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Ductile Design and Predicted Inelastic Response of Steel Moment Frame Buildings for Extreme Wind LoadsGiles, Tyler Eric 29 July 2021 (has links)
Inelastic design methods have been used in seismic design for several years and are well accepted in engineering practice. In contrast, an inelastic wind design method is yet to be developed, in part due to the inherent differences between seismic forces and wind forces. Current wind design practice follows a linear method to find a design windspeed for the location where the structure will be built. Once the design windspeed has been determined, the lateral force resisting system is designed such that it will behave elastically. This study was conducted with the hypothesis that by providing ductility at the material level, member level, and system level it may be possible to use a reduced design force for wind (i.e., a design force reduction that is proportional to a wind response modification factor). A three-story office building that uses steel moment frames as the primary lateral force resisting system was examined to test the hypothesis. Various levels of ductility were included based on ductility requirements for material strength, section stability and system stability originally developed for seismic design. Moment frames were designed for a range of design windspeeds and for three levels of ductility. For each design windspeed, a non-ductile (representing the moment frame as it would be designed by current standards), moderately-ductile and highly-ductile moment frame were developed. A finite element model of the building was made to capture inelastic material behavior and large displacements. The finite element model was subjected to wind loads based on wind tunnel tests data, and the static pushover, vibration, and dynamic responses of the building were evaluated. The performance of each moderately-ductile and highly-ductile moment frame was compared to the performance of each non-ductile frame of a higher design windspeed. The results show that for moderately-ductile moment frames, a wind response modification factor equal to 2 provided a collapse capacity that met or exceeded the collapse capacity of the comparative nonductile moment frame. For highly-ductile moment frames, a wind response modification factor equal to 3 met or exceeded the collapse capacity of the comparative non-ductile moment frame. In many instances, the collapse capacity of the moderately-ductile moment frame was similar to the collapse capacity of the highly-ductile moment frame. Thus, the results indicate that the use of a response modification factor for wind may be viable.
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[en] A CELL DYNAMICAL MODEL APPLIED TO GRANULAR SYSTEMS / [pt] UM MODELO DE CÉLULAS DINÂMICAS APLICADO A SISTEMAS GRANULARESEDSON VERNEK 11 June 2003 (has links)
[pt] Neste trabalho estudamos o comportamento dinâmico de um gás
granular a baixa densidade do ponto de vista hidrodinâmico.
Fizemos também uma análise de instabilidade linear das
equações de Navier-Stockes para tais sistemas. Finalmente,
construímos um modelo de sistema de celulas dinâmicas para
simular computacionalmente esses sistema e o aplicamos a um
gás granular, a fim de entender um pouco mais sobre seus
comportamentos dinâmicos, sob diversas condições de
contornos externos. / [en] In this work we study the dynamic behavior of a granular
gas at low density from the hydrodynamic point of view. We
also perform a linear instability analysis of the Navier-
Stockes for such systems. Finally we construct a cell
dynamic systems model to simulate computationally these
systems and apply it for a granular gas in order to
understand a little more about its dynamic behavior, under
several boundary conditions.
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A Contribution to the Modeling of Metal Plasticity and Fracture: From Continuum to Discrete DescriptionsKeralavarma, Shyam Mohan 2011 December 1900 (has links)
The objective of this dissertation is to further the understanding of inelastic behavior in metallic materials. Despite the increasing use of polymeric composites in aircraft structures, high specific strength metals continue to be used in key components such as airframe, fuselage, wings, landing gear and hot engine parts. Design of metallic structures subjected to thermomechanical extremes in aerospace, automotive and nuclear applications requires consideration of the plasticity, creep and fracture behavior of these materials. Consideration of inelasticity and damage processes is also important in the design of metallic components used in functional applications such as thin films, flexible electronics and micro electro mechanical systems.
Fracture mechanics has been largely successful in modeling damage and failure phenomena in a host of engineering materials. In the context of ductile metals, the Gurson void growth model remains one of the most successful and widely used models. However, some well documented limitations of the model in quantitative prediction of the fracture strains and failure modes at low triaxialities may be traceable to the limited representation of the damage microstructure in the model. In the first part of this dissertation, we develop an extended continuum model of void growth that takes into account details of the material microstructure such as the texture of the plastically deforming matrix and the evolution of the void shape. The need for such an extension is motivated by a detailed investigation of the effects of the two types of anisotropy on the materials' effective response using finite element analysis. The model is derived using the Hill-Mandel homogenization theory and an approximate limit analysis of a porous representative volume element. Comparisons with several numerical studies are presented towards a partial validation of the analytical model.
Inelastic phenomena such as plasticity and creep result from the collective behavior of a large number of nano and micro scale defects such as dislocations, vacancies and grain boundaries. Continuum models relate macroscopically observable quantities such as stress and strain by coarse graining the discrete defect microstructure. While continuum models provide a good approximation for the effective behavior of bulk materials, several deviations have been observed in experiments at small scales such as an intrinsic size dependence of the material strength. Discrete dislocation dynamics (DD) is a mesoscale method for obtaining the mechanical response of a material by direct simulation of the motion and interactions of dislocations. The model incorporates an intrinsic length scale in the dislocation Burgers vector and potentially allows for size dependent mechanical behavior to emerge naturally from the dynamics of the dislocation ensemble. In the second part of this dissertation, a simplified two dimensional DD model is employed to study several phenomena of practical interest such as strain hardening under homogeneous deformation, growth of microvoids in a crystalline matrix and creep of single crystals at elevated temperatures. These studies have been enabled by several recent enhancements to the existing two-dimensional DD framework described in Chapter V.
The main contributions from this research are: (i) development of a fully anisotropic continuum model of void growth for use in ductile fracture simulations and (ii) enhancing the capabilities of an existing two-dimensional DD framework for large scale simulations in complex domains and at elevated temperatures.
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[en] A CONTRIBUTION TO THE THEORY OF INELASTIC RODS / [pt] UMA CONTRIBUIÇÃO À TEORIA DE ESTRUTURAS UNIDIMENSIONAIS INELÁSTICASFERNANDO ALVES ROCHINHA 03 September 2012 (has links)
[pt] No presente trabalho é feito um apanhado de teorias de estruturas unidimensionais que não se utilizam da teoria tridimensional como ponto de partida. São discutidos alguns modelos sob a mesma ótica, ressaltando-se seus pontos comuns e suas diferenças.
Posteriormente é desenvolvido um modelo exato para estruturas unidimensionais. São discutidos em profundidade medidas de deformação e esforços internos. É tomado um modelo constitutivo elasto-plástico. A modelagem utilizada não faz restrições quanto ao tamanho das deformações e considera a extensibilidade da estrutura.
Através de técnicas numéricas simples, conhecidas como métodos do Tiro, são resolvidos alguns problemas de estruturas unidimensionais modelados pela teoria desenvolvida neste trabalho. Dentro destes casos estuda-se o problema da instabilidade, o efeito do cisalhamento para vigas e o comportamento não linear de materiais (plasticidade). Os resultados são apresentados graficamente.
Por fim são indicados novos caminhos que dão continuidade a este trabalho. / [en] A survey of rod’s models which are not based in the three-dimensional theory is presented. One of the models is picked out and discussed in details (kinematics, efforts and balance laws). An elasto-plastic constitutive model is considered. This model takes into account large deformations and the extensibility of the tods.
A series of numerical simulations of rod’s problems which utilize the shooting methods are considered. These applications study the non linear behavior of rods, in cases which shear. Geometric instability and plasticity are treated.
At the end, suggestions for the continuity of this work are presented.
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Beobachterkonzepte und Darstellungsformen der nichtlinearen Kontinuumsmechanik / Observer concepts and tensorial representations within the framework of nonlinear mechanicsIhlemann, Jörn 11 September 2014 (has links) (PDF)
Im Rahmen der geometrisch und physikalisch nichtlinearen Kontinuumsmechanik werden Beobachterkonzepte und Darstellungsformen tensorieller Größen diskutiert und zum Teil neu eingeführt, die insbesondere die Modellierung und FEM-Implementierung komplizierter Modelle für inelastisches Materialverhalten bei großen Deformationen wirkungsvoll unterstützen. / Observer concepts and several kinds of representations of tensorial quantities are discussed and partly introduced within the framework of geometrically und physically nonlinear continuum mechanics. They are intended to support the modelling of complicated inelastic materials undergoing large deformations.
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Beobachterkonzepte und Darstellungsformen der nichtlinearen Kontinuumsmechanik / Observer concepts and tensorial representations within the framework of nonlinear mechanicsIhlemann, Jörn 27 March 2014 (has links) (PDF)
Im Rahmen der geometrisch und physikalisch nichtlinearen Kontinuumsmechanik werden Beobachterkonzepte und Darstellungsformen tensorieller Größen diskutiert und zum Teil neu eingeführt, die insbesondere die Modellierung und FEM-Implementierung komplizierter Modelle für inelastisches Materialverhalten bei großen Deformationen wirkungsvoll unterstützen. / Observer concepts and several kinds of representations of tensorial quantities are discussed and partly introduced within the framework of geometrically und physically nonlinear continuum mechanics. They are intended to support the modelling of complicated inelastic materials undergoing large deformations.
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[en] A CELL DYNAMIC SYSTEM MODEL APPLIED TO A GRANULAR GAS IN PRESENCE OF CLUSTERS / [pt] UM MODELO DE CÉLULAS DINÂMICAS APLICADO AO GÁS GRANULAR NA PRESENÇA DE AGLOMERADOSADRIANO JOSE AGUIAR MARCAL 05 January 2005 (has links)
[pt] Neste trabalho estudamos o comportamento dinâmico de um gás
granular a baixa densidade do ponto de vista hidrodinâmico.
Fazemos também uma análise de instabilidade linear das
equações de Navier-Stockes para tais sistemas. Finalmente,
construímos um modelo de sistema de Células Dinâmicas para
simular computacionalmente esses sistemas e o aplicamos a
um gás granular, a fim de entender um pouco mais sobre seus
comportamentos dinâmicos, inclusive a formação de
aglomerados, sob as mais variadas condições de contorno. / [en] In this work we study the dynamic behavior of a granular
gas at low density from the hydrodynamic point of view. We
also perform a linear instability analysis of the Navier-
Stockesfor for such systems. Finally, we construct a cell
dynamic systems model to simulate computationally these
systems and apply it for a granular gas in order to
understand a little more about its dynamic behavior,
enclose formation of clusters, under several boundary
conditions.
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[en] THE STATIONARY STATE OF A GRANULAR GAS / [pt] O ESTADO ESTACIONÁRIO DO GÁS GRANULARRIGOBERTO CARLOS PROLEON PATRICIO 22 September 2004 (has links)
[pt] Estendemos o formalismo de Fokker-Planck que foi usado
previamente para descrever, a partir de primeiros
princípios, o comportamento de um gás granular em
esfriamento, com potencial de contato Hertziano e força
de
atrito viscoelástica o qual resulta em um sistema com
coeficiente de restituição que depende da velocidade.
Nesta
tese é estudado, também a partir de primeiros princípios,
o
caso mais geral, o de um estado estacionário com energia
cinética finita e fora do equilíbrio, devido ao
acoplamento
a um mecanismo externo de alimentação de energia. Estende-
se assim a validade do resultado prévio. / [en] We extend the Fokker-Planck formalism used previously to
describe the behavior of a cooling granular gas, with a
Hertzian contact potential and viscoelastic radial
friction, giving a velocity dependent coeficient of
restitution. In this thesis, we study the more general case
of a steady-state with finite kinetic, energy and far from
equilibrium, due to the coupling to an external energy-
feeding mechanism, also from first-principles, and extend
the validity of the former results.
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[en] UNIFORMLY PROBABLE DESIGN RESPONSE SPECTRUM FOR INELASTIC SECONDARY SYSTEMS / [pt] ESPECTRO DE RESPOSTA DE PROJETO UNIFORMEMENTE PROVÁVEL PARA SISTEMAS SECUNDÁRIOS INELÁSTICOSREGINA AUGUSTA CAMPOS SAMPAIO 15 December 2003 (has links)
[pt] Estuda-se a consideração de comportamento inelástico do
material na geração de espectros de resposta de projeto.
Para tanto, trabalha-se sobre um sistema secundário
simplificado acoplado a um pórtico de cinco andares com
características dinâmicas ajustadas para modelar um sistema
principal real, de uma usina nuclear. Faz-se um estudo
paramétrico sobre estes sistemas acoplados onde são
variados os parâmetros: fator de escoamento, a intensidade
da excitação e o nível de amortecimento. É proposto um
fator de dutilidade global formulado em termos de trabalho
externo realizado sobre o sistema secundário. São obtidos
espectros de dutilidade e de resposta. A análise de tais
espectros fornece informações sobre o desempenho do sistema
secundário e seus suportes e conclui por fatores de
transposição entre os espectros elástico e inelástico.
Propõe-se metodologia para obtenção de espectros de
resposta elásticos e inelásticos que levam em conta o
acoplamento entre os sistemas principal e secundário, o
movimento relativo dos suportes e o compromisso
probabilístico entre as ordenadas do espectro e a
sismicidade da região expressa em termos de uma função
densidade de espectro de potência objetivo para a
aceleração do terreno. Um exemplo de obtenção de espectros
de resposta acoplada de projeto uniformemente provável
inelástico é apresentado. / [en] The authors concern includes two main points in the subject
of design response spectra generation for secondary systems
in nuclear power plant structures: the consideration of
inelastic behavior in the secondary systems materials and
the production of uniformly probable design response
spectra. One works with a previously developed secondary
system model attached to primary structure model tuned to
the frequency range of a nuclear power plant building.
A global ductility factor is formulated relating the
plastic to the overall work done by the seismic external
forces on the secondary system. This factor together with a
particular definition of the yielding factor allows one to
determine elastic to inelastic spectrum transpose factors.
A methodology is proposed to generate uniformly probable
coupled response spectra for multiply supported inelastic
secondary systems. The seismic excitation is prescribed by
a target power spectrum density function of the ground
acceleration and an internal pressure condition is added to
the seismic action. Examples illustrate the application of
this proposed methodology.
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Beobachterkonzepte und Darstellungsformen der nichtlinearen KontinuumsmechanikIhlemann, Jörn 28 July 2007 (has links)
Im Rahmen der geometrisch und physikalisch nichtlinearen Kontinuumsmechanik werden Beobachterkonzepte und Darstellungsformen tensorieller Größen diskutiert und zum Teil neu eingeführt, die insbesondere die Modellierung und FEM-Implementierung komplizierter Modelle für inelastisches Materialverhalten bei großen Deformationen wirkungsvoll unterstützen. / Observer concepts and several kinds of representations of tensorial quantities are discussed and partly introduced within the framework of geometrically und physically nonlinear continuum mechanics. They are intended to support the modelling of complicated inelastic materials undergoing large deformations.
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