# SSI Modeling Challenge

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 Eastchester on earthquake-tsunami multi-hazard effects on transportation structures. The colleagues are still here, but the student went on to do a Ph.D. and post-doc in another US west coast college town that also has a Woodstock’s Pizza restaurant.

The column/shaft is a 1.1 m diameter reinforced concrete section and the soil is a dense sand with relative density $D_r=90\%$. You can find more details on the soil-bridge model here, but for this challenge, I’d like to keep the model simple. I don’t want variance in the results to be attributed to approximations of concrete stiffness.

So, let’s say the column/shaft is linear-elastic with modulus $E=25$ GPa. Also, let’s assume free field conditions in formulating the soil resistance and a pinned condition at the base of the shaft.

What is the horizontal displacement (units=mm) at the top of the column?

E-mail me your answer or post your answer in the comments section below by August 31. You don’t have to use OpenSees, but please let me know how you modeled the soil.

I look forward to your responses. I will share anonymized results in another post after the deadline.

## 3 thoughts on “SSI Modeling Challenge”

1. ZHU says:

need some soil properties, such as unit weight, internal friction angle.

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1. Hello ZHU,
My geotechnical consultant says relative density is all you need, i.e., you can make reasonable estimates of the unit weight and friction angle of sand from the relative density. What appears to be large variance to a structural engineer is low variance in the eyes of a geotechnical engineer 🙂
PD

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