Applying surface loads (pressure loads) to solid and shell elements in OpenSees is difficult. The typical approach is to use equivalent nodal loads, but that's intractable for anything beyond simple meshes. Do you want to calculate equivalent nodal loads (in your script, after the model is defined) for a triangulated mesh? Yeah, me neither. It … Continue reading How to Apply Surface Loads
Tag: Shells
Minimal Plate Buckling Example
OpenSees is not built to perform linear buckling analysis. But a few years ago, Luigi Caglio shared a workaround described in this post. In the post, the example application is a frame model, but there’s no reason the approach cannot work for shell models. So, here’s a minimal working example. Consider a rectangular steel plate with simple boundary … Continue reading Minimal Plate Buckling Example
Plate Rebar Material
Where fiber sections integrate stresses over two dimensions for beam-column line elements, fiber sections integrate stresses through only one dimension for shell elements. Either way, you're performing volume integrals, whether it's two dimensions in the section and one in the element or one dimension in the section and two in the element. The LayeredShellFiberSection, where … Continue reading Plate Rebar Material
How to Mesh Shells
If you have created a mesh of planar (2D) elements in OpenSees, creating a mesh of shell elements (3D) is not that different. You can use either the block2D command or Minjie's line and mesh commands. However, you will quickly find that the block2D command--2D because the mesh is planar, not because the command is … Continue reading How to Mesh Shells
The Three Node Quad
Depending on your experience with finite elements, this post will either be totally obvious or it will blow your mind. The standard bilinear, isoparametric four node quad element degenerates to a three node constant strain triangle when you assign two consecutive element nodes to the same location. This fun fact is due to the math, … Continue reading The Three Node Quad
OpenSees Shells by the Seashore
Other than state-of-the-art material and geometrically nonlinear frame element formulations, it's fair to say OpenSees is not known for its breadth of structural finite elements like quads, bricks, and shells. There are solid elements for geotechnical applications and fluid elements for fluid-structure interaction via the PFEM, but what's the story on shell elements in OpenSees? … Continue reading OpenSees Shells by the Seashore
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