# 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
[PERSON] and [PERSON] note that different grains have different rates of discharge, abrasiveness, shape, size, and non-biodegradability,  
Figure 4: (**a**) Mass flow (**b**) funnel flow [67]. Figure 5: Types of obstructions in the flow of bulk solids: (**a**) arching (**b**) funnel flow with long residence times (**c**) ritholing (**d**) segregation (**e**) noise and vibrations [67]. which influences the risk of material stagnation [66]. Non-biodegradable and abrasive solids assume a funnel flow pattern, which in turn increases the risk of solid accumulation. Similarly, the design of the silo predicts the risk of solid bulk stagnation. In particular, shallow-hopped and flat-bottomed silos have a greater risk of funnel flows. Additionally, the stagnation is common in taller and slender hoppers, and squat silos are at risk of the funnel/obstructed flow [66]. Considering that the silos could be adopted for different applications and storage of different types of bulk solids, the risk of overpressures linked to funnel flows and extended flows may not be mitigated by new designs. From a theoretical point of view, the pressure is lower in the flow loads because the outflow can be regulated at the outlet. The temporary stoppage of the flow does not have a domino effect on the pressure placed on the silo walls. In contrast, the initial fills phenomenon is characterized by the filling of an empty silo with bulk materials; there is no outlet of the materials. The funnel flow discharge is observed in cases where there is no intersection between the cylinder walls and the bulk solids. A contrary phenomenon (effective transition) is observed when there is an intersection with the cylinder walls, which translates to higher wall pressure, especially in the hopper section [47]. The pressure buildup is considered to be marginal in the cylinder section owing to the contraction and expansion of the bulk solids due to temperature differences during the day. The mass changes in the bulk solids trigger drastic pressure changes at the point at which the cylinder transitions into the hopper, and the pressure reduces to zero at the vertex. In brief, the different flow conditions translate to different pressure distributions regardless of the materials employed in the construction of the silos. Considering that the design codes are unideal sources of reference in mitigating the accumulation of solids and materials in expanded and funnel flow, engineers should take into consideration the impact of segregation on funnel flow, mass flow, and extended flow as noted by [PERSON], [PERSON], and [PERSON] [26]. The segregation phenomenon is initially observed during the filling in of the silo with bulk solids. The conveyor belt led to uneven transportation of the bulk particles based on their weight/density. As expected, the finer particles are transported further compared to the denser particles. The cumulative effect is the uneven distribution of materials in a segregated pattern. An issue of concern is that the phenomenon is not corrected by material baffling--a rebound of bulk material segregation has been documented after the baffling effects have dissipated [26]. According to the latter study, segregation helps to predict whether the flow of bulk solids would result in tilting. The segregation is observed in nearly all design silo types, which contrast with industry data, which presume that segregation cannot be observed in center-filled silo types. The observation of segregation in the latter case is linked to a lack of asymmetric flow. From an engineering point of view, the impact of baffling and segregation on the engineering structure could be best predicted based on the impact of fine and bulkier particles on the hopper walls and the internal flows. The outflow is higher in the sections with coarse materials--the tilting in favor of coarse materials rather than the fine materials has a domino effect on the distribution of the bulk-grain induced pressure within the silo, especially within the sections that the grain has tilted towards.