Dépouillements

Regularization of inverse problems in reinforced concrete fracture / I. M. Nazmul in Journal of engineering mechanics, Vol. 134 N°10 (Octobre 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp.811–819. Titre : Regularization of inverse problems in reinforced concrete fracture Type de document : texte imprimé Auteurs : I. M. Nazmul, Auteur ; T. Matsumoto, Auteur Année de publication : 2008 Article en page(s) : pp.811–819. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Reinforced  concrete  Concrete  beams  Bridges  concrete  Cracking  Transformation  Steel  Reinforcement Résumé : Reinforced concrete beams with flexural cracks are simulated by the bridged crack model. The weight function method of determining stress intensity factors has been followed to derive a transformation between the crack bridging force (the rebar force) and the crack opening displacements (CODs). The matrix of the transformation is then approximated by its finite difference equivalent within finite dimensional vector spaces. Direct problem of the transformation solves for CODs, which require a known rebar force. Alternatively, the inverse problem works out the rebar force from known CODs. However, the inverse transformations of such convolution type integral equations become ill-posed if input CODs are perturbed. The Tikhonov regularization method is followed in its numerical form to regularize the linear ill-posed inverse problem. Restoration of mathematical stability and consistency are demonstrated by specific examples, where the results of the direct and the corresponding inverse problem are cross checked. Results of the direct problem (i.e., the analytical CODs) are deliberately perturbed by adding machine generated random numbers of a certain width. The inverse problems are solved with these CODs to simulate practical situations, where measured CODs data will inevitably be noisy. Computations reveal that the inverse analysis of CODs satisfactorily determines the rebar force without cross-section information ISSN : 0733-9399 En ligne : Reinforced concrete, Concrete beams, Bridges, concrete, Cracking, Transformation [...] [article] Regularization of inverse problems in reinforced concrete fracture [texte imprimé] / I. M. Nazmul, Auteur ; T. Matsumoto, Auteur . - 2008 . - pp.811–819. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp.811–819. Mots-clés : Reinforced  concrete  Concrete  beams  Bridges  concrete  Cracking  Transformation  Steel  Reinforcement Résumé : Reinforced concrete beams with flexural cracks are simulated by the bridged crack model. The weight function method of determining stress intensity factors has been followed to derive a transformation between the crack bridging force (the rebar force) and the crack opening displacements (CODs). The matrix of the transformation is then approximated by its finite difference equivalent within finite dimensional vector spaces. Direct problem of the transformation solves for CODs, which require a known rebar force. Alternatively, the inverse problem works out the rebar force from known CODs. However, the inverse transformations of such convolution type integral equations become ill-posed if input CODs are perturbed. The Tikhonov regularization method is followed in its numerical form to regularize the linear ill-posed inverse problem. Restoration of mathematical stability and consistency are demonstrated by specific examples, where the results of the direct and the corresponding inverse problem are cross checked. Results of the direct problem (i.e., the analytical CODs) are deliberately perturbed by adding machine generated random numbers of a certain width. The inverse problems are solved with these CODs to simulate practical situations, where measured CODs data will inevitably be noisy. Computations reveal that the inverse analysis of CODs satisfactorily determines the rebar force without cross-section information ISSN : 0733-9399 En ligne : Reinforced concrete, Concrete beams, Bridges, concrete, Cracking, Transformation [...]

Bayesian probabilistic inference for nonparametric damage detection of structures / Xiaomo Jiang in Journal of engineering mechanics, Vol. 134 N°10 (Octobre 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp.820–831. Titre : Bayesian probabilistic inference for nonparametric damage detection of structures Type de document : texte imprimé Auteurs : Xiaomo Jiang, Auteur ; Sankaran Mahadevan, Auteur Année de publication : 2008 Article en page(s) : pp.820–831. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Bayesian  analysis  Damage  assessment  Structural  safety  Bench  marks  Identification  Probability  Parameters Résumé : This paper presents a Bayesian hypothesis testing-based probabilistic assessment method for nonparametric damage detection of building structures, considering the uncertainties in both experimental results and model prediction. A dynamic fuzzy wavelet neural network method is employed as a nonparametric system identification model to predict the structural responses for damage evaluation. A Bayes factor evaluation metric is derived based on Bayes’ theorem and Gaussian distribution assumption of the difference between the experimental data and model prediction. The metric provides quantitative measure for assessing the accuracy of system identification and the state of global health of structures. The probability density function of the Bayes factor is constructed using the statistics of the difference of response quantities and Monte Carlo simulation technique to address the uncertainties in both experimental data and model prediction. The methodology is investigated with five damage scenarios of a four-story benchmark building. Numerical results demonstrate that the proposed methodology provides an effective approach for quantifying the damage confidence in the structural condition assessment. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A10%288 [...] [article] Bayesian probabilistic inference for nonparametric damage detection of structures [texte imprimé] / Xiaomo Jiang, Auteur ; Sankaran Mahadevan, Auteur . - 2008 . - pp.820–831. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp.820–831. Mots-clés : Bayesian  analysis  Damage  assessment  Structural  safety  Bench  marks  Identification  Probability  Parameters Résumé : This paper presents a Bayesian hypothesis testing-based probabilistic assessment method for nonparametric damage detection of building structures, considering the uncertainties in both experimental results and model prediction. A dynamic fuzzy wavelet neural network method is employed as a nonparametric system identification model to predict the structural responses for damage evaluation. A Bayes factor evaluation metric is derived based on Bayes’ theorem and Gaussian distribution assumption of the difference between the experimental data and model prediction. The metric provides quantitative measure for assessing the accuracy of system identification and the state of global health of structures. The probability density function of the Bayes factor is constructed using the statistics of the difference of response quantities and Monte Carlo simulation technique to address the uncertainties in both experimental data and model prediction. The methodology is investigated with five damage scenarios of a four-story benchmark building. Numerical results demonstrate that the proposed methodology provides an effective approach for quantifying the damage confidence in the structural condition assessment. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A10%288 [...]

Pseudopotentials and loading surfaces for an endochronic plasticity theory with isotropic damage / Silvano Erlicher in Journal of engineering mechanics, Vol. 134 N°10 (Octobre 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp.832–842. Titre : Pseudopotentials and loading surfaces for an endochronic plasticity theory with isotropic damage Type de document : texte imprimé Auteurs : Silvano Erlicher, Auteur ; Nelly Point, Auteur Année de publication : 2008 Article en page(s) : pp.832–842. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Plasticity  Thermodynamics  Damage  Isotropy Résumé : The endochronic theory, developed in the early 70s, allows the plastic behavior of materials to be represented by introducing the notion of intrinsic time. With different viewpoints, several authors discussed the relationship between this theory and the classical theory of plasticity. Two major differences are the presence of plastic strains during unloading phases and the absence of an elastic domain. Later, the endochronic plasticity theory was modified in order to introduce the effect of damage. In the present paper, a basic endochronic model with isotropic damage is formulated starting from the postulate of strain equivalence. Unlike the previous similar analyses, in this presentation the formal tools chosen to formulate the model are those of convex analysis, often used in classical plasticity: namely pseudopotentials, indicator functions, subdifferentials, etc. As a result, the notion of loading surface for an endochronic model of plasticity with damage is investigated and an insightful comparison with classical models is made possible. A damage pseudopotential definition allowing a very general damage evolution is given. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A10%288 [...] [article] Pseudopotentials and loading surfaces for an endochronic plasticity theory with isotropic damage [texte imprimé] / Silvano Erlicher, Auteur ; Nelly Point, Auteur . - 2008 . - pp.832–842. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp.832–842. Mots-clés : Plasticity  Thermodynamics  Damage  Isotropy Résumé : The endochronic theory, developed in the early 70s, allows the plastic behavior of materials to be represented by introducing the notion of intrinsic time. With different viewpoints, several authors discussed the relationship between this theory and the classical theory of plasticity. Two major differences are the presence of plastic strains during unloading phases and the absence of an elastic domain. Later, the endochronic plasticity theory was modified in order to introduce the effect of damage. In the present paper, a basic endochronic model with isotropic damage is formulated starting from the postulate of strain equivalence. Unlike the previous similar analyses, in this presentation the formal tools chosen to formulate the model are those of convex analysis, often used in classical plasticity: namely pseudopotentials, indicator functions, subdifferentials, etc. As a result, the notion of loading surface for an endochronic model of plasticity with damage is investigated and an insightful comparison with classical models is made possible. A damage pseudopotential definition allowing a very general damage evolution is given. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A10%288 [...]

Bouc–wen-type models with stiffness degradation / Silvano Erlicher in Journal of engineering mechanics, Vol. 134 N°10 (Octobre 2008)

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp. 843–855. Titre : Bouc–wen-type models with stiffness degradation : Thermodynamic analysis and applications Type de document : texte imprimé Auteurs : Silvano Erlicher, Auteur ; Oreste S. Bursi, Auteur Année de publication : 2008 Article en page(s) : pp. 843–855. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Thermodynamics,  Stiffness,  Energy Résumé : In this paper, a thermodynamic analysis of Bouc–Wen models endowed with both strength and stiffness degradation is provided. This analysis is based on the relationship between the flow rules of these models and those of the endochronic plasticity theory with damage, discussed in a companion paper. Using the theoretical framework of that extended endochronic theory, it is shown that an elastic Bouc–Wen model with damage, i.e., without plastic strains, can be formulated. Moreover, a proper definition of the dissipated energy of these Bouc–Wen models with degradation is given and some thermodynamic constraints on the parameters defining the models behavior are emphasized and discussed. In particular, some properties of the energetic linear stiffness degradation rule as well as the so-called pivot rule, well known in the seismic engineering field, are illustrated and commented upon. An improved energetic stiffness degradation rule and a new stiffness degradation rule are proposed. ISSN : 0733-9399 [article] Bouc–wen-type models with stiffness degradation : Thermodynamic analysis and applications [texte imprimé] / Silvano Erlicher, Auteur ; Oreste S. Bursi, Auteur . - 2008 . - pp. 843–855. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp. 843–855. Mots-clés : Thermodynamics,  Stiffness,  Energy Résumé : In this paper, a thermodynamic analysis of Bouc–Wen models endowed with both strength and stiffness degradation is provided. This analysis is based on the relationship between the flow rules of these models and those of the endochronic plasticity theory with damage, discussed in a companion paper. Using the theoretical framework of that extended endochronic theory, it is shown that an elastic Bouc–Wen model with damage, i.e., without plastic strains, can be formulated. Moreover, a proper definition of the dissipated energy of these Bouc–Wen models with degradation is given and some thermodynamic constraints on the parameters defining the models behavior are emphasized and discussed. In particular, some properties of the energetic linear stiffness degradation rule as well as the so-called pivot rule, well known in the seismic engineering field, are illustrated and commented upon. An improved energetic stiffness degradation rule and a new stiffness degradation rule are proposed. ISSN : 0733-9399

Virtual internal pair-bond model for quasi-brittle materials / Kyoungsoo Park, in Journal of engineering mechanics, Vol. 134 N°10 (Octobre 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp. 856-866 Titre : Virtual internal pair-bond model for quasi-brittle materials Type de document : texte imprimé Auteurs : Kyoungsoo Park,, Auteur ; Glaucio H. Paulino, Auteur ; Jeffery R. Roesler, Auteur Année de publication : 2008 Article en page(s) : pp. 856-866 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Brittleness  Cracking  Models  Material  properties Résumé : The present multiscale investigation employs the initial and total fracture energy through a virtual internal pair-bond (VIPB) model. The proposed VIPB model is an extension of the traditional virtual internal bond (VIB) model. Two different types of potentials, a steep short-range potential and a shallow long-range potential, are employed to describe the initial and the total fracture energies, respectively. The Morse potential function is modified for the virtual bond potential so that it is independent of specific length scales associated with the lattice geometry. This feature is incorporated in the VIPB model, which uses both fracture energies and cohesive strength. With respect to the discretization by finite elements, we address the element size dependence in conjunction with the J integral. Parameters in the VIPB model are evaluated by numerical simulations of a pure tension test in conjunction with measured fracture parameters. We also validate the VIPB model by predicting load versus crack mouth opening displacement curves for geometrically similar specimens, and the measured size effect. Finally, we provide an example involving fiber-reinforced concrete, which demonstrates the advantage of the VIPB model over the usual VIB model. ISSN : 0733-9399 En ligne : http://cedb.asce.org/cgi/WWWdisplay.cgi?167247 [article] Virtual internal pair-bond model for quasi-brittle materials [texte imprimé] / Kyoungsoo Park,, Auteur ; Glaucio H. Paulino, Auteur ; Jeffery R. Roesler, Auteur . - 2008 . - pp. 856-866. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp. 856-866 Mots-clés : Brittleness  Cracking  Models  Material  properties Résumé : The present multiscale investigation employs the initial and total fracture energy through a virtual internal pair-bond (VIPB) model. The proposed VIPB model is an extension of the traditional virtual internal bond (VIB) model. Two different types of potentials, a steep short-range potential and a shallow long-range potential, are employed to describe the initial and the total fracture energies, respectively. The Morse potential function is modified for the virtual bond potential so that it is independent of specific length scales associated with the lattice geometry. This feature is incorporated in the VIPB model, which uses both fracture energies and cohesive strength. With respect to the discretization by finite elements, we address the element size dependence in conjunction with the J integral. Parameters in the VIPB model are evaluated by numerical simulations of a pure tension test in conjunction with measured fracture parameters. We also validate the VIPB model by predicting load versus crack mouth opening displacement curves for geometrically similar specimens, and the measured size effect. Finally, we provide an example involving fiber-reinforced concrete, which demonstrates the advantage of the VIPB model over the usual VIB model. ISSN : 0733-9399 En ligne : http://cedb.asce.org/cgi/WWWdisplay.cgi?167247

Second-order sensitivities of inelastic finite-element response by direct differentiation / A. Bebamzadeh in Journal of engineering mechanics, Vol. 134 N°10 (Octobre 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp.867–880. Titre : Second-order sensitivities of inelastic finite-element response by direct differentiation Type de document : texte imprimé Auteurs : A. Bebamzadeh, Auteur ; T. Haukaas, Auteur Année de publication : 2008 Article en page(s) : pp.867–880. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Sensitivity  analysis  Finite  element  method  Inelasticity  Computation Résumé : In this paper analytical equations are developed and implemented to obtain second-order derivatives of finite-element responses with respect to input parameters. The work extends previous work on first-order response sensitivity analysis. Of particular interest in this study is the computational feasibility of obtaining second-order response sensitivities. In the past, the straightforward finite difference approach has been available, but this approach suffers from serious efficiency and accuracy concerns. In this study it is demonstrated that analytical differentiation of the response algorithm and subsequent implementation on the computer provides second-order sensitivities at a significantly reduced cost. The sensitivity results are consistent with and have the same numerical precision as the ordinary response. The computational cost advantage of the direct differentiation approach increases as the problem size increases. Several novel implementation techniques are developed in this paper to optimize the computational efficiency. The derivations and implementations are demonstrated and verified with two finite-element analysis examples. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A10%288 [...] [article] Second-order sensitivities of inelastic finite-element response by direct differentiation [texte imprimé] / A. Bebamzadeh, Auteur ; T. Haukaas, Auteur . - 2008 . - pp.867–880. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp.867–880. Mots-clés : Sensitivity  analysis  Finite  element  method  Inelasticity  Computation Résumé : In this paper analytical equations are developed and implemented to obtain second-order derivatives of finite-element responses with respect to input parameters. The work extends previous work on first-order response sensitivity analysis. Of particular interest in this study is the computational feasibility of obtaining second-order response sensitivities. In the past, the straightforward finite difference approach has been available, but this approach suffers from serious efficiency and accuracy concerns. In this study it is demonstrated that analytical differentiation of the response algorithm and subsequent implementation on the computer provides second-order sensitivities at a significantly reduced cost. The sensitivity results are consistent with and have the same numerical precision as the ordinary response. The computational cost advantage of the direct differentiation approach increases as the problem size increases. Several novel implementation techniques are developed in this paper to optimize the computational efficiency. The derivations and implementations are demonstrated and verified with two finite-element analysis examples. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A10%288 [...]

Random plastic analysis using a constitutive model to predict the evolutionary stress-related responses and time passages to failure / T. L. Attard in Journal of engineering mechanics, Vol. 134 N°10 (Octobre 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp.881–891. Titre : Random plastic analysis using a constitutive model to predict the evolutionary stress-related responses and time passages to failure Type de document : texte imprimé Auteurs : T. L. Attard, Auteur ; M. P. Mignolet, Auteur Année de publication : 2008 Article en page(s) : pp.881–891. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Plasticity  Constitutive  models  Predictions  Failures  Statistics  Nonlinear  analysis  Probability  distribution  Strain  distribution Résumé : The random vibration analyses of gradually yielding shear-frame buildings are considered using a recently proposed constitutive model that is used to calculate the detailed degradation of the stiffness of structures which permits the prediction of their global responses, as well as the states of stress in their members. It is shown that the detailed stress degradation model can also be used in connection with a global force-displacement model, such as the Bouc and Wen model, to predict the time evolution of the various stress-related variables and time passages to failure. The two models are applied in separate analyses and are exemplified using both a single-story building and a four-story building subjected to artificial ground motions. The corresponding probability density functions of the various stress-related responses, including the strains and plastic hinge lengths, and the first time passages to failure are presented and discussed. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A10%288 [...] [article] Random plastic analysis using a constitutive model to predict the evolutionary stress-related responses and time passages to failure [texte imprimé] / T. L. Attard, Auteur ; M. P. Mignolet, Auteur . - 2008 . - pp.881–891. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp.881–891. Mots-clés : Plasticity  Constitutive  models  Predictions  Failures  Statistics  Nonlinear  analysis  Probability  distribution  Strain  distribution Résumé : The random vibration analyses of gradually yielding shear-frame buildings are considered using a recently proposed constitutive model that is used to calculate the detailed degradation of the stiffness of structures which permits the prediction of their global responses, as well as the states of stress in their members. It is shown that the detailed stress degradation model can also be used in connection with a global force-displacement model, such as the Bouc and Wen model, to predict the time evolution of the various stress-related variables and time passages to failure. The two models are applied in separate analyses and are exemplified using both a single-story building and a four-story building subjected to artificial ground motions. The corresponding probability density functions of the various stress-related responses, including the strains and plastic hinge lengths, and the first time passages to failure are presented and discussed. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A10%288 [...]

What did and did not cause collapse of world tade center twin towers in New York? / Zdenek P. Bazant in Journal of engineering mechanics, Vol. 134 N°10 (Octobre 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp. 892–906. Titre : What did and did not cause collapse of world tade center twin towers in New York? Type de document : texte imprimé Auteurs : Zdenek P. Bazant, Auteur ; Jia-Liang Le, Auteur ; Frank R. Greening, Auteur Année de publication : 2008 Article en page(s) : pp. 892–906. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Collapse  Buildings  high-rise  Towers  New  York  New Résumé : Previous analysis of progressive collapse showed that gravity alone suffices to explain the overall collapse of the World Trade Center Towers. However, it remains to be determined whether the recent allegations of controlled demolition have any scientific merit. The present analysis proves that they do not. The video record available for the first few seconds of collapse is shown to agree with the motion history calculated from the differential equation of progressive collapse but, despite uncertain values of some parameters, it is totally out of range of the free fall hypothesis, on which these allegations rest. It is shown that the observed size range (0.01–0.1mm) of the dust particles of pulverized concrete is consistent with the theory of comminution caused by impact, and that less than 10% of the total gravitational energy, converted to kinetic energy, sufficed to produce this dust (whereas, more than 150t of TNT per tower would have to be installed, into many small holes drilled into concrete, to produce the same pulverization). The air ejected from the building by gravitational collapse must have attained, near the ground, the speed of almost 500 miles per hour (or 223m/s , or 803km/h ) on average, and fluctuations must have reached the speed of sound. This explains the loud booms and wide spreading of pulverized concrete and other fragments, and shows that the lower margin of the dust cloud could not have coincided with the crushing front. The resisting upward forces due to pulverization and to ejection of air, dust, and solid fragments, neglected in previous studies, are indeed found to be negligible during the first few seconds of collapse but not insignificant near the end of crush-down. The calculated crush-down duration is found to match a logical interpretation of seismic record, while the free fall duration grossly disagrees with this record. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A10%288 [...] [article] What did and did not cause collapse of world tade center twin towers in New York? [texte imprimé] / Zdenek P. Bazant, Auteur ; Jia-Liang Le, Auteur ; Frank R. Greening, Auteur . - 2008 . - pp. 892–906. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp. 892–906. Mots-clés : Collapse  Buildings  high-rise  Towers  New  York  New Résumé : Previous analysis of progressive collapse showed that gravity alone suffices to explain the overall collapse of the World Trade Center Towers. However, it remains to be determined whether the recent allegations of controlled demolition have any scientific merit. The present analysis proves that they do not. The video record available for the first few seconds of collapse is shown to agree with the motion history calculated from the differential equation of progressive collapse but, despite uncertain values of some parameters, it is totally out of range of the free fall hypothesis, on which these allegations rest. It is shown that the observed size range (0.01–0.1mm) of the dust particles of pulverized concrete is consistent with the theory of comminution caused by impact, and that less than 10% of the total gravitational energy, converted to kinetic energy, sufficed to produce this dust (whereas, more than 150t of TNT per tower would have to be installed, into many small holes drilled into concrete, to produce the same pulverization). The air ejected from the building by gravitational collapse must have attained, near the ground, the speed of almost 500 miles per hour (or 223m/s , or 803km/h ) on average, and fluctuations must have reached the speed of sound. This explains the loud booms and wide spreading of pulverized concrete and other fragments, and shows that the lower margin of the dust cloud could not have coincided with the crushing front. The resisting upward forces due to pulverization and to ejection of air, dust, and solid fragments, neglected in previous studies, are indeed found to be negligible during the first few seconds of collapse but not insignificant near the end of crush-down. The calculated crush-down duration is found to match a logical interpretation of seismic record, while the free fall duration grossly disagrees with this record. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A10%288 [...]

Improvement of the eigenvalue-counting method based on the argument principle / Hyung-Jo Jung in Journal of engineering mechanics, Vol. 134 N°10 (Octobre 2008) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp.907–912. Titre : Improvement of the eigenvalue-counting method based on the argument principle Type de document : texte imprimé Auteurs : Hyung-Jo Jung, Auteur ; Ji-Seong Jo, Auteur ; Byoung-Wan Kim, Auteur Année de publication : 2008 Article en page(s) : pp.907–912. Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Eigenvalues  Damping  Algorithms Résumé : This note proposes an improved eigenvalue-counting method based on the argument principle by introducing Rombouts’ algorithm, which is a stable, efficient, and accurate algorithm to calculate the coefficients of the characteristic polynomial of a general square matrix. In addition, this note comprehensively investigates the effectiveness of the proposed method from the viewpoint of the practical consideration by comparing with the modified Sturm sequence property-based counting method which has been recently developed and also known as the well-proven method. In this note, the operation counts in each method are carefully compared and numerically verified. According to analytical and numerical comparison, the argument principle-based counting method is much better than the modified Sturm sequence property-based method from a practical point of view, even if the latter method is much well-established one theoretically. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A10%289 [...] [article] Improvement of the eigenvalue-counting method based on the argument principle [texte imprimé] / Hyung-Jo Jung, Auteur ; Ji-Seong Jo, Auteur ; Byoung-Wan Kim, Auteur . - 2008 . - pp.907–912. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 134 N°10 (Octobre 2008) . - pp.907–912. Mots-clés : Eigenvalues  Damping  Algorithms Résumé : This note proposes an improved eigenvalue-counting method based on the argument principle by introducing Rombouts’ algorithm, which is a stable, efficient, and accurate algorithm to calculate the coefficients of the characteristic polynomial of a general square matrix. In addition, this note comprehensively investigates the effectiveness of the proposed method from the viewpoint of the practical consideration by comparing with the modified Sturm sequence property-based counting method which has been recently developed and also known as the well-proven method. In this note, the operation counts in each method are carefully compared and numerically verified. According to analytical and numerical comparison, the argument principle-based counting method is much better than the modified Sturm sequence property-based method from a practical point of view, even if the latter method is much well-established one theoretically. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282008%29134%3A10%289 [...]

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