## Non linear analysis parameters definition

## Non linear analysis parameters definition

(OP)

Can someone explain to me the logic behind non linear analysis parameters in sap2000? mainly the total steps, null steps and convergence tolerence?

thank you

thank you

## RE: Non linear analysis parameters definition

Convergence tolerance is what you tell the program to shoot for before considering the nonlinear analysis "complete." Essentially, after an iteration, SAP will total something like the net support reactions - and this will never be quite equal to 0 for most nonlinear cases. So you tell SAP, "as long as the total unbalanced force after the run is less than X force - I think we are close enough to call the analysis there and I trust the results within a few percent." I'm not sure what exactly the convergence tolerance input is for SAP, sometimes they let you put in a scalar and it takes the total applied load times that scalar as the convergence tolerance so you don't have to manually update it every time the load input changes. For example, if I apply 1000 kips of force to a model with a 0.05 convergence tolerance, once the unbalanced load comes out below 50 kips - the nonlinear analysis will consider itself "converged."

Null steps - not too sure. My guess is maybe that SAP skips steps that produce the same results as previous iterations?

## RE: Non linear analysis parameters definition

## RE: Non linear analysis parameters definition

## RE: Non linear analysis parameters definition

Do you have any references you recommend for the nonlinear solution process, have the McGuire Gallagher and Ziemian book but always looking for more.

## RE: Non linear analysis parameters definition

Not yet. I've got personal favorites for a lot of things:

Response Spectra: Response Spectrum Method by AK Gupta

Frame FEM analysis: Matrix Structural Analysis by McGuire, Gallagher and Ziemian

Unfortunately, I haven't found a favorite on non-linear analysis. At least not yet. In the past, I've mostly dug through various analysis references that came with software. Then I've looked up papers on the preferred methods used by that software.

The online book by Ed Wilson might be a decent place to start. We're getting to the point where more and more books can only be found in electronic form and not as print versions. Maybe that's part of the problem.

## RE: Non linear analysis parameters definition