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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This study aimed to investigate the influence of storage time (0, 48 hours) of Pinus elliottii pieces and the tests to obtaining modulus of elasticity (static bending and transversal vibration) in glued laminated timber beams, produced with resorcinol based adhesive and 0.8 MPa compaction pressure. After pieces were properly prepared, part of them was used in immediate three manufacturing glulam beams, tested after adhesive cure, and part stored for 48 hours under a roof with a temperature of 25°C and relative humidity of 60% for subsequent manufacturing and testing three other glulam beams. Results of analysis of variance (ANOVA) revealed that the storage period was significant influence in modulus of elasticity obtained in static bending test (8% reduction from 0 to 48 hours). This not occurred with modulus of elasticity obtained by transversal vibration test (no significant influence). ANOVA results showed equivalence of means in both test procedures. New researches ire needed to better understand the investigated phenomenon, using new wood species, other storage conditions and a great number of samples.

This research aimed to present an alternative methodology to determine the tensile modulus of elasticity based on the least squares method, allowing multiple uses of load and displacements values obtained from the experiment, giving greater reliability in the calculation of timber stiffness. Were used twelve specimens of Eucalyptus grandis wood species, tested in tensile parallel to the grain according to the assumptions of the Brazilian standard ABNT NBR 7190:1997. The modulus of elasticity obtained from the proposed calculation approaches were compared with the elastic moduli obtained from Brazilian standard recommendations. Results of analyzes of variance (Kruskal-Wallis) showed statistical equivalence between the modulus of elasticity obtained for both forms of calculation. However, considering the non-homogeneity of wood, to generalize the conclusions, it is necessary new set tests involving all strength classes indicate by NBR 7190:1997.