I knew nothing about wood design until I started teaching it. Although there are accommodations for LRFD, which is all I learned as a student, wood design is entirely ASD, or allowable stress design. The required stress, f, determined from structural analysis for the controlling ASD load combination, must be less than the available stress, … Continue reading Glulam Volume Factor
Category: Programming
Section X
You can record section response in a frame element if you know the section number, or integration point, of the section whose response you would like to record. This is straightforward for distributed plasticity integration such as Lobatto or Legendre where section number 1 is at end I of the element and section number N … Continue reading Section X
No Exit
Have you ever seen OpenSees.exe vanish all of a sudden or received a "Kernel died" message when running OpenSeesPy in a Jupyter Notebook? The C++ exit() function is the likely culprit. Or a segmentation fault. But this post will focus on the exit() function. Some grepping and line counting reveals over 2,000 calls to exit() … Continue reading No Exit
Parameter Updates in the Loop
Besides visualization and writing output to files, there's some pretty useful things you can do during an OpenSees analysis. One of those things is updating model parameters. Before getting into parameter updating, it is worth showing that OpenSees analyses can be run one step at a time. Many examples online show a dynamic analysis, e.g., … Continue reading Parameter Updates in the Loop
How to Record Fiber Response
Recording the response of a single fiber in a fiber section is a common ask. You will need to use an Element recorder, but what you can record in each fiber is defined in the UniaxialMaterial::setResponse() method. The most common option is 'stressStrain', which gives the fiber stress-strain response history. After setResponse() drills down to … Continue reading How to Record Fiber Response
Polymorphic Pitfall
Polymorphism is what makes OpenSees, and other object-oriented software, flexible and extensible. With polymorphism, you can program to an interface, not an implementation. You see this approach all over OpenSees--elements don't care how materials compute stress and tangent (more here); integrators don't care how the elements form resisting force and tangent stiffness (more here); and … Continue reading Polymorphic Pitfall
Tcl as a Front End for Python
I know I'm not the only one who enjoys converting between scripting languages or between structural analysis programs. I've had fun writing bespoke Tcl middleware between OpenSees and MATLAB, but now OpenSeesPy makes all of that obsolete. But, let's say you have an OpenSees Tcl script that you'd like to run in OpenSeesPy. There's a … Continue reading Tcl as a Front End for Python
Wipe Out!
I am often reminded that what seems basic to me is not so obvious to others who use OpenSees. For example, the wipe command. What it does--and what it does not do--can be confusing. The wipe command clears out the entire OpenSees model domain (nodes, elements, materials, loads, etc.) and analysis options (algorithm, system, etc.). … Continue reading Wipe Out!
How Many Clicks Does It Take?
Coding single degree of freedom (SDF) response in order to generate earthquake response spectra is a rite of passage in earthquake engineering research and education. I wrote my first response spectrum in MATLAB. Nowadays, people are likely to use Python. To generate response spectra in OpenSees, you can create a simple one-dimensional model of SDF … Continue reading How Many Clicks Does It Take?
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
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