Inelastic Response of Extended Pile Shafts in Laterally Spreading Ground During Earthquakes-Article

Article

Pdf Summary

The study examines how earthquake-induced structural inertia and liquefaction-driven lateral spreading combine to affect reinforced-concrete extended pile shafts. The authors used two-dimensional nonlinear dynamic finite-element analyses in OpenSees, modeling soil behavior, pore-pressure generation, pile–soil interaction, and inelastic pile response. Forty ground motions and a range of soil, structural, and loading conditions were considered.<br /><br />Analyses compared the combined loading case with cases representing lateral spreading or inertia separately. Neither separate case, nor simply taking the larger of the two demands, reliably captured the combined response. Adding the separate demands gave a closer estimate, showing that interaction between the loads can govern pile-shaft performance.<br /><br />The study also compared the dynamic results with Caltrans equivalent static analysis (ESA) guidance. For the conditions examined, the ESA procedure underestimated displacement and ductility demands during liquefaction and lateral spreading. Conversely, its requirement that lateral-spreading moment alone remain below 20% of the shaft’s plastic moment capacity often indicated unacceptable performance even when displacement and curvature criteria suggested acceptable behavior.<br /><br />The authors conclude that design methods should account for the combined effects of inertia and lateral spreading rather than evaluate them independently. Because the comparisons covered a limited set of conditions and used a two-dimensional model, broader analyses and three-dimensional validation were identified as important next steps in developing improved ESA guidance.

Keywords

earthquake-induced inertia

liquefaction

lateral spreading

reinforced-concrete pile shafts

OpenSees

finite-element analysis

pile-soil interaction

dynamic analysis

Caltrans ESA

plastic moment capacity