Recent Advances in Non-Linear Site Response Analysis

Studies of earthquakes over the last 50 years and the examination of dynamic soil behavior reveal that soil behavior is highly nonlinear and hysteretic even at small strains. Non-linear behavior of soils during a seismic event has a predominant role in current site response analysis. The pioneering work of H. B. Seed and I. M. Idriss during the late 1960’s introduced modern site response analysis techniques. Since then significant efforts have been made to more accurately represent the non-linear behavior of soils during earthquake loading. This paper reviews recent advances in the field of non-linear site response analysis with a focus on 1-D site response analysis commonly used in engineering practice. The paper describes developments of material models for both total and effective stress considerations as well as the challenges of capturing the measured small and large strain damping within these models. Finally, inverse analysis approaches are reviewed in which measurements from vertical arrays are employed to improve material models. This includes parametric and non-parametric system identification approaches as well as the use of Self Learning Simulations to extract the underlying dynamic soil behavior unconstrained by prior assumptions of soil behavior

Simplified Model for Small-Strain Nonlinearity and Strength in 1D Seismic Site Response Analysis

Commonly used simplified one-dimensional nonlinear seismic site response analyses employ constitutive models based on a variation of the hyperbolic model to represent the initial stress-strain backbone curve. Desirable features of the backbone curve include provision of (1) an initial shear modulus at zero shear strain, (2) a limiting shear stress at large shear strains, and (3) flexible control of the nonlinear behavior between those boundary conditions. Available hyperbolic models have combinations of two of these features. A new general quadratic/hyperbolic (GQ/H) model is developed from the bivariate quadratic equation to provide all desired features. Nonlinear behavior is controlled by a shear-strain-dependent curve-fitting function. The model's unload-reload rules and coupling with pore-water pressure generation are also presented. Several total-stress site response analyses are presented to demonstrate the performance of the GQ/H model relative to a commonly used hyperbolic model in which the maximum shear stress cannot be defined. The analyses show the importance of properly representing the maximum shear stress in the constitutive model because it may lead to underestimation or overestimation of the computed site response.ope