In a recent post, I pointed out that the LobattoBeamIntegration class uses only ten, instead of 16, significant figures for the locations and weights of the integration points. Those six missing digits made for a perfectly fine demonstration of how to use the isclose function for verification. But, in the bigger picture, omitting six significant … Continue reading Getting the Digits
Critical Buckling Loads via CBDI
Curvature-based displacement interpolation (CBDI) is a method of approximating the transverse deflection at each integration point, or section, of a force-based frame element in order to account for geometric nonlinearity within the basic system, i.e., "P-little-delta" effects. Neuenhofer and Filippou (1998) describe the complete CBDI formulation for force-based elements. But one piece of the formulation, … Continue reading Critical Buckling Loads via CBDI
OpenSeesing as if Readers Matter
I am always on the lookout for books on academic writing. So, over the summer, when I heard about Leonard Cassuto's Academic Writing as if Readers Matter ahead of its release, I set a reminder to order a copy when the book came out. https://www.amazon.com/Academic-Writing-Readers-Matter-Scholars/dp/0691263604 The book arrived in early October, but I haven't finished … Continue reading OpenSeesing as if Readers Matter
The Good, the Not So Bad, and the Full General
Just like shopping for a new refrigerator, picking a linear equation solver in OpenSees (via the system command) can lead to paralysis of choice. And while you can consult Consumer Reports for the pros and cons of refrigerators A, B, and C, the only way to figure out the pros and cons of OpenSees solvers … Continue reading The Good, the Not So Bad, and the Full General
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
Portwood Digital 