A graduate student and I are developing an OpenSees model of the water tower described in this paper. Thankfully, the model is pretty straightforward, i.e., reproducible from what's written in the paper. The authors of the paper did a pushover analysis of the water tower using dynamic response to a "slow, ramped, horizontal ground acceleration … Continue reading Pushover with Constant Ground Jerk
Category: Structural Dynamics
Modal Participation Factors
Computing modal participation factors (yes, I know it's a misnomer) from an OpenSees model is straightforward if you define only nodal mass with no element mass. Examples are available online showing how to compute the factors in OpenSees using Tcl, but let's go over how to do it with OpenSeesPy. After you define your model … Continue reading Modal Participation Factors
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
Be Careful with Modal Damping
Modal damping is kind of the it-spell in the dark art that is modeling viscous damping in structures. Although modal damping is pretty straightforward, you should be aware of an important aspect of its implementation in OpenSees. The issue, which is described in section 9 of this paper, is that OpenSees assembles the dynamic tangent … Continue reading Be Careful with Modal Damping
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