Applicability of Bouc-Wen Model to Capture Asymmetric Behavior of Sand at High Cyclic Shear Strain

Seismic response evaluation of the site of interest subjected to a bedrock motion is one of the most important problems in earthquake geotechnical engineering. For one-dimensional (1D) nonlinear site response analysis in the time domain, a stress-strain relationship is inevitable. Most of the available stress-strain relationships provide greater hysteresis damping for medium to large strains compared with the damping values obtained in dynamic tests because hysteresis loops become progressively asymmetric with increasing shear strain. In the present study, a calibration scheme is proposed for a generalized Bouc-Wen model to capture the asymmetric behavior of soil at the high cyclic shear strain. The degradation parameters and pore-water pressure are expressed as a function of dissipated hysteretic energy. Particle swarm optimization (PSO) is used to identify the model parameters with the experimental data. The calibrated model could successfully capture the stiffness decay, loss of strength, excess pore-water pressure, and asymmetric behavior of saturated sand and silty sand for the high cyclic shear strain.