Material Nonlinear analysis using SAP2000

[hasithadamruwan]

I want to do material nonlinear analysis using SAP2000. But I have a doubt whether the SAP2000 actually follows the material nonlinear curve. To check that one I created a simple model (one end fixed and other end free, vertical column), then I applied different compression forces and checked whether the actual stresses and strains in the model were according the given nonlinear material curve.

In the elastic region, stresses and strains in the model were on the defined stress-strain curve(follows the stress-strain curve)
But I found following problems in the nonlinear analysis.

Problems

1)Beyond the yield point (when I increase the load), actual stresses and strains in the model were not on the curve (model doesn't follow the stress-strain curve in the plastic region).

2)For very high loads such that stresses are higher than the maximum allowable stress in the curve, still model run without any warning messages or collapse of the model.

3)For both linear and nonlinear analysis, I found same results for a given load.

 

[hasithadamruwan]

Model for 50 kN axial load

 

[hasithadamruwan]

model for 60 kN axial load

 

[bkal]

I suggest you post this query on a forum dedicated to SAP2000 in Engineering Computer Programs. Otherwise, you need to give us more details including calculated stress strain curve (some of us might not be able to open the file you have posted).

 

[crisb]

I think you may need to adjust the geometric nonlinearity parameters under the loadcase settings. At present these seem to be set at "none" in your sdb file. I don't think its enough just to show that the analysis is nonlinear, as this probably doesn't include nonlinear geometry effects.

 

[hasithadamruwan]

I like to thank all of you for your guidance and the suggestions.

Even though I did the geometric non linear analysis (with small deformations) I couldn't see any different in the results.

When I did the geometric non linear analysis (with large deformations), I could observe slightly changes in the results.But still model doesn't do material non linear analysis.

Then I assigned a hinge to the column and did my analysis.I found that the software does the non linear analysis only at hinge but not in the entire element.

If you have any suggestions, please kindly inform me.

 

[utkk]

You must be set nonlinear geometry and model plasticity properties of your FE model before analyse it .
good luck

Rubber engineering