Effective Incremental Ground Velocity for Estimating the Peak Sliding Displacement of Rigid Structures to Pulse-Like Earthquake Ground Motions

Abstract

A major consideration in the seismic design of unanchored tanks and equipment and sliding isolation systems is estimation of the peak sliding displacement, which is typically controlled by ground motions with near-fault directivity pulses. Closed-form solutions to the sliding response of a rigid block, subjected to an idealized acceleration pulse, demonstrate that the peak sliding displacement is primarily a function of the area under the acceleration pulse and the coefficient of sliding friction. The solution also shows that the displacement is not strongly dependent on the shape of the acceleration pulse. Based on these observations, an expression is developed to determine the peak sliding displacement as a function of peak acceleration of the ground motion pulse, the pulse duration, and the interface coefficient of friction. A simplified ground motion intensity parameter, termed the effective incremental ground velocity (EIGV), is then proposed to estimate the peak sliding displacement as a function of the ratio of the peak ground acceleration to the friction coefficient and the pulse duration. Comparisons to numerical solutions demonstrate that the EIGV provides a reliable estimate of peak sliding displacement for rigid structures subjected to pulse-like ground motions. EIGV is particularly effective for sliding systems with high-friction coefficients (greater than .1), where the sliding response is generally controlled by a single sliding excursion resulting from a dominant ground motion pulse.