Documents disponibles écrits par cet auteur

Numerical modeling of shear behavior of reinforced concrete pile caps / Alan G. Bloodworth in Journal of structural engineering, Vol. 138 N° 6 (Juin 2012) 

Public ISBD [article]  in Journal of structural engineering > Vol. 138 N° 6 (Juin 2012) . - pp. 708–717 Titre : Numerical modeling of shear behavior of reinforced concrete pile caps Type de document : texte imprimé Auteurs : Alan G. Bloodworth, Auteur ; Jing Cao, Auteur ; Xu, Ming, Auteur Année de publication : 2012 Article en page(s) : pp. 708–717 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Pile  caps  Shear  resistance  Reinforced  concrete  Finite-element  method  Numerical  models Résumé : The application of bending theory based methods and strut-and-tie models for the design of pile caps to resist shear is still a subject of debate, with the latest Eurocodes permitting both methods but not giving much guidance as to their use. The former UK design standards for concrete buildings and bridges, recently withdrawn, gave more guidance, and it is likely that these methods will continue to be used by designers. However, there is considerable discrepancy between these standards, particularly with regard to the width of cap over which shear enhancement at short spans may be applied, and how much longitudinal reinforcement to take as a tie in the strut-and-tie method. Both standards are also seen as conservative. To gain a better understanding of the problem and assess the available design methods, nonlinear finite-element analysis has been performed to investigate the shear behavior of four-pile reinforced concrete pile caps, under full-width wall loading. The models were validated against an experimental program that included an optical photogrammetric method for measuring full-field displacements. An extensive parametric study was carried out, varying shear span, cap width, and reinforcement ratio over a practical range. The conservatism of the UK design standards, and the real shear capacity of the pile caps were found to be a function of shear enhancement factor and the width of the cap over which shear enhancement is applied. Strut-and-tie behavior was observed in the models, and a commonly used strut-and-tie method was found to give fairly good predictions. A modified strut-and-tie method is suggested for this particular configuration of a four-pile cap under full-width loading, which gives more accurate predictions. This is especially so for samples with large transverse pile spacing, where a significant proportion of the longitudinal reinforcement over the width of the cap can be assumed to participate in the yielding ties. ISSN : 0733-9445 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29ST.1943-541X.0000499 [article] Numerical modeling of shear behavior of reinforced concrete pile caps [texte imprimé] / Alan G. Bloodworth, Auteur ; Jing Cao, Auteur ; Xu, Ming, Auteur . - 2012 . - pp. 708–717. Génie Civil Langues : Anglais (eng) in Journal of structural engineering > Vol. 138 N° 6 (Juin 2012) . - pp. 708–717 Mots-clés : Pile  caps  Shear  resistance  Reinforced  concrete  Finite-element  method  Numerical  models Résumé : The application of bending theory based methods and strut-and-tie models for the design of pile caps to resist shear is still a subject of debate, with the latest Eurocodes permitting both methods but not giving much guidance as to their use. The former UK design standards for concrete buildings and bridges, recently withdrawn, gave more guidance, and it is likely that these methods will continue to be used by designers. However, there is considerable discrepancy between these standards, particularly with regard to the width of cap over which shear enhancement at short spans may be applied, and how much longitudinal reinforcement to take as a tie in the strut-and-tie method. Both standards are also seen as conservative. To gain a better understanding of the problem and assess the available design methods, nonlinear finite-element analysis has been performed to investigate the shear behavior of four-pile reinforced concrete pile caps, under full-width wall loading. The models were validated against an experimental program that included an optical photogrammetric method for measuring full-field displacements. An extensive parametric study was carried out, varying shear span, cap width, and reinforcement ratio over a practical range. The conservatism of the UK design standards, and the real shear capacity of the pile caps were found to be a function of shear enhancement factor and the width of the cap over which shear enhancement is applied. Strut-and-tie behavior was observed in the models, and a commonly used strut-and-tie method was found to give fairly good predictions. A modified strut-and-tie method is suggested for this particular configuration of a four-pile cap under full-width loading, which gives more accurate predictions. This is especially so for samples with large transverse pile spacing, where a significant proportion of the longitudinal reinforcement over the width of the cap can be assumed to participate in the yielding ties. ISSN : 0733-9445 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%29ST.1943-541X.0000499

Robust simulation of global warming policies using the DICE model / Zhaolin Hu in Management science, Vol. 58 N° 12 (Décembre 2012) 

Public ISBD [article]  in Management science > Vol. 58 N° 12 (Décembre 2012) . - pp. 2190-2206 Titre : Robust simulation of global warming policies using the DICE model Type de document : texte imprimé Auteurs : Zhaolin Hu, Auteur ; Jing Cao, Auteur ; L. Jeff Hong, Auteur Année de publication : 2013 Article en page(s) : pp. 2190-2206 Note générale : Management Langues : Anglais (eng) Mots-clés : Environment  Global  warming  Programming  Semidefinite  Simulation  Applications Résumé : Integrated assessment models that combine geophysics and economics features are often used to evaluate and compare global warming policies. Because there are typically profound uncertainties in these models, a simulation approach is often used. This approach requires the distribution of the uncertain parameters clearly specified. However, this is typically impossible because there is often a significant amount of ambiguity (e.g., estimation error) in specifying the distribution. In this paper, we adopt the widely used multivariate normal distribution to model the uncertain parameters. However, we assume that the mean vector and covariance matrix of the distribution are within some ambiguity sets. We then show how to find the worst-case performance of a given policy for all distributions constrained by the ambiguity sets. This worst-case performance provides a robust evaluation of the policy. We test our algorithm on a famous integrated model of climate change, known as the Dynamic Integrated Model of Climate and the Economy (DICE model). We find that the DICE model is sensitive to the means and covariance of the parameters. Furthermore, we find that, based on the DICE model, moderately tight environmental policies robustly outperform the no controls policy and the famous aggressive policies proposed by Stern and Gore. ISSN : 0025-1909 En ligne : http://mansci.journal.informs.org/content/58/12/2190.abstract [article] Robust simulation of global warming policies using the DICE model [texte imprimé] / Zhaolin Hu, Auteur ; Jing Cao, Auteur ; L. Jeff Hong, Auteur . - 2013 . - pp. 2190-2206. Management Langues : Anglais (eng) in Management science > Vol. 58 N° 12 (Décembre 2012) . - pp. 2190-2206 Mots-clés : Environment  Global  warming  Programming  Semidefinite  Simulation  Applications Résumé : Integrated assessment models that combine geophysics and economics features are often used to evaluate and compare global warming policies. Because there are typically profound uncertainties in these models, a simulation approach is often used. This approach requires the distribution of the uncertain parameters clearly specified. However, this is typically impossible because there is often a significant amount of ambiguity (e.g., estimation error) in specifying the distribution. In this paper, we adopt the widely used multivariate normal distribution to model the uncertain parameters. However, we assume that the mean vector and covariance matrix of the distribution are within some ambiguity sets. We then show how to find the worst-case performance of a given policy for all distributions constrained by the ambiguity sets. This worst-case performance provides a robust evaluation of the policy. We test our algorithm on a famous integrated model of climate change, known as the Dynamic Integrated Model of Climate and the Economy (DICE model). We find that the DICE model is sensitive to the means and covariance of the parameters. Furthermore, we find that, based on the DICE model, moderately tight environmental policies robustly outperform the no controls policy and the famous aggressive policies proposed by Stern and Gore. ISSN : 0025-1909 En ligne : http://mansci.journal.informs.org/content/58/12/2190.abstract