# Concrete Silos: Failures, Design Issues and Repair/Strengthening Methods
## 2 Failure of Reinforced Concrete Silos
### Reverse Effects of the Stored Bulk Solids--Corrosion, Thermal Gradient, and Differentials  
The impact of materials on the quality of grains stored in silos has a'reverse effect.' For example, the accumulation of moisture on the grains triggers bacterial and fungal activity, which may trigger bacterial-induced corrosion of steel-reinforced concrete structures. In other cases, pore-water pressure can result in hoop compression [39]. Microbial induced corrosion of steel and reinforced concrete structures by heterotrophic bacteria and fungi [40], and sulfate-reducing bacteria [41] such as _Pseudomonas sp._[42] via cathodic depolarization is well documented in the literature. A pertinent issue is whether the reverse effect linked to microbial corrosion could be mitigated by post-harvest treatment of the grains. Apart from inducing corrosion, high moisture (and dampness in the bulk solids) content is a risk factor for cohesive arching and caking [36]. [PERSON] and [PERSON] noted that dampness triggered the collapse of a rapeseed meal silo through caking and arching. However, structural failure is only possible if the silo walls have been subjected to dampness for an extended period because caking and arching are gradual processes. In addition to the risk of corrosion, different grains have different Poisson's ratio, coefficient of wall friction, internal bulk density, internal angles of friction, cohesion, and interval voids ratio. The relationship between the internal voids ratio and structural properties is predicted by the hypo-plasticity theory, which indicates that the silo wall stress rate is a function of both the void ratio and the strain rate [43]. Each of the listed parameters contributes to the stress on the internal walls of the silos [38]. Considering that wheat and maize have higher angles of internal friction (\(\phi\)) compared to soya beans (30, 31 versus 26, respectively) [38], silos should be designed to handle specific grains or built to higher standards to withstand the internal pressures associated with the incorporation of different grains. The standards should also factor variations in experimental data--[PERSON], [PERSON], and [PERSON] [10], and [PERSON], [PERSON], and [PERSON] [38] have published different values for the internal angle of friction for wheat (28 and 39, respectively). From a design perspective, the extent of variability is significant and may result in design errors or even failure. The risk of failure due to the under-appreciation of the properties of the bulk solids is high because scholarly research illustrates that properties of the stored bulk solids are not always taken into consideration during the design process, as confirmed in the failure analysis of cylindrical wall silos [44]. [PERSON], [PERSON], and [PERSON] noted that the properties of stored bulk solids had an overbearing effect on the propagation of cracks in cylindrical silos [44]. However, crack initiation is dependent on the following criteria; (i) the optimal plastic strain should be positive; (ii) the tensile equivalent  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \multirow{2}{*}{**Type of Storage Silo**} & **Storage Period** & **Moisture** & \multirow{2}{*}{**Protein**} & \multicolumn{3}{c}{**Maze Quality Parameters (\%)**} \\  & **(Months)** & & & **Content (\%)** & & **Oil** & **Crude** & **Starch** & **Ash** \\  & **(Months)** & & & **Content** & **Content** & **Fiber** & **Content** & **Content** \\ \hline  & 0 & 11.2(0.1) & 10.6(0.1) & 5.1(0.1) & 0.2(0.0) & 60.6(0.1) & 1.06(0.03) \\  & 2 & 11.8(0.1) & 10.3(0.1) & 4.8(0.2) & 0.2(0.1) & 60.5(0.5) & 1.01(0.03) \\ \hline  & 4 & 11.7(0.2) & 9.  
plastic strain should be greater than zero [43]. The bulk solids caused a temperature gradient at the interface with the concrete walls. Under standard conditions, the cement plaster in the inner walls acts as an insulation barrier that facilitates the diffusion of heat to the concrete walls leading to a slowdown in the thermal flow gradient and temperature differentials.