1,720,973 research outputs found
Numerical simulations of site response and seismic settlements at Kashiwazaki-Kariwa Nuclear Power Plant, Japan
Get PDFConstructed on the west coast of Japan, the Kashiwazaki-Kariwa Nuclear Power Plant was strongly shaken by Mw 6.6 Niigata-ken Chuetsu-oki earthquake in 2007. Significant seismic settlements were observed in dry sand deposits at both the free-field site and around the power plant structure components. These total and differential settlements were reported to be the main reasons for water and oil leakage, which eventually led to flooding and fire. This study focuses on three-dimensional, soil-porewater pressure coupled numerical modeling of multi-directional shear and volumetric response of Service Hall free-field site and Arahama Site on which the reactor and turbine buildings, as well as the transformer house are located using a newly developed soil-constitutive model in LS-DYNA. The Service Hall site consists of claystone overlain by loose sand whereas Arahama site has dense sand deposits on top of claystone. The comparison of measured and computed responses at the Service Hall vertical array site showed that the simulations captured the spectral responses. In addition, the simulation with multi-directional loading provided best estimates for seismic settlements and showed significant amount of settlements occurred in the dry sand deposits.
The free-field model was then extended to three-dimensional soil-structure interaction (SSI) model to investigate the seismic response of soil under and adjacent the Unit 1 reactor and Unit 3 turbine buildings at Arahama Site. The soil-structure interaction models successfully captured the measured response spectra at the base of Unit 1 reactor building and the surface response around Unit 3 turbine building, which was significantly greater than the surface response calculated from the simplified free-field simulations. Computed seismic settlements at the ground surface adjacent to the reactor, turbine building, and transformer house were consistent with field observations of ground subsidence, whereas the settlements of the structures themselves were negligible. These results demonstrate that the developed three-dimensional simulations of seismic soil-structure interaction provide reliable estimates of the potential effects of differential settlements which cannot be represented using free-field simplifications.Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2020-02-28 without embargo termsThe student, Alvin Bayudanto, accepted the attached license on 2019-12-03 at 15:22.The student, Alvin Bayudanto, submitted this Thesis for approval on 2019-12-03 at 15:38.This Thesis was approved for publication on 2019-12-04 at 15:07.DSpace SAF Submission Ingestion Package generated from Vireo submission #14673 on 2020-02-28 at 17:15:01Made available in DSpace on 2020-03-02T21:58:22Z (GMT). No. of bitstreams: 2
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Previous issue date: 2019-12-0
Numerical simulations of site response and seismic settlements at Kashiwazaki-Kariwa Nuclear Power Plant, Japan
No full textConstructed on the west coast of Japan, the Kashiwazaki-Kariwa Nuclear Power Plant was strongly shaken by Mw 6.6 Niigata-ken Chuetsu-oki earthquake in 2007. Significant seismic settlements were observed in dry sand deposits at both the free-field site and around the power plant structure components. These total and differential settlements were reported to be the main reasons for water and oil leakage, which eventually led to flooding and fire. This study focuses on three-dimensional, soil-porewater pressure coupled numerical modeling of multi-directional shear and volumetric response of Service Hall free-field site and Arahama Site on which the reactor and turbine buildings, as well as the transformer house are located using a newly developed soil-constitutive model in LS-DYNA. The Service Hall site consists of claystone overlain by loose sand whereas Arahama site has dense sand deposits on top of claystone. The comparison of measured and computed responses at the Service Hall vertical array site showed that the simulations captured the spectral responses. In addition, the simulation with multi-directional loading provided best estimates for seismic settlements and showed significant amount of settlements occurred in the dry sand deposits.
The free-field model was then extended to three-dimensional soil-structure interaction (SSI) model to investigate the seismic response of soil under and adjacent the Unit 1 reactor and Unit 3 turbine buildings at Arahama Site. The soil-structure interaction models successfully captured the measured response spectra at the base of Unit 1 reactor building and the surface response around Unit 3 turbine building, which was significantly greater than the surface response calculated from the simplified free-field simulations. Computed seismic settlements at the ground surface adjacent to the reactor, turbine building, and transformer house were consistent with field observations of ground subsidence, whereas the settlements of the structures themselves were negligible. These results demonstrate that the developed three-dimensional simulations of seismic soil-structure interaction provide reliable estimates of the potential effects of differential settlements which cannot be represented using free-field simplifications
Evaluation of cyclic behavior of dense sands under multidirectional loading using centrifuge tests
Get PDFThe seismic performance of nuclear power plant (NPP) structures constructed on compacted, coarse-grained soil depends on the soil’s cyclic shear stress – shear strain – volumetric strain response. NPPs founded on a thick deposit of dense coarse-grained soil may experience nontrivial settlements due to small, but accumulated volumetric strains during an earthquake. Studies that have investigated the seismic response of granular are primarily limited to unidirectional loading. However, since seismic events are multidirectional in nature, design based on unidirectional studies may lead to underestimation of vertical strains, and nontrivial settlements that can impact structures. While correlations to estimate vertical strains from drained and undrained cyclic element tests are available, they do not all explicitly incorporate multidirectional shaking. Moreover, typical drainage conditions in the field may be partially drained while shaking-induced vertical strains accumulate. This work forms a unique database of dynamic centrifuge “case-histories” that provide insight into the shear and volumetric response of dense coarse-grained soils under unidirectional and bidirectional loading under partially drained conditions. Dynamic centrifuge tests were performed on thick (up to 20m) layers of saturated dense Ottawa sand (D = 95%) with models representing both free-field and a soil-structure (near field) system excited using unidirectional and bidirectional historical broadband motions.
Free-field centrifuge experiments highlight that shear response in each orthogonal direction is not affected by multidirectionality. Thus, site shear response can be estimated for use in one-dimensional non-linear site response analysis. In contrast, centrifuge tests illustrated that volumetric strains (v) and excess porewater pressures (evaluated in terms of excess porewater pressure ratio, ru) are affected by multidirectionality irrespective of density, with the ratios of bidirectional to unidirectional v and ru ranging from 1 to 4. Consequently, multidirectional factors relationships for v and ru are proposed as a function of FSliq. Furthermore, Energy-based intensity measures (Arias and Housner intensities) provided nearly unique estimates of excess PWP and (v) for both 1D and 2D motions, indicating that they capture multi-directionality effects, while vectored peak accelerations and velocities (PGA and PGV) yielded different relationships for 1D and 2D motions.
A semi-empirical hyperbolic (GQ/H), simplified model based on ground motion intensity parameters (e.g., Housner Intensity), and shear wave velocity (Vs) is proposed to estimate vertical strains in dense coarse-grained soils under free field conditions. Comparison of GQ/H model predictions and estimates based on undrained cyclic shear tests indicated that the latter consistently overpredicts the measured settlements in the dense sand profiles. In contrast, the approach based on drained cyclic shear tests reasonably agrees with both measured settlements and GQ/H-v model. Further comparison of recorded near field settlements from centrifuge test data indicate that the (GQ/H) simplified free model underestimates settlements beneath the structures tested here.
Lastly, a semi-empirical near field model to estimate vertical strains beneath structures is proposed. This model also includes ground motion intensity measures to account for duration (e.g., Housner intensity) in conjunction with a rocking stiffness parameter (originally proposed by Gazetas 1991) derived from shear wave velocity Vs. The vertical strain model requires estimates of Housner Intensity by means of nonlinear site response analysis. The proposed vertical strain models reasonably capture free field and near field settlements on dense sands recorded in dynamic centrifuge tests.
The aforementioned two semi-empirical models are used in conjunction to estimate settlements of structures founded primarily on dense sands during shaking.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2020-05-01The student, Alfonso Cerna Diaz, accepted the attached license on 2018-04-17 at 14:57.The student, Alfonso Cerna Diaz, submitted this Dissertation for approval on 2018-04-17 at 15:02.This Dissertation was approved for publication on 2018-04-20 at 08:15.DSpace SAF Submission Ingestion Package generated from Vireo submission #12217 on 2018-08-31 at 17:27:46Made available in DSpace on 2018-09-04T20:47:11Z (GMT). No. of bitstreams: 2
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Previous issue date: 2018-04-20Embargo set by: Seth Robbins for item 107391
Lift date: 2020-09-04T20:47:38Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemEmbargo set by: Seth Robbins for item 107391
Lift date: 2020-09-04T20:50:11Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 107391 on 2020-09-05T09:15:20Z
Site response analysis using downhole array recordings during the March 2011 Tohoku, Japan, earthquake
No full textAn investigation of liquefied shear strength using novel centrifuge tests, direct simple shear tests, and field case histories
No full textRecent high-profile catastrophic ash pond and tailings dam failures, which have been classified as flow liquefaction failures, renewed interest in the mobilized shear strength during flow liquefaction failures, usually termed the liquefied shear strength, su(liq). Statistics indicate that although the number of failures and incidents at tailings storage facilities decreased in the past 30 years or so, the number of “very serious” and “serious” failures actually constituted an increasing percentage since 1960, and the average financial loss for each “very serious” failure was found to be at least $500 million. This trend in the mining and coal ash industries indicates an urgent need for safety improvement, which highly relies on the shear strength of the deposited material within the impoundment. To improve the understanding of the behavior of soils within a tailings or coal ash impoundment as well as other problematic soils and to better quantify the shear strength of the soil if liquefaction occurs, three research methodologies were adopted in this study: (1) field flow liquefaction failure back-analysis; (2) element-level direct simple shear testing; and (3) novel centrifuge modeling. Corresponding results were compared and discussed. Field cases of flow liquefaction provide valuable information for liquefied shear strength because those failures provide realistic estimates of su(liq). An updated database of liquefaction-induced flow failures (now totaling 71 cases) was compiled as part of this study, including 13 new cases identified and evaluated. Previously studied cases were reviewed and adjusted if needed to maintain consistency in the analyses for all 71 cases. Two predictive models for su(liq) based on field test indices – cone penetration test (CPT) tip resistance and standard penetration test (SPT) blow count, were developed using the best-quality cases analyzed using the most rigorous procedures. The predictive models developed in this study highlighted: (1) the importance of compressibility of the liquefied soil in the field; and (2) the relationship between su(liq) and pre-failure effective vertical stress might be slightly nonlinear. Direct simple shear (DSS) laboratory element tests under controlled drainage conditions performed were used to characterize the critical state properties of three nonplastic soils, including the one used in the centrifuge modeling. In addition, various strain rates were used in DSS tests to supplement the strain rate range used in the centrifuge modeling. These DSS tests indicated a negligible to minor strain rate effect. Moreover, various complicated loading scenarios were adopted in DSS tests to closely mimic the loadings experienced in the centrifuge modeling to provide insights for interpreting those centrifuge test results. A series of novel centrifuge tests, which involved pulling (at constant velocity) a thin metal plate (referred to as a coupon) horizontally through liquefied soil, were performed to mimic shearing along a critical slip surface in a flow liquefaction failure and to produce additional data pairs of su(liq) and CPT tip resistance. Porewater pressure along the coupon shear surface was directly measured using a miniature pressure transducer embedded in the coupon. With similar initial states, the variation of coupon velocity induced different degrees of dilation and led to two distinct shear surface porewater pressure responses. Potential void redistribution was identified for faster coupon pulls with a larger extent of dilation. Values of su(liq) were extracted from select coupon pulls where the shear-surface excess porewater pressure ratio ≥ 0.8. Coupon pull su(liq) generally were comparable to case history back-calculated su(liq) and exhibited a dependency on strain rate. Lastly, dimensionless mechanics-based parameters were investigated to interpret the physics of the liquefied soil. The adopted dimensionless parameters, Savage number, NSav, and dispersive-viscous ratio, Dv*, linked the behavior of liquefied soils at multiple scales – from element scale to centrifuge model scale to field scale. Specifically, NSav successfully explained the controversy regarding strain rate effects on su(critical) or su(liq) observed in laboratory element (including DSS tests in this study) and centrifuge tests. In addition, Dv* revealed that the shear strength of the liquefied soil, which resembled a neutrally buoyant mixture of solid grains and fluid, could increase linearly (i.e., a Bingham plastic model) or quadratically with the strain rate. The preliminary comparison of coupon pull su(liq) and case history back-calculated su(liq) suggested that the Bingham plastic model may capture the behavior of the liquefied soil in the field reasonably well. As a result, using the dimensionless parameters helped reconcile the soil mechanics interpretation and the fluid mechanics interpretation of the liquefied soil
Estimation of Non-Linear Seismic Site Effects for Deep Deposits of the Mississippi Embayment
Get PDFThis report describes the development of a new one-dimensional nonlinear site response model and application of the model in probabilistic hazard analysis of the Mississippi embayment (ME) for estimation of depth dependent site coefficients.is peer reviewedSubmitted by Jessica Vlna ([email protected]) on 2008-12-02T16:20:52Z
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Previous issue date: 2004-10National Science Foundation EEC-9701785published or submitted for publicatio
Shared memory parallelization for large scale 3D polyhedral particle simulations
Get PDFGranular materials such as sands, gravels, railroad ballast, and rock are inherently highly heterogeneous and anisotropic. While they are known as one of the most widely used materials in industry, their complex behaviors remain not fully understood. Particle-based numerical methods were introduced to account for complex particle interactions yet are computationally demanding. Significant algorithmic developments have been made to enhance the computational performance, nevertheless simulations with realistic particle shape are still computationally expensive due to its complex geometry.
In this study, novel parallel algorithms for polyhedral particle simulations were developed and implemented to reduce the computational cost. The parallelization study showed that the code achieved approximately 30 times speed-up with 48 cores on a LINUX machine. With this parallelized particle-based code, engineering applications were conducted: large-scale particle granular flow simulation, full-scale ballasted track simulations, and parametric study of angle of repose:
The code successfully captured the runout distances of dry granular flow. This novel approach extended the capability of simulation size up to 52 million 3D polyhedral particles.
In the ballast simulation, the simulations employed similar particle sizes and shapes of the ballast, as well as the full-scale geometry as the physical setup. The simulations successfully reproduced the displacement and vibration of ties in the experiment.
In the angle of repose simulation, the simulations investigated the effects of input parameters on microscopic particle interactions by measuring angle of repose. The simulations demonstrated the ability to capture self-organized criticality related to natural complex system by showing the distribution of sliding mass that followed a power law relationship.
The parallelized particle-based simulation extends the limits of application size by reducing computational cost. The parallelized code is successfully exploited for the study of granular material behaviors. The large-scale particle-based simulation contributes our understanding of complex behaviors of granular materials.Submission original under an indefinite embargo labeled 'Open Access'. The submission was exported from vireo on 2020-08-25 without embargo termsThe student, Eun Hyun Park, accepted the attached license on 2020-05-05 at 23:39.The student, Eun Hyun Park, submitted this Dissertation for approval on 2020-05-05 at 23:42.This Dissertation was approved for publication on 2020-05-08 at 12:05.DSpace SAF Submission Ingestion Package generated from Vireo submission #15236 on 2020-08-25 at 17:12:32Made available in DSpace on 2020-08-26T21:54:55Z (GMT). No. of bitstreams: 2
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Previous issue date: 2020-05-0
Evaluation of cyclic behavior of dense sands under multidirectional loading using centrifuge tests
No full textThe seismic performance of nuclear power plant (NPP) structures constructed on compacted, coarse-grained soil depends on the soil’s cyclic shear stress – shear strain – volumetric strain response. NPPs founded on a thick deposit of dense coarse-grained soil may experience nontrivial settlements due to small, but accumulated volumetric strains during an earthquake. Studies that have investigated the seismic response of granular are primarily limited to unidirectional loading. However, since seismic events are multidirectional in nature, design based on unidirectional studies may lead to underestimation of vertical strains, and nontrivial settlements that can impact structures. While correlations to estimate vertical strains from drained and undrained cyclic element tests are available, they do not all explicitly incorporate multidirectional shaking. Moreover, typical drainage conditions in the field may be partially drained while shaking-induced vertical strains accumulate. This work forms a unique database of dynamic centrifuge “case-histories” that provide insight into the shear and volumetric response of dense coarse-grained soils under unidirectional and bidirectional loading under partially drained conditions. Dynamic centrifuge tests were performed on thick (up to 20m) layers of saturated dense Ottawa sand (D = 95%) with models representing both free-field and a soil-structure (near field) system excited using unidirectional and bidirectional historical broadband motions.
Free-field centrifuge experiments highlight that shear response in each orthogonal direction is not affected by multidirectionality. Thus, site shear response can be estimated for use in one-dimensional non-linear site response analysis. In contrast, centrifuge tests illustrated that volumetric strains (v) and excess porewater pressures (evaluated in terms of excess porewater pressure ratio, ru) are affected by multidirectionality irrespective of density, with the ratios of bidirectional to unidirectional v and ru ranging from 1 to 4. Consequently, multidirectional factors relationships for v and ru are proposed as a function of FSliq. Furthermore, Energy-based intensity measures (Arias and Housner intensities) provided nearly unique estimates of excess PWP and (v) for both 1D and 2D motions, indicating that they capture multi-directionality effects, while vectored peak accelerations and velocities (PGA and PGV) yielded different relationships for 1D and 2D motions.
A semi-empirical hyperbolic (GQ/H), simplified model based on ground motion intensity parameters (e.g., Housner Intensity), and shear wave velocity (Vs) is proposed to estimate vertical strains in dense coarse-grained soils under free field conditions. Comparison of GQ/H model predictions and estimates based on undrained cyclic shear tests indicated that the latter consistently overpredicts the measured settlements in the dense sand profiles. In contrast, the approach based on drained cyclic shear tests reasonably agrees with both measured settlements and GQ/H-v model. Further comparison of recorded near field settlements from centrifuge test data indicate that the (GQ/H) simplified free model underestimates settlements beneath the structures tested here.
Lastly, a semi-empirical near field model to estimate vertical strains beneath structures is proposed. This model also includes ground motion intensity measures to account for duration (e.g., Housner intensity) in conjunction with a rocking stiffness parameter (originally proposed by Gazetas 1991) derived from shear wave velocity Vs. The vertical strain model requires estimates of Housner Intensity by means of nonlinear site response analysis. The proposed vertical strain models reasonably capture free field and near field settlements on dense sands recorded in dynamic centrifuge tests.
The aforementioned two semi-empirical models are used in conjunction to estimate settlements of structures founded primarily on dense sands during shaking.LimitedAuthor requested closed access (OA after 2yrs) in Vireo ETD syste
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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