# Concrete Silos: Failures, Design Issues and Repair/Strengthening Methods
## 1 Introduction  
The review article investigates the performance of the reinforced concrete (RC) silo structures, including the engineering and material factors that result in structural failure. The concrete silos of interest are used in the storage of bulk grains after farm harvesting. The silos used in the storage of non-agricultural produce were excluded from this study. The reinforced concrete silos under consideration are primarily made of concrete reinforced with steel bars/rebar, and alternative materials, especially at the foundation and hopper wall sections. The current issues facing traditional RC silos include bulk solid abrasion, which exposes the steel bars to the environment leading to corrosion. Additional challenges include design code limitations, poor design and failure due to periodical loading and unloading. The possible solutions include the reinforcement of concrete with materials, which are not susceptible to corrosion such as fiber reinforced polymers, the revision of existing design codes and adoption of better designs. The outcomes of this review have significant implications for RC silo engineers and operators, because they demonstrate the limitations of standard methods of construction and maintenance. Additionally, the findings provide tangible solutions for mitigating the risk of failure. The main loading and unloading scenarios of interest are hopper geometry (vertical end walls with a wedge, square pyramid, and single symmetrical cone), the filling and the discharge conditions (patch loads, funnel flow, mass flow, pipe flow, mixed flow, extended flow, and silo quacking),thermal ratcheting, internals, external equipment, grain swelling, and effect of gas pressure [1]. The specific cases of failure are investigated to determine the contribution of design to structural failure. Each factor that contributes to the failure of reinforced concrete silo structures is considered in Sections 2 and 3. The main factors under considerations include the errors in the design phase (attributed to the inadequacy of the international design codes) and the challenges in maintaining the concrete walls/inappropriate care in the construction phase are reviewed. Other factors of interest include the adoption of adjustable formwork in the building and the differences in the temperature gradients linked to bulk grain storage [2]. Moreover, the lack of thermal protection coating or the availability of inadequate thermal protection; moisture accumulation and contact between the concrete wall and the vibrator steel bars are investigated. The investigation of the thermal protection also informed the analysis of improper spacing between the horizontal and vertical steel bars, the inclusion of an inadequate number of reinforced steel bars. The latter factors trigger wall shrinkage, non-symmetric pressure linked to poor design, large temperature gradients due to weather changes, wind-induced horizontal pressure changes, and pressure induced by the incorporation of inserts. Additionally, the factors are responsible for wall stiffness linked to reinforced concrete additives, circular hopper bending attributed to the eccentric withdrawals, variations in the strength and the diameters of the steel reinforcements, uneven distribution of the cement strength, wall bulking due to inadequate structural support, corrosion, concrete carbonization, and cracking. The imperfections in the steel reinforcements caused by poor adhesion, inclusion of incorrect materials are reviewed. In addition, design factors that cause poor foundation, changes in design during construction, explosions, disregard of the possible flow patterns during the design phase and inclusion of poor quality lap slices [2] are analyzed to determine the extent to which they influence silo structural strength.