Seismic Considerations for Extended Pile Foundations

Abstract

Current seismic design relies on built-in ductility at strategic locations to cope with any anticipated inelastic demand in the structure at the design level earthquake. A satisfactory response can be ensured by detailing the regions of inelastic deformation for ductility while non-ductile failures in other regions are protected by a hierarchy of strength between competing ductile and non-ductile failures. For bridge structures supported on extended pile-shafts, yielding may occur in the pile at some distance below the ground level depending on the soil condition. Unlike fixed-base columns, bending moment in extended pile-shafts is more gradual due to the distributed resistance of the soil. The lateral restraint provided by the surrounding soil enhances the ultimate compressive strain of the concrete, which in turn increases the ultimate curvature that can be tolerated by the pile. In this paper, a simple model suitable for estimating the lateral stiffness, lateral strength and ductility of the extended p...