When checking members to AS 4100 or NZS 3404 you may occasionally see a situation where increasing the steel yield strength for a member reduces the reported critical load factor for that member. This can occur when increasing the steel grade invalidates the use of a "higher tier" design criterion, such as that for the out-of-plane capacity of compression members in Cl. 8.4.4.1 of AS 4100. The more complex expression for Mox, the nominal out-of-plane member moment capacity, can only be used for sections having a form factor of unity. For example, a 460UB82.1 column in grade 250 has a form factor of unity but the same section in grade 300 does not. The column in higher grade steel therefore has to be checked with a lower tier formula that produces a lower capacity. It would seem reasonable in such cases to accept the strength of the lower grade member for the higher grade member.
Microstran V8 permits the design and checking to AS 4100 and NZS 3404 of members with an unsymmetrical I section. The UI design type is the only section in Microstran where the sign of the bending moment affects the design. When a UI section is oriented so that the smaller flange is never in compression design economies may be achieved. Other monosymmetric sections, such as tees, are checked in Microstran as if the section were oriented in the weaker direction for bending.
Using the Section Library Manager you can easily add UIs to the Microstran steel library so you may achieve economies in the design of beams with an unsupported compression flange, crane girders, for example.