Hi,
Presently i am using Staad Pro V8i (Select series 4) 20.07.09.31, and input given as below for example,
DEFINE DIRECT ANALYSIS
FLEX 1 ALL
FYLD 345000 ALL
AXIAL ALL
NOTIONAL LOAD FACTOR 0.002
END
LOAD 201 1.2 DL+ 1.6 LL
REPEAT LOAD
5 1.2 6 1.2 7 1.6
NOTIONAL LOAD
5 X 0.0024 6 X 0.0024 7 X 0.0032
PERFORM DIRECT ANALYSIS
1) For the analysis i have chosen Direct analysis to design the members for stability to AISC 360-10 (LRFD). Hope that the Direct Analysis Procedures are included as per Chapter C of AISC 360-10, please clarify (as per reference in Staad Help 1.18.2.1.4 AISC 360-05 Direct Analysis mentioned as AISC 360-05 Appendix 7).
2) Hope that the displacement results available in the post processing after Direct Analysis are using the full stiffness and not with reduced stiffness used in the direct analysis, please clarify.
Thank You,
K. Mahesh Kumar
Yes STAAD does follow the analysis procedure outlined in Appendix 7 of the AISC 360-05 code which has now been moved to Chapter C of 360-10 code.
I created a wiki item based on your second query and you can find the answer at
communities.bentley.com/.../10599.aspx
While using the REDUCEDEI 1 or 0, there is no change in the deflection values (i.e. getting the same deflection values while running with REDUCEDEI 0 or 1 ), please advice (may i assume that the deflections are calculated with full EI in all the cases and reduced EI is used for arriving the member internal forces {REQUIRED STRENGTHS} alone to account for the stability analysis as outlined in Chapter C AISC 360-10?) .
The below results with command
PERFORM DIRECT ANALYSIS LRFD TAUTOL 0.01 DISPtol 0.002 -ITERDIRECT 10 REDUCEDEI 1 PDiter 15
The below results with command,
PERFORM DIRECT ANALYSIS LRFD TAUTOL 0.01 DISPtol 0.002 -ITERDIRECT 10 REDUCEDEI 0 PDiter 15
I am getting the same displacement by changing the REDUCEDEI also, please refer to the below and advice,
The displacement results shows that the full EI is used for calculating the deflections? please advice
Although I could not see the images, but I am guessing that you are looking at the nodal displacements as opposed to section displacements. The REDUCEDEI 0 ensures that displacements at intermediate locations within the member are computed using the full E and I. The section displacements are the ones that are used for checking whether the member satisfies deflection limits ( L/240, L/360 etc ). The displacements at the nodes on the other hand comes from the analysis with reduced E and I.
Exactly, the displacement i have compared are the nodal displacement to check the drift of the structure. Is it possible to get the displacement of the nodes with full EI after analysis to check the serviceability (drift) limits, i believe that the reduced stiffness are to be used for calculating the required strength only as per Cl. C2.3 Adjustments to Stiffness (Chapter C AISC 360-10). Please advice.