I occasionally go down rabbit holes of numerical integration. These trips led me to Gauss-Radau integration, all the element integration options available in OpenSees, and, recently, Chebyshev integration. The latest rabbit hole, described in this post, deals with different ways to integrate section moment-curvature response using only two fibers. Consider a rectangular cross-section with EPP … Continue reading Two Fibers, Five Ways
Verifying Will Never Be Easy
A previous post compared the natural periods computed by OpenSees for a relatively simple one-story, one-bay, elastic frame to published ETABS results. Many easy to make modeling choices (mass distribution, rigid joint offsets, relative stiffness, etc.) led to "incorrect" periods. The "correct" modeling choices gave periods from OpenSees that were very close to ETABS--close enough … Continue reading Verifying Will Never Be Easy
The Stiffness Matrix Isn’t Everything
After several deliveries of graduate level courses in linear and nonlinear structural analysis, I have started to think that we over-emphasize the stiffness matrix in linear structural analysis. And this emphasis can lead to conceptual difficulties in nonlinear structural analysis. The steps to a linear analysis are presented as: Form the stiffness matrix Form the … Continue reading The Stiffness Matrix Isn’t Everything
Start Over Again
This week is International Blog Delurking Week. If you read the blog but never comment, please say Hello in the Comments section below and let us know how you came across the blog. Don't be shy. Frequent and infrequent commenters are also welcome to say Hello and give their back stories. Now, on to important … Continue reading Start Over Again
More Solutions Than Problems
OpenSees has its share of problems: documentation is a work in progress; solid finite element analysis capabilities are not fully developed; benchmarking and verification don't happen too often; and volunteerism drives maintenance and support. Yeah, I know, what support? OpenSees has also generated--or, better yet, been used to generate--more than its fair share of solutions, … Continue reading More Solutions Than Problems
OpenSees Tcl to Python Converter
Although Python is a more popular programming language than Tcl, I suspect Tcl remains the most used language for OpenSees. Python is gaining ground though as it appeals to newer users of OpenSees. I don't have data to back any of this up. To help the transition from Tcl to Python, OpenSeesPy was designed to … Continue reading OpenSees Tcl to Python Converter
Three-Dimensional Meshing
Two previous posts showed how to use Minjie's meshing functions to create line meshes for beam-column elements and 2D meshes for solid elements. This post will complete the trilogy by showing how to make a 3D mesh for solid elements. The bar shown below is the same model used in the post on 2D meshing. … Continue reading Three-Dimensional Meshing
Glulam Volume Factor
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
Two Paths You Can Go By
I am confident we can use OpenSees to solve every truss, beam, and frame problem from any statics or structural analysis textbook as well as every single degree-of-freedom and rigid shear frame problem from a structural dynamics textbook. We can also solve any reasonable problem from a finite element textbook. My confidence starts to wane … Continue reading Two Paths You Can Go By
NaBloPoMo Recap
I made it through my second NaBloPoMo. 30 posts in November by strong equilibrium (one every day), not weak equilibrium (average one per day). Motivation bottomed out on November 18 when I squeaked out this post. I'm glad I managed to keep going. 15 posts contained technical information about OpenSees. The other 15 were some … Continue reading NaBloPoMo Recap