Gimme All Your Damping, All Your Mass and Stiffness Too

Just because OpenSees is open source does not mean it is a fully transparent box. This is mostly because documentation has lagged behind development. So, pessimists would say the box is semi-opaque while optimists would characterize it as semi-transparent. But a few parts of OpenSees are definitely housed in an opaque box. Take, for instance, … Continue reading Gimme All Your Damping, All Your Mass and Stiffness Too

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

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

Is Plastic Hinge Integration a Fruit or a Vegetable?

If distributed plasticity elements are fruits and concentrated plasticity elements are vegetables, then plastic hinge integration is something like a tomato. Based on papers I've read, manuscripts I've reviewed, presentations I've seen, etc., there's some confusion as to whether plastic hinge integration is a fruit or a vegetable. Here's my two cents. Concentrated plasticity elements … Continue reading Is Plastic Hinge Integration a Fruit or a Vegetable?

How to Cite OpenSees

In the $latex R^{42}$ space that defines academic performance evaluation, citation-based metrics comprise a small but often over-emphasized subspace. Based on the developers' Google Scholar profiles, it is clear that OpenSees generates a lot of citations from various corners of cyberspace. In the citation-stingy field of structural engineering, the numbers are impressive. On the other … Continue reading How to Cite OpenSees

No CAPS When You Spell the Framework’s Name

MF DOOM is one of the greatest lyricists (rap or otherwise) that you've probably never heard of. In his 2004 track "All Caps" with Madlib, DOOM states that his stage name should be written in all caps. All CAPS when you spell the man's name.MF DOOM, 2004 The preferred capitalization of OpenSees is not so … Continue reading No CAPS When You Spell the Framework’s Name

Be Careful with Modal Damping

Modal damping is kind of the it-spell in the dark art that is modeling viscous damping in structures. Although modal damping is pretty straightforward, you should be aware of an important aspect of its implementation in OpenSees. The issue is that OpenSees assembles the dynamic tangent in to the matrix storage scheme you choose via … Continue reading Be Careful with Modal Damping