This study aimed to investigate the influence of moisture content variation on 12 mechanical properties of the Cedrelinga catenaeformis species. Of the 12 properties, four were significantly affected (based on analysis of variance at 5% significance level), and the compression and shear strengths in the direction parallel to the fibers exhibited the greatest difference in values from the saturated moisture condition of up to 12% (approximately 34% increase). Toughness exhibited a behavior different from that predicted by the normative equation, in which increase in moisture content implied increase (approximately 59%) of the property studied. Because a good part of the properties was not significantly affected and Brazilian standard ABNT NBR 7190 (1997) considers expressions that lead to a considerable increase in mechanical properties with the reduction of moisture content, this approach was unfavorable to the safety of the project, motivating the development of other studies to collaborate in revisions of this normative document.
Wood is a renewable material, presenting wide use in building construction. For its better employability, it is necessary to perform physical and mechanical characterization of the several species available for application. In this respect, Brazilian Code ABNT NBR 7190:1997-Timber Structures Design, in its Annex B, prescribes the proper tests and adds some relations between properties and strength classes for coniferous and dicotyledonous. The strength classes are function of characteristics values of strength in compression parallel to grain (f c0). However, density is a more easy-determination property and the cited Code presents the mean value of density for each strength class. Therefore, this research aimed to evaluate the possibility of inferring f c0 based on density obtained on tests of three Brazilian tropical wood species: Canafístula (Cassia ferruginea); Angelim araroba (Vataireopsis araroba) e Castelo (Gossypiospermum sp.). Statistical procedures shown it is possible to conclude that, in some cases, density is not a good estimator of f c0 .
ABSTRACT. Improve quality of timber structures design is an aim that must be systematically sought by engineers in this area. An important topic that can contribute directly to be achieved in this subject is the more consistent knowledge related to structural properties of wood. Know values of longitudinal modulus of elasticity (E) and shear modulus (G) is essential for proper evaluation of plate structures performance, as example. It has been usual to adopt statistical equivalence for E and G values in plans longitudinal-radial and longitudinal-tangential, although experimental confirmation of this hypothesis is required. In this context, the aim of this work is to determine values of E LR , E LT , G LR and G LT , based on static bending tests, to five dicotyledonous species. Results showed statistical equivalence between the elastic properties in both plans, and the relation E = 35G was obtained for the five wood species here considered.Keywords: static bending test, timber, shear modulus, longitudinal modulus of elasticity.Módulo de elasticidade transversal e longitudinal da madeira: relações baseadas nos ensaios de flexão RESUMO. Melhorias no projeto das estruturas de madeira são metas que devem ser sistematicamente almejadas por profissionais da área. Um tópico importante que pode contribuir diretamente para isso está relacionado a um conhecimento mais profundo a respeito das propriedades de resistência e de rigidez da madeira. O conhecimento dos módulos de elasticidade longitudinal (E) e transversal (G) é essencial para a avaliação do desempenho de placas entre outros elementos estruturais. No dimensionamento estrutural tem sido comum adotar equivalência estatística dos valores de E e G nas direções longitudinal-radial e longitudinais-transversal. Este trabalho objetivou determinar valores dos módulos de elasticidade E LR , E LT , G LR e G LT com base em testes de flexão estática para cinco espécies dicotiledôneas, possibilitando avaliar a equivalência ou não destas propriedades (E LR e E LT ; G LR e G LT ) assim como de estabelecer correlações adequadas entre E e G. Os resultados revelaram equivalência estatística entre as propriedades elásticas em ambas as direções, e a relação E = 35·G foi obtida para espécies de madeira estudadas.Palvras-chave: ensaio de flexão estática, madeira, módulo de elasticidade transversal, módulo de elasticidade longitudinal.
In Brazil, wood is a material which has been used for years in different purposes. The variety of Brazilian tropical wood species is expressive, nonetheless only a few of them are considered in structural design. Taking in account possibility of eventual shortages of these well-known wood species, characterization of alternative essences is presented as fundamental for maintenance of wood supply for civil construction. In Brazil, the structural dimensioning and timber characterization are specified by ABNT NBR 7190:1997 (Timber structures design), in its Annex B. This work aimed, with the aid of Brazilian Code, determining physical (4) and mechanical (13) properties of Angelim Saia (Vatairea sp.). Besides, with regression model (linear, exponential, geometric and logarithmic) based in analysis of variance (ANOVA), it was aimed to estimate resistance values and stiffness in function of the density, once this is an easy-obtainable property for wood. From a set of twelve aleatory pieces, twelve specimens were produced for each test type, totalizing 204 experimental measurements. Results of mechanical properties showed compatible performance with other species already established for use in structure, which shows the potential of Angelim Saia for structural purposes. From regression models for estimate strength and stiffness values, it was possible conclude that not all properties can be estimate by density. Better results were showed by the geometric model in estimation of hardness parallel to grain, who provided determination coefficient (R²) close to 70%.
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