Tag: Geometric nonlinearity

Ways to Analyze This

A previous post challenged readers to analyze a simple frame model subjected to static loads. The model had material nonlinearity via tension-only diagonal cables and geometric nonlinearity via the P-Δ effects in the columns. The Challenge Despite these rather simple nonlinearities, analysis of the frame for the given vertical and lateral loads will fail using the default analysis options … Continue reading Ways to Analyze This →

The Three-Act Verification

Although I would like to write more posts on OpenSees verification examples, I believe a post still needs context, or a story, to not become a dull trope. “I found this example, here’s the OpenSees model and some assertions, and look, the assertions pass” is not a compelling three-act structure of setup, confrontation (or conflict), and resolution. … Continue reading The Three-Act Verification →

Buckling of Restrained Plates

The plate buckling analysis in a previous post demonstrated flexural buckling–definitely minimal and definitely necessary if you’re going to tackle more complex cases of plate buckling. Having passed the minimal example, Mark Denavit, a frequent collaborator, suggested I take a look at buckling of plates that are restrained on all four sides. Mark always has good … Continue reading Buckling of Restrained Plates →

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 →

Apples and Oranges

Good articles on finite element formulations combine accessible theory with reproducible examples. One such article, Alemdar and White (2005), balances theory and examples for distributed plasticity frame element formulations quite well. I never did more than skim the article and give indirect, second hand citations over the years. So, when I recently rolled up my sleeves … Continue reading Apples and Oranges →

One Is All You Need

It is fairly well known that you can use a single force-based element to simulate the material nonlinear response of a frame member. Likewise, using a corotational mesh of displacement-based elements is an effective approach to simulate combined material and geometric nonlinearity. A previous post looked at geometric nonlinearity with linear-elastic response in a single … Continue reading One Is All You Need →

Two Paths You Can Go By

I am confident we can use OpenSees to solve every truss, beam, and frame problem from any statics or structural analysis textbook as well as every single degree-of-freedom and rigid shear frame problem from a structural dynamics textbook. We can also solve any reasonable problem from a finite element textbook. My confidence starts to wane … Continue reading Two Paths You Can Go By →