I receive a lot of questions about the pinching parameters for the HystereticMaterial in OpenSees. Despite the best of intentions, one-off responses to these queries often went unanswered. But now, with the blog, a one-off response has staying power. So, here goes. The HystereticMaterial dates back to the G3 days. Along with Steel01 and Concrete01, … Continue reading Hysteretic Pinching Parameters
Author: Positive Definite
Every Ending Is a New Beginning
Simulation of structural response to sequential hazards, e.g., fire following earthquake or tsunami following earthquake, is something OpenSees can handle. But suppose you want to look at different tsunami scenarios after a single earthquake. Tsunami loading occurs over a few seconds where the preceding earthquake lasted a minute or two. Do you want to repeat … Continue reading Every Ending Is a New Beginning
When a Deal Breaker Is Not a Deal Breaker
We often place too much emphasis on obtaining mathematically exact solutions for structural models. While it's important to obtain exact solutions, e.g., for element development and comparing softwares, it's not always necessary and definitely not always a deal breaker. The important thing is to know whether or not an exact solution is possible and the … Continue reading When a Deal Breaker Is Not a Deal Breaker
Uniaxial Multi-Tool
UniaxialMaterial models are the work horses of OpenSees. Originally developed for the truss element, these models have proliferated thanks to fiber section models. However, because they are simply scalar functions, UniaxialMaterial models can be used in several other contexts. The calling function knows the context, not the UniaxialMaterial model--it only provides an output for a … Continue reading Uniaxial Multi-Tool
OpenSees Fire v2.0
OpenSees modules for thermal loading and thermo-mechanical behavior were developed by Usmani et al in the early 2010s. This was the first foray for OpenSees outside its earthquake engineering comfort zone and highlighted the benefits of an open, collaborative software framework--an opportunity for the research community to share modeling methodologies, develop new applications, and ensure … Continue reading OpenSees Fire v2.0
A Little Secret About OpenSees Tcl
Putting load and fiber commands inside braces {} preceded by pattern and section commands, respectively, was a conscious choice in the early days of G3/OpenSees. The intent was to enforce the same scoping rules that Tcl uses for procedures, loops, and conditional statements; however, the braces and scoping were totally unnecessary. We scrapped the scoping … Continue reading A Little Secret About OpenSees Tcl
The Linear Algorithm Strikes Again
This post on the OpenSees message board reminded of another reason not to ever use the Linear algorithm, even when you have a linear model. Some elements need that second iteration in order to record all of their response. Not only shellMITC4 mentioned on the message board, but also the beloved forceBeamColumn. If you define … Continue reading The Linear Algorithm Strikes Again
Make Room for Storage
In a previous post, I showed how equation numberers can reduce the bandwidth of the tangent stiffness matrix. In addition to reducing the solution time for linear systems of equations, a smaller bandwidth reduces the data required to store the tangent stiffness matrix. To discuss matrix storage in this post, I'll use the frame model … Continue reading Make Room for Storage
OpenSees Thanksgiving
Happy Thanksgiving everyone! Even if you don't celebrate Thanksgiving, I'm thankful that you're here reading the blog. Last year's Thanksgiving post was a little preachy. This year, I simply want to reiterate that I'm thankful to have been a part of OpenSees from the beginning. Some exciting things are happening with OpenSees right now and … Continue reading OpenSees Thanksgiving
OpenSees Facebook Group
I've been answering questions on the OpenSees message board lately. Mostly responding with quick answers, nothing that requires me to download or copy/paste scripts to run locally. A friend suggested I drop in on the OpenSees Facebook group to answer some questions. The group has been around since 2008 and has over 3,000 members (not … Continue reading OpenSees Facebook Group