Most Solvers Can Be Marplots

Have you ever tried to replicate the familiar beam stiffness coefficients $latex 12EI/L^3$, $latex 6EI/L^2$, $latex 4EI/L$, and $latex 2EI/L$ (there's a poem about them here) by imposing unit displacements and rotations at fixed supports? It should be one of the first sanity checks you make when using or developing new structural analysis software. You … Continue reading Most Solvers Can Be Marplots →

Handle Your Constraints with Care

Manipulating the nodal equilibrium equations is necessary to enforce constraints between degrees of freedom (DOFs) at two or more nodes in a structural model. These multi-point constraints arise from assumptions of axial and flexural rigidity of frame elements, e.g., rigid diaphragms, and also between two nodes at the same location where some of the DOFs … Continue reading Handle Your Constraints with Care →

Be Careful with Modal Damping

Modal damping is kind of the it-spell in the dark art that is modeling viscous damping in structures. Although modal damping is pretty straightforward, you should be aware of an important aspect of its implementation in OpenSees. The issue, which is described in section 9 of this paper, is that OpenSees assembles the dynamic tangent … Continue reading Be Careful with Modal Damping →