A study on shape memory alloy materials as vibration dampers is reported. An important component is the strain rate-dependent and temperature-dependent constitutive behavior of shape memory alloy, which can significantly change its energy dissipation capacity under cyclic loading. The constitutive model used accounts for the thermo-mechanical strain rate-dependent behavior and phase transformation. With increasing structural flexibility, the hysteretic loop size of shape memory alloy dampers increases due to increasing strain rates, thus further decreasing the response of the structure to cyclic excitation. The structure examined is a beam, and its behavior with shape memory alloy dampers is compared to the same beam with conventional dampers. Parametric studies reveal the superior performance of the shape memory alloy over the conventional dampers even at the resonance frequency of the beam-damper system. An important behavior of the shape memory alloy dampers is discovered, in that they absorb energy from the fundamental and higher vibration modes. In contrast, the conventional dampers transfer energy to higher modes. For the same beam control, the stiffness requirement for the shape memory alloy dampers is significantly less than that of the conventional dampers. Response quantities of interest show improved performance of the shape memory alloy over the conventional dampers under varying excitation intensity, frequency, temperature, and strain rate.

The inland waterway system in the United States is fundamental to the transportation system as a whole and the success of the nation’s economy. Barge transportation in these waterways levitates congestion on the highway system and is beneficial when comparing barge transportation to other modes of freight transportation in measures of capacity, congestion, emissions, and safety. Unavoidably, the highway system intersects with the waterways, resulting in the risk of vessels collision into bridge structures. Particularly for barge impact, the literature is questioning the accuracy and oversimplification of the current design specifications. The impact problem was investigated in this research using three-dimensional finite-element analyses. To investigate the collision of a barge into a bridge pier, a range of material models are first investigated through simulating a drop-hammer impact onto a reinforced concrete beam. A detailed model of a jumbo hopper barge is then developed, with particular detail in the bow. The barge model is examined for its response to impact into rigid piers of different size and shape. RC piers, having different shape and boundary conditions, are impacted by the barge model and assessed using selected metrics. The final part of the research examines the response of an existing bridge pier subject to an impact by a chemical transporter barge that frequently travels in the waterway.

The response of wide flange steel columns subjected to constant axial loads and lateral blast loads was examined. The finite element program ABAQUS was used to model W8x40 sections with different slendernesses and boundary conditions. For the response calculations, a constant axial force was first applied to the column and the equilibrium state was determined. Next, a short duration, lateral blast load was applied and the response time history was calculated. Changes in displacement time histories and plastic hinge formations resulting from varying the axial load were examined. The cases studied include single-span and two-span columns. In addition to ideal boundary conditions, columns with linear elastic, rotational supports were also studied. Non-uniform blast loads were considered. Major axis, minor axis, and biaxial bending were investigated. The effects of strain rate and residual stresses were examined. The results for each column configuration are presented as a set of curves showing the critical blast impulse versus axial load. The critical blast impulse is defined as the impulse that either causes the column to collapse or to exceed the limiting deflection criterion. A major goal of this effort was to develop simplified design and analysis methods. To accomplish this, two single-degree-of-freedom approaches that include the effects of the axial load were derived. The first uses a bilinear resistance function that is similar to the one used for beam analysis. This approach provides a rough estimate of the critical impulse and is suitable only for preliminary design or quick vulnerability calculations. The second approach uses a nonlinear resistance function that accounts for the gradual yielding that occurs during the dynamic response. This approach can be easily implemented in a simple computer program or spreadsheet and provides close agreement with the results from the finite element method. / Ph. D.

Un modèle phénoménologique 3D de visco-plasticité couplée avec les évolutions microstructurales et l'endommagement est proposé pour les superalliages monogranulaires base Nickel, les matériaux des aubes de turbine à haute pression de moteurs d'hélicoptères. L'anisotropie de la mise en radeaux, la croissance et la dissolution de la phase durcissante sont modélisés. Une variable tensorielle et sa loi d'évolution permettent la description de la variation de la largeur des couloirs de matrice. Ce travail s'appuie sur la décomposition en modes de Kelvin du tenseur d'élasticité. Cette décomposition conduit également à une description multi-critère mésoscopique de la visco-plasticité cubique. Une formulation en (visco-)plasticité cristalline a été également proposée. Une loi d'endommagement avec seuil de type dD/dt=... est formulée pour la modélisation du fluage tertiaire et pour la prévision de la ductilité en traction. Une expression originale du seuil d'endommagement rend compte des effets de vitesse sur l'amorçage de l'endommagement par visco-plasticité. Une étude expérimentale a été conduite sur le CMSX-4, l'alliage au centre de cette étude, parallèlement aux travaux de modélisation. Des essais de dissolution ont été réalisés afin de mesurer la variation de la fraction volumique des précipités avec la température. Les mécanismes de déformation du matériau ont été observés en fluage isotherme à 850°C et 1050°C selon les principales directions cristallines du triangle stéréographique standard et constituent une base d'identification pour le modèle, la réponse mécanique du matériau obtenue. Trois essais de traction ont été réalisés selon la direction <111>, deux à vitesse de chargement constante, le troisième à vitesse variable. Des essais cyclés thermiquement de type 150h-moteur ont été réalisées sur le banc MAATRE. Des analyses EBSD et MET ont été réalisés sur les échantillons orientés selon les directions cristallines <011>, <111> et <112> et testés à 850°C. Ces analyses ont montré que le mâclage est le principal mécanisme de déformation pour des déformations supérieures à $1-2%$ selon ces orientations cristallines en fluage à cette température et à haute contrainte (>400 MPa). Enfin, le modèle a été implanté dans le code à élément Finis ZéBuLon, sans ou avec endommagement, et des calculs de structures ont été réalisés / A 3D phenomenological model coupling viscoplasticity, microstructural evolutions and damage is proposed for Ni-based single crystal superalloys, which are widely used materials for high pressure turbine blade in helicopter engines. The anisotropy of the gamma'-rafting, the gamma'-coarsening and the dissolution of the hardening gamma' phase are modeled. A tensorial variable and its evolution law allow to describe the variation of the gamma channels. The modeling is based on the Kelvin decomposition of the elasticity tensor. This decomposition leads to a phenomenological multi-criterion description of the cubic visco-plasticity. A formulation based on the single crystal (visco-)plasticity framework is also proposed. A damage law of type dD/dt=… is introduced in order to model the tertiary creep stage and the ductility. A novel rate sensitive damage threshold is introduced in order to account for the rate sensitivity of the damage onset by visco-plasticity. An experimental study has been carried out on the CMSX-4 alloy, which is the material of main interest in this study, in parallel to the modeling work. Dissolution tests have been carried out to measure the gamma'-volume fraction variation with temperature. The deformation mechanisms of the CMSX-4 alloy have been observed by performing tensile creep tests at 1050°C and 850°C. These tests have also constituted a database for the model identification. Three tensile tests have been realized along the <111> crystal direction, two at constant strain rate and the third by varying the strain rate. Non-isothermal creep tests reproducing the 150h-type engine test have been performed on the MAATRE bench. EBSD and TEM analysis have been realized on the specimens oriented along the <011>, <011> and <112> crystal directions and crept at 850° C. These analysis have shown that micro-twinning governs the deformation along these crystal directions during creep at this temperature and at high stresses (> 400 MPa) for deformation in excess of 1-2%. Finally, the model (with and without damage) has been encoded in the ZéBuLoN Finite Element solver and structure computations have been performed.

Offshore developments for hydrocarbon resources have now progressed to water depths approaching 2500 m. Due to the difficulties and high cost in recovering high quality samples from deepwater site, there is increasing reliance on in situ tests such as piezocone and full-flow (i.e. T-bar and ball) penetration tests for determining the geotechnical design parameters. This research was undertaken in collaboration with the Norwegian Geotechnical Institute (NGI), as part of a joint industry project, to improve the reliability of in situ tests in determining design parameters and to improve offshore site investigation practice in deepwater soft sediments. In this research, a worldwide high quality database was assembled and used to correlate intact and remoulded shear strengths (measured from laboratory and vane shear tests) with penetration resistances measured by piezocone, T-bar and ball penetrometers. The overall statistics showed similar and low levels of variability of resistance factors for intact shear strength (N-factors) for all three types of penetrometer. In the correlation between the remoulded penetration resistance and remoulded shear strength, the resistance factors for remoulded shear strength (Nrem-factors) were found higher than the N-factors. As a result, the resistance sensitivity is less than the strength sensitivity. The correlations between the derived N-factors and specific soil characteristics indicated that the piezocone N-factors are more influenced by rigidity index than those for the T-bar and ball penetrometers. The effect of strength anisotropy is only apparent in respect of N-factors for the T-bar and ball penetrometers correlated to shear strengths measured in triaxial compression. On the other hand, the Nrem-factors showed slight tendency to increase with increasing strength sensitivity but were insensitive to soil index properties. These findings suggest that the full-flow penetrometers may be used to estimate remoulded shear strength and are potentially prove more reliable than the piezocone in estimating average or vane shear strength for intact soil but the reverse is probably true for the estimation of triaxial compression strength.

This doctoral research work focuses on the simulation of progressive collapse of reinforced concrete structures. It aims at contributing to the ‘alternate load path’ design approach suggested by the General Services Administration (GSA) and the Department of Defense (DoD) of the United States, by providing a detailed yet flexible numerical modelling tool. <p><p>The finite element formulation adopted here is based on a multilevel approach where the response at the structural level is naturally deduced from the behaviour of the constituents (concrete and steel) at the material level. One-dimensional nonlinear constitutive laws are used to model the material response of concrete and steel. These constitutive equations are introduced in a layered beam approach, where the cross-sections of the structural members are discretised through a finite number of layers. This modelling strategy allows deriving physically motivated relationships between generalised stresses and strains at the sectional level. Additionally, a gradual sectional strength degradation can be obtained as a consequence of the progressive failure of the constitutive layers. This means that complex nonlinear sectional responses exhibiting softening can be obtained even for simplified one dimensional constitutive laws for the constituents.<p><p>This numerical formulation is used in dynamic progressive collapse simulations to study the structural response of a multi-storey planar frame subject to a sudden column loss. The versatility of the proposed methodology allows assessing the influence of the main material and design parameters in the structural failure. Furthermore, the effect of particular modelling options of the progressive collapse simulation technique, such as the column removal time or the strategy adopted for the structural verification, can be evaluated.<p><p>The potential strain rate effects on the structural response of reinforced concrete frames are also investigated. To this end, a strain rate dependent material formulation is developed, where the rate effects are introduced in both the concrete and steel constitutive response. These effects are incorporated at the structural level through the multilayered beam approach. In order to assess the degree of rate dependence in progressive collapse, the results of rate dependent simulations are presented and compared to those obtained via the rate independent approach. The influence of certain parameters on the rate dependent structural failure is also studied.<p><p>The differences obtained in terms of progressive failure degree for the considered parametric variations and modelling options are analysed and discussed. The parameters observed to have a major influence on the structural response in a progressive collapse scenario are the ductility of the steel bars, the degree of symmetry and/or continuity of the reinforcement and the column removal time. The results also depend on the strategy considered (GSA vs DoD). The strain rate effects are confirmed to play a significant role in the failure pattern. Based on these observations, general recommendations for the design of progressive collapse resisting structures are finally derived.<p><p><p><p><p>L’effondrement progressif est un sujet de recherche qui a connu un grand développement suite aux événements désastreux qui se sont produits au cours des dernières décennies. Ce phénomène est déclenché par la défaillance soudaine d’un nombre réduit d’éléments porteurs de la structure, qui provoque une propagation en cascade de l’endommagement d’élément en élément jusqu’à affecter une partie importante, voire la totalité de l’ouvrage. Le résultat est donc disproportionné par rapport à la cause. La plupart des codes de construction ont inclus des prescriptions pour le dimensionnement des structures face aux actions accidentelles. Malheureusement, ces procédures se limitent à fournir des ‘règles de bonne pratique’, ou proposent des calculs simplifiés se caractérisant par un manque de détail pour permettre leur mise en oeuvre.<p><p>Cette thèse de doctorat intitulée Simulation de l’Effondrement Progressif des Structures en Béton Armé: Influence des Paramètres Materiaux et de Dimensionnement et Investigation des Effets de Vitesse a pour but de contribuer à la simulation numérique de l’effondrement progressif des structures en béton armé. Une formulation aux éléments finis basée sur une approche multi-échelles a été développée, où la réponse à l’échelle structurale est déduite à partir de la réponse au niveau matériel des constituants (le béton et l’acier). Les sections des éléments structuraux sont divisées en un nombre fini de couches pour lesquelles des lois constitutives unidimensionnelles sont postulées. Cet outil permet une dégradation graduelle de la résistance des sections en béton armé suite à la rupture progressive des couches. Des comportements complexes au niveau des points de Gauss peuvent être ainsi obtenus, et cela même à partir de lois unidimensionnelles pour les constituants.<p><p>Cette formulation est utilisée pour la simulation de l’effondrement progressif d’ossatures 2D, avec prise en compte des effets dynamiques. La versatilité de la présente stratégie numérique permet d’analyser l’influence de différents paramètres matériaux et de dimensionnement, ainsi que d’autres paramètres de modélisation, sur la réponse structurale face à la disparition soudaine d’une colonne.<p><p>Les effets de la vitesse de déformation sur le comportement des matériaux constituants est aussi un sujet d’attention dans ce travail de recherche. Des lois constitutives prenant en compte ces effets sont postulées et incorporées au niveau structural grâce à l’approche multi-couches. Le but est d’étudier l’influence des effets de la vitesse de chargement sur la réponse structurale face à la disparition d’un élément porteur. Les resultats obtenus à l’aide de cette approche avec effets de vitesse sont comparés à ceux obtenus avec des lois indépendantes de la vitesse.<p><p>Les différences dans la réponse à la disparition d’une colonne sont analysées pour les variations paramétriques étudiées. Les paramètres ayant une influence importante sont notamment: la ductilité des matériaux constituants et la disposition et/ou la symétrie des armatures. Les effets de vitesse sont également significatifs. Sur base de ces résultats, des recommandations sont proposées pour le dimensionnement et/ou l’analyse des structures face à l’effondrement progressif.<p> / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

Diploma thesis is focused on the description of the parameters of nonlinear material models of concrete, which are implemented in a computational system LS-DYNA, interacting with performance of nonlinear test calculations in system LS-DYNA on selected problems, which are formed mainly by simulations of tests of mechanical and physical properties of concrete in uniaxial compressive and tensile on cylinders with applying different boundary conditions and by simulation of bending slab, with subsequent comparison of some results of test calculations with results of the experiment. The thesis includes creation of appropriate geometric models of selected problems, meshing of these geometric models, description of parameters and application of nonlinear material models of concrete on selected problems, application of loads and boundary conditions on selected problems and performance of nonlinear calculations in a computational system LS-DYNA. Evaluation of results is made on the basis of stress-strain diagrams and load-displacement diagrams based on nonlinear calculations taking into account strain rate effects and on the basis of hysteresis curves based on nonlinear calculations in case of application of cyclic loading on selected problems. Verification of nonlinear material models of concrete is made on the basis of comparison of some results of test calculations with results obtained from the experiment.