Nonlinear Site Amplification as Function of 30 m Shear Wave Velocity

Choi, Yoojoong; Stewart, Jonathan P.

doi:10.1193/1.1856535

Cited by 192 publications

(177 citation statements)

References 25 publications

(69 reference statements)

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“…The principal difference between b value trends in the two prior models is the significant dip between 0.1s and 1.0s in the simulation-based results (Walling et al 2008). Interestingly, the centrifuge data are more consistent with the relatively flat trend of the model derived from data (Choi and Stewart 2005). …”

Section: Spectral Amplification Of Ground Motionssupporting

confidence: 65%

Centrifuge Modeling Studies of Site Response in Soft Clay over Wide Strain Range

Afacan

Brandenberg

Stewart

2014

J. Geotech. Geoenviron. Eng.

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Centrifuge modeling studies of site response in soft clay over wide strain range Abstract: Centrifuge models of soft clay deposits were shaken with suites of earthquake ground motions to study site response over a wide strain range. The models were constructed in an innovative hinged-plate container to effectively reproduce one dimensional ground response boundary conditions. Dense sensor arrays facilitate back-calculation of modulus reduction and damping values that show modest misfits from empirical models. Low amplitude base motions produced nearly elastic response in which ground motions were amplified through the soil column and the fundamental site period was approximately 1.0s. High intensity base motions produced shear strains higher than 10%, mobilizing shear failure in clay at stresses larger than the undrained monotonic shear strength. We attribute these high mobilized stresses to rate effects, which should be considered in strength parameter selection for nonlinear analysis. This nonlinear response de-amplified short period spectral accelerations and lengthened the site period to 3.0s. The nonlinearity in spectral amplification is parameterized in a form used for site terms in ground motion prediction equations to provide empirical constraint unavailable from ground motion databases.

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Section: Spectral Amplification Of Ground Motionssupporting

confidence: 65%

Centrifuge Modeling Studies of Site Response in Soft Clay over Wide Strain Range

Afacan

Brandenberg

Stewart

2014

J. Geotech. Geoenviron. Eng.

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“…In this section, this variability is investigated by computing the spectral amplification at different periods for the alternative site-response methodologies at the three sites in the LA basin, and comparing results to the values suggested by parts 1 and 2 of BSSC (2001) and to recently published amplification factors for tectonically active regions (Choi and Stewart, 2005) for the corresponding site conditions (classes C, D, and E). Figure 19a-c depicts the variation of site amplification relative to the reference site (NEHRP BC boundary) PGA, evaluated by means of the linear elastic, equivalent-linear, and average nonlinear models for the Obregon Park (class C), La Cienega (class D), and Meloland (class E) sites, respectively.…”

Section: Site-amplification Factors In Seismic Design Codes and Attenmentioning

confidence: 99%

“…The amplification factors of Choi and Stewart (2005), which were derived based on 1828 recordings from 154 earthquakes, using recordings from worldwide shallow crustal earthquakes near active plate margins and excluding subduction and interplate events. In contrast to published studies by Boore and Atkinson (2006), Chiou and Youngs (2006) (http://peer.berkeley.edu/prod-ucts/ nga_project.html), and Campbell and Bozorgnia (2007), Choi and Stewart (2005) derived their factors as continuous functions of both PGA RO and V s30 , and they converted the reference site conditions to a consistent BC-boundary reference profile, which eliminates inconsistencies in the description of the reference soil profile as a source of divergence in the compared siteamplification factors illustrated in Figure 20. 3.…”

Section: Site-amplification Factors In Seismic Design Codes and Attenmentioning

confidence: 99%

Quantifying Nonlinearity Susceptibility via Site-Response Modeling Uncertainty at Three Sites in the Los Angeles Basin

Assimaki¹,

Li²,

Steidl³

et al. 2008

Bulletin of the Seismological Society of America

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The effects of near-surface soil stratigraphy on the amplitude and frequency content of ground motion are accounted for in most modern U.S. seismic design codes for building structures as a function of the soil conditions prevailing in the area of interest. Nonetheless, currently employed site-classification criteria do not adequately describe the nonlinearity susceptibility of soil formations, which prohibits the development of standardized procedures for the computationally efficient integration of nonlinear ground response analyses in broadband ground-motion simulations. In turn, the lack of a unified methodology for nonlinear site-response analyses affects both the prediction accuracy of site-specific ground-motion intensity measures and the evaluation of site-amplification factors when broadband simulations are used for the development of hybrid attenuation relations. In this article, we introduce a set of criteria for quantification of the nonlinearity susceptibility of soil profiles based on the site conditions and incident ground-motion characteristics, and we implement them to identify the least complex ground response prediction methodology required for the simulation of nonlinear site effects at three sites in the Los Angeles basin. The criteria are developed on the basis of a comprehensive nonlinear site-response modeling uncertainty analysis, which includes both detailed soil profile descriptions and statistical adequacy of ground-motion time histories. Approximate and incremental nonlinear models are implemented, and the limited site-response observations are initially compared to the ensemble site-response estimates. A suite of synthetic ground motions for rupture scenarios of weak, medium, and large magnitude events (M 3:5-7:5) is next generated, parametric studies are conducted for each fixed magnitude scenario by varying the source-to-site distance, and the variability introduced in ground-motion predictions is quantified for each nonlinear site-response methodology. A frequency index is developed to describe the frequency content of incident ground motion relative to the resonant frequencies of the soil profile, and this index is used in conjunction with the rock-outcrop acceleration peak amplitude (PGA RO ) to identify the site conditions and ground-motion characteristics where incremental nonlinear analyses should be employed in lieu of approximate methodologies. We show that the proposed intensity-frequency representation of ground motion may be implemented to describe the nonlinearity susceptibility of soil formations in broadband simulations by accounting both for the magnitude-distance-orientation characteristics of seismic motion and the profile stiffness characteristics. The synthetic ground-motion predictions are next used for the development of site-amplification factors for the alternative site-response methodologies, and the results are compared to published site factors of attenuation relations. For the site conditions investigated, currently established amplification fac...

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“…Ambraseys and Douglas [9] employed a linear function to indicate the site e ect. This type of classi cation leads to inaccurate results, especially for soft-clay-soil sites or saturated sandy sites, because nonlinearity is not considered in the site response, Choi and Stewart [18]. In other attenuation relations, the site condition is modeled by using a function with two linear and nonlinear components.…”

Section: Comparison With Previous Studies 81 Comparison With Nga Eqmentioning

confidence: 99%

“…The function recommended by Boore and Atkinson [17], which is slight modi cation of the site amplication given by Choi and Stewart [18], is adopted in this paper. These equations are applicable to 180 V s30 1300 m/s and should not be applied for very hard rock sites, i.e.…”

Section: Site Response Term (F Site )mentioning

confidence: 99%

Attenuation Relation for Near Field Shallow Crustal Earthquakes Using NGA-West Database with Mixed-Effect Model in Comparison with Attenuation Relations for Iran

Neam

Taghikhany

2017

Scientia Iranica

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Abstract. This study presents a new empirical equation for the estimation of horizontal strong ground motions caused by shallow crustal earthquakes. This model was developed empirically by regression of the database, which was used by the NGA-West2 GMPE developers with a fault rupture distance less than 60 kilometers. The data set consisted of corrected and processed accelerograms of 1545 strong-motion records of earthquakes between 5.2 and 7.9 Mw. The model was a function of earthquake magnitude, distance of source from site, local average shear wave velocity, nonlinear soil response, sediment depth, rupture dip, faulting mechanism, and hanging wall e ect. This equation was derived by a stable algorithm for regression analysis called mixed e ect model. The algorithm was used to develop PGA and PSA (T 1 ) for periods from 0.01 to 10.0 seconds. Major di erences between this model and the recently developed attenuation relations for the world and Iran were observed for large-magnitude ground motions, which were recorded at small-tomoderate distances from seismic source. The results showed that the near-eld a ected the predicted values, especially in soil sites. Moreover, comparison with the attenuation relations developed by Iranian data set con rmed that the equation in this region was sensitive more to distance than to other parameters.

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Nonlinear Site Amplification as Function of 30 m Shear Wave Velocity

Cited by 192 publications

References 25 publications

Centrifuge Modeling Studies of Site Response in Soft Clay over Wide Strain Range

Centrifuge Modeling Studies of Site Response in Soft Clay over Wide Strain Range

Quantifying Nonlinearity Susceptibility via Site-Response Modeling Uncertainty at Three Sites in the Los Angeles Basin

Attenuation Relation for Near Field Shallow Crustal Earthquakes Using NGA-West Database with Mixed-Effect Model in Comparison with Attenuation Relations for Iran

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