Effects of Near-Fault Ground Shaking on Sliding Systems

A numerical study is presented for a rigid block supported through a Coulomb friction contact surface on a horizontal or an inclined plane, and subjected to horizontal or parallel excitation. The latter is described with idealized pulses and near-fault seismic records strongly influenced by forward-directivity or fling-step effects (from Northridge 1994, Kobe 1995, Kocaeli 1999, Chi-Chi 1999, Aegion 1995). In addition to the well known (ever since Newmark) dependence of the resulting block slippage on variables such as the peak base velocity, the peak base acceleration, and the critical acceleration ratio, our study has consistently and repeatedly revealed a profound sensitivity of both maximum and residual slippage on: 1 the (unpredictable) sequence and even the details of the pulses contained in the excitation, 2 the (also unpredictable) direction (+ or –) in which the shaking of an inclined plane is imposed. By contrast, the slippage is not affected to any measurable degree by even the strongest vertical components of the accelerograms! Moreover, the slippage is often poorly correlated with Arias Intensity of the base excitation. These findings contradict some of the prevailing beliefs that emanate from statistical correlation studies.