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Rebar Placement and the Minimum Steel Calculation

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How does the module handle top and bottom rebar mats and the minimum reinforcing area calculation?

 

The General Footing module provides an input for number and size of bars parallel to the x axis and parallel to the z axis.

 

When the footing is loaded with downward loads so that the tension is on the bottom, the resulting moment will be compared to the moment capacity assuming that the specified bars are located on the bottom of the footing.

 

If a footing happens to be subjected to net uplift so that tension is on the top, the resulting moment will be compared to the moment capacity assuming that the specified bars are ALSO provided in a top mat.

 

The Footing Bending tab clearly indicates which surface is in tension, so you can quickly decide whether you need to specify a top mat or not.

 

This method makes input efficient, but the current implementation comes with some limitations that need to be understood:

 

1.If a top mat is required, it will automatically be assumed to be of the same number and size of bars as the bottom mat.  If different bar sizes are desired top and bottom, or if a different number of bars are desired top and bottom, it would require multiple runs.

2.If top and bottom mats are required, both will automatically be assumed to have the same clear cover, because there is only one clear cover input at present.

3.In situations where only a bottom mat is provided, the results of the T&S check are clear and straightforward, because the program does not automatically assume that you will be specifying two mats.  But in situations where top and bottom mats will be specified, you are actually providing twice the area of steel, so you may choose to make some hand notes on the calcs to demonstrate that the minimum area for T&S has been satisfied by the total area of steel.