The AISC 360-05 Appendix 7 describes a method of
analysis, called Direct Analysis, which 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
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 Tau-b is less than the tau_tolerance, If the maximum
change in any Tau-b is less than 100*tau_tolerance and the maximum
change in any displacement degree of freedom is less than the disp_tolerance;
then the solution has converged for this case.
There are two steps involved in setting up a Direct
- Specify the
definition with a
DEFINE DIRECT command.
- Specify a direct
analysis method with the command
PERFORM DIRECT ANALYSIS
Like all other
analysis methods, by specifying the direct analysis parameters and only
including a PERFORM ANALYSIS command, will result in only a first order elastic
analysis, not a direct analysis to be performed.