Misalignment with OpenSees

OpenSees has been around, solving various earthquake engineering and other problems, for over 20 years. So, I become skeptical when someone reports an error in the fundamental mathematical formulations of OpenSees.

Typically, the “error” comes down to misalignment of what you think OpenSees should do, e.g., based on your experience with another structural analysis software, and what you have told OpenSees to do. For example:

  • The element formulations are different. Should you include shear and torsional deformations?
  • You think moment-rotation and moment-curvature are the same thing.
  • Geometric transformations are incorrect.
  • Constraints are not handled correctly.
  • You used the Linear algorithm.
  • You used an explicit time integrator with large time steps.
  • You applied more load than you think. Or less.
  • Units are inconsistent.
  • Either mass or gravity load is not defined.
  • You assumed pseudo-time was the load factor.
  • Boundary conditions are wrong.
  • You recorded and plotted the wrong response.
  • You overwrote an important variable in your script.

There are several other reasons for misalignment.

Sure. There are a few bugs in the low levels of OpenSees, e.g., the inconsistent tangent returned by Concrete23.

But, solving the wave equation? OpenSees has that down.

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