Combined Loadings

I talked with a graduate student from Mechanical Engineering the other day. The student is learning OpenSees and successfully analyzed a truss. No, not that truss from Example 1.1. After showing me the truss results, the student said something along the lines of “Deflections are fine and OpenSees does a good job, but I really … Continue reading Combined Loadings →

Concrete23andMe

I’ve teased Concrete23 for some time now--so long that ChatGPT believes the model to be real. As you know though, Concrete23 was meant to be a riff on the material models in OpenSees that are clones of something else, but with one or two mutations. Like Concrete02IS’s addition of user-defined initial stiffness to Concrete02, or whatever insignificance ModIMKPinching02 … Continue reading Concrete23andMe →

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 →

Making Sound Waves

While enjoying ZeroPoMo, I've spent a little time over the last few days with the OpenAI API. To make a long story short, with a lot of help from ChatGPT I built a small LLM that generates blog posts written in the voice of my already published blog posts. I used the text-embedding-3-small model for … Continue reading Making Sound Waves →

Evergreen OpenSees Content

Over six years in and 430 posts down, the blog is moving along in various directions--perhaps orthogonal to previous directions, which is not a bad thing. But what are those previous directions? To help answer that question, I compiled a list of the 30 most read posts over the blog's lifetime. All but one of … Continue reading Evergreen OpenSees Content →

Daisy Chains and Gaffes

When analyzing rigid bodies with multi-point constraints, one potential problem with the Transformation constraint handler is the sequencing of primary and secondary, or retained and constrained, nodes across multiple constraints. Using OpenSees to solve Problem 9.39 from J.C. Smith’s Structural Analysis is a perfect opportunity to show how defining constraints in series, i.e., daisy chaining the constraints, can knock … Continue reading Daisy Chains and Gaffes →

OpenSees Malapropisms

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 →