The primary purpose of this dissertation is to investigate the stability of reticulated domes under multiple static and dynamic loads. Two elastic geometrically nonlinear structural models of a reticulated dome with 21 and 39 degrees of freedom are considered. The nonlinear response of the system to static loads is obtained using nonlinear programming and discrete perturbation techniques. The nonlinear programming technique is used to obtain a starting solution for the discrete perturbation technique and to optimize the choice of the perturbation parameter. Convergence criteria and error estimates to limit errors in a perturbation scheme are developed. A method for selecting a "suitable" perturbation parameter for imperfection sensitive systems is proposed. The investigation of stability of equilibrium of the system subjected to finite disturbances is based on the concept of "degree of stability" and the associated sufficient stability condition. The stability condition is derived from a theorem on extent of asymptotic stability of Liapunov's direct method of the theory of stability of motion. Its application requires the determination of the nonlinear fundamental path and the "nearest" unstable post-buckling path. This is obtained via static analysis. The perturbed motion of the system under a given set of perturbations is obtained by numerically integrating the nonlinear equations of motion. The dynamic stability tests confirm the sufficiency of the dynamic stability condition. However, they also indicate that there is a dynamic disturbance with a specific spatial distribution for which the sufficient condition of stability is also a necessary condition for each equilibrium state tested. Since in practice, the spatial distribution of the disturbances cannot be controlled, the sufficient dynamic stability condition employed is practical for the design of reticulated domes. The stability boundaries corresponding to two independent loads on the models are presented. Limit points lie on a boundary which is convex towards the region of stability. Bifurcation points lie on a continuous but piecewise differentiable boundary. Each piece of the boundary containing bifurcation points appears to be convex towards the region of stability. / Ph. D.

Afin de faire face aux nouveaux challenges de l’industrie automobile, les ingénieurs souhaitent appliquer des méthodes d’optimisation à chaque étape du processus de conception. En élargissant l’espace de conception aux paramètres de forme, en augmentant leur nombre et en étendant les plages de variation, de nouveaux verrous sont apparus. C’est le cas de la résistance aux chocs. Avec les temps de calcul long, la non-linéarité, l’instabilité et la dispersion numérique de ce problème de dynamique rapide, la méthode usuellement employée, l’optimisation par plan d’expériences et surfaces de réponse, devient trop coûteuse pour être utilisée industriellement. Se pose alors la problématique suivante : Comment faire de l’optimisation de forme en dynamique rapide avec un nombre élevé de paramètres ?. Pour y répondre, les méthodes d’optimisation par gradient s’avèrent être les plus judicieuses. Le nombre de paramètres a une influence réduite sur le coût de l’optimisation. Elles permettent donc l’optimisation de problèmes ayant de nombreux paramètres. Cependant, les méthodes classiques de calcul du gradient sont peu pertinentes en dynamique rapide : le coût en nombre de simulations et le bruit empêchent l’utilisation des différences finies et le calcul du gradient en dérivant les équations de dynamique rapide n’est pas encore disponible et serait très intrusif vis-à-vis des logiciels. Au lieu de déterminer le gradient, au sens classique du terme, des problèmes de crash, nous avons cherché à l’estimer. L’Equivalent Static Loads Method est une méthode permettant l’optimisation à moindre coût basée sur la construction d’un problème statique linéaire équivalent au problème de dynamique rapide. En utilisant la dérivée du problème équivalent comme estimation du gradient, il nous a été possible d’optimiser des problèmes de dynamique rapide ayant des épaisseurs comme variables d’optimisation. De plus, si l’on construit les équations du problème équivalent avec la matrice de rigidité sécante, l’approximation du gradient n’en est que meilleure. De cette manière, il est aussi possible d’estimer le gradient par rapport à la position des nœuds du modèle de calcul. Comme il est plus courant de travailler avec des paramètres CAO, il faut déterminer la dérivée de la position des nœuds par rapport à ces paramètres. Nous pouvons le faire de manière analytique si nous utilisons une surface paramétrique pour définir la forme et ses points de contrôle comme variables d’optimisation. Grâce à l’estimation du gradient et à ce lien entre nœuds et paramètres de forme, l’optimisation de forme avec un nombre important de paramètres est désormais possible à moindre coût. La méthode a été développée pour deux familles de critères issues du crash automobile. La première est liée au déplacement d’un nœud, objectif important lorsqu’il faut préserver l’intégrité de l’habitacle du véhicule. La seconde est liée à l’énergie de déformation. Elle permet d’assurer un bon comportement de la structure lors du choc. / In order to face their new industrial challenges, automotive constructors wish to apply optimization methods in every step of the design process. By including shape parameters in the design space, increasing their number and their variation range, new problematics appeared. It is the case of crashworthiness. With the high computational time, the nonlinearity, the instability and the numerical dispersion of this rapid dynamics problem, metamodeling techniques become to heavy for the standardization of those optimization methods. We face this problematic: ”How can we carry out shape optimization in rapid dynamics with a high number of parameters ?”. Gradient methods are the most likely to solve this problematic. Because the number of parameters has a reduced effect on the optimization cost, they allow optimization with a high number of parameters. However, conventional methods used to calculate gradients are ineffective: the computation cost and the numerical noise prevent the use of finite differences and the calculation of a gradient by deriving the rapid dynamics equations is not currently available and would be really intrusive towards the software. Instead of determining the real gradient, we decided to estimate it. The Equivalent Static Loads Method is an optimization method based on the construction of a linear static problem equivalent to the rapid dynamic problem. By using the sensitivity of the equivalent problem as the estimated gradient, we have optimized rapid dynamic problems with thickness parameters. It is also possible to approximate the derivative with respect to the position of the nodes of the CAE model. But it is more common to use CAD parameters in shape optimization studies. So it is needed to have the sensitivity of the nodes position with these CAD parameters. It is possible to obtain it analytically by using parametric surface for the shape and its poles as parameters. With this link between nodes and CAD parameters, we can do shape optimization studies with a large number of parameters and this with a low optimization cost. The method has been developed for two kinds of crashworthiness objective functions. The first family of criterions is linked to a nodal displacement. This category contains objectives like the minimization of the intrusion inside the passenger compartment. The second one is linked to the absorbed energy. It is used to ensure a good behavior of the structure during the crash.

Efeitos de interferência aerodinâmica por vizinhança ocorrem inevitavelmente em edificações imersas em contexto urbano. Com base nas características da vizinhança que envolve o entorno de uma edificação, estes efeitos consequentemente podem reduzir ou majorar as ações do vento sobre a mesma. Tendo em vista a complexidade do problema em estimar o real ambiente em que um edifício estará situado e sua influência no comportamento do vento, torna-se muito difícil a codificação destes efeitos em documentos normativos, específicos para cada situação de projeto. No entanto, fatores de redução e majoração das ações do vento sobre as edificações podem ser determinados de acordo com as características da vizinhança presente no ambiente em que estão inseridas. Neste trabalho são analisados quatro modelos reduzidos de edifícios altos e suas vizinhanças adjacentes. Os modelos foram testados em túnel de vento, no Laboratório de Aerodinâmica das Construções da Universidade Federal do Rio Grande do Sul, sob duas configurações de ensaios, uma com a edificação isolada e outra com a edificação na presença da vizinhança na qual estará imerso. A partir dos resultados obtidos no túnel, foram calculados coeficientes de força para cada modelo, em relação a dois eixos ortogonais com origem próxima ao centro de torção da secção transversal correspondente ao pavimento tipo. Dos quatro casos estudados, todos apresentaram variações significativas dos coeficientes de força quando na presença de edificações vizinhas. Para estes edifícios, foram calculados fatores de vizinhança respectivos aos ângulos de vento mais influentes ao dimensionamento estrutural dos mesmos. A respeito das análises, notou-se que sob vizinhança densa, houve uma grande redução das ações do vento, enquanto que brechas entre as estruturas de interferência, traduziram em aumentos das ações do vento sobre as edificações estudadas. / Neighborhood interference effects due to nearby strucutres, inevitably occur on buildings immersed in urban context. Based on the characteristics of the neighborhood surrounding the vicinity of a building, these effects therefore can reduce or increase wind actions. Given the complexity of the problem in estimating the real environment where a building is located and its influence on wind behavior, it is extreme hard to encode these effects in regulation codes by specifying situations for each proposed project. However, reduction and increase factors on the wind actions over buildings can be determined according to the caracteristics of its neighborhood at the environment in which they locate. This paper analyzes four scale models of tall buildings and its surrounding structures. The models were tested in the wind tunnel at the Laboratório de Aerodinâmica das Construções of the Universidade Federal do Rio Grande do Sul, in two configurations tests, one with the building in isolated situation and the other with the building in the corresponding vicinity. The results obtained in the wind tunnel tests were used to determine strength coefficients for each model in relation to the both orthogonal axes with its origin near the torsional center of the transversal section correspondent to the standard floor of the buildings. For the four cases studied, all the test results showed significant variations at force coefficients in the presence of neighboring structures. For each case studied, interference factors were calculated due to sorrounding structures for the most influential wind angles for the structural design. Regarding the analysis it was noticed that under dense neighborhood, there was a large reduction of the wind loads, while gaps between interference structures resulted in increases of wind actions over the studied buildings.

Efeitos de interferência aerodinâmica por vizinhança ocorrem inevitavelmente em edificações imersas em contexto urbano. Com base nas características da vizinhança que envolve o entorno de uma edificação, estes efeitos consequentemente podem reduzir ou majorar as ações do vento sobre a mesma. Tendo em vista a complexidade do problema em estimar o real ambiente em que um edifício estará situado e sua influência no comportamento do vento, torna-se muito difícil a codificação destes efeitos em documentos normativos, específicos para cada situação de projeto. No entanto, fatores de redução e majoração das ações do vento sobre as edificações podem ser determinados de acordo com as características da vizinhança presente no ambiente em que estão inseridas. Neste trabalho são analisados quatro modelos reduzidos de edifícios altos e suas vizinhanças adjacentes. Os modelos foram testados em túnel de vento, no Laboratório de Aerodinâmica das Construções da Universidade Federal do Rio Grande do Sul, sob duas configurações de ensaios, uma com a edificação isolada e outra com a edificação na presença da vizinhança na qual estará imerso. A partir dos resultados obtidos no túnel, foram calculados coeficientes de força para cada modelo, em relação a dois eixos ortogonais com origem próxima ao centro de torção da secção transversal correspondente ao pavimento tipo. Dos quatro casos estudados, todos apresentaram variações significativas dos coeficientes de força quando na presença de edificações vizinhas. Para estes edifícios, foram calculados fatores de vizinhança respectivos aos ângulos de vento mais influentes ao dimensionamento estrutural dos mesmos. A respeito das análises, notou-se que sob vizinhança densa, houve uma grande redução das ações do vento, enquanto que brechas entre as estruturas de interferência, traduziram em aumentos das ações do vento sobre as edificações estudadas. / Neighborhood interference effects due to nearby strucutres, inevitably occur on buildings immersed in urban context. Based on the characteristics of the neighborhood surrounding the vicinity of a building, these effects therefore can reduce or increase wind actions. Given the complexity of the problem in estimating the real environment where a building is located and its influence on wind behavior, it is extreme hard to encode these effects in regulation codes by specifying situations for each proposed project. However, reduction and increase factors on the wind actions over buildings can be determined according to the caracteristics of its neighborhood at the environment in which they locate. This paper analyzes four scale models of tall buildings and its surrounding structures. The models were tested in the wind tunnel at the Laboratório de Aerodinâmica das Construções of the Universidade Federal do Rio Grande do Sul, in two configurations tests, one with the building in isolated situation and the other with the building in the corresponding vicinity. The results obtained in the wind tunnel tests were used to determine strength coefficients for each model in relation to the both orthogonal axes with its origin near the torsional center of the transversal section correspondent to the standard floor of the buildings. For the four cases studied, all the test results showed significant variations at force coefficients in the presence of neighboring structures. For each case studied, interference factors were calculated due to sorrounding structures for the most influential wind angles for the structural design. Regarding the analysis it was noticed that under dense neighborhood, there was a large reduction of the wind loads, while gaps between interference structures resulted in increases of wind actions over the studied buildings.

Efeitos de interferência aerodinâmica por vizinhança ocorrem inevitavelmente em edificações imersas em contexto urbano. Com base nas características da vizinhança que envolve o entorno de uma edificação, estes efeitos consequentemente podem reduzir ou majorar as ações do vento sobre a mesma. Tendo em vista a complexidade do problema em estimar o real ambiente em que um edifício estará situado e sua influência no comportamento do vento, torna-se muito difícil a codificação destes efeitos em documentos normativos, específicos para cada situação de projeto. No entanto, fatores de redução e majoração das ações do vento sobre as edificações podem ser determinados de acordo com as características da vizinhança presente no ambiente em que estão inseridas. Neste trabalho são analisados quatro modelos reduzidos de edifícios altos e suas vizinhanças adjacentes. Os modelos foram testados em túnel de vento, no Laboratório de Aerodinâmica das Construções da Universidade Federal do Rio Grande do Sul, sob duas configurações de ensaios, uma com a edificação isolada e outra com a edificação na presença da vizinhança na qual estará imerso. A partir dos resultados obtidos no túnel, foram calculados coeficientes de força para cada modelo, em relação a dois eixos ortogonais com origem próxima ao centro de torção da secção transversal correspondente ao pavimento tipo. Dos quatro casos estudados, todos apresentaram variações significativas dos coeficientes de força quando na presença de edificações vizinhas. Para estes edifícios, foram calculados fatores de vizinhança respectivos aos ângulos de vento mais influentes ao dimensionamento estrutural dos mesmos. A respeito das análises, notou-se que sob vizinhança densa, houve uma grande redução das ações do vento, enquanto que brechas entre as estruturas de interferência, traduziram em aumentos das ações do vento sobre as edificações estudadas. / Neighborhood interference effects due to nearby strucutres, inevitably occur on buildings immersed in urban context. Based on the characteristics of the neighborhood surrounding the vicinity of a building, these effects therefore can reduce or increase wind actions. Given the complexity of the problem in estimating the real environment where a building is located and its influence on wind behavior, it is extreme hard to encode these effects in regulation codes by specifying situations for each proposed project. However, reduction and increase factors on the wind actions over buildings can be determined according to the caracteristics of its neighborhood at the environment in which they locate. This paper analyzes four scale models of tall buildings and its surrounding structures. The models were tested in the wind tunnel at the Laboratório de Aerodinâmica das Construções of the Universidade Federal do Rio Grande do Sul, in two configurations tests, one with the building in isolated situation and the other with the building in the corresponding vicinity. The results obtained in the wind tunnel tests were used to determine strength coefficients for each model in relation to the both orthogonal axes with its origin near the torsional center of the transversal section correspondent to the standard floor of the buildings. For the four cases studied, all the test results showed significant variations at force coefficients in the presence of neighboring structures. For each case studied, interference factors were calculated due to sorrounding structures for the most influential wind angles for the structural design. Regarding the analysis it was noticed that under dense neighborhood, there was a large reduction of the wind loads, while gaps between interference structures resulted in increases of wind actions over the studied buildings.

Wellen und Achsen im Bereich der Antriebstechnik erfahren in den überwiegenden Anwendungen zyklische Beanspruchungen. Folglich ist für die Festigkeitsberechnung im Nennspannungskonzept eine möglichst exakte Kenntnis der Bauteilwöhlerlinie von zentraler Bedeutung. Halbzeug-Größe, Spannungsformzahl und die statischen Maximallasten beeinflussen neben weiteren Faktoren die Charakteristik der Wöhlerlinie bzw. die Dauerfestigkeit. Im Zusammenhang mit der Weiterentwicklung der Norm DIN 743 gilt diesen Größen der Fokus. Die vorliegende Arbeit betrachtet die Abschätzung der Zug-Druck-Wechselfestigkeit basierend auf dem technologischen Größeneinflussfaktor sowie der Makrohärte und deren Übertragbarkeit auf große Bauteildimensionen. In dem Zusammenhang wird der technologische Größeneinflussfaktor für Durchmesser bis 700 mm anhand einer numerisch-analytischen Simulation ermittelt und zudem mit Härtemessungen validiert. Ferner wird auf Grundlage von Treppenstufenversuchen die Abschätzung der Zug-Druck-Wechselfestigkeit aus der Härte für große Halbzeugdimensionen betrachtet. Neben dem technologischen Größeneinflussfaktor abhängig von der Härtbarkeit liegen als Ergebnisse Zusammenhänge zur Abschätzung der Zug-Druck-Wechselfestigkeit aus der Härte für große Halbzeuge vor. Darüber hinaus wird mit experimentellen Untersuchungen die Wöhlerlinie im Zeitfestigkeitsbereich analysiert. Basierend darauf werden der Wöhlerexponent sowie die Knick-Schwingspielzahl zur Dauerdauerfestigkeit in Abhängigkeit von der Formzahl abgeleitet. Abschließend widmet sich die Arbeit den Auswirkungen von statischen Maximallasten auf die Dauerfestigkeit. Dazu werden die lokalen elastisch-plastischen Beanspruchungen infolge von Maximallasten mit dem Örtlichen Konzept erfasst und in Treppenstufenversuchen die Dauerfestigkeit mit zusätzlicher Maximallast betrachtet. Ausgehend davon wird ein Konzept zur Abschätzung der lokalen Beanspruchungen sowie der lokalen Dauerfestigkeit bei Berücksichtigung des Einflusses der Maximallasten vorgestellt. / Shafts and axles of drive systems are stressed by cyclic loads in most applications. Therefore, an accurate calculation of the S-N-curve is fundamental for the system’s strength assessment based on nominal stresses. Component size, the stress concentration factor, and static loads influence the behavior of the S-N-curve and the fatigue strength, among others. In the context of a further development of the standard DIN 743, the scope is these values. This thesis focuses on the estimation of the fatigue strength for tension/compression based on the technological size factor as well as the macro hardness and their transferability to larger component sizes. In this context the technological size factor is determined by a numeric-analytical simulation for diameters up to 700 mm and is also validated with hardness measurements. Furthermore, the estimation of the fatigue strength for larger component sizes based on the hardness is supported by fatigue tests. In addition to the technological size factor depending on the hardenability, the results are obtained by an estimation approach for large components between the fatigue strength for tension/compression and the hardness. In the next step, the S-N-curve is analyzed with experimental investigations for the finite life area. Based on this, the slope of the S-N-curve (“Woehler slope”) and the knee point for the endurance limit depending on the stress concentration factor are determined. Finally, the thesis deals with the impact of static loads on fatigue strength. For this purpose, the local elastic-plastic stress-strain behavior due to static loads is calculated with the strain life assessment (local concept) and the fatigue strength influenced by static loads is analyzed as well. Based on this, an approach for the estimation of local stress-strain behavior and for the fatigue strength considering the static loads are proposed.

[pt] Sabe-se que a maioria das estruturas reais estão sujeitas à diferentes casos de carregamentos, relacionadas à diferentes solicitações estruturais e à ação de forças naturais, como ventos e ondas. Neste contexto, é importante levar em consideração o efeito da maior quantidade de cenários possíveis que possam atuar em uma estrutura ao realizar um estudo de otimização topológica. A maneira tradicional de solução deste tipo de probema envolve uma análise caso a caso dos cenários, o que no contexto de um algoritmo de otimização estrutural requer a solução de um problema de elementos finitos para cada cenário em cada passo do algoritmo, ficando limitada pelo elevado custo computacional associado. Esta limitação abre espaço para abordagens baseadas em redução de dimensões como a aproximação estocástica e a decomposição em valores singulares. Este trabalho verifica a viabilidade do uso destes dois métodos na solução de problemas de otimização topológica estrutural com muitos casos de carga. Duas aplicações são apresentadas, otimização robusta e o problema de cargas dinâmicas usando o método do carregamento estático equivalente. Com isso, situações envolvendo carregamentos mais complexos podem ser estudadas através de algoritmos eficientes de otimização topológica. Para ambos os casos, são mostrados resultados comparando os resultados obtidos através da metodologia desenvolvida neste trabalho com resultados da literatura. / [en] It is known that most real structures are subject to different loading scenarios, related to different structural solicitations and the action of natural forces, such as winds and sea waves. In this context, it is important to consider the effect of the largest number of possible scenarios that can act on a structure when performing a topology optimization study. The traditional way of solving this type of problem involves a case-by-case analysis of the scenarios, which in the context of a structural optimization algorithm requires the solution of one finite element problem for each scenario and at each step of the algorithm, being limited by the high associated computational cost. This limitation leave room for approaches based on dimenson reduction such as stochastic approximation and decomposition into singular values. This work verifies the feasibility of using these two approaches to solve structural topology optimization problems with many load cases. Two applications are presented, robust optimization and the problem of dynamic loads using the equivalent static loading method. Thus, situations involving more complex loads can be studied through efficient topology optimization algorithms. For both cases, comparisons are established between the results obtained through the methodology developed in this work and the ones from the literature.

The process for assessing the condition of a composite bridge via strain measurements is detailed in this thesis. Field measurements were utilized to conduct the assessment of a bridge located in the northern region of Sweden. The bridge is constructed with a trough and two beams, and its structure is supported by two retaining walls that enclose a 21.8-meter-long compartment. A one hundred and sixty kilo Newton vehicle cargo of trains passes the bridge. The objective is to measure and assess the bridge in the event that the axial load increases to 300 kN. Testing commenced in February of 2023. The measurement of strain was conducted using test cases. To determine the bridge's behaviour, modelling was conducted in accordance with the measurements. For this thesis, a set of models with finite elements was established and analysed. Models are made using data taken in the field and the properties of the materials. With these models as guides, he was able to make a model that is 97% accurate of how the bridge really is. The retaining walls were left out of the models because measurements showed that they were very rigid.  The influence line was also created to find the positions of the axial loads, resulting in the largest value of bending moment. After that, those positions were used for a new model with 350 KN of axial loads. Next, the stresses resulting from the actual axial loads are computed and validated using Eurocode criteria. The last step was to compare the results of the calculation with the results of the finite element analysis. The modelling results showed values that were similar to the test results, so these were used to compare the results. The modelling results serve by measuring strain interactions d as an evaluation of the bridge's condition. The assessment shows that the bridge is stronger than when standard methods are used. / Detta examenarbete beskriver i detalj hur töjningsmätningar används för att bedöma en kompositbros tillstånd. En bro i den norra regionen av Sverige bedömdes med hjälp av fältmätningar. Bron är konstruerad med ett tråg och två balkar. Två stödmurar omsluter utrymmet på 21,8 meter. En godsvagn som väger 160 kN går över bron. Målet är att mäta och utvärdera bron i händelse av att den axiella belastningen stiger till 300 kN.  Testningen började i februari 2023. Det användes testfall för att mäta töjning. Modellering utfördes i enlighet med mätningarna för att avgöra brons beteende. En uppsättning modeller med ändliga element konstruerades och analyserades för denna avhandling. Data från fältet och materialegenskaper användes för att skapa modellerna. En modell som är 97 % korrekt av brons verkliga form kan skapas med hjälp av dessa modeller som vägledning. Modellerna inkluderade inte stödmurarna eftersom mätningar visade att de var extremt styva. Det största böjningsmomentet uppnåddes genom att använda inflytelselinjen för att hitta axiella belastningspositioner. En ny studie använde dessa positioner för 350 kN axiella belastningar. Nästa steg var att beräkna och verifiera spänningarna från de verkliga axiella belastningarna med hjälp av Eurocode-standarderna.  Det sista steget var att göra en jämförelse mellan resultaten från den ändliga elementanalysen och beräkningen. Värden som visades i modellresultaten var liknande de värden som visades i testet, så dessa användes för att jämföra resultaten. Modelleringsresultaten använder töjningsinteraktioner för att bedöma brotillståndet. Undersökningen visar att bron är starkare än med standardmetoder.

Efficient road network and connectivity play vital role in the development of any country. Majority of the rural roads are unpaved and connectivity of rural roads is always a major challenge. Unpaved roads are also used for temporary transportation facilities like access roads, haul roads for mines, forest roads and parking lots. Since these roads do not have asphalt surfacing, they are subjected to early failures due to distresses like rutting, pot holes and depressions . Stabilization of unpaved roads using geosynthetics has been proved to be promising in increasing the lifespan of these roads because they facilitate economical, aesthetic and effective design of the roads. Inclusion of geosynthetic layers at the interface of subgrade soil and granular sub-base, reduces the surface heave, ensures a better stress distribution and reduces the stresses transferred to the subgrade soil, as demonstrated by earlier researchers. Wide variety of geosynthetics like woven and nonwoven geotextiles, uniaxial and biaxial geogrids and geocells are used as reinforcement in road sections. Geotextiles improve the strength by interfacial friction, lateral restraint and membrane effect. Geogrids provide additional benefit of interlocking. Geocells are honeycomb shaped geosynthetic cellular confining systems filled with aggregates in which the reinforcement action is derived not only by friction and interlocking, but also by confinement. Load-deformation characteristics of reinforced soil-aggregate systems under static, repeated and cyclic loads is a potential topic of interest considering the fact that the design of geosynthetic reinforced unpaved roads is still under development and experimentation. The objective of the present study is to understand the beneficial use of geosynthetics in unpaved roads and to provide clear insight into the influence of geosynthetics on the cyclic loading characteristics of unpaved roads through laboratory experiments. California Bearing Ratio (CBR) tests were carried out on unreinforced and reinforced soil-aggregate systems to study the effect of various parameters such as type of reinforcement, form of reinforcement, quantity of reinforcement, and water content of the subgrade soil on the load-penetration response of the various systems. Modified CBR tests were also carried out to understand the influence of boundary of the mould and anchorage of reinforcement on the behavior of reinforced soil-aggregate systems. Behavior of unreinforced and reinforced soil-aggregate systems under repeated and cyclic loading is also studied to understand the resilience of the composite systems. From the measured stress-strain response, the elastic and plastic strains developed in various systems are compared. Different moduli such as secant modulus, cyclic modulus and resilient modulus are computed for different systems and compared. To investigate the effectiveness of geosynthetics in improving the load - bearing capacity, repeated load tests were carried out on model sections of unpaved road constructed in a steel test tank of size 750 mm × 750 mm × 620 mm. The effect of various parameters like the form of reinforcement, quantity of reinforcement, height of geocell layer and the position of geocell layer on the load-deformation behaviour of the unpaved model road sections was studied. Static and cyclic triaxial tests were carried out on unreinforced and reinforced granular sub-base materials to understand their stress strain behavior under static and cyclic loading conditions. The influence of quantity and form of reinforcement on the stress-strain behaviour of these materials was studied. From the studies it is observed that the use of reinforcement increases the CBR value of the soil-aggregate systems. Studies with two different sizes of CBR moulds indicated that the boundary effect in the standard CBR mould leads to the overestimation of the CBR value, resulting in unconservative design of road sections. Providing anchorage to the reinforcement in CBR tests did not produce an appreciable change in the load-penetration behavior. From the repeated load tests it was observed that the reinforced systems did not show any improvement in the load-deformation behaviour at low levels of rut depth. At higher rut depths, the reinforced systems developed less plastic settlements and more elastic settlements and low resilient modulus compared to unreinforced systems. From the model tests on unpaved road sections, it was observed that the improvement in the cyclic load resistance of the road due to the inclusion of geocell layer depends on the height of the geocell layer and its position. Increasing the height of geocell layer resulted in improved performance up to certain height of the geocell layer, beyond which, further increase in the height reduced the load resistance because of the inadequate granular overlay thickness and inadequate compaction of aggregate within the geocell pockets. Static and cyclic triaxial tests showed that the geogrid and geocell reinforced granular sub-base material sustained higher peak stresses and exhibited increase in modulus compared to the unreinforced specimens. Results of element and model tests carried out in this study gave important insight into the load-deformation characteristics of reinforced soil-aggregate systems under static, repeated and dynamic loads. The results provide guidelines regarding the selection of type, quantity and configuration of geosynthetic reinforcement while designing unpaved roads and the expected performance of these reinforced unpaved roads.