It is commonplace in industry for unexpected phenomena to occur during operation: blockages, failures, poor distribution of material and loads, among others. In such cases, a costly solution would be to obtain new machinery. A structural assessment, on the other hand, is often a less costly solution, in which the problem is analyzed and modifications are proposed for the equipment already in the company's plant.

In this article, learn how Kot Engenharia applied structural engineering knowledge to propose solutions for silo operating conditions. If you are interested in learning about other Kot Engenharia success stories, click here. 

Structural analysis of silo modifications

A silo is defined as a metal or concrete structure used for storing granular materials. It is usually part of a building, which is responsible for loading and/or unloading the bulk.

Kot carried out a structural assessment of silos at an industrial plant and found a problem with access to these silos during operation, due to the accumulation of material. Possible solutions were therefore proposed, including altering the geometry of these assets so that the material is better distributed. To verify the applicability of the suggested change, Kot carried out a new structural analysis based on the finite element method. 

First, the possibilities of altering the operating conditions were evaluated, so that the decrease in productivity was as small as possible. Structural modifications were then made, arriving at the model shown in Figure 1.

Figure 1: Finite element model of the silos after structural modifications. [1] 

The asset then underwent different types of analysis, which will be explained in more detail below:

• Static Analysis:

It was used to carry out the first structural check of the new geometry. Here, the stress acting on each element was indicated using a color scale, with red revealing levels above those allowed by the standard. At this point, the need to include reinforcements was noted so that there were no localized stress concentrators in the structure. The final result is shown in Figure 2, where the structure is approved.

Figure 2: Result of the static analysis. [1] 

• Fatigue Analysis:

At this stage, the useful life of the structure was checked based on the number of operating cycles, considering the profiles, plates and metal connections of the silos. After reinforcement, the most critical region in Figure 3 showed a useful life of 20 years, which is in line with what was expected for the asset.

Figure 3: Fatigue analysis results. [1] 

• Buckling Analysis:

The buckling analysis used a linear approach to extract eigenvalues from the structure's stiffness system. The eigenvalue consists of the ratio between the stress that would cause the element to buckle and the acting stress. Therefore, results greater than 1 indicate that the acting load is lower than its buckling load. The entire system showed admissible values in the analysis.

Figure 4: Result of wall buckling analysis. [1]  

Given the successful changes to the silos, the building they form part of was checked by applying the new load conditions. The beam-column finite element model is shown in Figure 5.

Figure 5: Finite element model of the building. [1] 

• Superstructure analysis: 

The analysis of the superstructure included static checks and metal connections. In this analysis, the connections that had to be altered in the support of the silos were indicated, including the installation processes and which inspections were necessary in this case. The altered connections are shown in Figure 6.

Figure 6: Altered connections on the silo support. [1]

• Flexibility Analysis:

The study also included the base connections, where reinforcements were designed for areas of non-conformity. For this reason, in the flexibility analysis, the displacements of the region of the main structure of the building affected by the modifications to the loading of the silos were checked, and it was concluded that all the values were lower than the permissible displacements. Therefore, the modification of the silo has no impact on the structure's compliance with its displacement service limit states.

• Civil Analysis

Finally, the infrastructure was analyzed. When checking the reinforced concrete radier foundation that supports the building's pillars, the calculated stresses did not exceed the permissible ones. The soil also showed sufficient resilience to withstand the stresses.

It is clear from reading this Succes story that it is important to carry out a structural check once changes have been made to a particular asset. This decision applies not only to the object in question, but to the entire set that includes it. Carrying out installations and modifications before inspections, calculations and simulations can result in choices that only mask a non-conformity and, in the near future, new problems could arise. 

To understand which solutions should be applied to your assets, contact our team for more information!

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References:

[1] Kot Engenharia Collection.