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 →

How to Use pytest with OpenSees

Despite plentiful constitutive models and analysis options, testing and verifying OpenSees has been quite limited. At this point, going back and testing all the contributions from the last 25 years is a nearly insurmountable task. But, as the saying goes: The best time to start testing OpenSees was 25 years ago.The second best time is … Continue reading How to Use pytest with OpenSees →

Hold on Loosely

Today I was setting up some GitHub Actions involving private repository A checking out and doing some stuff with private repository B, which happens to be home to BennySparse. After spending a couple hours generating personal access tokens and creating GitHub secrets then attempting to use the tokens and secrets in a .yml file, I … Continue reading Hold on Loosely →

Distributed Moments

I have often posited that we can use OpenSees to solve every reasonable problem from any textbook on structural analysis, dynamics, or mechanics. I even put together a few posts, e.g., here and here, on how OpenSees can solve rigid body dynamics problems, the ones that torment every civil engineering sophomore. But a seemingly easy structural analysis problem that OpenSees … Continue reading Distributed Moments →