Author: Positive Definite

I definitely attempt to stay positive all the time. I have been involved in the development, maintenance, and growth of OpenSees since its early days. Recently, I've taken an interest in learning Python and improving my academic writing.

Hysteretic Pinching Parameters

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 →

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 →