Making Sense Out of Concrete02

Those three extra parameters for Concrete02 are usually enough to make me stick with Concrete01. I struggle to come up with good values for the parameters $latex \lambda$, $latex f_t$, and $latex E_{ts}$ shown in the following image from the OpenSees Concrete02 wiki page. Image developed by Dr. Silvia Mazzoni The four compressive backbone parameters … Continue reading Making Sense Out of Concrete02

Parameter Updates in the Loop

Besides visualization and writing output to files, there's some pretty useful things you can do during an OpenSees analysis. One of those things is updating model parameters. Before getting into parameter updating, it is worth showing that OpenSees analyses can be run one step at a time. Many examples online show a dynamic analysis, e.g., … Continue reading Parameter Updates in the Loop

Nobody Wants to Read Your Sh!t

Although far removed from earthquake engineering and academic writing, we can learn a lot from writers of advertising and fiction. The most important lesson I've learned is that nobody wants to read your shit. Steven Pressfield wrote an entire book about it, but I'm pretty sure the phrase was around long before the book. https://www.amazon.com/Nobody-Wants-Read-Your-Sh-ebook/dp/B01GZ1TJBIContinue reading Nobody Wants to Read Your Sh!t

Building Blocks

I gave a presentation last week for the 6th International Short Course on Seismic Analysis of Structures, hosted remotely and on-site at the University of Palermo, Italy, organized by Prof. Giovanni Minafo and Prof. Cristoforo Demartino. As you can see in the video, my presentation re-packaged leveraged several blog posts. https://youtu.be/p4tgafYuk74 Not every slide was … Continue reading Building Blocks

How to Record Fiber Response

Recording the response of a single fiber in a fiber section is a common ask. You will need to use an Element recorder, but what you can record in each fiber is defined in the UniaxialMaterial::setResponse() method. The most common option is 'stressStrain', which gives the fiber stress-strain response history. After setResponse() drills down to … Continue reading How to Record Fiber Response

Polymorphic Pitfall

Polymorphism is what makes OpenSees, and other object-oriented software, flexible and extensible. With polymorphism, you can program to an interface, not an implementation. You see this approach all over OpenSees--elements don't care how materials compute stress and tangent (more here); integrators don't care how the elements form resisting force and tangent stiffness (more here); and … Continue reading Polymorphic Pitfall

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

Verifying Ain’t Easy

I've posted a few modeling challenges on frame analysis (strongback, Ziemian, and stability) and soil-structure interaction. However, I recently accepted a challenge from George Chamosfakidis to see if OpenSees can give the same periods and mode shapes reported in the ETABS verification example shown below. Published verification examples typically just show the "correct" result and … Continue reading Verifying Ain’t Easy

Absolutely, It’s Relative

One of the most frequently asked OpenSees questions is whether node recorders record absolute or relative displacement (relative to the ground) when a model is subjected to a uniform excitation. There's several approaches to find the answer to this question. One solution is to apply a simple uniform excitation--like a constant ground acceleration--to an SDF … Continue reading Absolutely, It’s Relative