Effective length factor 1

[Saedhalteh]

hello all,

When running a P_delta analysis in STAAD, I need to specify the Effective length factor K for the columns, My question Is if I assigned a value of K=1 to all columns will that be conservative or it is a wrong behavior and I need to calculate K for each column and assign a suitable value for each one separately ?

 

[JoshPlumSE]

This isn't as simple of a question as it first sounds. My thoughts:

1) When you specify K that is usually for DESIGN or code checks, not for the analysis.
2) If you are using the Direct Analysis Method (per AISC), then you would usually specify a K value equal to 1.0 for all members. That's because this method (which requires P-Big Delta & P-little delta analysis, notional loads, and stiffness reduction) DIRECTLY accounts for member buckling in the analysis (for the most part).
3) If, however, you are no using the Direct Analysis method, then it is generally UN-Conservative to use K= 1.0 for sway frames. Though it is generally conservative to use them for non-sway or braced frames.

Standard Caveat: I'm not a STAAD expert and have spent most of my professional life working for competitors such RISA and SAP2000, so understand that I'm not exactly an unbiased observer when it comes to the discussion of structural analysis and design programs.

 

[Saedhalteh]

Thank you very much, this was very helpful.