Concrete Damaged Plasticity

[turantug]

hi,
i am trying to model a concrete bridge girder using Abaqus CAE. I solved the problem using linear material properties and i got no error or warning messages. When i used the concrete damaged plasticity model, after 8 succesful iterations i got "The plasticity/creep/connector friction algorithm did not converge at X points" and "The system matrix has Y negative eigenvalues" warning messages and a couple of steps later i got "Time increment required is less than the minimum specified" (my time increment is 1e-10)error message. how could i solve this problem ? I would be glad if you could help me in this manner. thanks in advance, have a nice day.

 

[jrosco22]

I am experienceing the same problem with a full scale concrete slab on steel girder bridge model that I am creating. I am puzzled by this and was wondering if you have since solved or altered your model to get a solution. Thanks for you input!

 

[turantug]

since the failure of the concrete is highly brittle the residual is becoming very high when the concrete starts to crack and this unbalanced force creates unstability. define density and use "stabilization with" option that will create inertia forces so that the residual is not going to be very high and the system is going to reach equilibrium in this step, or use damping in the same menu (in this case no need to define density) and after the analysis check the damping factor. it should be very low (if it is not, it is not the correct solution because in your system there is no damping).
since you are working on concrete structures,i would be glad to discuss the modeling of concrete.
have a nice day.