Concrete members that are to be designed by STAAD must have certain section properties input under the MEMBER PROPERTIES command. The following example demonstrates the required input:

UNIT  MM
MEMBER  PROPERTIES
1 3  TO 7 9 PRISM YD 450. ZD 300.
11 14  PR YD 300.

In the above input, the first set of members are rectangular (450mm depth and 300mm width) and the second set of members, with only depth and no width provided, will be assumed to be circular with a 300mm diameter