To instruct the program to perform a direct analysis
as per AISC 360, use the following procedure.
Note: You must have one
or more members with Direct Analysis parameters defined in order to use a
direct analysis.
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.
-
Either:
-
select the
Analysis page
- on
the
Analysis and Design ribbon tab, select the
Analysis Commands tool in the
Analysis Data group
The
Analysis/Print Commands dialog
opens.
-
Select the
Perform Direct Analysis tab.
-
Select to use either the
LRFD or
ASD design method.
-
Type values for both
Tau and
Displacement Tolerances.
Note: Leave either
field empty to use the default tolerances of 0.01 for Tau and 0.01 inches and
0.01 radians for displacement.
-
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.