Question

The differences can be explained using an example (see the image) that compares the results of a nonlinear calculation with the results of a linear calculation. You can find the model file under Downloads below.

The left and middle models have linear line hinges. In the left model, end releases are defined in u_x and u_y, and in the middle model, it is only defined in the direction u_x. In the right model, end releases are defined in u_x and u_y; however, there is a pressure contact between the surfaces. These surfaces can, therefore, not intersect under pressure.

When checking the results, it is obvious that the left model is too weak: the surfaces intersect into u_y due to the end releases. On the other hand, the middle and the right models give the same results.

It is often reasonable to keep on one linear calculation, if possible. Therefore, the middle model is most favorable for the numerical analysis, although the right (nonlinear) model is closer to the reality. However, the example is only a small comparison model. In reality, you would probably not use the spring in u_y/u_z, but instead assign the force to a tie rod. Furthermore, that is why the middle model without u_y is recommended.

The consideration of end releases between surfaces is also described in a technical article of our Knowledge Base, which you can find under Links below.

Model Analysis with Line Hinge and Line Release