Hysteretic Damping Correction and Its Effect on Non-Linear Site Response Analyses

Both of equivalent linear and non-linear site response analyses utilize soil dynamic properties expressed by strain amplitude dependent modulus reduction and damping ratio relations. Most of the non-linear site response methods use Masing rule to define the unloading and re-loading paths that results in overestimated hysteretic damping at large shear strain amplitude. In this paper, site response analyses of a soft clay site under very strong input motions at the rock base are performed using the equivalent linear approach (SHAKE analysis) and a non-linear approach (i.e. program FLAC with a user-defined soil model). A 'generalized Masing rule' was implemented in the user defined soil model to correct the hysteretic damping for the unloading and re-loading stress-strain loops to be consistent with the experimental damping. The non-linear site response analyses, we performed, indicate that, with the hysteretic damping correction, the computed surface acceleration and peak shear stress along the depth do not change significantly compared with those without hysteretic damping correction. But the induced peak shear strains in the soft layers are noticeably different between the case with hysteretic damping correction through the generalized Masing rule and that using the original Masing rule.