Dépouillements

Dynamic load simulator / Swaroop K. Yalla in Journal of engineering mechanics, Vol. 133 N°8 (Août 2007) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.855–863. Titre : Dynamic load simulator : actuation strategies and applications Type de document : texte imprimé Auteurs : Swaroop K. Yalla, Auteur ; Ahsan Kareem, Auteur Année de publication : 2007 Article en page(s) : pp.855–863. Note générale : Applied mechanics Langues : Anglais (eng) Mots-clés : Dynamic  loads  Simulation  Feedback  control  Structural  control Résumé : The development of a multiple-actuator dynamic load simulator (DLS), for the simulation of correlated dynamic loads on small-scale structural components and substructures, or on bench-scale system assemblage is presented in this paper. Conceptually, the DLS employs actuators to simulate a desired dynamic loading environment due to wind, waves, or earthquakes, which in special cases may serve as a replacement for conventional facilities such as wind tunnels, wave tanks and shaking tables. The actuation strategy of the DLS is based on force-control rather than the customary motion control (displacement/velocity) scheme. The load simulator is ideal for structural components and for systems that can be idealized as lumped mass systems. An actuation strategy for the DLS based on an innovative scheme that utilizes the coupled control system is developed. For implementation of this scheme, the nonlinear control system toolbox in MATLAB is used. In this scheme, the tuning of control parameters in the time domain is carried out by solving a constrained optimization problem. A suite of loading protocols that includes sinusoidal, two-point correlated fluctuations in wind loading, earthquake induced loading and loads characterized by strong non-Gaussian features is simulated by employing the control scheme introduced here. The load simulation examples presented here demonstrate that the loading time histories generated by utilizing the DLS matched the target values with high fidelity. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2885 [...] [article] Dynamic load simulator : actuation strategies and applications [texte imprimé] / Swaroop K. Yalla, Auteur ; Ahsan Kareem, Auteur . - 2007 . - pp.855–863. Applied mechanics Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.855–863. Mots-clés : Dynamic  loads  Simulation  Feedback  control  Structural  control Résumé : The development of a multiple-actuator dynamic load simulator (DLS), for the simulation of correlated dynamic loads on small-scale structural components and substructures, or on bench-scale system assemblage is presented in this paper. Conceptually, the DLS employs actuators to simulate a desired dynamic loading environment due to wind, waves, or earthquakes, which in special cases may serve as a replacement for conventional facilities such as wind tunnels, wave tanks and shaking tables. The actuation strategy of the DLS is based on force-control rather than the customary motion control (displacement/velocity) scheme. The load simulator is ideal for structural components and for systems that can be idealized as lumped mass systems. An actuation strategy for the DLS based on an innovative scheme that utilizes the coupled control system is developed. For implementation of this scheme, the nonlinear control system toolbox in MATLAB is used. In this scheme, the tuning of control parameters in the time domain is carried out by solving a constrained optimization problem. A suite of loading protocols that includes sinusoidal, two-point correlated fluctuations in wind loading, earthquake induced loading and loads characterized by strong non-Gaussian features is simulated by employing the control scheme introduced here. The load simulation examples presented here demonstrate that the loading time histories generated by utilizing the DLS matched the target values with high fidelity. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2885 [...]

Adaptive control strategy for dynamic substructuring tests / C. N. Lim in Journal of engineering mechanics, Vol. 133 N°8 (Août 2007) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.864–873. Titre : Adaptive control strategy for dynamic substructuring tests Type de document : texte imprimé Auteurs : C. N. Lim, Auteur ; S. A. Neild, Auteur ; D. P. Stoten, Auteur Année de publication : 2007 Article en page(s) : pp.864–873. Note générale : Applied mechanics Langues : Anglais (eng) Mots-clés : Substructures  Structural  control  Dynamic  tests  Hybrid  methods Résumé : Real-time dynamic substructuring, or hybrid testing, is a technique that enables experimental testing of critical elements of a complete structure. The structure in question is decomposed into at least two parts: the critical element, which is physically tested, and the remainder of the structure, which is modeled numerically. For accurate replication of the system to be emulated, the two parts must interact, via a controller to compensate for the actuator dynamics, in real-time, and with minimal errors at their interfaces. During development, the adaptive minimal controller synthesis (MCS) algorithm controller has previously been implemented for substructuring of a one-degree-of-freedom mass-spring-damper system. The potential advantage that MCS has over a traditional linear controller is its lack of reliance on detailed knowledge of the experimental specimen dynamics. This paper presents the MCSmd control strategy, an improved MCS-based strategy for substructure testing, using a modified demand (md) signal. Experimental and simulation studies of the MCSmd controller applied to a two-degree-of-freedom mass spring damper system are presented along with an analysis of the transient gain behavior. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2886 [...] [article] Adaptive control strategy for dynamic substructuring tests [texte imprimé] / C. N. Lim, Auteur ; S. A. Neild, Auteur ; D. P. Stoten, Auteur . - 2007 . - pp.864–873. Applied mechanics Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.864–873. Mots-clés : Substructures  Structural  control  Dynamic  tests  Hybrid  methods Résumé : Real-time dynamic substructuring, or hybrid testing, is a technique that enables experimental testing of critical elements of a complete structure. The structure in question is decomposed into at least two parts: the critical element, which is physically tested, and the remainder of the structure, which is modeled numerically. For accurate replication of the system to be emulated, the two parts must interact, via a controller to compensate for the actuator dynamics, in real-time, and with minimal errors at their interfaces. During development, the adaptive minimal controller synthesis (MCS) algorithm controller has previously been implemented for substructuring of a one-degree-of-freedom mass-spring-damper system. The potential advantage that MCS has over a traditional linear controller is its lack of reliance on detailed knowledge of the experimental specimen dynamics. This paper presents the MCSmd control strategy, an improved MCS-based strategy for substructure testing, using a modified demand (md) signal. Experimental and simulation studies of the MCSmd controller applied to a two-degree-of-freedom mass spring damper system are presented along with an analysis of the transient gain behavior. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2886 [...]

Free-vibration analysis and material constants identification of laminated composite sandwich plates / C. R. Lee in Journal of engineering mechanics, Vol. 133 N°8 (Août 2007) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.874–886. Titre : Free-vibration analysis and material constants identification of laminated composite sandwich plates Type de document : texte imprimé Auteurs : C. R. Lee, Auteur ; Kam, T. Y., Auteur ; S. J. Sun, Auteur Année de publication : 2007 Article en page(s) : pp.874–886. Note générale : Applied mechanics Langues : Anglais (eng) Mots-clés : Composite  materials  Sandwich  panels  Plates  Vibration  Laminates Résumé : Free vibration of symmetrically laminated composite sandwich plates with elastic edge restraints is studied via the Rayleigh–Ritz approach. The proposed Rayleigh–Ritz method is constructed on the basis of the layer-wise linear displacement theory. The accuracy of the method in predicting natural frequencies of composite sandwich plates with different boundary conditions is verified by the results reported in the literature or the experimental data obtained in this study. The proposed method is then applied to the material constant identification of free composite sandwich plates using the first six theoretical natural frequencies of the plates. In the identification process, trial material constants are used in the present method to predict the theoretical natural frequencies, a frequency discrepancy function is established to measure the sum of the squared differences between the experimental and theoretical natural frequencies, and a stochastic global minimization algorithm is used to search for the best estimates of the material constants by making the frequency discrepancy function a global minimum. Applications of the material constant identification technique are demonstrated by means of several examples. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2887 [...] [article] Free-vibration analysis and material constants identification of laminated composite sandwich plates [texte imprimé] / C. R. Lee, Auteur ; Kam, T. Y., Auteur ; S. J. Sun, Auteur . - 2007 . - pp.874–886. Applied mechanics Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.874–886. Mots-clés : Composite  materials  Sandwich  panels  Plates  Vibration  Laminates Résumé : Free vibration of symmetrically laminated composite sandwich plates with elastic edge restraints is studied via the Rayleigh–Ritz approach. The proposed Rayleigh–Ritz method is constructed on the basis of the layer-wise linear displacement theory. The accuracy of the method in predicting natural frequencies of composite sandwich plates with different boundary conditions is verified by the results reported in the literature or the experimental data obtained in this study. The proposed method is then applied to the material constant identification of free composite sandwich plates using the first six theoretical natural frequencies of the plates. In the identification process, trial material constants are used in the present method to predict the theoretical natural frequencies, a frequency discrepancy function is established to measure the sum of the squared differences between the experimental and theoretical natural frequencies, and a stochastic global minimization algorithm is used to search for the best estimates of the material constants by making the frequency discrepancy function a global minimum. Applications of the material constant identification technique are demonstrated by means of several examples. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2887 [...]

Large-eddy simulations on indoor/outdoor air quality relationship in an isolated urban building / Murphy K. K. Lai in Journal of engineering mechanics, Vol. 133 N°8 (Août 2007) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.887–898. Titre : Large-eddy simulations on indoor/outdoor air quality relationship in an isolated urban building Type de document : texte imprimé Auteurs : Murphy K. K. Lai, Auteur ; Andy T. Y. Chan, Auteur Année de publication : 2007 Article en page(s) : pp.887–898. Note générale : Applied mechanics Langues : Anglais (eng) Mots-clés : Air  flow  Air  pollution  Computational  fluid  dynamics  technique  Simulation  Air  quality  Indoor  air  pollution  Urban  areas Résumé : The airflow, pollutant dispersion and penetration of outdoor pollutants indoor in an isolated urban building are investigated computationally. The computation involves solving the two-dimensional Navier–Stokes equations using large eddy simulations based on the Smagorinsky subgrid scale model. The simulations involve investigations of the phenomena of airflow and pollutant dispersion in both indoor and outdoor environments under different Reynolds numbers with distinct combinations of building height, floor height, and building width. Pollutants originate from outdoor, located at the datum level of the windward side of the building. The objective is to study how outdoor pollutants penetrate indoor and relate this pattern to different building geometric configurations. The gradual increase in Reynolds number significantly favors pollutant transportation into the indoor environment and thus eventually changes the indoor/outdoor (IO) air ratio. Moreover, the value of the IO air ratio is particularly found to be highly affected by building height due to the capability of climbing over and escaping from the roof of the building. Results also show that the IO air ratio is dependent on the position of the sampling, which has been ignored in many previous experimental works. The research work poses important questions of indoor air quality as well as field measurements of the IO parameter. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2888 [...] [article] Large-eddy simulations on indoor/outdoor air quality relationship in an isolated urban building [texte imprimé] / Murphy K. K. Lai, Auteur ; Andy T. Y. Chan, Auteur . - 2007 . - pp.887–898. Applied mechanics Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.887–898. Mots-clés : Air  flow  Air  pollution  Computational  fluid  dynamics  technique  Simulation  Air  quality  Indoor  air  pollution  Urban  areas Résumé : The airflow, pollutant dispersion and penetration of outdoor pollutants indoor in an isolated urban building are investigated computationally. The computation involves solving the two-dimensional Navier–Stokes equations using large eddy simulations based on the Smagorinsky subgrid scale model. The simulations involve investigations of the phenomena of airflow and pollutant dispersion in both indoor and outdoor environments under different Reynolds numbers with distinct combinations of building height, floor height, and building width. Pollutants originate from outdoor, located at the datum level of the windward side of the building. The objective is to study how outdoor pollutants penetrate indoor and relate this pattern to different building geometric configurations. The gradual increase in Reynolds number significantly favors pollutant transportation into the indoor environment and thus eventually changes the indoor/outdoor (IO) air ratio. Moreover, the value of the IO air ratio is particularly found to be highly affected by building height due to the capability of climbing over and escaping from the roof of the building. Results also show that the IO air ratio is dependent on the position of the sampling, which has been ignored in many previous experimental works. The research work poses important questions of indoor air quality as well as field measurements of the IO parameter. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2888 [...]

Sediment resuspension and hydrodynamics in lake okeechobee during the late summer / Kang-Ren Jin in Journal of engineering mechanics, Vol. 133 N°8 (Août 2007) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.899–910. Titre : Sediment resuspension and hydrodynamics in lake okeechobee during the late summer Type de document : texte imprimé Auteurs : Kang-Ren Jin, Auteur ; Detong Sun, Auteur Année de publication : 2007 Article en page(s) : pp.899–910. Note générale : Applied mechanics Langues : Anglais (eng) Mots-clés : Hydrodynamics  Water  circulation  Lakes  Sediment  Florida Résumé : In this study, in order to better understand the mechanisms affecting sediment resuspension, extensive data sets were collected in September and October of 2002 including wind velocity, wave, current velocity, water temperature, total suspended solid, suspended sediment concentration, and total phosphorus. Analyses of these data indicate that waves are the dominant factors in sediment resuspension while wind-induced currents are the primary forces to transport suspended sediments. Surface and bottom currents frequently flow in opposite directions, forming a stratified water column. A time lag exists between currents near lake bottom and wind forcing at the surface. The diurnal thermal stratification occurs in the deep region of the lake. A time lag is also found between suspended sediment concentration and wind speed. The study provides valuable storm-event data and mechanism analyses, which can improve our understanding of the lake circulation, wave dynamics, and their impact on sediment resuspension and vertical mixing in Lake Okeechobee. The data resulting from this study will be used to validate the Lake Okeechobee Environment Model which is used to predict the impacts of different management scenarios on lake activities. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2889 [...] [article] Sediment resuspension and hydrodynamics in lake okeechobee during the late summer [texte imprimé] / Kang-Ren Jin, Auteur ; Detong Sun, Auteur . - 2007 . - pp.899–910. Applied mechanics Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.899–910. Mots-clés : Hydrodynamics  Water  circulation  Lakes  Sediment  Florida Résumé : In this study, in order to better understand the mechanisms affecting sediment resuspension, extensive data sets were collected in September and October of 2002 including wind velocity, wave, current velocity, water temperature, total suspended solid, suspended sediment concentration, and total phosphorus. Analyses of these data indicate that waves are the dominant factors in sediment resuspension while wind-induced currents are the primary forces to transport suspended sediments. Surface and bottom currents frequently flow in opposite directions, forming a stratified water column. A time lag exists between currents near lake bottom and wind forcing at the surface. The diurnal thermal stratification occurs in the deep region of the lake. A time lag is also found between suspended sediment concentration and wind speed. The study provides valuable storm-event data and mechanism analyses, which can improve our understanding of the lake circulation, wave dynamics, and their impact on sediment resuspension and vertical mixing in Lake Okeechobee. The data resulting from this study will be used to validate the Lake Okeechobee Environment Model which is used to predict the impacts of different management scenarios on lake activities. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2889 [...]

Crack bridging in polymer nanocomposites / Muralidhar Seshadri in Journal of engineering mechanics, Vol. 133 N°8 (Août 2007) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.911–918. Titre : Crack bridging in polymer nanocomposites Type de document : texte imprimé Auteurs : Muralidhar Seshadri, Auteur ; Sunil Saigal, Auteur Année de publication : 2007 Article en page(s) : pp.911–918. Note générale : Applied mechanics Langues : Anglais (eng) Mots-clés : Polymers  Fractures  Cracking Résumé : Carbon nanotube reinforced composites offer enhancements in fracture properties since the reinforcing nanotubes provide a bridging mechanism to resist crack growth. In this paper, a study of crack bridging by nanotubes in a nanotube-reinforced polymer composite is presented. The process of crack bridging is idealized as normal pullout of the participating nanotubes from the polymer matrix. The resistance to crack growth due to bridging is taken as the aggregate of the resistance offered by all the nanotubes, ignoring any interaction among the nanotubes themselves. The pullout of a single nanotube from the polymer matrix is modeled as an axisymmetric, nearly one-dimensional problem. This is done by assuming that fracture along the nanotube–polymer interface is dominated by shear openings, and that the nanotube behaves as a rigid body. When the polymer is a linear elastic material, the force–displacement relation for pullout is obtained as a function of dimensionless variables representing the interfacial fracture energy and the pullout length scale. Applying the correspondence principle, the elastic results are extended to the case where the polymer is a linear viscoelastic material with a single relaxation time. The force–displacement relation is then a function of the viscoelastic properties of the polymer and the pullout velocity as well. Using these results, the apparent enhancement in the fracture energy of the composite is obtained. This provides a guideline to design these composites for desired fracture properties in terms of the interfacial strength of the nanotube–polymer interface and the volume fraction of the nanotubes. Results of numerical simulations of nanotube pullout are compared to the predictions of the analytical model. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2891 [...] [article] Crack bridging in polymer nanocomposites [texte imprimé] / Muralidhar Seshadri, Auteur ; Sunil Saigal, Auteur . - 2007 . - pp.911–918. Applied mechanics Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.911–918. Mots-clés : Polymers  Fractures  Cracking Résumé : Carbon nanotube reinforced composites offer enhancements in fracture properties since the reinforcing nanotubes provide a bridging mechanism to resist crack growth. In this paper, a study of crack bridging by nanotubes in a nanotube-reinforced polymer composite is presented. The process of crack bridging is idealized as normal pullout of the participating nanotubes from the polymer matrix. The resistance to crack growth due to bridging is taken as the aggregate of the resistance offered by all the nanotubes, ignoring any interaction among the nanotubes themselves. The pullout of a single nanotube from the polymer matrix is modeled as an axisymmetric, nearly one-dimensional problem. This is done by assuming that fracture along the nanotube–polymer interface is dominated by shear openings, and that the nanotube behaves as a rigid body. When the polymer is a linear elastic material, the force–displacement relation for pullout is obtained as a function of dimensionless variables representing the interfacial fracture energy and the pullout length scale. Applying the correspondence principle, the elastic results are extended to the case where the polymer is a linear viscoelastic material with a single relaxation time. The force–displacement relation is then a function of the viscoelastic properties of the polymer and the pullout velocity as well. Using these results, the apparent enhancement in the fracture energy of the composite is obtained. This provides a guideline to design these composites for desired fracture properties in terms of the interfacial strength of the nanotube–polymer interface and the volume fraction of the nanotubes. Results of numerical simulations of nanotube pullout are compared to the predictions of the analytical model. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2891 [...]

Modeling cross anisotropy in granular materials / Abelev, Andrei V. in Journal of engineering mechanics, Vol. 133 N°8 (Août 2007) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.919–932. Titre : Modeling cross anisotropy in granular materials Type de document : texte imprimé Auteurs : Abelev, Andrei V., Auteur ; Suresh K. Gutta, Auteur ; Poul V. Lade, Auteur Année de publication : 2007 Article en page(s) : pp.919–932. Note générale : Applied mechanics Langues : Anglais (eng) Mots-clés : Granular  materials  Anisotropy  Isotropic  materials  Compression  tests  Triaxial  tests  Models Résumé : A constitutive model has been developed to capture the behavior of cross-anisotropic frictional materials. The elastoplastic, single hardening model for isotropic materials serves as the basic framework. Based on the experimental results of cross-anisotropic sands in isotropic compression tests, the principal stress coordinate system is rotated such that the model operates isotropically within the rotated framework. Experimental plastic work contours on the octahedral plane are plotted for a series of true triaxial tests on dense Santa Monica Beach sand to study the effects of cross anisotropy on the evolution of yield surfaces. The amount of rotation of the yield and plastic potential surfaces decreases to zero (isotropic state) with loading. The model is constructed for cases where the principal stress and material symmetry axes are collinear and no significant rotation of principal stresses occur. The model incorporates fourteen parameters that can be determined from simple experiments, such as isotropic compression, drained triaxial compression, and triaxial extension tests. A series of true triaxial and isotropic compression tests on dense Santa Monica Beach sand are used as a basis for verification of the capabilities of the proposed model. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2891 [...] [article] Modeling cross anisotropy in granular materials [texte imprimé] / Abelev, Andrei V., Auteur ; Suresh K. Gutta, Auteur ; Poul V. Lade, Auteur . - 2007 . - pp.919–932. Applied mechanics Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.919–932. Mots-clés : Granular  materials  Anisotropy  Isotropic  materials  Compression  tests  Triaxial  tests  Models Résumé : A constitutive model has been developed to capture the behavior of cross-anisotropic frictional materials. The elastoplastic, single hardening model for isotropic materials serves as the basic framework. Based on the experimental results of cross-anisotropic sands in isotropic compression tests, the principal stress coordinate system is rotated such that the model operates isotropically within the rotated framework. Experimental plastic work contours on the octahedral plane are plotted for a series of true triaxial tests on dense Santa Monica Beach sand to study the effects of cross anisotropy on the evolution of yield surfaces. The amount of rotation of the yield and plastic potential surfaces decreases to zero (isotropic state) with loading. The model is constructed for cases where the principal stress and material symmetry axes are collinear and no significant rotation of principal stresses occur. The model incorporates fourteen parameters that can be determined from simple experiments, such as isotropic compression, drained triaxial compression, and triaxial extension tests. A series of true triaxial and isotropic compression tests on dense Santa Monica Beach sand are used as a basis for verification of the capabilities of the proposed model. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2891 [...]

Closed-form solutions for flexural response of fiber-reinforced concrete beams / C. Soranakom in Journal of engineering mechanics, Vol. 133 N°8 (Août 2007) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.933–941. Titre : Closed-form solutions for flexural response of fiber-reinforced concrete beams Type de document : texte imprimé Auteurs : C. Soranakom, Auteur ; B. Mobasher, Auteur Année de publication : 2007 Article en page(s) : pp.933–941. Note générale : Applied mechanics Langues : Anglais (eng) Mots-clés : Concrete  reinforced  Fiber  reinforced  materials  Bending  moments  Closed  form  solutions  Flexural  strength Résumé : A constitutive law for fiber-reinforced concrete materials consisting of an elastic perfectly plastic model for compression and an elastic-constant postpeak response for tension is presented. The material parameters are described by using Young’s modulus and first cracking strain in addition to four nondimensional parameters to define postpeak tensile strength, compressive strength, and ultimate strain levels in tension and compression. The closed-form solutions for moment-curvature response are derived and normalized with respect to their values at the cracking moment. Further simplification of the moment-curvature response to a bilinear model, and the use of the moment-area method results in another set of closed-form solutions to calculate midspan deflection of a beam under three- and four-point bending tests. Model simulations are correlated with a variety of test results available in literature. The simulation of a three- and four-point bending test reveals that the direct use of uniaxial tensile response underpredicts the flexural response. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2893 [...] [article] Closed-form solutions for flexural response of fiber-reinforced concrete beams [texte imprimé] / C. Soranakom, Auteur ; B. Mobasher, Auteur . - 2007 . - pp.933–941. Applied mechanics Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.933–941. Mots-clés : Concrete  reinforced  Fiber  reinforced  materials  Bending  moments  Closed  form  solutions  Flexural  strength Résumé : A constitutive law for fiber-reinforced concrete materials consisting of an elastic perfectly plastic model for compression and an elastic-constant postpeak response for tension is presented. The material parameters are described by using Young’s modulus and first cracking strain in addition to four nondimensional parameters to define postpeak tensile strength, compressive strength, and ultimate strain levels in tension and compression. The closed-form solutions for moment-curvature response are derived and normalized with respect to their values at the cracking moment. Further simplification of the moment-curvature response to a bilinear model, and the use of the moment-area method results in another set of closed-form solutions to calculate midspan deflection of a beam under three- and four-point bending tests. Model simulations are correlated with a variety of test results available in literature. The simulation of a three- and four-point bending test reveals that the direct use of uniaxial tensile response underpredicts the flexural response. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2893 [...]

Identification of concentrated damages in euler-bernoulli beams under static loads / G. Buda in Journal of engineering mechanics, Vol. 133 N°8 (Août 2007) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.942–956. Titre : Identification of concentrated damages in euler-bernoulli beams under static loads Type de document : texte imprimé Auteurs : G. Buda, Auteur ; S. Caddemi, Auteur Année de publication : 2007 Article en page(s) : pp.942–956. Note générale : Applied mechanics Langues : Anglais (eng) Mots-clés : Damage  Beams  Static  loads  Parameters  Stiffness  Structural  elements Résumé : An identification procedure of concentrated damages in Euler-Bernoulli beams under static loads is presented in this work. The direct analysis problem is solved first by modeling concentrated damages as Dirac’s delta distributions in the flexural stiffness. Closed-form solutions for both statically determinate and indeterminate beams are presented in terms of damage intensities and positions. On this basis, for the inverse damage identification problem, a nonquadratic optimization procedure is proposed. The presented procedure relies on the minimization of an error function measuring the error between the analytical model response and experimental data. The procedure allows to recognize “a posteriori” some sufficient conditions for the uniqueness of the solution of the damage identification problem. The influence of the instrumental noise on the identified parameters is also explored. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2894 [...] [article] Identification of concentrated damages in euler-bernoulli beams under static loads [texte imprimé] / G. Buda, Auteur ; S. Caddemi, Auteur . - 2007 . - pp.942–956. Applied mechanics Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.942–956. Mots-clés : Damage  Beams  Static  loads  Parameters  Stiffness  Structural  elements Résumé : An identification procedure of concentrated damages in Euler-Bernoulli beams under static loads is presented in this work. The direct analysis problem is solved first by modeling concentrated damages as Dirac’s delta distributions in the flexural stiffness. Closed-form solutions for both statically determinate and indeterminate beams are presented in terms of damage intensities and positions. On this basis, for the inverse damage identification problem, a nonquadratic optimization procedure is proposed. The presented procedure relies on the minimization of an error function measuring the error between the analytical model response and experimental data. The procedure allows to recognize “a posteriori” some sufficient conditions for the uniqueness of the solution of the damage identification problem. The influence of the instrumental noise on the identified parameters is also explored. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2894 [...]

Asymptotic derivation of shear beam theory from timoshenko theory / Dewey H. Hodges in Journal of engineering mechanics, Vol. 133 N°8 (Août 2007) 

Public ISBD [article]  in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.957–961. Titre : Asymptotic derivation of shear beam theory from timoshenko theory Type de document : texte imprimé Auteurs : Dewey H. Hodges, Auteur Année de publication : 2007 Article en page(s) : pp.957–961. Note générale : Applied mechanics Langues : Anglais (eng) Mots-clés : Beams  Shear  modulus  Young’s  modulus  Theories Résumé : A systematic reduction of Timoshenko beam theory to shear beam theory is presented and compared to a parallel reduction to Euler–Bernoulli theory. The agreement between Timoshenko and shear theories is seen to improve as the ratio of Young’s modulus to shear modulus increases, as the mode number increases, and as the beam becomes fatter, which are the opposite trends for agreement between Timoshenko and Euler–Bernoulli theories. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2895 [...] [article] Asymptotic derivation of shear beam theory from timoshenko theory [texte imprimé] / Dewey H. Hodges, Auteur . - 2007 . - pp.957–961. Applied mechanics Langues : Anglais (eng) in Journal of engineering mechanics > Vol. 133 N°8 (Août 2007) . - pp.957–961. Mots-clés : Beams  Shear  modulus  Young’s  modulus  Theories Résumé : A systematic reduction of Timoshenko beam theory to shear beam theory is presented and compared to a parallel reduction to Euler–Bernoulli theory. The agreement between Timoshenko and shear theories is seen to improve as the ratio of Young’s modulus to shear modulus increases, as the mode number increases, and as the beam becomes fatter, which are the opposite trends for agreement between Timoshenko and Euler–Bernoulli theories. ISSN : 0733-9399 En ligne : http://ascelibrary.org/doi/abs/10.1061/%28ASCE%290733-9399%282007%29133%3A8%2895 [...]

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