This paper addresses the probabilistic analysis of casing tubulars, regarding the failure modes defined in API 5C3 code, which refers to the violation of elastic regime due to internal and external pressures, and axial force. The casing system performs important structural and isolation functions, ensuring the well integrity through its life cycle. The reliability-based casing design handles rigorously the uncertainties associated with the tube manufacturing, as variations in geometrical and mechanical properties, allowing to evaluate the probability of failure. It is presented a parametric analysis over different steel grades and tube slenderness, besides the application to a design scenario, by using Monte Carlo simulation and firstorder reliability method. The results indicate that: collapse is the dominant failure mode; wall thickness and the yield limit govern the probabilistic response; the triaxial envelopes, revisited in a probabilistic framework, consist in a powerful tool, supporting the decision-making process in casing design.

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This work is devoted to the numerical analysis of saturated porous media, taking into account the damage phenomenon on the solid skeleton. The porous media is taken into poroelastic framework, in full-saturated condition, based on the Biot's Theory. A scalar damage model is assumed for this analysis. An implicit Boundary element Method (BEM) formulation, based on time-independent fundamental solutions, is developed and implemented to couple the fluid flow and the elasto-damage problems. The integration over boundary elements is evaluated by using a numerical Gauss procedure. A semi-analytical scheme for the case of triangular domain cells is followed to carry out the relevant domain integrals. The non-linear system is solved by a Newton-Raphson procedure. Numerical examples are presented, in order to validate the implemented formulation and to illustrate its efficiency.

RESUMOAs treliças constituem um sistema estrutural de grande aplicabilidade em soluções de Engenharia. No campo da engenharia de estruturas, são diversas as iniciativas para melhorar a representação teórica e numérica do comportamento de sistemas estruturais. O desenvolvimento de modelos computacionais permite uma avaliação robusta do desempenho mecânico de estruturas, tanto na fase de projeto quanto ao longo de sua vida em serviço. Considerando-se a não linearidade observada na resposta de grande parte dos materiais estruturais, modelos elastoplásticos figuram como uma ferramenta adequada à descrição do comportamento de materiais dúcteis. A análise de confiabilidade estrutural permite que a probabilidade de falha da estrutura seja prevista, ainda na fase de projeto. Esta pode ser construída com base na avaliação das incertezas associadas às variáveis de projeto, as quais são descritas estatisticamente. Propõe-se neste trabalho uma análise confiabilística aplicada a modelos de elementos finitos para treliças metálicas, em regime elastoplástico, segundo um modelo de encruamento isotrópico. Incertezas oriundas da variabilidade do carregamento e das propriedades geométricas e mecânicas das barras são consideradas, de forma a estimar os níveis de segurança associados a estados limites últimos e de serviço, tais como ruptura da seção transversal, flambagem das barras e deslocamentos inadmissíveis. Palavras-chave: Confiabilidade Estrutural, Plasticidade, Elementos Finitos. ABSTRACTThe trusses stand out as a structural system widely applied in engineering solutions. In the field of Structural engineering, several efforts have been done to improve the theoretical and numerical representation of structural systems behavior. The development of computer models enables a robust assessment of the mechanical behavior of structures, both in the design phase and throughout its service life. Considering the nonlinearity observed in the response of most of the structural materials, elastoplastic models arise as a proper choice to the description of the behavior of several ductile materials. Reliability analysis allows the assessment of the structural probability of failure, so that it can be predicted since the design stage. This analysis can be built based on the evaluation of the uncertainties associated with design variables, which are described by random models. This paper addresses a reliability-based analysis applied to finite element models for steel plane trusses in elastoplastic regime, according to an isotropic hardening model. Some uncertainties related to the loads and to geometrical and mechanical properties of the bars are considered, in order to estimate the safety levels associated to ultimate and service limit states, such as cross-section rupture, buckling of bars and inadmissible displacements.