Geostructures experience repetitive load cycles, which gradually affect their long-term performance. This thesis explores the long-term response of soils subjected to mechanical load-unload, heat-cool, freeze-thaw, and atmospheric pressure oscillations. The research methodology involves new instrumented cells (oedometer, temperature-controlled triaxial chamber, and pressure-controlled drying chamber), various geophysical monitoring methods (X-ray micro-CT, NMR, S-wave, and EM-waves), and simulations using discrete element modeling. Results show that soils subjected to repetitive mechanical or environmental loading experience shear and volumetric strain accumulation and changes in saturation (during barometric pressure cycles). In all cases, soils evolve towards an asymptotic terminal void ratio; the change in void ratio is pronounced when the soil exhibits grain-displacive ice formation during freeze-thaw cycles. The initial stress obliquity defines the shear strain response, which may be either shakedown -at low stress obliquity-, or ceaseless shear strain accumulation in ratcheting mode when the maximum stress obliquity approaches failure conditions. Finally, we provide simple engineering guidelines to estimate the long-term behavior of soils subjected to repetitive mechanical or environmental loading.

Ziel der vorliegenden Dissertation war die Erweiterung der Kenntnisse über das nichtlinear-elastische Spannungs-Verformungsverhalten von Tragschichten ohne Bindemittel (ToB). Ein analytisches Bemessungsverfahren ist aufgrund der schwierigen Modellierbarkeit des Verformungsverhalten der einzelnen Straßenbaustoffe bisher nicht existent. Die Dissertation soll einen Beitrag zur Entwicklung eines solchen Bemessungsverfahrens leisten. Eine Literaturrecherche zum Verformungsverhalten von ToB bildet die Grundlage für die Festlegung der Vorgehensweise. Basis der weiteren Untersuchungen sind Triaxialversuche, die an der Universität Nottingham an verschiedenen Gesteinskörnungen durchgeführt wurden. Mit Hilfe der Shakedown-Theorie konnte belegt werden, dass sich ToB in unterschiedlichen Beanspruchungsbereichen nach verschiedenen Gesetzmäßigkeiten verhalten und dass Modelle zur Beschreibung des Verformungsverhaltens von ToB bereichsweise verschieden formuliert werden müssen. Somit ist es möglich, Gültigkeitsgrenzen für elastische Stoffmodelle zu ermitteln sowie Beanspruchungsgrenzen für ToB festzulegen. Mit ausgewählten Stoffmodellen erfolgten Beanspruchungsberechnungen nach der Finite-Elemente Methode (FEM). Die beste Annäherung zwischen Messwerten und Rechenergebnissen ergibt sich bei Anwendung des DRESDNER Modells. Berechnungen für Befestigungen nach den RStO 01 haben gezeigt, dass die Beanspruchungen auf den ToB bei Anwendung des DRESDNER Modells stark von denen bei Anwendung linearer Elastizität abweichen können. Durch unterschiedliche Überbauungsdicken der ToB besitzen diese einen verschieden hohen Anteil am Tragverhalten der Befestigung. Abschließend wird eine Methode zur Ermittlung von Sicherheitsniveaus vorgestellt. Bei Kenntnis der entsprechenden Schichtparameter lassen sich die Beanspruchungen jeder beliebigen Bauweise mit denen von Bauweisen nach RStO vergleichen. Als Ergebnis kann festgehalten werden, dass das Sicherheitsniveau einer bestimmten Bauweise nach RStO genauso groß ist, wie eine Befestigung mit einer dünneren Asphalttragschicht, dafür jedoch einer steiferen ToB. / The aim of this thesis was the extension of the knowledge about the resilient stress-deformation behaviour of unbound granular materials (UGM). Due to difficulties in modelling the behaviour of the single materials an analytical design method does not exist at present. Therefore this thesis makes a contribution for developing such a design method. A study of international publications about the current knowledge of the stress-deformation behaviour of UGM and repeated load triaxial tests, which have been performed at Nottingham University, were the base for all further investigations. With the shakedown concept it could be shown that materials behave in a different manner depending on the applied stress level and that material laws for describing the resilient deformation behaviour of UGM have to be formulated separately for different stress ranges. Within this thesis a method is introduced which helps to find boarders for the applicability of different material laws and limiting stress lines where below the lines stable behaviour and admissible deformations for the material are expected. Applying selected material laws finite element calculations have been performed. Comparing calculation results with measurement results it can be shown that the Dresden model offers the best approach. Calculations for pavement constructions applying the Dresden model have resulted that the vertical stresses differ very much in comparison with elastic behaviour for the UGM. It can be concluded that the thickness of the covering bounded layers have an effect to the contribution of the unbound granular layers at the complete deformation behaviour of the pavement construction. Finishing a method is introduced to determine the safety levels of pavement constructions. It seems to be possible to compare the stress-strain levels of any pavement construction with those from the german standard RStO 01. Existing functions could be modified to determine safety coefficients, i. e. ratios between admissible and existing numbers of load cycles. It can be concluded that there are the same safety levels for different pavement constructions ? a thinner asphalt layer can be compensated with a stiffer UGM.

Studies conducted in 2016 show that 58% of the highways in Brazil presents any deficiency in the pavement, signaling or in its geometry. These deficiencies are, on average, the cause for about 6% of the accidents and for the increase of the operational cust by 91,6%. Among them we can stress the permanent deformation, the so called wheel tracks, which is harmful to the dynamic of the loads, to the comfort provided by the pavement, increasing its risk. To the correct design of the pavement it is very important to better know the characteristics of the materials to be used. In this context, stands out the subgrade, the foundation for the whole structure of the pavement, which one is studied in the present reseach by considering three typical soils used as highway subgrade in Santa Maria, Rio Grande do Sul State, and having the permanent deformations as the main focus. The metodology aplied in this work consisted in the location, sampling and characterization of the soil fields, lab tests and empirical machanistic design. Besides the physical, chemical and mechanical characterizations, it was performed the repeated triaxial load test aiming to obtain the resilient modulus and the permanent deformation parameters, according to the Brazilian Petroleum Corporation Manual (PETROBRAS). The Resilient Modulus model presented the better results with frequencies of 1 Hz and 2 Hz, and the presence of silt in one of the soils affected its resilient behaviour. The permanent deformation tests were performed with the frequency of 2 Hz and 150.000 load cicles. The average statistic correlation, according to Guimaraes (2009)´s methodology, was 0.91, bigger than the one provided by the Monismith and Barksdale´s models. However, the dominance of fine grained soils, along with low compactation energy, lead to a higher deformation rates, motivating the use of intermediate energy. With this new approach the permanent deformation was reduced 40% and the resilient modulus increased 78,8%. However, the numerical simulation according to the mechanistic approach, and using the layer thickness obtained from the Departamento Nacional de Infraestrutura de Transportes (DNIT) method, under 8,2 ton standard axle load, showed that the wheel tracks deeping would be small, based on the low stresses observed in the subgrade. On the other hand, the fatigue behaviour presented an inferior performance, reducing the project´s useful life. It was observed the presence of shakedown in the ranges A, B and C. / Pesquisas realizadas no ano de 2016 mostram que 58,2 % das rodovias de todo o país apresentam alguma deficiência no pavimento, na sinalização ou na geometria da via. Em média, esses defeitos são responsáveis por cerca de 6% do número de acidentes, além de aumentar o custo operacional das vias em até 91,6%. Dentre essas anomalias, destaca-se a deformação permanente denominada de afundamento na trilha de roda (ATR), que prejudica a dinâmica das cargas, afeta o conforto ao rolamento e causa risco à segurança. Para o adequado dimensionamento de um pavimento, é fundamental o conhecimento dos materiais que o compõem. Neste contexto, destaca-se o subleito, por ser a fundação sobre a qual são assentes todas as camadas, motivo pelo qual o objetivo geral desta pesquisa é analisar três solos típicos de subleitos rodoviários de Santa Maria, estado do Rio Grande do Sul, em especial quanto aos parâmetros de deformação permanente. A metodologia aplicada neste trabalho consistiu na localização, coleta e caracterização das jazidas de solos, realização de ensaios laboratoriais e dimensionamento mecanístico - empírico. Assim, além da caracterização física, química e mecânica, foram realizados ensaios triaxiais de cargas repetidas para obtenção do módulo de resiliência e dos parâmetros de deformação permanente, segundo recomendações do manual de execução de trechos monitorados da empresa Petróleo Brasileiro Sociedade Anônima (PETROBRAS). O modelo composto do módulo de resiliência apresentou os melhores resultados, a partir de ensaios com frequência de 1 Hz e 2 Hz, sendo que a presença de silte em um dos solos afetou seu comportamento resiliente. Os ensaios de deformação permanente foram conduzidos a 2 Hz, com 150.000 ciclos de aplicação de carga, cuja correlação estatística média, empregando a metodologia de Guimarães (2009), foi de 0,91 – superior a dos modelos de Monismith e Barksdale. Entretanto, a predominância de materiais finos, aliada à baixa energia de compactação (normal), resultaram em elevadas taxas de deformação, o que motivou o estudo de um dos solos também com uso da energia intermediária. Esse procedimento reduziu a deformação permanente em 40% e elevou o módulo de resiliência em 78,8%. Entretanto, a simulação numérica do pavimento sob a ótica mecanicista, a partir das espessuras calculadas pelo método do Departamento Nacional de Infraestrutura de Transportes (DNIT), aplicando-se a carga padrão de 8,2 toneladas, mostrou que o ATR seria pequeno, em face das baixas tensões atuantes no subleito, em contraposição ao desempenho à fadiga, que reduziu sensivelmente a vida útil de projeto. Constatouse a ocorrência de shakedown nos domínios A, B e C.

Ziel der vorliegenden Dissertation war die Erweiterung der Kenntnisse über das nichtlinear-elastische Spannungs-Verformungsverhalten von Tragschichten ohne Bindemittel (ToB). Ein analytisches Bemessungsverfahren ist aufgrund der schwierigen Modellierbarkeit des Verformungsverhalten der einzelnen Straßenbaustoffe bisher nicht existent. Die Dissertation soll einen Beitrag zur Entwicklung eines solchen Bemessungsverfahrens leisten. Eine Literaturrecherche zum Verformungsverhalten von ToB bildet die Grundlage für die Festlegung der Vorgehensweise. Basis der weiteren Untersuchungen sind Triaxialversuche, die an der Universität Nottingham an verschiedenen Gesteinskörnungen durchgeführt wurden. Mit Hilfe der Shakedown-Theorie konnte belegt werden, dass sich ToB in unterschiedlichen Beanspruchungsbereichen nach verschiedenen Gesetzmäßigkeiten verhalten und dass Modelle zur Beschreibung des Verformungsverhaltens von ToB bereichsweise verschieden formuliert werden müssen. Somit ist es möglich, Gültigkeitsgrenzen für elastische Stoffmodelle zu ermitteln sowie Beanspruchungsgrenzen für ToB festzulegen. Mit ausgewählten Stoffmodellen erfolgten Beanspruchungsberechnungen nach der Finite-Elemente Methode (FEM). Die beste Annäherung zwischen Messwerten und Rechenergebnissen ergibt sich bei Anwendung des DRESDNER Modells. Berechnungen für Befestigungen nach den RStO 01 haben gezeigt, dass die Beanspruchungen auf den ToB bei Anwendung des DRESDNER Modells stark von denen bei Anwendung linearer Elastizität abweichen können. Durch unterschiedliche Überbauungsdicken der ToB besitzen diese einen verschieden hohen Anteil am Tragverhalten der Befestigung. Abschließend wird eine Methode zur Ermittlung von Sicherheitsniveaus vorgestellt. Bei Kenntnis der entsprechenden Schichtparameter lassen sich die Beanspruchungen jeder beliebigen Bauweise mit denen von Bauweisen nach RStO vergleichen. Als Ergebnis kann festgehalten werden, dass das Sicherheitsniveau einer bestimmten Bauweise nach RStO genauso groß ist, wie eine Befestigung mit einer dünneren Asphalttragschicht, dafür jedoch einer steiferen ToB. / The aim of this thesis was the extension of the knowledge about the resilient stress-deformation behaviour of unbound granular materials (UGM). Due to difficulties in modelling the behaviour of the single materials an analytical design method does not exist at present. Therefore this thesis makes a contribution for developing such a design method. A study of international publications about the current knowledge of the stress-deformation behaviour of UGM and repeated load triaxial tests, which have been performed at Nottingham University, were the base for all further investigations. With the shakedown concept it could be shown that materials behave in a different manner depending on the applied stress level and that material laws for describing the resilient deformation behaviour of UGM have to be formulated separately for different stress ranges. Within this thesis a method is introduced which helps to find boarders for the applicability of different material laws and limiting stress lines where below the lines stable behaviour and admissible deformations for the material are expected. Applying selected material laws finite element calculations have been performed. Comparing calculation results with measurement results it can be shown that the Dresden model offers the best approach. Calculations for pavement constructions applying the Dresden model have resulted that the vertical stresses differ very much in comparison with elastic behaviour for the UGM. It can be concluded that the thickness of the covering bounded layers have an effect to the contribution of the unbound granular layers at the complete deformation behaviour of the pavement construction. Finishing a method is introduced to determine the safety levels of pavement constructions. It seems to be possible to compare the stress-strain levels of any pavement construction with those from the german standard RStO 01. Existing functions could be modified to determine safety coefficients, i. e. ratios between admissible and existing numbers of load cycles. It can be concluded that there are the same safety levels for different pavement constructions ? a thinner asphalt layer can be compensated with a stiffer UGM.

Darbo tikslas – tampriųjų-plastinių strypų konstrukcijų (santvaros, rėmų), veikiamų kartotinės kintamosios apkrovos, prisitaikomumo proceso ir būvio įtempių ir deformacijų analizė optimalaus konstrukcijų projektavimo kontekste. Darbo aktualumas grindžiamas prisitaikančių konstrukcijų optimizavimo uždaviniuose figūruojančių standumo sąlygų-apribojimų kokybės gerinimo būtinumu. Prisitaikančių konstrukcijų deformacijų būvis priklauso nuo apkrovimo istorijos, o poslinkių ribojimui taikoma nepakankamai tiksli Koiterio sąlyga arba liekamųjų poslinkių influentinė matrica, nepagrįstai laikant, kad plastinio deformavimo procesas yra išimtinai holonominis. Anotuojamame darbe apkrovimo istoriją siūloma įvertinti, atliekant papildomą inkrementinę deformacijų būvio analizę. Tyrimai atlikti taikant idealiai tamprių plastinių santvarų ir rėmų techniškosios skaičiavimo teorijos prielaidas (maži poslinkiai ir deformacijos). Taikomi ekstreminiai energiniai mechanikos principai, matematinio programavimo teorija ir metodai. Inkrementinės analizės matematiniai modeliai sudaryti, besikeičiančias plastines deformacijas tapatinant su distorsijomis. Taip nustatomos konkrečios apkrovimo istorijos liekamųjų poslinkių kitimo maksimalios ir minimalios reikšmės. Gautieji rezultatai panaudoti optimizavimo uždavinių sprendiniams tikslinti ir, esant būtinumui, leidžiantys keisti pradines pagrindinio optimizavimo uždavinio sąlygas. Pateikti išsamūs skaitinių eksperimentų rezultatai. / The purpose of this work is analysis of stress-deformation state of perfectly elastic-plastic shakedown structures (truss, frames) subjected to repeated variable load in the context of optimal design. Relevance of this work is based on a need of improvement of accurateness of stiffness constrains in optimization problems of structures. Stress-deformation state of shakedown structures depends on its loading history, while for the restriction of displacements inaccurate Koiter’s condition or an influence matrix of residual displacements, on the wrong supposition that the process of plastic deformation is exclusively holonomic, is used. In this work is proposed to evaluate loading history by performing an additional incremental analysis of stress-deformation state. This research was performed invoking the assumptions of technical computing theory of perfectly elastic-plastic trusses and frames (small deformations and displacements). Mechanics extremum energy principles, mathematical programming theory and methods are applied. Mathematical models of incremental analysis are composed by indentifying volatile plastic deformations with distortions. Thus particular maximum and minimum values of residual displacements are found. Obtained results are used to verify optimal design problems solutions and change the restrictions of main optimimization problem if necessary. Comprehensive results of numerical experiments presented.

Engineering assemblies are very frequently subject to fretting fatigue, which is a damage process that results when very small slip displacements arise at nominally stationary frictional interfaces. Fretting accelerates the initiation and early propagation of fatigue cracks, thereby causing significant reductions in the fatigue performance of many critical engineering components. A majority of the previous research on fretting fatigue has focused on incomplete (i.e. smooth-edged) contacts, while complete (i.e. sharp-edged) contacts have received less attention. The aim of this thesis is to contribute to the theoretical understanding of complete contacts, especially when they are subject to fatigue conditions. This problem is addressed in two separate ways. First, because fretting failures almost invariably initiate from the edge of contact, a detailed understanding of the conditions in this region should enable more accurate assessments of fatigue performance to be made. Thus, an asymptotic analysis is presented, which provides an accurate description of the contact edge under many conditions. This is done by using the elasticity solution for a semi-infinite notch to represent the state of stress near the contact edge in an asymptotic sense. Attention is then placed on the fact that cyclically loaded frictional contacts tend toward a steady-state response in which less frictional slip (and energy dissipation) occurs than in the first few load cycles. To investigate this effect, a numerical sub-structuring procedure is described, which significantly reduces the number of degrees of freedom in finite element models of frictional contact. This reduced model is then used to calculate the shakedown limit, i.e. the amplitude of cyclic load above which frictional slip is guaranteed to persist in the steady state. The sensitivity of the steady-state solution to the initial residual displacement state is then investigated, and it is shown that initial conditions can have a large influence on the steady-state behaviour of complete contacts.

Traditionally, flexible pavement design relies on past experience and semi-empirical methods developed through a combination of element testing and modelling. Element testing in this area especially, has centred on the performance of clean sands. This is in conflict with actual practice where a wide range of fines and soil gradations could be present in a real-world project. This research investigates the characteristics of natural sands and examines the influence of these marginal materials in pavement design using element testing and controlled modelling of an actual flexible pavement system. The element tests concentrated on separate, natural soils sourced from Kazakhstan which had similar mineralogy, but varying amounts of fines. One of the key parameters examined was equivalent void ratio and its efficiency to account for the behaviour change in granular materials which comes from increased fines content. Starting with monotonic triaxial results combined with strength-dilatancy methods it was shown that prediction of shear strength in a silty-sand could be improved by 13%. Incorporating this finding into repeat load triaxial tests, the transitions between elastic, plastic, and ratcheting failure behaviours (i.e. shakedown boundaries), commonly used to help predict the lifespan of a flexible pavement, were examined. It was seen that cycling a silty-sand, the stress path and yield surface could change depending on the fines content. The Cambridge Airfield Pavement Tester (APT) was designed and constructed to measure permanent subgrade deformation resulting from various surface loads. The number of input variables required to design flexible pavements is one of the most frequently stated problems in the field; variation of aircraft types, environmental conditions, and materials makes mechanistic design of the soil foundation problematic. Accordingly physical pavement modelling continues to be the only experimental method that allows input parameters and material characteristics to be examined simultaneously. Digital image correlation (DIC) was incorporated into the system; the first time this technology has been used in flexible pavement research. A Null Pressure System was also installed to measure soil stress distributions. It was observed that the critical failure mechanisms for thin and thick surficial layers are different, resulting in changes in the rates of surface rutting. Finally, by combining element and APT results, knowledge of the causal relationships between subsurface deformation and failure mechanisms in flexible pavement were advanced. In-situ soils, which are frequently incorporated into subgrade designs, were found to have a substantial role in the serviceability of the pavement. Correlations between element tests and APT results highlighted the complicated loading and boundary conditions present in a pavement.

It is generally assumed that monetary incentivization is the most effective means of motivating organizationally-beneficial behaviors. Individuals, under this line of thought, pursue their own objective self-interest above all else. However, evidence is being uncovered that indicates that human motivation may be a much more complicated facet of the human psyche. The purpose of this study is to examine the deeper underpinnings that drive people work that might lie beyond financial rewards. In order to do this, the Shakedown Café, a student-run restaurant on Pitzer College’s campus, will be examined. This specific organization is of particular interest because it does not have the ability to reward employees in the manner that most businesses are able to employ. In looking at the Shakedown, the author's direct experiences while working in the restaurant, observations, a variety or intra-organizational correspondences, and modern organizational behavior theories will be utilized. The findings of this research indicate that the human drives to learn, bond with others, and defend oneself and one's surroundings are all just as important aspects of motivation as is the drive to acquire money. Within the organization of interest, these drives manifest themselves through organizational purpose, group learning, and shared leadership. From this example of the Shakedown Café, it is suggested that proliferation of financial rewards in today's organizations may well be an outdated model of motivating which could be prohibiting organizations and the people within them from reaching their full potentials.

A rather complete picture of automatic plastic-hinge analysis onto steel frames under static loads is made in the present thesis. One/two/three-linear behaviours of mild steel are considered. The frames are submitted to fixed or repeated load. The geometric nonlinearity is taken into account. The beam-to-column joints of structures could be rigid or semi-rigid. The compact or slender cross-sections are examined. The investigation is carried out using direct or step-by-step methods. Both analysis and optimization methodologies are applied. From the fundamental theory to the computer program aspect are presented. Various benchmarks in open literatures are tested demonstrating the efficiency of the implementation.

Improvements in quality of life, population growth, and environmental restrictions associated with the burning of fossil fuels will accentuate the need for renewable energy and energy geo-storage. A salient characteristic of these systems is that they impose numerous cycles of effective stress, temperature, and humidity on the surrounding geomaterials. This thesis quantifies future energy consumption based on realizable scenarios and explores the behavior of geomaterials subjected to mechanical and thermal cycles in view of energy-related applications. The long-term behavior of geotechnical systems subjected to a large number of mechanical load cycles is studied with a new numerical scheme based on a hybrid finite element formulation. The numerical scheme satisfies initial conditions as well as fundamental characteristics of soil behavior, such as threshold strain, terminal density, and long-term ratcheting. Numerical results show that shallow foundations subjected to repetitive loading experience strain accumulation and stress redistribution. On the other hand, the long-term behavior of energy piles, exposed geomembranes on slopes, and jointed rock masses subjected to cyclic thermal changes is studied using a combination of numerical, analytical, and experimental methods. Results show that thermal cycles lead to the gradual accumulation of plastic displacements, which may be amplified by thermally-induced wedging in jointed rock masses. In general, cumulative effects caused by repetitive loads increase with the number of cycles, the static factor of safety, the amplitude of the cyclic excitation, and the magnitude of the cyclically-induced displacement with respect to the critical elastic displacement.