| Applies To | |||
| Product(s): | STAAD.Pro | ||
| Version(s): | All | ||
| Environment: | N/A | ||
| Area: | Analysis | ||
| Subarea: | Direct Analysis | ||
| Original Author: | Sye Chakraborty, Technical Support Group | ||
1. In a DIRECT ANALYSIS, are the deflections for serviceability checks computed using the unreduced E and I values ?
By default STAAD uses the reduced E and I for calculating displacements. However in the section 5.37.5 of the
Technical Reference Manual ( titled Direct Analysis ), you will find mention of a parameter named REDUCEDEI which can be set to a value of 0, for the full E and I to be considered for computing section displacements.
2. What is the value that I have to enter for the FLEX parameter ? Also why does Taub change from iteration to iteration ?
The value you enter for the FLEX parameter is the value of Taub that is considered for the first iteration. Taub is a function of Pr/Py where Pr is the axial force in the member and Py the yield strength. Although Py (= AFy) cannot change but Pr changes between iterations because the axial force changes due to Pdelta effects (both large and small). The Taub will not see the effect of the change in Pr until later exceeds 50% of the yield strength. Once Pr > 0.5 Py, Taub values are no longer 1 but are calculated using the equation provided for Taub in the AISC code ( Appendix 7 in the AISC 360-05 & chapter C in AISC 360-10) .