A colleague in Eastchester tweeted this graphic, created by Stephen Ressler. It's a fun interpretation of social distancing, but a little abstract compared to other, more concrete, guidelines going around. For example, in Florida, the rule of thumb is to maintain a distance equal to an adult alligator length. You can visualize an alligator, but … Continue reading Close to the Edge
Author: Positive Definite
I am a professor of structural engineering at a land grant university in Eastchester, Pacific Northwest, US. I have been involved in the development, maintenance, and growth of OpenSees since its early days. Recently, I've taken an interest in learning Python and improving my academic writing.
Better Late than Never
Frame finite elements abound in OpenSees, but something very useful has always been missing--a linear-elastic beam element with moment releases. Sure, you can define two nodes at the release location and use the equalDOF command; however, that can be error prone and you're at the mercy of the constraint handler. On the positive side, this … Continue reading Better Late than Never
A Semi-Blind Kind of Contest
Contests where researchers and practitioners blindly predict the response of structural systems have produced some rather interesting results. And by "interesting", I mean "all over the place". So much so, that in an effort to protect the contestants, the contest organizers rarely make the results publicly available. Nonlinear structural analysis is hard though. Even with … Continue reading A Semi-Blind Kind of Contest
A Tale of Two Element Formulations
The question of whether to use the force-based or displacement-based formulation for material nonlinear frame analysis is one that comes up a lot. The answer depends on a few factors, mostly the material and the element length. To get a sense of the basic issues, I will compare the two element formulations with a numerical … Continue reading A Tale of Two Element Formulations
With or Without You
Citation-based metrics are like lottery tickets--they are not for investment purposes and should be used for entertainment only. Unfortunately, some promotion and tenure evaluators treat citation-based metrics like investment decisions. To aid in evaluation, citation-based metrics are readily available online, ranging from Web of Science, which indexes only archival publications, to Google Scholar, which indexes … Continue reading With or Without You
Better than Ideal Conditions
In simulating the nonlinear response of structural models, the Newton-Raphson algorithm converges quadratically as the iterations approach equilibrium at a time step. Quadratic convergence means the error at the current iteration is less than some constant times the square of the error at the previous iteration, e.g., the error is on the order of $latex … Continue reading Better than Ideal Conditions
Abstract Thoughts
Abstracts are an important part of scholarly publications. Journal editors select reviewers based on the abstract, conference organizers select presentations and invite full length papers based on an abstract (sometimes an extended abstract), and online databases crawl the abstract when indexing search results. In this post, I will give my two cents on journal abstracts. … Continue reading Abstract Thoughts
Start with the Correct Static Resisting Force
Thanks to my involvement with OpenSees, I have been asked to review several manuscripts on nonlinear dynamic structural analysis. It's always wonderful to see what other researchers are up to and how they use OpenSees or other software to achieve their research objectives. A brief overview of the governing dynamic equilibrium equation, i.e., the equation … Continue reading Start with the Correct Static Resisting Force
Incompetence, Not Malice
"Never attribute to malice that which can be explained by incompetence" is a form of Hanlan's razor, an aphorism that explains many actions in academia and elsewhere. For example, we often perceive omissions of important details in published work as intentional acts to prevent reproduction of the research. In some cases, this is true, while … Continue reading Incompetence, Not Malice
Recognizable Dates as Self-Imposed Deadlines
A few years ago, a colleague in Eastchester pointed out the July 4 submission date of an article they had just read. We thought it was a bold move for the author to have submitted a manuscript on a national holiday, in the summertime, when very few US academics are working. But perhaps there was … Continue reading Recognizable Dates as Self-Imposed Deadlines
