## 2 Structural Typology and Arrangement of Circular Silos
### Buckling Types and Analysis
The paper deals with numerical modelling of the elasto-plastic collapse of the columns and it was revealed that the buckling resistances obtained by the proposed numerical approach were greater than their counterparts yielded by the European standard, appearing to be more realistic. In the same context, [PERSON] and [PERSON] [78] presented a study devoted to assess the stability of steel cold formed silo stiffeners, through a FE analysis. In this study, different modelling approaches were considered along with the symmetric and axisymmetric loads imposed by the stored material, according to EN 1991-4 [71]. The numerical calculations addressed a real cylindrical silo of corrugated sheets, with a 17.62 m height, 8.02 m diameter, and was strengthen by 18 vertical stiffeners of open thin-walled load-bearing profiles. The stability FE studies showed that the methods provided by EN 1993-1-6 [72] could be conservative, especially when considering the stiffener as a beam resting on elastic foundation, while the orthotropic shell theory is more realistic when compared to the FE outcomes. Thus, authors suggested a modification on the column elastic foundation stiffness resulting in comparable outcomes to the obtained FE solutions. The same authors proposed a method for the buckling strength estimate for stiffened corrugated silo with different geometry and including a simplified model. Another way to increase the mass efficiency of thin-walled shells is represented by ring stiffeners. [PERSON] and [PERSON] [18] proposed a design procedure to bridge the gap in the standards related to quantifying the beneficial effect of ring stiffeners attached to the shell body under axial compression. The study investigated the applicability of the available design procedures for structures with significate radius/thickness ratio up to 10,000 (this ratio is limited to 5000 in EN 1993-1-6 [72]). The study revealed that high slender stiffened cylinders showed about 380% strength gains as benefit from the ring-stiffening, if compared to the unstiffened case. Recently, a numerical study calibrated with experimental series presented by [PERSON] et al. [80]. The study employed the 3D scanning technology to measure imperfection, and the FE analysis yielded very close result to the ones of experiments. The research evaluated the influence of different factors (ring-stiffener parameters, imperfection amplitude, ring geometry) on the buckling load of cylindrical shell. Authors concluded mainly that the buckling capacity of ring-stiffened shells decreases significantly until the stiffener spacing is greater than two buckling half-wavelengths. A conclusive summary of the topics about structural typology and arrangement of circular silos is reported in Table 1.  
Figure 5: Silo corrugated walls in combination with the vertical stiffeners (well-known as silo columns). Source: [79]. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Reference** & **Typology** & **Motivation** & **Stored Material** & **H/R** & **R/h** & **Specimen** & **Investigation Strategy** \\ \hline [PERSON] et al. [88] & Elevated steel silos discretely & Shell-column attachment, & & & & & & \\ supported on columns & geometry improving. & & & & & & \\  & Elevated steel silos discretely & connection geometrical & & & & & \\  & supported on columns & enhancements & & & & & \\  & Elevated steel silos discretely & Shell-column attachment & & & & & \\  & supported on columns & and behavior description. & & & & \\  & & Ring griefer, stiffness & & & & \\  & Elevated steel silos & criterion, arrangements of & - & - & - & - & Numerical \\  & & supporting system & & & & & \\  & & Steel cylindrical shell & & & & & \\  & [PERSON] [55] & Steel cylindrical shells & & & & & \\  & Steel smig [56] & & & & & \\  & & Steel cylindrical shells & & & & \\  & [PERSON] et al. [58] & & & & & \\  & & & & & & \\  & & & & & & \\  & & &