Hydrostatic Loading on a Wall

One of the simplest examples of fluid-structure interaction is hydrostatic loading on a beam, an analysis the PFEM in OpenSees should be able to handle. Suppose the right wall of the tank shown below is a 1.25 cm (1/2 inch) thick steel plate, which we can model with beam elements in two dimensions. The left … Continue reading Hydrostatic Loading on a Wall →

OpenSees Mandela Effect

The Mandela Effect refers to a belief that is widely held, but completely false. Examples, some of which are admittedly a stretch, range from common misspellings to frequently misquoted movie lines. The Mandela Effect applies to OpenSees as well. Along the lines of misspellings, there is a widely held belief that OpenSees is capitalized OpenSEES. … Continue reading OpenSees Mandela Effect →

Corotational Rigid Offsets

Unlike Linear and PDelta, rigid joint offsets are not an option for the Corotational geometric transformation in OpenSees. And the lack of corotational rigid offsets is not due to theoretical limitations, simply no one has taken the time to implement the equations. The two-dimensional case would not be terrible. But three-dimensional offsets? No thanks, not … Continue reading Corotational Rigid Offsets →

A Return to FORM

The structural reliability modules Terje Haukaas implemented in OpenSees comprised one of the last groups of commands to be ported from Tcl to Python. So, performing reliability analysis in OpenSeesPy has been slow to catch on. But the porting is done and there are some slight differences between Tcl and Python. This post shows basic … Continue reading A Return to FORM →

The Sound of “OpenSees”

The term "OpenSees" appears throughout this blog. Usually as a noun, referring to the Open System for Earthquake Engineering Simulation, and sometimes as a verb. Although an OpenSees homophone is rare for the blog, you may see sentences like the following in other contexts. I enjoy sailing the open seas. The open sea's calling my … Continue reading The Sound of “OpenSees” →

Plate Rebar Material

Where fiber sections integrate stresses over two dimensions for beam-column line elements, fiber sections integrate stresses through only one dimension for shell elements. Either way, you're performing volume integrals, whether it's two dimensions in the section and one in the element or one dimension in the section and two in the element. The LayeredShellFiberSection, where … Continue reading Plate Rebar Material →

Show Me Don’t Tell Me

If there's one thing this blog excels at, it's simple, minimal examples. Yeah, sometimes too minimal and other times too simple--or both. But, when I have a problem with OpenSees, I make a minimal example to be sure I understand the issue. Usually, the issue is me, not OpenSees. You say OpenSeesPy is 2-3 times … Continue reading Show Me Don’t Tell Me →

OpenSees Retractions

Citation cartels, peer-review rings, paper mills, and other schemes have eroded the integrity of scholarly publications. In some cases, articles can be retracted from journals; however, this outcome is rare. I set out to find if any OpenSees articles, i.e., articles that refer to OpenSees, have been retracted. Google Scholar is usually a good place … Continue reading OpenSees Retractions →

Is It Close Enough?

The locations and weights for Gauss-Lobatto beam integration, the de facto beam integration for force-based elements, are hard-coded in the OpenSees source code. For most cases in the LobattoBeamIntegration class, the locations and weights are written to only ten significant figures instead of 16 or more. Although I am certain that leaving six sig-figs on … Continue reading Is It Close Enough? →

A Load at a Fixed DOF

If you apply a nodal load in the direction of a fixed DOF, will you get a reaction? The answer depends on which structural analysis software you use. Let's see what happens in OpenSees with a minimal working example. All we need is one fixed node and an applied load, P. This is one of … Continue reading A Load at a Fixed DOF →