Structural design of piles with respect to buckling in Sweden is commonlymade in accordance with the calculation model from the Commission ofPile Research, PKR. A prerequisite for this model is that the elasticbuckling length of the pile is shorter than the physical length. For shortpiles this assumption might not be valid, meaning that anotherappropriate calculation model may be used instead. This situation occurswhen designing end-bearing piles in typical geological conditions foreastern Sweden, consisting of soft clay and shallow bedrock.This thesis compared the PKR-model with alternative models for thedesign of short piles. One of the alternate calculation models was a finiteelement model where Winkler springs represented the soil. It was used tosimulate cases with various diameters and undrained shear strengths.Furthermore, the results using the PKR- and FEM-model was comparedto calculations according to Eurocode 3 considering the pile as a freestandingcolumn. By the help of the FEM-model, a method to considergreater initial deflections in the Eurocode 3-model was also developed.In conclusion, the PKR-model was non-conservative for some of thetested cases. With some precautions taken for those cases, the model wasvalid to use for elastic buckling lengths up to two times the physicallength of the pile. The results from the Eurocode 3-model were bothconservative and non-conservative depending on the pile- and soilconditions. It was seen that the analytical models were not comparablesince they handle prerequisites and design assumptions in different ways.A sensitivity analysis was also made which resulted in suggestions forfurther research on the topic.

Elementos estruturais como as placas finas fazem parte de um grande número de aplicações nas mais diversas áreas da engenharia e são de grande importância para a engenharia naval e aeronáutica, na construção de cascos de embarcações e estruturas offshore, e na construção de fuselagens de aviões. Por constituírem-se em um elemento estrutural esbelto, estão sujeitas a um comportamento mecânico diferenciado denominado de flambagem, proveniente de um carregamento de compressão uniaxial. O fenômeno da flambagem pode ser dividido em flambagem elástica e elasto-plástica, sendo dependente de aspectos dimensionais, construtivos e/ou operacionais. A inclusão de perfurações em placas provoca uma redistribuição de suas tensões internas, afetando não apenas a sua resistência, mas também as suas características de flambagem. Neste trabalho, desenvolveu-se a análise do comportamento mecânico de placas finas perfuradas de aço, simplesmente apoiadas em suas bordas, e submetidas à compressão. Serão analisados dois graus de liberdade: H/L e H0/L0. Para H/L, serão analisadas placas com H/L = 1,00 e H/L = 0,50, sendo que H e L representam, respectivamente, a largura e o comprimento da placa. Para H0/L0, serão analisadas infinitas possibilidades, sendo que H0 e L0 representam, respectivamente, a largura e o comprimento da perfuração. As placas utilizadas possuem espessura (h) de 10,00 mm e perfuração centralizada. Quanto às perfurações, estas serão dos tipos: oblonga longitudinal, oblonga transversal, elíptica, retangular, losangular, hexagonal longitudinal e hexagonal transversal. Ainda em relação às perfurações, serão consideradas as seguintes frações ϕ = 0,08; 0,10; 0,15; 0,20 e 0,25, sendo que (ϕ) corresponde ao volume da perfuração. Para a determinação das cargas crítica e última de flambagem, foi utilizada a simulação numérica com o auxílio do software Ansys®, que é baseado no método dos elementos finitos. A aplicação do método Design Construtal, possibilitou a determinação das geometrias ótimas para todos os tipos de perfurações, todos os valores de (ϕ) e para todas as relações de H/L. Os resultados obtidos mostram que há influência do tipo, da forma e do tamanho da perfuração na definição das curvas limites à flambagem e das curvas à flambagem elasto-plástica. Foi possível definir, para cada tipo de perfuração e para todos os valores de (ϕ), os pontos de transição entre a flambagem elástica e à elasto-plástica, assim como os pontos que definem os valores máximos para o fator TLNMáx (tensão limite normalizadora). / Structural elements such as thin plates are part of a large number of applications in various areas of engineering and are of great importance for marine and aerospace engineering, construction and offshore structures hulls, and the construction of airplane fuselages. Being a slender structural element, they are subject to a different mechanical behavior known as buckling, caused by a compressive loading. The phenomenon of buckling can be divided in elastic and elasto-plastic buckling, being dependent dimensional, construction and / or operational aspects. The inclusion of perforations in plates causes a redistribution of its internal stress, affecting not only their resistance but also their buckling characteristics. In this work it was performed the analysis of the mechanical behavior of thin perforated steel plates, simply supported on its edges, and subjected to compression. In the analysis it was considered two degrees of freedom: H/L and H0/L0. For H/L will be analyzed plates with H/L = 1.00 and H/L = 0.50, wherein H and L represent respectively the width and length of the plate. There are endless possibilities for the relation H0/L0. The studied plates have a thickness (h) of 10.00 mm and centralized perforation. The following types of perforation will be used: longitudinal oblong, transverse oblong, elliptical, rectangular, diamond, longitudinal hexagonal and transverse hexagonal. Also in relation to perforations, it will be considered the following fractions (ϕ = 0.08; 0.10; 0.15; 0.20 and 0.25), wherein (ϕ) corresponds to the volume ratio of the perforation. For determining the critical and ultimate buckling loads it was utilized numerical simulation with the assistance of Ansys® software, which is based on the finite element method. The application of the Constructal Design method of this study made it possible to determine the optimal geometries for all types of perforations, for all values of (ϕ) and all the relations H/L. The results show that there is an influence of the perforation type, shape and size, in defining the limit curves of the buckling and the curves of the elasto-plastic buckling. It was also possible to define, for each type of perforation and for all (ϕ) values, the transition points between elastic and elasto-plastic buckling; as well as the points that define the maximum values for the TLNMáx factor (normalized limit stress).

The recent substantial increase in world demand for energy and raw material resources has accelerated oil and gas exploration and production. At the same time, the depletion of onshore and shallow water oil resources presents a challenge to engineers to develop new means of harvesting and transporting oil and gas from harsh and remote areas. Sandwich Pipe (SP) is a relatively new design concept developed to address the transportation of oil in deep and ultra-deep waters as well as in cold environments. The main focus of this thesis is on the characterization of the structural performance of these novel systems. Deep and ultra-deep water offshore pipelines are subjected to excessive hydrostatic external pressure during installation and operation. In this research, an innovative analytical solution was developed to evaluate the external pressure capacity of SPs by calculating the linear eigenvalues of the characteristic equations of the system. In the proposed solution, the interface condition between the layers of the system is accounted for in the governing equations. As well, a set of comprehensive parametric studies using the Finite Element (FE) method was developed to investigate both the elastic and plastic buckling response of SPs. The influence of various structural parameters such as the material, geometrical and intra-layer interaction properties on the characteristic behavior and the buckling pressure of SPs was examined. In addition to the proposed analytical solution, two sets of semi-empirical equations based on the FE analysis results were recommended in calculating the elastic and plastic buckling pressure of SPs. As bending represents an important loading state in the installation and service life of SPs, it should be considered a governing loading scenario. In this thesis, the behavior of SPs under bending was investigated using a comprehensive set of parametric studies. SP systems with a wide practical range of physical parameters were analyzed using the FE method, and the influence of various structural parameters on the characteristic response and bending capacity of the system was explored, including pipe geometry, core layer properties, material yield anisotropy of high-grade steel pipes, and various intra-layer adhesion configurations.

Elementos estruturais como as placas finas fazem parte de um grande número de aplicações nas mais diversas áreas da engenharia e são de grande importância para a engenharia naval e aeronáutica, na construção de cascos de embarcações e estruturas offshore, e na construção de fuselagens de aviões. Por constituírem-se em um elemento estrutural esbelto, estão sujeitas a um comportamento mecânico diferenciado denominado de flambagem, proveniente de um carregamento de compressão uniaxial. O fenômeno da flambagem pode ser dividido em flambagem elástica e elasto-plástica, sendo dependente de aspectos dimensionais, construtivos e/ou operacionais. A inclusão de perfurações em placas provoca uma redistribuição de suas tensões internas, afetando não apenas a sua resistência, mas também as suas características de flambagem. Neste trabalho, desenvolveu-se a análise do comportamento mecânico de placas finas perfuradas de aço, simplesmente apoiadas em suas bordas, e submetidas à compressão. Serão analisados dois graus de liberdade: H/L e H0/L0. Para H/L, serão analisadas placas com H/L = 1,00 e H/L = 0,50, sendo que H e L representam, respectivamente, a largura e o comprimento da placa. Para H0/L0, serão analisadas infinitas possibilidades, sendo que H0 e L0 representam, respectivamente, a largura e o comprimento da perfuração. As placas utilizadas possuem espessura (h) de 10,00 mm e perfuração centralizada. Quanto às perfurações, estas serão dos tipos: oblonga longitudinal, oblonga transversal, elíptica, retangular, losangular, hexagonal longitudinal e hexagonal transversal. Ainda em relação às perfurações, serão consideradas as seguintes frações ϕ = 0,08; 0,10; 0,15; 0,20 e 0,25, sendo que (ϕ) corresponde ao volume da perfuração. Para a determinação das cargas crítica e última de flambagem, foi utilizada a simulação numérica com o auxílio do software Ansys®, que é baseado no método dos elementos finitos. A aplicação do método Design Construtal, possibilitou a determinação das geometrias ótimas para todos os tipos de perfurações, todos os valores de (ϕ) e para todas as relações de H/L. Os resultados obtidos mostram que há influência do tipo, da forma e do tamanho da perfuração na definição das curvas limites à flambagem e das curvas à flambagem elasto-plástica. Foi possível definir, para cada tipo de perfuração e para todos os valores de (ϕ), os pontos de transição entre a flambagem elástica e à elasto-plástica, assim como os pontos que definem os valores máximos para o fator TLNMáx (tensão limite normalizadora). / Structural elements such as thin plates are part of a large number of applications in various areas of engineering and are of great importance for marine and aerospace engineering, construction and offshore structures hulls, and the construction of airplane fuselages. Being a slender structural element, they are subject to a different mechanical behavior known as buckling, caused by a compressive loading. The phenomenon of buckling can be divided in elastic and elasto-plastic buckling, being dependent dimensional, construction and / or operational aspects. The inclusion of perforations in plates causes a redistribution of its internal stress, affecting not only their resistance but also their buckling characteristics. In this work it was performed the analysis of the mechanical behavior of thin perforated steel plates, simply supported on its edges, and subjected to compression. In the analysis it was considered two degrees of freedom: H/L and H0/L0. For H/L will be analyzed plates with H/L = 1.00 and H/L = 0.50, wherein H and L represent respectively the width and length of the plate. There are endless possibilities for the relation H0/L0. The studied plates have a thickness (h) of 10.00 mm and centralized perforation. The following types of perforation will be used: longitudinal oblong, transverse oblong, elliptical, rectangular, diamond, longitudinal hexagonal and transverse hexagonal. Also in relation to perforations, it will be considered the following fractions (ϕ = 0.08; 0.10; 0.15; 0.20 and 0.25), wherein (ϕ) corresponds to the volume ratio of the perforation. For determining the critical and ultimate buckling loads it was utilized numerical simulation with the assistance of Ansys® software, which is based on the finite element method. The application of the Constructal Design method of this study made it possible to determine the optimal geometries for all types of perforations, for all values of (ϕ) and all the relations H/L. The results show that there is an influence of the perforation type, shape and size, in defining the limit curves of the buckling and the curves of the elasto-plastic buckling. It was also possible to define, for each type of perforation and for all (ϕ) values, the transition points between elastic and elasto-plastic buckling; as well as the points that define the maximum values for the TLNMáx factor (normalized limit stress).

Elementos estruturais como as placas finas fazem parte de um grande número de aplicações nas mais diversas áreas da engenharia e são de grande importância para a engenharia naval e aeronáutica, na construção de cascos de embarcações e estruturas offshore, e na construção de fuselagens de aviões. Por constituírem-se em um elemento estrutural esbelto, estão sujeitas a um comportamento mecânico diferenciado denominado de flambagem, proveniente de um carregamento de compressão uniaxial. O fenômeno da flambagem pode ser dividido em flambagem elástica e elasto-plástica, sendo dependente de aspectos dimensionais, construtivos e/ou operacionais. A inclusão de perfurações em placas provoca uma redistribuição de suas tensões internas, afetando não apenas a sua resistência, mas também as suas características de flambagem. Neste trabalho, desenvolveu-se a análise do comportamento mecânico de placas finas perfuradas de aço, simplesmente apoiadas em suas bordas, e submetidas à compressão. Serão analisados dois graus de liberdade: H/L e H0/L0. Para H/L, serão analisadas placas com H/L = 1,00 e H/L = 0,50, sendo que H e L representam, respectivamente, a largura e o comprimento da placa. Para H0/L0, serão analisadas infinitas possibilidades, sendo que H0 e L0 representam, respectivamente, a largura e o comprimento da perfuração. As placas utilizadas possuem espessura (h) de 10,00 mm e perfuração centralizada. Quanto às perfurações, estas serão dos tipos: oblonga longitudinal, oblonga transversal, elíptica, retangular, losangular, hexagonal longitudinal e hexagonal transversal. Ainda em relação às perfurações, serão consideradas as seguintes frações ϕ = 0,08; 0,10; 0,15; 0,20 e 0,25, sendo que (ϕ) corresponde ao volume da perfuração. Para a determinação das cargas crítica e última de flambagem, foi utilizada a simulação numérica com o auxílio do software Ansys®, que é baseado no método dos elementos finitos. A aplicação do método Design Construtal, possibilitou a determinação das geometrias ótimas para todos os tipos de perfurações, todos os valores de (ϕ) e para todas as relações de H/L. Os resultados obtidos mostram que há influência do tipo, da forma e do tamanho da perfuração na definição das curvas limites à flambagem e das curvas à flambagem elasto-plástica. Foi possível definir, para cada tipo de perfuração e para todos os valores de (ϕ), os pontos de transição entre a flambagem elástica e à elasto-plástica, assim como os pontos que definem os valores máximos para o fator TLNMáx (tensão limite normalizadora). / Structural elements such as thin plates are part of a large number of applications in various areas of engineering and are of great importance for marine and aerospace engineering, construction and offshore structures hulls, and the construction of airplane fuselages. Being a slender structural element, they are subject to a different mechanical behavior known as buckling, caused by a compressive loading. The phenomenon of buckling can be divided in elastic and elasto-plastic buckling, being dependent dimensional, construction and / or operational aspects. The inclusion of perforations in plates causes a redistribution of its internal stress, affecting not only their resistance but also their buckling characteristics. In this work it was performed the analysis of the mechanical behavior of thin perforated steel plates, simply supported on its edges, and subjected to compression. In the analysis it was considered two degrees of freedom: H/L and H0/L0. For H/L will be analyzed plates with H/L = 1.00 and H/L = 0.50, wherein H and L represent respectively the width and length of the plate. There are endless possibilities for the relation H0/L0. The studied plates have a thickness (h) of 10.00 mm and centralized perforation. The following types of perforation will be used: longitudinal oblong, transverse oblong, elliptical, rectangular, diamond, longitudinal hexagonal and transverse hexagonal. Also in relation to perforations, it will be considered the following fractions (ϕ = 0.08; 0.10; 0.15; 0.20 and 0.25), wherein (ϕ) corresponds to the volume ratio of the perforation. For determining the critical and ultimate buckling loads it was utilized numerical simulation with the assistance of Ansys® software, which is based on the finite element method. The application of the Constructal Design method of this study made it possible to determine the optimal geometries for all types of perforations, for all values of (ϕ) and all the relations H/L. The results show that there is an influence of the perforation type, shape and size, in defining the limit curves of the buckling and the curves of the elasto-plastic buckling. It was also possible to define, for each type of perforation and for all (ϕ) values, the transition points between elastic and elasto-plastic buckling; as well as the points that define the maximum values for the TLNMáx factor (normalized limit stress).

The flexural capacity of the new hollow flange steel section known as LiteSteel beam (LSB) is limited by lateral distortional buckling for intermediate spans, which is characterised by simultaneous lateral deflection, twist and web distortion. Recent research based on finite element analysis and testing has developed design rules for the member capacity of LiteSteel beams subject to this unique lateral distortional buckling. These design rules are limited to a uniform bending moment distribution. However, uniform bending moment conditions rarely exist in practice despite being considered as the worst case due to uniform yielding across the span. Loading position or load height is also known to have significant effects on the lateral buckling strength of beams. Therefore it is important to include the effects of these loading conditions in the assessment of LSB member capacities. Many steel design codes have adopted equivalent uniform moment distribution and load height factors for this purpose. But they were derived mostly based on data for conventional hot-rolled, doubly symmetric I-beams subject to lateral torsional buckling. In contrast LSBs are made of high strength steel and have a unique crosssection with specific residual stresses and geometrical imperfections along with a unique lateral distortional buckling mode. The moment distribution and load height effects for LSBs, and the suitability of the current steel design code methods to accommodate these effects for LSBs are not yet known. The research study presented in this thesis was therefore undertaken to investigate the effects of nonuniform moment distribution and load height on the lateral buckling strength of simply supported and cantilever LSBs. Finite element analyses of LSBs subject to lateral buckling formed the main component of this study. As the first step the original finite element model used to develop the current LSB design rules for uniform moment was improved to eliminate some of the modelling inaccuracies. The modified finite element model was validated using the elastic buckling analysis results from well established finite strip analysis programs. It was used to review the current LSB design curve for uniform moment distribution, based on which appropriate recommendations were made. The modified finite element model was further modified to simulate various loading and support configurations and used to investigate the effects of many commonly used moment distributions and load height for both simply supported and cantilever LSBs. The results were compared with the predictions based on the current steel code design rules. Based on these comparisons, appropriate recommendations were made on the suitability of the current steel code design methods. New design recommendations were made for LSBs subjected to non-uniform moment distributions and varying load positions. A number of LSB experiments was also undertaken to confirm the results of finite element analysis study. In summary the research reported in this thesis has developed an improved finite element model that can be used to investigate the buckling behaviour of LSBs for the purpose of developing design rules. It has increased the understanding and knowledge of simply supported and cantilever LSBs subject to non-uniform moment distributions and load height effects. Finally it has proposed suitable design rules for LSBs in the form of equations and factors within the current steel code design provisions. All of these advances have thus further enhanced the economical and safe design of LSBs.

Cette étude vise à analyser la coque qui est en contact avec un matériau qui la confine, et qu’elle subite une pression latérale externe. Les conditions de contact entre les deux corps, frottant ou pas, la rigidité du confinement ainsi que les conditions de chargement, la pression qui peut être directement appliquée à la coque comme elle peut être induite par le matériau de confinement qui par retrait ou retreint ou convergence radiale induit des contraintes, ceux sont là les paramètres qui nous paraissent essentiels à jauger pour la problématique du flambage avec contact d’une coque sous pression externe. Une campagne expérimentale où plusieurs configurations de confinement sont considérées. La nature du milieu extérieur associé au confinement et donc sa rigidité, le type de confinement, discret ou locale au bien total (surface entière de la coque), sont évalués. Une instrumentation adéquate, couplant des mesures ponctuelles et de champ nous a permis de correctement mettre en exergue la phénoménologie. Les simulations numériques par éléments finis à l’aide du code de calcul Abaqus/Standard 6.12-3 intègrent les différentes non linéarité mise en musique dans ce problème, les grands déplacements et rotations du fait du flambage, la non linéarité matériau. Ces travaux montrent que même pour un confinement externe avec une très faible rigidité de membrane, comme pour le sable ou le polystyrène expansé, un gain important de capacité portante est observé, le flambage est retardé. L’augmentation est substantielle dans le cas d’un confinement total, non négligeable et consistante dans le cas d’un confinement local. Nous avons aussi constaté que la charge de flambage et le mode associé dépendent de la configuration de contact, notamment de la rigidité à la flexion du confinement. / Motivated by practical engineering applications, thin-walled cylindrical shells are widely used as structural elements. Because of their low flexural strength, these structures are very sensitive to buckling when exposed to external pressur. Conventional stiffening which makes it possible to improve the bearing capacity is to add stiffening rings connected by axial stiffeners or axial stiffeners. In these configurations the stiffening elements are an integral part of the structure with a continuity of material. One can ask the question of the effect of contiguous but non-continuous adjacent external structures ensuring total or local surface external contact. These are real configurations, such as those of buried pipelines, pipelines, or the case of insulated structures. This study aims to analyze these cases where the shell is in contact with a material which confines it, and that it undergoes an external lateral pressure. The contact conditions between the two bodies, whether rubbing or not, the stiffness of the confinement as well as the loading conditions, the pressure which can be directly applied to the shell as it may be induced by the confinement material which by withdrawal or shrinkage or Radial convergence induces stresses, these are the parameters that we consider essential for gauging the problem of buckling with contact of an external pressure shell. To answer these questions, we conducted an experimental campaign where several configurations of confinement are considered. The nature of the external environment associated with the confinement and therefore its rigidity, the type of confinement, discrete local or the total property (entire surface of the shell), are evaluated. Appropriate instrumentation, coupling point and field measurements, has allowed us to correctly highlight the phenomenology. Numerical modeling is also carried out using finite element method by Abaqus/Standard 6.12-3 code. Numerical simulations integrate the different nonlinearities in this problem, large displacements and rotations due to buckling, nonlinearity material, in some cases the buckling is plastic, but also the nonlinearity induced by an evolutionary contact. The modeling is carried out in 2D and 3D mesh, and in the latter case either by means of shell elements or by massive elements, the first aim being to corroborate the experimental observations more or less precisely. This work shows that even for external confinement with very low membrane rigidity, as for sand or expanded polystyrene, a significant gain in bearing capacity is observed, the buckling is delayed. The increase is substantial in the case of a total confinement which is not negligible and consistent in the case of local confinement. We have also found that the buckling load and the associated mode depend on the contact configuration, in particular the flexural rigidity of the confinement.

The considerable progress in the research and development of thin-walled beam structures responds to their growing use in engineering construction and to their increased need for efficiency in strength and cost. The result is a structure that exhibits large shear strains and important non uniform warping under different loadings, such as non uniform torsion, shear bending and distortion.<p><p>A unified approach is formulated in this thesis for 3D thin walled beam structures with arbitrary profile geometries, loading cases and boundary conditions. A single warping function, defined by a linear combination of longitudinal displacements at cross sectional nodes (derived from Prokic work), is enhanced and adapted in order to qualitatively and quantitatively reflect and capture the nature of a widest possible range of behaviors. Constraints are prescribed at the kinematics level in order to enable the study of arbitrary cross sections for general loading. This approach, differing from most published theories, has the advantage of enabling the study of arbitrary cross sections (closed/opened or mixed) without any restrictions or distinctions related to the geometry of the profile. It generates automatic data and characteristic computations from a kinematical discretization prescribed by the profile geometry. The amount of shear bending, torsional and distortional warping and the magnitude of the shear correction factor is computed for arbitrary profile geometries with this single formulation.<p><p>The proposed formulation is compared to existing theories with respect to the main assumptions and restrictions. The variation of the location of the torsional center, distortional centers and distortional rotational ratio of a profile is discussed in terms of their dependency on the loading cases and on the boundary conditions.<p><p>A 3D beam finite element model is developed and validated with several numerical applications. The displacements, rotations, amount of warping, normal and shear stresses are compared with reference solutions for general loading cases involving stretching, bending, torsion and/or distortion. Some examples concern the case of beam assemblies with different shaped profiles where the connection type determines the nature of the warping transmission. Other analyses –for which the straightness assumption of Timoshenko theory is relaxed– investigate shear deformation effects on the deflection of short and thin beams by varying the aspect ratio of the beam. Further applications identify the cross sectional distortion and highlight the importance of the distortion on the stresses when compared to bending and torsion even in simple loading cases. <p><p>Finally, a non linear finite element based on the updated lagrangian formulation is developed by including torsional warping degrees of freedom. An incremental iterative method using the arc length and the Newton-Raphson methods is used to solve the non linear problem. Examples are given to study the flexural, torsional, flexural torsional and lateral torsional buckling problems for which a coupling between the variables describing the flexural and the torsional degrees of freedom occurs. The finite element results are compared to analytical solutions based on different warping functions and commonly used in linear stability for elastic structures having insufficient lateral or torsional stiffnesses that cause an out of plane buckling. <p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished