Documents disponibles écrits par cet auteur

Bayesian framework for characterizing geotechnical model uncertainty / J. Zhang in Journal of geotechnical and geoenvironmental engineering, Vol. 135 N° 7 (Juillet 2009) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 7 (Juillet 2009) . - pp. 932–940 Titre : Bayesian framework for characterizing geotechnical model uncertainty Type de document : texte imprimé Auteurs : J. Zhang, Auteur ; Zhang, L. M., Auteur ; Wilson H. Tang, Auteur Année de publication : 2009 Article en page(s) : pp. 932–940 Note générale : Geotechnical and geoenvironmental engineering Langues : Anglais (eng) Mots-clés : Bayesian  analysis  Uncertainty  principles  Slope  stability  Centrifuge  model  Reliability Résumé : As any model is only an abstraction of the real world, model uncertainty always exists. The magnitude of model uncertainty is important for geotechnical decision making. If model uncertainty is not considered, the geotechnical predictions and hence the decisions based on the geotechnical predictions might be biased. In this study, a framework for characterizing geotechnical model uncertainty using observation data is proposed. The framework is based on the concept of multivariable Bayesian updating, in which the statistics of model uncertainty are updated using observed performance data. Uncertainties in both input parameters and observed data can be considered in the proposed framework. To bypass complex computational works involved in the proposed framework, a practical approximate solution is presented. The proposed framework is illustrated by characterizing the model uncertainty of four limit equilibrium methods for slope stability analysis using quality centrifuge test data. Parametric study in the illustrative example shows that both quality and quantity of the performance data could affect the determination of the model uncertainty, and that such effects can be systematically quantified with the proposed method. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000018 [article] Bayesian framework for characterizing geotechnical model uncertainty [texte imprimé] / J. Zhang, Auteur ; Zhang, L. M., Auteur ; Wilson H. Tang, Auteur . - 2009 . - pp. 932–940. Geotechnical and geoenvironmental engineering Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 135 N° 7 (Juillet 2009) . - pp. 932–940 Mots-clés : Bayesian  analysis  Uncertainty  principles  Slope  stability  Centrifuge  model  Reliability Résumé : As any model is only an abstraction of the real world, model uncertainty always exists. The magnitude of model uncertainty is important for geotechnical decision making. If model uncertainty is not considered, the geotechnical predictions and hence the decisions based on the geotechnical predictions might be biased. In this study, a framework for characterizing geotechnical model uncertainty using observation data is proposed. The framework is based on the concept of multivariable Bayesian updating, in which the statistics of model uncertainty are updated using observed performance data. Uncertainties in both input parameters and observed data can be considered in the proposed framework. To bypass complex computational works involved in the proposed framework, a practical approximate solution is presented. The proposed framework is illustrated by characterizing the model uncertainty of four limit equilibrium methods for slope stability analysis using quality centrifuge test data. Parametric study in the illustrative example shows that both quality and quantity of the performance data could affect the determination of the model uncertainty, and that such effects can be systematically quantified with the proposed method. En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29GT.1943-5606.0000018

Efficient probabilistic back-analysis of slope stability model parameters / J. Zhang in Journal of geotechnical and geoenvironmental engineering, Vol. 136 N° 1 (Janvier 2010) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 1 (Janvier 2010) . - pp. 99-109 Titre : Efficient probabilistic back-analysis of slope stability model parameters Type de document : texte imprimé Auteurs : J. Zhang, Auteur ; Wilson H. Tang, Auteur ; Zhang, L. M., Auteur Article en page(s) : pp. 99-109 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Landslides  Slope  stability  Failure  investigation  Probability  methods  Reliability  Bayesian  analysis Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : Back-analysis of slope failure is often performed to improve one's knowledge on parameters of a slope stability analysis model. In a failed slope, the slip surface may pass through several layers of soil. Therefore, several sets of model parameters need to be back-analyzed. To back-analyze multiple sets of slope stability parameters simultaneously under uncertainty, the back-analysis can be implemented in a probabilistic way, in which uncertain parameters are modeled as random variables, and their distributions are improved based on the observed slope failure information. In this paper, two methods are presented for probabilistic back-analysis of slope failure. For a general slope stability model, its uncertain parameters can be back-analyzed with an optimization procedure that can be implemented in a spreadsheet. When the slope stability model is approximately linear, its parameters can be back-analyzed with sensitivity analysis instead. A feature of these two methods is that they are easy to apply. Two case studies are used to illustrate the proposed methods. The case studies show that the degrees of improvement achieved by the back-analysis are different for different parameters, and that the parameter contributing most to the uncertainty in factor of safety is updated most. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JGGEFK&smode=strres [...] [article] Efficient probabilistic back-analysis of slope stability model parameters [texte imprimé] / J. Zhang, Auteur ; Wilson H. Tang, Auteur ; Zhang, L. M., Auteur . - pp. 99-109. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 136 N° 1 (Janvier 2010) . - pp. 99-109 Mots-clés : Landslides  Slope  stability  Failure  investigation  Probability  methods  Reliability  Bayesian  analysis Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : Back-analysis of slope failure is often performed to improve one's knowledge on parameters of a slope stability analysis model. In a failed slope, the slip surface may pass through several layers of soil. Therefore, several sets of model parameters need to be back-analyzed. To back-analyze multiple sets of slope stability parameters simultaneously under uncertainty, the back-analysis can be implemented in a probabilistic way, in which uncertain parameters are modeled as random variables, and their distributions are improved based on the observed slope failure information. In this paper, two methods are presented for probabilistic back-analysis of slope failure. For a general slope stability model, its uncertain parameters can be back-analyzed with an optimization procedure that can be implemented in a spreadsheet. When the slope stability model is approximately linear, its parameters can be back-analyzed with sensitivity analysis instead. A feature of these two methods is that they are easy to apply. Two case studies are used to illustrate the proposed methods. The case studies show that the degrees of improvement achieved by the back-analysis are different for different parameters, and that the parameter contributing most to the uncertainty in factor of safety is updated most. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.aip.org/vsearch/servlet/VerityServlet?KEY=JGGEFK&smode=strres [...]

Efficient spreadsheet algorithm for first-order reliability method / B. K. Low in Journal of engineering mechanics, Vol. 133 N°12 (Decembre 2007) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 133 N°12 (Decembre 2007) . - pp.1378–1387. Titre : Efficient spreadsheet algorithm for first-order reliability method Type de document : texte imprimé Auteurs : B. K. Low, Auteur ; Wilson H. Tang, Auteur Année de publication : 2007 Article en page(s) : pp.1378–1387. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Probability  Reliability  Correlation  Optimization  Computer  software  Computation Résumé : A new spreadsheet-cell-object-oriented algorithm for the first-order reliability method is proposed and illustrated for cases with correlated nonnormals and explicit and implicit performance functions. The new approach differs from the writers earlier algorithm by obviating the need for computations of equivalent normal means and equivalent normal standard deviations. It obtains the solution faster and is more efficient, robust, and succinct. Other advantages include ease of initialization prior to constrained optimization, ease of randomization of initial values for checking robustness, and fewer required optimization constraints during spreadsheet-automated search for the design point. Two cases with implicit performance functions, namely an asymmetrically loaded beam on Winkler medium and a strut with complex supports are analyzed using the new approach and discussed. Comparisons are also made between the proposed approach and that based on Rosenblatt transformation. ISSN : 0733-9399 En ligne : http://ascelibrary.org/action/showAbstract?page=1378&volume=133&issue=12&journal [...] [article] Efficient spreadsheet algorithm for first-order reliability method [texte imprimé] / B. K. Low, Auteur ; Wilson H. Tang, Auteur . - 2007 . - pp.1378–1387. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 133 N°12 (Decembre 2007) . - pp.1378–1387. Mots-clés : Probability  Reliability  Correlation  Optimization  Computer  software  Computation Résumé : A new spreadsheet-cell-object-oriented algorithm for the first-order reliability method is proposed and illustrated for cases with correlated nonnormals and explicit and implicit performance functions. The new approach differs from the writers earlier algorithm by obviating the need for computations of equivalent normal means and equivalent normal standard deviations. It obtains the solution faster and is more efficient, robust, and succinct. Other advantages include ease of initialization prior to constrained optimization, ease of randomization of initial values for checking robustness, and fewer required optimization constraints during spreadsheet-automated search for the design point. Two cases with implicit performance functions, namely an asymmetrically loaded beam on Winkler medium and a strut with complex supports are analyzed using the new approach and discussed. Comparisons are also made between the proposed approach and that based on Rosenblatt transformation. ISSN : 0733-9399 En ligne : http://ascelibrary.org/action/showAbstract?page=1378&volume=133&issue=12&journal [...]

Efficient spreadsheet algorithm for first-order reliability method / B. K. Low in Journal of engineering mechanics, Vol. 133 N°11 (Novembre 2007) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 133 N°11 (Novembre 2007) . - pp.1378–1387. Titre : Efficient spreadsheet algorithm for first-order reliability method Type de document : texte imprimé Auteurs : B. K. Low, Auteur ; Wilson H. Tang, Auteur Année de publication : 2007 Article en page(s) : pp.1378–1387. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Probability  Reliability  Correlation  Optimization  Computer  software  Computation Résumé : A new spreadsheet-cell-object-oriented algorithm for the first-order reliability method is proposed and illustrated for cases with correlated nonnormals and explicit and implicit performance functions. The new approach differs from the writers earlier algorithm by obviating the need for computations of equivalent normal means and equivalent normal standard deviations. It obtains the solution faster and is more efficient, robust, and succinct. Other advantages include ease of initialization prior to constrained optimization, ease of randomization of initial values for checking robustness, and fewer required optimization constraints during spreadsheet-automated search for the design point. Two cases with implicit performance functions, namely an asymmetrically loaded beam on Winkler medium and a strut with complex supports are analyzed using the new approach and discussed. Comparisons are also made between the proposed approach and that based on Rosenblatt transformation. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A12%281 [...] [article] Efficient spreadsheet algorithm for first-order reliability method [texte imprimé] / B. K. Low, Auteur ; Wilson H. Tang, Auteur . - 2007 . - pp.1378–1387. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 133 N°11 (Novembre 2007) . - pp.1378–1387. Mots-clés : Probability  Reliability  Correlation  Optimization  Computer  software  Computation Résumé : A new spreadsheet-cell-object-oriented algorithm for the first-order reliability method is proposed and illustrated for cases with correlated nonnormals and explicit and implicit performance functions. The new approach differs from the writers earlier algorithm by obviating the need for computations of equivalent normal means and equivalent normal standard deviations. It obtains the solution faster and is more efficient, robust, and succinct. Other advantages include ease of initialization prior to constrained optimization, ease of randomization of initial values for checking robustness, and fewer required optimization constraints during spreadsheet-automated search for the design point. Two cases with implicit performance functions, namely an asymmetrically loaded beam on Winkler medium and a strut with complex supports are analyzed using the new approach and discussed. Comparisons are also made between the proposed approach and that based on Rosenblatt transformation. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A12%281 [...]

Reliability-based optimization of geotechnical systems / J. Zhang in Journal of geotechnical and geoenvironmental engineering, Vol. 137 N° 12 (Décembre 2011) 

Public ISBD [article]  in Journal of geotechnical and geoenvironmental engineering > Vol. 137 N° 12 (Décembre 2011) . - pp. 1211- 1221 Titre : Reliability-based optimization of geotechnical systems Type de document : texte imprimé Auteurs : J. Zhang, Auteur ; Zhang, L. M., Auteur ; Wilson H. Tang, Auteur Année de publication : 2012 Article en page(s) : pp. 1211- 1221 Note générale : Géotechnique Langues : Anglais (eng) Mots-clés : Reliability  Optimization  Shallow  foundation  Retaining  wall  Probabilistic  method Résumé : Reliability-based optimization (RBO) intends to minimize the cost involved in a design while satisfying all technical requirements specified by using reliability theory. Although this idea is attractive, its implementation is generally difficult because an accurate evaluation of the reliability constraints is often computationally prohibitive when it is coupled with the minimization of a cost function. This paper suggests an indirect method for RBO of geotechnical systems initially on the basis of the mean first-order reliability method (MFORM). Because reliability analysis with MFORM is very efficient, the computational work involved in RBO is greatly reduced. The major concern about MFORM is that it is not an accurate reliability method. A reliability index mapping function was used to relate the reliability index calculated by MFORM to that calculated by a more accurate method. When the mapping function perfectly reflects the relationship between MFORM reliability index and that from an accurate reliability method, the RBO from MFORM and the original RBO problem are equivalent. When a perfect mapping function cannot be built, a procedure has been suggested to fine-tune the optimal design such that accurate reliability constraints can be maintained in the final optimal design. The proposed method is illustrated with two geotechnical examples: the optimal design of a shallow foundation and a gravity retaining wall. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v137/i12/p1211_s1?isAuthorized=no [article] Reliability-based optimization of geotechnical systems [texte imprimé] / J. Zhang, Auteur ; Zhang, L. M., Auteur ; Wilson H. Tang, Auteur . - 2012 . - pp. 1211- 1221. Géotechnique Langues : Anglais (eng) in Journal of geotechnical and geoenvironmental engineering > Vol. 137 N° 12 (Décembre 2011) . - pp. 1211- 1221 Mots-clés : Reliability  Optimization  Shallow  foundation  Retaining  wall  Probabilistic  method Résumé : Reliability-based optimization (RBO) intends to minimize the cost involved in a design while satisfying all technical requirements specified by using reliability theory. Although this idea is attractive, its implementation is generally difficult because an accurate evaluation of the reliability constraints is often computationally prohibitive when it is coupled with the minimization of a cost function. This paper suggests an indirect method for RBO of geotechnical systems initially on the basis of the mean first-order reliability method (MFORM). Because reliability analysis with MFORM is very efficient, the computational work involved in RBO is greatly reduced. The major concern about MFORM is that it is not an accurate reliability method. A reliability index mapping function was used to relate the reliability index calculated by MFORM to that calculated by a more accurate method. When the mapping function perfectly reflects the relationship between MFORM reliability index and that from an accurate reliability method, the RBO from MFORM and the original RBO problem are equivalent. When a perfect mapping function cannot be built, a procedure has been suggested to fine-tune the optimal design such that accurate reliability constraints can be maintained in the final optimal design. The proposed method is illustrated with two geotechnical examples: the optimal design of a shallow foundation and a gravity retaining wall. DEWEY : 624.1 ISSN : 1090-0241 En ligne : http://ascelibrary.org/gto/resource/1/jggefk/v137/i12/p1211_s1?isAuthorized=no

Slope reliability analysis considering site-specific performance information / J. Zhang in Journal of geotechnical and geoenvironmental engineering, Vol. 137 N° 3 (Mars 2011) 

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