Beam With Hinges Interior Redux

When it was but a wee blog, I wrote a post expressing second thoughts on how I presented the elastic interior of the beamWithHinges element in Scott and Fenves (2006). The post had a lot of words, but no figures or examples. So, let's try again. Consider a simple span comprised of one beamWithHinges element, … Continue reading Beam With Hinges Interior Redux →

What Is a Good Penalty Number?

I often see the penalty constraint handler used with seemingly high penalty numbers like the following: ops.constraints('Penalty',1e18,1e18) I'm not sure why these specific numbers are used so often in scripts, but I suspect these values were used in an old example and have been passed down. And while the 1e18 values might have worked for … Continue reading What Is a Good Penalty Number? →

The Sensitivity Is in the Details

Although the Hardening and Steel01 uniaxial materials can be calibrated to give the same response, the DDM response sensitivity with respect to the same parameter can be different due to how the material models are implemented. Consider the truss model from a previous post on minimal DDM examples. The stress-strain response shows the elastoplastic tangent … Continue reading The Sensitivity Is in the Details →

Making a Point Load

The midterm exam in my graduate course on matrix methods of structural analysis was based on a linear-elastic, geometrically linear model of what is essentially Lee's frame. I asked the students to analyze the model using two elements and treat the point load as a member load instead of defining an additional node and applying … Continue reading Making a Point Load →

How to Apply Ground Motions in Multiple Directions

A common question is can I apply ground motions in more than one direction to a model in OpenSees? The answer is Yes. Let's say you have files for three ground motion recordings: gm000.txt, gm090.txt, and gmUP.txt. Define a time series for each ground motion, then associate each time series with a uniform excitation load … Continue reading How to Apply Ground Motions in Multiple Directions →

Will OpenSees Ever Be Un-Seen?

OpenSees contains sophisticated solution algorithms and element and constitutive models for simulating the nonlinear response of structural and geotechnical systems to natural and human-made hazards. But sometimes these sophisticated models are put to less than sophisticated use. I've been kicking this idea around in my head for a while, but what xykademiqz wrote in a … Continue reading Will OpenSees Ever Be Un-Seen? →

Rectangular Hollow Structural Sections

A hollow structural section (HSS) is manufactured from steel and is either rectangular, square, or circular. This post will address rectangular HSS, inclusive of square HSS. Round HSS is a little easier to define and will be the subject of another post. There are a couple options in OpenSees for defining material nonlinear rectangular HSS … Continue reading Rectangular Hollow Structural Sections →

Cheesy OpenSees Jokes

Although the technical aspects of OpenSees are fondue write about, from brine to brine, I come up with curdy OpenSees jokes. Many of the following jokes were inspired by this list. If OpenSees is a gouda name, what would be cheddar?OpenCheese Which programming language is cheddar than C++?C Sharp Why did the OpenSees analysis of … Continue reading Cheesy OpenSees Jokes →

It Takes Two

While it might be advantageous for some modes of response in some solid finite element formulations, using a single integration point in a frame element is not OK because the element needs to integrate quadratic polynomials--something you just can't do with one integration point. The result of using one integration point is generally pretty bad … Continue reading It Takes Two →

Losing Displacement Control

The DisplacementControl static integrator is commonly employed in nonlinear static pushover analysis. Unlike LoadControl, a displacement-controlled analysis is able to get past limit points of the model response. Displacement control requires a reference load pattern, a linear time series, and a nodal DOF to control during the analysis. This post will address ways to win … Continue reading Losing Displacement Control →