The Design Compressive Strength (LRFD), ϕ_c×P_n , and the Allowable Compressive Strength (ASD), P_n/Ω_c , are calculated by the program.

The Nominal Compressive Strength, P_n, for a particular member is calculated by STAAD.Pro according to the procedure outlined in Chapter E, section E3 to E5, of the unified code specifications. For slender elements, the procedure described in section E7 is used.

The compressive strength of single angle members in compression is determined according to clause E5. As the choice of the method (a) or (b) is dependent on data not included in the analytical model, for design to any AISC 360 design code prior to AISC 360-16, the program will determine the strength on the basis that the member conforms to the requirements of clause E5(b). With AISC 360-16, by using the parameters IMM and E5P, it is possible to indicate that the conditions of E5(a) are met and the strength determined accordingly.

Effective length for calculation of compression resistance may be provided through the use of the parameters KY and KZ. If not provided, the entire member length will be taken into consideration.

In addition to the compression resistance criterion, compression members are required to satisfy slenderness limitations which are a function of the nature of use of the member (main load resisting component, bracing member, etc.). In both the member selection and code checking process, STAAD.Pro immediately does a slenderness check on appropriate members before continuing with other procedures for determining the adequacy of a given member.