I know enough soil-structure interaction (SSI) to be dangerous. This means I'm no expert in the subject, only someone who is capable of describing an SSI modeling challenge. The subject of this challenge is the soil-bridge model shown below. The model is based on research by a former M.S. student and a couple colleagues in … Continue reading SSI Modeling Challenge
Author: Positive Definite
I am a professor of structural engineering at a land grant university in Eastchester, Pacific Northwest, US. I have been involved in the development, maintenance, and growth of OpenSees since its early days. Recently, I've taken an interest in learning Python and improving my academic writing.
There’s a Wrapper for That
Many publications describe software design patterns for reusing object-oriented software. The most widely read book on design patterns is so influential that it has its own Wikipedia page. In this book, the "Gang of Four" offers two guiding principles for software design patterns. The first principle is to program to an interface, not an implementation, … Continue reading There’s a Wrapper for That
Integration Points with Negative Weight
A colleague in Eastchester once told me that faculty have three, maybe four, good ideas over their career. In other words, a faculty member could have over a hundred papers, but there's only three or four underlying concepts. Perhaps it was "two, maybe three", but you get the point. Playing with integration points and weights, … Continue reading Integration Points with Negative Weight
Where Is Eastchester?
I often mention Eastchester in posts, referring to a conversation with "a colleague in Eastchester" or showing an example from "a class I teach in Eastchester". But where is Eastchester? You won't find it on any map of the US Pacific Northwest. Eastchester is the home of fictional Cascadia College in Bernard Malamud's novel A … Continue reading Where Is Eastchester?
Results of a New Challenge
After proposing a modeling challenge for linear-elastic analysis of a strongback frame, I proposed a second challenge for linear-elastic analysis of the Ziemian frame. There were eight participants in this challenge, an increase from five for the first challenge. Due to the light gravity loads on the frame, whether or not the analysis included self-weight … Continue reading Results of a New Challenge
Not Just a Modeling Term
Master/slave is common terminology to describe relationships in many technical fields, e.g., between tables in databases or between devices in control systems. The terminology also appears in finite element analysis where the response of one node controls the response of another node through constraints. However, this terminology is based on archaic relationships within our society. … Continue reading Not Just a Modeling Term
Handle Your Constraints with Care
Manipulating the nodal equilibrium equations is necessary to enforce constraints between degrees of freedom (DOFs) at two or more nodes in a structural model. These multi-point constraints arise from assumptions of axial and flexural rigidity of frame elements, e.g., rigid diaphragms, and also between two nodes at the same location where some of the DOFs … Continue reading Handle Your Constraints with Care
Gimme All Your Damping, All Your Mass and Stiffness Too
Just because OpenSees is open source does not mean it is a fully transparent box. This is mostly because documentation has lagged behind development. So, pessimists would say the box is semi-opaque while optimists would characterize it as semi-transparent. But a few parts of OpenSees are definitely housed in an opaque box. Take, for instance, … Continue reading Gimme All Your Damping, All Your Mass and Stiffness Too
Meshing for Column Loads
For material nonlinear analysis of frame models, you can improve the computed response by using more displacement-based elements or more integration points in a force-based element. The material nonlinearity occurs inside the basic system, also known as the natural system or the kernel. To capture geometric nonlinearity due to large displacements, you have to go … Continue reading Meshing for Column Loads
A New Challenge
The results from a previous modeling challenge were excellent with 100% of entries correct. But before we deep dive into the dark world of modeling nonlinear structural response, let's do one more challenge with linear analysis. The frame model shown below is UP50HA from a series of low-rise industrial structures whose reliability under gravity loading … Continue reading A New Challenge
