The Toy Reliability Problem

In Fundamentals of Structural Mechanics, Hjelmstad uses the "little BVP" to introduce boundary value problems. Chopra uses a two-story rigid shear frame throughout Dynamics of Structures. And in Structural and System Reliability, Der Kiureghian uses a "toy problem" for various types of reliability analyses. The toy reliability problem is defined by two random variables with … Continue reading The Toy Reliability Problem →

Earthquake Engineering Experts Hate Me for This One Weird Trick

I was a structural engineer who dabbled in earthquake engineering simulation. Then one day I stumbled upon a weird trick to get ground displacement history from a ground acceleration record. The trick was simple. It worked right away. I couldn't believe it. The trick did not require additional libraries or writing a loop. Just a … Continue reading Earthquake Engineering Experts Hate Me for This One Weird Trick →

Effective Earthquake Forces

There's nothing special about the UniformExcitation load pattern in OpenSees. The pattern is a convenience for defining effective earthquake forces due to uniform ground acceleration as plain 'ol mechanical loads on your model. Consider the equation of motion for uniform ground acceleration, with linear inertia and damping forces, and influence vector $latex {\boldsymbol\iota}$ for the … Continue reading Effective Earthquake Forces →

OpenSees Bean Counting

Based on review invitations, new paper announcements on social media, and Google Scholar citation alerts, I've seen a lot of OpenSees-based journal articles. I'm sure you have as well. With a few exceptions, the journals that house OpenSees-based articles have been the usual suspects in earthquake engineering. But recently, it's felt like the distribution of … Continue reading OpenSees Bean Counting →

Wrapper’s Delight

What is the output produced by this analysis? Sure, you can copy and paste the script to get the answer. But that's no fun. Think about the model and analysis. Can you explain what's going on before getting the answer? import openseespy.opensees as ops ops.wipe() ops.model('basic','-ndm',1,'-ndf',1) N = 365 ops.uniaxialMaterial('Elastic',0,1.0) for i in range(N): ops.uniaxialMaterial('Multiplier',i+1,i,1.01) … Continue reading Wrapper’s Delight →

Is OpenSees Pythonic?

OpenSeesPy is sometimes criticized for not being "Pythonic". But what does "Pythonic" even mean? And does achieving "Pythonic" status matter? From what I gathered in this blog post, Pythonic code uses the idioms, i.e., the specific syntax and constructs, of Python. That definition is circular--an example from the post better demonstrates the meaning. If you … Continue reading Is OpenSees Pythonic? →

Material Testing with White Noise

Pushes, pulls, and cyclic strain histories of increasing magnitude are solid approaches to testing the stress-strain response of material models. But I'm not convinced these tests will hit every code block of a material model implementation. I mean, have you seen all the nested if-statements and uninitialized local variables that went into Concrete23? Although I … Continue reading Material Testing with White Noise →

OpenSees Command Line Arguments

While graphical user interfaces are good for general purpose use, the command line remains the most versatile way to run OpenSees and other computer programs. Passing command line arguments to an OpenSees Tcl or Python script is useful when creating standalone applications for building and analyzing specialized models. Both Tcl and Python have constructs similar … Continue reading OpenSees Command Line Arguments →

It Hides in Plain Sight

It's no secret that engineers write technical documents in a style that no one would actually speak. Like, if I'm explaining plastic hinge integration to you in person, it would sound nothing like what's written in the journal article. It's difficult to measure the amount of nonsense in technical writing, but qualitatively, you know it … Continue reading It Hides in Plain Sight →

Spreader Beam Analysis

Problems involving beams are few and far between in Hibbeler 14th edition Engineering Mechanics: Dynamics. The problems mostly deal with springs, friction, pulleys, and things that rotate. So, Problem 15-3 was a welcome sight. A six foot long beam weighing 5000 lb is lifted from rest to a velocity of 8 ft/sec in 1.5 sec … Continue reading Spreader Beam Analysis →