Nonlinear Site Response Analysis Research Articles

Effective input velocity and depth for deep and shallow sites for site response analysis

ABSTRACT Ground motion input layer depth and Vs are crucial parameters in computing representative surface amplification factor, especially for deep deposits where bedrock depth is unknown. For many soil sites, seismic bedrock depth is unknown and randomly assigning the input motion to any layer may result in bias response. The aim of this study is to understand the effect of input layer velocity or depth on surface response parameters. Further determining the appropriate layer for giving the input ground motion for reliable estimation of response parameters by carrying out detailed site-response analysis. For the analysis, surface and bedrock ground motion recordings from KiK-Net downhole are used. Total stress nonlinear site-response analysis has been carried out by varying the velocity and depth to input the ground motion recorded at the bottom most layer for deep and shallow profiles. Using linear mixed effect models on residuals calculated from recorded and predicted surface spectra, fixed bias and σ are calculated. Layer having Vs ≥ 1500 (150) m/s is suitable for capturing the surface amplification spectra for both deep and shallow deposits.

Development of Site Classification System and Seismic Site Coefficients for Korea

ABSTRACT The contemporary two-parameter-based site classification system of Korea, which is depth to bedrock and averaged shear wave velocity of soil deposits overlying the bedrock, has been reported to be ineffective in representing the unique amplification characteristics of shallow bedrock profiles. A new site classification scheme conditioned on site natural period and corresponding intensity-dependent seismic coefficients for Korean site conditions is proposed based on extensive one-dimensional non-linear site response analysis outputs. It is highlighted that the proposed site classification system and site coefficients coupled with a new elastic response spectrum considerably reduce the residuals with the computed site response analysis outputs.

Nonlinear site response analysis approach to investigate the effect of pore water pressure on liquefaction in Palu

On 28 September 2018, a M w 7.5 earthquake hit Donggala Regency, Indonesia province of central Sulawesi, resulting in extensive liquefaction, land subsidence, and flow slides. Extensive liquefaction is caused by an increased development of pore water pressure. During an earthquake, the development of pore water pressure (PWP) causes soil to become soft and potential liquefaction on loose sands. A PWP development model was combined with a generalized/Hyperbolic constitutive model (GQ/H+PWP) in a one-dimensional seismic site response to investigate pore water pressure development beneath the soil layer. This model provided reasonable estimates of pore water pressure increase and stress-strain role. Analysis was carried out for three boreholes in Balaroa, Petobo, and Jono Oge sites. The effective stress approach, nonlinear site response analysis was used to conduct a parametric study of soil profiles. The potential liquefaction at Balaroa and Petobo sites were 9 m and 10 meters in depth, respectively. With a groundwater level of 14 meters below the ground surface, the liquefaction potential in Jono Oge was 16-17 meters in depth. These results indicated that the liquefaction potential in Jono Oge was influenced by the infiltration of irrigation water from the surface which caused liquefaction to occur on the ground surface.

Effect of Soil Properties and Input Motion on Site Amplification Using Validated Nonlinear Soil Model

Three-dimensional (3-D) nonlinear site response analyses are conducted using finite element models of actual soil profiles from ten nuclear power plant (NPP) sites in the United States to investigate the effects of soil properties and input motions on site amplification. The modeling approach developed in this study combines several novel elements, such as 3-D analysis (including vertical motions), nonlinear inelastic behavior of soil (strain-dependent shear modulus reduction and hysteretic damping), formulation of nonreflecting boundary conditions at the base, and generation of realistic outcrop ground motions for specific sites. All these elements of the modeling approach are first validated using actual data from five earthquakes at three downhole array stations recorded in the Kiban-Kyoshin network (KiK-net), Japan. The same approach is then used to develop site models of ten NPP sites in the United States and corresponding ground motions that are spectrally matched to the site hazard spectra. Eight sets of three-component input motions are used in the study and are categorized on the basis of presence or absence of a near-field pulse in the seed ground motions used for spectral matching. It is found that all sites retain a definite site amplification function regardless of the input motion, provided that the seed motion is spectrally matched to the site hazard spectra. The magnitude of site amplification and frequencies at which they occur depend upon soil properties, particularly the shear wave velocity profile and the constitutive relationship (strain-dependent shear modulus reduction and hysteretic damping) of soil. Amplification of spectral acceleration in the vertical direction (up-down motion) is found to be just as much as, if not more than, the amplification in the horizontal direction. Peak shear strain is found to be about 20% larger for near-field motions compared to far-field motions whereas maximum horizontal site amplification for far-field motions is found to be consistently larger than that of near-field motions, even though the differences between the two remain within the scatter resulting from individual ground motions.

Assessment of Isparta Basin by Using 1D Nonlinear Site Response Analysis Approach; 1914 Burdur (Ms: 7.0) Earthquake Scenario

Depremlerin meydana getirdiği yapı hasarlarının sadece depremin fiziksel özelliklerinden değil aynı zamanda zeminin özelliklerine de bağlı olduğu bilinmektedir. Bu durum zemin tepkisinin kuvvetli yer hareketi öncesi belirlenmesini deprem mühendisliği ve sismolojinin ana hedeflerinden birisi haline getirmiştir. Bu çalışmada, belirlenen 24 noktada kayma dalgası (Vs) ve sondaj verileri kullanılarak Türkiye’nin en önemli tektonik elemanlarından birinin merkezinde yer alan Isparta ovasının zemin tepkisinin öngörülmesi hedeflenmiştir. Türkiye Bina Deprem Yönetmeliği (TBDY-2018) zemin sınıflama kriterlerine göre ZC ve ZD zemin grupları karakterize edilen çalışma alanında 1 boyutlu doğrusal olmayan zemin tepki analizi yaklaşımı DEEPSOIL programı kullanılarak gerçekleştirilmiştir. Mw:6.9 İrpinia kuvvetli yer hareketi kaydı kullanılarak yapılan çözümlemede çalışma alanının en büyük yer ivmesi (Pga) ve spektral ivme (Sa) dağılım haritası oluşturulmuştur. Çalışma alanında yüzeydeki Pga değerleri 0.28-0.41 g aralığında, maksimum Sa değerleri ise 0.77-1.82 g aralığında dağılım gösterdiği tespit edilmiştir. Ayrıca havza içerisinde birbirine dik iki kesit üzerinde Pga ve Vs30 arasındaki uyum irdelenmiştir. Elde edilen sonuçlar şehir merkezi ve yeni yapılaşma alanlarının yoğun olduğu Çünür bölgesinde zeminin kuvvetli yer hareketinin etkilerini önemli bir şekilde arttıracağını göstermiştir.

A wave propagation algorithm for nonlinear site response analysis of layered soil accounting for liquefaction

A constitutive model is developed for the ground response analysis of layered sites. The model is a one-dimensional version of Ta-Ger (2016) and involves critical state compatibility, anisotropic plastic flow rule and Bouc-Wen type hardening law. After being downgraded to the p-q stress space the model is reformulated to provide a unified framework of analysis for both drained and undrained loading conditions and for sand and clay. The calibration of the model parameters for sand is based on a procedure that targets to the optimum performance in both drained and undrained load conditions by simultaneously matching the response in terms of: (a) the cyclic resistance ratio curves as per the NCEER/NSF methodology, and (b) widely-used experimental shear modulus and damping ratio curves available in the literature. For the clay-like soil the calibration involves only the second step under the assumption of fully undrained conditions. The model is implemented through an explicit finite difference algorithm into an in-house computer code which performs integration of the wave equations to obtain the non-linear response of the soil. The accuracy of the algorithm is verified through comparison with analytical solutions for the amplification function of soil deposits with linearly increasing Vs, subjected to vertically propagating shear waves. It is then validated against experimental data from two centrifuge experiments. Finally, the records of the Port Island array from Kobe 1995 earthquake are employed to test the ability of the model to predict the observed response.

Site‐specific liquefaction fragility analysis: Cloud, stripe, and incremental approaches

AbstractThis article adapts a handful of procedures from performance‐based earthquake engineering for use in estimating the probability of liquefaction triggering. The resulting approach, defined as liquefaction fragility analysis (LFA), produces site‐specific fragility functions for liquefaction. These fragility functions incorporate site‐specific, system‐level effects not captured by existing, broader methods, but require more detailed knowledge of both the subsurface conditions and the seismic hazard at the site. LFA accounts for system‐level effects such as pore pressure migration, dynamic layer‐to‐layer interaction, and partial saturation to the extent that these phenomena can be captured in the constitutive models used in nonlinear site response analyses. Multiple approaches for selecting ground motions for LFA are discussed and illustrated using a case study of a site in Los Angeles, California. The computational expense of using LFA for probabilistic estimate of future liquefaction seismic performance is also discussed.

1D nonlinear site response analysis of the Isparta Basin (Southwestern Turkey) with surface wave (ReMi) and borehole data

This study presents a soil-response analysis of Isparta basin, is situated in the one of most important tectonic areas, using surface wave (ReMi™) and borehole data at 24 points. In the analysis, the nonlinear site response analysis approach was carried out using the DeepSoil software. The study area was characterized by C and D soil class according to NEHRP (National Earthquake Hazards Reduction Program) and TBEC-2018 (Turkish Building Earthquake Code-2018) soil classification criteria. For the modelling, the strong ground motion recordings of 6.9 Mw Irpinia and 6.4 Mw Dinar were used and the largest peak ground acceleration (PGA) and spectral acceleration (SA) maps of the study area were created. The Bdr-1914 model was made using Irpinia record, PGA values in the study area were determined in the range of 0.28–0.41 g and SA in the range of 0.77–1.82 g. In the Dnr-1995 model, the PGA values in the basin were found to be between 0.05–0.1 g and SA was within the range of 0.21–0.48 g. It was observed that the spectral accelerations on the surface, which significantly increased the effects of strong ground motion, particularly for Mw 6.9, near the city center and the Cunur area where new settlement areas were dense. The results indicate that ground specific design is required for construction in these areas, which are above the risk threshold in acceleration design spectra. At the same time, these results show the site response studies have critical importance and may make a significant contribution to the design of safe structures in the alluvial basins.

Prediction of different depth amplifications of deep soil sites for potential scenario earthquakes

Deep soil basin is one of the geographical features which significantly alter the response to earthquakes. Around the world, there are regions where bedrock is at a substantial depth upon which are different layers of soil. Larger depths of soil alter the response toward earthquakes and have been reported in the past. Indo-Gangetic Basin (IGB) of India is one of the seismically vulnerable deep soil basins of the Asian continent. The present paper attempts to study the site amplifications in IGB at the surface and different depths to understand the amplification behavior of the deep soil basins worldwide. Sixteen different probable scenario earthquakes are identified based on past seismic gaps, history and seismic studies and simulated at 270 sites covering whole deep soil region of the IGB. Representative depths of input motion, density, shear wave velocity, location of the water table, suitable shear modulus reduction and damping curves have been used. One-dimensional nonlinear site response analysis was carried out using DEEPSOIL. Peak ground acceleration (PGA), peak spectral acceleration (PSA), amplification factors using the ratio of zero period, peak spectral acceleration, site factors Fa and Fv as per the National Earthquake Hazards Reduction Programme (NEHRP) and spectral accelerations at specific periods of 0.2 and 1 s are calculated and deliberated at the surface and also at different layers up to 100 m depth. Maps for spatial variation in average and maximum values of amplification as well as site factors have been presented. Average values of FPGA, FPSA, Fa and Fv at the surface were found in the range of 1.16–7.94, 1.13–7.93, 1.43–7.89 and 2.11–7.51, respectively. Around 14% of sites in the IGB have amplification values at subsurface levels exceeding those at corresponding surface levels. Amplifications observed at the subsurface level are less than that of the surface for a considerable number of sites.

Influence of site conditions on seismic design parameters for foundations as determined via nonlinear site response analysis

Site conditions, including geotechnical properties and the geological setting, influence the near-surface response of strata subjected to seismic excitation. The geotechnical parameters required for the design of foundations include mass density (ρ), damping ratio (βs), shear wave velocity (Vs), and soil shear modulus (Gs). The values of the last three parameters are sensitive to the level of nonlinear strain induced in the strata due to seismic ground motion. In this study, the effect of variations in soil properties, such as plasticity index (PI), effective stress (σ′), over consolidation ratio (OCR), impedance contrast ratio (ICR) between the bedrock and the overlying strata, and depth of soil strata over bedrock (H), on seismic design parameters (βs, Vs, and Gs) was investigated for National Earthquake Hazards Reduction Program (NEHRP) site classes C and D, through 1D nonlinear seismic site response analysis. The Morris one-at-a-time (OAT) sensitivity analysis indicated that βs, Vs, and Gs were significantly influenced by variations in PI, while ICR affected βs more than it affected Vs and Gs. However, the influence of H on these parameters was less significant. It was also found that variations in soil properties influenced seismic design parameters in soil type D more significantly than in soil type C. Predictive relationships for βs, Vs, and Gs were derived based on the 1D seismic site response analysis and sensitivity analysis results. The βs, Vs, and Gs values obtained from the analysis were compared with the corresponding values in NEHRP to determine the similarities and differences between the two sets of values. The need to incorporate PI and ICR in the metrics for determining βs, Vs, and Gs for the seismic design of foundations was highlighted.

Non-Linear Site Response Analysis of Bangkok Subsoils Due to Earthquakes Triggered by Three Pagodas Fault

Non-Linear Site Response Analysis of Bangkok Subsoils Due to Earthquakes Triggered by Three Pagodas Fault

Simulation-based site amplification model for shallow bedrock sites in Korea

A new simulation-based site amplification model for shallow sites with thickness less than 30 m in Korea is developed. The site amplification model consists of linear and nonlinear components that are developed from one-dimensional linear and nonlinear site response analyses. A suite of measured shear wave velocity profiles is used to develop corresponding randomized profiles. A VS30 scaled linear amplification model and a model dependent on both VS30 and site period are developed. The proposed linear models compare well with the amplification equations developed for the western United States (WUS) at short periods but show a distinct curved bump between 0.1 and 0.5 s that corresponds to the range of site natural periods of shallow sites. The response at periods longer than 0.5 s is demonstrated to be lower than those of the WUS models. The functional form widely used in both WUS and central and eastern North America (CENA), for the nonlinear component of the site amplification model, is employed in this study. The slope of the proposed nonlinear component with respect to the input motion intensity is demonstrated to be higher than those of both the WUS and CENA models, particularly for soft sites with VS30 < 300 m/s and at periods shorter than 0.2 s. The nonlinear component deviates from the models for generic sites even at low ground motion intensities. The comparisons highlight the uniqueness of the amplification characteristics of shallow sites that a generic site amplification model is unable to capture.

A new effective stress method for nonlinear site response analyses

AbstractA generic loosely coupled effective stress method is presented in this article for one‐, two‐ and three‐ dimensional (1D, 2D and 3D) nonlinear site response analyses. In this method, the 1D non‐Masing hysteretic constitutive model of Chen et al (2020) is extended into 2D and 3D stress conditions, by presenting a clever generalized formulation of equivalent shear strain (γeq). The element‐level simulation tests show that the proposed algorithm of γeq is conceptually simple with high precision to capture the strain reversals under complex multidirectional shakings. The coupling between the cyclic stiffness degradation and the excess pore water pressure (EPWP) generation during irregular cyclic loadings is established using the proposed algorithm of γeq in conjunction with the Chen et al (2019a) EPWP generation model and the extended non‐Masing hysteretic constitutive model. The simulations of the undrained cyclic triaxial tests using the new effective stress method reproduce excellently the observed response of the saturated sand specimens, demonstrating the ability to represent the undrained behavior of liquefiable sands during uniform cyclic loadings. The new effective stress method is then used to simulate the response of a downhole array liquefied site in Japan, which shows an excellent agreement between the simulations and the recordings in both horizontal and vertical components of ground motions at different depths.

Nonlinear site response analysis by coupling scaled boundary finite element method and finite element method

Nonlinear site response analysis by coupling scaled boundary finite element method and finite element method

2D nonlinear site response analysis of shallow bedrock sites using integrated subsurface profiles

In this study, an attempt has been made to generate the subsurface profiles using integrated geophysical approach and a site-specific 2-D nonlinear site response analysis at shallow bedrock sites in Peninsular India. The site selected for the study is Tarapur, India in which three survey lines were selected for the sub-surface mapping. The subsurface profiling of these three locations was done by an integrated geophysical approach by carrying out Multichannel Analysis of Surface Waves - 2D survey, Ground Penetrating Radar survey, and conventional drilling borehole and measurement of Standard Penetration Test N values. Thirteen intraplate recordings from all around the world are selected for the site response analysis. The subsurface profiles generated by the integrated geophysical approaches are modeled in FLAC - 2D nonlinear module and site response parameters are estimated. Further 1D site response analyses are carried out at selected points in 2- D profiles using the program DEEPSOIL and the 2D site response results are compared. Results of site response analysis are expressed in terms of short-period amplification factor (Fc) and long period amplification factor (Fs) and the results show that the 2D geometry of sub-surface is more sensitive to the higher frequency content of ground motion especially for subsurface with more heterogeneities. Also, a parametric study has been done on a synthetic 2D profile to quantitatively evaluate the effect of different ground motion characteristics like amplitude and frequency content on 2D site response analysis. The parametric study shows that underground heterogeneity is very sensitive to the ground motions with high-frequency content and low amplitude.

1D Effective Stress Site Response Analysis; Using Stress Based Pore Pressure Model and Plasticity Model

The accumulated stress based porewater pressure (PWP) generation model is a simplified model using the concept of damage parameter. The only input of this PWP model is liquefaction resistance curve (CRR-N). The model is very useful since the CSR-N curves can be developed empirically from in-situ penetration tests measurements. In this research work the estimation of excess PWP development during seismic loading by using stress based PWP generation model is compared with a rigorous plasticity model. One dimensional (1D) effective stress nonlinear site response analyses were conducted in DEEPSOIL and Opensees using the stress based PWP model and PressureDependentMultiYield02 (PDMY2) model, respectively. The site response analysis were performed on a sand column 30 m in depth comprises of a low density liquefiable layer in between two dense non-liquefiable layers. Three bed rock outcropping motions with peak ground acceleration (PGA) level of 0.11 g, 0.124 g and 0.357 g were used as input motion in the analysis. The maximum ru profiles computed from the two models were compared and analyzed. The ru time histories at the center of the non-liquefiable layers and liquefiable layer were also compared. The comparisons revealed that the two models used in this study compute most comparable ru values. The computed ru is also found in line with density of soil and the PGA of the input ground motions where the ru increases with increase in the PGA and decreases with increasing density.

1D Effective Stress Site Response Analysis; Using Stress Based Pore Pressure Model and Plasticity Model

The accumulated stress based porewater pressure (PWP) generation model is a simplified model using the concept of damage parameter. The only input of this PWP model is liquefaction resistance curve (CRR-N). The model is very useful since the CSR-N curves can be developed empirically from in-situ penetration tests measurements. In this research work the estimation of excess PWP development during seismic loading by using stress based PWP generation model is compared with a rigorous plasticity model. One dimensional (1D) effective stress nonlinear site response analyses were conducted in DEEPSOIL and Opensees using the stress based PWP model and PressureDependentMultiYield02 (PDMY2) model, respectively. The site response analysis were performed on a sand column 30 m in depth comprises of a low density liquefiable layer in between two dense non-liquefiable layers. Three bed rock outcropping motions with peak ground acceleration (PGA) level of 0.11 g, 0.124 g and 0.357 g were used as input motion in the analysis. The maximum r u profiles computed from the two models were compared and analyzed. The r u time histories at the center of the non-liquefiable layers and liquefiable layer were also compared. The comparisons revealed that the two models used in this study compute most comparable r u values. The computed r u is also found in line with density of soil and the PGA of the input ground motions where the r u increases with increase in the PGA and decreases with increasing density.

1D Effective Stress Site Response Analysis; Using Stress Based Pore Pressure Model and Plasticity Model

The accumulated stress based porewater pressure (PWP) generation model is a simplified model using the concept of damage parameter. The only input of this PWP model is liquefaction resistance curve (CRR-N). The model is very useful since the CSR-N curves can be developed empirically from in-situ penetration tests measurements. In this research work the estimation of excess PWP development during seismic loading by using stress based PWP generation model is compared with a rigorous plasticity model. One dimensional (1D) effective stress nonlinear site response analyses were conducted in DEEPSOIL and Opensees using the stress based PWP model and PressureDependentMultiYield02 (PDMY2) model, respectively. The site response analysis were performed on a sand column 30 m in depth comprises of a low density liquefiable layer in between two dense non-liquefiable layers. Three bed rock outcropping motions with peak ground acceleration (PGA) level of 0.11 g, 0.124 g and 0.357 g were used as input motion in the analysis. The maximum r u profiles computed from the two models were compared and analyzed. The r u time histories at the center of the non-liquefiable layers and liquefiable layer were also compared. The comparisons revealed that the two models used in this study compute most comparable r u values. The computed r u is also found in line with density of soil and the PGA of the input ground motions where the r u increases with increase in the PGA and decreases with increasing density.

2D nonlinear site response analysis of typical stiff and soft soil sites at shallow bedrock region with low to medium seismicity

In this study, an attempt has been made to estimate 2D nonlinear seismic site response of a small scale basin on typical stiff and soft soil sites in Peninsular India (PI). Six survey sites were selected from three shallow bedrock regions such as Kalpakkam, Bangalore and Vizag for which subsurface profiles are generated at these locations using Multichannel Analysis of Surface Wave -2D (MASW-2D) method. The subsurface profiles generated are classified as stiff and soft sites based on average 30 m shear wave velocity and further used for the 2D nonlinear site response analysis using the commercial program FLAC -2D. Thirteen intraplate ground motions from all around the world are selected for the site response analysis based on seismicity of the region. Results of the site response analysis were expressed in terms of short-period amplification factor (Fc) and long period amplification factor (Fs) for the intraplate shallow bedrock region. The results show that the Fc gives higher values than Fs in the case of stiff soil and it is showing a reverse trend in the case of soft soil. The trend of Fc is becoming more complex than that of the Fs especially in the case of stiff soil sites. Also, the 2D site response results were compared with conventional 1D nonlinear site response results using the program DEEPSOIL and aggravation factors were generated. Further, a parametric study has been carried out to quantitatively evaluate the effect of amplitude of ground motion on 2D site response analysis. Parametric study results show that subsurface heterogeneity is very sensitive to the low amplitude of input motion, especially in the case of stiff soil sites.

Role of SSI on seismic performance of nuclear reactors: A case study for a UK nuclear site

The role of soil-structure interaction (SSI) on the risk of unacceptable performance of five non-structural components of a nuclear reactor is investigated through a representative case study consisting of a pressurized-water reactor sited at Holyhead, United Kingdom. The seismic hazard at the site is defined by a 10,000 years uniform hazard spectrum, and its corresponding design response spectrum computed for a target structural performance goal of 1 × 10−5. Nine hypothetical soil profiles, with shear wave velocities ranging from 300 m/s to 1,200 m/s, are considered. Non-linear site response analyses are performed to determine the input motion at the foundation level; seismic capacity and demand of the components are computed using response-history analyses. To obtain high-confidence performance estimates from a limited number of results, Monte-Carlo simulation is used to expand the seismic demand matrix. It is shown that the probability of unacceptable performance of the reactor is highly sensitive to SSI effects. Specifically, the beneficial effects induced by SSI on the seismic performance of the reactor are limited to models sited on stiffer soil deposits (ie, Vs ≥ 900 m/s), whereas, the median probability of unacceptable performance increases for medium-to-soft deposits.