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SSI Modeling Challenge Results

Original Post - 02 Sep 2020 - Michael H. Scott

Visit Structural Analysis Is Simple on Substack.

After two modeling challenges (here and here) for the linear-elastic response of frame structures, I thought it would be a good idea to do a soil-structure interaction (SSI) modeling challenge.

I feared the large uncertainty of geotechnical engineering relative to structural engineering would stifle participation, but I received four entries. Three participants submitted a single displacement and the fourth gave a range of displacements based on a range of soil stiffness.

Below are the results. There are seven points (one each for three participants), plus four discrete values pulled from the range of displacements given by the fourth participant. The median displacement is 0.31 mm.

My geotechnical consultant for this challenge said the results look pretty good, then explained that “pretty good” means within reasonable bounds and of the same order of magnitude.

A perfectly reasonable lower bound on the displacement is the fixed-at-the-ground-surface, no SSI model (the structural engineer’s worldview). This 6.1 m long cantilever leads to a displacement of 0.042 mm, which is shown in the results above. A marginally reasonable upper bound is a fixed-at-the-bottom-of-the-pile, no SSI model. This 26.1 m long cantilever gives a 3.29 mm displacement.

All entries are within these bounds and are the same order of magnitude. So, good job everyone!