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
Tag: OpenSees
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, e.g., here and here. 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 … 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
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
OpenSees Is Simple
OpenSees, and nonlinear structural analysis in general, is a simple endeavor. It's 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. You … Continue reading OpenSees Is Simple
Stress Resultant Verification
Verifying material nonlinear frame element formulations is pretty difficult. There are only a handful of analytical solutions that do not rely on bilinear uniaxial constitutive response. You're much better off verifying geometric nonlinearity. However, an example based on a relatively straightforward biaxial stress resultant plasticity model has intrigued me over the years. The example, described … Continue reading Stress Resultant Verification
Did You Pass Your Patch Test?
The patch test is one of the standard "sanity checks" of finite element implementations. To pass a patch test, an irregular mesh of elements must be able to reproduce a constant stress field. Interior nodes of the mesh should also displace according to a linear displacement field. OpenSees is not known so much for its … Continue reading Did You Pass Your Patch Test?
