Moments At Supports For 3D Models
- Mark Mlynarski, P.E.
- Herman Lee, P.E.
Date | April, 2022 (Updated 3/2024) |
Product | AASHTOWare BrDR |
Version | 7.2 |
Description | What to do when your model has moments at free supports for 3D. |
What do I do if my model has moments at free end supports for 3D FEM Analysis?
For 3D analysis, a general recommendation to avoid moments at a pinned support is to model the support for only one of the girders as pinned, with all of the remaining girders’ supports defined as roller. Modeling all of the girder supports as pinned at a support line will draw more load to the support line resulting in non-zero end moments.
For 3D, a pinned support is defined as fixing the translation support in the X, Y, and Z directions. A roller support can fix the translation in the Y and Z directions. (see below).
For one girder in the cross section, set one support to Pinned, with “Local translation constraints” in the X, Y, and Z directions, and all others to Roller, with translation constraints in the Y and Z directions only. If, after making these changes there are still end moments, experiment with removing the Z direction constraints from the roller supports as well. Depending on your model, it may still be stable even with this constraint removed.
For all other girders, set the “Local translation constraints” to the Y direction only:
