Whether it's Yogi Berra describing switch hitters or Charles Shackleford remarking on his ability to sink shots right-handed or left-handed, "amphibious" was not the word these athletes were looking for to describe ambidexterity. This type of humorous mistake, from the misuse of similar sounding words, is known as a malapropism. The best malapropisms come from … Continue reading OpenSees Malapropisms
Positive OpenSees Contact
Flipping through J.C. Smith’s Structural Analysis textbook, I’m confident OpenSees can handle every problem. Same goes for any other textbook on structural analysis. However, I totally paused on Problem 9.34 as it hinted at contact nonlinearity. The cantilever and the simple span have flexural stiffness EI=5120 kip-ft2, something in the ballpark of W6x12 steel members, but fudged to … Continue reading Positive OpenSees Contact
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
Analyze This
I have posted modeling challenges where I describe a model and loading then ask for a specific response quantity. Usually, the model is linear-elastic, e.g., strongback frame, Ziemian frame, and soil-bridge SSI, so the challenge is building the model and the ensuing analysis is straightforward. But what if I gave you an already built model, described the loading, … Continue reading Analyze This
Minimal Random Process Example
I know just enough about random vibrations and ground motions to be dangerous. I would like to become less of a liability on these topics, so bear with me on this post. OpenSees has two time series for random processes, both implemented by Terje Haukaas. A DiscretizedRandomProcess uses random variables to construct a time series from filtered unit … Continue reading Minimal Random Process Example
Rotated Local Axes
OpenSeesing through the SeismoStruct Verification Report (v2025), I expected smooth sailing across Chapter 2, Comparison with Independent Hand-Calcs, where “hand-calcs” means SAP2000 analysis results. But light storm clouds set in on Example 2, Rotated Local Axes. The model is a W12x106 cantilever rotated 30 degrees about its longitudinal axis. A uniform distributed load (roughly the member self-weight) is … Continue reading Rotated Local Axes
OpenSees Pirate Jokes
Today is International Talk Like a Pirate Day, a "holiday" that originated in 1995 just up the road from Eastchester. Corollaries between OpenSees and pirate speak be plenty. Whether you are a landlubber getting your OpenSees legs or an old salt who doesn't need documentation, Google, or ChatGPT to define a 3D model of RC … Continue reading OpenSees Pirate Jokes
Celestial OpenSeesing
The three-body problem is an application of Newton’s laws of motion where each of three bodies moves through space according to gravitational forces exerted by the other two bodies. Despite its simplicity, there is no general closed-form solution for the trajectories of the three bodies. However, you can approximate the trajectories with numerical methods. And since it’s … Continue reading Celestial OpenSeesing
Double Inverted Pendulum
A double inverted pendulum (DIP) consists of two masses connected in series by rods to a pinned base. Without some form of control at the base, a DIP system is unstable. Consider the DIP shown below in the upright (inverted) position. The DIP is controlled by vertical base excitation, e.g., imparted by a motor with … Continue reading Double Inverted Pendulum
Scribbled Lines
Like many people who were, have been, or will be around for long enough after 1973, every listen of Pink Floyd's Dark Side of the Moon amazes me. The album covers themes ranging from greed to existentialism. My standout track is Time. Most of the song's lyrics hit right on the nose: The sun is … Continue reading Scribbled Lines
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