concrete model does not converge

Hi Dinesh.  I'm having similar problem as well.  I'm working on composite beam model and it seems that the ABAQUS solver can't get pass the peak portion of tensile curve of concrete model (either smeared cracking or damage plasticity model).  I've tried full Newton with line search, Riks, quasi-Newton, but none of them gave convergence solution.  I read on the internet and some people suggested using damping to stabilize the model.  I think this is a very last resort (after redefining mesh, changing solution control don't work).  You can try this by either specifying the energy dissipation coefficient in STEP definition, or specifying viscocity when assigning element type to your model.  However, be careful to check the ratio of damping energy and total energy of the system in your result.  There is an acceptable limit on the ratio stated in the manual, which I can't remember.  This method didn't work for me though because in order to get convergence, the coefficient becomes so large that the whole model loses equilibrium.  Let me how it works for you.

I've read several papers that used built-in concrete model in ABAQUS.  I wish they've mentioned how to overcome convergence problem.  But no luck so far.  Has anyone else in this forum experienced this same problem?