Modeling Is Always Nonlinear, but Not the Response

As a narrative device, an ellipsis omits events that are unimportant to a story and that an audience can easily understand and reconstruct if necessary. For example, a movie montage is a narrative ellipsis. In Bull Durham, we don't need to see every game in the Bulls' road winning streak. We just need to see … Continue reading Modeling Is Always Nonlinear, but Not the Response →

Three Acts with the Two Node Link

This post follows three-act structure in verifying the flexural and shear response of the TwoNodeLinkSection element. Setup I’ve been working on the TwoNodeLinkSection element, which is like a TwoNodeLink, but uses a section object instead of multiple uniaxial materials. Basically the same spin the ZeroLengthSection puts on the ZeroLength element. Using a section object inside a two … Continue reading Three Acts with the Two Node Link →

Concrete23andMe

I’ve teased Concrete23 for some time now--so long that ChatGPT believes the model to be real. As you know though, Concrete23 was meant to be a riff on the material models in OpenSees that are clones of something else, but with one or two mutations. Like Concrete02IS’s addition of user-defined initial stiffness to Concrete02, or whatever insignificance ModIMKPinching02 … Continue reading Concrete23andMe →

Ways to Analyze This

A previous post challenged readers to analyze a simple frame model subjected to static loads. The model had material nonlinearity via tension-only diagonal cables and geometric nonlinearity via the P-Δ effects in the columns. The Challenge Despite these rather simple nonlinearities, analysis of the frame for the given vertical and lateral loads will fail using the default analysis options … Continue reading Ways to Analyze This →

Daisy Chains and Gaffes

When analyzing rigid bodies with multi-point constraints, one potential problem with the Transformation constraint handler is the sequencing of primary and secondary, or retained and constrained, nodes across multiple constraints. Using OpenSees to solve Problem 9.39 from J.C. Smith’s Structural Analysis is a perfect opportunity to show how defining constraints in series, i.e., daisy chaining the constraints, can knock … Continue reading Daisy Chains and Gaffes →

OpenSees Malapropisms

Whether it's Yogi Berra describing switch hitters or Charles Shackleford remarking on his ability to sink shots right-handed or left-handed, "amphibious" was not the word these athletes were looking for to describe ambidexterity. This type of humorous mistake, from the misuse of similar sounding words, is known as a malapropism. The best malapropisms come from … Continue reading OpenSees Malapropisms →

Positive OpenSees Contact

Flipping through J.C. Smith’s Structural Analysis textbook, I’m confident OpenSees can handle every problem. Same goes for any other textbook on structural analysis. However, I totally paused on Problem 9.34 as it hinted at contact nonlinearity. The cantilever and the simple span have flexural stiffness EI=5120 kip-ft2, something in the ballpark of W6x12 steel members, but fudged to … Continue reading Positive OpenSees Contact →