Documents disponibles écrits par cet auteur

Approximations in progressive collapse modeling / Alashker, Yasser in Journal of structural engineering, Vol. 137 N° 9 (Septembre 2011) 

Public ISBD [article]  in Journal of structural engineering > Vol. 137 N° 9 (Septembre 2011) . - pp. 914-924 Titre : Approximations in progressive collapse modeling Type de document : texte imprimé Auteurs : Alashker, Yasser, Auteur ; Honghao Li, Auteur ; Sherif El-Tawil, Auteur Année de publication : 2011 Article en page(s) : pp. 914-924 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Collapse  Model  Macro  model  Composite  Seismic  Steel  Failure Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Assumptions must necessarily be made when the collapse response of structures is investigated using simulation models. The type and extent of modeling assumptions depend on the computational resources available, modeling expertise, and results sought. Modeling choices that are commonly made include planar versus three-dimensional (3D) representation, simplification of member response for modeling purposes, and the use of macroelements to mimic behavior instead of using elements that are based on fundamental constitutive relationships. Using four different types of models, this paper sheds light on the effect of some commonly employed approximations in collapse modeling. The models represent a 10-story seismically designed steel building and encompass computationally expedient planar and 3D macromodels as well as continuum models of individual frames and the full 3D structural system. After a validation exercise, the simulation models are exercised to investigate system collapse response when columns are forcibly removed and to highlight the effects of the various modeling approaches. The simulation studies show that the floor system contributes significantly to collapse response. It is also shown that well calibrated macromodels can be relied on for accuracy when modeling progressive collapse and that the results of planar analyses cannot always be viewed as conservative. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v137/i9/p914_s1?bypassSSO=1 [article] Approximations in progressive collapse modeling [texte imprimé] / Alashker, Yasser, Auteur ; Honghao Li, Auteur ; Sherif El-Tawil, Auteur . - 2011 . - pp. 914-924. Génie Civil Langues : Anglais (eng) in Journal of structural engineering > Vol. 137 N° 9 (Septembre 2011) . - pp. 914-924 Mots-clés : Collapse  Model  Macro  model  Composite  Seismic  Steel  Failure Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : Assumptions must necessarily be made when the collapse response of structures is investigated using simulation models. The type and extent of modeling assumptions depend on the computational resources available, modeling expertise, and results sought. Modeling choices that are commonly made include planar versus three-dimensional (3D) representation, simplification of member response for modeling purposes, and the use of macroelements to mimic behavior instead of using elements that are based on fundamental constitutive relationships. Using four different types of models, this paper sheds light on the effect of some commonly employed approximations in collapse modeling. The models represent a 10-story seismically designed steel building and encompass computationally expedient planar and 3D macromodels as well as continuum models of individual frames and the full 3D structural system. After a validation exercise, the simulation models are exercised to investigate system collapse response when columns are forcibly removed and to highlight the effects of the various modeling approaches. The simulation studies show that the floor system contributes significantly to collapse response. It is also shown that well calibrated macromodels can be relied on for accuracy when modeling progressive collapse and that the results of planar analyses cannot always be viewed as conservative. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v137/i9/p914_s1?bypassSSO=1

Full operator algorithm for hybrid simulation / Chung-Chan Hung in Earthquake engineering structural dynamics, Vol. 38 N° 13 (Octobre 2009) 

Public ISBD [article]  in Earthquake engineering structural dynamics > Vol. 38 N° 13 (Octobre 2009) . - pp. 1545-1561 Titre : Full operator algorithm for hybrid simulation Type de document : texte imprimé Auteurs : Chung-Chan Hung, Auteur ; Sherif El-Tawil, Auteur Article en page(s) : pp. 1545-1561 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Hybrid  simulation;  Tangent  stiffness;  Corrector  step;  Nonlinear  model;  Dynamics;  OpenSees;  Error  control Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : One of the weaknesses of the operator splitting method (OSM) is that its corrector step employs the approximation that incremental forces are linearly related to the tested structure's initial stiffness matrix. This paper presents a new predictor-corrector technique in which the assumptions about the tested structure's response are shifted to the predictor step, which results in an enhancement in overall simulation accuracy, especially for nonlinear structures. Unlike OSM, which splits the displacement and velocity operators into explicit and implicit terms, the new method uses predicted accelerations to compute fully explicit displacement and velocity values in the predictor step. Another advantage of the proposed technique, termed the full operator method (FOM) is that its formulation makes it suitable for both quasi-static and real-time hybrid simulation. The effectiveness of FOM is first evaluated by investigating error propagation in an undamped single degree-of-freedom model. It is shown that the corrector step in FOM is able to significantly suppress aberrant simulation results caused by incorrect estimation of the structure's stiffness matrix. The performance of FOM is demonstrated by exercising two additional models, which exhibit significant inelastic behavior under the prescribed excitation. The simulation results show that the proposed FOM algorithm is capable of producing accurate solutions and that the corrector step is influential in effectively reducing simulation errors. It is also shown that FOM suppresses actuator displacement control errors because of its reliance on measured quantities in the corrector step. ISSN : 0098-8847 En ligne : www.interscience.wiley.com/journal/eqe [article] Full operator algorithm for hybrid simulation [texte imprimé] / Chung-Chan Hung, Auteur ; Sherif El-Tawil, Auteur . - pp. 1545-1561. Génie Civil Langues : Anglais (eng) in Earthquake engineering structural dynamics > Vol. 38 N° 13 (Octobre 2009) . - pp. 1545-1561 Mots-clés : Hybrid  simulation;  Tangent  stiffness;  Corrector  step;  Nonlinear  model;  Dynamics;  OpenSees;  Error  control Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : One of the weaknesses of the operator splitting method (OSM) is that its corrector step employs the approximation that incremental forces are linearly related to the tested structure's initial stiffness matrix. This paper presents a new predictor-corrector technique in which the assumptions about the tested structure's response are shifted to the predictor step, which results in an enhancement in overall simulation accuracy, especially for nonlinear structures. Unlike OSM, which splits the displacement and velocity operators into explicit and implicit terms, the new method uses predicted accelerations to compute fully explicit displacement and velocity values in the predictor step. Another advantage of the proposed technique, termed the full operator method (FOM) is that its formulation makes it suitable for both quasi-static and real-time hybrid simulation. The effectiveness of FOM is first evaluated by investigating error propagation in an undamped single degree-of-freedom model. It is shown that the corrector step in FOM is able to significantly suppress aberrant simulation results caused by incorrect estimation of the structure's stiffness matrix. The performance of FOM is demonstrated by exercising two additional models, which exhibit significant inelastic behavior under the prescribed excitation. The simulation results show that the proposed FOM algorithm is capable of producing accurate solutions and that the corrector step is influential in effectively reducing simulation errors. It is also shown that FOM suppresses actuator displacement control errors because of its reliance on measured quantities in the corrector step. ISSN : 0098-8847 En ligne : www.interscience.wiley.com/journal/eqe

A method for estimating specimen tangent stiffness for hybrid simulation / Chung-Chan Hung in Earthquake engineering structural dynamics, Vol. 38 N°1 (Janvier 2009) 

Public ISBD [article]  in Earthquake engineering structural dynamics > Vol. 38 N°1 (Janvier 2009) . - pp. 115-134 Titre : A method for estimating specimen tangent stiffness for hybrid simulation Type de document : texte imprimé Auteurs : Chung-Chan Hung, Auteur ; Sherif El-Tawil, Auteur Article en page(s) : pp. 115-134 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Hybrid  simulation;  Tangent  stiffness;  Implicit  methods  ;  Operator-splitting  method;  Accuracy;  Stability Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : Researchers have long recognized the importance and potential benefits of utilizing the tangent stiffness matrix of a test specimen in hybrid simulations employing implicit and mixed-integration schemes. However, the computation of the tangent stiffness matrix during testing has proved to be challenging, particularly for test specimens with more than one degree of freedom (dof). This paper presents a new methodology that is more straightforward and simpler than existing techniques for computing the tangent stiffness matrix of a multi-dof test specimen. The proposed method is combined with the operator-splitting method (OSM), and the capabilities, advantages and limitations of the new formulation are demonstrated through several examples. The accuracy, stability, and error propagation characteristics of the modified OSM are also studied theoretically as well as numerically. The research results show that the proposed algorithm provides results that are better than those produced via the regular OSM alone, especially for damped structures undergoing highly inelastic behavior during testing. ISSN : 0098-8847 En ligne : http://www3.interscience.wiley.com/journal/121397333/abstract [article] A method for estimating specimen tangent stiffness for hybrid simulation [texte imprimé] / Chung-Chan Hung, Auteur ; Sherif El-Tawil, Auteur . - pp. 115-134. Génie Civil Langues : Anglais (eng) in Earthquake engineering structural dynamics > Vol. 38 N°1 (Janvier 2009) . - pp. 115-134 Mots-clés : Hybrid  simulation;  Tangent  stiffness;  Implicit  methods  ;  Operator-splitting  method;  Accuracy;  Stability Index. décimale : 624.1 Infrastructures.Ouvrages en terre. Fondations. Tunnels Résumé : Researchers have long recognized the importance and potential benefits of utilizing the tangent stiffness matrix of a test specimen in hybrid simulations employing implicit and mixed-integration schemes. However, the computation of the tangent stiffness matrix during testing has proved to be challenging, particularly for test specimens with more than one degree of freedom (dof). This paper presents a new methodology that is more straightforward and simpler than existing techniques for computing the tangent stiffness matrix of a multi-dof test specimen. The proposed method is combined with the operator-splitting method (OSM), and the capabilities, advantages and limitations of the new formulation are demonstrated through several examples. The accuracy, stability, and error propagation characteristics of the modified OSM are also studied theoretically as well as numerically. The research results show that the proposed algorithm provides results that are better than those produced via the regular OSM alone, especially for damped structures undergoing highly inelastic behavior during testing. ISSN : 0098-8847 En ligne : http://www3.interscience.wiley.com/journal/121397333/abstract

Progressive collapse resistance of steel-concrete composite floors / Alashker, Yasser in Journal of structural engineering, Vol. 136 N° 10 (Octobre 2010) 

Public ISBD [article]  in Journal of structural engineering > Vol. 136 N° 10 (Octobre 2010) . - pp. 1187-1196 Titre : Progressive collapse resistance of steel-concrete composite floors Type de document : texte imprimé Auteurs : Alashker, Yasser, Auteur ; Sherif El-Tawil, Auteur ; Sadek, Fahim, Auteur Année de publication : 2011 Article en page(s) : pp. 1187-1196 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Composite  floor  systems  Robustness  Disproportionate  collapse  Finite-element  analysis  Progressive  collapse  Shear  connections  Shear  tab  Connection Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper discusses the progressive collapse resistance of steel-concrete composite floors in which steel beams are attached to columns through shear tabs. This is a common type of system used for the gravity bay portions of steel buildings. The study is conducted using computational simulation models validated through extensive comparisons to disparate test data. The models are used to investigate key parameters influencing the robustness of generic composite floors subjected to the removal of a center column. In particular, the effects of deck thickness, steel reinforcement, and the numbers of bolts in the shear tab connection on the behavior of the system are studied as a function of the loading scheme. The simulation results show that the majority of collapse resistance comes from the steel deck and that, for the system considered, increasing connection strength by adding more bolts might not be that beneficial in increasing overall collapse strength. The dynamic impact factor, which is widely used to account for dynamic effects within a static design framework, is also computed and the DIF value recommended in existing design guidelines is evaluated. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v136/i10/p1187_s1?isAuthorized=no [article] Progressive collapse resistance of steel-concrete composite floors [texte imprimé] / Alashker, Yasser, Auteur ; Sherif El-Tawil, Auteur ; Sadek, Fahim, Auteur . - 2011 . - pp. 1187-1196. Génie Civil Langues : Anglais (eng) in Journal of structural engineering > Vol. 136 N° 10 (Octobre 2010) . - pp. 1187-1196 Mots-clés : Composite  floor  systems  Robustness  Disproportionate  collapse  Finite-element  analysis  Progressive  collapse  Shear  connections  Shear  tab  Connection Index. décimale : 624 Constructions du génie civil et du bâtiment. Infrastructures. Ouvrages en terres. Fondations. Tunnels. Ponts et charpentes Résumé : This paper discusses the progressive collapse resistance of steel-concrete composite floors in which steel beams are attached to columns through shear tabs. This is a common type of system used for the gravity bay portions of steel buildings. The study is conducted using computational simulation models validated through extensive comparisons to disparate test data. The models are used to investigate key parameters influencing the robustness of generic composite floors subjected to the removal of a center column. In particular, the effects of deck thickness, steel reinforcement, and the numbers of bolts in the shear tab connection on the behavior of the system are studied as a function of the loading scheme. The simulation results show that the majority of collapse resistance comes from the steel deck and that, for the system considered, increasing connection strength by adding more bolts might not be that beneficial in increasing overall collapse strength. The dynamic impact factor, which is widely used to account for dynamic effects within a static design framework, is also computed and the DIF value recommended in existing design guidelines is evaluated. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v136/i10/p1187_s1?isAuthorized=no

Seismic behavior of a coupled wall system with HPFRC materials in critical regions / Chung-Chan Hung in Journal of structural engineering, Vol. 137 N° 12 (Décembre 2011) 

Public ISBD [article]  in Journal of structural engineering > Vol. 137 N° 12 (Décembre 2011) . - pp. 1499-1507 Titre : Seismic behavior of a coupled wall system with HPFRC materials in critical regions Type de document : texte imprimé Auteurs : Chung-Chan Hung, Auteur ; Sherif El-Tawil, Auteur Année de publication : 2012 Article en page(s) : pp. 1499-1507 Note générale : Génie Civil Langues : Anglais (eng) Mots-clés : Coupled  walls  Fiber-reinforced  materials  High-performance  fiber-reinforced  concrete  Concrete  structures  Earthquake-resistant  structures  Earthquake  engineering Résumé : High-performance fiber-reinforced concrete (HPFRC) materials have a unique strain-hardening behavior in tension that translates into enhanced structural response, especially under reversed cyclic loading. Recent experimental research has shown that the use of HPFRC to replace regular concrete in components subjected to high cyclic deformation demands can lead to significant benefits, such as relaxation of detailing requirements and reduction in the amount of reinforcing steel. A structural system that is a good candidate to benefit from HPFRC is reinforced concrete coupled walls, where coupling beams and plastic hinge zones undergo large cyclic deformation demands during the design seismic event. This paper discusses the seismic performance of a prototype 18-story coupled-wall system in which the wall plastic hinge zones and the coupling beams are made of HPFRC materials instead of regular reinforced concrete. Computational simulation models are used to investigate system performance under various hazard levels, and system response is evaluated through various parameters including interstory drift, rotation, and distortion of critical structural parts. The simulation results show that the use of HPFRC in place of regular concrete leads to good overall seismic response with enhanced plastic hinging behavior in the wall piers and crack control in the coupling beams and piers. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v137/i12/p1499_s1?isAuthorized=no [article] Seismic behavior of a coupled wall system with HPFRC materials in critical regions [texte imprimé] / Chung-Chan Hung, Auteur ; Sherif El-Tawil, Auteur . - 2012 . - pp. 1499-1507. Génie Civil Langues : Anglais (eng) in Journal of structural engineering > Vol. 137 N° 12 (Décembre 2011) . - pp. 1499-1507 Mots-clés : Coupled  walls  Fiber-reinforced  materials  High-performance  fiber-reinforced  concrete  Concrete  structures  Earthquake-resistant  structures  Earthquake  engineering Résumé : High-performance fiber-reinforced concrete (HPFRC) materials have a unique strain-hardening behavior in tension that translates into enhanced structural response, especially under reversed cyclic loading. Recent experimental research has shown that the use of HPFRC to replace regular concrete in components subjected to high cyclic deformation demands can lead to significant benefits, such as relaxation of detailing requirements and reduction in the amount of reinforcing steel. A structural system that is a good candidate to benefit from HPFRC is reinforced concrete coupled walls, where coupling beams and plastic hinge zones undergo large cyclic deformation demands during the design seismic event. This paper discusses the seismic performance of a prototype 18-story coupled-wall system in which the wall plastic hinge zones and the coupling beams are made of HPFRC materials instead of regular reinforced concrete. Computational simulation models are used to investigate system performance under various hazard levels, and system response is evaluated through various parameters including interstory drift, rotation, and distortion of critical structural parts. The simulation results show that the use of HPFRC in place of regular concrete leads to good overall seismic response with enhanced plastic hinging behavior in the wall piers and crack control in the coupling beams and piers. DEWEY : 624.17 ISSN : 0733-9445 En ligne : http://ascelibrary.org/sto/resource/1/jsendh/v137/i12/p1499_s1?isAuthorized=no

Seismic design of hybrid coupled wall systems / Sherif El-Tawil in Journal of structural engineering, Vol. 136 N° 7 (Juillet 2010) 

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