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.

For single angle members in compression designed per AISC 360-16, the conditions in E5 for use of the modified slenderness ratio in Cl. E5.(a) are assumed to be met by default. However, the engineer can specify these conditions by use of the E5P parameter. Further, the modified slenderness ratio for box or space trusses can be utilized by using the IMM parameter.

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.