Abstract
Wood is a natural material and so many factors interfere in estimation of its physical and mechanical properties. Consequently variability in properties should be taken into account to rationalize its application. Longitudinal modulus of elasticity is one of the main mechanical properties of the material, and its value can be obtained via standardized tests. The aim of this study is to evaluate the influence of test conditions compatible with ABNT NBR 7190:1997 Code requirements to determine modulus of elasticity in static bending. For each of eight species, eight specimens were tested, all of them four times, with the sample oriented on each of its four faces related to load application. Data analysis was performed independently of species and their respective strength class, using hypothesis testing to evaluate influence of specimens’ orientations to determination. It was concluded that specimen orientation is significant in determining modulus of elasticity in static bending according to ABNT NBR 7190:1997. This aspect can lead to a future normative review by the National Committee responsible by redaction of this Code. To represent natural variability of wood in specimens’ volume by only one bending test, values of the modulus of elasticity should be lessened in 8%.
Highlights
IntroductionInternal variations of wood can be expressed by differences between earlywood and latewood; between heartwood and sapwood; between regions in directions pith-bark and along of tree height (Nassur 2010)
According to table 2, the highest variation among values of modulus of elasticity in static bending was found to Pinus elliottii (6,7%), while the lowest variation was obtained by Hymenaea stilbocarpa (3,9%)
This result is consistent with those obtained by Silva et al (2012b), which assessed the influence of the face choice to determine modulus of elasticity in static bending for three wood species, and found variations up to 5,2% between the E of opposite faces analyzed
Summary
Internal variations of wood can be expressed by differences between earlywood and latewood; between heartwood and sapwood; between regions in directions pith-bark and along of tree height (Nassur 2010). Authors such as Haselein et al (2000), Ballarin and Palma (2003), Evans et al (2000) and for trees with 30, 37 and 40 years old, respectively, found that strength and stiffness properties in static bending are seriously affected by the juvenile wood presence. Wood variability must be considered to determine the properties of a single specie or else to design a timber structure (Calil Junior et al 2003)
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