Estudo de Sensibilidade do Algoritmo de Colônia de Vagalumes para um Problema de Engenharia Envolvendo Dimensionamento de Treliças

Timber application is viable in constructive systems because of its mechanical properties, suitable for structural applications in engineering. Timber is even more interesting to use since it is a renewable source. Among its several applications, timber is widely used in roofing structures, with several typologies of trusses. Therefore, it is necessary to understand the behavior of plane truss in different loading conditions, including dead load, service load, and wind suction load. The mechanical performance of two trusses (Pratt and Scissor) was analyzed and compared, according to the Brazilian standard of timber structures ABNT NBR 7190 (1997) (methods and calculus premises), with the finite element method, an algorithm of swarm intelligence optimization (structure weight minimization), and a parametric study. Based on minimum weight and maximum displacement as a function of span variation, Pratt typology presented lower weight (3-19%) when compared with Scissor, under the same span and loading conditions. Regarding maximum displacements, Pratt typology presented lower displacement values than the Scissor typology. The difference between these values ranged from two to seven times, indicating that Scissor typology can better distribute normal loads (maximum displacement closer to the normative limit displacement). Variance analysis (5% of significance) confirmed these results.

RESUMO A curva tensão-deformação do concreto é importante para o dimensionamento de estruturas, pois por meio dela é possível obter sua resistência à compressão, sua deformação de pico, o módulo de elasticidade e a tenacidade do concreto. Entretanto, essa é uma propriedade que não é comumente determinada nos ensaios de controle de qualidade do concreto, sendo normalmente controlada apenas a resistência à compressão. Contudo, quando se utiliza de métodos mais refinados para projeto de estruturas de concreto, como, por exemplo, a análise não linear física com o emprego do método dos elementos finitos, essa é uma propriedade fundamental para a análise da estrutura. Neste caso, a curva tensão-deformação à compressão deveria ser controlada em laboratório, mesmo quando se utiliza de curvas recomendadas em códigos de projeto. Deste modo, o objetivo deste artigo é apresentar uma metodologia para avaliação da curva completa tensão-deformação à compressão do concreto simples e reforçado com fibras de aço a partir de máquinas de ensaio de baixo custo, disponível na maioria dos laboratórios de controle de qualidade de concreto. Adicionalmente, é apresentada uma metodologia numérica para análise inversa da curva tensão-deformação à compressão com o objetivo de estimar parâmetros para modelagem de estruturas de concreto por meio da mecânica do Dano.

To avoid the intrinsic difficulties regarding the characterization of wood (i.e., different applications in different directions), various normative documents present the relationships between properties; the Brazilian standard is of particular interest in this regard, because Brazil has a huge diversity of tree species from tropical forests, usually used in construction. In view of this, this research aimed to propose a new list of properties to be inserted in future versions of the Brazilian standards in order to help identify the species shear strength. It is expected that there is a correlation between the characteristic values of flexural strength (f_m,k) and shear strength in the direction parallel to the wood fibers (f_v,0,k), leading to models that make it possible to estimate one of the properties if the other is known, which was the main objective of this research. After finding a strong correlation between the properties, various regression models were evaluated. It can be concluded that the linear model composed only by the angular coefficient (equation with only one variable) presented a determination coefficient of 76.45%, which shows the good precision achieved in the estimation of one of the two variables compared if the other is known. Additionally, an attempt was made to define which probability distribution represents the resistance data by applying maximum likelihood (MLE), concluding that there is little difference between the representation by the normal distribution and the generalized extreme value (GEV) distribution. Another approach was to define the undermining coefficient to ensure the reliability of the prediction equation by the experiment-based calibration methodology defined by Eurocode.