Asymmetric ‘Newmark' sliding caused by motions containing severe ‘directivity' and ‘fling' pulses

Abstract

Sliding of a rigid mass supported on an inclined, seismically shaking plane serves as a conceptual and computational model for a variety of problems in geotechnical earthquake engineering. A series of parametric analyses are presented in the paper using as excitation numerous near-fault-recorded severe ground motions and idealised wavelets, bearing the effects of ‘forward-directivity' and ‘fling-step'. Using as key parameters the angle β of the sloping plane (mimicking the sliding surface), as well as the frequency content, intensity, nature and polarity of the excitation, the paper aims at developing a deeper insight into the mechanics of the asymmetric sliding process and the role of key parameters of the excitation. It is shown that ‘directivity' and ‘fling' affected motions containing long-period acceleration pulses and large velocity steps, are particularly ‘destructive' for the examined systems. The amount of accumulating slip on a steep slope is particularly sensitive to reversal of the polarity of excitation. With some special ground motions, in particular (such as the Sakarya and Yarimca accelerograms, both recorded 3 km from the surface expression of the North Anatolian Fault that ruptured in the 1999 Kocaeli earthquake), what might at first glance appear elusively as ‘small details' in the record may turn out to exert a profound influence on the magnitude of slippage – far outweighing the effects of peak acceleration, peak velocity and Arias intensity. The results are compiled in both dimensionless and dimensional charts, and compared with classical charts from the literature. Finally, it is shown that no convincingly robust correlation could exist between accumulated slip and the Arias intensity of excitation.