Transformation Cross-Training

Athletes often cross-train in secondary activities in order to improve performance in their primary sport. For example, football players may practice ballet in order to improve their flexibility and endurance. Using OpenSees, you practically have to be a mathlete to understand the geometric transformation in three dimensions. But instead of fumbling your way through space … Continue reading Transformation Cross-Training →

Cargo Cult OpenSeesing

In recent conversation, a colleague in Eastchester mentioned "cargo cult science", a term with which I was previously unfamiliar. A cargo cult scientist attempts to produce outcomes without understanding the actual processes that lead to those outcomes. Although the associated cultural behaviors have been around for centuries, the popular term "cargo cult" was coined during … Continue reading Cargo Cult OpenSeesing →

Concrete Zero

What is the depth of concrete uniaxial stress-strain models compared to the pinnacle that is Concrete23? No, it's not Concrete01--that's base camp for all the ConcreteXY that followed. The most basic uniaxial concrete model in OpenSees, "Concrete00" if you will, is elastic-no-tension, or ENTMaterial. As its name implies, the ENTMaterial response is elastic in compression … Continue reading Concrete Zero →

Runnin’ Down a Leak

Issue #1214 by zAlexliu-8895 on OpenSees GitHub demonstrated a memory leak with creating patches for fiber sections. The script posted with the GitHub issue is reproduced below. import openseespy.opensees as ops Counter = 0 while Counter < 100000000: Counter += 1 ops.wipe() ops.model('basic', '-ndm', 2, '-ndf', 3) ops.uniaxialMaterial("Concrete02", 1, -33, -0.0015, -20, -0.005, 0.1, 2.2, … Continue reading Runnin’ Down a Leak →

Minimal Creep and Shrinkage Example

In class, I tend to avoid talking about creep and shrinkage of concrete. I say "compression steel is good because long term deflections due to creep are bad", then move on to seemingly more interesting topics like how to find the neutral axis, bypassing shrinkage altogether. However, creep and shrinkage remain large mysteries to most … Continue reading Minimal Creep and Shrinkage Example →

How to Keep Your OpenSees Code Private on GitHub

I often mention the Concrete23 material model, but you won't find it in the main OpenSees GitHub repository or in any of the repo's public forks. You won't find Concrete23 because it doesn't exist. Or maybe the model does exist but I keep it in a private fork of OpenSees. You'll never know... Let's assume … Continue reading How to Keep Your OpenSees Code Private on GitHub →

Arc Length Parameters

Beyond load control, which cannot get past peaks in load-displacement response, OpenSees has several "continuation" methods for nonlinear static analysis of structural models. Implementation of continuation methods is based on the incremental-iterative framework by Clarke and Hancock (1990) with displacement control, minimum unbalanced displacement norm (MUDN), and arc length among the most frequently used in … Continue reading Arc Length Parameters →