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.

A Rigid Bar Walks Into a Bar

OpenSees has two rigidLink commands that enforce constraints between a primary node (pNode) and a secondary node (sNode). ops.rigidLink('-beam',pNode,sNode) ops.rigidLink('-bar',pNode,sNode) The beam option works well, enforcing linear kinematic constraints as if the two nodes were connected by a beam of infinite axial and flexural stiffness. The bar option should give constraints assuming only infinite axial … Continue reading A Rigid Bar Walks Into a Bar →

My Favorite Ternary Operation

Most native C++ operations are binary, taking two arguments, e.g., a + b, or unary, taking one argument, e.g., a++. But C++ (and many other languages) has a native "conditional operator", which is ternary, taking three arguments. Known simply as ?:, the conditional operator has the following syntax (condition) ? true_outcome : false_outcome; The conditional … Continue reading My Favorite Ternary Operation →

Shutting Off the Containment Unit

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 →

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 →