A Semi-Blind Kind of Contest

Contests where researchers and practitioners blindly predict the response of structural systems have produced some rather interesting results. And by "interesting", I mean "all over the place". So much so, that in an effort to protect the contestants, the contest organizers rarely make the results publicly available. Nonlinear structural analysis is hard though. Even with … Continue reading A Semi-Blind Kind of Contest

A Tale of Two Element Formulations

The question of whether to use the force-based or displacement-based formulation for material nonlinear frame analysis is one that comes up a lot. The answer depends on a few factors, mostly the material and the element length. To get a sense of the basic issues, I will compare the two element formulations with a numerical … Continue reading A Tale of Two Element Formulations

With or Without You

Citation-based metrics are like lottery tickets--they are not for investment purposes and should be used for entertainment only. Unfortunately, some promotion and tenure evaluators treat citation-based metrics like investment decisions. To aid in evaluation, citation-based metrics are readily available online, ranging from Web of Science, which indexes only archival publications, to Google Scholar, which indexes … Continue reading With or Without You

Better than Ideal Conditions

In simulating the nonlinear response of structural models, the Newton-Raphson algorithm converges quadratically as the iterations approach equilibrium at a time step. Quadratic convergence means the error at the current iteration is less than some constant times the square of the error at the previous iteration, e.g., the error is on the order of $latex … Continue reading Better than Ideal Conditions

Start with the Correct Static Resisting Force

Thanks to my involvement with OpenSees, I have been asked to review several manuscripts on nonlinear dynamic structural analysis. It's always wonderful to see what other researchers are up to and how they use OpenSees or other software to achieve their research objectives. A brief overview of the governing dynamic equilibrium equation, i.e., the equation … Continue reading Start with the Correct Static Resisting Force

Incompetence, Not Malice

"Never attribute to malice that which can be explained by incompetence" is a form of Hanlan's razor, an aphorism that explains many actions in academia and elsewhere. For example, we often perceive omissions of important details in published work as intentional acts to prevent reproduction of the research. In some cases, this is true, while … Continue reading Incompetence, Not Malice

The Fiber Content of OpenSees

OpenSees is pretty well known for its fiber sections. Although fiber sections are not unique to OpenSees, where else can you choose from 23 uniaxial concrete models and 18 uniaxial steel models to define a reinforced concrete section? There's also a handful of multiaxial material models that capture the interaction of axial and shear stresses … Continue reading The Fiber Content of OpenSees

OpenSees Shells by the Seashore

Other than state-of-the-art material and geometrically nonlinear frame element formulations, it's fair to say OpenSees is not known for its breadth of structural finite elements like quads, bricks, and shells. There are solid elements for geotechnical applications and fluid elements for fluid-structure interaction via the PFEM, but what's the story on shell elements in OpenSees? … Continue reading OpenSees Shells by the Seashore