Two Node Link’s Awakening

The twoNodeLink, implemented by Andreas Schellenberg, is one of the lesser utilized general purpose elements in OpenSees. In simple terms, the twoNodeLink element is a zeroLength element with length. And the element is not dis-similar to the link elements you will find in SAP. Like the zeroLength element, the twoNodeLink element uses uncoupled uniaxial materials to define force-deformation response between two nodes where the deformation … Continue reading Two Node Link’s Awakening →

Eccentrically Loaded Bolt Groups with Bolt Hole Clearance

Standard bolt holes punched in steel elements are either 1/16 inch or 1/8 inch wider than the bolt diameter. Oversized bolt holes can have larger clearances in order to make fit-up easier. While the bolt hole clearance can affect the available strength of an eccentrically loaded bolt group, Tables 7-6 to 7-13 of the AISC … Continue reading Eccentrically Loaded Bolt Groups with Bolt Hole Clearance →

Flipping Rotation Axes

Zero length rotational springs are a popular approach to model concentrated plasticity in frame members. Although distributed plasticity formulations are not perfect either, the zero length concentrated plasticity approach has a number of issues: implicit plastic hinge length (at best, it's a unitless 1) and having to define equalDOF constraints. There's also the outcomes of … Continue reading Flipping Rotation Axes →

Eccentrically Loaded Bolt Groups

Tables 7-6 through 7-13 of the AISC Steel Manual contain values for C, the effective number of bolts that resist shear in eccentrically loaded bolt groups. For example, in a bolt group with three vertical rows of 4 bolts spaced s=3 inch with srow=3 inch row spacing and a load at $latex \theta$=30 degrees from … Continue reading Eccentrically Loaded Bolt Groups →

Switching Sides

Used for flexible supports and flexible connections, among other things, zero length elements are perhaps the most versatile modeling tools available in OpenSees. One of the confusing things about zero length elements is how to properly define asymmetric response. For example, with a bridge abutment, you want to ensure the zero length element correctly interprets … Continue reading Switching Sides →

Fuzzy Zero Length Logic

There's a few interpretations floating around regarding the length--real or implied--of zero length elements in OpenSees. So, I made a Twitter poll to assess popular opinion. https://twitter.com/mikusscott/status/1516085441895624705 Despite being an "easy" question, only 50% of respondents chose the correct answer. Like "When was the War of 1812?", the question gives it away--zero length elements have … Continue reading Fuzzy Zero Length Logic →