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