Documents disponibles écrits par cet auteur

Capacity, settlement, and energy dissipation of shallow footings subjected to rocking / Sivapalan Gajan in Journal of geotechnical and geoenvironmental engineering, Vol. 134 n°8 (Août 2008) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 134 n°8 (Août 2008) . - pp. 1129–1141 Titre : Capacity, settlement, and energy dissipation of shallow footings subjected to rocking Type de document : texte imprimé Auteurs : Sivapalan Gajan, Auteur ; Kutter, Bruce L., Auteur Année de publication : 2008 Article en page(s) : pp. 1129–1141 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Settlement  Energy  Dissipation  Footings  Shallow  foundations  Seismic  loads Résumé : The effectiveness of structural fuse mechanisms used to improve the performance of buildings during seismic loading depends on their capacity, ductility, energy dissipation, isolation, and self-centering characteristics. Although rocking shallow footings could also be designed to possess many of these desirable characteristics, current civil engineering practice often avoids nonlinear behavior of soil in design, due to the lack of confidence and knowledge about cyclic rocking. Several centrifuge experiments were conducted to study the rocking behavior of shallow footings, supported by sand and clay soil stratums, during slow lateral cyclic loading and dynamic shaking. The ratio of the footing area to the footing contact area required to support the applied vertical loads (A∕Ac) , related to the factor of safety with respect to vertical loading, is correlated with moment capacity, energy dissipation, and permanent settlement measured in centrifuge and 1 g model tests. Results show that a footing with large A∕Ac ratio (about 10) possesses a moment capacity that is insensitive to soil properties, does not suffer large permanent settlements, has a self-centering characteristic associated with uplift and gap closure, and dissipates seismic energy that corresponds to about 20% damping ratio. Thus, there is promise to use rocking footings in place of, or in combination with, structural base isolation and energy dissipation devices to improve the performance of the structure during seismic loading. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282008%29134%3A8%2811 [...] [article] Capacity, settlement, and energy dissipation of shallow footings subjected to rocking [texte imprimé] / Sivapalan Gajan, Auteur ; Kutter, Bruce L., Auteur . - 2008 . - pp. 1129–1141. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 134 n°8 (Août 2008) . - pp. 1129–1141 Mots-clés : Settlement  Energy  Dissipation  Footings  Shallow  foundations  Seismic  loads Résumé : The effectiveness of structural fuse mechanisms used to improve the performance of buildings during seismic loading depends on their capacity, ductility, energy dissipation, isolation, and self-centering characteristics. Although rocking shallow footings could also be designed to possess many of these desirable characteristics, current civil engineering practice often avoids nonlinear behavior of soil in design, due to the lack of confidence and knowledge about cyclic rocking. Several centrifuge experiments were conducted to study the rocking behavior of shallow footings, supported by sand and clay soil stratums, during slow lateral cyclic loading and dynamic shaking. The ratio of the footing area to the footing contact area required to support the applied vertical loads (A∕Ac) , related to the factor of safety with respect to vertical loading, is correlated with moment capacity, energy dissipation, and permanent settlement measured in centrifuge and 1 g model tests. Results show that a footing with large A∕Ac ratio (about 10) possesses a moment capacity that is insensitive to soil properties, does not suffer large permanent settlements, has a self-centering characteristic associated with uplift and gap closure, and dissipates seismic energy that corresponds to about 20% damping ratio. Thus, there is promise to use rocking footings in place of, or in combination with, structural base isolation and energy dissipation devices to improve the performance of the structure during seismic loading. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282008%29134%3A8%2811 [...]

Centrifuge modeling of bridge systems designed for rocking foundations / Lijun Deng in Journal of geotechnical and geoenvironmental engineering, Vol. 138 N° 3 (Mars 2012) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 138 N° 3 (Mars 2012) . - pp. 335-344 Titre : Centrifuge modeling of bridge systems designed for rocking foundations Type de document : texte imprimé Auteurs : Lijun Deng, Auteur ; Kutter, Bruce L., Auteur ; Sashi K. Kunnath, Auteur Année de publication : 2012 Article en page(s) : pp. 335-344 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Earthquake  Shallow  foundation  Rocking  Bridge  Centrifuge  modeling Résumé : In good soil conditions, spread footings for bridges are less expensive than deep foundations. Furthermore, rocking shallow foundations have some performance advantages over conventional fixed-base foundations; they can absorb some of the ductility demand that would typically be absorbed by the columns, and they have better recentering characteristics than conventional reinforced-concrete (RC) columns. Foundations designed for elastic behavior do not have these benefits of nonlinear soil-structure interaction. One potential disadvantage of rocking systems is that they can produce significant settlement in poor soil conditions. Centrifuge model tests were performed to account for the interaction between soil, footing, column, deck and abutments systems. Bridge systems with rocking foundations on good soil conditions are shown to perform well and settlements are small. An improved method for quantification of settlements is presented. The model tests are described in some detail. One of the important factors limiting the use of rocking foundations is the perception that they might tip over; experiments show that tipping instability is unlikely if the foundations are properly sized. In one experiment, a column for a system with large fixed-base foundation collapsed while the systems with smaller rocking foundations did not collapse. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v138/i3/p335_s1?isAuthorized=no [article] Centrifuge modeling of bridge systems designed for rocking foundations [texte imprimé] / Lijun Deng, Auteur ; Kutter, Bruce L., Auteur ; Sashi K. Kunnath, Auteur . - 2012 . - pp. 335-344. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 138 N° 3 (Mars 2012) . - pp. 335-344 Mots-clés : Earthquake  Shallow  foundation  Rocking  Bridge  Centrifuge  modeling Résumé : In good soil conditions, spread footings for bridges are less expensive than deep foundations. Furthermore, rocking shallow foundations have some performance advantages over conventional fixed-base foundations; they can absorb some of the ductility demand that would typically be absorbed by the columns, and they have better recentering characteristics than conventional reinforced-concrete (RC) columns. Foundations designed for elastic behavior do not have these benefits of nonlinear soil-structure interaction. One potential disadvantage of rocking systems is that they can produce significant settlement in poor soil conditions. Centrifuge model tests were performed to account for the interaction between soil, footing, column, deck and abutments systems. Bridge systems with rocking foundations on good soil conditions are shown to perform well and settlements are small. An improved method for quantification of settlements is presented. The model tests are described in some detail. One of the important factors limiting the use of rocking foundations is the perception that they might tip over; experiments show that tipping instability is unlikely if the foundations are properly sized. In one experiment, a column for a system with large fixed-base foundation collapsed while the systems with smaller rocking foundations did not collapse. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v138/i3/p335_s1?isAuthorized=no

Contact interface model for shallow foundations subjected to combined cyclic loading / Sivapalan Gajan in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N°3 (Mars 2009) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N°3 (Mars 2009) . - pp. 407–419 Titre : Contact interface model for shallow foundations subjected to combined cyclic loading Type de document : texte imprimé Auteurs : Sivapalan Gajan, Auteur ; Kutter, Bruce L., Auteur Année de publication : 2009 Article en page(s) : pp. 407–419 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Shallow  foundations  Ductility  Cyclic  loads  Combined  loads  Contact  pressure Résumé : It has been recognized that the ductility demands on a superstructure might be reduced by allowing rocking behavior and mobilization of the ultimate capacity of shallow foundations during seismic loading. However, the absence of practical reliable foundation modeling techniques to accurately design foundations with the desired capacity and energy dissipation characteristics and concerns about permanent deformations have hindered the use of nonlinear soil–foundation–structure interaction as a designed mechanism for improving performance of structural systems. This paper presents a new “contact interface model” that has been developed to provide nonlinear relations between cyclic loads and displacements of the footing–soil system during combined cyclic loading (vertical, shear, and moment). The rigid footing and the soil beneath the footing in the zone of influence, considered as a macroelement, are modeled by keeping track of the geometry of the soil surface beneath the footing, along with the kinematics of the footing–soil system, interaction diagrams in vertical, shear, and moment space, and the introduction of a parameter, critical contact area ratio (A∕Ac) ; the ratio of footing area (A) to the footing contact area required to support vertical and shear loads (Ac) . Several contact interface model simulations were carried out and the model simulations are compared with centrifuge model test results. Using only six user-defined model input parameters, the contact interface model is capable of capturing the essential features (load capacities, stiffness degradation, energy dissipation, and deformations) of shallow foundations subjected to combined cyclic loading. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282009%29135%3A3%2840 [...] [article] Contact interface model for shallow foundations subjected to combined cyclic loading [texte imprimé] / Sivapalan Gajan, Auteur ; Kutter, Bruce L., Auteur . - 2009 . - pp. 407–419. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N°3 (Mars 2009) . - pp. 407–419 Mots-clés : Shallow  foundations  Ductility  Cyclic  loads  Combined  loads  Contact  pressure Résumé : It has been recognized that the ductility demands on a superstructure might be reduced by allowing rocking behavior and mobilization of the ultimate capacity of shallow foundations during seismic loading. However, the absence of practical reliable foundation modeling techniques to accurately design foundations with the desired capacity and energy dissipation characteristics and concerns about permanent deformations have hindered the use of nonlinear soil–foundation–structure interaction as a designed mechanism for improving performance of structural systems. This paper presents a new “contact interface model” that has been developed to provide nonlinear relations between cyclic loads and displacements of the footing–soil system during combined cyclic loading (vertical, shear, and moment). The rigid footing and the soil beneath the footing in the zone of influence, considered as a macroelement, are modeled by keeping track of the geometry of the soil surface beneath the footing, along with the kinematics of the footing–soil system, interaction diagrams in vertical, shear, and moment space, and the introduction of a parameter, critical contact area ratio (A∕Ac) ; the ratio of footing area (A) to the footing contact area required to support vertical and shear loads (Ac) . Several contact interface model simulations were carried out and the model simulations are compared with centrifuge model test results. Using only six user-defined model input parameters, the contact interface model is capable of capturing the essential features (load capacities, stiffness degradation, energy dissipation, and deformations) of shallow foundations subjected to combined cyclic loading. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%291090-0241%282009%29135%3A3%2840 [...]

Contraction, dilation, and failure of sand in triaxial, torsional, and rotational shear tests / Chen, Yie-Ruey in Journal of engineering mechanics, Vol. 135 N° 10 (Octobre 2009) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 135 N° 10 (Octobre 2009) . - pp. 1155-1165 Titre : Contraction, dilation, and failure of sand in triaxial, torsional, and rotational shear tests Type de document : texte imprimé Auteurs : Chen, Yie-Ruey, Auteur ; Kutter, Bruce L., Auteur Article en page(s) : pp. 1155-1165 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Sand  Triaxial  tests  Torsion  Rotation  Failures  Contraction  Soil  tests. Résumé : The response of a saturated fine sand (Nevada sand No. 120) with relative density Dr[approximate]70% in drained and undrained conventional triaxial compression and extension tests and undrained cyclic shear tests in a hollow cylinder apparatus with rotation of the stress directions was studied. It was observed that the peak mobilized friction angle for this dilatant material was different in undrained and drained tests; the difference is attributed to the fact that the rate of dilation is smaller in an undrained test than it is in a drained test. Consistent with the findings of others, the material is more resistant to undrained cyclic loading for triaxial compression than for triaxial extension. In rotational shear tests in which the second invariant of the deviatoric stress tensor is held constant, the shear stress path (after being normalized by the mean normal effective stress) approached an envelope that is comparable but not identical in shape to a Mohr-Coulomb failure surface. As the stress path approached the envelope, the shear end deviatoric strains continued to increase in an unsymmetrical smooth spiral path. During the rotational shear tests, the direction of the deviatoric strain-rate vector (deviatoric strain increment divided by the magnitude of change in Lode angle) was observed to be about midway between the deviatoric stress increment vector and the normal to a Mohr-Coulomb failure surface in the deviatoric plane. The stress ratio at the transition from contractive to dilative behavior (i.e., “phase transformation”) was also observed to depend on the direction of the stress path; therefore this stress ratio is not a fundamental property. Results from torsional hollow cylinder tests with rotation of stress directions are presented in new graphical formats to help understand and interpret the fundamental soil behavior. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JENMDT&smode=strres [...] [article] Contraction, dilation, and failure of sand in triaxial, torsional, and rotational shear tests [texte imprimé] / Chen, Yie-Ruey, Auteur ; Kutter, Bruce L., Auteur . - pp. 1155-1165. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 135 N° 10 (Octobre 2009) . - pp. 1155-1165 Mots-clés : Sand  Triaxial  tests  Torsion  Rotation  Failures  Contraction  Soil  tests. Résumé : The response of a saturated fine sand (Nevada sand No. 120) with relative density Dr[approximate]70% in drained and undrained conventional triaxial compression and extension tests and undrained cyclic shear tests in a hollow cylinder apparatus with rotation of the stress directions was studied. It was observed that the peak mobilized friction angle for this dilatant material was different in undrained and drained tests; the difference is attributed to the fact that the rate of dilation is smaller in an undrained test than it is in a drained test. Consistent with the findings of others, the material is more resistant to undrained cyclic loading for triaxial compression than for triaxial extension. In rotational shear tests in which the second invariant of the deviatoric stress tensor is held constant, the shear stress path (after being normalized by the mean normal effective stress) approached an envelope that is comparable but not identical in shape to a Mohr-Coulomb failure surface. As the stress path approached the envelope, the shear end deviatoric strains continued to increase in an unsymmetrical smooth spiral path. During the rotational shear tests, the direction of the deviatoric strain-rate vector (deviatoric strain increment divided by the magnitude of change in Lode angle) was observed to be about midway between the deviatoric stress increment vector and the normal to a Mohr-Coulomb failure surface in the deviatoric plane. The stress ratio at the transition from contractive to dilative behavior (i.e., “phase transformation”) was also observed to depend on the direction of the stress path; therefore this stress ratio is not a fundamental property. Results from torsional hollow cylinder tests with rotation of stress directions are presented in new graphical formats to help understand and interpret the fundamental soil behavior. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JENMDT&smode=strres [...]

Effects of moment-to-shear ratio on combined cyclic load-displacement behavior of shallow foundations from centrifuge experiments / Sivapalan Gajan in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 8 (Août 2009) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 8 (Août 2009) . - pp. 1044–1055 Titre : Effects of moment-to-shear ratio on combined cyclic load-displacement behavior of shallow foundations from centrifuge experiments Type de document : texte imprimé Auteurs : Sivapalan Gajan, Auteur ; Kutter, Bruce L., Auteur Année de publication : 2009 Article en page(s) : pp. 1044–1055 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Footings  Settlement  Cyclic  loads  Shallow  foundations  Centrifuge  models  Seismic  loads Résumé : Current design guidelines for shallow foundations supporting building and bridge structures discourage footing rocking or sliding during seismic loading. Recent research indicates that footing rocking has the potential to reduce ductility demands on structures by dissipating earthquake energy at the footing-soil interface. Concerns over cyclic and permanent displacements of the foundation during rocking and sliding along with the dependence of foundation capacity on uncertain soil properties hinder the use of footing rocking in practice. This paper presents the findings of a series of centrifuge experiments conducted on shear wall-footing structures supported by dry dense to medium dense sand foundations that are subjected to lateral cyclic loading. Two key parameters, static vertical factor of safety (FSV) , and the applied normalized moment-to-shear ratio (M∕(H⋅L)) at the footing-soil interface, along with other parameters, were varied systematically and the effects of these parameters on footing-soil system behavior are presented. As expected, the ratio of moment to the horizontal load affects the relative magnitude of rotational and sliding displacement of the footing. Results also show that, for a particular FSV , footings with a large moment to shear ratio dissipate considerably more energy through rocking and suffer less permanent settlement than footings with a low moment to shear ratio. The ratio of actual footing area (A) to the area required to support the vertical and shear loads (Ac) , called the critical contact area ratio (A∕Ac) , is used to correlate results from tests with different moment to shear ratio. It is found that footings with similar A∕Ac display similar relationships between cyclic moment-rotation and cumulative settlement, irrespective of the moment-to-shear ratio. It is suggested that shallow foundations with a sufficiently large A∕Ac suffer small permanent settlements and have a well defined moment capacity; hence they may be used as effective energy dissipation devices that limit loads transmitted to the superstructure. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000034 [article] Effects of moment-to-shear ratio on combined cyclic load-displacement behavior of shallow foundations from centrifuge experiments [texte imprimé] / Sivapalan Gajan, Auteur ; Kutter, Bruce L., Auteur . - 2009 . - pp. 1044–1055. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 8 (Août 2009) . - pp. 1044–1055 Mots-clés : Footings  Settlement  Cyclic  loads  Shallow  foundations  Centrifuge  models  Seismic  loads Résumé : Current design guidelines for shallow foundations supporting building and bridge structures discourage footing rocking or sliding during seismic loading. Recent research indicates that footing rocking has the potential to reduce ductility demands on structures by dissipating earthquake energy at the footing-soil interface. Concerns over cyclic and permanent displacements of the foundation during rocking and sliding along with the dependence of foundation capacity on uncertain soil properties hinder the use of footing rocking in practice. This paper presents the findings of a series of centrifuge experiments conducted on shear wall-footing structures supported by dry dense to medium dense sand foundations that are subjected to lateral cyclic loading. Two key parameters, static vertical factor of safety (FSV) , and the applied normalized moment-to-shear ratio (M∕(H⋅L)) at the footing-soil interface, along with other parameters, were varied systematically and the effects of these parameters on footing-soil system behavior are presented. As expected, the ratio of moment to the horizontal load affects the relative magnitude of rotational and sliding displacement of the footing. Results also show that, for a particular FSV , footings with a large moment to shear ratio dissipate considerably more energy through rocking and suffer less permanent settlement than footings with a low moment to shear ratio. The ratio of actual footing area (A) to the area required to support the vertical and shear loads (Ac) , called the critical contact area ratio (A∕Ac) , is used to correlate results from tests with different moment to shear ratio. It is found that footings with similar A∕Ac display similar relationships between cyclic moment-rotation and cumulative settlement, irrespective of the moment-to-shear ratio. It is suggested that shallow foundations with a sufficiently large A∕Ac suffer small permanent settlements and have a well defined moment capacity; hence they may be used as effective energy dissipation devices that limit loads transmitted to the superstructure. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000034

Fast stacking and phase corrections of shear wave signals in a noisy environment / Scott J. Brandenberg in Journal of geotechnical and geoenvironmental engineering, Vol. 134 n°8 (Août 2008) 

Permalink

Postshaking shear strain localization in a centrifuge model of a saturated sand slope / Erik J. Malvick in Journal of geotechnical and geoenvironmental engineering, Vol. 134 N°2 (Fevrier 2008) 

Permalink