ABSTRACT
Forward engineering applications often use modulus reduction and damping ratio curves (MRD) to represent the non-linear response of the soil as a strain dependent equivalent-linear response. While a multitude of such models are available for the shear-modulus, G, only a handful of studies have attempted to constrain MRD models for the compressional-related constrained modulus, M. In this study, nonlinearity associated with the constrained modulus was studied using an extensive analysis of records from 27 KiK-net seismic stations. To represent the response of dry soil, stations with at least 10 m ground water depth (GWD) were analysed. Using frequency shifts, the modulus degradation of the horizontal (H), the vertical (V) and the vertical P-wave window (PV) components were characterized. Degradation models for the constrained modulus, for a coupled and uncoupled analysis with the shear component are suggested. We find that for PGA>0.1 g, the H component has 91% probability of developing non-linear response, while for the V and PV components it is only 55% and 43%, respectively. We further find that within those records in which nonlinearity was observed, the PGA threshold for H, V, and PV, is 0.1 g, 0.08 g, and 0.03 g, respectively. Finally, the differences we observe between the full vertical component and the extracted P-wave window suggest that the V component includes a combination of P and SV waves, implying that vertical site-response analysis should include both shear and compression-related soil properties.
Disclosure Statement
No potential conflict of interest was reported by the author(s).
Supplementary Material
Supplemental data for this article can be accessed online at https://doi.org/10.1080/13632469.2022.2120112