Nonlinear Soil Amplification Research Articles

Characterization of Site Amplification by a Parametric Study

ABSTRACT The reliability of V s30 and the performance of alternative time averaged shear wave velocities (V sz ) and shear wave travel times (T tz ) at various depths, z, were investigated for the estimation of site amplification and fundamental frequency (f 0) characterization by considering the linear and nonlinear soil behavior. The study revealed that alternative parameters performed better than V s30 and the best performing z parameters changed by switching from convex to concave theoretical profiles and by increasing ground motions. For a practical usage in site investigations, guidelines to estimate nonlinear soil amplification factor and fundamental frequency from the linear ones were presented.

Development of correlation between SPT-N value and shear wave velocity and estimation of non-linear seismic site effects for soft deposits in Kolkata city

ABSTRACT In the present paper, the site-specific response spectra at bedrock level are generated by deterministic seismic hazard analysis and soil amplification study for Kolkata (India) is performed. The site-specific bedrock spectra are obtained by enveloping 10 response spectra corresponding to 10 attenuation relationships with pga 0.104 g. Eighteen seismic downhole test data upto 50 m depth are collected from various sites in Kolkata, along with the SPT-N value profile. An empirical relationship between shear wave velocity and SPT-N value is proposed considering nonlinear power law for soft soil. The results of this study can be used for site response study of Kolkata. The average of Kolkata soil varies from 146 to 295 m/sec. As per NEHRP classification, the sites are classified as Class D and E. Nonlinear soil amplification study is conducted in all borehole locations and uncertainty of soil parameters, like shear wave velocity with plasticity of soil, are considered. A total of 1170 soil profiles are analyzed, and site-specific response spectrum is proposed. A maximum surface PGA of 0.18 g is obtained corresponding to 3.8 times amplification in peak spectrum. The proposed acceleration time history and the response spectra may be used for design and safety evaluation of infrastructures in Kolkata.

A Site Amplification Model for Crustal Earthquakes

A global dataset which is composed of more than 20,000 records is used to develop an empirical nonlinear soil amplification model for crustal earthquakes. The model also includes the deep soil effect. The soil nonlinearity is formulated in terms of input rock motion and soil stiffness. The input rock motion is defined by the pseudo-spectral acceleration at rock site condition (PSArock) which is also modified with between-event residual. Application of PSArock simplifies the usage of the site model by diminishing the need of using the period-dependent correlation coefficients in hazard studies. The soil stiffness is expressed by a Gompertz sigmoid function which restricts the nonlinear effects at both of the very soft soil sites and very stiff soil sites. In order to surpass the effect of low magnitude and long-distant recordings on soil nonlinearity, the nonlinear site coefficients are constrained by using a limited dataset. The coefficients of linear site scaling and deep soil effect are obtained with the full database. The period average of site-variability is found to be 0.43. The sigma decreases with decreasing the soil stiffness or increasing input rock motion. After employing residual analysis, the region-dependent correction coefficients for linear site scaling are also obtained.

Nonlinear Horizontal Site Amplification for Constraining the NGA-West2 GMPEs

The nonlinear soil amplification models developed by Walling et al. (2008) are revisited for three main reasons: (a) the simulation database on which the models were developed has been updated and extended, (b) two alternatives for the input shaking parameter—(PGA and Sa( T))—are explored, and (c) a constraint on the nonlinearity at long periods is removed. The model is based on site amplification factors, relative to a V S30 = 1;180 m/s site. Simulations included a wide range of soil profiles, shaking amplitudes and soil properties, from which only a subset was used herein. Finally, four models for the nonlinear site amplification are developed using two nonlinear material property models (peninsular range and EPRI) and two input-shaking parameters ( PGA1180 and Sa1180( T)). These results are intended for use by the NGA-West2 developers to constrain the nonlinear scaling of the site response for the horizontal ground motion models.

연약지반의 비선형성이 탄성 및 비탄성 지진응답스펙트럼에 미치는 영향

Inelastic seismic analysis is necessary for the seismic design due to the nonlinear behavior of a structure-soil system, and the importance of the performance based design considering the soil-structure interaction is recognized for the reasonable seismic design. In this study, elastic and inelastic seismic response analyses of a single degree of freedom system on the soft soil layer were peformed considering the nonlinearity of the soil for the 11 weak or moderate, and 5 strong earthquakes scaled to the nominal peak acceleration of 0.075g, 0.15g, 0.2g and 0.3g. Seismic response analyses for the structure-soil system were peformed in one step applying the earthquake motions to the bedrock In the frequency domain, using a pseudo 3-D dynamic analysis software. Study results indicate that it is necessary to consider the nonlinear soil-structure interaction effects and to perform the performance based seismic design for the various soil layers rather than to follow the routine procedures specified in the seismic design codes. Nonlinearity of the soft soil excited with the weak earthquakes also affected significantly to the elastic and inelastic responses due to the nonlinear soil amplification of the earthquake motions, and it was pronounced especially for the elastic ones.

비선형 연약지반을 고려한 약진에 의한 비탄성 응답스펙트럼

Seismic design codes developed taking into account the strong earthquakes may result in unnecessary economical loss in the low seismic area, and the importance of the performance based design considering the soil-structure interaction is recognized for the reasonable seismic design. In this study. elastic and inelastic seismic response analyses of a single degree of freedom system on the soft soil layer were performed considering the nonlinearity of the soil for the 1 weak earthquakes scaled to the nominal peak accelerations of 0.07g and 0.11g. The seismic response analyses were performed in one step applying the earthquake motions to the bedrock, utilizing a pseudo 3-D dynamic analysis software of the soil-structure system. The study results indicated that seismic response spectra of a system assuming the rigid base or the linear soil layer does not represent the true behavior of a structure-soil system, and it is necessary to take into account the nonlinear soil-structure interaction effects and to perform the performance based seismic design for the various soil layers, having different characteristics, rather than to follow the routine design procedures specified in the design codes for the reasonable seismic design. The nonlinearity of the soft soil excited with the weak seismic motions also affected significantly on the elastic and inelastic seismic response spectra of a system due to the nonlinear soil amplification of the earthquake motions, and it was pronounced especially for the elastic response spectra.

Seismic hazard model for loss estimation and risk management in Taiwan

We developed a seismic hazard model for Taiwan that integrates all available tectonic, seismicity, and seismic hazard information in the region to provide risk managers and engineers with a model they can use to estimate earthquake losses and manage seismic risk in Taiwan. The seismic hazard model is composed of two major components: a seismotectonic model and a ground-shaking model. The seismotectonic model incorporates earthquakes that are expected to occur on the Ryukyu and Manila subduction zones, on the intermediate-depth Wadati-Benioff seismicity zones, on the active crustal faults, and within seismotectonic provinces. The active crustal faults include the Chelungpu fault zone, the source of the damaging M W 7.6 Chi-Chi earthquake, and the Huangchi-Hsiaoyukeng fault zone that forms the western boundary of the Taipei Basin. The ground-shaking model uses both US, worldwide, and Taiwanese attenuation relations to provide robust estimates of peak ground acceleration and response spectral acceleration on a reference site condition for shallow crustal and subduction zone earthquakes. The ground shaking for other site conditions is obtained by applying a nonlinear soil-amplification factor defined in terms of the average shear-wave velocity in the top 30 m of the soil profile, consistent with the methodology used in the current US and proposed Taiwan building codes.

Simplified inverse stiffness design for nonlinear soil amplification

An efficient stiffness design method for building structures is proposed in which nonlinear soil amplification and soil–structure interaction are taken into account in terms of equivalent linearization. A sway-rocking shear building model with appropriate ground impedances derived from both finite-element analysis and the equivalent linearization technique is used as a simplified design model and super-structure stiffnesses satisfying a desired stiffness performance condition are determined for a ground-surface response spectrum. The ground-surface response spectrum is transformed from the design response spectrum defined at the upper surface level of the engineering bedrock via the equivalent linearization technique and the one-dimensional wave propagation theory. In the process of the super-structure stiffness design, an improved and advanced inverse formulation is developed which regards the fundamental natural frequency of the interaction model as a principal design parameter. The reliability and accuracy of the proposed stiffness design method are examined by a two-dimensional finite-element model. Inelastic response characteristics of the so-designed model are also investigated.

Nonlinear soil amplification: its corroboration in Taiwan : I. A. Beresnev, Kuo-Liang Wen & Yeong Tein Yeh, Bulletin — Seismological Society of America, 85(2), 1995, pp 496–515

Nonlinear soil amplification: its corroboration in Taiwan : I. A. Beresnev, Kuo-Liang Wen & Yeong Tein Yeh, Bulletin — Seismological Society of America, 85(2), 1995, pp 496–515

Nonlinear soil amplification inferred from downhole strong seismic motion data: Kuo-Liang Wen, I. A. Beresnev & Yeong Tein-Yeh, Geophysical Research Letters, 21(24), 1994, pp 2625–2628

Nonlinear soil amplification inferred from downhole strong seismic motion data: Kuo-Liang Wen, I. A. Beresnev & Yeong Tein-Yeh, Geophysical Research Letters, 21(24), 1994, pp 2625–2628

Nonlinear soil amplification: Its corroboration in Taiwan

Nonlinear ground response at two strong-motion arrays in Taiwan is studied using the spectral ratio technique. At the SMART1 array, we calculate the frequency-dependent soil amplification functions as a ratio of the spectra at alluvium to rock sites, and study their dependence on the excitation level. Hor- izontal components of shear waves are considered. We compare (1) the average spectral ratios on and strong motions, (2) the ratios for the mainshocks and aftershocks, and (3) the ratios for the strong shear waves and their coda. At the SMART1 array, weak motions have a peak horizontal acceleration (PHA) less than 30 Gal. Strong motions are in the range of 100 to 267 Gal. Comparison of the average weak- and strong-motion spectral ratios shows a significant deamplification of strong motion between 2 and 9 Hz, exceeding the error margin estimated by the standard deviations. The maximum deamplifi- cation occurs at approximately 6.5 Hz where the average weak-motion ampli- fication is 2.9 versus 0.40 in the strong motion. A similar pattern is exhibited by the ratios calculated for the mainshocks and the aftershocks, as well as for the shear waves and their coda. The spectral ratio calculated from a single re- alization of coda is identical to the average ratio obtained from many small earthquakes. At the SMART2, we analyze spectral ratios between the stations on Pleistocene terrace deposits and recent alluvium, which characterize the rel- ative response at these two types of sediments. Weak motion is PHA less than 13 Gal, while strong motion extends from 100 to 295 Gal. Strong-motion spec- tral ratios between terrace and alluvial sites are consistently reduced in the fre- quency range from -1 to 10 Hz, compared with the motion. This effect is insensitive to the variation in distance between stations from 7.9 to 11.4 km, as well as the azimuthal change of up to 80 ° in the station pair strike. We attribute the observed discrepancies between weak- and strong-motion ampli- fications to the differential nonlinear response occurring at terrace and alluvial sites. Our results document a significant nonlinear ground response at both ar- rays.

Nonlinear soil amplification inferred from downhole strong seismic motion data

Nonlinear seismic response of soil is studied by comparison of the frequency‐dependent soil amplification functions calculated on weak and strong motion. Amplifications are obtained by dividing Fourier amplitude spectra of acceleration at the ground surface by the spectra at the depths of 11 and 47 m in a borehole. Observed weak and strong motion spectral ratios are compared with those theoretically deduced from the one of the nonlinear soil models adopted in geotechnical engineering. Significant deamplification of the strong motion having PGA (peak ground acceleration) greater than 0.16 g, relative to the weak motion, is exhibited by the experimental ratios in the frequency range that is consistent with the model prediction. Existence of the different frequency bands, in which specific features of the nonlinear soil response are recognized in the theory, is also confirmed. These results give evidence of that nonlinear response can be observed at soft sedimentary sites from the real strong motion data.

Probabilistic seismic hazard and stochastic ground motions

Recent advances in probabilistic seismic hazard analysis and stochastic ground motion modelling are presented. First, an extended seismic hazard analysis is presented. It is based on the concept of hazard-consistent seismic parameters, and allows one to deal with multivariate decision problems related to seismic hazard. Engineering applications are developed on the generation of risk consistent earthquake motions and probability-based determination of specific scenario earthquakes. The second part deals with the evaluation of ground motion uncertainties and the development of their stochastic models. The topics include reduction of uncertainties with an increase in site information, nonlinear soil amplification, and application to closed-form solution for stochastic response spectra. The last part consists of a theoretical basis for the stochastic interpolation of ground motions that will be useful as a tool for postearthquake emergency operations. Developments of the theory of conditional random field constitute the main part of the paper.

Non-Linear Soil Amplification Identified Empirically from Strong Earthquake Ground Motions.

Strong earthquake ground motions are influenced remarkably by local soil conditions. Though various factors of local soil conditions contribute to the effect, the effect owing mainly to the stress-strain relationship of surface soils is discussed in this paper with the aid of statistical analyses. An empirical regression model is presented first to obtain separately the effects due to seismic source, propagation path of waves and local site conditions from strong-motion spectra observed at the ground surface. The model is extended so as to derive soil due to the material non-linearity of surface soils using the proportionality of soil strain to particle velocity and to lead to site-specific soil dependent on the motion level which is called non-linear soil amplification in this paper. The extended regression model is applied to 228 strong-motion earthquake records observed at 26 sites in Japan. The soil amplifications identified by the regression analysis show quite site-dependent and period-dependent characteristics. Although being derived purely based on a statistical technique, the soil amplifications have a compatible relation with the physical response function resulting from the S-wave theory. The comparison between the soil and their corresponding soil profiles reveals that the non-linearity of local site response is well correlated with the softness and formation of soils, particularly, with the N value distribution at each observation site.

A response surface technique for fuzzy—random evaluations of local seismic hazard

Local soil amplification is one of the main phenomena contributing to local seismic hazard and consequently to local seismic risk. It is influenced both by randomness and by fuzziness. This paper offers a general fuzzy—random formulation, applicable to nonlinear soil amplification studies and hence to evaluations of local seismic hazard. The results obtainable by probabilistic analysis and also those arrived at using fuzzy analysis can be considered as consequences of particularizations of this formulation. The treatment is rendered explicit by adapting the response surface technique to the problem, as this is advantageous in terms of computational economy.