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문성우,Youssef M. A Hashash,박두희 대한토목학회 2017 KSCE Journal of Civil Engineering Vol.21 No.1
Integrated probabilistic seismic hazard and site response analysis procedure, denoted as 2014 PSHA-NL, are performed to derive probabilistic site coefficients of the Upper Mississippi Embayment (UME). The site coefficients are determined for upland and lowland profiles, and NEHRP site classes C, D, and E. The probabilistically derived coefficients are compatible with 2008 USGS hazard maps and account for the thickness of the embayment. Randomized soil profiles and four sets of pressure-dependent dynamic soil curves are used to account for the uncertainties in the dynamic soil properties. It is shown that NEHRP coefficients are only applicable for site class D soil columns less than 50 m in thickness. NEHRP coefficients greatly underestimate short-period site coefficient (Fa) for site class C profiles and overestimate Fa for site classes D and E exceeding 100 m in thickness. Long-period coefficient (Fv) is shown to have a higher depth-dependency compared to Fa. For site classes C and D, the calculated site coefficients are larger than NEHRP values for all soil columns exceeding 50 m. The pronounced depth-dependency and discrepancy with the NEHRP coefficients highlight the need to use UME specific site coefficients in assessing the seismic hazard in the embayment.
Rate-dependent soil behavior in seismic site response analysis
Park, Duhee,Hashash, Youssef M.A. Canadian Science Publishing 2008 Canadian geotechnical journal: Revue canadienne de Vol.45 No.4
<P> One-dimensional site response analysis is widely used in estimating local seismic site effects. The soil behavior in the analysis is often assumed to be independent of the rate of seismic loading. Laboratory test results, on the other hand, indicate that cyclic cohesive soil behavior is influenced by the rate of loading. Three models of rate-dependent dynamic soil behavior were derived based on available laboratory data. The models were implemented and evaluated in a modified one-dimensional equivalent linear site response analysis approach. Results show that rate-dependent shear modulus and damping can have a pronounced influence on propagated weak ground motion but a secondary influence on propagated strong motion. Rate dependence of the damping ratio has a greater impact on the computed response than rate dependence of the shear modulus. This paper highlights the relevance of the compatibility between frequencies at which dynamic soil properties are measured and their use in site response analysis. </P>