Mauro de Vasconcellos Real

Constructal design applied to the elastic buckling of thin plates with holes

Elastic buckling is an instability phenomenon that can occur if a slender and thin plate is subjected to axial compression. An important characteristic of the buckling is that the instability may occur at a stress level that is substantially lower than the material yield strength. Besides, the presence of holes in structural plate elements is common. However these perforations cause a redistribution in plate membrane stresses, significantly altering their stability. In this paper the Bejan’s Constructal Design was employed to optimize the geometry of simply supported, rectangular, thin perforated plates subjected to the elastic buckling. Three different centered hole shapes were considered: elliptical, rectangular and diamond. The objective function was to maximize the critical buckling load. The degree of freedom H/L (ratio between width and length of the plate) was kept constant, while H0/L0 (ratio between the characteristic dimensions of the holes) was optimized for several hole volume fractions (ϕ). A numerical model employing the Lanczos method and based on the finite element method was used. The results showed that, for lower values of ϕ the optimum geometry is the diamond hole. For intermediate and higher values of ϕ, the elliptical and rectangular hole, respectively, led to the best performance.

STUDY ABOUT BUCKLING PHENOMENON IN PERFORATED THIN STEEL PLATES EMPLOYING COMPUTATIONAL MODELING AND CONSTRUCTAL DESIGN METHOD

PERFORATED STEEL THIN PLATES ARE COMMONLY USED IN STRUCTURAL ENGI-NEERING. DUE TO THEIR GEOMETRIC CHARACTERISTICS, THESE PANELS CAN SUFFER THE UNDESIRED BUCKLING PHENOMENON. IN THIS CONTEXT, THE PRESENT WORK ASSOCIATES THE COMPUTATIONAL MODELING AND THE CONSTRUCTAL DESIGN METHOD TO EVALUATE THE INFLUENCE OF THE GEOMETRIC CONFIGURATION IN THE PLATE BUCKLING BEHAVIOR, USING THE EXHAUSTIVE SEARCH METHOD TO DETERMINE WHICH GEOMETRIES CONDUCT TO SUPERIOR MECHANICAL BEHAVIOR. TO DO SO, NUMERICAL MODELS ARE EMPLOYED TO SOLVE ELASTIC AND ELASTO-PLASTIC BUCKLING OF PLATES HAVING A CENTERED PERFORATION. DIFFERENT HOLE TYPES (LONGITUDINAL OBLONG, TRANSVERSAL OBLONG, ELLIPTICAL, RECTANGULAR, DIAMOND, LONGITUDINAL HEXAGONAL, OR TRANSVERSAL HEXAGONAL) WITH DIFFERENT SHAPES (VARIATION OF CHARACTERISTICS DIMENSIONS OF EACH HOLE TYPE) ARE ANALYZED. LIMIT CURVES TO AVOID BUCKLING WERE OBTAINED, AS WELL AS THE DEFINITION OF THE GEOMETRIES THAT CAN IMPROVE UP TO 107% THE PLATE PERFORMANCE.

Flow of Stresses: Constructal Design of Perforated Plates Subjected to Tension or Buckling

It is possible to state that improving systems configuration for achieving better performance is the major goal in engineering. In the past, the scientific and technical knowledge combined with practice and intuition has guided engineers in the design of man-made systems for specific purposes. Soon after, the advent of the computational tools has permitted to simulate and evaluate flow architectures with many degrees of freedom. However, while system performance was analyzed and evaluated on a scientific basis, system design was kept at the level of art [1].

Numerical analysis of reinforced concrete beams strengthened with high strength cement-based composite material

A aplicacao de materiais compositos a base de resinas polimericas e fibras no reforco de estruturas de concreto armado se tornou uma tecnica bastante difundida nos ultimos tempos. O uso dos compositos reforcados com fibras de carbono, ou outros tipos de fibras sinteticas, se consolidou pelas suas excelentes caracteristicas, tais como elevada resistencia, baixo peso, resistencia a corrosao, etc. Este material, na forma de lâminas ou laminados, e colado no substrato de concreto atraves de adesivos a base de epoxi. Apesar do uso do epoxi apresentar excelentes resultados em termos de colagem e resistencia, algumas desvantagens podem ser citadas, tais como: baixa permeabilidade, baixa compatibilidade termica em relacao ao concreto, baixa resistencia ao fogo, etc. Para evitar alguns desses problemas, um sistema composito a base de tecidos ou malhas de fibras sinteticas coladas na superficie de concreto com argamassa de cimento pode ser usado. O objetivo deste trabalho e fazer uma analise numerica, atraves de um modelo nao linear de elementos finitos, do comportamento estrutural de vigas de concreto armado reforcadas a flexao com compositos baseados na combinacao de tecidos de fibras sinteticas de alta resistencia e argamassa de cimento. Os resultados numericos sao comparados aos resultados experimentais publicados em artigos tecnicos internacionais, que demonstram a eficiencia da tecnica de reforco e a capacidade do modelo numerico.

Ultimate flexural strength of prestressed concrete beams: validation and model error evaluation

Resumo In this work a computational model is presented to evaluate the ultimate bending moment capacity of the cross section of reinforced and prestressed concrete beams. The computational routines follow the requirements of NBR 6118: 2014. This model is validated by comparing the results obtained with forty-one experimental tests found in the international bibliography. It is shown that the model is very simple, fast and reaches results very close to the experimental ones, with percentage difference of the order of 5%. This tool proved to be a great ally in the structural analysis of reinforced and prestressed concrete elements, besides it is a simplified alternative to obtain the cross section ultimate bending moment.

SIMULAÇÃO NUMÉRICA E MÉTODO DESIGN CONSTRUTAL APLICADOS AO ESTUDO DE FLAMBAGEM EM PLACAS DE AÇO COM PERFURAÇÃO HEXAGONAL

RESUMO Placas finas de aco sao componentes muito utilizados em estruturas navais e oceânicas. Por se tratarem de elementos esbeltos, essas placas sao propensas a sofrerem o fenomeno da flambagem, quando submetidas a um carregamento de compressao axial. A realizacao de perfuracoes nestes componentes pode ser necessaria, o que gera uma redistribuicao de tensoes, causando mudancas no desempenho mecânico. Este trabalho propoe um estudo do fenomeno de flambagem em placas quadradas ou retangulares, simplesmente apoiadas e com perfuracao hexagonal longitudinal. A simulacao numerica foi utilizada para determinar a carga critica de flambagem e a carga de colapso da placa. O metodo Design Construtal foi aplicado, permitindo avaliar a influencia do grau de liberdade H 0 / L 0 (sendo H 0 a altura e L 0 o comprimento da perfuracao hexagonal), no comportamento mecânico das placas. A fracao de volume da perfuracao na placa ( ϕ ) tambem foi considerada, correspondendo a 10%, 15%, 20% e 25% do volume total da placa. Os resultados mostraram a direta influencia da relacao H 0 /L 0 na ocorrencia da flambagem, para cada valor de fracao de volume estudada. Alem disso, o metodo Design Construtal, associado ao mecanismo de busca exaustiva, permitiu definir a geometrias otima para a perfuracao hexagonal nas placas. Palavras-chave: Placas de aco; Flambagem; Simulacao numerica; Design Construtal.

APLICAÇÃO DO MÉTODO DESIGN CONSTRUTAL NA ANÁLISE DE TUBOS PERFURADOS SOB FLAMBAGEM

RESUMO Os tubos metalicos sao componentes empregados nas obras de engenharia devido a sua vida util e facilidade de utilizacao. Quando esbeltos, os tubos podem sofrer o fenomeno de flambagem. Submetidos a presenca de perfuracoes, apenas analises experimentais ou numericas podem ser empregadas para obter o valor da carga critica de flambagem elastica. Assim, desenvolveu-se um modelo computacional no software ANSYS, baseando no Metodo dos Elementos Finitos (MEF) para a analise da influencia de perfuracoes no seu comportamento mecânico. Alem disso, empregou-se o Metodo Design Construtal para determinar geometrias que possam avaliar a presenca de perfuracoes no tubo, alem da influencia da variacao geometrica dos furos, retangulares, circulares e hexagonais, na carga critica de flambagem. Sendo assim, o trabalho objetiva determinar a geometria otima para as perfuracoes nos tubos, considerando o parâmetro ϕ dado como o volume removido e o volume total da coluna igual a 0,05; 0,10; 0,15 e 0,20, com um grau de liberdade variando a forma geometrica do furo. Por fim, o estudo mostrou que a relacao de volume retirado e a carga critica de flambagem sao inversamente proporcionais, obtendo uma geometria otima para todos os valores de ϕ, prevalecendo a geometria retangular em todas as variacoes volumetricas. Palavras-chave: Flambagem; Tubos estruturais; Metodo dos Elementos Finitos; Design Construtal.

A PROBABILISTIC ANALISYS OF THE FORCES IN THE PILES OF A CONTAINER TERMINAL WHARF UNDER SHIP BERTHING ACTIONS

ABSTRACT In this work a probabilistic structural analysis of a container terminal wharf is presented. Through the application of the Monte Carlo Simulations in a finite element structural model, the statistics of the axial forces at the pile heads were evaluated. Considering only ship berthing conditions, but varying equipment type, number and positions, ten external load combinations were analyzed and compared. Both finite element model and probabilistic analysis were performed in ANSYS software, v.16, on its APDL Mechanical and Probabilistic Design System packages respectively. The random input parameters considered were the concrete structure, pavement and rear landfill self-weight, live loads and ship sizes, for which statistical parameters were attributed based on bibliography or data collection. PIANC’s berthing energy method for fender systems design was applied for the evaluation of ship berthing forces acting on the structure. Considering the axial forces as the main parameters in the design of partially embedded piles, the random output parameters obtained were the minimum and maximum axial forces on each simulation. That approach, applied due to the possibility of ANSYS to be programmed through its Parametric Design Language (APDL), proved to be a powerful tool for probabilistic analysis of complex structural systems. The results present a comparison between the statistical parameters and probability density curves for the ten cases analyzed, by which the worst combinations from a probabilistic point of view could be defined. Keywords: Container terminal berth; Probabilistic Analisys; Monte Carlo Method; Finite Element Method; ANSYS.

NUMERICAL SIMULATION ANDCONSTRUCTAL DESIGN APPLIED TO THE STUDY OF ELASTIC BUCKLING IN THIN STEEL PLATES WITH OBLONG PERFORATIONS

ABSTRACT Buckling is an instability phenomenon that can happen when a slender plate is subjected to axial compression loads. In addition, perforated plates are often necessary in the engineering field. Throughout this article, the Constructal Design Method, which is based on the Constructal Theory, has been used to evaluate the influence of the hole on thin steel plates under elastic buckling. For that, the different types of holes analyzed were both transversal and longitudinal oblong. They were all placed in the center of the plate. The geometry of the hole varied according to the degree of freedom H 0 /L 0 , which relates the dimensions of each type of different hole. The size of the perforation are varied by means the hole volume fraction (f) parameter, that represents the relation between the volume of the hole and the total volume of the plate (without hole). The main goal is to achieve the greatest critical load for the perforated plates. To do so, the ANSYS software, based on the Finite Element Method (FEM), has been used to numerically analyze the elastic buckling in each case. It has been observed the importance of the geometry when seeking superior performances: through a simple fluctuation of the geometry of the hole, once the volume fraction was kept constant, it was possible to achieve a significant increase on the critical loads. Key words: Buckling; Computational Modeling; Critical Load; Constructal Design.

Statistical analysis and conformity testing of concrete in port construction work

Conformity control of concrete is part of a range of control and standard methods which must be employed in all construction work to assure its compliance with quality requirements. The compressive strength of the concrete is considered as a random variable that must be controlled by standardized sampling and testing in order to ensure the structural safety. Therefore, the use of a large amount of compressive strength test results of concretes with similar characteristics has been seen as an important tool in the assessment of current standard norms. This paper describes an analysis based on the conformity control used in large port construction works which have recently been carried out in the Rio Grande Port, located in Rio Grande, RS, Brazil. Statistical analyses were performed and acceptance tests of the product were conducted. They were based on the acceptance criteria of different methodologies from different continents and showed the variations that can occur in the results of the conformity testing, depending on the adopted model. It is worth mentioning that the concrete used in port construction works in the region has been in accordance with current Brazilian norms.