No / Concrete filled steel columns have been used widely in structures throughout the world in recent years especially in Australia and the Far East. This increase in use is due to the significant advantages that concrete filled steel columns offer in comparison to more traditional construction methods. Composite columns consist of a combination of concrete and steel and make use of these constituent material's best properties. The use of composite columns can result in significant savings in column size, which ultimately can lead to significant economic savings. This reduction in column size can provide substantial benefits where floor space is at a premium such as in car parks and office blocks. The use of stainless steel column filled with concrete is new and innovative, not only provides the advantage mentioned above, but also durability associated with the stainless steel material. This paper concentrates on the axial capacity of the concrete filled stainless steel columns. A series of tests was performed to consider the behaviour of short composite stainless steel columns under axial compressive loading, covering austenitic stainless steels square hollow sections filled with normal and high strength concrete. Comparisons between Eurocode 4, ACI-318 and the Australian Standards with the findings of this research were made and comment.

When a structure with an in-plane discontinuous frame is used, a discontinuous load path is formed due to the irregularity. This is continuous load path can lead to the failure of certain elements and the structure as a whole when the structure is exposed to lateral loading. In this study, an in-plane discontinuous frame structure is exposed to gravity as well as lateral loading due to which a discontinuous load path is formed. Due to the discontinuous load path, higher value of axial load is developed on a beam which is generally designed considering it as a flexural member. The main objective of this thesis is to determine if the beam can be designated as the critical member in the in-plane discontinuous frame and the comparison of the critical element with the corresponding element in a frame that has no structural irregularities. The objective is also to design the critical member considering it as a beam-column element considering the combined effect of bending and compression.

<div>Underground structures must be able to support static overburden loads, as well as to accommodate additional deformations imposed by seismic motions. Progress has been made in the last few years in understanding the soil-structure interaction mechanisms and the stress and displacement transfer from the ground to the structure during a seismic event. It seems well established that, for most tunnels, the most critical demand to the structure is caused by shear waves traveling perpendicular to the tunnel axis. Those waves cause distortions of the cross section (ovaling for a circular tunnel, and racking for a rectangular tunnel) that result in axial forces (thrusts) and bending moments. While all this has been well-studied for structures placed in linear-elastic ground, there is little information regarding the behavior of buried structures placed in nonlinear ground, especially under undrained conditions, i.e., when excess pore pressures generate and accumulate during the earthquake.</div><div><br></div><div><div>Two-dimensional dynamic numerical analyses are conducted to assess the seismic response of deep circular tunnels located far from the seismic source, under drained or undrained loading conditions. It is assumed that the liner remains elastic and that plane strain conditions apply. </div><div> A new cyclic nonlinear elastoplastic constitutive model is developed and verified, to simulate the nonlinear behavior and excess pore pressures accumulation with cycles of loading in the ground. The results of the numerical analyses show negligible effect of input frequencies on the normalized distortions of a tunnel for input frequencies smaller than 5 Hz (the distortions of the tunnel are normalized with respect to those of the free field); that is, for ratios between the wavelength of the seismic input and the tunnel opening larger than about eight to ten. The results also show that undrained conditions, compared with drained conditions, tend to reduce deformations for flexible liners and increase them for stiffer tunnels, when no accumulation of pore pressures with cycles of loading is assumed. However, when pore pressures increase with the number of cycles, the differences in distortions between drained and undrained loading are reduced, i.e., the normalized distortions increase for flexible and decrease for stiff tunnels, compared to those with drained conditions. </div></div><div><br></div><div><div>Undrained loading produces larger thrust in the liner than drained loading for stiff tunnels with flexibility ratio F ≤ 2.0.</div><div>For more flexible tunnels with F > 2.0, the behavior is the opposite, i.e., smaller axial forces are obtained for undrained loading than for drained loading. Including excess pore pressure accumulation does not introduce significant changes in the axial forces of the liner, irrespective of the flexibility of the tunnel, compared to those obtained from undrained loading without pore pressure accumulation.</div><div>The drainage loading condition (drained or undrained) or the magnitude of the free-field excess pore pressures during undrained loading do not affect the normalized bending moments for flexible tunnels, with F ≥ 2. For stiffer tunnels, with F < 2, the normalized bending moments increase from drained to undrained loading, and with the free field excess pore pressures.</div></div><div><br></div><div><div>It is found that the tunnel’s response is determined by the load on the liner, or by the distortions of the cross section, depending on the flexibility ratio. For stiff structures, with F ≤ 2.0, important axial forces and bending moments are produced in the structure, with larger magnitudes for the undrained case; while the distortions of the cross section are very small. When the tunnel becomes more flexible, the loading on the liner decreases, but the distortions of the cross section start to be important. For flexible structures with initial F ≥ 10 (for the cases investigated), the performance is largely determined by the distortions of the cross section, while the axial forces and bending moments are almost negligible. Such distortions are drastically affected by the drainage loading condition and by the magnitude of pore pressures in the free field. </div></div><div><br></div>

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Power transformers are essential and a large part of the asset cost structure of the electrical power system. When they present any defect or failure, it will be required high costs to repair or replace them, due their commercial costs and by the capability loss to transmit power during a period of time. Generally, transformer failure can occur as a result of the weakness insulation caused by the electrochemical processes involving the cooling liquid (oil), by vibrations due the electromagnetic forces in normal operation, i.e., steady state, and also by winding deformation as the result of short-circuits. It is expected that a transformer will experience and survive a number of short circuits during its service life. But one such event will cause some slight winding movement, which can gradually increasing and the ability of the transformer to withstand further electromechanical forces will be then reduced. It is therefore very important to check the mechanical condition of transformers periodically, particularly for older units, to provide an early warning of an impending catastrophic failure. Thus a specialist technique is required for the monitoring and assessment of mechanical condition of winding transformer. Despite designers and manufacturers, as well as the operation and maintenance technicians of power supply companies worry about this subject, new methodologies and tools to assess the strength effects as the result of short circuits in transformers are still necessaries. So, this work proposes to know the strength characteristics caused by the radial and axial forces in winding transformers. In this context, it will be presented different strengths that can occur in winding transformer, identifying the principal failures as the result of these stresses. Besides, it will be developed an analytical method to evaluate the forces and stresses in winding three phase transformer under a three phase short circuit. Finally, the analytical method results will be compared with a computer simulation based in time domain using the software FEMM, which applies the finite element method. / Transformadores de potência são equipamentos essenciais aos sistemas elétricos e também um de seus componentes de maior preço. Quando estes equipamentos se danificam ou apresentam algum tipo de falha, o seu reparo ou até mesmo sua substituição demanda altíssimos custos financeiros, tanto pelo alto valor comercial destes equipamentos como pela perda temporária da capacidade de transmissão de energia elétrica. Muitas falhas destes equipamentos devem-se à redução da suportabilidade da isolação dos seus condutores/enrolamentos causado pelos fenômenos eletroquímicos do líquido de resfriamento (óleo), pelas vibrações produzidas pelas forças eletromecânicas durante a sua operação normal, ou seja, em regime permanente, e também pelas deformações dos enrolamentos causadas pelas altas correntes de curto-circuito. Espera-se, no entanto, que um transformador suporte um determinado número de curtos-circuitos durante seu tempo de operação. No entanto, verifica-se que cada evento poderá provocar pequenos deslocamentos relativos nos enrolamentos, os quais podem aumentar cumulativamente, reduzindo desta forma a capacidade do transformador de suportar novos esforços eletromecânicos. Neste contexto, torna-se importante a verificação periódica das suas condições mecânicas, principalmente nas unidades com muito tempo de operação, de forma a se obter subsídios para impedir falhas catastróficas. O emprego de técnicas especiais é requerido para o monitoramento e avaliação das condições mecânicas do enrolamento de um transformador. Apesar de este assunto ser uma preocupação constante dos projetistas e fabricantes de transformadores, bem como dos profissionais de manutenção e operação das empresas de energia elétrica, há certa carência de metodologias e ferramentas consistentes para se avaliar os efeitos dos esforços mecânicos decorrentes das elevadas correntes transitórias sobre estes equipamentos. Nessa perspectiva, este trabalho tem por meta o entendimento das características dos esforços mecânicos causados pelas forças radiais e axiais nos enrolamentos dos transformadores. Para tanto, esta dissertação mostrará os diferentes tipos de esforços eletromecânicos passíveis de ocorrer nos enrolamentos de um transformador, identificando os principais tipos de falhas provocadas por essas solicitações. Em seguida, será desenvolvida uma metodologia analítica para estimar as forças e estresses nos enrolamentos de um transformador trifásico submetidos a um curto-circuito trifásico. Assim, os valores obtidos pela metodologia analítica serão confrontados com resultados de uma simulação computacional no domínio do tempo utilizando-se o programa FEMM baseado na técnica de elementos finitos. / Mestre em Ciências

In this master’s thesis I study statical solution of new office building. The load – bearing elements are appraised according to ultimate limit state. Structural analysis contains of dimensioning ceiling plate with ribs, the most stressed support column and footing. There will be applied computer simulation to finding out values of internal forces. The solution is checked by simple method of replacement frames. The main purpose of this thesis consists of elaboration structural analysis, drawing up the technical report and creation design documents of load – bearing elements.