loading and Seismic Response of Silos
[PERSON] and [PERSON] [83] investigated the effects of different aspect ratios on the dynamic buckling behavior of steel silos subjected to horizontal base excitations. Incremental dynamic analysis was considered for this study considering ten different earthquake records. The main findings by this study suggested that, in presence of ground motions, slender silos are more vulnerable to buckling failure, while squat silos present a considerably higher resistance under same seismic conditions. Recently, the same authors extended their investigation about aspect ratio influence on the silo dynamic behavior [94], by considering stepped walls steel silos under seismic excitation. Considering horizontal and vertical components of ground motion accelerations, different buckling modes were found, depending on the aspect ratio. Particularly, local diagonal shear wrinkles were observed in the elastic range for squat and intermediate slender silos, while elephant's foot buckling modes in the elasto-plastic range were observed at the base for slender ones. Regarding the vertical component of the seismic excitation, it was stated that for silos, this component has a quite marginal effect, and it could be ignored. [PERSON] et al. [95] presented a study reporting a series of shaking table tests on a full-scale flat-bottom steel silo filled with wheat. The experimental study aimed to evaluate some parameters, such as the static pressure, the basic dynamic properties of the considered silo, and the dynamic overpressure. To this aim, the fundamental frequency of vibration, the dynamic amplification, and the dynamic overpressure were observed. On the level of static pressure, this study stated that, the horizontal static pressure distribution is qualitatively consistent with the theoretical expectations and, during the dynamic tests, a redistribution of static pressures occurs due to the compaction of the granular solids. On the other hand, regarding the dynamic response, this study revealed that the damping ratio increases with increasing acceleration, and consequently, the dynamic amplification factor decreases. However, the dynamic amplification factor generally increases along the silo wall height (up to values around 1.4 at the top surface for earthquake inputs with a close-to-resonance frequency content). The resonance frequency (around 11 Hz for the case at hand) depends to a certain extent on the acceleration and on the granular solid compaction. In addition, the study stated that the measured dynamic overpressures seemed to be different from the EN1998-4 [87] expectations with slightly larger values. However, the upper portion of the silos showed a qualitative consistency with [PERSON]'s theory suggested in [21] (especially in terms of dynamic overpressure vs. height profile), but not in lower portion. [PERSON] et al. [96] presented a series of shaking table tests on flat-bottom ground-supported steel silos with corrugated walls. The experimental program aimed to evaluate the dynamic response and energy dissipation capacity of the system considering three different aspect ratios and their different seismic records. The results emphasized the fact that the energy dissipation capacity is much larger for the silos with full or half filling conditions (aspect ratio = 1, 0.5) compared to the empty condition (aspect ratio = 0). Furthermore, the study concluded that the acceleration vertical profile is a function of the aspect ratio, and the silo with full filling condition (aspect ratio = 1) had a smaller dynamic response than the one with half filling condition (aspect ratio = 0.5).