# How can a simply supported boundary condition be defined in a solid model?

ashansys
Member Posts:

**3**For example in the beam model, one can specify the following boundary condition at both the ends of a slender circular bar:

Ux = Uy = Uz = 0 ;

Rx = Ry = Rz = free

If a solid model is used instead of a beam model, applying Ux = Uy = Uz = 0 at the end faces would also arrest rotational degrees of freedom on those faces and it would act as a fixed boundary condition.

So how can a simply supported condition be applied in the solid model?

## Answers

11,369@ashansys

Select the end face of the solid and select Remote Displacement from the Support category. You can fix three translations and leave the three rotations Free. Repeat on the other end except you cannot leave three rotations free at both ends. One end must have rotation about the axis along the beam length set to zero, otherwise the solver would see a zero pivot error. This is true for a beam model and a solid model with Remote Displacements.

3@peteroznewman@peteroznewman Thanks for the answer. I am aware of the option of applying remote displacements on remote points created with surfaces, however, I am looking for answers based on the physics of formulations of 1D and 3D elements.

11,369@ashansys

The answer I gave is how to create a pinned connection on 3D solid elements meshed on a solid body. This gives the same boundary conditions as a 1D beam. I can only add that you should set the Behavior of the Remote Displacement as Rigid to fully match the 1D beam condition. What information is missing?

Are you asking how to do that if you just have nodes and elements and no solid body?

3@peteroznewman

In a way, yes!

So I want to know whether the answer can be derived from the very basics, i.e. based on various elemental formulations? For example for Euler Bernoulli beam theory or Timoshenko beam theory for beam models vs solid models.

11,369@ashansys

ANSYS BEAM188 implements Timoshenko beam theory, which includes Shear Deformation, so will have the closest agreement with a solid model.

ANSYS BEAM4 implements Euler-Bernoulli beam theory, which ignores Shear Deformation, so will differ from a solid model, especially for short beam lengths.

Solid elements will need about 4 quadratic elements or 8 linear elements through the thickness of the beam to accurately capture the bending stress.