Abstract: Wood is a material that has been used by humankind for a long time. However, wood researchers and industry have always been concerned about the issues during wood drying and the permeability problems of certain species. In this sense, microwave technology has been applied for wood drying and improving permeability. This paper investigates the microwave drying of two Portuguese wood species, Pinus pinaster sap and heartwood, and Eucalyptus globulus heartwood using small clear specimens. The samples were grouped into six during each microwave treatment run according to their similarity of initial moisture content. Once the drying was completed, control and microwave-treated samples were impregnated with desalinated water to analyze their improvement in water absorption, and the compression strength parallel to the grain was analyzed. The results showed that each wood species behaves differently under microwave drying and initial moisture content. The impregnation results demonstrated that pine and Eucalyptus microwave-treated heartwood samples improved their capability to absorb water. Finally, only the microwave-treated specimens of Eucalyptus heartwood presented a decrease in the values of compression strength parallel to the grain compared to the control group. Therefore, MW treatment presents possibilities for further applications for the wood industry with supporting results.

RESUMO O recente interesse pela construção de estruturas altas e robustas em madeira tem estimulado a investigação de propriedades físicas e mecânicas, assim como a correlação delas com outros parâmetros importantes do material de espécies tropicais como o angelim-amargoso (Vatairea sp.) utilizada especialmente em estruturas de telhados de grandes vãos. No Brasil, a norma de projetos de madeira recomenda a utilização de modelos lineares para a correção ou estimativa da resistência e/ou rigidez da madeira correlacionada ao teor de umidade, bem como traz a classificação das folhosas segundo sua resistência característica. Entretanto, por ser um material natural, heterogêneo e anisotrópico, certas propriedades podem não ser afetadas por diferenças no teor de umidade. Portanto, nesse trabalho, investigou-se a influência do teor de umidade em 15 propriedades físicas e mecânicas da madeira de Vatairea sp., através da sua caracterização. Os ensaios foram realizados em 12 corpos-de-prova para cada propriedade e para dois grupos: com teor de umidade de 12% e no ponto de saturação das fibras. O teste de Anderson-Darling foi empregado para verificar a normalidade dos resultados e a análise de variância (ANOVA) para analisar a influência do teor de umidade nessas propriedades. Além disso, classificou-se a madeira segundo as classes de resistência da norma brasileira e estimou-se a resistência e rigidez segundo os modelos lineares propostos pela mesma norma. Os resultados estimados foram comparados com os experimentais através do cálculo da diferença e o erro percentual dos valores. Concluiu-se que a maioria das propriedades não foram afetadas pelo teor de umidade e que os maiores erros obtidos nas estimativas foram para as propriedades que foram influenciadas significativamente pelo teor de umidade.

ABSTRACT The recent interest in constructing high and robust wooden structures has stimulated the investigation of physical and mechanical properties as well as their correlation with other important parameters of the material of tropical species like the Vatairea sp., whose popular name is angelim-amargoso, used especially in roof structures with large spans. The Brazilian Standard for wood constructions recommends using linear models to correct or estimate the strength and/or stiffness of wood correlated with moisture content and also provides the classification of hardwoods according to their characteristic strength. However, because wood is a natural, heterogeneous, and anisotropic material, certain properties may not be affected by significant differences in moisture content. Therefore, in this study, the influence of moisture content on fifteen physical and mechanical properties of Vatairea sp. wood was investigated through its characterization. The tests were carried out on 12 specimens for each property and two groups: with the moisture content of 12% and at the fiber saturation point. The Anderson-Darling test was performed to verify the results’ normality and the analysis of variance (ANOVA) to analyze the influence of moisture content on these properties. In addition, the wood was classified according to the strength classes of the Brazilian Standard, and the strength and stiffness were estimated according to the linear models proposed by the same norm. The estimated results were compared with the experimental ones through the difference calculation and percentual error of the values. It was concluded that most properties were not affected by the moisture content, and the most significant errors obtained in the estimates were for properties that were significantly influenced by the moisture content.

RESUMO Existem diversas tecnologias para recuperar e reforçar estruturas de madeira. Duas alternativas usuais são: a utilização de chapas de aço parafusadas e a utilização de mantas de fibra de carbono coladas com adesivo epóxi. Foi observado uma lacuna na literatura quanto ao estudo de reforço em vigas de madeira com perda de seção transversal, comumente encontrado em ataques de agentes bióticos ou abióticos. O objetivo desse estudo foi analisar a capacidade de recuperação da rigidez à flexão da chapa de aço parafusada em uma viga de madeira folhosa com diferentes perdas de seção transversal, com especial interesse no efeito provocado por diferentes arranjos de parafusos. Os resultados foram comparados com simulações feitas utilizando manta de fibra de carbono (FC). Foi possível observar que, apesar de apresentar eficiência inferior à FC, a utilização da chapa de aço parafusada teve capacidade de retornar a rigidez inicial em alguns modelos e a especificação dos parafusos possui relevância na obtenção dos resultados.

ABSTRACT There are several technologies to recover and strengthen timber structures. Two usual alternatives are: the use of steel plates screwed and carbon fiber mats glued with epoxy adhesive. A gap was observed in the literature regarding the study of reinforcement in hardwood timber beams with cross-section loss, commonly found in attacks by biotic or abiotic agents. This study aimed to analyze the flexural stiffness recovery capacity of steel plate screwed to a timber beam with different cross-sectional losses, with a special interest in the effect caused by different bolt arrangements. The results were compared with simulations made using a carbon fiber mat (CF). It was possible to observe that, despite presenting lower efficiency than the CD, the use of steel plate screwed could return the initial stiffness in some models, and the specification of the bolts is relevant in obtaining the results.

Abstract According to the Brazilian standard for wooden structures, strength and stiffness increase linearly with decreasing moisture; however, as wood is a natural, heterogeneous and anisotropic material, certain strength and stiffness properties may not be affected even by large differences in moisture. Therefore, this work aims to evaluate the reliability of the resistance and rigidity transformation equations as a function of moisture, used to correct the properties when the test was not performed at 12% moisture. Furthermore, it was checked whether the humidity affects the properties of the studied species. Of the 15 properties analyzed, 2 did not show changes when analyzed at the fiber saturation point and at 12% moisture. Additionally, the correction equations of the Brazilian standard showed errors of up to 24% in the estimation of properties at 12% moisture. Thus, the need to correct the Brazilian standard for wooden structures is evident.