...
For 4-sided precast structures, use the greater of 5.10.8/5.10.6 or 0.002Ag, except that 5.10.8/5.10.6 does not apply to sections less than 16 feet in length. For 3-sided structures, see 12.14.5.8, which requires a minimum of 0.002Ag. Article 5.10.8/5.10.6 does not apply to 3-sided structures. LRFD does not provide any guidance for fill depths greater than 2 feet, therefore the program applies the above logic, as other minimum steel requirements will probably control in the design.
For CIP structures at all depths, see Article 5.10.8/5.10.6.
Standard Specification
For 4-sided precast structures, use the greater of 0.125 in2/ft (8.20), or 0.002Ag (16.7.4.8), however note that 8.20 does not apply for structures with lengths under 16 feet. For 3-sided precast structures, see 16.8.5.8 (0.002Ag), however, 8.20 does not apply for any length structure. While there is no guidance for fill depths greater than 2 feet, the program applies the same logic as listed above, as it is likely that other minimum steel criteria will ultimately control.
...