Influence of the Wood Specimen Position on Calculus of the Bending Modulus of Elasticity (original) (raw)
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Anisotropy Influence in Obtaining Stiffness Property in Bending of Brazilian Wood Species
International Journal of Materials Engineering, 2014
The design of timber structures, and other materials, must follow the procedures and methods of calculation of normative standards. Some normative documents in the design of timber structures adopt quite simple arithmetical relationships to relate wood properties in order to make it simple and quick evaluation of the behavior of structural elements, as is the specific case of Brazilian standard ABNT NBR 7190:1997, establishing a single relation for the shear (G) and the longitudinal (E) modulus of elasticity [E=G/20], which implies taking statistical equivalence to the values of the elastic moduli in the longitudinal-radial (G LR ) and longitudinal-tangential (G LT ) directions, which are important properties in relation to the requirements of structural projects. In this context, this study aimed to investigate, with the aid of four and three points static bending tests performed on the of dicotyledonous wood species grown in Brazil, the determination of the values of E LR , E LT , G LR and G LT to confirm the possibility of its equivalence (E LR and E LT , G LR and G LT ), and for establishing correlations among them. The results of the hypothesis testing between the shear and longitudinal modulus of elasticity exhibited equivalent by species and simultaneously for all species, and the results of the linear regression model showed not possible to estimate the shear modulus of elasticity with knowledge of the longitudinal modulus of elasticity, and the optimal coefficient found by least squares method to the relation between the modulus of elasticity was equal to 35 (E=G/35), suggesting the need for an adjustment of the coefficient for this scale more safe wooden structures.
Comparison of Two Methods to Determine the Bending Modulus of Elasticity of Wood
International Journal of Materials Engineering, 2018
The modulus of elasticity is among the main properties required for the dimensioning of a wood structure. It can be calculated using different test methods, the most commonly used are the 3 and 4 points bending tests. The Brazilian standard, ABNT NBR 7190: 1997, recommends the 3-point static bending test. Studies about the influence of testing methods to determine the bending modulus of elasticity are always relevant, since can improve its reliability. Thus, the aim of this study is to examine the bending modulus of elasticity of samples of nine Brazilian wood species: Cambará Rosa (Erisma uncinatum Warm), Caxeta (Tabebuia cassinoides), Tatajuba (Bagassa guianensis), Itaúba (Mezilaurus itauba), Branquilho (Termilalia spp), Cedro Amazonense (Cedrelinga catenaeformis Ducke), Roxinho (Peltogyne spp.), Cumaru (Dipteryx odorata) and Cambará (Gochnatia polymorpha). The results of the confidence intervals have showed that the moduli of elasticity for both test methods were equivalent at 5% significance level.
BioResources
In Brazil, standard ABNT NBR 7190 (1997) prescribes the determination of strength (fM) and modulus of elasticity (EM) in static bending from specimens measuring 5 cm × 5 cm × 115 cm. Thus, the relationship between the test span (L) and the specimen height (h) greater than or equal to 21 (L/h ≥ 21) is respected, ensuring that the effect of shear in the calculation of displacements is negligible (Euler Bernoulli Theory). Considering the expressive number of tree species cataloged in the Brazilian Amazon Forest, any procedure that aims to facilitate the realization of experimental tests is highly desirable because it provides the knowledge of unusual species. These wood species may potentially replace woods that have been traditionally used and historically exploited. Using five hardwood species, this research aimed to verify, while maintaining constant L/h ≥ 21 ratios, the influence of specimens dimensions in the determination of fM and EM. For all species studied, the statistical ana...
Evaluation of Longitudinal Modulus of Elasticity in Wood Species for Structural Application
Advanced Materials Research, 2014
This research aimed to investigate possible differences in values of longitudinal modulus of elasticity (E) for wood species usually employed for structural purposes, as Castanheira (Bertholletia excelsa), Cambará (Erisma uncinatum), Cumaru (Dipteryx odorata), Jatobá (Hymenaea stilbocarpa), Garapa (Apuleia leiocarpa) and Peroba Rosa (Aspidosperma polyneuron).
This study compares variability in the longitudinal Modulus of Elasticity (MOE) values, measured by three different methods, for eight tropical wood species covering a wide range of densities, a property that has been little described in the literature for some of the species studied. The modulus of elasticity in wood species is one of the main mechanical properties measured to characterize wood materials. However, this property is seldom described for the tropical wood species studied here, and the method used is often variable. The aim is to answer the following questions. In the methods used, what are the main variability factors which influence modulus measurement? Is the modulus different with regard to the solicitation direction (radial or tangential)? Which relationship exists between modulus and density for these species? The samples were subjected to the four-point bending test, then to the free vibration test and to the forced-vibration test (which allows tests on small sa...
For structural use, the properties of large size specimens are preferred to those of small clear specimens because of unavoidable defects such as knots and shakes found in wood. The objective of this study was to assess the bending strength, modulus of elasticity properties and failure behaviour of ten Lesser-used Species (LUS) by use of structural size dimensions (50mm x 120 mm x 2000 mm). The ten species were Albizia ferruginea, (Gulland Perr) Beuth., Sterculia rhinopetala,(K. Schum), Blighia sapida,(Koenig), Canarium schweinfurthii (Engl.), Petersianthus macrocarpus, (P. Beauv.) Liben, Sterculia oblonga, (Mast.) Cola gigantea, (A.Chev.) Celtis zenkeri, (Engl.) Antiaris toxicaria (Lesch.) and Amphimas pterocarpoides (Harms.). The moisture contents of the 10 timber species used ranged from 16.1% (Antiaris toxicaria) to 51.0% (Albizia ferruginea). It was observed during loading under flexure that the elastic stiffness and rate of increase in the strength capacity of the beams did not change after three cycles of loading and unloading. All the beams failed in a form of tension rupture. The breaks were usually splintering tension failure or brittle (brashness) tension failure or a combination of the two modes of failure. Sterculia rhinopetala exhibited the highest bending strength with a 5 th percentile bending strength of 56.8 /mm 2 and a mean local modulus of elasticity of 15,973 /mm 2 . Sterculia oblonga was also found to be the 2 nd best in terms of material properties with a 5 th percentile bending strength of 52.1 /mm 2 and a mean local modulus of elasticity of 16,408 /mm 2 . Celtis zenkeri which had the highest mean local modulus of elasticity, however, had the 6 th best 5 th percentile bending strength of 39.9 /mm 2 . A good linear correlation (69.6-91.3%) was established between mechanical strength properties for average density, average bending strength, average local modulus of elasticity and average global modulus of elasticity.
Shear and longitudinal modulus of elasticity in wood: relations based on static bending tests
Acta Scientiarum. Technology, 2017
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.
A group of databases making a total of approximately 9300 sawn timber pieces from Spanish coniferous species, tested according to European standards and visually graded mainly according Spanish standards were analyzed. The percentiles ratio 20 th /5 th of bending strength, modulus of elasticity and density distribution were obtained for different combinations of species and visual stress grade. The Eurocode 5 proposes this percentile ratio by a coefficient k fi which is used to determine the design values of mechanical properties in fire situation. The percentile ratios obtained were compared with the specified value in Eurocode 5 for solid timber (k fi = 1,25). In lower grades of Spanish coniferous timber, this value was overly conservative. A value of k fi of 1,4 seems to be more adequate for the case of the bending modulus of elasticity and 1,4 to 1,5 for the bending strength. It is noted that, in the case of the upper grades, this value should be of 1,3; close to the Eurocode proposal. Furthermore, in the case of density, the value should be of 1,1; hence lower than suggested in the code.
International Journal of Materials Engineering, 2017
Toughness is the mechanical property that determines the wood strength when a force acts in a short time interval. Its value is determined in the bending impact test. Timber has to resist to impact forces in several applications, nevertheless this property is not widely studied to tropical wood species from Brazil. This study aimed to correlate the toughness and the impact strength of wood with the modulus of elasticity and the strength in the compression parallel to grain test. Therefore ten tropical species, from different strength classes, grown in Brazil were tested according to the Brazilian Standard Code ABNT NBR 7190:1997. The studied species were: Cedro (Cedrella sp.), Cambará Rosa (Erisma uncinatum Warm), Cedrorana (Cedrelinga cateniformis), Catanudo (Calophyllum sp.), Cupiúba (Goupia glabra), Angelim Saia (Parkia spp.), Tatajuba (Bagassa guianensis Aubl.), Guaiçara (Luetzelburgia sp.), Cumaru (Dipteryx odorata) and Angelim Vermelho (Dinizia excelsa Ducke). It was developed a relation between the studied properties through regression models, evaluated according to the variance analysis (ANOVA). The results of the statistical analysis revealed led to the conclusion that there is no correlation between the proposed properties for the analyzed species.
BioResources, 2020
Accurate estimation of average modulus of elasticity in compression parallel to the grain (Ec0) is of paramount importance for rational sizing of timber structures, given the use of this property in the estimation of stability of compressed parts (ultimate limit state, ULS) and in calculation of excessive strains (serviceability limit state, SLS). In Brazil, if values cannot be experimentally determined, ABNT NBR 7190 (1997) allows for estimation of Ec0 through relations to average modulus of elasticity both in tension parallel to the grain (Et0) (Ec0 = Et0) and in bending (EM) (Ec0 = EM/0.90). This research aimed to access the efficiency of these relations by testing 30 tropical wood species. The analysis of variance results showed that Ec0 and Et0 were statistically equal. However, Ec0 and EM/0.90 were not statistically equal, and the method of least squares resulted in a coefficient of 0.98, which was 8.89% higher than the one suggested by ABNT NBR 7190 (1997) and close to 1, thu...