Non-Convergence Is Not Structural Collapse

Legend has it that some published research results based on nonlinear dynamic analysis--incremental dynamic analyses, seismic fragility curves, Monte Carlo simulations, etc.--considered a non-convergent OpenSees model to indicate structural collapse or failure. Let's think about this for a minute. Here is the displacement response in two orthogonal directions at the top of a nearly 50 … Continue reading Non-Convergence Is Not Structural Collapse

Failed to Get Compatible …

If you've used the force-based beam-column element in OpenSees, you've likely come across this warning involving element forces and deformations: I've encountered this warning many times and so have others. In fact, I lifted the above image from a recent post on the OpenSees Facebook group. I tried to come up with a MWE to … Continue reading Failed to Get Compatible …

A Marathon, Not a Sprint

When tasked with developing an OpenSees model for simulating the nonlinear dynamic response of, let's say, a multi-story reinforced concrete frame, you may be tempted to go straight to force-based frame elements with fiber sections comprised of Concrete23 and Steel08 material models. This sprint to the finish line will undoubtedly lead to an analysis that … Continue reading A Marathon, Not a Sprint

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

Non-Convergence Does Not Mean OpenSees Crashed

I once had the following conversation with a concerned user (CU) of OpenSees: CU: "I was running a response history analysis, then all of a sudden OpenSees crashed." PD: "Really, it crashed? Did you get the blue screen of death?" CU: "No. The analysis stopped and I saw 'Failed to converge'. It crashed." PD: "Oh, … Continue reading Non-Convergence Does Not Mean OpenSees Crashed