You can do a lot with UniaxialMaterials in OpenSees--springs, fibers, trusses, section aggregators, etc. Although over 130 UniaxialMaterials are available, it's likely that only about a dozen see regular use. So, with all due respect to Concrete23, my favorite regular is HardeningMaterial. It's straight out of Simo and Hughes and was the example material for … Continue reading Elastoplastic Calibration
Striking YouTube Gold
It's been a busy week, one in which I have not managed my time very well. While 71 posts sit in my Drafts folder, I haven't sat down to get one to the finish line. So, why not add more to the Drafts folder? While the history and use of reliability modules in OpenSees will … Continue reading Striking YouTube Gold
No Framework for Old Men
You've run a bunch of OpenSees analyses with Concrete23 and developed some fragility functions. Now you need to write about it. This blog occasionally addresses academic writing, and while there's a lot of good (and bad) writing advice out there, some of the best advice comes from outside engineering. For example, I recently found this … Continue reading No Framework for Old Men
Reaction and Unbalance
A confluence of recent inquiries led me to take a look at what the nodeReaction and nodeUnbalance commands return in an OpenSees dynamic analysis. While I have a pretty good handle on nodeReaction, going in to this post, I was unsure about nodeUnbalance. We can learn a lot from a couple springs, so I created … Continue reading Reaction and Unbalance
Trapezoidal Beam Loads
OpenSees will never win any awards for documentation. Although many features, e.g., Concrete23, are not documented because no one uses them, a few useful items lack documentation. For instance, did you know that you can apply trapezoidal member loads to beam elements? You can do so with additional arguments to the eleLoad command with the … Continue reading Trapezoidal Beam Loads
Release the Plastic Hinge
How close to a true moment release can you make the plastic hinge at one end of an OpenSees beamWithHinges element? It's a question I've thought about before, and it came up again recently. A simple fixed-fixed beam can start to answer the question. Imposing a unit rotation at one end will produce moment reactions … Continue reading Release the Plastic Hinge
Syllabus by Blogging
Since joining the faculty at Eastchester, I've taught nonlinear structural analysis many times. The course content is shaped by what I learned, and continue to learn, from Frank, Greg, Filip, and Silvia. The blog is another outcropping of what I've learned. So I've integrated many of the posts into the course, which consists of the … Continue reading Syllabus by Blogging
Heavy as a Chebyshev
Numerical integration, or quadrature, is essential for material nonlinear finite element formulations. Gauss, Gauss-Lobatto, or a plastic hinge approach is all you need for frame elements. And for fiber sections, midpoint integration gets the job done. Besides some highly specialized cases, there's no need to use other types of numerical integration in nonlinear structural analysis. … Continue reading Heavy as a Chebyshev
How to Cite a Blog Post
How to cite OpenSees was one of the blog's first posts. Several posts have been made since. Most of them non-sense, but there's a couple that have enough technical content to be citation-worthy. Based on its style guide, ASCE treats blog posts like a website where you provide the author, title and publication year of … Continue reading How to Cite a Blog Post
Its Power and Its Problem
A recent LinkedIn post by the creator of FEA Academy raised an important issue about the difference between an algorithm and an integrator. The image from the post is shown below. In other corners of the FEA world, the algorithm and the integrator are a package deal--the Newton-Raphson method is commonly understood to mean load … Continue reading Its Power and Its Problem
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