Perform Direct Analysis tab

Used to instruct STAAD.Pro to perform a direct analysis per AISC 360 Appendix 7.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.

This analysis method is to be used in conjunction with Direct Analysis definition command. The Define Direct command should be added prior to instructing the program to perform this type of analysis.

Additionally, a direct analysis typically requires the definition of Notional Loads.

Note: Refer to TR.37.5 Direct Analysis and AD.2007-03.2.2 Direct Analysis for additional information.

Setting

Description

Option

Select if the design methodology is Load Resistance and Factor (LRFD) or Allowable Stress (ASD).

Tolerances

Setting	Description
Tau	The limit to the change in the τ_b value in each iteration. If this value is exceeded by any member, then an additional iteration will be required unless the maximum number of iterations has been achieved
Displacement	The limit to the change in the maximum displacement in each iteration. If this has been exceeded, then an additional iteration will be required unless the maximum number of iterations has been achieved.

No. of Iterations

Specify the maximum number of iterations.

PDelta Iterations

Select the number of iterations to be used for a PDelta with Small Delta analysis. Typically this should be from 5 to 25. The default number of 15 is recommended.

Reduced EI

Check this option to use the reduced EI (Tau-b × 0.8 ×EI) for member section moment & section displacement. Clear the check box to use the full EI value.

Perform Tau-b Iteration

Check this box to instruct the program to iterate Tau-b.

Print Option

Standard STAAD.Pro analysis print options:

Setting	Description
No Print	No analysis results will be printed to the output file.
Load Data	Prints all the load data.
Statics Check	Provides a summation of the applied loads and support reactions as well as a summation of moments of the loads and reactions taken around the origin.
Statics Load	Prints everything that Statics Check does, plus a summation of all internal and external forces at each joint. This option potentially generates a large volume of output. Note: Since `PRINT STATIC LOAD` generates voluminous output, the printing of summation of internal and external forces at each joint is done for structures which have less than 1,000 joints. If the structure has 1,000 joints or more, this printing will be skipped.
Mode Shapes	Prints mode shape values at the joints for all calculated mode shapes.
Both	This option is equivalent to the Load Data plus Statics Check options.
All	This option is equivalent to the Load Data plus Statics Check.