Rate-dependent soil behavior in seismic site response analysis

One-dimensional site response analysis is widely used in estimating local seismic site effects. The soil behavior in the analysis is often assumed to be independent of the rate of seismic loading. Laboratory test results, on the other hand, indicate that cyclic cohesive soil behavior is influenced by the rate of loading. Three models of rate-dependent dynamic soil behavior were derived based on available laboratory data. The models were implemented and evaluated in a modified one-dimensional equivalent linear site response analysis approach. Results show that rate-dependent shear modulus and damping can have a pronounced influence on propagated weak ground motion but a secondary influence on propagated strong motion. Rate dependence of the damping ratio has a greater impact on the computed response than rate dependence of the shear modulus. This paper highlights the relevance of the compatibility between frequencies at which dynamic soil properties are measured and their use in site response analysis.