A. To specify a direct analysis
To instruct the program to perform a direct analysis as per AISC 360, use the following procedure.
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 τb is less than the tau tolerance (τtol ), If the maximum change in any τb is less than 100×τtol and the maximum change in any displacement degree of freedom is less than the displacement tolerance (δtol ); then the solution has converged for this case.
- Select the Perform Direct Analysis tab.
- Select to use either the LRFD or ASD design method.
- Type values for both Tau and Displacement Tolerances.
- Type the Number of Iterations to use. Leave this field empty (zero) to use the default of one iteration.
- Select the number of PDelta Iterations to perform in the iterative PDelta with small delta analysis procedure with a direct analysis. The default value of 15 is recommended.
- (Optional) Clear the Reduced EI option to use the full EI for member section moment and section displacement calculations.
- (Optional) Clear the Perform Tau-b Iteration option prevent the program from iterating τb.
- Select the Print Option you want to use.
- Click Add. The perform direct analysis command is added to the input file.