Why Chapter E if Instability is Now by Direct Method? 2

[IJR]

Pals

The Direct method(DM) is found to be practical because INTERACTION equation with this method and with the old effective length method(ELM) seem to give similar results. Makes sense if things turn out that equal with K=1.00

Does this mean DM is to be used only in P+M situation(interaction)? not for P only situation(no interaction)? Is that why Chapter E is retained?

Your comment will be highly appreciated.Thanks in advance

respects
ijr

 

[JoshPlumSE]

The Direct Method of analsyis is not sufficient for predicting all aspects and methods of buckling. Or, analysis programs are not yet sufficient to capture that buckling behavior.

The DM does a good (but approximate) job capturing elastic and inelastic flexural buckling of FRAMES. It's ability to do this with individual members is imperfect. I suppose with engineering judgement, you could do so by introducing some member out-of-straightness directly in your analysis. Also, it still may not adequately capture the flexural-torsional or torsional buckling failure modes very well.

Perhaps eventually we will get to the point where buckling is captured entirely from the analysis and chapter E will be elimintated or greatly simplified. If that happens, I think the DM will be viewed as the first major step down that road. But, by itself it doesn't get us there.

 

[ash060]

Also, DM is mainly for the lateral force resisting system of the building not so much the gravity system (C1-3c). But the gravity columns will still buckle, and other things that are in compression that are not really part of the LRFS will need to be designed per the chapter E provisions, as well