Effect of The Shape of Cyclic Loading on Damping Ratio at Small Strains

Abstract

A series of 69 cyclic tests was conducted to study the damping properties of two reconstituted sands and three laboratory-made clays at small cyclic shear strain amplitudes γ c ~ 0.001-0.04%. A recently developed constant-volume equivalent-undrained direct simple shear device for small-strain testing was employed. The specific effect of the shape of cyclic strain-time history on the equivalent viscous damping ratio, λ, was investigated. The results show that λ can be significantly affected by the shape of the cyclic strain-time history because of the viscous nature of soil material response and the associated effects of creep and relaxation. As the shape of the cyclic strain-time history is changed from triangular to sinusoidal, and further from trapezoidal to square, λ at small strains may increase by a factor of two or more. The test results show that this effect was largest for clays, smaller for silty sand and negligible for clean sand.