For material nonlinear analysis of frame models, you can improve the computed response by using more displacement-based elements or more integration points in a force-based element. The material nonlinearity occurs inside the basic system, also known as the natural system or the kernel. To capture geometric nonlinearity due to large displacements, you have to go … Continue reading Meshing for Column Loads
A New Challenge
The results from a previous modeling challenge were excellent with 100% of entries correct. But before we deep dive into the dark world of modeling nonlinear structural response, let's do one more challenge with linear analysis. The frame model shown below is UP50HA from a series of low-rise industrial structures whose reliability under gravity loading … Continue reading A New Challenge
More Is Not Always Better
I sometimes run across simulations where frame member response is computed using displacement-based beam-column elements with more than two Gauss points per element. These elements require at least two Gauss points to ensure a complete solution and to capture the exact solution for a linear-elastic, prismatic member. While it is well known that you can … Continue reading More Is Not Always Better
Semi-Blind Kind of Contest Results
I proposed a simplified model of a strongback frame system as a modeling challenge and five people took the bait. I am happy to report that all five computed the expected roof displacement of 0.0128 mm, give or take 0.0001 mm. Good job, everyone! Having given this problem as an OpenSeesPy assignment for a couple … Continue reading Semi-Blind Kind of Contest Results
Close to the Edge
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
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
