Your DLL Might Be Ignored

I am not a fan of DLLs (dynamic-link library) for material and element models in OpenSees. There are many technical reasons for my dislike of DLLs--fragile code, multiple versions swirling around online, keeping up to date with the latest OpenSees executable, debugging difficulty, and cross-platform compatibility to name a few. So, if you've published your … Continue reading Your DLL Might Be Ignored →

You Get What You Give

In the early days of OpenSees, conventional wisdom was "You get what you pay for". Sure, the internet was around, but the only OpenSees resources were the wiki, the examples manuals, and the message board. Those resources are still around today. But there's a ton of other OpenSees resources available including packages, pre- and post-processors, … Continue reading You Get What You Give →

You Didn’t Build That

At what point does a "customized version" of OpenSees become distinct from the main OpenSees? After tinkering with OpenSees, when does it become "your own"? In most cases, the answer to both of these questions is "never". Sure, you will learn a lot by implementing Concrete24, even if it is only an incremental improvement over … Continue reading You Didn’t Build That →

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 →