Marcílio Sousa da Rocha Freitas

Confiabilidade estrutural utilizando o método de Monte Carlo e redes neurais.

Structural reliability analysis due to the great number of random variables or large number of simulations needed may result in a high computational cost. Two techniques largely used for structural reliability assess are Monte Carlo Simulation and the analytic methods FORM/SORM. These may present some inaccuracy in the assessment of the probability of failure. The Monte Carlo Method is easy to implement and absolutely general, but the great number of required simulations may result in high computational cost making the application impracticable. This work used a trained neural network to substitute the structural analysis needed for each Monte Carlo Simulation, in order to reduce the computational cost. The applications produced good results with low computational cost, certifying its application viability.

Efficiency increment in 3d multi‐zone boundary element algorithms by use of iterative solvers

Abstract In this work general aspects of developing efficient generic multi‐zone BEM algorithms are discussed, focusing specifically on three‐dimensional formulations. The main idea followed in the article for coupling a certain number of subregions discretized with boundary elements is that the global sparse matrix of the coupled system is implicitly considered, without condensing the problem quantities into the interface variables and also without manipulating any of the zero blocks appearing in the system matrix. Thereby an algorithm, optimum in respect to storage requirements, is developed. Also, the performance of the proposed coupling algorithm is further increased by making use of iterative solvers. Recently reported research emphasising the efficiency of such solvers in comparison with direct ones and the results obtained in this paper for a simple 3D elasticity problem are used to show the efficiency of the multi‐zone BEM strategy presented.

Análise de ligações em perfis tubulares de aço do tipo K e KT com afastamento entre as diagonais e o montante

This work presents a study of welded gap K- and KT-joints formed by seamless steel hollow structural sections with rectangular hollow section for the chords and circular hollow section for the members. The study involves the generation, analysis and calibration of numerical models based on the finite element method, by comparison with experimental results previously obtained with full-scale prototypes. Several models were analyzed with shell elements, evaluating the radius of corner influence on the rectangular hollow section, as well as some modeling alternatives of the welds in the connections. The results of the computational analysis are in good agreement with the experimental results.

Confiabilidade de vigas metálicas dimensionadas pela norma brasileira NBR 8800.

The study of structural reliability is related to the assessment the probability of limit state violations in a structural system. Once the designer defines the relevant limits of the structural system, the safety level of these limits must be evaluated. A reliability study of hot-rolled I beams in a flexure limited state, designed in accordance with Brazilian Code NBR 8800 (1986) and draft of new NBR 8800 (2003) was done by the First Order Reliability Method (FORM). Variations of the reliability index (b) versus slenderness are plotted, and finally a methodology to obtain uniform reliability in a limited-state domain by adopting correction procedures for the strength factor is presented.

Estudo teórico experimental de ligações "T" e "KT", em perfis tubulares de aço

This work presents a study of welded T and KT gap joints, formed by a seamless hollow section with rectangular hollow chord sections and circular hollow sections for the members. The developed study considers theoretical and numerical analyses for the joints, experimental tests in full scale prototypes, and tests for residual stress in the rectangular hollow section. The experimental results were used in order to obtain the overall joint behavior, ultimate load, and collapse mode. The numerical analysis using finite elements methods involved the generation, testing and calibration of the experimental results. The model represents the behavior and load capacity of the tested joints. The numerical models considered or not the welding and geometric imperfections and the results were compared with the experimental data. The accomplished analyses present good correlation with the experimental results.

Análise teórico-experimental de elementos formados a frio perfurados submetidos à compressão

Storage rack systems are widely used in the world due their practical and economic character. They possess some structural settings, for example, the existence of perforations in the height of the columns, to fit the connections, which make more difficult the prediction of their strength. So the manufacturers associations prescribe tests to determine this resistance. This work presents the use of the finite element method to preview the resistance of the column, and alternatives to the tests are showed.

Reliability analysis of welded and bolted connections in cold-formed steel sections

This article shows a study of the level of reliability of welded and bolted connections in cold formed steel members, for some limiting states, adopted by AISI and Brazilian codes. The aim of this study is the assessment of the reliability index β for a variation of the nominal live-to-dead load ratios as well as comparison of the value found considering different load combinations. The first order reliability method is used to calculate the reliability index β. In this study, reliability indices smaller than 3.5 were obtained, especially for bolted connections. Consideration of the model errors and FORM method, lead to significant reductions in reliability indices, which are found to be less than the recommended target reliability levels.

Vibration behavior of thin-walled steel members subjected to uniform bending

This article reports the results of an investigation on the effects of internal moments on the vibration behavior of thin-walled steel members. The analyses are based on the Generalized Beam Theory (GBT), a thin-walled bar theory accounting for crosssection in-plane deformations – its main distinctive feature is the representation of the member deformed configuration by means of a linear combination of cross-section deformation modes, multiplied by their longitudinal amplitude functions. The study concerns a simply supported T-section (with unequal flanges) members exhibiting a wide range of lengths and subjected to uniform internal moment diagrams – their magnitudes are specified as percentages of the corresponding critical buckling values. After providing a brief overview of the main concepts and procedures involved in performing a GBT-based structural analysis, the vibration behavior of load-free and loaded T-section members is addressed – the influence of the applied loadings is assessed in terms of (i) the fundamental frequency difference and (ii) the change in the corresponding vibration mode shape. For validation purposes, some GBT results are compared with values yielded by shell finite element analysis performed in the code ABAQUS (Simulia, 2008).

Structural reliability analysis of steel plane frames with semi-rigid connections

The design codes for structural design traditionally establish the adoption of partial safety factors to deal with uncertainties. These standards do not allow one to know the real probabilities of failure of a structure. What is needed, from a practical and scientific point of view, is a more consistent approach, based on reliability theory. This article addresses an initial attempt at determining the safety levels of structures based on advanced analysis and design with structural reliability theory. In this context, the authors consider the effects of the geometric nonlinearity and flexibility of connections in the reliability analysis, which aims at setting a certain displacement as the service limit state. For this purpose, a computer program was written called Structural Reliability Module. This program uses a First Order Reliability Method to analyse reliability. To carry out the structural analysis of steel structures, this study uses the program Computational System for Advanced Structural Analysis. Validating the Structural Reliability Module involved comparing the results from other authors with those generated by the program. Results for the structures under study indicate the efficiency of the implemented measures. Results suggest that, when a certain displacement is set as a service limit state, the reliability of the structures under analysis are only slightly influenced by geometric nonlinearity but considerably so by semi-rigid connections.

Análise de fadiga de ligações tubulares soldadas de pontes treliçadas

Nesse trabalho e apresentada uma analise de fadiga de ligacoes soldadas formadas por perfis estruturais tubulares de aco sem costura. E apresentado o procedimento de estimativa de vida util a fadiga dessas ligacoes por meio dos metodos da tensao geometrica e da tensao nominal, estabelecidos no CIDECT 8 e Eurocode 3, com abordagem baseada em ciclos de tensao (curvas S-N). A filosofia de projeto associada a esta abordagem e a de vida garantida, que deve proporcionar um nivel aceitavel de confiabilidade da estrutura sem inspecoes periodicas. O modelo analisado foi o de uma ponte metalica trelicada, sendo apresentada uma discussao entre esses dois metodos abordando vantagens e limitacoes. Os resultados obtidos permitiram determinar qual metodo e melhor aplicavel para uma dada situacao de projeto