Inertia and Kinematic Soil-structure Interaction Foundation Design in Response to Seismic Events

Y.Y. Tay
EDG Consulting Pty. Ltd., Australia.

G. Carnero, A. Beall & R. E. May
WSP Australia Pty. Ltd., Australia.

ABSTRACT

In the field of earthquake engineering, structural response studies address the inertial loading of the superstructure that results in tower lateral, rotational and torsional movements. The swaying of a tower causes its pile foundations to move, where structural forces are transferred to the top of the piles. As a first approximation, the lateral loads of the tower are resisted by the upper portions of the piles, and overturning moments resisted by push–pull pile actions. In addition to inertia loading, kinematic loading due to seismic shear waves travelling up through a soil column from bedrock causes soil to move against piles, therefore generating additional pile lateral loads and moments along the pile lengths. This paper presents an approach undertaken for inertia and kinematic soil-structure interaction assessments of a tower in a seismic-sensitive area in the Pacific. The project site geology is complex, comprising rock formation that had been subjected to tectonic deformation, causing intense folding, faulting and the rock head dipping steeply by nearly 30 m over the tower footprint. As a result, 3-dimensional numerical modelling has been adopted for inertia soil-structure interaction assessment. For kinematic soil-pile interaction assessment, free-field movements were assessed one-dimensionally and then superimposed onto pile foundations based on pseudo-static analysis for the determination of pile actions. Pile actions from both inertia and kinematic loading were then combined for design.