# Combined actions resistance - Member capacity (Columns: AS 4100)

The combined actions member capacity check is performed according to AS 4100 clause 8.4

The higher tier equations will be used automatically if the conditions for their use are met.

In the higher tier equation for M_{i}, the ratio β_{m} will be based
on the relevant strut length; if the strut length has bending induced by transverse
load within its length then β_{m} will be taken as -1.0, and the ratio of
end moments otherwise.

In the higher tier equation for M_{ox}, the ratio β_{m} will be based
on the LTB segment length, and taken as the ratio of end moments, using real moments
only.

In the member capacity check, the design forces are the maxima in the design length being considered, where the design lengths are based on the major and minor strut lengths within a loop of LTB lengths.

Therefore, since any one design length will comprise both major and minor strut lengths, the design axial force for each design length will be taken as the maximum axial compression or axial tension force from the major and minor strut lengths considered together.

Note that if the design axial force exceeds the design axial member capacity then the check will automatically be set as Fail.

Since both axial compression and axial tension are to be considered, but make use of different equations, then in cases where both axial forces exist within a design length the compression equations and tension equations will both be evaluated and the worst case of the two will be reported.

Note that in bi-axial bending cases, zero axial force will be treated as compression.