Long Term Column Loading

Practically all analyses of reinforced concrete columns in OpenSees assume the loading is short term--concrete as strong as it was at 28 days out of the hopper. Depending on what you're doing, not accounting for long term load effects, i.e., concrete creep and shrinkage, may not be a big deal. But the effects of creep … Continue reading Long Term Column Loading →

Plate Rebar Material

Where fiber sections integrate stresses over two dimensions for beam-column line elements, fiber sections integrate stresses through only one dimension for shell elements. Either way, you're performing volume integrals, whether it's two dimensions in the section and one in the element or one dimension in the section and two in the element. The LayeredShellFiberSection, where … Continue reading Plate Rebar Material →

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 →

Concrete Zero

What is the depth of concrete uniaxial stress-strain models compared to the pinnacle that is Concrete23? No, it's not Concrete01--that's base camp for all the ConcreteXY that followed. The most basic uniaxial concrete model in OpenSees, "Concrete00" if you will, is elastic-no-tension, or ENTMaterial. As its name implies, the ENTMaterial response is elastic in compression … Continue reading Concrete Zero →

P-M Interaction by the Book

Find any indeterminate beam, frame, or truss problem from a structural analysis textbook, and you can make OpenSees solve it. But sometimes, replicating the basics is not so easy. Take, for instance, an axial-moment (P-M) interaction diagram of reinforced concrete (RC) sections. The typical approach advocated with OpenSees is to use repeated moment-curvature analyses over … Continue reading P-M Interaction by the Book →

Slender Things

Using fiber sections and the corotational geometric transformation is an easy way to simulate combined material and geometric nonlinearity in column members. A previous post examined this approach for steel columns where residual stresses play an important role in the axial load capacity. In this post, I will show the corotational mesh approach for non-sway … Continue reading Slender Things →

How to Record Fiber Response

Recording the response of a single fiber in a fiber section is a common ask. You will need to use an Element recorder, but what you can record in each fiber is defined in the UniaxialMaterial::setResponse() method. The most common option is 'stressStrain', which gives the fiber stress-strain response history. After setResponse() drills down to … Continue reading How to Record Fiber Response →

The Basics of Frame Element Localization

Those strain softening constitutive models we like to use for concrete can lead to material nonlinearity that isolates, or localizes, in a single element or single integration point of your model. The resulting global response becomes non-objective, non-unique, or mesh-dependent. The objective of this post is to show the localization problem then describe solutions that … Continue reading The Basics of Frame Element Localization →