# Concrete Silos: Failures, Design Issues and Repair/Strengthening Methods
## 5 Conclusions  
The review affirmed that there were multiple factors that influenced the performance, design, failure, and repair of RC silo structures. First, the sustainability of these structures was influenced by material factors. The strength of the silo was as strong as the material used in the reinforcement. Even though alternative materials have been developed, such as carbon-reinforced fibers, steel remains as the material of choice because it is widely available and cheap. However, the continued utilization of steel in the reinforcement of silo structures poses considerable structural challenges considering the susceptibility to environmental degradation and corrosion.  
Considering that the replacement of steel reinforcement bars with non-metals is not a practical alternative during the repair process, alternative methods have been proposed including the creation of a shear zone to prevent slip-stick intermittent flow; placement of liners and sacrificial plates on  
Figure 7: Concrete wall cross-section illustrating the location of near-surface mounted FRP bars and traditional steel reinforcements [82].  
the inner walls; the utilization of materials with a low probability of moisture accumulation, and the incorporation of additives in the cement. The pressure associated with the loading and unloading of the silo structure can be mitigated by aligning the withdrawal point with the vertical center-line, placement of inserts, design modifications to enhance mass flows, and limit bulk grain obstruction at the exit. The listed proposals should be implemented within the silo design code guidelines to limit the risk of silo failure. However, the relevance of existing silo design codes (BS EN 1991-4:2006, Australian Standard AS 3774-1996 and American Society of Agricultural Engineers ANSI/ASAE EP433 DEC1988 (R2011), and American Concrete Institute ACI 313-97, Indian Standard--IS 4995: 1974 and German standard--DIN 1055-6: 2005-03) to the timeline of adoption can be contested. Three of the six listed four standards were developed in the 20 th century and did not take into account the new advances in engineering, such as finite element analysis ANN and new alternative reinforcing materials such as CNTs, and only focused on specific hopper geometries. Additionally, there is wide variability in the adoption of the design codes--the ANSI and the DIN are preferred in the US and Germany, respectively. In brief, cases of the structural failure of silos will continue to be reported until existing design codes are revised and harmonized.  
The proposed methods for repairing and strengthening silos involve a tradeoff between mechanical strength and structural integrity and risk of failure over the long-term, attributed to corrosion, brittle fracture, and inability to support transverse and large longitudinal forces. Other practical solutions include addressing the maintenance limitations, construction, and design errors and environmental variables such as seismic activity, wind, and rain. The ability to address the design code limitations is not a conclusive solution, considering that designers/engineers bear the responsibility for design errors, the use of substandard materials, and construction errors, which are, to a certain degree, influenced by the budgeting and planning.  
This research received no external funding.  
The authors declare no conflict of interest.