Numerical (quantitative) process is usually followed to evaluate the structures and as a qualitative structural analyses. The structural designers with this process can easily define the values for dimensions and loads and also they can calculate bending moments and reactions. Before starting with the numerical structural analysis, also is very important the step for preliminary analysis. Here, the dimensions of elements are taken before the start of the analysis. Detailed numerical analysis is initiated to verify the values that were implemented in the preliminary analysis. It is recommended to size the structural elements properly or the analysis will be repeated several times (on a computer or manual calculation). The link bellow will give you full explanation about this.

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