Input ground motions for tall buildings with subterranean levels

Abstract

AbstractGround motion prediction equations and seismic hazard analyses are used to evaluate design‐basis ground motions that apply to a free‐field and ground surface condition. In this paper, we address the manner by which those motions can be utilized for the analysis and design of buildings with subterranean levels. Procedures for specifying ground motions in buildings that are utilized in current practice fail to account for kinematic interaction effects, which cause reductions of ground motion translation and the introduction of rocking for embedded foundations. Simple models that describe those effects (reduction of translation, introduction of rocking) for embedded rigid cylinders are reviewed. Those models are well validated by recordings from two nuclear reactor structures that have very stiff embedded foundations. Most building structures will not have foundations as stiff as those from the nuclear reactor structures, and hence the degree to which foundation flexibility might affect the motions of embedded foundations was investigated using data from appropriately instrumented buildings. Preliminary analysis of the data suggests that: (a) the foundations are not rigid and rigid body displacements and rotations of the foundation explain only 60–80% of the power of the motion at the ground level; (b) using available models for kinematic interaction of embedded foundations, translational motions at the ground level of the investigated sites are dominated by base translation, with relatively small contributions from base rocking; and (c) for the investigated buildings, base rocking from inertial interaction appears to be more significant in the frequency range of principal interest than base rocking from kinematic interaction. Copyright © 2007 John Wiley & Sons, Ltd.