In this lecture, we'll cover the following:

• Extracting the maximum vertical displacement from the global displacement vector.
• Identifying the location of the maximum displacement within the mesh.
• Reusing post-processing functions to visualise the deflected shape.
• Comparing results from custom finite element code with OpenSeesPy output.
• Diagnosing discrepancies and identifying zero-energy (spurious) displacement modes.

In this lecture, we focus on post-processing our finite element results by extracting the maximum vertical displacement and identifying its location within the mesh. We flatten the global displacement vector and isolate the vertical displacement degrees of freedom, allowing us to compute and compare peak values directly with those obtained from an OpenSeesPy model. This comparison reveals noticeable discrepancies in both magnitude and position, signalling that something in our formulation is not quite right.

We then visualise the deflected shape using a previously developed plotting function, which exposes non-physical zigzag patterns in the displacement field. We recognise these as zero-energy modes arising from reduced (selective) integration used in the shear stiffness calculation. While this approach was introduced to mitigate shear locking, it has introduced spurious deformation patterns. This sets the stage for the next lecture, where we will investigate the root cause of these issues and develop a robust solution to ensure our custom implementation aligns with the benchmark OpenSeesPy results.

Next up

The comparison reveals some unexpected displacement patterns. In the next lecture, we will investigate the root cause of these discrepancies.