Question on NBC element Frame

[Saravana]

Hi,
I'm doing 2-D Frame analysis. when I did the model with ElasticBeamColoumn elements, I didn't find any problem. but if I change the model to nonlinearbeamcolumn element I face converging problem with Reinforce Concrete(RC) properties. I use fiber section with concrete01 and steel01 material. if I do with steel properties, thats with only steel01 material then the model converging. also if I change the beams only to elastic section then it converging. So, could any one please answer why it didn't converge with RC properties?
Thanks in advance.

[juanoviedo]

Hello Saravana!

I am also facing quite same problem you are having. I am trying to do a nonlinear analysis of 2-D R/C frame using nonlinearbeamcolumn for columns and beamwithhinges for beams.
The first try, I used hardening material for beams (bending) and I combined elastic and hardening for columns with section aggregator (no P-M). I ran the model and it was ok, no converging problem.
Then I wanted to have P-M interaction in columns, then I changed to fiber section with concrete02 and steel01 and I got convergence problems even at the gravity analysis state.

So, I am also in need of any comment on this matter..

Thanks

[silvia]

you really should be using concrete02 and steel02, which tells me you guys haven't looked at the examples manual....

[juanoviedo]

Hello Silvia!

Thanks for your reply.
I certainly forgot to tell you that I also tried the Concrete02 and Steel02 combination as recommended. However, there are still convergence problems even with gravity analysis.
It keeps saying me "failed to get compatible element forces and deformations"

Any other suggestion?

Thanks!

[Saravana]

Hi Silvia,
Thanks for your comments.
I too tried with concrete02 and steel02. but it doesn't converge. I'm doing static pushover test. it run upto 2.7 mm. This time if I change the beam section to elastic, even it doesn't converge. But it run upto 47 mm.
my model is similar to Ex4 in manual, but hight is 5 m.
So, could you comment on this.
Thanks,

[silvia]

i haven't looked at your model.
something is wrong with your model if it is not converging for the elastic case. look at the response to that point and see. otherwise, compare carefully to the example.

[Saravana]

hi
I would like to clear one point. fully elastic model run without any problem. fully nonlineear model doesn't converge. then I changed the beam element only to elastic section as in Ex4 in manual. that also doesn't converge with steel02 and concrete02 materials. compare to Ex4 my cross sections (0.5m*0.3m) are smaller.
thanks for your time,

[silvia]

you may have pushed your section too far.
look at the critical-section response.