## 2 Structural Typology and Arrangement of Circular Silos
### Supporting Arrangements  
Silos vary in the supporting system depending on the capacity, usage, and operation. Hence, a significant variation in the structural behavior and the response to different excitations (e.g., seismic loads) occurs as a function of the supporting arrangement. Assuming that ground supported silos rest directly on the foundations, different support arrangements could be recognized for elevated silos (for instance, see Figure 3) depending on the silo size and on the magnitude of the force introduced into the shell body by the local support. Light silos could be discretely supported by columns, where a limited number of equidistant isolated columns are used with [37] or without [38, 39] transition ring girder around the circumference. In addition, different means are developed to arrange the column-shell attachment, so that the resistance of the shell body to the local buckling and local failure is increased. Talking about the discretely supported silos, the main deficiency is that the structure suffers high local axis compressive stresses concentration, thus possible local failures can occur such as plastic yielding or elastic buckling. Concerning this topic, [PERSON] et al. [38] introduced a study in which a possible solution is suggested to increase the failure load of silos for this configuration. It consisted in adding longitudinal stiffeners as localized above each support resulting in a positive significant influence on the buckling behavior/loads. Nevertheless, it proves to be disadvantageous from a certain critical height over which the column is attached to the silo. The dependency of the buckling behavior and the failure load on the thickness and radial width of the stiffeners was investigated in [40]. Small silos with discrete supports could also be supported on local brackets attached to the side of the shell (for instance, see Figure 3). Later, [PERSON] and [PERSON] [41] presented a study outlining the behavior of discretely supported silos on several brackets rigidly connected to stiff columns. This study observed the local pre-buckling deformations and bifurcation mode and the local plastic collapse. Another aspect that gains more interest among researchers is the ring girder, since it has a major role in reducing the potential buckling. The ring girder beneath the silo is responsible for redistributing reactions forces from supports into a more uniform stress state in the cylindrical shell body [37]. This aspect is dependent on the relative stiffness between columns and shell. In addition to that, the silo ring girder has a main role in carrying the circumferential force and to resist the radial component of the inclined tension in the hopper [42]. In discretely supported structures, a nonuniform axial compressive stress is developed in the shell wall. The uniformity degree of the stresses could be assessed by the criterion developed by [PERSON] and [PERSON] [9] based on the relative stiffness of the ring beam and the cylindrical shell. [PERSON] and [PERSON] [10] presented a study aimed to assess the applicability of this criterion to cylindrical shells, accounting for global shear and bending. Combinations of different ring beam and cylindrical shell under global shear and bending actions were numerically analyzed, where the non-uniformity in the axial stresses was quantified. In conclusion, the result confirmed the applicability of using this criterion for the mentioned load conditions. The ratio between shell and beam stiffness was also addressed by [PERSON] et al. [43], where a closed section ring beam with less stiffness than the ideal one was investigated. Still, the effect of the stiffness ratio on the ring beam stresses and on the buckling capacity of the shell was observed. The resultants' stresses were  
Figure 3: Alternative arrangement for silos with different supporting structures. recorded using a finite element (FE) parametric study and the analytic solution of [PERSON]'s curved beam theory [44].