Nonlinear coupled seismic sliding analysis of earth structures

Earthquake-induced sliding displacements of earth structures are generally evaluated using simplified sliding block analyses that do not accurately mo del the seismic response of the sliding mass nor the seismic forces along t he slide plane. The decoupled approximation introduced to capture each of t hese effects separately is generally believed to be conservative. However, recent studies using linear viscoelastic sliding mass models have revealed instances where the decoupled approximation is unconservative. In this pape r, a coupled analytical model that captures simultaneously the fully nonlin ear response of the sliding mass (necessary for intense motions) and the no nlinear stick-slip sliding response along the slide plane is presented. The proposed sliding model is validated against shaking table experiments of d eformable soil columns sliding down an inclined plane. The effect of slidin g on the response of earth structures is evaluated, and comparisons are mad e between sliding displacements calculated using coupled and decoupled anal ytical procedures with linear and nonlinear material properties. Nonlineari ty resulting from stick-slip episodes is often the dominant source of nonli nearity in this problem. The decoupled approximation was unconservative pri marily for intense ground motions for systems with low values of k(y), larg er values of k(y)/k(max), and high period ratios (T-a/T-m). Results indicat e that a decoupled analysis is adequate for earth structures that are not e xpected to experience intense, near-fault motions. However, for projects un dergoing intense, near-fault ground motions, a fully nonlinear, coupled sti ck-slip analysis is recommended.