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
Could Not Invert Element Flexibility
Due to inversion of section stiffness to flexibility, then inversion of element flexibility to stiffness, the force-based frame element implementation in OpenSees is finicky, to say the least. A common error message spawned from the force-based element is "could not invert flexibility..." You will see the same message many times, but, ultimately, you will get … Continue reading Could Not Invert Element Flexibility
An Ode to Concrete23
You may know Trent Reznor as that Nine Inch Nails (NIN) guy who in 1994 released the controversial single "Closer" from the album The Downward Spiral. Alternative rock stations still play the radio edit of the song, where the verb in the chorus line is dubbed out. You may also know that Reznor had already … Continue reading An Ode to Concrete23
One and Only One
Two element formulations in OpenSees--forceBeamColumnCBDI and mixedBeamColumn--are capable of handling geometric nonlinearity within the basic system, i.e., P-little-delta effects. The CBDI formulation, described in Neuenhofer and Filippou (1998), approximates the transverse deflection using Lagrange polynomials fit through the curvature at each integration point. Due to the added computational expense and coding details, the forceBeamColumnCBDI element … Continue reading One and Only One
Section Integration
If we can use procedures in Tcl or Python to lay out fiber patches and layers for standard section types, e.g., doubly-reinforced RC sections and wide flange steel sections, then why do we need the SectionIntegration class? You cannot say that it is not useful to have commands that define fibers in terms of basic … Continue reading Section Integration
Portwood Digital 