To specify a direct analysis

To specify a direct analysis per AISC 360 Appendix 7, use the following procedure.

You should also assign Direct Analysis attributes to members who flexural or axial stiffness contributes to the lateral stability of the structure.

This method accounts for the second order effects resulting from deformation in the structure due to applied loading, imperfections and reduced bending stiffness of members due to the presence of axial load.

This is a non-linear iterative analysis as the stiffness of the members is dependent upon the forces generated by the load. The analysis will iterate, in each step changing the member characteristics until the maximum change in any τ_b is less than the Tau tolerance. If the maximum change in any τ_b is less than 100x the Tau tolerance and the maximum change in any displacement degree of freedom is less than the Displacement tolerance; then the solution has converged for this case.

Add or edit an existing analysis set in the Analysis Commands dialog .
To add an analysis set
Select AISC Direct from the Analysis type drop-down list. This instructs the analysis engine to perform a direct analysis per AISC 360, Appendix 7.
Select the desired Print option for including analysis results in the output file.
Select to use either the LRFD or ASD option for the design method.
Type the maximum No. of iterations to use in the analysis.
(Optional) Type the number of iterations to be used for a P-Delta with Small delta analysis.
Typically this should be from 5 to 25. The default number of 15 is recommended.
Check the Reduced EI option to use the reduced stiffness for member section moment & section displacement.
Check the Tau-b iterations option to iterate the values for τ_b.
(Optional) Type tolerance values for Tau and Displacement to control the convergence.
Click OK.