The use of new wood species in construction requires knowledge of their properties for safer and more economical structural sizing. In Brazil, structural projects are carried out according to the standard document ABNT NBR 7190:1997. Tests required by this standard for the complete characterization of species require large machines with high costs, which are present only in large research centers. Considering the lack of experimental determination, this study aimed, with the help of analysis of variance of regression models, to investigate the possibility of estimating, through apparent density, wood properties obtained in tests where failure is considered fragile, allowing the estimation of properties of species still little used. Ten wood species belonging to the hardwood group (cambara, cedro, cedrorana, copaiba, angelim-araroba, castelo, oiticicaamarela, guarucaia, guaicara, and garapa), covering all strength classes established in the standard ABNT NBR 7190:1997, were used. The results showed that shear strength parallel to the grain (fv0) was the only property that could be estimated by apparent density (ρ12), with an R 2 above 50%. Tensile strength normal to the grain (ft90) and splitting strength (fs0) showed poor fit quality.
Timber is part of society's evolutionary process. It presents several utilities because it is versatile and easy to apply. However, it is often extracted incorrectly from nature and used in inappropriate ways. In civil construction it is predominantly applied temporarily and, when it has structural purpose, it is used without knowledge about its properties and absence of structural projects. Thus, this research aims to assess the viability of employing not so usual species, with class resistance C-20 and C-30, in its usage as component structural element of industrial sheds with truss structures for roof (parallel flange) "Howe" type (20º inclination -steel roof tile); span 16, 18, 20, 22, 24 and 26 meters; typologies of edification lateral openings -1:1, 2:1, 6:1 and opened. Therefore, it was determined the ratio between timber volume (m³) and constructed area (m²) according to NBR 7190:1997 standards, making it possible to verify the applicability of C-20 and C-30 species to industrial sheds typology determined in this research.
Wood is a material, when compared with other materials applied in civil construction, displays several advantages such an elevated mechanical strength when related with its apparent density. The wood manufacturing industry has great representativeness in the Brazilian economy however, the irrational consumption of determined species brought damages to the forest, causing extinction of some species and consequently, rising wood prices in market. The characterization of unknown wood species presents an alternative for a more rational exploration and expand wood use in structural purpose, enabling the use of this species determining its properties. The study aimed to characterize 3 physical properties and 12 mechanical properties of Angelim vermelho (Dinizia excelsa Ducke.) based on Brazilian Standard ABNT NBR 7190. Twelve models were used for each test, totalizing 180 experimental results. The analysis of variance (ANOVA) handling the regression models will be used to predict the strength and stiffness as function of apparent density. The results presented on tests demonstrated compatible performance with common wood species used in civil construction, considered high strength wood and with adequate use in this activity. According the regression models, only three properties were considered significant with apparent density estimation.
Resumo O documento normativo NBR 7190:1997 estabelece os métodos de ensaio para obtenção das propriedades físicas e mecânicas do material, porém as premissas exigem procedimentos realizados em laboratórios especializados e de alto custo. Considerando a impossibilidade da realização dos ensaios, o próprio documento estabelece relações entre propriedades visando facilitar a caracterização do material. No que se refere às relações entre as propriedades de resistência ao cisalhamento e a resistência à compressão paralela às fibras a norma apresenta valores distintos em seu texto. O trabalho objetivou investigar, considerando os resultados de ensaios experimentais, a relação entre essas propriedades obtidas com auxílio do método dos mínimos quadrados, considerando para tanto dez espécies de madeiras do grupo das folhosas. Os resultados foram comparados com os valores de relações estabelecidas pela NBR 7190:1997, em que o coeficiente ótimo encontrado considerando o conjunto de todas as espécies foi 86,4% superior ao apresentado pela norma brasileira. Em relação à variação da relação entre as propriedades investigadas considerando as diferentes classes de resistência da madeira no presente estudo, não foi identificado decréscimo nos valores dos coeficientes ótimos conforme as classes aumentam (situação que a NBR 7190:1997 expõe em seu texto), apresentando assim outro resultado divergente.
Resumo No Brasil, o documento normativo NBR 7190 (ABNT, 1997) estabelece os métodos de ensaio para obtenção das propriedades físico-mecânicas da madeira. Na impossibilidade da determinação dos resultados experimentais, a norma estabelece relações entre propriedades. Porém as relações entre as propriedades de rigidez apresentadas foram determinadas com base no antigo referencial normativo MB-26:1940 (NBR 6230), que considerava outro modelo de cálculo e não ao utilizado pela norma brasileira. Nesse contexto, este trabalho objetivou investigar a equivalência entre os módulos de elasticidade na flexão (EM), compressão (Ec0) e tração (Et0) paralela às fibras de dez espécies de madeiras tropicais, assim como de estabelecer correlações adequadas entre tais propriedades em caso de não equivalência. Os resultados da ANOVA acusaram que Ec0 e Et0 são estatisticamente equivalentes, o mesmo não ocorreu entre EM e 0,90∙Ec0, implicando a determinação do coeficiente ótimo de 0,98 pelo método dos mínimos quadrados. Tal coeficiente mostrou ser 8,89% superior ao apresentado pela norma brasileira.
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