You Gotta Keep ’em Aggregated

The SectionAggregator was one of my few useful OpenSees ideas. This class gives a flexible way to combine, or aggregate, modes of force-deformation in a single section model. The idea for SectionAggregator came from the Decorator software design pattern, the same pattern from which so many UniaxialMaterial wrappers were spawned (here and here). In fact, … Continue reading You Gotta Keep ’em Aggregated

Fibers of Higher Dimensions

When we talk about fiber sections in OpenSees, we often refer to Bernoulli sections where each fiber is in a state of uniaxial stress. This approach captures axial-moment interaction, which is important for reinforced concrete columns, whose cross-sections are defined using patch and layer commands. Those same patch and layer commands can be used for … Continue reading Fibers of Higher Dimensions

The Fiber Content of OpenSees

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 in beam fibers, as well as fiber models for … Continue reading The Fiber Content of OpenSees

Torsion with Fiber Sections

I won't blog about every pull request to OpenSees on GitHub, but I will blog about pull requests that could affect backward compatibility of user scripts. Pull request #142 is one such case. It affects how torsion is added to fiber sections in three-dimensional models. The frame elements require torsional stiffness in order to prevent … Continue reading Torsion with Fiber Sections

Be More Specific than “Fiber Element”

I hear the term "fiber element" a lot, as in "We used fiber elements to model the response of this reinforced concrete moment frame". Usually, when people say something like this, they are referring to "force-based distributed plasticity frame elements with fiber-discretized cross sections". That is a mouthful. I can see the desire to shorten … Continue reading Be More Specific than “Fiber Element”