Per ACI 318-11, Section 7.12.2.1(b), r MIN = 0.0018 for temperature and shrinkage. For a mat with thickness of 30 inch. As MIN = 0.0018 x 12 inch x 30 inch = 0.648 in2/ft. In commentary, R7.12.2, ACI states that As MIN may be placed near the top or bottom of the slab or may be distributed between the top and bottom faces of the slab as deemed appropriate.
STAAD ERROR: STAAD Fndn is computing As MIN = 0.648 in2/ft for both the top face and bottom face of the mat foundation. Therefore, on lightly loaded mat foundations where As MIN governs, STAAD Fndn is providing twice the reinforcing permitted by the code. A box to mark if the temperature and shrinkage reinforcing is used on the top face, bottom face, or equally on both faces would be beneficial with STAAD Fndn correctly distributing the reinforcing between the two faces if that box is checked.
I would add that STAAD Fnd has a setting option for this purpose on rigid foundations in the Global Settings in the ‘Rigid Foundation Settings’ tab. However, I selected that option for my recent designs and do not think it is applying the minimum to top and bottom combined. This would be a separate error.
How do we fix this. Version 8.3.0.20