If you've used OpenSees--even if you're a geotech--you've used the force-based element. When Remo implemented the force-based element, it was the only material nonlinear frame element available in OpenSees (G3 at the time); thus, the original name nonlinearBeamColumn. Only after a standard displacement-based frame element (dispBeamColumn) was added did we change the name from nonlinearBeamColumn … Continue reading Shutting Off the Containment Unit
Not Everything Should Be a Direct Translation
Like learning another language, not everything in OpenSees, and programming in general, is a direct translation from textbooks. Your mother tongue could be $latex {\bf x} = {\bf A}^{-1}{\bf b}$, but you should never invert the matrix then multiply. Instead, call an equation solver. For small matrices in OpenSees, use A.Solve(b, x) from the Matrix … Continue reading Not Everything Should Be a Direct Translation
Pruning OpenSees
Most OpenSees pull requests add to the code base. Often incremental and sometimes innovative, the new additions keep OpenSees moving forward, offering something for everyone. But it's rare that we remove code. Although it would be great to purge OpenSees of Concrete23 and all its unused variations, to prune code in frequently used OpenSees classes … Continue reading Pruning OpenSees
Modal and Stiffness Proportional Damping
OpenSees allows you to use both modal damping and stiffness proportional damping in a dynamic analysis. This combination of damping models is useful when you want to control damping in the low frequency modes and not let undamped high frequency response tarnish the analysis. Consider a simplified model of a 40 story building. The story … Continue reading Modal and Stiffness Proportional Damping
Eigenvalues of the Stiffness Matrix
Students are exposed to eigenvalues and eigenvectors a few times through their structural engineering education. After the math department's obligatory treatment to sophomores with definitions, characteristic polynomials, and toy matrices, two to three years pass before students see eigenanalysis again as first year graduate students: Structural dynamics - find natural modes of vibration of a … Continue reading Eigenvalues of the Stiffness Matrix
How to Use Block2D
Although the mesh commands outlined in previous posts (here and here) are more powerful, the block2D and block3D commands remain useful, especially if you want to use quadrilateral or brick elements. Ed C++ Love based the OpenSees block commands on the meshing functionality in FEAP. So, if you are familiar with FEAP, these commands should … Continue reading How to Use Block2D
Two Thousand Concrete23!
Happy new year! Although the long-awaited Concrete23 will not be released this year, I look forward to what lies ahead with OpenSees. Being the first full week of January, it's blog delurking time. Long time listeners, first time callers, say hello in the comments section and let everyone know what you're OpenSeesing in 2023.
Eccentrically Loaded Bolt Groups
Tables 7-6 through 7-13 of the AISC Steel Manual contain values for C, the effective number of bolts that resist shear in eccentrically loaded bolt groups. For example, in a bolt group with three vertical rows of 4 bolts spaced s=3 inch with srow=3 inch row spacing and a load at $latex \theta$=30 degrees from … Continue reading Eccentrically Loaded Bolt Groups
On OpenSeesing Well
Every modern motivational technique, strategy, and hack boils down to implementing William Zinsser's advice from On Writing Well. Decide what you want to do. Then decide to do it. Then do it. William Zinsser OpenSees is no different. Decide what you want to OpenSees. Then decide to OpenSees it. Then OpenSees it.
More Ado About Damping
Only a few years ago I realized that you do not have to use natural frequencies--you know, the ones you obtain from an eigenvalue analysis--to compute Rayleigh damping coefficients. This may not be news to some of you--I am often a little slow on the uptake. But I actually read a couple papers (here and … Continue reading More Ado About Damping
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