Inelastic displacement ratios (IDRs) of nonlinear soil-structure interaction (SSI) systems located at sites with cohesive soils are investigated in this study. To capture the effects of inelastic cyclic behavior of the supporting soil, the Beam on Nonlinear Winkler Foundation (BNWF) model is used. The superstructure is modeled using an inelastic single-degree-of-freedom (SDOF) system model.Nonlinear SSI systems representing various combinations of unconfined compressive strengths and shear wave velocities are considered in the analysis. A set of strong ground motions recorded at sites with soft to stiff soils is used for considering the record-to-record variability of IDRs. It is observed that IDRs for nonlinear SSI systems are sensitive to the strength and the stiffness properties of both the soil and the structure. For the case of SSI systems on the top of cohesive soils, the compressive strength of the soil has a significant impact on the IDRs, which cannot be captured by considering only the shear wave velocity of the soil. Based on the results of nonlinear time-history analysis, a new equation is proposed for estimating the mean and the dispersion of IDRs of SSI systems depending on the characteristic properties of the supporting soil, dimensions of the foundation, and properties of the superstructure. A probabilistic framework is presented for the performance-based seismic design of SSI systems located at sites with cohesive soils.

Highlights:Graphical/Tabular Abstract  Soil-structure interaction in performance-based earthquake engineering  Assessment of nonlinear seismic displacement demand  Influence of soil-structure interaction on the displacement demands for systems on sites with cohesionless soilsIn the assessment of earthquake performance of structures, maximum displacement demand is considered as the main parameter. Inelastic displacement ratio is used in earthquake engineering for obtaining estimates of maximum displacement demand. Inelastic displacement ratio, CRSSI is defined as the ratio of peak inelastic displacement to the peak displacement of the equivalent linear elastic system. Displacement ratios for equivalent nonlinear single-degree-of-freedom systems located at sites with sandy soil conditions are investigated in this study. Figure A. Maximum elastic and inelastic displacements and the equivalent single-degree-of-freedom systemPurpose: Aim of this work is to assess the level of sensitivity of the displacement ratio to soil-structure interaction effects to the fundamental period of vibration of the superstructure, strength of soil and the strength reduction coefficient of the system. Theory and Methods:The "Beam-on Nonlinear-Winkler-Foundation" (BNWF) model is utilized to represent the effects of soil-structure interaction on the dynamic response. Seismic response of a range of systems that represent various super-structure and soil conditions, were computed by means of nonlinear time history analysis. In total, 10'800 analyzes were carried out using 54 records for capturing the ground motion record variability. Results:For the systems with short vibration periods (T<0.6s) and high strength reduction coefficients (R>3), it is observed that the displacement ratio is sensitive to the bearing capacity of the soil. It was observed that the displacement ratios are greater for the systems built on soils with low bearing capacity, compared to those on soils with high bearing capacity. Resulting displacement ratios are compared against those that are obtained using the existing methods. Conclusion:Results of the time history analyzes indicate that the mean inelastic displacement ratios are inversely correlated with the strength of the soil. In the case when the soil strength is low (qult = 180 kPa), a significant portion of the total displacement is due to deformation of the soil. On the otherhand, in the case of high soil strength (qult = 1080 kPa), the largest contribution to the total displacement of the system is due to deformations within the superstructure. Displacement [m] T ime, t [s] Linear Nonlinear d ssi in RSSI S C ) (   B K str M str Nonlinear soil springs h B Idealized superstructure model Foundation model Equivalent height Nonlinear flexural hinge Article Info ABSTRACT Research Article