Resumo Para o dimensionamento correto de estruturas de madeira, as premissas da norma brasileira são de extrema valia como norte para os engenheiros estruturais, pois exibem valores padrão de resistência. Dessa forma, este estudo tem como objetivo analisar se o valor do módulo de elasticidade da classe C60 exibido na norma brasileira confere com os valores obtidos em ensaio de 23 espécies brasileiras, utilizando a metodologia Bootstrap com 1 milhão de simulações. Além disso, analisa-se, com modelos de regressão, se é possível estimar a propriedade de rigidez (E c0 ) dessas 23 espécies em função da densidade aparente. É possível concluir que a norma brasileira superestima o módulo de elasticidade das madeiras brasileiras, apresentado um valor quase 35% superior ao que realmente elas resistem, evidenciando que a norma necessita passar por revisão. Outro ponto é que os modelos de regressão não mostram significância, ou seja, com a densidade aparente não é possível estimar a propriedade de rigidez analisada.

Abstract For correct dimensioningof wood structures, the premises of the Brazilian standard are extremely valuable as a guide for structural engineers, as it exhibits standard values of resistance. Thus, this study aims to analyze whether the value of the class C60 elasticity module shown in the Brazilian standard matches the values obtained in the test of 23 Brazilian species, using the Bootstrap methodology with 1 million simulations. In addition, it sought to analyze, with regression models, whether it is possible to estimate this rigidity property (E c0 ) of these 23 species as a function of apparent density. Finally, it was possible to conclude that the Brazilian standard overestimates the modulus of elasticity of Brazilian woods, presenting a value almost 35% higher than what actually resists, showing that the standard needs to be revised. Another point was that the regression models do not show significance, in other words, with the apparent density it was not possible to estimate the analyzed rigidity property.

RESUMO A madeira é um excelente material estrutural, além de possuir excelente resistência tanto à tração como compressão. Para o dimensionamento correto, as premissas da norma brasileira são de estrema valia como norte para os engenheiros estruturais, pois exibe valores padrão de resistência. Dessa forma, esse estudo tem como objetivo analisar se o valor de resistência ao cisalhamento característico paralelo às fibras da classe C60 exibido na norma brasileira confere com os valores obtidos em ensaio de 23 espécies brasileiras, utilizando a metodologia Bootstrap com 1 milhão de simulações. Além disso, buscou analisar, com modelos de regressão, se é possível estimar a propriedade de resistência (fν0) dessas 23 espécies em função da densidade aparente, buscando assim uma obtenção rápida das propriedades dessas espécies com apenas a densidade aparente. Por final, foi possível concluir que a norma brasileira subestima a resistência ao cisalhamento das madeiras brasileiras, apresentado um valor 26% menor ao que realmente resiste, evidenciando que a norma necessita passar por revisão. Outro ponto foi que os modelos de regressão não mostram significância, ou seja, com a densidade aparente não foi possível estimar a propriedade de resistência.

ABSTRACT Wood is an excellent structural material, in addition to having excellent resistance in traction and compression. For correct dimensioning, the premises of the Brazilian standard are extremely valuable as a guide for structural engineers, as it exhibits standard values of resistance. Thus, this study aims to analyze whether the characteristic shear strength value parallel to class C60 fibers shown in the Brazilian standard matches the values obtained in the test of 23 Brazilian species, using the Bootstrap methodology with 1 million simulations. In addition, it sought to analyze, with regression models, whether it is possible to estimate the resistance property (fν0) of these 23 species as a function of apparent density, thus seeking to obtain quickly the properties of these species with only apparent density. Finally, it was possible to conclude that the Brazilian standard underestimates the shear strength of Brazilian woods, presenting a value 26% smaller to what actually resists, showing that the standard needs to be revised. Another point was that the regression models do not show significance, in other words, with the apparent density it was not possible to estimate the resistance property.

Abstract: In wood structures, the elements subjected to bending stresses, such as the beams, present a fracture initiated in the tensile region, and under these conditions, the use of laminated composite materials is presented as an alternative solution in the form of repair or reinforcement. This research aimed to evaluate the influence of the use of carbon fibers laminated composites in tensile reinforcement in the direction parallel to grain of Pinus elliotti and Manilkara huberi wood species. The Viapol two-component epoxy adhesive was used in the lamination and fixation of the unidirectional carbon fiber in the wood species. Ten specimens with no defects (reference) and 10 specimens were prepared for each crack length (25 and 50mm) with and without the reinforcement (60mm × 50mm) by the laminated composite. The tensile tests were performed in accordance with the requirements of the Brazilian standard. From the results of the statistical analysis, the use of the carbon fiber composite was able to restore the tensile strength of the cracked samples (partial or total) in relation to samples without defects, demonstrating the potential of the laminates in carbon fibers as an alternative solution in repair for both wood species.

Brazilian Standard ABNT NBR7190:1997 for timber structures design, adopts a first degree equation to describe the influence of wood moisture content. Periodically, when necessary, the referred standard is revised in order to analyze inconsistencies and to adopt considerations according new realities verified. So, the present paper aims to examine the adequacy of its equation which corrects to 12% of moisture the values of rigidity properties obtained on experimental tests. To quantify the moisture influence on modulus of elasticity, it was applied tests of compression parallel to the grain for six specimens of different strength classes, considering nominal moisture of 12; 20; 25; 30%. As results, modulus of elasticity in the moisture range 25-30% showed statistically equivalents, and was obtained a first degree equation to correlate the studied variables which leads to statically equivalent estimations when compared with results by ABNT NBR7190:1997 equation. However, it was indicated to maintain the current expression for the next text of the referred document review, without prejudice to statistical significance of the estimates.