Don’t Think, Just Throw

The uncertainty of an OpenSees analysis often stops people in their tracks. What will happen if I use this input for that model? Will I be able to simulate this behavior? What if the analysis fails to converge? Don't think. Just throw. https://youtu.be/qa3EseH3Hgc Nothing bad is going to happen if you have an incorrect input … Continue reading Don’t Think, Just Throw →

Off the Hooke

To grasp nonlinear structural analysis, unlearn Hooke's Law, $latex \sigma = E\varepsilon$. And all derivative outcomes of Hooke's Law. Like $latex \kappa=M/EI$ and $latex {\bf K} {\bf U} = {\bf P}$. https://www.youtube.com/watch?v=z4jeREy7Pbc When steel yields, concrete cracks, etc., Hooke's Law no longer applies and holding on to it can lead to erroneous interpretations of nonlinear … Continue reading Off the Hooke →

Minimal Working Example

When people post online or e-mail me about what could be a bug in OpenSees, I'll ask for a minimal working example (MWE), i.e., a simple script that demonstrates the problem. I don't want to deal with elaborate scripts--yours or mine. So, what does an MWE look like for OpenSees? Here's a non-exhaustive list of … Continue reading Minimal Working Example →

It’s a Fine Line

The OpenSees Twitter bot started in December 2019 but didn't "like and retweet" #OpenSees tweets retroactively. So, out of curiosity, I searched Twitter the other day for the first use of the #OpenSees hashtag. This tweet from 2011 came up as the winner: https://twitter.com/drescolano/status/45099760868274176 Not an uncommon sentiment. Now, ten years later, I asked David … Continue reading It’s a Fine Line →

OpenSees Is Simple

OpenSees, and nonlinear structural analysis in general, is a simple endeavor. It is not complicated. It does not need to be complex. Although this clip from Bull Durham, the best baseball movie of all time, refers to throwing, hitting, and catching the ball, the simplicity translates to nonlinear structural analysis. https://www.youtube.com/watch?v=PhML1WAGkCs You build the model. … Continue reading OpenSees Is Simple →

Stability Challenge Results

I posted a modeling challenge for the famous, perhaps now infamous, three member truss example of OpenSees. The members are very slender, so I wanted to see how well we can account for geometric nonlinearity. First, the results. There were five entries--three reported a load factor of about 0.47 and two gave a load factor … Continue reading Stability Challenge Results →

A Very Stable Challenge

With linear structural analysis, a number is a number. However, reality starts to creep in when physics dictates that you need to account for nonlinear effects. The three member structure shown below is a perfect example--Example1.1.tcl, one of the most OG OpenSees examples. Have you ever paid attention to the member sizes though? If so, … Continue reading A Very Stable Challenge →

OpenSees Facebook Group

I've been answering questions on the OpenSees message board lately. Mostly responding with quick answers, nothing that requires me to download or copy/paste scripts to run locally. A friend suggested I drop in on the OpenSees Facebook group to answer some questions. The group has been around since 2008 and has over 3,000 members (not … Continue reading OpenSees Facebook Group →

OpenSees Documentation

The documentation for OpenSees is moving to a GitHub repository and will be in RST format, a markup style language that is easy to learn. Being on GitHub, anyone can contribute to the documentation. But, I was recently reminded by the author of the OpenSees manual that "easy to learn" and "anyone can contribute" were … Continue reading OpenSees Documentation →

SSI Modeling Challenge Results

After two modeling challenges (here and here) for the linear-elastic response of frame structures, I thought it would be a good idea to do a soil-structure interaction (SSI) modeling challenge. I feared the large uncertainty of geotechnical engineering relative to structural engineering would stifle participation, but I received four entries. Three participants submitted a single … Continue reading SSI Modeling Challenge Results →