Stability Analysis - Direct Analysis Method
Stability Analysis - Direct Analysis Method
(OP)
I am looking for some clarification on a stability analysis and the Direct Analysis method. Is the DAM a type of stability analysis, or is the DAM just one step in the stability analysis?
Additionally, it seems that everyone I talk to has a different interpretation of the process for completing the DAM. I have always used a K=1.0, applied a notional load equal to 0.003Yi (with tau=1.0) for ALL load combinations, used a reduced stiffness = 0.8EI, and applied B1 (not B2) factors. Does this seem correct? Does it matter what the lateral system is that you are using (i.e. moment frames, braced frames, etc.)?
Additionally, it seems that everyone I talk to has a different interpretation of the process for completing the DAM. I have always used a K=1.0, applied a notional load equal to 0.003Yi (with tau=1.0) for ALL load combinations, used a reduced stiffness = 0.8EI, and applied B1 (not B2) factors. Does this seem correct? Does it matter what the lateral system is that you are using (i.e. moment frames, braced frames, etc.)?






RE: Stability Analysis - Direct Analysis Method
RE: Stability Analysis - Direct Analysis Method
RE: Stability Analysis - Direct Analysis Method
Shankar Nair has a bunch of good articles explaining the rationale for direct analysis method and the application of direct analysis method. Should be able to find them on AISC's website.
RE: Stability Analysis - Direct Analysis Method
http://www.modernsteel.com/Uploads/Issues/Septembe...
And I agree with above, DAM is an approximate method for stability analysis, among many options.
RE: Stability Analysis - Direct Analysis Method
I agree with the other posters. Your analysis seems reasonable provided your software is already doing P-Big delta as part of the analysis.
On your last question: The type of lateral system doesn't really matter. Both braced and moment frames can be analyzed and designed using the DA Method.
However, you will probably find that the method is more useful for moment frames than braced frames. I tend to use it for braced frames as well because I think it is simpler to treat all of my structures the same. But, some folks will want to run a simpler analysis (with no stiffness reductions) for braced frames.