Non-linear Solution not Converging

[StrucEng23]

hi,

I am currently trying to conduct a non linear analysis of a 2d 3 bay steel frame which is loaded with a udl along the top of the beam and two point loads at the end of the beams. The aim is to test the ultimate load capacity of the frame.

The solution uses the arc length method and runs well until it reaches a load factor of 1.2 and i can not get the solution to converge so that it continue on to the ultimate load which i know should be 1.8. I have a attached the script being run.

if anyone could give me any tips please.

 

[Drej]

These analyses can be tricky. It looks like you're using a bi-linear material model with a tangent modulus that gives you perfect-plasticity. This is extremely unstable for this type of analysis, and is difficult to solve implicitly. Check the material tensile data and reconsider using a modulus which represents the material (or even a small modulus).


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[StrucEng23]

Thanks, but the frame i am modelling is from a research paper, and all the parameters applied to the script have been determined. so i am still trying solve why my solution will not converge. So is there anything else that i can do?

 

[corus]

If you have perfect elastic plastic behaviour then try setting the plastic part of the curve to have a slope slightly greater than zero.

Tata

 

[rb1957]

how about asking the authors (how they got it to run) ?