# Concrete Silos: Failures, Design Issues and Repair/Strengthening Methods
## 3 Design Issues in Reinforced Concrete Silos
### Design Factors
#### 3.1.3 Mass Flow and Funnel Flow Design Issues  
The design of the silo predicts the flow depicted in Figure 4; funnel flow and mass flows [65] are associated with the stagnation of the bulk solids near the exit point through arching and ratholing, as shown in Figure 5. The primary distinction between the funnel and the mass flow was the flow of each grain out of the hopper [66] in the latter and the development of a flow channel boundary (FCB) and an effective transition point in the former. The effective transition point and the FCB are characterized by overpressures on the hopper walls and a greater risk of failure. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Back-** & **Optimum** & & **Training** & **Test** & & **Training** & **R2** \\
**Propagation** & **Number** & **ANN** & **Error** & **Error** & **Iteration** & **Time** & **R2** \\
**Methods** & **of HN** & **Structure** & **(\%)** & **(\%)** & **Number** & **(Second)** & **(\%)** \\ \hline BFG & 6 & 3:6:1 & 0.38 & 1.80 & 2813 & 49.17 & 98.37 \\ CGB & 6 & 3:6:1 & 3.21 & 3.20 & 1148 & 7.97 & 98.45 \\ CGF & 6 & 3:6:1 & 0.41 & 3.12 & 839 & 5.91 & 98.38 \\ CGP & 6 & 3:6:1 & 0.44 & 3.19 & 658 & 4.61 & 98.19 \\ GDA & 4 & 3:4:1 & 3.59 & 5.27 & 5000 & 11.96 & 96.55 \\ GDM & 6 & 3:6:1 & 6.55 & 8.27 & 5000 & 12.05 & 92.68 \\ GDX & 4 & 3:4:1 & 2.34 & 5.76 & 5000 & 11.61 & 95.78 \\ LM & 4 & 3:4:1 & 0.27 & 1.28 & 3900 & 19.08 & 99.65 \\ OSS & 4 & 3:4:1 & 0.63 & 1.11 & 5000 & 43.02 & 99.87 \\ RP & 4 & 3:4:1 & 2.69 & 3.61 & 5000 & 13.22 & 98.22 \\ SCG & 4 & 3:4:1 & 0.25 & 0.58 & 5000 & 23.87 & 99.94 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Relationship between ANN back-propagation methods and HN and errors (\(\mathrm{N}_{\mathrm{CROWN}}\)) [63]. The buildup of overpressure on the hopper walls linked to funnel flows and extended flows can be mitigated by two methods: One, the outlet design can be modified through finite element analysis based inserts. Two, regulating the flow of the bulk solids and customizing the silo design. Addressing the stagnation of materials in funnel flow and extended flow is a basic requirement in industrial processes because mass flows of the bulk solids are economical and have a predictable (first-in-first-out) rate of discharge [66]. [PERSON], [PERSON], [PERSON], and [PERSON] [68] noted that the funnel and expanded flows could be converted into mass flows through the placement of a double-cone insert. The insert was proven effective in expanding the moving zone in the hopper or cylinder sections. The main concern is the long-term viability of the double-cone cylinder insert. Even though the flow properties are a critical consideration in the design of silos, lack of consideration of the flow properties is common [67], especially in the silo design codes. According to [PERSON] and [PERSON] [60], the BS EN 1991-4:2006 and the DIN 1055-6:2005-03 dictate that the bulk solid materials should be non-biodegradable, free-flowing, and coarse. The primary criteria for coarseness the particle sizes (\(>\)3 mm) [60]. From a practical point of view, it is not feasible to expect that all bulk materials stored within the silo would exhibit free-flowing properties given that arching is a common challenge. On the downside, these considerations might not be feasible for multi-purpose silo hoppers that are inherently designed to hold both free-flowing and non-free flowing materials. In brief, it is evident that the DIN 1055-6: 2005-03 and BS EN 1991-4: 2006 design codes are not relevant for non-free flowing materials. Despite the design code limitations, ratholing and arching related obstructions can be corrected post-design. On the downside, the inserts might be unviable, especially in large silos with a shallow funnel flow. The bulk solid-based solution to funnel flow involves the careful selection of solids; this could be a challenge if the silo was not designed to handle a specific type of grain.