# Non-Prismatic Frame Elements

Long before the BeamIntegration abstraction, there was only Gauss-Lobatto integration for force-based elements, with a single section model copied to each integration point. This made it impossible to use a single element to simulate the response of an RC member with different reinforcing details along its length, or any member that was inherently non-prismatic. While … Continue reading Non-Prismatic Frame Elements

# Failed to Get Compatible …

If you've used the force-based beam-column element in OpenSees, you've likely come across this warning involving element forces and deformations: I've encountered this warning many times and so have others. In fact, I lifted the above image from a recent post on the OpenSees Facebook group. I tried to come up with a MWE to … Continue reading Failed to Get Compatible …

# Every OpenSees Tutorial

There's plenty of excellent OpenSees tutorials online. But some other OpenSees tutorials feel like this sardonic, mock programming tutorial. When you watch the video, replace "outdated library" with "OpenSees", "Java" with "Tcl", and "Minecraft" with "incremental dynamic analyses for a portfolio of 3D reinforced concrete frames". https://youtu.be/MAlSjtxy5ak Pretty accurate, right? Let me know in the … Continue reading Every OpenSees Tutorial

# Direct Moment-Curvature

That the force-based frame element and fiber sections are in an open relationship should come as no surprise. The displacement-based and mixed frame elements can use fiber sections and all three element formulations can use stress resultant sections. While this post used a coupled stress resultant plasticity model, you can also use the section aggregator … Continue reading Direct Moment-Curvature

# Like Spinning Nodes

After posting on reasons that the solution to Ax=b fails, I realized I omitted an important case: truss nodes in a frame model. Although this post might be a stretch for an LBU (least bloggable unit), the blogging equivalent of an LPU, there are important factors to consider for structural models comprised of truss and … Continue reading Like Spinning Nodes

# Failure to Solve

Solving a system of simultaneous linear equations, canonically referred to as solving Ax=b in math speak, is at the heart of every equilibrium solution algorithm for nonlinear analysis. In the context of OpenSees, A is the effective tangent stiffness matrix, x is the vector of displacement increments, and b is the residual force vector. However, … Continue reading Failure to Solve

# Non-Fungible OpenSees

The latest spam to creep into the OpenSees universe has come from digital artists looking to sell their NFTs (non-fungible tokens) to members of the OpenSees Facebook group. The art is sold through the NFT marketplace, opensea.io, so I can see the confusion with OpenSees. Before the group admins remove the NFT posts, I ask … Continue reading Non-Fungible OpenSees

# RBOC for the Fall

I am teaching graduate level Structural Mechanics at Eastchester for the first time this fall. I will use the Fundamentals of Structural Mechanics book by Keith Hjelmstad. Expect some posts on how to use OpenSees to solve structural mechanics problems for beams, plates, shells, etc.I will do NaBloPoMo again this November. Writing a post every … Continue reading RBOC for the Fall

# Multiple-Support Excitation

Structural systems typically have different ground accelerations at supports separated by long distances. These systems can be a single structure such as a long span bridge or multiple structures in a region. While most OpenSees analyses use uniform excitation with effective earthquake forces applied to the dynamic DOFs of the model, the framework also accommodates … Continue reading Multiple-Support Excitation

# Making Sense Out of Concrete02

Those three extra parameters for Concrete02 are usually enough to make me stick with Concrete01. I struggle to come up with good values for the parameters $latex \lambda$, $latex f_t$, and $latex E_{ts}$ shown in the following image from the OpenSees Concrete02 wiki page. Image developed by Dr. Silvia Mazzoni The four compressive backbone parameters … Continue reading Making Sense Out of Concrete02