Dépouillements

New analytical model for composite materials containing local resonance units / Zhang Bo in Journal of engineering mechanics, Vol. 137 N° 1 (Janvier 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.1-7 Titre : New analytical model for composite materials containing local resonance units Type de document : texte imprimé Auteurs : Zhang Bo, Auteur ; Zongjin Li, Auteur Année de publication : 2011 Article en page(s) : pp.1-7 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Density  Resonance  Composite  materials  Vibration  Stiffness. Résumé : In this research, a new approach has been developed to calculate the effective mass density for a composite containing local resonance units consisting of a hard sphere core, a soft shell layer surrounding, and a stiff host medium. The composite has been developed as low-frequency sound shielding material. Different from the model in the original paper based on wave propagation theory, the new approach is based on vibration theory. The natural frequency of local resonance unit is calculated, and then the composite behavior under harmonic load is investigated. It is shown that the effective mass density of the composite can turn to negative and infinitely close to the local resonance. In order to examine the influence of important parameters on the resonant frequency and effective mass density, a parametric study has been carried out. It is found that a thicker soft layer with smaller modules can lead to lower resonant frequency. The predictions of wave spectral gap from the new approach and from the model in the literature are almost identical. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p1_s1?isAuthorized=no [article] New analytical model for composite materials containing local resonance units [texte imprimé] / Zhang Bo, Auteur ; Zongjin Li, Auteur . - 2011 . - pp.1-7. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.1-7 Mots-clés : Density  Resonance  Composite  materials  Vibration  Stiffness. Résumé : In this research, a new approach has been developed to calculate the effective mass density for a composite containing local resonance units consisting of a hard sphere core, a soft shell layer surrounding, and a stiff host medium. The composite has been developed as low-frequency sound shielding material. Different from the model in the original paper based on wave propagation theory, the new approach is based on vibration theory. The natural frequency of local resonance unit is calculated, and then the composite behavior under harmonic load is investigated. It is shown that the effective mass density of the composite can turn to negative and infinitely close to the local resonance. In order to examine the influence of important parameters on the resonant frequency and effective mass density, a parametric study has been carried out. It is found that a thicker soft layer with smaller modules can lead to lower resonant frequency. The predictions of wave spectral gap from the new approach and from the model in the literature are almost identical. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p1_s1?isAuthorized=no

Validation of a new 2D failure mechanism for the stability analysis of a pressurized tunnel face in a spatially varying sand / Guilhem Mollon in Journal of engineering mechanics, Vol. 137 N° 1 (Janvier 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.8-21 Titre : Validation of a new 2D failure mechanism for the stability analysis of a pressurized tunnel face in a spatially varying sand Type de document : texte imprimé Auteurs : Guilhem Mollon, Auteur ; Phoon, Kok-Kwang, Auteur ; Daniel Dias, Auteur Année de publication : 2011 Article en page(s) : pp.8-21 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Tunnels  Limit  analysis  Failures  Shear  strength  Parameters. Résumé : A new two-dimensional (2D) limit analysis failure mechanism is presented for the determination of the critical collapse pressure of a pressurized tunnel face in the case of a soil exhibiting spatial variability in its shear strength parameters. The proposed failure mechanism is a rotational rigid block mechanism. It is constructed in such a manner to respect the normality condition of the limit analysis theory at every point of the velocity discontinuity surfaces taking into account the spatial variation of the soil angle of internal friction. Thus, the slip surfaces of the failure mechanism are not described by standard curves such as log-spirals. Indeed, they are determined point by point using a spatial discretization technique. Though the proposed mechanism is able to deal with frictional and cohesive soils, the present paper only focuses on sands. The mathematical formulation used for the generation of the failure mechanism is first detailed. The proposed kinematical approach is then presented and validated by comparison with numerical simulations. The present failure mechanism was shown to give results (in terms of critical collapse pressure and shape of the collapse mechanism) that compare reasonably well with the numerical simulations at a significantly cheaper computational cost. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p8_s1?isAuthorized=no [article] Validation of a new 2D failure mechanism for the stability analysis of a pressurized tunnel face in a spatially varying sand [texte imprimé] / Guilhem Mollon, Auteur ; Phoon, Kok-Kwang, Auteur ; Daniel Dias, Auteur . - 2011 . - pp.8-21. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.8-21 Mots-clés : Tunnels  Limit  analysis  Failures  Shear  strength  Parameters. Résumé : A new two-dimensional (2D) limit analysis failure mechanism is presented for the determination of the critical collapse pressure of a pressurized tunnel face in the case of a soil exhibiting spatial variability in its shear strength parameters. The proposed failure mechanism is a rotational rigid block mechanism. It is constructed in such a manner to respect the normality condition of the limit analysis theory at every point of the velocity discontinuity surfaces taking into account the spatial variation of the soil angle of internal friction. Thus, the slip surfaces of the failure mechanism are not described by standard curves such as log-spirals. Indeed, they are determined point by point using a spatial discretization technique. Though the proposed mechanism is able to deal with frictional and cohesive soils, the present paper only focuses on sands. The mathematical formulation used for the generation of the failure mechanism is first detailed. The proposed kinematical approach is then presented and validated by comparison with numerical simulations. The present failure mechanism was shown to give results (in terms of critical collapse pressure and shape of the collapse mechanism) that compare reasonably well with the numerical simulations at a significantly cheaper computational cost. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p8_s1?isAuthorized=no

Multimetric sensing for structural damage detection / S. H. Sim in Journal of engineering mechanics, Vol. 137 N° 1 (Janvier 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.22-23 Titre : Multimetric sensing for structural damage detection Type de document : texte imprimé Auteurs : S. H. Sim, Auteur ; B.F Spencer, Auteur ; T. Nagayama, Auteur Année de publication : 2011 Article en page(s) : pp.22-23 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Structural  reliability  Monitoring  Damage  Infrastructure. Résumé : Vibration-based damage detection methods have been widely studied for structural health monitoring of civil infrastructure. Acceleration measurements are frequently employed to extract the dynamic characteristics of the structure and locate damage because they can be obtained conveniently and possess relatively little noise. However, considering the fact that damage is a local phenomenon, the sole use of acceleration measurements that are intrinsically global structural responses limits damage detection capabilities. This paper investigates the possibility of using both global and local measurements to improve the accuracy and robustness of damage detection methods. A multimetric approach based on the damage locating vector method is proposed. Numerical simulations are conducted to verify the efficacy of the proposed approach. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p22_s1?isAuthorized=no [article] Multimetric sensing for structural damage detection [texte imprimé] / S. H. Sim, Auteur ; B.F Spencer, Auteur ; T. Nagayama, Auteur . - 2011 . - pp.22-23. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.22-23 Mots-clés : Structural  reliability  Monitoring  Damage  Infrastructure. Résumé : Vibration-based damage detection methods have been widely studied for structural health monitoring of civil infrastructure. Acceleration measurements are frequently employed to extract the dynamic characteristics of the structure and locate damage because they can be obtained conveniently and possess relatively little noise. However, considering the fact that damage is a local phenomenon, the sole use of acceleration measurements that are intrinsically global structural responses limits damage detection capabilities. This paper investigates the possibility of using both global and local measurements to improve the accuracy and robustness of damage detection methods. A multimetric approach based on the damage locating vector method is proposed. Numerical simulations are conducted to verify the efficacy of the proposed approach. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p22_s1?isAuthorized=no

Adjoint sensitivity analysis of contaminant concentrations in water distribution systems / Roseanna M. Neupauer in Journal of engineering mechanics, Vol. 137 N° 1 (Janvier 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.31-46 Titre : Adjoint sensitivity analysis of contaminant concentrations in water distribution systems Type de document : texte imprimé Auteurs : Roseanna M. Neupauer, Auteur Année de publication : 2011 Article en page(s) : pp.31-46 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Water  distribution  systems  Sensitivity  analysis  Water  pollution  Mathematical  models  Adjoint  state. Résumé : Sensitivity analysis is used to determine how a system state or a model output changes due to a change in the value of a system parameter or a model input. We present the adjoint approach for determining the sensitivity of the concentration of a contaminant in a water distribution system to a change in a system parameter such as the location of the source of contamination, the reaction rate of the contaminant, and others. With the adjoint method, the sensitivity of the model output to any number of parameters can be obtained with one simulation of the adjoint model. If the number of parameters of interest exceeds the number of model outputs for which the sensitivity is desired, the adjoint method is more efficient than traditional direct methods of calculating sensitivities. We develop the adjoint equations for water quality in a water distribution system, verify the adjoint-based sensitivity equation using an analytical example, and demonstrate the numerical calculation of adjoint sensitivities using EPANET. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p31_s1?isAuthorized=no [article] Adjoint sensitivity analysis of contaminant concentrations in water distribution systems [texte imprimé] / Roseanna M. Neupauer, Auteur . - 2011 . - pp.31-46. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.31-46 Mots-clés : Water  distribution  systems  Sensitivity  analysis  Water  pollution  Mathematical  models  Adjoint  state. Résumé : Sensitivity analysis is used to determine how a system state or a model output changes due to a change in the value of a system parameter or a model input. We present the adjoint approach for determining the sensitivity of the concentration of a contaminant in a water distribution system to a change in a system parameter such as the location of the source of contamination, the reaction rate of the contaminant, and others. With the adjoint method, the sensitivity of the model output to any number of parameters can be obtained with one simulation of the adjoint model. If the number of parameters of interest exceeds the number of model outputs for which the sensitivity is desired, the adjoint method is more efficient than traditional direct methods of calculating sensitivities. We develop the adjoint equations for water quality in a water distribution system, verify the adjoint-based sensitivity equation using an analytical example, and demonstrate the numerical calculation of adjoint sensitivities using EPANET. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p31_s1?isAuthorized=no

Outer scaling for open channel flow over a gravel bed / Brian J. Belcher in Journal of engineering mechanics, Vol. 137 N° 1 (Janvier 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.40-46 Titre : Outer scaling for open channel flow over a gravel bed Type de document : texte imprimé Auteurs : Brian J. Belcher, Auteur ; James F. Fox, Auteur Année de publication : 2011 Article en page(s) : pp.40-46 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Turbulence  Velocity  profile  Open  channel  flow  Gravel  River  beds. Résumé : Similarity analysis is performed for hydraulically rough open channel flow over a gravel bed to provide mixed outer scaling of the mean-velocity profile. The analysis is based on equilibrium turbulent boundary-layer theory derived using the asymptotic invariance principle. Outer scaling based on the similarity theory is validated with velocity measurements from the laboratory and field, having a Reynolds number range that includes 1×104, 1×105, and 1×106 and a Froude number range from 0.26 to 0.83. The results show that the free-stream velocity is an appropriate outer scale for gravel-bed river flows at moderate and bankfull stage. The results agree well with the velocity measurements and collapse laboratory and field data, which allow an important connection between open channel research in the laboratory and the applications for which the research is performed in the field. The results show that the R/aD84 roughness parameter is consistent with the mixed scale used in boundary-layer velocity scaling. This is in agreement with the consistent turbulent structure of the flow for both flat plate boundary-layer and open channel flow scenarios. While R/D84 has been used empirically with depth-averaged velocity and roughness laws for many years, this roughness parameter is shown in a theoretical context due to its influence on the turbulent structure of the flow. The results are applicable to modeling the velocity distribution under fundamental gravel-bed flow cases that span to the bankfull flow regime, which provides a contribution to stream engineering. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p40_s1?isAuthorized=no [article] Outer scaling for open channel flow over a gravel bed [texte imprimé] / Brian J. Belcher, Auteur ; James F. Fox, Auteur . - 2011 . - pp.40-46. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.40-46 Mots-clés : Turbulence  Velocity  profile  Open  channel  flow  Gravel  River  beds. Résumé : Similarity analysis is performed for hydraulically rough open channel flow over a gravel bed to provide mixed outer scaling of the mean-velocity profile. The analysis is based on equilibrium turbulent boundary-layer theory derived using the asymptotic invariance principle. Outer scaling based on the similarity theory is validated with velocity measurements from the laboratory and field, having a Reynolds number range that includes 1×104, 1×105, and 1×106 and a Froude number range from 0.26 to 0.83. The results show that the free-stream velocity is an appropriate outer scale for gravel-bed river flows at moderate and bankfull stage. The results agree well with the velocity measurements and collapse laboratory and field data, which allow an important connection between open channel research in the laboratory and the applications for which the research is performed in the field. The results show that the R/aD84 roughness parameter is consistent with the mixed scale used in boundary-layer velocity scaling. This is in agreement with the consistent turbulent structure of the flow for both flat plate boundary-layer and open channel flow scenarios. While R/D84 has been used empirically with depth-averaged velocity and roughness laws for many years, this roughness parameter is shown in a theoretical context due to its influence on the turbulent structure of the flow. The results are applicable to modeling the velocity distribution under fundamental gravel-bed flow cases that span to the bankfull flow regime, which provides a contribution to stream engineering. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p40_s1?isAuthorized=no

Multidimensional performance limit state for hazard fragility functions / G. P. Cimellaro in Journal of engineering mechanics, Vol. 137 N° 1 (Janvier 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.47-60 Titre : Multidimensional performance limit state for hazard fragility functions Type de document : texte imprimé Auteurs : G. P. Cimellaro, Auteur ; A. M. Reinhorn, Auteur Année de publication : 2011 Article en page(s) : pp.47-60 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Hazards  Limit  states  Structural  reliability  Rehabilitation  Safety  California  Health  care  facilities. Résumé : This paper addresses an alternative methodology to calculate fragility functions that considers multiple limit states parameters, such as combinations of response variables of accelerations and interstory drifts. Limit states are defined using a generalized multidimensional limit states function that allows considering dependencies among limit thresholds modeled as random variables in the calculation of fragility curves that are evaluated as function of the return period. A California hospital is used as example to illustrate the proposed approach for developing fragility curves. The study investigates the sensitivity of the proposed approach for evaluating fragility curves when uncertainties in limit states are considered. Influence of structural and response parameters, such as stiffness, damping, acceleration and displacement thresholds, ground motion input, and uncertainties in structural modeling, are also investigated. The proposed approach can be considered as an alternative approach for describing the vulnerable behavior of nonstructural components that are sensitive to multiple parameters such as displacements and accelerations (e.g., partition walls, piping systems, etc.). DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p47_s1?isAuthorized=no [article] Multidimensional performance limit state for hazard fragility functions [texte imprimé] / G. P. Cimellaro, Auteur ; A. M. Reinhorn, Auteur . - 2011 . - pp.47-60. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.47-60 Mots-clés : Hazards  Limit  states  Structural  reliability  Rehabilitation  Safety  California  Health  care  facilities. Résumé : This paper addresses an alternative methodology to calculate fragility functions that considers multiple limit states parameters, such as combinations of response variables of accelerations and interstory drifts. Limit states are defined using a generalized multidimensional limit states function that allows considering dependencies among limit thresholds modeled as random variables in the calculation of fragility curves that are evaluated as function of the return period. A California hospital is used as example to illustrate the proposed approach for developing fragility curves. The study investigates the sensitivity of the proposed approach for evaluating fragility curves when uncertainties in limit states are considered. Influence of structural and response parameters, such as stiffness, damping, acceleration and displacement thresholds, ground motion input, and uncertainties in structural modeling, are also investigated. The proposed approach can be considered as an alternative approach for describing the vulnerable behavior of nonstructural components that are sensitive to multiple parameters such as displacements and accelerations (e.g., partition walls, piping systems, etc.). DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p47_s1?isAuthorized=no

Torsional stiffness of prestressing tendons in double-T beams / Yong-Hak Lee in Journal of engineering mechanics, Vol. 137 N° 1 (Janvier 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.61-72 Titre : Torsional stiffness of prestressing tendons in double-T beams Type de document : texte imprimé Auteurs : Yong-Hak Lee, Auteur ; Won-Jin Sung, Auteur ; Kee-Won Seong, Auteur Année de publication : 2011 Article en page(s) : pp.61-72 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Beams  Prestressing  Warpage  Rotation  Finite  element  method  Stiffness. Résumé : When a prestressed double-T beam is subjected to torsion, a pair of prestressing tendons resists torsional rotation because of the restoring action of the displaced prestressing tendons. A comprehensive formulation to account for the torsional restoring action of double-T beams is presented, based on Vlasov’s hypothesis of considering warping displacement in an open-section. The deformation energies of prestressing tendons and reinforcing bars are calculated based on the deformed geometry to obtain the total potential energy. A two-noded beam element with seven degrees of freedom per node approximates an axial displacement, two translations, two flexural, and one torsional rotations, and a warping displacement to derive the finite-element equilibrium equations by minimizing the potential energy function. The role of prestressing forces of the tendons on the torsional resistance and the limitations of the traditional transformed section approach are addressed when it is applied to torsional problems. As a numerical example, an existing three-span continuous double-T beam is analyzed, and the bimoment and angle of twist are compared to those calculated using conventional three-dimensional finite-element analysis and the analytical solution of governing differential equations. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p61_s1?isAuthorized=no [article] Torsional stiffness of prestressing tendons in double-T beams [texte imprimé] / Yong-Hak Lee, Auteur ; Won-Jin Sung, Auteur ; Kee-Won Seong, Auteur . - 2011 . - pp.61-72. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.61-72 Mots-clés : Beams  Prestressing  Warpage  Rotation  Finite  element  method  Stiffness. Résumé : When a prestressed double-T beam is subjected to torsion, a pair of prestressing tendons resists torsional rotation because of the restoring action of the displaced prestressing tendons. A comprehensive formulation to account for the torsional restoring action of double-T beams is presented, based on Vlasov’s hypothesis of considering warping displacement in an open-section. The deformation energies of prestressing tendons and reinforcing bars are calculated based on the deformed geometry to obtain the total potential energy. A two-noded beam element with seven degrees of freedom per node approximates an axial displacement, two translations, two flexural, and one torsional rotations, and a warping displacement to derive the finite-element equilibrium equations by minimizing the potential energy function. The role of prestressing forces of the tendons on the torsional resistance and the limitations of the traditional transformed section approach are addressed when it is applied to torsional problems. As a numerical example, an existing three-span continuous double-T beam is analyzed, and the bimoment and angle of twist are compared to those calculated using conventional three-dimensional finite-element analysis and the analytical solution of governing differential equations. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p61_s1?isAuthorized=no

Buckling analysis of nonuniform and axially graded columns with varying flexural rigidity / Y. Huang in Journal of engineering mechanics, Vol. 137 N° 1 (Janvier 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.73-81 Titre : Buckling analysis of nonuniform and axially graded columns with varying flexural rigidity Type de document : texte imprimé Auteurs : Y. Huang, Auteur ; X.-F. Li, Auteur Année de publication : 2011 Article en page(s) : pp.73-81 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Buckling  Critical  loads  Bending  Stiffness  Columns. Résumé : In this paper, we present a novel analytic approach to solve the buckling instability of Euler-Bernoulli columns with arbitrarily axial nonhomogeneity and/or varying cross section. For various columns including pinned-pinned columns, clamped columns, and cantilevered columns, the governing differential equation for buckling of columns with varying flexural rigidity is reduced to a Fredholm integral equation. Critical buckling load can be exactly determined by requiring that the resulting integral equation has a nontrivial solution. The effectiveness of the method is confirmed by comparing our results with existing closed-form solutions and numerical results. Flexural rigidity may take a majority of functions including polynomials, trigonometric and exponential functions, etc. Examples are given to illustrate the enhancement of the load-carrying capacity of tapered columns for admissible shape profiles with constant volume or weight, and the proposed method is of benefit to optimum design of columns against buckling in engineering applications. This method can be further extended to treat free vibration of nonuniform beams with axially variable material properties. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p73_s1?isAuthorized=no [article] Buckling analysis of nonuniform and axially graded columns with varying flexural rigidity [texte imprimé] / Y. Huang, Auteur ; X.-F. Li, Auteur . - 2011 . - pp.73-81. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.73-81 Mots-clés : Buckling  Critical  loads  Bending  Stiffness  Columns. Résumé : In this paper, we present a novel analytic approach to solve the buckling instability of Euler-Bernoulli columns with arbitrarily axial nonhomogeneity and/or varying cross section. For various columns including pinned-pinned columns, clamped columns, and cantilevered columns, the governing differential equation for buckling of columns with varying flexural rigidity is reduced to a Fredholm integral equation. Critical buckling load can be exactly determined by requiring that the resulting integral equation has a nontrivial solution. The effectiveness of the method is confirmed by comparing our results with existing closed-form solutions and numerical results. Flexural rigidity may take a majority of functions including polynomials, trigonometric and exponential functions, etc. Examples are given to illustrate the enhancement of the load-carrying capacity of tapered columns for admissible shape profiles with constant volume or weight, and the proposed method is of benefit to optimum design of columns against buckling in engineering applications. This method can be further extended to treat free vibration of nonuniform beams with axially variable material properties. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p73_s1?isAuthorized=no

Why the observed motion history of world trade center towers is smooth / Jia-Liang Le in Journal of engineering mechanics, Vol. 137 N° 1 (Janvier 2011) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.82-84 Titre : Why the observed motion history of world trade center towers is smooth Type de document : texte imprimé Auteurs : Jia-Liang Le, Auteur ; Bažant, Zdeněk P., Auteur Année de publication : 2011 Article en page(s) : pp.82-84 Note générale : Mécanique appliquée Langues : Anglais (eng) Mots-clés : Structural  dynamics  Structural  failures  Damage  Monitoring  Building  high-rise  New  York  City  Velocity  Imaging  techniques. Résumé : The collapse of the World Trade Center towers was initiated by the impact of the upper falling part onto the underlying intact story. At the moment of impact, the velocity of the upper part must have decreased. The fact that no velocity decrease can be discerned in the videos of the early motion of the tower top has been recently exploited to claim that the collapse explanation generally accepted within the structural mechanics community was invalid. This claim is here shown to be groundless. Calculations show that the velocity drop is far too small to be perceptible in amateur video records and is much smaller than the inevitable error of such video records. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p82_s1?isAuthorized=no [article] Why the observed motion history of world trade center towers is smooth [texte imprimé] / Jia-Liang Le, Auteur ; Bažant, Zdeněk P., Auteur . - 2011 . - pp.82-84. Mécanique appliquée Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 137 N° 1 (Janvier 2011) . - pp.82-84 Mots-clés : Structural  dynamics  Structural  failures  Damage  Monitoring  Building  high-rise  New  York  City  Velocity  Imaging  techniques. Résumé : The collapse of the World Trade Center towers was initiated by the impact of the upper falling part onto the underlying intact story. At the moment of impact, the velocity of the upper part must have decreased. The fact that no velocity decrease can be discerned in the videos of the early motion of the tower top has been recently exploited to claim that the collapse explanation generally accepted within the structural mechanics community was invalid. This claim is here shown to be groundless. Calculations show that the velocity drop is far too small to be perceptible in amateur video records and is much smaller than the inevitable error of such video records. DEWEY : 620.1 ISSN : 0733-9399 En ligne : http://ascelibrary.org/emo/resource/1/jenmdt/v137/i1/p82_s1?isAuthorized=no

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