Documents disponibles écrits par cet auteur

Earth Dam on Liquefiable Foundation and Remediation: Numerical Simulation of Centrifuge Experiments / Yang, Zhaohui in Journal of engineering mechanics, Vol. 130 N°10 (Octobre 2004)

Public ISBD [article]  in Journal of engineering mechanics > Vol. 130 N°10 (Octobre 2004) . - 1168-1176 p. Titre : Earth Dam on Liquefiable Foundation and Remediation: Numerical Simulation of Centrifuge Experiments Titre original : Barrage de la Terre sur la Base et la Remédiation Liquéfiables : Simulation Numérique des Expériences de Centrifugeuse Type de document : texte imprimé Auteurs : Yang, Zhaohui, Auteur ; Ahmed Elgamal, Auteur ; Adalier, Korhan ; Sharp, Michael K. ; Ghanem, Roger G., Editeur scientifique Article en page(s) : 1168-1176 p. Note générale : Génie Mécanique Langues : Anglais (eng) Mots-clés : Dam  Earth  Dam  foundations  Liquefaction  Soil  compaction  Numerical  models  Earthquakes  Barrages  La  terre  Bases  de  barrage  Action  réparatrice  Liquéfaction  Tassement  de  sol  Modèles  numériques  Tremblements  de  terre Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : A series of four dynamic centrifuge model tests was performed to investigate the effect of foundation densification on the seismic performance of a zoned earth dam with a saturated sand foundation. In these experiments, thickness of the densified foundation layer was systematically increased, resulting in a comprehensive set of dam-foundation response data. Herein, Class-A and Class-B numerical simulations of these experiments are conducted using a two-phase (solid and fluid) fully coupled finite element code. This code incorporates a plasticity-based soil stress–strain model with the modeling parameters partially calibrated based on earlier studies. The physical and numerical models both indicate reduced deformations and increased crest accelerations with the increase in densified layer thickness. Overall, the differences between the computed and recorded dam displacements are under 50%. At most locations, the computed excess pore pressure and acceleration match the recorded counterparts reasonably well. Based on this study, directions for further improvement of the numerical model are suggested. Une série de quatre essais dynamiques sur maquette de centrifugeuse a été réalisée pour étudier l'effet du densification de base sur l'exécution séismique d'un barrage réparti en zones de la terre avec une base saturée de sable. Dans ces expériences, l'épaisseur du densified la couche de base a été systématiquement augmentée, ayant pour résultat un ensemble complet de données de réponse de base de barrage. Ci-dessus, des simulations numériques de la classe A et de la classe B de ces expériences sont conduites en utilisant (plein et liquide) un code fini entièrement couplé biphasé d'élément. Ce code incorpore un modèle basé plasticit de contrainte-tension de sol avec les paramètres modelants partiellement calibrés basés sur des études plus tôt. Les modèles physiques et numériques tous les deux indiquent que les déformations réduites et les accélérations accrues de crête avec l'augmentation de densified l'épaisseur de couche. De façon générale, les différences entre les déplacements calculés et enregistrés de barrage être au-dessous de 50%. À la plupart des endroits, le match excessif calculé de pression et d'accélération de pore les contre-parties enregistrées jaillissent raisonnablement. Basé sur cette étude, des directions pour davantage d'amélioration du modèle numérique sont suggérées. DEWEY : 620.1 ISSN : 0733-9399 [article] Earth Dam on Liquefiable Foundation and Remediation: Numerical Simulation of Centrifuge Experiments = Barrage de la Terre sur la Base et la Remédiation Liquéfiables : Simulation Numérique des Expériences de Centrifugeuse [texte imprimé] / Yang, Zhaohui, Auteur ; Ahmed Elgamal, Auteur ; Adalier, Korhan ; Sharp, Michael K. ; Ghanem, Roger G., Editeur scientifique . - 1168-1176 p. Génie Mécanique Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 130 N°10 (Octobre 2004) . - 1168-1176 p. Mots-clés : Dam  Earth  Dam  foundations  Liquefaction  Soil  compaction  Numerical  models  Earthquakes  Barrages  La  terre  Bases  de  barrage  Action  réparatrice  Liquéfaction  Tassement  de  sol  Modèles  numériques  Tremblements  de  terre Index. décimale : 620.1 Essais des matériaux. Défauts des matériaux. Protection des matériaux Résumé : A series of four dynamic centrifuge model tests was performed to investigate the effect of foundation densification on the seismic performance of a zoned earth dam with a saturated sand foundation. In these experiments, thickness of the densified foundation layer was systematically increased, resulting in a comprehensive set of dam-foundation response data. Herein, Class-A and Class-B numerical simulations of these experiments are conducted using a two-phase (solid and fluid) fully coupled finite element code. This code incorporates a plasticity-based soil stress–strain model with the modeling parameters partially calibrated based on earlier studies. The physical and numerical models both indicate reduced deformations and increased crest accelerations with the increase in densified layer thickness. Overall, the differences between the computed and recorded dam displacements are under 50%. At most locations, the computed excess pore pressure and acceleration match the recorded counterparts reasonably well. Based on this study, directions for further improvement of the numerical model are suggested. Une série de quatre essais dynamiques sur maquette de centrifugeuse a été réalisée pour étudier l'effet du densification de base sur l'exécution séismique d'un barrage réparti en zones de la terre avec une base saturée de sable. Dans ces expériences, l'épaisseur du densified la couche de base a été systématiquement augmentée, ayant pour résultat un ensemble complet de données de réponse de base de barrage. Ci-dessus, des simulations numériques de la classe A et de la classe B de ces expériences sont conduites en utilisant (plein et liquide) un code fini entièrement couplé biphasé d'élément. Ce code incorpore un modèle basé plasticit de contrainte-tension de sol avec les paramètres modelants partiellement calibrés basés sur des études plus tôt. Les modèles physiques et numériques tous les deux indiquent que les déformations réduites et les accélérations accrues de crête avec l'augmentation de densified l'épaisseur de couche. De façon générale, les différences entre les déplacements calculés et enregistrés de barrage être au-dessous de 50%. À la plupart des endroits, le match excessif calculé de pression et d'accélération de pore les contre-parties enregistrées jaillissent raisonnablement. Basé sur cette étude, des directions pour davantage d'amélioration du modèle numérique sont suggérées. DEWEY : 620.1 ISSN : 0733-9399

Large-scale passive earth pressure load-displacement tests and numerical simulation / Patrick Wilson in Journal of geotechnical and geoenvironmental engineering, Vol. 136 N° 12 (Décembre 2010) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 12 (Décembre 2010) . - pp. 1634-1643 Titre : Large-scale passive earth pressure load-displacement tests and numerical simulation Type de document : texte imprimé Auteurs : Patrick Wilson, Auteur ; Ahmed Elgamal, Auteur Année de publication : 2011 Article en page(s) : pp. 1634-1643 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Passive  pressure  Retaining  wall  Large-scale  tests  Soil-structure  interaction Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : Passive earth pressure is recorded in two different tests, using a 6.7-m long, 2.9-m wide soil container. In these tests, sand with 7% silt content is densely compacted behind a moveable test wall to a supported height of 1.68 m (5.5 ft). Lateral load is applied to the vertical reinforced concrete wall section, which displaces freely along with the adjacent backfill in the horizontal and vertical directions. The recorded passive resistance is found to increase until a peak is reached at a horizontal displacement of 2.7–3% of the supported backfill height, decreasing thereafter to a residual level. In this test configuration, a triangular failure wedge shape is observed, due to the low mobilized wall-soil friction. Backfill strength parameters are estimated based on this observed failure mechanism. From these estimates, along with triaxial and direct shear test data, theoretical predictions are compared with the measured passive resistance. Using the test data, a calibrated finite-element model is employed to produce additional load-displacement curves for a wider range of practical applications (e.g., potential bridge deck displacement during a strong earthquake). Hyperbolic model approximations of the load-displacement curves are also provided. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v136/i12/p1634_s1?isAuthorized=no [article] Large-scale passive earth pressure load-displacement tests and numerical simulation [texte imprimé] / Patrick Wilson, Auteur ; Ahmed Elgamal, Auteur . - 2011 . - pp. 1634-1643. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 12 (Décembre 2010) . - pp. 1634-1643 Mots-clés : Passive  pressure  Retaining  wall  Large-scale  tests  Soil-structure  interaction Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : Passive earth pressure is recorded in two different tests, using a 6.7-m long, 2.9-m wide soil container. In these tests, sand with 7% silt content is densely compacted behind a moveable test wall to a supported height of 1.68 m (5.5 ft). Lateral load is applied to the vertical reinforced concrete wall section, which displaces freely along with the adjacent backfill in the horizontal and vertical directions. The recorded passive resistance is found to increase until a peak is reached at a horizontal displacement of 2.7–3% of the supported backfill height, decreasing thereafter to a residual level. In this test configuration, a triangular failure wedge shape is observed, due to the low mobilized wall-soil friction. Backfill strength parameters are estimated based on this observed failure mechanism. From these estimates, along with triaxial and direct shear test data, theoretical predictions are compared with the measured passive resistance. Using the test data, a calibrated finite-element model is employed to produce additional load-displacement curves for a wider range of practical applications (e.g., potential bridge deck displacement during a strong earthquake). Hyperbolic model approximations of the load-displacement curves are also provided. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v136/i12/p1634_s1?isAuthorized=no

Mitigation of liquefaction-induced lateral deformation in a sloping stratum / Ahmed Elgamal in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 11 (Novembre 2009) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 11 (Novembre 2009) . - pp. 1672–1682 Titre : Mitigation of liquefaction-induced lateral deformation in a sloping stratum : three-dimensional numerical simulation Type de document : texte imprimé Auteurs : Ahmed Elgamal, Auteur ; Jinchi Lu, Auteur ; Davide Forcellini, Auteur Année de publication : 2009 Article en page(s) : pp. 1672–1682 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Soil  liquefactionStone  columnsSoil  dynamicsSlopesSoil  deformationEarthquake  engineeringThree-dimensional  modelsRemediation Résumé : Finite-element (FE) simulations are increasingly providing a versatile environment for conducting lateral ground deformation studies. In this environment, mitigation strategies may be assessed in order to achieve economical and effective solutions. On the basis of a systematic parametric study, three-dimensional FE simulations are conducted to evaluate mitigation by the stone column (SC) and the pile-pinning approaches. Mildly sloping saturated cohesionless strata are investigated under the action of an applied earthquake excitation. For that purpose, the open-source computational platform OpenSees is employed, through a robust user interface that simplifies the effort-intensive pre- and postprocessing phases. The extent of deployed remediation and effect of the installed SC permeability are investigated. The influence of mesh resolution is also addressed. Generally, SC remediation was found to be effective in reducing the sand stratum lateral deformation. For a similar stratum with permeability in the silt range, SC remediation was highly ineffective. In contrast, pile pinning appeared to be equally effective for the sand and silt strata permeability scenarios. Overall, the conducted study highlights the potential of computations for providing insights toward the process of defining a reliable remediation solution. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000137 [article] Mitigation of liquefaction-induced lateral deformation in a sloping stratum : three-dimensional numerical simulation [texte imprimé] / Ahmed Elgamal, Auteur ; Jinchi Lu, Auteur ; Davide Forcellini, Auteur . - 2009 . - pp. 1672–1682. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 11 (Novembre 2009) . - pp. 1672–1682 Mots-clés : Soil  liquefactionStone  columnsSoil  dynamicsSlopesSoil  deformationEarthquake  engineeringThree-dimensional  modelsRemediation Résumé : Finite-element (FE) simulations are increasingly providing a versatile environment for conducting lateral ground deformation studies. In this environment, mitigation strategies may be assessed in order to achieve economical and effective solutions. On the basis of a systematic parametric study, three-dimensional FE simulations are conducted to evaluate mitigation by the stone column (SC) and the pile-pinning approaches. Mildly sloping saturated cohesionless strata are investigated under the action of an applied earthquake excitation. For that purpose, the open-source computational platform OpenSees is employed, through a robust user interface that simplifies the effort-intensive pre- and postprocessing phases. The extent of deployed remediation and effect of the installed SC permeability are investigated. The influence of mesh resolution is also addressed. Generally, SC remediation was found to be effective in reducing the sand stratum lateral deformation. For a similar stratum with permeability in the silt range, SC remediation was highly ineffective. In contrast, pile pinning appeared to be equally effective for the sand and silt strata permeability scenarios. Overall, the conducted study highlights the potential of computations for providing insights toward the process of defining a reliable remediation solution. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000137

Shake table testing of a utility - scale wind turbine / Ian Prowell in Journal of engineering mechanics, Vol. 138 N° 7 (Juillet 2012) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 138 N° 7 (Juillet 2012) . - pp.900–909. Titre : Shake table testing of a utility - scale wind turbine Type de document : texte imprimé Auteurs : Ian Prowell, Auteur ; Chia-Ming Uang, Auteur ; Ahmed Elgamal, Auteur Année de publication : 2012 Article en page(s) : pp.900–909. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Renewable  energy  Green  energy  Earthquake  Seismic  Shake  table  Wind  turbine Résumé : Shake table tests were undertaken on a full-scale wind turbine (65-kW rated power, 22.6-m hub height, and 16-m rotor diameter) using the Network for Earthquake Engineering Simulation Large High Performance Outdoor Shake Table at the University of California, San Diego. Structural response characteristics and modal parameters are presented for base shaking imparted in two configurations, both parallel (configuration 1) and perpendicular (configuration 2) to the axis of rotation of the rotor. Results are summarized for a series of progressively stronger motions imparted in configuration 1, with analysis identifying damage sources leading to an overall loss in stiffness. Two sources of observed softening are identified and quantified: (1) degradation of grout at the tower base, and (2) loss of bolt torque at the connections between tower segments. Results showed that the two configurations had little difference in structural response and demand parameters. For the tested turbine, with appropriate consideration of boundary conditions and modal characteristics, linear theory for a single degree-of-freedom system can explain most of the observed dynamics. Although not significant for the tested turbine, it was observed that higher mode behavior may be important for large turbines. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EM.1943-7889.0000391 [article] Shake table testing of a utility - scale wind turbine [texte imprimé] / Ian Prowell, Auteur ; Chia-Ming Uang, Auteur ; Ahmed Elgamal, Auteur . - 2012 . - pp.900–909. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 138 N° 7 (Juillet 2012) . - pp.900–909. Mots-clés : Renewable  energy  Green  energy  Earthquake  Seismic  Shake  table  Wind  turbine Résumé : Shake table tests were undertaken on a full-scale wind turbine (65-kW rated power, 22.6-m hub height, and 16-m rotor diameter) using the Network for Earthquake Engineering Simulation Large High Performance Outdoor Shake Table at the University of California, San Diego. Structural response characteristics and modal parameters are presented for base shaking imparted in two configurations, both parallel (configuration 1) and perpendicular (configuration 2) to the axis of rotation of the rotor. Results are summarized for a series of progressively stronger motions imparted in configuration 1, with analysis identifying damage sources leading to an overall loss in stiffness. Two sources of observed softening are identified and quantified: (1) degradation of grout at the tower base, and (2) loss of bolt torque at the connections between tower segments. Results showed that the two configurations had little difference in structural response and demand parameters. For the tested turbine, with appropriate consideration of boundary conditions and modal characteristics, linear theory for a single degree-of-freedom system can explain most of the observed dynamics. Although not significant for the tested turbine, it was observed that higher mode behavior may be important for large turbines. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EM.1943-7889.0000391