Author: Michael H. Scott

I have been involved in the development, maintenance, and growth of OpenSees since its early days. I am interested in learning Python and improving my academic writing.

Two Fibers Explain So Much

In a previous post, I asked how well we can capture the moment-curvature response of a rectangular section with EPP material using different integration methods with two fibers. For flexural response, two is the minimum number of fibers necessary to satisfy section equilibrium--one fiber for tension, the other fiber for compression. The previous post showed … Continue reading Two Fibers Explain So Much →

Much Ado About Damping

I do not remember why I was searching the internet for "damping" a couple weeks ago, but I came across this document on constructing a Rayleigh damping matrix, $latex {\bf C}=\alpha {\bf M}+\beta {\bf K}$. But instead of taking the usual approach of specifying damping ratios for exactly two frequencies of vibration, the document describes … Continue reading Much Ado About Damping →

Two Fibers, Five Ways

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 →

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 →