Rebar Placement and the Minimum Steel Calculation |
  
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Rebar Placement and the Minimum Steel Calculation |
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The General Footing module provides an input for number and size of bars parallel to the x axis and parallel to the z axis for the bottom mat.
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. The program automatically incorporates the minimum reinforcing check from Section 7.6.1.1, and the commentary to Section 7.6.1.1 is clear that this amount applies independently to each tension surface.
If a footing happens to be subjected to net uplift so that tension is on the top, there is now and option to specify a top mat of reinforcing. When a top mat is specified, the resulting moment will be compared to the moment capacity assuming that the specified bars are located based on the specified top clear cover.
The Footing Bending tabs still clearly indicate which surface is in tension, so you can quickly decide whether you need to specify a top mat or not.
Note: ACI is now clear that Section 7.6.1.1 provides a minimum steel ratio for footings. The value is typically 0.0018Ag. This is NOT temperature and shrinkage reinforcing. This is a minimum amount of flexural reinforcing that must be provided, and in situations where top and bottom mats will be specified, this amount cannot be split between the two mats. The commentary to Section 7.6.1.1 is clear that this amount applies independently to each tension surface.
