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1
Jeong, Seokho. "Topographic amplification of seismic motion including nonlinear response". Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/50325.
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Topography effects, the modification of seismic motion by topographic features, have been long recognized to play a key role in elevating seismic risk. Site response, the modification of ground motion by near surface soft soils, has been also shown to strongly affect the amplitude, frequency and duration of seismic motion. Both topography effects and 1-D site response have been extensively studied through field observations, small-scale and field experiments, analytical models and numerical simulations, but each one has been studied independently of the other: studies on topography effects are based on the assumption of a homogeneous elastic halfspace, while 1-D site response studies are almost exclusively formulated for flat earth surface conditions.
This thesis investigates the interaction between topographic and soil amplification, focusing on strong ground motions that frequently trigger nonlinear soil response. Recently, a series of centrifuge experiments tested the seismic response of single slopes of various inclination angles at the NEES@UCDavis facility, to investigate the effects of nonlinear soil response on topographic amplification. As part of this collaborative effort, we extended the search space of these experiments using finite element simulations. We first used simulations to determine whether the centrifuge experimental results were representative of free-field conditions. We specifically investigated whether wave reflections caused by the laminar box interfered with mode conversion and wave scattering that govern topographic amplification; and whether this interference was significant enough to qualitatively alter the observed amplification compared to free-field conditions. We found that the laminar box boundaries caused spurious reflections that affected the response near the boundaries; however its effect to the crest-to-free field spectral ratio was found to be insignificant. Most importantly though, we found that the baseplate was instrumental in trapping and amplifying waves scattered and diffracted by the slope, and that in absence of those reflections, topographic amplification would have been negligible. We then used box- and baseplate-free numerical models to study the coupling between topography effects and soil amplification in free-field conditions.
Our results showed that the complex wavefield that characterizes the response of topographic features with non-homogeneous soil cannot be predicted by the superposition of topography effects and site response, as is the widespread assumption of engineering and seismological models. We also found that the coupling of soil and topographic amplification occurs both for weak and strong motions, and for pressure-dependent media (Nevada sand), nonlinear soil response further aggravates topographic amplification; we attributed this phenomenon to the reduction of apparent velocity that the low velocity layers suffer during strong ground motion, which intensifies the impedance contrast and accentuates the energy trapping and reverberations in the low strength surficial layers. We finally highlighted the catalytic effects that soil stratigraphy can have in topographic amplification through a case study from the 2010 Haiti Earthquake. Results presented in this thesis imply that topography effects vary significantly with soil stratigraphy, and the two phenomena should be accounted for as a coupled process in seismic code provisions and seismological ground motion predictive models.
2
Eshun, Kow Okyere. "Quantification of the Effects of Soil Uncertainties on Nonlinear Site Response Analysis: Brute Force Monte Carlo Approach". University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1367510751.
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Schaedlich, Mirko. "Nonlinear transient structural response analysis". Thesis, University of Southampton, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438667.
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Karbassi, A. A. "Nonlinear response analysis of guyed masts". Thesis, University of Westminster, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.376451.
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Lessi, Cheimariou Angeliki. "Optimal treatment of nonlinear site response through a set of novel methodologies". Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/30818.
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Different methods of analysis, such as site-specific site response analysis or the use of ground-motion prediction equations can be adopted to account for the modification of the seismic ground-motion by the near-surface stratigraphy. Each approach is associated with a different degree of complexity and associated computational and temporal cost. This thesis identifies the main limitations of these methods as broadly employed in both academia and industry and suggests a new set of methodologies for their application. In the first part of the thesis ground-motion prediction equations and their ability to model response associated with site-specific soil layering is broadly assessed. Special emphasis is paid to the description and application of the Vs-κ_0 adjustment. This ensures that the response of a ground-motion model, particularly in the upper frequency range, is representative of the characteristics of a given site-specific shallow crustal profile. Then the effect of employing a standard deviation representative of a single site is examined. This is based on the removal of the site-ergodic assumption from the published standard deviations of the models. The effect on the hazard curves and any further implications of using this site-specific standard deviation is demonstrated by performing a Probabilistic Seismic Hazard Assessment. The second part of the thesis focuses on the main limitations and ranges of applicability of 1D site-specific site response analysis. Firstly, the Equivalent Linear approximation and the Nonlinear analysis for the constitutive modified model of Kodner and Zelasko (Matasovic and Vucetic, 1993) are tested for different magnitude-distance scenarios and strain ranges. The uncertainty in the different soil properties within site-specific site response analyses and their effect on the surface predictions is also quantified. As a result, a new set of period and soil-class dependent adjustment factors are developed which can be used as an alternative to approaches based upon randomisation of the dynamic soil properties. As part of the performed analyses, the potential bias introduced through the scaling of input motions, used in site response analysis, is addressed. Finally, the significance of using different reference depths within 1D site response analysis is considered. Consequently, through progressively more complicated parametric analyses, two new approaches, are established. These can be employed individually or in combination to select a depth for site investigation as well as a reference depth for site response analysis. Ultimately, the surface spectral ordinates obtained using site response analyses and ground-motion prediction equations are compared for an active tectonic region. Each of the previously developed methods is applied in the examined case study and the results are assessed against the traditional application of the methods. In addition, the surface predictions of each of the different methods of analysis are examined in relation to their uncertainty. This comparative analysis allows one to address the question of whether increased complexity in site-response analysis has a justifiable reward in terms of the reduction of uncertainty and also enables one to identify the most appropriate level of complexity to adopt for a given project.
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Wu, Chunquan. "Fault zone damage, nonlinear site response, and dynamic triggering associated with seismic waves". Diss., Georgia Institute of Technology, 2011. http://hdl.handle.net/1853/41143.
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My dissertation focuses primarily on the following three aspects associated with passing seismic waves in the field of earthquake seismology: temporal changes of fault zone properties, nonlinear site response, and dynamic triggering.
Quantifying the temporal changes of material properties within and around active fault zones (FZ) is important for better understanding of rock rheology and estimating the strong ground motion that can be generated by large earthquakes. As high-amplitude seismic waves propagate through damaged FZ rocks and/or shallow surface layers, they may produce additional damage leading to nonlinear wave propagation effects and temporal changes of material properties (e.g., seismic velocity, attenuation). Previous studies have found several types of temporal changes in material properties with time scales of tens of seconds to several years. Here I systematically analyze temporal changes of fault zone (FZ) site response along the Karadere-Düzce branch of the North Anatolian fault that ruptured during the 1999 İzmit and Düzce earthquake sequences. The coseismic changes are on the order of 20-40%, and are followed by a logarithmic recovery over an apparent time scale of ~1 day. These results provide a bridge between the large-amplitude near-instantaneous changes and the lower-amplitude longer-duration variations observed in previous studies. The temporal changes measured from this high-resolution spectral ratio analysis also provide a refinement for the beginning of the longer more gradual process typically observed by analyzing repeating earthquakes.
An improved knowledge on nonlinear site response is critical for better understanding strong ground motions and predicting shaking induced damages. I use the same sliding-window spectral ratio technique to analyze temporal changes in site response associated with the strong ground motion of the Mw6.6 2004 Mid-Niigata earthquake sequence recorded by the borehole stations in Japanese Digital Strong-Motion Seismograph Network (KiK-Net). The coseismic peak frequency drop, peak spectral ratio drop, and the postseismic recovery time roughly scale with the input ground motions when the peak ground velocity (PGV) is larger than ~5 cm/s, or the peak ground acceleration (PGA) is larger than ~100 Gal. The results suggest that at a given site the input ground motion plays an important role in controlling both the coseismic change and postseismic recovery in site response.
In a follow-up study, I apply the same sliding-window spectral ratio technique to surface and borehole strong motion records at 6 KiK-Net sites, and stack results associated with different earthquakes that produce similar PGAs. In some cases I observe a weak coseismic drop in the peak frequency when the PGA is as small as ~20-30 Gal, and near instantaneous recovery after the passage of the direct S waves. The percentage of drop in the peak frequency starts to increase with increasing PGA values. A coseismic drop in the peak spectral ratio is also observed at 2 sites. When the PGA is larger than ~60 Gal to more than 100 Gal, considerably stronger coseismic drops of the peak frequencies are observed, followed by a logarithmic recovery with time. The observed weak reductions of peak frequencies with near instantaneous recovery likely reflect nonlinear response with essentially fixed level of damage, while the larger drops followed by logarithmic recovery reflect the generation (and then recovery) of additional rock damage. The results indicate clearly that nonlinear site response may occur during medium-size earthquakes, and that the PGA threshold for in situ nonlinear site response is lower than the previously thought value of ~100-200 Gal.
The recent Mw9.0 off the Pacific coast of Tohoku earthquake and its aftershocks generated widespread strong shakings as large as ~3000 Gal along the east coast of Japan. I systematically analyze temporal changes of material properties and nonlinear site response in the shallow crust associated with the Tohoku main shock, using seismic data recorded by the Japanese Strong Motion Network KIK-Net. I compute the spectral ratios of windowed records from a pair of surface and borehole stations, and then use the sliding-window spectral ratios to track the temporal changes in the site response of various sites at different levels of PGA The preliminary results show clear drop of resonant frequency of up to 70% during the Tohoku main shock at 6 sites with PGA from 600 to 1300 Gal. In the site MYGH04 where two distinct groups of strong ground motions were recorded, the resonant frequency briefly recovers in between, and then followed by an apparent logarithmic recovery. I investigate the percentage drop of peak frequency and peak spectral ratio during the Tohoku main shock at different PGA levels, and find that at most sites they are correlated.
The third part of my thesis mostly focuses on how seismic waves trigger additional earthquakes at long-range distance, also known as dynamic triggering. Previous studies have shown that dynamic triggering in intraplate regions is typically not as common as at plate-boundary regions. Here I perform a comprehensive analysis of dynamic triggering around the Babaoshan and Huangzhuang-Gaoliying faults southwest of Beijing, China. The triggered earthquakes are identified as impulsive seismic arrivals with clear P- and S-waves in 5 Hz high-pass-filtered three-component velocity seismograms during the passage of large amplitude body and surface waves of large teleseismic earthquakes. I find that this region was repeatedly triggered by at least four earthquakes in East Asia, including the 2001 Mw7.8 Kunlun, 2003 Mw8.3 Tokachi-oki, 2004 Mw9.2 Sumatra, and 2008 Mw7.9 Wenchuan earthquakes. In most instances, the microearthquakes coincide with the first few cycles of the Love waves, and more are triggered during the large-amplitude Rayleigh waves. Such an instantaneous triggering by both the Love and Rayleigh waves is similar to recent observations of remotely triggered 'non-volcanic' tremor along major plate-boundary faults, and can be explained by a simple Coulomb failure criterion. Five earthquakes triggered by the Kunlun and Tokachi-oki earthquakes were recorded by multiple stations and could be located. These events occurred at shallow depth (< 5 km) above the background seismicity near the boundary between NW-striking Babaoshan and Huangzhuang-Gaoliying faults and the Fangshan Pluton. These results suggest that triggered earthquakes in this region likely occur near the transition between the velocity strengthening and weakening zones in the top few kms of the crust, and are likely driven by relatively large dynamic stresses on the order of few tens of KPa.
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Ferreira, Janito Vaqueiro. "Dynamic response analysis of structures with nonlinear components". Thesis, Imperial College London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299871.
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Kasinos, Stavros. "Seismic response analysis of linear and nonlinear secondary structures". Thesis, Loughborough University, 2018. https://dspace.lboro.ac.uk/2134/33728.
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Understanding the complex dynamics that underpin the response of structures in the occurrence of earthquakes is of paramount importance in ensuring community resilience. The operational continuity of structures is influenced by the performance of nonstructural components, also known as secondary structures. Inherent vulnerability characteristics, nonlinearities and uncertainties in their properties or in the excitation pose challenges that render their response determination as a non-straightforward task. This dissertation settles in the context of mathematical modelling and response quantification of seismically driven secondary systems. The case of bilinear hysteretic, rigid-plastic and free-standing rocking oscillators is first considered, as a representative class of secondary systems of distinct behaviour excited at a single point in the primary structure. The equations governing their full dynamic interaction with linear primary oscillators are derived with the purpose of assessing the appropriateness of simplified analysis methods where the secondary-primary feedback action is not accounted for. Analyses carried out in presence of pulse-type excitation have shown that the cascade approximation can be considered satisfactory for bilinear systems provided the secondary-primary mass ratio is adequately low and the system does not approach resonance. For the case of sliding and rocking systems, much lighter secondary systems need to be considered if the cascade analysis is to be adopted, with the validity of the approximation dictated by the selection of the input parameters. Based on the premise that decoupling is permitted, new analytical solutions are derived for the pulse driven nonlinear oscillators considered, conveniently expressing the seismic response as a function of the input parameters and the relative effects are quantified. An efficient numerical scheme for a general-type of excitation is also presented and is used in conjunction with an existing nonstationary stochastic far-field ground motion model to determine the seismic response spectra for the secondary oscillators at given site and earthquake characteristics. Prompted by the presence of uncertainty in the primary structure, and in line with the classical modal analysis, a novel approach for directly characterising uncertainty in the modal shapes, frequencies and damping ratios of the primary structure is proposed. A procedure is then presented for the identification of the model parameters and demonstrated with an application to linear steel frames with uncertain semi-rigid connections. It is shown that the proposed approach reduces the number of the uncertain input parameters and the size of the dynamic problem, and is thus particularly appealing for the stochastic assessment of existing structural systems, where partial modal information is available e.g. through operational modal analysis testing. Through a numerical example, the relative effect of stochasticity in a bi-directional seismic input is found to have a more prominent role on the nonlinear response of secondary oscillators when compared to the uncertainty in the primary structure. Further extending the analyses to the case of multi-attached linear secondary systems driven by deterministic seismic excitation, a convenient variant of the component-mode synthesis method is presented, whereby the primary-secondary dynamic interaction is accounted for through the modes of vibration of the two components. The problem of selecting the vibrational modes to be retained in analysis is then addressed for the case of secondary structures, which may possess numerous low frequency modes with negligible mass, and a modal correction method is adopted in view of the application for seismic analysis. The influence of various approaches to build the viscous damping matrix of the primary-secondary assembly is also investigated, and a novel technique based on modal damping superposition is proposed. Numerical applications are demonstrated through a piping secondary system multi-connected on a primary frame exhibiting various irregularities in plan and elevation, as well as a multi-connected flexible secondary system. Overall, this PhD thesis delivers new insights into the determination and understanding of the response of seismically driven secondary structures. The research is deemed to be of academic and professional engineering interest spanning several areas including seismic engineering, extreme events, structural health monitoring, risk mitigation and reliability analysis.
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Mahmoodi, Seyed Nima. "Nonlinear vibration and frequency response analysis of nanomechanical cantilever beams". Connect to this title online, 2007. http://etd.lib.clemson.edu/documents/1193080354/.
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Sweitzer, Karl Albert. "Random vibration response statistics for fatigue analysis of nonlinear structures". Thesis, University of Southampton, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427343.
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Lester, Alanna Paige. "An Examination of Site Response in Columbia, South Carolina: Sensitivity of Site Response to "Rock" Input Motion and the Utility of Vs(30)". Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/33467.
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This study examines the sensitivity of calculated site response in connection with alternative assumptions regarding input motions and procedures prescribed in the IBC 2000 building code, particularly the use of average shear wave velocity in the upper 30 meters as an index for engineering design response spectra. Site specific subsurface models are developed for four sites in and near Columbia, South Carolina using shear wave velocity measurements from cone penetrometer tests. The four sites are underlain by thin coastal plain sedimentary deposits, overlying high velocity Paleozoic crystalline rock. An equivalent-linear algorithm is used to estimate site response for vertically incident shear waves in a horizontally layered Earth model. Non-linear mechanical behavior of the soils is analyzed using previously published strain-dependent shear modulus and damping degradation models.
Two models for material beneath the investigated near-surface deposits are used: B-C outcrop conditions and hard rock outcrop conditions. The rock outcrop model is considered a geologically realistic model where a velocity gradient, representing a transition zone of partially weathered rock and fractured rock, overlies a rock half-space. Synthetic earthquake input motions are generated using the deaggregations from the 2002 National Seismic Hazard Maps, representing the characteristic Charleston source. The U. S. Geological Survey (2002) uniform hazard spectra are used to develop 2% in 50 year probability of exceedance input ground motions for both B-C boundary and hard rock outcrop conditions. An initial analysis was made for all sites using an 8 meter thick velocity gradient for the rock input model. Sensitivity of the models to uncertainty of the weathered zone thickness was assessed by randomizing the thickness of the velocity gradient. The effect of the velocity gradient representing the weathered rock zone increases site response at high frequencies.
Both models (B-C outcrop conditions and rock outcrop conditions) are compared with the International Building Code (IBC 2000) maximum credible earthquake spectra. The results for both models exceed the IBC 2000 spectra at some frequencies, between 3 and 10 Hz at all four sites. However, site 2, which classifies as a C site and is therefore assumed to be the most competent of the four sites according to IBC 2000 design procedures, has the highest calculated spectral acceleration of the four sites analyzed. Site 2 has the highest response because a low velocity zone exists at the bottom of the geotechnical profile in immediate contact with the higher velocity rock material, producing a very large impedance contrast. An important shortcoming of the IBC 2000 building code results from the fact that it does not account for cases in which there is a strong rock-soil velocity contrast at depth less than 30 meters. It is suggested that other site-specific parameters, specifically, depth to bedrock and near-surface impedance ratio, should be included in the IBC design procedures.Master of Science
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Teng, Thanat Sae. "In-situ shear wave measurement and ground response analysis for developing site-dependent response spectra in Macau". Thesis, University of Macau, 2009. http://umaclib3.umac.mo/record=b2099641.
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Motamed, Maryam. "Effects of Site Response on the Correlation Structure of Ground Motion Residuals". Thesis, Virginia Tech, 2014. http://hdl.handle.net/10919/25333.
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Seismic hazard analyses require an estimate of earthquake ground motions from future events. These predictions are achieved through Ground Motion Prediction Equations, which include a prediction of the median and the standard deviation of ground motion parameters. The differences between observed and predicted ground motions, when normalized by the standard deviation, are referred to as epsilon (𝜖). For spectral accelerations, the correlation structure of normalized residuals across oscillator periods is important for guiding ground motion selection. Correlation structures for large global datasets have been studied extensively. These correlation structures reflect effects that are averaged over the entire dataset underlying the analyses. This paper considers the effects of site response, at given sites, on the correlation structure of normalized residuals. This is achieved by performing site response analyses for two hypothetical soil profiles using a set of 85 rock input motions. Results show that there is no significant difference between correlation coefficients for rock ground motions and correlation coefficients after considering the effects of site response for the chosen sites.Master of Science
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Alves, Fernandes Vinicius. "Numerical analysis of nonlinear soil behavior and heterogeneity effects on railway track response". Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2014. http://www.theses.fr/2014ECAP0055/document.
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Une forte progression du transport ferroviaire est observée les dernières années dans plusieurs pays. L’augmentation de la capacité du réseau ferroviaire demande à la fois l’évaluation de l’infrastructure existante selon le trafic attendu, la vitesse des trains, la charge à l’essieu, ainsi que la réduction des interventions de maintenance. Une performance accrue de la voie ferrée par rapport à ces critères nécessite l’amélioration des normes de conception et des outils de prédiction qui puissent prendre en compte toute la durée de vie de la structure. Dans ce contexte, l’objectif de cette thèse est d’apporter un point de vue géotechnique à la modélisation numérique du comportement des voies ferrées sous charge mobile. Un modèle numérique rationnel est développé dans la thèse, composé de trois aspects principaux:(i) comportement dynamique de la voie ferrée, (ii) analyse probabiliste et (iii) comportement non linéaire des géomatériaux. Cette approche permet d’appréhender le comportement mécanique de la voie ferrée à différents instants de son cycle de vie. La première partie de cette thèse est consacrée au développement d’un modèle numérique en dynamique de la voie ferrée, adapté à l’analyse probabiliste et au comportement non linéaire. Une modélisation par Eléments Finis dans le domaine temporel est choisie pour cadre général. Ainsi, un modèle 2D en déformation plane avec épaisseur est proposé dans cette thèse, l’épaisseur hors plan étant calibrée à partir des calculs 3D en statique. Les avantages et inconvénients de cette méthodologie sont discutés selon la représentativité du champ de contraintes dans le plan et du temps de calcul associé, paramètre important pour l’analyse probabiliste. Une méthodologie pour la mise en charge est discutée et implémentée afin de réduire la génération d’ondes parasites. La réponse dynamique de la voie ferrée et l’influence croisée de la vitesse de la charge et de la rigidité de la plateforme sont évaluées sous hypothèse de comportement élastique linéaire. L’influence de la variabilité des propriétés mécaniques de la voie ferrée dans la mesure de la raideur de voie est discutée dans la deuxième partie de cette thèse. Des variations spatiales du module d’Young des couches ferroviaires sont modélisées par des champs aléatoires invariants scalaires. La densité de probabilité de la loi marginale d’ordre 1 associée au champ est obtenue grâce à une analyse statistique des mesures in situ. L’influence croisée du support discret et de la distance de corrélation des champs d’entrée dans les variations de la raideur de voie est mise en évidence à partir de différentes structures de corrélation. Afin de vérifier l’importance de chaque paramètre d’entrée sur les variations de raideur de voie, une analyse de sensibilité globale est effectuée pour différentes configurations de voie. La raideur de voie est principalement affectée par des variations de rigidité de la plateforme et des semelles. L’importance du comportement non linéaire des géomatériaux est soulignée dans la dernière partie de la thèse. Le modèle de comportement élastoplastique développé à l’Ecole Centrale Paris fournit un cadre approprié pour l’étude du comportement des géomatériaux sous chargement cyclique. Cette approche est bien adaptée au comportement des matériaux pendant leur “conditionnement initial”, ou les premiers cycles de charge, quand les tassements permanents sont plus importants et les matériaux cumulent des déformations plastiques élevées. Les paramètres du modèle sont calibrés pour les différents géomatériaux ferroviaires (ballast, couche intermédiaire, sol de la plateforme) à partir d’essais triaxiaux disponibles dans la littérature. Les résultats obtenus illustrent les mécanismes prépondérants dans cette phase : densification et augmentation de la rigidité des différents matériaux par accumulation des déformations plastiques. [...]An increasing demand for railway transportation is observed in many countries around the world. Achieving higher network capacity requires the evaluation of the existing structure regarding the required traffic, speed and axle load, as well as the reduction of maintenance interventions. A higher track performance in terms of these metrics can be achieved by enhanced design standards and predictive tools accounting for the whole structure’s life span.Within this context, this thesis aims to provide a global framework for combining geotechnical perspective and numerical modeling for the railway infrastructure. A rational approach for railway track modeling is proposed. It is composed by three main aspects: (i) railway track dynamics, (ii) probabilistic analysis and (iii) geomaterials’ non linear behavior. This approach allows assessing the track behavior during different instants of its life span. The first step of this thesis is the development of a dynamic numerical model of the railway track for both probabilistic and non linear analysis. For this purpose, the Finite Element method in time domain is chosen as general modeling framework. A 2D planestrain model with a modified width is used in this thesis, the out-of-plane width being calibrated from 3D static analysis. The advantages and drawbacks of such methodology are discussed in the light of the representativeness of the in-plane stress field and associated computational cost for probabilistic analysis. A loading methodology for reducing spurious wave generation is also discussed and implemented. With the developed model, the track structural response and the crossed influence of speed and subgrade stiffness are first analyzed under linear elasticity hypothesis.The influence of track properties variability in the track stiffness measurement is discussed in the second part of this thesis. Spatial variations are introduced by considering the rigidity of each track layer as an invariant scalar random field. The first-order marginal probability distributions are calibrated from statistical analysis of in situ measurements. By considering different theoretical correlation structures, the crossed influence of the discrete sleeper support and the input correlation length on the track stiffness field is highlighted. In order to verify the importance of each input parameter in the track stiffness’ variability, a global sensitivity analysis is conducted for different track configurations. It is shown that track stiffness variations are primarily caused by variations of subgrade stiffness and possible variations of rail pad stiffness. Furthermore, the importance of geomaterials’ non linear behavior is discussed in the last part of the thesis. A suitable framework for the description of geomaterials’ behavior under cyclic loading, for a large range of stress paths, is provided by a fully elastoplastic multimechanism model. This approach is well adapted for assessing the track behavior during the so-called “conditioning phase”, or the the first cycles when high track settlements are observed and materials cumulate high plastic strains. The model parameters are calibrated from triaxial test results available in the literature for different track materials (ballast, interlayer, subgrade soil). The model is able to capture the main mechanisms acting during the conditioning phase: densification and increase in stiffness of the different materials by accumulation of plastic strains. The load transfer mechanisms and the stress-strain response of the materials are then analyzed. Different stress-strain paths and plastic strains are observed in the ballast layer according to the position of the control point relative to the sleepers. The load speed influence on track permanent settlement and ballast stress-strain response is also studied. Finally, the influence of both interlayer and subgrade behavior on the track response is assessed via a parametric analysis
15
Kapoor, Hitesh. "Nonlinear Dynamic Response of Flexible Membrane Structures to Blast Loads". Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/41238.
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The present work describes the finite element (FE) modeling and dynamic response of lightweight, deployable shelters (tent) to large external blast loads. Flexible shelters have been used as temporary storage places for housing equipments, vehicles etc. TEMPER Tents, Small Shelter System have been widely used by Air Force and Army, for various field applications. These shelters have pressurized Collective Protection System (CPS), liner, fitted to the frame structure, which can provide protection against explosives and other harmful agents. Presently, these shelter systems are being tested for the force protection standards against the explosions like air-blast. In the field tests carried out by Air Force Research Laboratory, it was revealed that the liner fitted inside the tent was damaged due to the air blast explosion at some distant from the structure, with major damage being on the back side of the tent. The damage comprised of tearing of liner and separation of zip seals. To investigate the failure, a computational approach, due to its simplicity and ability to solve the complex problems, is used.
The response of any structural form to dynamic loading condition is very difficult to predict due to its dependence on multiple factors like the duration of the loading, peak load, shape of the pulse, the impulse energy, boundary conditions and material properties etc. And dynamic analysis of shell structures pose even much greater challenge. Obtaining solution analytically presents a very difficult preposition when nonlinearity is considered. Therefore, the numerical approach is sought which provide simplicity and comparable accuracy.
A 3D finite element model has been developed, consisting of fabric skin supported over the frames based on two approaches. ANSYS has been used for obtaining the dynamic response of shelter against the blast loads. In the first approach, the shell is considered as a membrane away from its boundaries, in which the stress couple is neglected in its interior region. In the second approach, stress coupling is neglected over the whole region. Three models were developed using Shell 63, Shell 181 and Shell 41. Shell 63 element supports both the membrane only and membrane-bending combined options and include stress stiffening and large deflection capabilities. Shell 181 include all these options as Shell 63 does and also, accounts for the follower loads. Shell 41 is a membrane element and does not include any bending stiffness. This element also include stress stiffening and large deflection capabilities.
A nonlinear static analysis is performed for a simple plate model using the elements, Shell 41 and Shell 63. The membrane dominated behavior is observed for the shell model as the pressure load is increased. It is also observed that the higher value of Young's modulus (E) increases the stresses significantly.
Transient analysis is a method of determining the structural response due to time dependent loading conditions. The full method has been used for performing the nonlinear transient analysis. Its more expensive in terms of computation involved but it takes into account all types of nonlinearities such as plasticity, large deflection and large strain etc. Implicit approach has been used where Newmark method along with the Newton-Raphson method has been used for the nonlinear analysis. Dynamic response comprising of displacement-time history and dynamic stresses has been obtained. From the displacement response, it is observed that the first movement of the back wall is out of the tent in contrast to the other sides whose first movement is into the tent. Dynamic stresses showed fluctuations in the region when the blast is acting on the structure and in the initial free vibration zone.
A parametric study is performed to provide insight into the design criteria. It is observed that the mass could be an effective means of reducing the peak responses. As the value of the Young's Modulus (E) is increased, the peak displacements are reduced resulting from the increase in stiffness. The increased stiffness lead to reduced transmitted peak pressure and reduced value of maximum strain. But a disproportionate increase lead to higher stresses which could result in failure. Therefore, a high modulus value should be avoided.Master of Science
16
Silwal, Baikuntha. "An Investigation of the Beam-Column and the Finite-Element Formulations for Analyzing Geometrically Nonlinear Thermal Response of Plane Frames". OpenSIUC, 2013. https://opensiuc.lib.siu.edu/theses/1160.
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The objective of this study is to investigate the accuracy and computational efficiency of two commonly used formulations for performing the geometrically nonlinear thermal analysis of plane framed structures. The formulations considered are the followings: the Beam-Column formulation and the updated Lagrangian version of the finite element formulation that has been adopted in the commercially well-known software SAP2000. These two formulations are used to generate extensive numerical data for three plane frame configurations, which are then compared to evaluate the performance of the two formulations. The Beam-Column method is based on an Eulerian formulation that incorporates the effects of large joint displacements. In addition, local member force-deformation relationships are based on the Beam-Column approach that includes the axial strain, flexural bowing, and thermal strain. The other formulation, the SAP2000, is based on the updated Lagrangian finite element formulation. The results for nonlinear thermal responses were generated for three plane structures by these formulations. Then, the data were compared for accuracy of deflection responses and for computational efficiency of the Newton-Raphson iteration cycles required for the thermal analysis. The results of this study indicate that the Beam-Column method is quite efficient and powerful for the thermal analysis of plane frames since the method is based on the exact solution of the differential equations. In comparison to the SAP2000 software, the Beam-Column method requires fewer iteration cycles and fewer elements per natural member, even when the structures are subjected to significant curvature effects and to restrained support conditions. The accuracy of the SAP2000 generally depends on the number of steps and/or the number of elements per natural member (especially four or more elements per member may be needed when structure member encounters a significant curvature effect). Succinctly, the Beam-Column formulation requires considerably fewer elements per member, fewer iteration cycles, and less time for thermal analysis than the SAP2000 when the structures are subjected to significant bending effects.
17
Li, Wei. "Nonlinear effects in ground motion simulations: modeling variability, parametric uncertainty and implications in structural performance predictions". Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34658.
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While site effects are accounted for in most modern U.S. seismic design codes for building structures, there exist no standardized procedures for the computationally efficient integration of nonlinear ground response analyses in broadband ground motion simulations. In turn, the lack of a unified methodology affects the prediction accuracy of site-specific ground motion intensity measures, the evaluation of site amplification factors when broadband simulations are used for the development of hybrid attenuation relations and the estimation of inelastic structural performance when strong motion records are used as input in aseismic structural design procedures.
In this study, a set of criteria is established, which quantifies how strong nonlinear effects are anticipated to manifest at a site by investigating the empirical relation between nonlinear soil response, soil properties, and ground motion characteristics. More specifically, the modeling variability and parametric uncertainty of nonlinear soil response predictions are studied, along with the uncertainty propagation of site response analyses to the estimation of inelastic structural performance. Due to the scarcity of design level ground motion recording, the geotechnical information at 24 downhole arrays is used and the profiles are subjected to broadband ground motion synthetics.
For the modeling variability study, the site response models are validated against available downhole array observations. The site and ground motion parameters that govern the intensity of nonlinear effects are next identified, and an empirical relationship is established, which may be used to estimate to a first approximation the error introduced in ground motion predictions if nonlinear effects are not accounted for.
The soil parameter uncertainty in site response predictions is next evaluated as a function of the same measures of soil properties and ground motion characteristics. It is shown that the effects of nonlinear soil property uncertainties on the ground-motion variability strongly depend on the seismic motion intensity, and this dependency is more pronounced for soft soil profiles. By contrast, the effects of velocity profile uncertainties are less intensity dependent and more sensitive to the velocity impedance in the near surface that governs the maximum site amplification.
Finally, a series of bilinear single degree of freedom oscillators are subjected to the synthetic ground motions computed using the alternative soil models, and evaluate the consequent variability in structural response. Results show high bias and uncertainty of the inelastic structural displacement ratio predicted using the linear site response model for periods close to the fundamental period of the soil profile. The amount of bias and the period range where the structural performance uncertainty manifests are shown to be a function of both input motion and site parameters.
18
Harting, Nina [Verfasser], Ulrike [Akademischer Betreuer] Krewer i Uwe [Akademischer Betreuer] Schröder. "Nonlinear Frequency Response Analysis of Lithium-Ion Batteries / Nina Harting ; Ulrike Krewer, Uwe Schröder". Braunschweig : Technische Universität Braunschweig, 2019. http://d-nb.info/119454620X/34.
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Sheikh, Md Neaz. "Simplified analysis of earthquake site response with particular application to low and moderate seismicity regions". Thesis, Hong Kong : University of Hong Kong, 2001. http://sunzi.lib.hku.hk/hkuto/record.jsp?B2353008x.
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De, Jager Charl. "A critical appraisal of existing models for nonlinear finite element analysis of reinforced concrete response". Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/20052.
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Thesis (MScEng)--Stellenbosch University, 2012.ENGLISH ABSTRACT: This study entails the appraisal of the constitutive models available for the non linear finite element analysis of reinforced concrete, using the DIANA finite element package and following generally accepted guidelines for non linear finite element analyses. The constitutive models considered are plasticity and total strain based (fixed and rotating crack) models. The appraisal consists of the analysis of various experiments performed on reinforced concrete beams that are governed by compressive, shear and tensile dominated failures. The investigation is not limited to the accuracy of the results obtained using these models but also of the consistency of the results obtained with regard to various mesh types and sizes, as well as a study of the individual influence of several material parameters. The intention of the study was to provide the reader with an indication of the performance capacity (accuracy and consistency) of the available constitutive models, where the notion of the use of the results obtained from non linear finite element analyses for design purposes is considered. The results obtained were varied. The models performed reasonably well in the compressive and tension dominated studies, with the importance of accurate material parameters being emphasized especially for the more advanced cementitious materials investigated. The total strain rotating crack model also showed a proclivity of simulating incorrect failure modes as well as exhibiting reluctance towards stress redistribution. All models used for the shear dominated study yielded mostly inaccurate and inconsistent results, but it was found that the four node quadrilateral element with selective reduced integration performed the best. The plasticity model did not capture shear failure well, and convergence was often not attained. The constant shear retention factor of the total strain fixed crack model was found to yield more detailed response curves for the smaller mesh sizes. The results of the tension dominated beams inspired more confidence in the models as quite accurate values were attained, especially by the plasticity model used. The ability of the available models to simulate realistic structural behaviour under various failure modes is very limited, as is evident from the results obtained. The development of a more advanced and robust model is required, which can provide consistently accurate results and failure modes, and even ‘anticipate’ potential failure modes not considered by the user.
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Degirmenci, Can. "Dynamic Pull Analysis For Estimating The Seismic Response". Master's thesis, METU, 2006. http://etd.lib.metu.edu.tr/upload/12607833/index.pdf.
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The analysis procedures employed in earthquake engineering can be classified as linear static, linear dynamic, nonlinear static and nonlinear dynamic. Linear procedures are usually referred to as force controlled and require less analysis time and less computational effort. On the other hand, nonlinear procedures are referred to as deformation controlled and they are more reliable in characterizing the seismic performance of buildings. However, there is still a great deal of unknowns for nonlinear procedures, especially in modelling the reinforced concrete structures.
Turkey ranks high among all countries that have suffered losses of life and property due to earthquakes over many centuries. These casualties indicate that, most regions of the country are under seismic risk of strong ground motion. In addition to this phenomenon, recent studies have demonstrated that near fault ground motions are more destructive than far-fault ones on structures and these effects can not be captured effectively by recent nonlinear static procedures.
The main objective of this study is developing a simple nonlinear dynamic analysis procedure which is named as &ldquoDynamic Pull Analysis&rdquo
for estimating the seismic response of multi degree of freedom (MDOF) systems. The method is tested on a six-story reinforced concrete frame and a twelve-story reinforced concrete frame that are designed according to the regulations of TS-500 (2000) and TEC (1997).
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Leung, Colin. "SENSITIVITY OF SEISMIC RESPONSE OF A 12 STORY REINFORCED CONCRETE BUILDING TO VARYING MATERIAL PROPERTIES". DigitalCommons@CalPoly, 2011. https://digitalcommons.calpoly.edu/theses/681.
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The main objective of this investigation is to examine how various material properties, governed by code specification, affect the seismic response of a twelve- story reinforced concrete building. This study incorporates the pushover and response history analysis to examine how varying steel yield strength (Fy), 28 day nominal compressive concrete strength (f’c), modes, and ground motions may affect the base shear capacity and displacements of a reinforced concrete structure.
Different steel and concrete strengths were found to have minimal impact on the initial stiffness of the structure. However, during the post-yielding phase, higher steel and concrete compressive strengths resulted in larger base shear capacities of up to 22%. The base shear capacity geometric median increased as f’c or Fy increased, and the base shear capacity dispersion measure decreased as f’c or Fy increased. Higher mode results were neglected in this study due to non-convergent pushover analyses results.
According to the response history analysis, larger yield and concrete compressive strengths result in lower roof displacement. The difference in roof displacement was less than 12% throughout. This displays the robustness of both analysis methods because material properties have insignificant impact on seismic response. Therefore, acceptable yield and compressive strengths governed by seismic code will result in acceptable building performance.
23
Scarpato, Alessandro. "Linear and nonlinear analysis of the acoustic response of perforated plates traversed by a bias flow". Thesis, Châtenay-Malabry, Ecole centrale de Paris, 2014. http://www.theses.fr/2014ECAP0038/document.
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Les instabilités thermo-acoustiques causent des problèmes récurrents dans les chambres de combustion pour une large gamme d'applications industrielles, allant des chaudières domestiques aux turbines à gaz, en passant par les moteurs fusées. Ces phénomènes résultent d’un couplage résonant entre la dynamique de la combustion et les modes acoustiques du foyer, et peuvent donner lieu à de fortes vibrations, un vieillissement prématuré des composants de la chambre, voire des dommages structurels. Les mécanismes physiques mis en jeu sont complexes et difficiles à modéliser, ainsi les oscillations thermo-acoustiques ne sont pas facilement prévisibles au stade de la conception d’une chambre de combustion. Dans de nombreux foyers, des systèmes d’amortissement passifs sont installés pour augmenter la dissipation d’énergie acoustique et empêcher le développement de ces instabilités. Dans ce travail, des systèmes d’amortissement basés sur des plaques perforées couplées à une cavité résonante et traversées par un écoulement moyen sont analysés. Les principaux objectifs sont : (i) d’améliorer et de simplifier la conception de systèmes d’amortissement robustes en maximisant leurs propriétés d’absorption acoustique en régime linéaire, (ii) d’analyser l’effet de l’amplitude des ondes sonores incidentes sur la réponse acoustique des plaques perforées et (iii) de développer des modèles capables de reproduire cette réponse aux hautes amplitudes. Tout d’abord, deux régimes asymptotiques intéressants sont identifiés où le système fonctionne à faibles et forts nombres de Strouhal respectivement. Dans ces régimes la conception d’un système d’amortissement maximisant l’absorption acoustique est grandement simplifiée, puisque les calculs de la vitesse optimale de l’écoulement et de la taille de la cavité sont découplés. Il est démontré qu’à faible nombre de Strouhal le système se comporte comme un résonateur quart d’onde, et dispose d’une bande d’absorption très large. À fort nombre de Strouhal, le système fonctionne comme un résonateur de Helmholtz, comportant une cavité de taille plus réduite, mais une bande d’absorption beaucoup plus étroite que dans le régime précédent. Ces prévisions sont confirmées par des mesures réalisées dans les différents régimes identifiés sur un dispositif expérimental dédié. L’évolution des propriétés acoustiques d’une plaque perforée lorsque l’amplitude de forçage augmente est ensuite examinée par le biais de simulations directes. Il est montré que la transition du régime linéaire au régime non linéaire se produit lorsque l’amplitude de la vitesse acoustique dans l’orifice est comparable à la vitesse de l’écoulement moyen dans les trous. Pour des amplitudes élevées, une inversion périodique de l’écoulement est observée dans l’orifice. Des anneaux tourbillonnaires sont alternativement éjectés en amont et en aval de l’orifice à une vitesse de convection qui augmente avec l’amplitude de la perturbation acoustique. Ces mécanismes influencent profondément l’absorption acoustique des plaques perforées dans le régime non linéaire. Deux nouveaux modèles décrivant la réponse non linéaire de ces systèmes sont ensuite développés en exploitant la trajectoire des vortex (modèle VC), et une approche quasi-stationnaire (modèle IDF). Les prévisions de ces modèles sont confrontées à des mesures effectuées dans le tube à impédance et aux résultats de simulations directes. Les résultats obtenus au cours de ces travaux peuvent être utilisés pour guider la conception de systèmes d’absorption robustes, capables de fonctionner dans des environnements difficiles avec des niveaux sonores élevés, comme ceux rencontrés lors d’instabilités thermo-acoustiquesThermo-acoustic instabilities are of primary concern in combustion chambers for a wide range of industrial applications, from domestic boiler to gas turbines or rocket engines. They are the consequence of a resonant coupling between the flame dynamics and the acoustic modes of the combustor, and can result in strong vibrations, early aging of combustor components and structural damage. The physical mechanisms involved are complex and difficult to model, thus thermo-acoustic oscillations are not easily predictable at the design stage of a combustor. In many combustors, passive dampers are implemented to increase the acoustic energy dissipation of the system and to hinder detrimental flame-acoustics interactions. In the present work, passive damping systems based on perforated screens backed by a resonant cavity and traversed by a bias flow are investigated. The main objectives are: (i) to improve and simplify the design of these dampers by maximizing their acoustic absorption properties in the linear regime, (ii) to analyze the effect of the sound wave amplitude on the acoustic response of these systems and (iii) to develop models capable of capturing absorption at high oscillation amplitudes. First, two interesting asymptotic regimes are identified where the plate operates at low and high Strouhal numbers respectively. In these regimes the design of a damper maximizing absorption is greatly simplified, since the choice of the optimal bias flow velocity and back cavity size can be decoupled. It is shown that at low Strouhal numbers the damper behaves as a quarter-wave resonator, and features a wide absorption bandwidth. At high Strouhal numbers, the system operates as a Helmholtz resonator, featuring shorter optimal back cavity sizes but narrower absorption bandwidths. These predictions are compared to measurements in a dedicated experimental setup for the different operating regimes identified. The dependence of the acoustic properties of a perforated plate on the forcing amplitude is then examined by means of direct numerical simulations. It is shown that transition from linear to nonlinear regimes occurs when the acoustic velocity amplitude in the orifice is comparable to the mean bias flow velocity. At high amplitudes, periodic flow reversal is observed within the perforation, vortex rings are alternatively shed upstream and downstream of the hole and convected away at a velocity which is increasing with the forcing amplitude. These mechanisms greatly influence the acoustic absorption of the perforate in the nonlinear regime. Two novel models capturing this nonlinear response are then inferred based on an analysis of the vortex trajectory (VC model), and on a quasi-steady description of the flow (IDF model). Their predictions are finally compared to measurements conducted in an impedance tube, and to results from numerical simulations. The results obtained in this work can be used to ease the design of robust dampers capable of operating in harsh environments with high sound levels, such as those found during self-sustained thermo-acoustic instabilities
24
Vasilescu, Adrian. "Analysis of geometrically nonlinear and softening response of thin structures by a new facet shell element". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape4/PQDD_0018/MQ57743.pdf.
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Mathison, Steve Richard. "Nonlinear analysis for the response and failure of compression- loaded angle-ply laminates with a hole". Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/45819.
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The objective of this study was to determine the effect of nonlinear material behavior on the response and failure of unnotched and notched angle-ply laminates under uniaxial compressive loading. The endochronic theory was chosen as the constitutive theory to model the AS4/3502 graphite-epoxy material system.
Three-dimensional finite element analysis incorporating the endochronic theory was used to determine the stresses and strains in the laminates. An incremental/iterative initial strain algorithm was used in the finite element program. To increase computational efficiency, a 180° rotational symmetry relationship was utilized and the finite element program was vectorized to run on a super computer. Laminate response was compared to experiment revealing excellent agreement for both the unnotched and notched angle-ply laminates. Predicted stresses in the region of the hole were examined and are presented, comparing linear elastic analysis to the inelastic endochronic theory analysis.
A failure analysis of the unnotched and notched laminates was performed using the quadratic tensor polynomial. Predicted fracture loads compared well with experiment for the unnotched laminates, but were very conservative in comparison with experiments for the notched laminates.
Master of Science
26
Vasilescu, Adrian Carleton University Dissertation Engineering Civil and Environmental. "Analysis of geometrically nonlinear and softening response of thin structures by a new Facet Shell Element". Ottawa, 2000.
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Maldonado, Gustavo Omar. "Stochastic response of single degree of freedom hysteretic oscillators". Thesis, Virginia Tech, 1987. http://hdl.handle.net/10919/45804.
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During strong ground shaking structures often become inelastic and respond hysteretically. Therefore, in this study some hysteretic models commonly used in seismic structural analysis are studied. In particular the characteristics of a popular endochronic model proposed by Bouc and Wen are examined in detail. In addition, analytical expressions have also been developed for most commonly used bilinear model as well as another model, herein called as the hyperbolic model.Master of Science
28
Cabas, Mijares Ashly Margot. "Improvements to the Assessment of Site-Specific Seismic Hazards". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/82352.
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The understanding of the impact of site effects on ground motions is crucial for improving the assessment of seismic hazards. Site response analyses (SRA) can numerically accommodate the mechanics behind the wave propagation phenomena near the surface as well as the variability associated with the input motion and soil properties. As a result, SRA constitute a key component of the assessment of site-specific seismic hazards within the probabilistic seismic hazard analysis framework. This work focuses on limitations in SRA, namely, the definition of the elastic half-space (EHS) boundary condition, the selection of input ground motions so that they are compatible with the assumed EHS properties, and the proper consideration of near-surface attenuation effects. Input motions are commonly selected based on similarities between the shear wave velocity (Vs) at the recording station and the materials below the reference depth at the study site (among other aspects such as the intensity of the expected ground motion, distance to rupture, type of source, etc.). This traditional approach disregards the influence of the attenuation in the shallow crust and the degree to which it can alter the estimates of site response. A Vs-κ correction framework for input motions is proposed to render them compatible with the properties of the assumed EHS at the site. An ideal EHS must satisfy the conditions of linearity and homogeneity. It is usually defined at a horizon where no strong impedance contrast will be found below that depth (typically the top of bedrock). However, engineers face challenges when dealing with sites where this strong impedance contrast takes place far beyond the depth of typical Vs measurements. Case studies are presented to illustrate potential issues associated with the selection of the EHS boundary in SRA. Additionally, the relationship between damping values as considered in geotechnical laboratory-based models, and as implied by seismological attenuation parameters measured using ground motions recorded in the field is investigated to propose alternative damping models that can match more closely the attenuation of seismic waves in the field.Ph. D.
29
Hata, Misako. "Non linear tolerance analysis by response surface methodology". Ohio : Ohio University, 2001. http://www.ohiolink.edu/etd/view.cgi?ohiou1173897314.
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Arefi, Mohammad Jawad. "Dynamic Characteristics and Evaluation of Ground Response for Sands with Non-Plastic Fines". Thesis, University of Canterbury. Civil & Natural Resources Engineering, 2014. http://hdl.handle.net/10092/9173.
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Deformational properties of soil, in terms of modulus and damping, exert a great influence on seismic response of soil sites. However, these properties for sands containing some portion of fines particles have not been systematically addressed. In addition, simultaneous modelling of the modulus and damping behaviour of soils during cyclic loading is desirable. This study presents an experimental and computational investigation into the deformational properties of sands containing fines content in the context of site response analysis. The experimental investigation is carried on sandy soils sourced from Christchurch, New Zealand using a dynamic triaxial apparatus while the computational aspect is based on the framework of total-stress one-dimensional (1D) cyclic behaviour of soil.
The experimental investigation focused on a systematic study on the deformational behaviour of sand with different amounts of fines content (particle diameter ≤ 75µm) under drained conditions. The silty sands were prepared by mixing clean sand with three different percentages of fines content. A series of bender element tests at small-strain range and stress-controlled dynamic triaxial tests at medium to high-strain ranges were conducted on samples of clean sand and silty sand. This allowed measurements of linear and nonlinear deformational properties of the same specimen for a wide strain range. The testing program was designed to quantify the effects of void ratio and fines content on the low-strain stiffness of the silty sand as well as on the nonlinear stress-strain relationship and corresponding shear modulus and damping properties as a function of cyclic shear strains.
Shear wave velocity, Vs, and maximum shear modulus, Gmax, of silty sand was shown to be significantly smaller than the respective values for clean sands measured at the same void ratio, e, or same relative density, Dr. However, the test results showed that the difference in the level of nonlinearity between clean sand and silty sands was small. For loose samples prepared at an identical relative density, the behaviour of clean sand was slightly less nonlinear as compared to sandy soils with higher fines content. This difference in the nonlinear behaviour of clean sand and sandy soils was negligible for dense soils. Furthermore, no systematic influence of fines content on the material damping curve was observed for sands with fines content FC = 0 to 30%.
In order to normalize the effects of fines on moduli of sands, equivalent granular void ratio, e*, was employed. This was done through quantifying the participation of fines content in the force transfer chain of the sand matrix. As such, a unified framework for modelling of the variability of shear wave velocity, Vs, (or shear modulus, Gmax) with void ratio was achieved for clean sands and sands with fines, irrespective of their fines content.
Furthermore, modelling of the cyclic stress-strain behaviour based on this experimental program was investigated. The modelling effort focused on developing a simple constitutive model which simultaneously models the soil modulus and damping relationships with shear strains observed in laboratory tests. The backbone curve of the cyclic model was adopted based on a modified version of Kondner and Zelasko (MKZ) hyperbolic function, with a curvature coefficient, a. In order to simulate the hysteretic cycles, the conventional Masing rules (Pyke 1979) were revised. The parameter n, in the Masing’s criteria was assumed to be a function of material damping, h, measured in the laboratory. As such the modulus and damping produced by the numerical model could match the stress-strain behaviour observed in the laboratory over the course of this study. It was shown that the Masing parameter n, is strain-dependent and generally takes values of n ≤ 2. The model was then verified through element test simulations under different cyclic loadings. It was shown that the model could accurately simulate the modulus and the damping simultaneously.
The model was then incorporated within the OpenSees computational platform and was used to scrutinize the effects of damping on one-dimensional seismic site response analysis. For this purpose, several strong motion stations which recorded the Canterbury earthquake sequence were selected. The soil profiles were modelled as semi-infinite horizontally layered deposits overlying a uniform half-space subjected to vertically propagating shear waves. The advantages and limitations of the nonlinear model in terms of simulating soil nonlinearity and associated material damping were further scrutinized.
It was shown that generally, the conventional Masing criteria unconservatively may underestimate some response parameters such as spectral accelerations. This was shown to be due to larger hysteretic damping modelled by using conventional Masing criteria. In addition, maximum shear strains within the soil profiles were also computed smaller in comparison to the values calculated by the proposed model. Further analyses were performed to study the simulation of backbone curve beyond the strain ranges addressed in the experimental phase of this study. A key issue that was identified was that relying only on the modulus reduction curves to simulate the stress-strain behaviour of soil may not capture the actual soil strength at larger strains. Hence, strength properties of the soil layer should also be incorporated to accurately simulate the backbone curve.
31
Wee, Boon Yu. "Analysis of mechanisms of chromosome restoration in response to a site-specific double-strand break in fission yeast". Thesis, University of Oxford, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432262.
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Grassi, Sabrina. "Characterization of active tectonic structures of the Etna volcano, through geophysical surveys, analysis of site response and deformation". Doctoral thesis, Università di Catania, 2017. http://hdl.handle.net/10761/3902.
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In this thesis are shown the results of a multidisciplinary research, including geophysical, structural and geodetic surveys, carried out along the Tremestieri-Trecastagni-San Gregorio-Acitrezza fault system with the aim to provide additional insightful about its geometry and kinematics; also, additional geophysical surveys were performed at various sites of the municipalities most affected by the fault segments presence in order to obtain information on site response. This fault system, considered as "laboratory structure", was selected for the different kinematic characteristics and different modes of strain-energy release, that characterized its fault segments.
In the northernmost portion, this system has a kinematic behavior of normal fault and releases energy during coseismic deformation, while in the southernmost portion presents a kinematic behavior of a right-lateral strike-slip fault with releases energy during aseismic creep. Furthermore, this fault system, which can be considered the southern boundary of the sliding of Etnean eastern slope, was less studied than the northern sliding boundary and very little is known about the depth geometry of its fault segments.
The surveys were performed after an analysis of the data relating to shallow geology and to morphological, structural, stratigraphic, geophysical and seismological aspects; these detailed surveys have confirmed and highlighted a variety of geological and geomorphological conditions that can determine the existence of different stress following the occurrence of an earthquake.
After have performed a detailed structural survey, the project has planned the acquisition and analysis of many ambient noise samplings, and of other geophysical surveys, undertaken within the municipalities affected by the presence of the fault segments, increasing the surveys near the fault. All this in order to reconstruct the resonance frequency distribution and detect the possible presence of areas affected by amplification effects.
Moreover, in some areas, the surface deformation process was characterized through the design, implementation and installation, across the fault segments, of a geodetic monitoring network, in order to obtain information on the fault kinematics and on the local stress field.
The integration of the results obtained from structural, geological and geophysical surveys, with a complete literature review has provided important information on the development in depth of the fault segments; it was thus possible to reconstruct a 3D model of geometry that characterized the southern boundary of Etnean eastern slope sliding.
Various deformation data such as GPS displacements, InSAR images, level data and measures with extensometers suggest that the slip along the fault system is not uniform, but can be better described by a distribution of dislocation sources along the fault surfaces. In order to model the slip distribution along the fault surfaces, an inverse modeling of DInSAR deformation data was carried out.
This project was aimed to the recognizing site effects, that characterize the studied areas, in order to highlight the seismo-stratigraphic and tectonic behavior of subsoil, as well as, to the characterization of the deformation field related to the fault segments, through the implementation of a new geodetic monitoring network (GEO-UNICT geodetic network).
The results allowed to obtain important information on all parameters that can increment the local seismic hazard; all these different but converging approaches, have permitted a complete study of the investigated area. This study providing essential information for a proper land use planning, having as main objective the mitigation of risks that can affect the population.
33
Kadyk, Thomas Verfasser], i Kai [Akademischer Betreuer] [Sundmacher. "Nonlinear frequency response analysis for the diagnosis of polymer electrolyte membrane fuel cells / Thomas Kadyk. Betreuer: Kai Sundmacher". Magdeburg : Universitätsbibliothek, 2012. http://d-nb.info/1053914431/34.
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Eifert, Joseph E. "Predictive modeling of the aerobic growth of Staphylococcus aureus 196E using a nonlinear model and response surface analysis /". This resource online, 1994. http://scholar.lib.vt.edu/theses/available/etd-06062008-164508/.
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Hardyniec, Andrew B. "An Investigation of the Behavior of Structural Systems with Modeling Uncertainties". Diss., Virginia Tech, 2014. http://hdl.handle.net/10919/56635.
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Recent advancements in earthquake engineering have caused a movement toward a probabilistic quantification of the behavior of structural systems. Analysis characteristics, such as ground motion records, material properties, and structural component behavior are defined by probabilistic distributions. The response is also characterized probabilistically, with distributions fitted to analysis results at intensity levels ranging from the maximum considered earthquake ground motion to collapse. Despite the progress toward a probabilistic framework, the variability in structural analysis results due to modeling techniques has not been considered.
This work investigates the uncertainty associated with modeling geometric nonlinearities and Rayleigh damping models on the response of planar frames at multiple ground motion intensity levels. First, an investigation is presented on geometric nonlinearity approaches for planar frames, followed by a critical review of current damping models. Three frames, a four-story buckling restrained braced frame, a four-story steel moment resisting frame, and an eight-story steel moment resisting frame, are compared using two geometric nonlinearity approaches and five Rayleigh damping models. Static pushover analyses are performed on the models in the geometric nonlinearities study, and incremental dynamic analyses are performed on all models to compare the response at the design based earthquake ground motion (DBE), maximum considered earthquake ground motion (MCE), and collapse intensity levels. The results indicate noticeable differences in the responses at the DBE and MCE levels and significant differences in the responses at the collapse level. Analysis of the sidesway collapse mechanisms indicates a shift in the behavior corresponding to the different modeling assumptions, though the effects were specific to each frame.
The FEMA P-695 Methodology provided a framework that defined the static and dynamic analyses performed during the modeling uncertainties studies. However, the Methodology is complex and the analyses are computationally expensive. To expedite the analyses and manage the results, a toolkit was created that streamlines the process using a set of interconnected modules. The toolkit provides a program that organizes data and reduces mistakes for those familiar with the process while providing an educational tool for novices of the Methodology by stepping new users through the intricacies of the process.
The collapse margin ratio (CMR), calculated in the Methodology, was used to compare the collapse behavior of the models in the modeling uncertainties study. Though it provides a simple scalar quantity for comparison, calculation of the CMR typically requires determination of the full set of incremental dynamic analysis curves, which require prohibitively large analysis time for complex models. To reduce the computational cost of calculating the CMR, a new parallel computing method, referred to as the fragility search method, was devised that uses approximate collapse fragility curves to quickly converge on the median collapse intensity value. The new method is shown to have favorable attributes compared to other parallel computing methods for determining the CMR.Ph. D.
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Citipitioglu, Ahmet Muhtar. "Development and assessment of response and strength models for bolted steel connections using refined nonlinear 3D finite element analysis". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2009. http://hdl.handle.net/1853/31691.
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Thesis (Ph.D)--Civil and Environmental Engineering, Georgia Institute of Technology, 2010.Committee Chair: Haj-Ali, Rami; Committee Co-Chair: Leon, Roberto; Committee Co-Chair: White, Donald; Committee Member: DesRoches, Reginald; Committee Member: Gentry, Russell. Part of the SMARTech Electronic Thesis and Dissertation Collection.
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Gunay, Mehmet Selim. "An Equivalent Linearization Procedure For Seismic Response Prediction Of Mdof Systems". Phd thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/3/12609447/index.pdf.
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Nonlinear response history analysis is accepted as the most accurate analytical tool for seismic response determination. However, accurate estimation of displacement responses using conceptually simple, approximate analysis procedures is preferable, since there are shortcomings in the application of nonlinear response history analysis resulting from its complexity.
An equivalent linearization procedure, which utilizes the familiar response spectrum analysis as the analysis tool and benefits from the capacity principles, is developed in this thesis study as an approximate method for predicting the inelastic seismic displacement response of MDOF systems under earthquake excitations. The procedure mainly consists of the construction of an equivalent linear system by reducing the stiffness of structural members which are expected to respond in the inelastic range. Different from similar studies in literature, equivalent damping is not explicitly employed in this study. Instead, predetermined spectral displacement demands are utilized in each mode of the equivalent linear system for the determination of global displacement demands.
Response predictions of the equivalent linearization procedure are comparatively evaluated by using the benchmark nonlinear response history analysis results and other approximate methods including conventional pushover analysis and modal pushover analysis (MPA). It is observed that the proposed procedure results in similar accuracy with approximate methods which employ nonlinear analysis. Considering the conceptual simplicity of the procedure and the conventional analysis tools used in its application, presented equivalent linearization procedure can be suggested as a practically applicable method for the prediction of inelastic seismic displacement response parameters with sufficient accuracy.
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Imamovic, Ismar. "Ultimate load limit analysis of steel structures accounting for nonlinear behaviour of connections". Thesis, Compiègne, 2017. http://www.theses.fr/2017COMP2373/document.
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Cette thèse traite de l'analyse limite des structures de châssis en acier, qui s'utilise souvent comme la structure principale de support des bâtiments. La structure du cadre en acier est caractérisée par une réponse très ductile et un grand potentiel pour dissiper l'énergie, ce qui est crucial pour la résistance par rapport aux tremblements de terre. La ductilité dans la réponse de la structure est la cause du comportement du matériau lui-même et du comportement des connexions entre les éléments de la structure. Les connexions entre les poutres et les poteaux peuvent influencer de manière significative la réponse de la structure du cadre en acier, parfois jusqu'à 30%. L'idée est de intégrer le comportement des connexions par les éléments de poutres qui seront situés dans les coins du cadre et la modélisation du reste serra fait avec des éléments de poutres non-linéaires qui décrirons le comportement des poutres en acier. Cette recherche est composée de deux parties. La première partie est consacrée au comportement des connexions structurelles, la deuxième partie présente le développement de l'élément fini du faisceau non linéaire capable de représenter le comportement ductile d'un élément de la structure en acier. Dans la première partie de la thèse, nous définissons la procédure d'identification des paramètres constitutifs pour le modèle couplé de plasticité-dégâts avec dix-huit inconnus. Ce modèle constitutif est très robuste et capable de représenter une large gamme de problèmes. La procédure définie a été utilisée dans la préparation de tests expérimentaux pour trois types de connexions en acier structuré. Les tests expérimentaux ont été effectués pour deux cas de charge. Pour la première, la charge a été appliquée dans un sens avec les cycles de chargement et de déchargement. À partir des mesures expérimentales, nous avons conclu que le modèle de plasticité peut bien représentée le comportement de la connexion structurale. Paramètres constitutifs ont été déterminés à partir des résultats de l'expérimentation, on a utilisé une poutre géométriquement exacte avec la loi bilinéaires renforcement du matériel et la loi linéaire pour le ramollissement. Également, on a effectué des essais expérimentaux de deux types de raccords en acier en cas de chargement cyclique. Les données mesurées montrent que le modèle de la plasticité n'est pas assez bon pour décrire le comportement de connexion pour ce type de charge. A savoir, en raison de changements du sens de l'application du chargement, les connexions montrent moins de rigidité, qui peut être décrite avec un modèle constitutif de dommages. Pour cette raison, nous avons développé un nouveau modèle plasticité-dommages qui est capable d'inclure le phénomène mentionné ci-dessus. A la fin de cette section est faite l'identification des paramètres constitutifs. La deuxième partie de la thèse de doctorat est composé de formulations théoriques et la mise en œuvre numérique des faisceaux géométriquement exacte. La réponse de durcissement de la poutre comprend l'interaction entre les forces de la section résultant du stress (N, T et M), et la réponse de ramollissement est définit par la loi non linéaire. Ce type d'élément fini de poutre est capable de décrire le comportement ductile des structures en acier et inclure les effets du second ordre, qui sont très importantes pour l'analyse ultime des structures de cadre en acier. L'élément fini développé de poutre géométriquement exacte et les lois définies de liaison de comportement dans la construction en acier, offrant la possibilité d'une analyse de haute qualité des structures en acier. En utilisant les modèles de poutre proposé et la méthodologie de modélisation des structures de châssis en acier, il est possible de déterminer une distribution réaliste des forces de section transversale , y compris la redistribution due à la formation de rotules plastiquesThis thesis deals with the ultimate load limit analysis of steel frame structures. The steel frame structure has a very ductile response and a large potential to dissipate energy, which is crucial in the case of earthquakes. The ductility in the response of the structure comes from the behavior of the material itself and the behavior of the semi-rigid structural connections. The semi-rigid connections between beams and columns can significantly influence the response of the structure, sometimes up to 30%. In this thesis, we propose a methodology for modeling steel frame structures with included connection behavior. The idea is to model the behavior of the structural connections by the beam elements positioned in the corners of the steel frame structure. Other members of the steel frame structure, steel beams, and columns, will be modeled with nonlinear beam elements. This research consists of two parts. The first part deals with the behavior of the structural steel connections. In the second part, we present the development of the nonlinear beam element capable of representing the ductile behavior of steel structural elements, beams and columns. In the first part of the thesis, we define constitutive parameters identification procedure for the coupled plasticity-damage model with eighteen unknowns. This constitutive model is very robust and capable of representing a wide range of problems. The identification procedure was used in the preparation of experimental tests for three different types of structural steel connections. The experimental tests have been performed for two load cases. In the first, the load was applied in one direction with both the loading and unloading cycles. From the experimental measurements, we have concluded that the response of the experimental structure can be represented by the plasticity model only because no significant change in the elastic response throughout the loading program was observed. Therefore, we have chosen an elastoplastic geometrically exact beam to describe connection behavior. The hardening response of the beam is governed by bilinear law, and the softening response is governed by nonlinear exponential law. The identification of the parameters has been successfully done with fifteen unknown parameters identified. The two types of the experimental structures were also exposed to the cyclic loading. Measured experimental data shows complex connection behavior that cannot be described by the plasticity model alone. Namely, after changing load direction stiffness of the connection decreases. This suggests that the damage model should be incorporated in the constitutive law for the connections behavior as well. Therefore, we propose a new coupled plasticity-damage model capable of representing the loss in the stiffness of the connection with the changing of the load direction. At the end of this part, we also give the constitutive parameters identification for the proposed model. The second part of the thesis deals with the theoretical formulation and numerical implementation of the elastoplastic geometrically exact beam. The hardening response of the beam includes interaction between stress resultant section forces (N, T and M), and the softening response of the beam, which is governed by the nonlinear law. This type of the beam element is capable of representing the ductile behavior of a steel frame structure, and it takes into account second order theory effects. Performed numerical simulations show that the proposed geometrically nonlinear beam element is very robust and is able to provide a more precise limit load analysis of steel frame structures. By using proposed methodology for modeling steel structures, we are able to obtain the real distribution of section forces, including their redistribution caused by forming of the hinges and the connections behavior
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Turner, Travis Lee. "Thermomechanical Response of Shape Memory Alloy Hybrid Composites". Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/29771.
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This study examines the use of embedded shape memory alloy (SMA)actuators for adaptive control of the themomechanical response of composite structures. Control of static and dynamic responses are demonstrated including thermal buckling, thermal post-buckling, vibration, sonic fatigue, and acoustic transmission. A thermomechanical model is presented for analyzing such shape memory alloy hybrid composite (SMAHC) structures exposed to thermal and mechanical loads. Also presented are (1) fabrication procedures for SMAHC specimens, (2) characterization of the constituent materials for model quantification, (3) development of the test apparatus for conducting static and dynamic experiments on specimens with and without SMA, (4) discussion of the experimental results, and (5) validation of the analytical and numerical tools developed in the study.
The constitutive model developed to describe the mechanics of a SMAHC lamina captures the material nonlinearity with temperature of the SMA and matrix material if necessary. It is in a form that is amenable to commercial finite element (FE) code implementation. The model is valid for constrained, restrained, or free recovery configurations with appropriate measurements of fundamental engineering properties. This constitutive model is used along with classical lamination theory and the FE method to formulate the equations of motion for panel-type structures subjected to steady-state thermal and dynamic mechanical loads. Mechanical loads that are considered include acoustic pressure, inertial (base acceleration), and concentrated forces. Four solution types are developed from the governing equations including thermal buckling, thermal post-buckling, dynamic response, and acoustic transmission/radiation. These solution procedures are compared with closed-form and/or other known solutions to benchmark the numerical tools developed in this study.
Practical solutions for overcoming fabrication issues and obtaining repeatable specimens are demonstrated. Results from characterization of the SMA constituent are highlighted with regard to their impact on thermomechanical modeling. Results from static and dynamic tests on a SMAHC beam specimen are presented, which demonstrate the enormous control authority of the SMA actuators. Excellent agreement is achieved between the predicted and measured responses including thermal buckling, thermal post-buckling, and dynamic response due to inertial loading.
The validated model and thermomechanical analysis tools are used to demonstrate a variety of static and dynamic response behaviors associated with SMAHC structures. Topics of discussion include the fundamental mechanics of SMAHC structures, control of static (thermal buckling and post-buckling) and dynamic responses (vibration, sonic fatigue, and acoustic transmission), and SMAHC design considerations for these applications. The dynamic response performance of a SMAHC panel specimen is compared to conventional response abatement approaches. SMAHCs are shown to have significant advantages for vibration, sonic fatigue, and noise control.Ph. D.
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Singleton, Michael David. "Nonlinear Hierarchical Models for Longitudinal Experimental Infection Studies". UKnowledge, 2015. http://uknowledge.uky.edu/epb_etds/7.
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Experimental infection (EI) studies, involving the intentional inoculation of animal or human subjects with an infectious agent under controlled conditions, have a long history in infectious disease research. Longitudinal infection response data often arise in EI studies designed to demonstrate vaccine efficacy, explore disease etiology, pathogenesis and transmission, or understand the host immune response to infection. Viral loads, antibody titers, symptom scores and body temperature are a few of the outcome variables commonly studied. Longitudinal EI data are inherently nonlinear, often with single-peaked response trajectories with a common pre- and post-infection baseline. Such data are frequently analyzed with statistical methods that are inefficient and arguably inappropriate, such as repeated measures analysis of variance (RM-ANOVA). Newer statistical approaches may offer substantial gains in accuracy and precision of parameter estimation and power. We propose an alternative approach to modeling single-peaked, longitudinal EI data that incorporates recent developments in nonlinear hierarchical models and Bayesian statistics. We begin by introducing a nonlinear mixed model (NLMM) for a symmetric infection response variable. We employ a standard NLMM assuming normally distributed errors and a Gaussian mean response function. The parameters of the model correspond directly to biologically meaningful properties of the infection response, including baseline, peak intensity, time to peak and spread. Through Monte Carlo simulation studies we demonstrate that the model outperforms RM-ANOVA on most measures of parameter estimation and power. Next we generalize the symmetric NLMM to allow modeling of variables with asymmetric time course. We implement the asymmetric model as a Bayesian nonlinear hierarchical model (NLHM) and discuss advantages of the Bayesian approach. Two illustrative applications are provided. Finally we consider modeling of viral load. For several reasons, a normal-errors model is not appropriate for viral load. We propose and illustrate a Bayesian NLHM with the individual responses at each time point modeled as a Poisson random variable with the means across time points related through a Tricube mean response function. We conclude with discussion of limitations and open questions, and a brief survey of broader applications of these models.
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Moghaddasi, Kuchaksarai Masoud. "Probabilistic Quantification of the Effects of Soil-Shallow Foundation-Structure Interaction on Seismic Structural Response". Thesis, University of Canterbury. Civil and Natural Resources, 2012. http://hdl.handle.net/10092/8446.
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Previous earthquakes demonstrated destructive effects of soil-structure interaction on structural response. For example, in the 1970 Gediz earthquake in Turkey, part of a factory was demolished in a town 135 km from the epicentre, while no other buildings in the town were damaged. Subsequent investigations revealed that the fundamental period of vibration of the factory was approximately equal to that of the underlying soil. This alignment provided a resonance effect and led to collapse of the structure. Another dramatic example took place in Adapazari, during the 1999 Kocaeli earthquake where several foundations failed due to either bearing capacity exceedance or foundation uplifting, consequently, damaging the structure. Finally, the Christchurch 2012 earthquakes have shown that significant nonlinear action in the soil and soil-foundation interface can be expected due to high levels of seismic excitation and spectral acceleration. This nonlinearity, in turn, significantly influenced the response of the structure interacting with the soil-foundation underneath.
Extensive research over more than 35 years has focused on the subject of seismic soil-structure interaction. However, since the response of soil-structure systems to seismic forces is extremely complex, burdened by uncertainties in system parameters and variability in ground motions, the role of soil-structure interaction on the structural response is still controversial. Conventional design procedures suggest that soil-structure interaction effects on the structural response can be conservatively ignored. However, more recent studies show that soil-structure interaction can be either beneficial or detrimental, depending on the soil-structure-earthquake scenarios considered.
In view of the above mentioned issues, this research aims to utilise a comprehensive and systematic probabilistic methodology, as the most rational way, to quantify the effects of soil-structure interaction on the structural response considering both aleatory and epistemic uncertainties. The goal is achieved by examining the response of established rheological single-degree-of-freedom systems located on shallow-foundation and excited by ground motions with different spectral characteristics. In this regard, four main phases are followed.
First, the effects of seismic soil-structure interaction on the response of structures with linear behaviour are investigated using a robust stochastic approach. Herein, the soil-foundation interface is modelled by an equivalent linear cone model. This phase is mainly considered to examine the influence of soil-structure interaction on the approach that has been adopted in the building codes for developing design spectrum and defining the seismic forces acting on the structure. Second, the effects of structural nonlinearity on the role of soil-structure interaction in modifying seismic structural response are studied. The same stochastic approach as phase 1 is followed, while three different types of structural force-deflection behaviour are examined. Third, a systematic fashion is carried out to look for any possible correlation between soil, structural, and system parameters and the degree of soil-structure interaction effects on the structural response. An attempt is made to identify the key parameters whose variation significantly affects the structural response. In addition, it is tried to define the critical range of variation of parameters of consequent. Finally, the impact of soil-foundation interface nonlinearity on the soil-structure interaction analysis is examined. In this regard, a newly developed macro-element covering both material and geometrical soil-foundation interface nonlinearity is implemented in a finite-element program Raumoko 3D. This model is then used in an extensive probabilistic simulation to compare the effects of linear and nonlinear soil-structure interaction on the structural response.
This research is concluded by reviewing the current design guidelines incorporating soil-structure interaction effects in their design procedures. A discussion is then followed on the inadequacies of current procedures based on the outcomes of this study.
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Eifert, Joseph D. "Predictive modeling of the aerobic growth of Staphylococcus aureus 196E using a nonlinear model and response surface analysis". Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/27970.
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Pathogenic bacteria in foods are affected by several factors which may interact to enhance or inhibit microbial growth. Staphylococcus aureus 196E was inoculated into Brain Heart Infusion broth formulated with either 0.5, 4.5 or 8.5% NaCI, adjusted to pH 5.0, 6.0 or 7.0, and incubated aerobically at 12, 20 or 28°C. Mathematical models to predict the growth of S. aureus 196E were developed using a modified Gompertz function and response surface methodology. Each predictive equation required the estimation of only 23 parameters with a biological meaning. These models determined the significance of time, incubation temperature, sodium chloride (NaCI) concentration, and either pH or the logₑ of the undissociated acid concentration and any interactions on growth kinetics. Separate models were developed for the cases where pH was altered with either acetic acid, acetic acid plus sodium hydroxide, lactic acid and hydrochloric acid.
All models adequately predicted the log growth of S. aureus 196E. Several interactive relationships between the independent variables upon population growth were significant. Predicted responses to multiple factor interactions were displayed with three-dimensional and contour plots. One model developed from a smaller subset of the growth data demonstrated that models could be produced with much less data collection. Generally, predictions of growth showed that acetic acid was more inhibitory to growth than lactic and hydrochloric acids. Furthermore, predicted and observed growth was slower or reduced when the undissociated acetic acid concentration was elevated at a specific pH.
This methodology can provide important information to food scientists about the growth kinetics of microorganisms and prediction ranges or confidence intervals for growth parameters. Consequently, the effects of food formulations and storage conditions on the growth kinetics of foodborne pathogens or spoilage microorganisms could be predicted.Ph. D.
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Arslan, Hakan. "A Numerical Study On Response Factors For Steel Wall-frame Systems". Master's thesis, METU, 2009. http://etd.lib.metu.edu.tr/upload/2/12610811/index.pdf.
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A numerical study has been undertaken to evaluate the response of dual systems which consist of steel plate shear walls and moment resisting frames. The primary objective of the study was to investigate the influence of elastic base shear distribution between the wall and the frame on the global system response. A total of 10 walls and 30 wall-frame systems, ranging from 3 to 15 stories, were selected for numerical assessment. These systems represent cases in which the elastic base shear resisted by the frame has a share of 10%, 25%, or 50% of the total base shear resisted by the dual system. The numerical study consisted of 1600 time history analyses employing three-dimensional finite elements. All 40 structures were separately analyzed for elastic and inelastic response by subjecting to the selected suite of earthquake records. Interstory drifts, top story drift, base shears resisted by the wall and the frame were collected during each analysis. Based on the analysis results, important response quantities such as the response modification, the overstrength, the displacement amplification and ductility reduction factors are evaluated herein. Results are presented in terms of several measures such as the interstory drift ratio
and the top story drift ratio. A discussion related to the influence of load share on the response factors is given.
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Oguz, Sermin. "Evaluation Of Pushover Analysis Procedures For Frame Structures". Master's thesis, METU, 2005. http://etd.lib.metu.edu.tr/upload/12606047/index.pdf.
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Pushover analysis involves certain approximations and simplifications that some
amount of variation is always expected to exist in seismic demand prediction of pushover
analysis. In literature, some improved pushover procedures have been proposed to
overcome the certain limitations of traditional pushover procedures.
The effects and the accuracy of invariant lateral load patterns utilised in pushover
analysis to predict the behavior imposed on the structure due to randomly selected
individual ground motions causing elastic and various levels of nonlinear response were
evaluated in this study. For this purpose, pushover analyses using various invariant lateral
load patterns and Modal Pushover Analysis were performed on reinforced concrete and
steel moment resisting frames covering a broad range of fundamental periods. Certain
response parameters predicted by each pushover procedure were compared with the 'exact'
results obtained from nonlinear dynamic analysis. The primary observations from the study showed that the accuracy of the pushover results depends strongly on the load path, properties of the structure and the characteristics of the ground motion. Pushover analyses were performed by both DRAIN-2DX and SAP2000. Similar pushover results were obtained from the two different softwares employed in the study provided that similar approach is used in modeling the nonlinear properties of members as well as their structural features. The accuracy of approximate procedures utilised to estimate target displacement was also studied on frame structures. The accuracy of the predictions was observed to depend on the approximations involved in the theory of the procedures, structural properties and ground motion characteristics.
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Ricci, Jaime. "Investigating environmental response to Afro-Arabian flood basalt volcanism with elemental analysis of oligocene carbonate sediments from Odp Leg 115 site 709, Indian Ocean". Thesis, University of Iowa, 2012. https://ir.uiowa.edu/etd/3374.
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The goal of this project is to investigate potential environmental responses to the extensive volcanism associated with the Afro-Arabian Large Igneous Province, by analyzing major and trace element contents in the carbonate phase of Oligocene sediments from Ocean Drilling Program Leg 115 Site 709. These sediments were deposited above the carbonate compensation depth and span the main eruption interval of the Afro-Arabian Province at ~30 Ma based on the presence of correlated volcanic ash layers. Large Igneous Provinces erupt large magma volumes (>0.1 million km3) over a short time period (<1 million years). Due to their size, many large igneous provinces coincide with episodes of global environmental change, as recorded in faunal extinction events, anomalies in the global carbon cycle, and changes in ocean water composition. A major issue with linking volcanic events to environmental change is determining synchronicity between volcanic and sedimentary records.The sediments of this study contain tephra layers that can correlated to specific onshore eruptions from the Afro-Arabian large igneous province, and provide a definitive record of the timing of volcanism. Major and trace element analysis of the sediments show five groups of elements that share similar chemical behaviors. The sediments can be divided into three stratigraphic groups with different compositions. The boundary between Group 2 (the middle group) and Group 3 (the shallow group) occurs at a depth of 243± 0.75 meters below sea floor, and is marked by a sudden increase in manganese and rare earth elements. Its inferred age of 30.45 ± 0.10 Ma is consistent with the onset of Afro-Arabian volcanism. The boundary between Group 1, the deepest stratigraphic group, and Group 2 may occur at a depth of 258.21 ± 0.75 meters below sea floor, with an inferred age of 32.31 ± 0.10 Ma, defined by a gradual decrease in manganese and rare earth elements. This chemical change might correlate with the timing of the Eocene-Oligocene Oi-1 global cooling event, however additional analyses of [delta]18 O and [delta]13 C stable isotopes are necessary to fully resolve any connection.
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Level, Pascal. "Contribution à l'élaboration d'une stratégie de calcul en dynamique des grandes structures : Développement et intégration des méthodes de réanalyse modale". Valenciennes, 1989. https://ged.uphf.fr/nuxeo/site/esupversions/ddd3277b-ac0d-4f10-a671-4f9e5d5af490.
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Etude de cinq méthodes de réanalyse modale, évitant le calcul direct des nouvelles solutions propres après modification de la structure; implantation numérique et calculs d'essai. Détermination de la meilleure méthode (méthode de partition des matrices de modification)
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Cornelio, Tony Justin. "Effect of infill panels on the seismic response of a typical R.C. frame". Master's thesis, Alma Mater Studiorum - Università di Bologna, 2011. http://amslaurea.unibo.it/2868/.
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Three structural typologies has been evaluated based on the nonlinear dynamic analysis (i.e. Newmark's methods for MDFs: average acceleration method with Modified Newton-Raphson iteration). Those structural typologies differ each other only for the infills presence and placement.
In particular, with the term BARE FRAME: the model of the structure has two identical frames, arranged in parallel. This model constitutes the base for the generation of the other two typologies, through the addition of non-bearing walls.
Whereas with the term INFILLED FRAME: the model is achieved by adding twelve infill panels, all placed in the same frame.
Finally with the term PILOTIS: the model has been generated to represent structures where the first floor has no walls. Therefore the infills are positioned in only one frame in its three upper floors.
All three models have been subjected to ten accelerograms using the software DRAIN 2000.
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Azarhoushang, Azin. "Dynamic response of fixed offshore platforms to environmental loads". Thesis, Curtin University, 2010. http://hdl.handle.net/20.500.11937/135.
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In this thesis a simplified method for dynamic response of jacket type offshore structures to extreme environmental load is investigated using existing experience and the procedures available within the industry. Fixed Jacket type offshore platforms may, under extreme wave loading conditions, exhibit significant nonlinear behavior. This must be accounted for in the design of such platforms, in order to ensure satisfactory structural safety. The complicated and nonlinear dynamic platform behavior implies that a wide number of significant uncertainties are introduced to the design process through the included mathematical models, analysis methods and the practical use of these methods. The major sources of nonlinear behavior are the wave loading, the damping mechanisms and the soil structure interaction. The inclusion of nonlinear dynamic platform behavior in the design process implies that nonlinear stochastic dynamic response based on time domain simulation methods must be applied. Time domain stochastic dynamic response analysis is an analysis method which will be a central element of the procedure. However, it seems not to be clear so far how this method should be integrated in a practical design procedure. Initially an overview of the different sources of nonlinear platform behavior is clarified with the underlying mechanism. Furthermore, it is outlined how those nonlinear effects may be accounted for with a special focus on estimation of extreme response and dynamic amplification factors. The discussion and outlines are illustrated by an example of fixed offshore platform. Finally the practical use of the method in the design of fixed jacket type offshore platforms is recommended.
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Moharrami, Gargari Mohammadreza. "Development of Novel Computational Simulation Tools to Capture the Hysteretic Response and Failure of Reinforced Concrete Structures under Seismic Loads". Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/71864.
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Reinforced concrete (RC) structures constitute a significant portion of the building inventory in earthquake-prone regions of the United States. Accurate analysis tools are necessary to allow the quantitative assessment of the performance and safety offered by RC structures. Currently available analytical approaches are not deemed adequate, because they either rely on overly simplified models or are restricted to monotonic loading. The present study is aimed to establish analytical tools for the accurate simulation of RC structures under earthquake loads. The tools are also applicable to the simulation of reinforced masonry (RM) structures.
A new material model is formulated for concrete under multiaxial, cyclic loading conditions. An elastoplastic formulation, with a non-associative flow rule to capture compression-dominated response, is combined with a rotating smeared-crack model to capture the damage associated with tensile cracking. The proposed model resolves issues which characterize existing concrete material laws. Specifically, the newly proposed formulation accurately describes the crack opening/closing behavior and the effect of confinement on the strength and ductility under compressive stress states. The model formulation is validated with analyses both at the material level and at the component level. Parametric analyses on RC columns subjected to quasi-static cyclic loading are presented to demonstrate the need to regularize the softening laws due to the spurious mesh size effect and the importance of accounting for the increased ductility in confined concrete. The impact of the shape of the yield surface on the results is also investigated.
Subsequently, a three-dimensional analysis framework, based on the explicit finite element method, is presented for the simulation of RC and RM components under cyclic static and dynamic loading. The triaxial constitutive model for concrete is combined with a material model for reinforcing steel which can account for the material hysteretic response and for rupture due to low-cycle fatigue. The reinforcing steel bars are represented with geometrically nonlinear beam elements to explicitly account for buckling of the reinforcement. The strain penetration effect is also accounted for in the models. The modeling scheme is validated with the results of experimental static and dynamic tests on RC columns and RC/RM walls. The analyses are supplemented with a sensitivity study and with calibration guidelines for the proposed modeling scheme.
Given the computational cost and complexity of three-dimensional finite element models in the simulation of shear-dominated structures, the development of a conceptually simpler and computationally more efficient method is also pursued. Specifically, the nonlinear truss analogy is employed to capture the response of shear-dominated RC columns and RM walls subjected to cyclic loading. A step-by-step procedure to establish the truss geometry is described. The uniaxial material laws for the concrete and masonry are calibrated to account for the contribution of aggregate interlock resistance across inclined shear cracks. Validation analyses are presented, for quasi-static and dynamic tests on RC columns and RM walls.Ph. D.
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Jarrett, Jordan Alesa. "Performance Assessment of Seismic Resistant Steel Structures". Diss., Virginia Tech, 2013. http://hdl.handle.net/10919/24773.
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This work stems from two different studies related to this performance assessment of seismic resistant systems. The first study compares the performance of newly developed and traditional seismic resisting systems, and the second study investigates many of the assumptions made within provisions for nonlinear response history analyses.
In the first study, two innovative systems, which are hybrid buckling restrained braces and collapse prevention systems, are compared to their traditional counterparts using a combination of the FEMA P-695 and FEMA P-58 methodologies. Additionally, an innovative modeling assumption is investigated, where moment frames are evaluated with and without the lateral influence of the gravity system. Each system has a unique purpose from the perspective of performance-based earthquake engineering, and analyses focus on the all intensity levels of interest. The comparisons are presented in terms consequences, including repair costs, repair duration, number of casualties, and probability of receiving an unsafe placard, which are more meaningful to owners and other decision makers than traditional structural response parameters. The results show that these systems can significantly reduce the consequences, particularly the average repair costs, at the important intensity levels.
The second study focuses on the assumptions made during proposed updates to provisions for nonlinear response history analyses. The first assumption investigated is the modeling of the gravity system's lateral influence, which can have significant effect on the system behavior and should be modeled if a more accurate representation of the behavior is needed. The influence of residual drifts on the proximity to collapse is determined, and this work concludes that a residual drift check is unnecessary if the only limit state of interest is collapse prevention. This study also finds that spectrally matched ground motions should cautiously be used for near-field structures. The effects of nonlinear accidental torsion are also examined in detail and are determined to have a significant effect on the inelastic behavior of the analyzed structure. The final investigation in this study shows that even if a structure is designed per ASCE 7, it may not have the assumed probability of collapse under the maximum considered earthquake when analyzed using FEMA P-695.Ph. D.