How to model 4 points bending reinforced concrete beam with ABAQUS?

Question

I have some questions about how to define boundary conditions for 4 points bending reinforced concrete with Abaqus. So I model this beam but I don't know how to define boundary conditions and step. Can You please help me? The model is 1/4 beam because the beam is symmetrical. In result the Force=0 in all model, I don't know how to solve that . I have another questions for modeling rebars, beam element isn't better than truss element?

Answer 1

Four point bending is an interesting test configuration.

Here are a few ideas to consider:

1. Symmetry at x = 0 means out-of-plane displacement ux and in-plane rotations txy and txz are zero for all points on the symmetry plane.
2. Four point bending doesn't mean no force on the beam. There are vertical reaction forces at each of the four bending points. They sum to zero, but their effect on the beam should be clear. You'll need to constrain the support points to have zero vertical displacement and apply either a displacement or load to the two loading points. You'll calculate how shear and bending vary along the length of the beam.
3. The fact that the beam is reinforced concrete is immaterial (no pun intended) to the boundary conditions applied.
4. You'll need beam elements at a minimum. They include bending effects. Truss elements only model axial loads.
5. Concrete is strong in compression but weak in shear and bending.
6. Make sure you have a good understanding of the failure model for concrete before you begin.

How are you modeling the concrete? Is this a continuum model with steel rebar elements surrounded by concrete, or are you smearing them out using an anisotropic composite model and beam elements? Are you modeling large aggregate using something like Eshelby tensor? Do you have to be concerned about the concrete/steel interface? What about fracture?

Great problem. Good luck.