Assessing Soil-Shaft Interaction at an Instrumented Bridge in California in Terms of Effects of Shaft Nonlinear Properties in Various Earthquake Scenarios-Paper

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This study evaluates soil–shaft interaction during earthquakes at the instrumented Hayward-I580/238 bridge in California. Using OpenSees, the authors refined earlier models by developing a three-dimensional nonlinear soil-column model to represent bidirectional shaking and an inelastic reinforced-concrete drilled-shaft model. The models were assessed using recorded motions and four earthquake scenarios, including hypothetical motions adjusted to represent shaking below, at, and above the site’s AASHTO-2009 design target.<br /><br />The recorded earthquakes were relatively weak, so soil and shaft responses remained largely elastic. Under these motions, one- and two-dimensional soil models produced similar results, as did elastic and inelastic shaft models. Under stronger scenarios, however, soil and shaft behavior became nonlinear. The one- and two-dimensional soil models then differed notably, showing that bidirectional effects matter when soil response is nonlinear. Likewise, the inelastic shaft model produced substantially different responses from the elastic model; the elastic model tended to overestimate the response under strong shaking.<br /><br />The findings show that accounting for nonlinear soil and shaft properties improves simulations of strong-earthquake behavior. The refined models provide a framework for interpreting instrumented bridge responses and informing seismic design of drilled shafts. The authors note that more detailed methods for generating site-specific earthquake scenarios and further validation would strengthen future analyses.

Keywords

soil-shaft interaction

earthquake response

Hayward-I580/238 bridge

OpenSees modeling

nonlinear soil model

reinforced-concrete drilled shaft

bidirectional shaking

AASHTO design target

instrumented bridge

seismic design