Influence of the effective strain ratio on equivalent linear ground response simulation

The design of buildings and infrastructures in seismic areas has to account for site effects, as they dramatically affect the expected ground shaking. The equivalent linear approach is commonly adopted for the numerical simulation of seismic site response. This scheme models the nonlinear soil behaviour as a linear viscoelastic medium, characterized by strain-compatible secant shear modulus and damping ratio extracted as a function of an equivalent uniform strain, usually termed effective shear strain. The effective strain is computed as the product between the maximum shear strain and the effective strain ratio, which is a scaling factor conventionally equal to 0.65 or linearly increasing with the magnitude. However, the proposed values are the result of recommendations without a rigorous demonstration and their reliability has been questioned. This study investigates the influence of this parameter on a collection of 1-D ground models, which are subjected to a set of acceleration time histories recorded from earthquakes with different intensities. Models are generated from a database of real soil profiles through a stochastic procedure and they are representative of a broad variety of soil deposits of engineering interest. The study addresses the sensitivity of the predicted ground motion amplification to variations in the effective strain ratio, considering the role of soil deformability, ground motion characteristics, and the investigated amplification parameter. This study contributes towards a more robust prediction of ground motion amplification of soil deposits, enhancing the reliability of design in seismic areas