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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
31

GFRP-reinforced concrete columns under simulated seismic loading / Colonnes en béton armé renforcées de PRFV sous un chargement sismique simulé

Mohammed, Mohammed Gaber Elshamandy January 2017 (has links)
Abstract : Steel and fiber-reinforced-polymer (FRP) materials have different mechanical and physical characteristics. High corrosion resistance, high strength to weight ratio, non-conductivity, favorable fatigue enable the FRP to be considered as alternative reinforcement for structures in harsh environment. Meanwhile, FRP bars have low modulus of elasticity and linear-elastic stress-strain curve. These features raise concerns about the applicability of using such materials as reinforcement for structures prone to earthquakes. The main demand for the structural members in structures subjected to seismic loads is dissipating energy without strength loss which is known as ductility. In the rigid frames, columns are expected to be the primary elements of energy dissipation in structures subjected to seismic loads. The present study addresses the feasibility of reinforced-concrete columns totally reinforced with glass-fiber-reinforced-polymer (GFRP) bars achieving reasonable strength and the drift requirements specified in various codes. Eleven full-scale reinforced concrete columns—two reinforced with steel bars (as reference specimens) and nine totally reinforced with GFRP bars—were constructed and tested to failure. The columns were tested under quasi-static reversed cyclic lateral loading and simultaneously subjected to compression axial load. The columns are 400 mm square cross-section with a shear span 1650 mm. The specimen simulates a column with 3.7 m in height in a typical building with the point of contra-flexure located at the column mid-height. The tested parameters were the longitudinal reinforcement ratio (0.63, 0.95 and 2.14), the spacing of the transverse stirrups (80, 100, 150), tie configuration (C1, C2, C3 and C4), and axial load level (20%, 30% and 40%). The test results clearly show that properly designed and detailed GFRP-reinforced concrete columns could reach high deformation levels with no strength degradation. An acceptable level of energy dissipation compared with steel-reinforced concrete columns is provided by GFRP reinforced concrete columns. The dissipated energy of GFRP reinforced concrete columns was 75% and 70% of the counter steel columns at 2.5% and 4% drift ratio respectively. High drift capacity achieved by the columns up to 10% with no significant loss in strength. The high drift capacity and acceptable dissipated energy enable the GFRP columns to be part of the moment resisting frames in regions prone to seismic activities. The experimental ultimate drift ratios were compared with the estimated drift ratios using the confinement Equation in CSA S806-12. It was found from the comparison that the confinement Equation underestimates values of the drift ratios thus the experimental drift ratios were used to modify transverse FRP reinforcement area in CSA S806-12. The hysteretic behavior encouraged to propose a design procedure for the columns to be part of the moderate ductile and ductile moment resisting frames. The development of design guidelines, however, depends on determining the elastic and inelastic deformations and on assessing the force modification factor and equivalent plastic-hinge length for GFRP-reinforced concrete columns. The experimental results of the GFRP-reinforced columns were used to justify the design guideline, proving the accuracy of the proposed design equations. / L’acier et les matériaux à base de polymères renforcés de fibres (PRF) ont des caractéristiques physiques et mécaniques différentes. La résistance à la haute corrosion, le rapport résistance vs poids, la non-conductivité et la bonne résistance à la fatigue font des barres d’armature en PRF, un renforcement alternatif aux barres d’armature en acier, pour des structures dans des environnements agressifs. Cependant, les barres d’armature en PRF ont un bas module d’élasticité et une courbe contrainte-déformation sous forme linéaire. Ces caractéristiques soulèvent des problèmes d'applicabilité quant à l’utilisation de tels matériaux comme renforcement pour des structures situées en forte zone sismique. La principale exigence pour les éléments structuraux des structures soumises à des charges sismiques est la dissipation d'énergie sans perte de résistance connue sous le nom de ductilité. Dans les structures rigides de type cadre, on s'attend à ce que les colonnes soient les premiers éléments à dissiper l'énergie dans les structures soumises à ces charges. La présente étude traite de la faisabilité des colonnes en béton armé entièrement renforcées de barres d’armature en polymères renforcés de fibres de verre (PRFV), obtenant une résistance et un déplacement latéral raisonnable par rapport aux exigences spécifiées dans divers codes. Onze colonnes à grande échelle ont été fabriquées: deux colonnes renforcées de barres d'acier (comme spécimens de référence) et neuf colonnes renforcées entièrement de barres en PRFV. Les colonnes ont été testées jusqu’à la rupture sous une charge quasi-statique latérale cyclique inversée et soumises simultanément à une charge axiale de compression. Les colonnes ont une section carrée de 400 mm avec une portée de cisaillement de 1650 mm pour simuler une colonne de 3,7 m de hauteur dans un bâtiment typique avec le point d’inflexion situé à la mi-hauteur. Les paramètres testés sont : le taux d’armature longitudinal (0,63%, 0,95% et 2,14 %), l'espacement des étriers (80mm, 100mm, 150 mm), les différentes configurations (C1, C2, C3 et C4) et le niveau de charge axiale (20%, 30 % et 40%). Les résultats des essais montrent clairement que les colonnes en béton renforcées de PRFV et bien conçues peuvent atteindre des niveaux de déformation élevés sans réduction de résistance. Un niveau acceptable de dissipation d'énergie, par rapport aux colonnes en béton armé avec de l’armature en acier, est atteint par les colonnes en béton armé de PRFV. L'énergie dissipée des colonnes en béton armé de PRFV était respectivement de 75% et 70% des colonnes en acier à un rapport déplacement latéral de 2,5% et 4%. Un déplacement supérieur a été atteint par les colonnes en PRFV jusqu'à 10% sans perte significative de résistance. La capacité d’un déplacement supérieur et l’énergie dissipée acceptable permettent aux colonnes en PRFV de participer au moment résistant dans des régions sujettes à des activités sismiques. Les rapports des déplacements expérimentaux ultimes ont été comparés avec les rapports estimés en utilisant l’Équation de confinement du code CSA S806-12. À partir de la comparaison, il a été trouvé que l’Équation de confinement sous-estime les valeurs des rapports de déplacement, donc les rapports de déplacement expérimentaux étaient utilisés pour modifier la zone de renforcement transversal du code CSA S806-12. Le comportement hystérétique encourage à proposer une procédure de conception pour que les colonnes fassent partie des cadres rigides à ductilité modérée et résistant au moment. Cependant, l'élaboration de guides de conception dépend de la détermination des déformations élastiques et inélastiques et de l'évaluation du facteur de modification de la force sismique et de la longueur de la rotule plastique pour les colonnes en béton armé renforcées de PRFV. Les résultats expérimentaux des colonnes renforcées de PRFV étudiées ont été utilisés pour justifier la ligne directrice de conception, ce qui prouve l’efficacité des équations de conception proposées.
32

Performance of Superelastic Shape Memory Alloy Reinforced Concrete Elements Subjected to Monotonic and Cyclic Loading

Abdulridha, Alaa January 2013 (has links)
The ability to adjust structural response to external loading and ensure structural safety and serviceability is a characteristic of Smart Systems. The key to achieving this is through the development and implementation of smart materials. An example of a smart material is a Shape Memory Alloy (SMA). Reinforced concrete structures are designed to sustain severe damage and permanent displacement during strong earthquakes, while maintaining their integrity, and safeguarding against loss of life. The design philosophy of dissipating the energy of major earthquakes leads to significant strains in the steel reinforcement and, consequently, damage in the plastic hinge zones. Most of the steel strain is permanent, thus leading to large residual deformations that can render the structure unserviceable after the earthquake. Alternative reinforcing materials such as superelastic SMAs offer strain recovery upon unloading, which may result in improved post-earthquake recovery. Shape Memory Alloys have the ability to dissipate energy through repeated cycling without significant degradation or permanent deformation. Superelastic SMAs possess stable hysteretic behavior over a certain range of temperature, where its shape is recoverable upon removal of load. Alternatively, Martensite SMAs also possess the ability to recover its shape through heating. Both types of SMA demonstrate promise in civil infrastructure applications, specifically in seismic-resistant design and retrofit of structures. The primary objective of this research is to investigate experimentally the performance of concrete beams and shear walls reinforced with superelastic SMAs in plastic hinge regions. Furthermore, this research program involves complementary numerical studies and the development of a proposed hysteretic constitutive model for superelastic SMAs applicable for nonlinear finite element analysis. The model considers the unique characteristics of the cyclic response of superelastic materials.
33

Amortisseurs passifs non linéaires pour le contrôle de l’instabilité de flottement / Influence of nonlinear passive aborbers on the flutter instability

Malher, Arnaud 17 October 2016 (has links)
Cette thèse est consacrée à l'étude d'amortisseurs passifs non linéaires innovants pour le contrôle de l'instabilité de flottement sur un profil d'aile à deux degrés de libertés. Lorsqu'un profil d'aile entre en flottement, il oscille de façon croissante jusqu'à se stabiliser sur un cycle limite dont l'amplitude peut être significative et détériorer sa structure. Le contrôle a ainsi deux objectifs principaux : retarder l'apparition de l'instabilité et réduire l'amplitude des cycles limites. Avant d'étudier l'influence des amortisseurs passifs, l'instabilité de flottement, et notamment le régime post-flottement, a été étudié. Une expérience de flottement sur une plaque plane a été menée et sa modélisation, prenant en compte le phénomène de décrochage dynamique, a été réalisée. Concernant le contrôle passif, le premier type d'amortisseur étudié est un amortisseur hystérétique réalisé à l'aide de ressorts en alliage à mémoire de forme. La caractéristique principale de tels amortisseurs est que leur force de rappel étant hystérétique, elle permet de dissiper une grande quantité d'énergie. L'objectif principal est ainsi de réduire l'amplitude des cycles limites provoqués par l'instabilité de flottement. Cet effet escompté a été observé et quantifié expérimentalement et numériquement à l'aide de modèles semi-empiriques. Le second type d'amortisseur utilisé est un amortisseur non linéaire de vibration accordé. Il est composé d'une petite masse connectée au profil d'aile à l'aide d'un ressort possédant une raideur linéaire et une raideur cubique. La partie linéaire de ce type d'amortisseur permet de retarder l'apparition de l'instabilité tandis que la partie non linéaire permet de réduire l'amplitude des cycles limites. L'influence de l'amortisseur non linéaire de vibration accordé a été étudiée analytiquement et numériquement. Il a été trouvé que l'apparition de l'instabilité est significativement retardée à l'aide de cet amortisseur, l'effet sur l'amplitude des cycles limites étant plus modeste. / The aim of this thesis is to study the effect of passive nonlinear absorbers on the two degrees of freedom airfoil flutter. When an airfoil is subject to flutter instability, it oscillates increasingly until stabilizing on a limit cycle, the amplitude of which can be possibly substantial and thus damage the airfoil structure. The control has two main objectives : delay the instability and decrease the limit cycle amplitude. The flutter instability, and the post-flutter regime in particular, were studied first. A flutter experiment on a flat plate airfoil was conducted and the airfoil behavior was modeled, taking into account dynamic stall. Regarding the passive control, the first absorber studied was a hysteretic damper, realized using shape memory alloys springs. The characteristic of such dampers is their hysteretic restoring force, allowing them to dissipate a large amount of energy. Their main goal was thus to decrease the limit cycle amplitude caused by the flutter instability. This expected effect was observed and quantified both experimentally and numerically, using heuristic model. The second absorber studied was a nonlinear tuned vibration absorber. This absorber consists of a light mass attached to the airfoil through a spring having both a linear and a cubic stiffness. The role of the linear part of such absorber was to repel the instability threshold, while the aim of the nonlinear part was to decrease the limit cycle amplitude. It was found, analytically and numerically, that the instability threshold is substantially shifted by this absorber, whereas the limit cycle amplitude decrease is relatively modest.
34

ヒステリシス特性を考慮した有限要素磁界解析の実用化に関する研究 / ヒステリシス トクセイ オ コウリョ シタ ユウゲン ヨウソ ジカイ カイセキ ノ ジツヨウカ ニカンスル ケンキュウ

北尾 純士, Junji Kitao 22 March 2017 (has links)
本論文では,鉄損算出精度向上を目的としたプレイモデルによるヒステリシス特性を考慮した磁界解析の実用化に向けて,ヒステリシスモデルのモデリング精度向上,計算機の記憶容量低減,有限要素磁界解析の計算時間削減に関する手法を提案した.さらに,ヒステリシス特性の考慮の有無が解析結果に与える影響を検討し,提案したヒステリシス特性を考慮した有限要素磁界解析の実用性を明らかにした. / In order to achieve the highly accurate analysis of an iron loss for electric machines, this paper proposes finite element magnetic field analyses taking account of the hysteretic property by using the play model. As a consequence, it is verified that the proposed method can accurately estimate an iron loss of a magnetic materials and decrease computational costs. Furthermore, this paper investigates the influence of the hysteretic property in finite element magnetic field analyses to demonstrate its effectiveness. / 博士(工学) / Doctor of Philosophy in Engineering / 同志社大学 / Doshisha University
35

SYSTEM-LEVEL SEISMIC PERFORMANCE QUANTIFICATION OF REINFORCED MASONRY BUILDINGS WITH BOUNDARY ELEMENTS

Ezzeldin, Mohamed January 2017 (has links)
The traditional construction practice used in masonry buildings throughout the world is limited to walls with rectangular cross sections that, when reinforced with steel bars, typically accommodate only single-leg horizontal ties and a single layer of vertical reinforcement. This arrangement provides no confinement at the wall toes, and it may lead to instability in critical wall zones and significant structural damage during seismic events. Conversely, the development of a new building system, constructed with reinforced masonry (RM) walls with boundary elements, allows closed ties to be used as confinement reinforcement, thus minimizing such instability and its negative consequences. Relative to traditional walls, walls with boundary elements have enhanced performance because they enable the compression reinforcement to remain effective up to much larger displacement demands, resulting in a damage tolerant system and eventually, more resilient buildings under extreme events. Research on the system-level (complete building) performance of RM walls with boundary elements is, at the time of publication of this dissertation, nonexistent in open literature. What little research has been published on this innovative building system has focused only on investigating the component-level performance of RM walls with boundary elements under lateral loads. To address this knowledge gap, the dissertation presents a comprehensive research program that covered: component-level performance simulation; system-level (complete building) experimental testing; seismic risk assessment tools; and simplified analytical models to facilitate adoption of the developed new building system. In addition, and in order to effectively mobilize the knowledge generated through the research program to stakeholders, the work has been directly related to building codes in Canada and the USA (NBCC and ASCE-7) as well as other standards including FEMA P695 (FEMA 2009) (Chapter 2), TMS 402 and CSA S304 (Chapter 3), FEMA P58 (FEMA 2012) (Chapter 4), and ASCE-41 (Chapter 5). Chapter 1 of the dissertation highlights its objectives, focus, scope and general organization. The simulation in Chapter 2 is focused on evaluating the component-level overstrength, period-based ductility, and seismic collapse margin ratios under the maximum considered earthquakes. Whereas previous studies have shown that traditional RM walls might not meet the collapse risk criteria established by FEMA P695, the analysis presented in this chapter clearly shows that RM shear walls with boundary elements not only meet the collapse risk criteria, but also exceed it with a significant margin. Following the component-level simulation presented in Chapter 2, Chapter 3 focused on presenting the results of a complete two-story asymmetrical RM shear wall building with boundary elements, experimentally tested under simulated seismic loading. This effort was aimed at demonstrating the discrepancies between the way engineers design buildings (as individual components) and the way these buildings actually behave as an integrated system, comprised of these components. In addition, to evaluate the enhanced resilience of the new building system, the tested building was designed to have the same lateral resistance as previously tested building with traditional RM shear walls, thus facilitating direct comparison. The experimental results yielded two valuable findings: 1) it clearly demonstrated the overall performance enhancements of the new building system in addition to its reduced reinforcement cost; and 2) it highlighted the drawbacks of the building acting as a system compared to a simple summation of its individual components. In this respect, although the slab diaphragm-wall coupling enhanced the building lateral capacity, this enhancement also meant that other unpredictable and undesirable failure modes could become the weaker links, and therefore dominate the performance of the building system. Presentation of these findings has attracted much attention of codes and standards committees (CSA S304 and TMS 402/ACI 530/ASCE 5) in Canada and the USA, as it resulted in a paradigm shift on how the next-generation of building codes (NBCC and ASCE-7) should be developed to address system-levels performance aspects. Chapter 4 introduced an innovative system-level risk assessment methodology by integrating the simulation and experimental test results of Chapters 2 and 3. In this respect, the experimentally validated simulations were used to generate new system-level fragility curves that provide a realistic assessment of the overall building risk under different levels of seismic hazard. Although, within the scope of this dissertation, the methodology has been applied only on buildings constructed with RM walls with boundary elements, the developed new methodology is expected to be adopted by stakeholders of other new and existing building systems and to be further implemented in standards based on the current FEMA P58 risk quantification approaches. Finally, and in order to translate the dissertation findings into tools that can be readily used by stakeholders to design more resilient buildings in the face of extreme events, simplified backbone and hysteretic models were developed in Chapter 5 to simulate the nonlinear response of RM shear wall buildings with different configurations. These models can be adapted to perform the nonlinear static and dynamic procedures that are specified in the ASCE-41 standards for both existing and new building systems. The research in this chapter is expected to have a major positive impact, not only in terms of providing more realistic model parameters for exiting building systems, but also through the introduction of analytical models for new more resilient building systems to be directly implemented in future editions of the ASCE-41. This dissertation presents a cohesive body of work that is expected to influence a real change in terms of how we think about, design, and construct buildings as complex systems comprised of individual components. The dissertation’s overarching hypothesis is that previous disasters have not only exposed the vulnerability of traditional building systems, but have also demonstrated the failure of the current component-by-component design approaches to produce resilient building systems and safer communities under extreme events. / Dissertation / Doctor of Philosophy (PhD)
36

Digitally assisted control techniques for high performance switching DC-DC converters

Khan, Qadeer Ahmad 25 June 2014 (has links)
Digitally controlled switching DC-DC converters have recently emerged as an attractive alternative to conventional switching converters based on analog control techniques. This research focuses on eliminating the issues associated with the state of the art switching converters by proposing three novel control techniques: (1) a digitally controlled Buck-Boost converter uses a fully synthesized constant ON/OFF time-based fractional-N controller to regulate the output over a 3.3V-to-5.5V input voltage range and provides seamless transition from buck to buck-boost modes (2) a hysteretic buck converter that employs a highly digital hybrid voltage/current mode control to regulate output voltage and switching frequency independently (3) a 10MHz continuous time PID controller using time based signal processing which alleviates the speed limitations associated with conventional analog and digital. All the three techniques employ digitally assisted control techniques and require no external compensation thus making the controllers fully integrated and highly cost effective. / Graduation date: 2013 / Access restricted to the OSU Community at author's request from June 25, 2012 - June 25, 2014
37

Advancements in rapid load test data regression

Stokes, Michael Jeffrey 01 June 2006 (has links)
Rate-dependent effects introduced during rapid and/or dynamic events have typically been oversimplified to compensate for deficiencies in present analyses. As load test results are generally considered as the basis of performance from which foundations can be designed, it is imperative that the analyzed load test data be as accurate as possible. In an attempt to progress the state of load test data regression, this dissertation addresses two common assumptions made during the regression process: (1) the statnamic damping coefficient is constant throughout the entire load test and (2) the concrete stress-strain relationship is linear-elastic. Also presented is a case study where the inherent features of a rapid load test proved useful in identifying the occurrence and proximity of a structural failure within a drilled shaft.
38

Low Cycle Fatigue Effects In The Damage Caused By The Marmara Earthquake Of August 17, 1999

Acar, Fikri 01 October 2004 (has links) (PDF)
This study mainly addresses the problem of estimating the prior earthquake damage on the response of reinforced concrete structures to future earthquakes. The motivation has arisen from the heavy damages or collapses that occurred in many reinforced concrete structures following two major earthquakes that recently occurred in the Marmara Region, Turkey. The analysis tool employed for this purpose is the package named IDARC2D. Deterioration parameters of IDARC&#039 / s hysteretic model have been calibrated using a search method. In the calibration process experimental data of a total of twenty-two beam and column specimens, tested under constant and variable amplitude displacement histories, has been used. Fine-tuning of deterioration parameters is essential for more realistic predictions about inelastic behavior and structural damage. In order to provide more realistic damage prediction, three ranges of parameters are proposed. Some damage controlling structural parameters have been assessed via a large number of two-dimensional section analyses, inelastic time history and damage analyses of SDOF systems and seismic vulnerability analyses of reinforced concrete buildings. Inelastic time history and damage analyses of numerous SDOF systems have been carried out to determine whether the loading history has an effect on damage and dissipated hysteretic energy. Then this emphasis is directed to the analyses of MDOF systems. In the analyses of the SDOF systems, various forms of constant and variable amplitude inelastic displacement reversals and synthetic ground motions composed of one of the four earthquake records preceded or followed by its modified records acted as a prior or successive earthquake, have been used. The analyses of two five-story R/C buildings have been caried out using synthetic accelerograms comprised of base input provided by the two recorded ground motions. It is shown that both damage progression and cumulative hysteretic energy dissipated along a path seem to depend on the number and amplitude of cycles constituting the path. However, final damage and accumulated hysteretic energy dissipated along a loading path are independent of the ordering of the same number and amplitude cycles along the path. There is a nonlinear relationship between the earthquake excitation intensity and final damage attained in the end. Increase in the acceleration amplitude leads to exponential increase in damage. As the prior earthquake intensity increases the damage from the succeding main earthquake decreases. A definite ground motion acting as prior and successive earthquake causes substantially different amount of damage. Prior earthquake damage does not substantially affect the maximum drift response in future larger earthquakes. A MDOF frame type structure with aprior damage suffers less overall damage in an earthquake in comparison with the one without a prior damage.
39

Colloidal flocks in challenging environments / Troupeaux colloïdaux en milieux défavorables

Morin, Alexandre 18 September 2018 (has links)
Le déplacement cohérent dirigé au sein de troupeaux, d’essaims, de nuées, prend place à toutes les échelles du vivant. En cherchant à rationaliser l’émergence de tels mouvements collectifs, les physiciens ont décrit ces assemblées comme des matériaux actifs. Ces matériaux sont formés de constituants auto-propulsés qui se déplacent spontanément dans une direction commune. Cette thèse expérimentale s’appuie sur la réalisation de troupeaux synthétiques pour explorer les propriétés de la matière active polaire dans des situations défavorables à son auto-organisation : leur dynamique en milieux désordonnés et leur réponse à des perturbations externes. Des rouleurs colloïdaux aux interactions d’alignement sont confinés au sein de dispositifs microfluidiques. Au-delà d’une densité seuil, ils forment un troupeau caractérisé par l’émergence d’un ordre en orientation de longue portée. Ces troupeaux colloïdaux font office de prototypes de la matière active polaire. Nous avons étudié la réponse d’un liquide actif polaire assemblé à partir de rouleurs colloïdaux. Nous avons montré que face à une perturbation longitudinale leur réponse est hystérétique. Nous avons expliqué théoriquement ce comportement non-linéaire et l’avons exploité pour réaliser des oscillateurs microfluidiques autonomes. Nous avons également étudié la dynamique de troupeaux colloïdaux qui se propagent dans des environnements hétérogènes. La présence d’obstacles distribués aléatoirement focalise les troupeaux le long de chemins privilégiés qui forment un réseau épars et tortueux. Augmenter le désordre conduit à la destruction du troupeau. Nous avons démontré que la suppression du mouvement collectif consiste en une transition discontinue, générique à tous les matériaux actifs polaires. / Directed collected motion within herds, swarms and flocks, is a phenomenon that takes place at all scales in living systems. Physicists have rationalized the emergence of such collective behavior. They have described these systems as active materials. These materials are assembled from self-propelled units that spontaneously move in the same direction. By experimentally studying synthetic flocks, this work uncovers some properties of polar active materials in situations that disfavor their self-organization: their dynamics in disordered environments and their response to external perturbations. Colloidal rollers with alignment interactions are confined within microfluidic devices. At high density, they spontaneously form a flock which is characterized by the emergence of orientational long-ranged order. These colloidal flocks are prototypical realizations of polar active matter. We have studied the response of a polar active liquid assembled from colloidal rollers. We have shown that they display a hysteretic response to longitudinal perturbations. We have theoretically accounted for this non-linear behavior. We have used this behavior to realize autonomous microfluidic oscillators. We have also studied the dynamics of colloidal flocks that propagate through heterogeneous environments. Randomly positioned obstacles focalize flocks along favored channels that form a sparse and tortuous network. Increasing disorder leads to the destruction of flocks. We have demonstrated that the suppression of collective motion is a discontinuous transition generic to all polar active materials.
40

Analyse de la vulnérabilité sismique des structures à ossature en bois : essais expérimentaux, modélisation numérique, calculs parasismiques / Probabilistic analysis of the seismic vulnerability of timber frame building

Boudaud, Clément 07 December 2012 (has links)
Les travaux de thèse visent à améliorer les connaissances sur le comportement parasismique des bâtiments à ossature en bois. Le comportement de ces bâtiments sous sollicitations sismiques est lié à celui de ses assemblages par connecteurs métalliques (pointes, vis, équerres, etc.). La modélisation numérique d'une telle structure s'appuie sur une démarche multi-échelles, afin de représenter les comportements locaux à l'échelle de l'ouvrage. Trois échelles sont définies. Échelle 1 : assemblages, échelle 2 : éléments de structure (mur, plancher, toiture), échelle 3 : bâtiment. A chaque échelle, une loi de comportement dédiée (hystérétique avec endommagement) permet la modélisation. Les calages ou validations s'appuient sur des campagnes d'essais expérimentaux. Diverses configurations de spécimen et divers chargements sont testés afin de construire une vaste base de données de résultats. Les essais sur les assemblages par connecteurs métalliques ont permis le calage du modèle numérique à l'échelle 1. Un modèle éléments finis (EF) détaillé de mur est validé expérimentalement en quasi-statique et en dynamique. Un modèle EF simplifié de mur (macro) permet de passer à l'échelle du bâti. Cet élément macro, calibré sur le modèle détaillé, permet de reproduire avec une précision satisfaisante le comportement dynamique d'un mur. L'assemblage d'éléments de murs (pleins ou avec ouverture) permet de tendre vers la modélisation tridimensionnelle d'une structure. Ce modèle numérique de structure permettra d'étudier, localement et globalement, le comportement parasismique des constructions à ossature bois afin de proposer des dispositifs constructifs et un dimensionnement adaptés à ces ouvrages en zone sismique. / This research aims at a better understanding of the vulnerability of timber-frame buildings against earthquakes. The behavior of these structures under seismic loading relies on their joints with metal fasteners (nails, screws, 3 dimensionnal connections, etc.). The numerical modeling of such a structure is based on a multi-scale approach, which allows to take into account the local behaviors at the structural scale. Three scales are defined: Scale 1: joints, scale 2: structural elements (shear walls, floors, roofs), scale 3: buildings. At each scale, a behavior law (hysteretic with damage) is used. The calibrations or validations are based on experimental tests. Tests on joints with metal fasteners are used to calibrate the numerical model at scale 1. A detailed finite elements (FE) model of shear wall is developped and its predictions are confronted to quasi-static and dynamic experimental results for validation. A simplified FE model of shear wall (macro element) is used to generate a numerical model at the building scale. This macro element, calibrated on the detailed FE model, accurately reproduces the dynamic behavior of a shear wall despite its simplicity. The numerical model of timber-frame buildings will be used to study, locally and globally, their behavior against earthquake in order to propose construction details and design adapted to these structures in seismic areas.

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