Influence of Wood Moisture Content on the Modulus of Elasticity in Compression Parallel to the Grain

Brazilian Standard ABNT NBR7190:1997 for timber structures design, adopts a first degree equation to describe the influence of wood moisture content. Periodically, when necessary, the referred standard is revised in order to analyze inconsistencies and to adopt considerations according new realities verified. So, the present paper aims to examine the adequacy of its equation which corrects to 12% of moisture the values of rigidity properties obtained on experimental tests. To quantify the moisture influence on modulus of elasticity, it was applied tests of compression parallel to the grain for six specimens of different strength classes, considering nominal moisture of 12; 20; 25; 30%. As results, modulus of elasticity in the moisture range 25-30% showed statistically equivalents, and was obtained a first degree equation to correlate the studied variables which leads to statically equivalent estimations when compared with results by ABNT NBR7190:1997 equation. However, it was indicated to maintain the current expression for the next text of the referred document review, without prejudice to statistical significance of the estimates.

Influence of wood moisture content on modulus of elasticity on tension paralllel to the grain of brasilian species

Periodically, when necessary, standard documents are revised in order to analyze inconsistencies and to include considerations according new realities verified. In this sense, aiming to quantify the wood moisture content influence on modulus of elasticity, it was applied tension tests parallel to the grain for six specimens of different strength classes of wood, considering nominal moisture of 12, 20, 25, and 30% in Brazil. The present paper examine the adequacy of the current Brazilian standard ABNT NBR7190:1997, in review, about the adoption of a first degree equation to describe the influence of wood moisture content for timber structures design. It was obtained a new first degree equation which leads to statically equivalent estimations when compared with results by ABNT NBR7190:1997 equation. However, as recommendations it could be maintain the current expression for the next text of the referred document review, without prejudice to statistical significance of the estimates.

Physical and mechanical properties of thermally modified wood from E. grandis

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Classificação Estrutural e Qualidade da Madeira do Clone GT 1 de Hevea brasiliensis Muell. Arg

Latex is the main product extracted from rubber trees (Hevea brasiliensis). In Brazil, at the end of the production cycle of latex, the wood of rubber tree is traditionally used for energy purposes, but several international studies have reported consolidated practices of adding value to it. The objective of this paper was to evaluate the quality of wood and classify it structurally based on its mechanical properties. Six 20-year-old trees of the clone GT 1 of rubber tree proceeding from Itajobi, State of Sao Paulo, Brazil were sampled. Reduced dimensions specimens in the radial direction of the wood were produced to evaluate the quality by compression parallel to the grain, static bending and Janka hardness tests. Two specimens, one from the lower log (since the ground up to breast height) and one from the higher log (from breast height up to 2.50 m) were produced for structural classification of the wood based on the characteristic strength in compression parallel to the grain (NBR 7190 norm, 1997). The wood was classified as C40 (fc0k ≥ 40 MPa) class. Results revealed that the strength was not statistically different in the radial direction (except for the Janka hardness), though tending to increase from pith to bark.

Poissons ratios for wood species for structural purposes

The broader knowledge about physical and mechanical properties of wood allows reliable timber structures design. Even little addressed in the literature, in several situations Poisson's ratios are required for the evaluation of stresses acting on structural elements. This study aimed to obtain values of Poisson's ratios (ν), plans Longitudinal-Radial (νLR) and Longitudinal-Tangential (νLT), for species Peroba Rosa (Aspidosperma polyneuron) and Jatobá (Hymenaea courbaril L.). For this purpose, forty samples Peroba Rosa and eight samples of Jatobá were prepared for testing in compression parallel to the grain, following the recommendations of ABNT NBR 7190 standard. The results of means confidence intervals, considered at the level of 5% significance, revealed that the Poisson's ratios νLR e νLT to Peroba Rosa are 0.27 and 0.42, respectively, and 0.25 and 0.43 to Jatobá.

Influence of the number of load cycles to obtain the stiffness properties of angico preto (Anadenanthera macrocarpa) wood specie

The tests used to obtain the stiffness properties of wood are made with two loading cycles, as defined by the Brazilian standard ABNT NBR 7190 (Design of Timber Structures). However, the possibility of reducing the number of cycles allows decrease the operating time of the machine, resulting in reduced spending on electricity used during the tests. This research aimed to investigate, with the aid of the analysis of variance (ANOVA), the influence of the use of three load cycles to obtain the modulus of elasticity in compression parallel to grain (Ec0), in tensile parallel to the grain (Et0), in bending (Em) and in compression perpendicular to the grain (Ec90) of Angico Preto (Anadenanthera macrocarpa) wood specie. For the number of cycles and stiffness were manufactured 12 samples, totaling 144 specimens. The results of the ANOVA revealed statistical equivalence between the stiffness properties for both load cycle numbers evaluated, indicating that it is possible to carry out the tests with a single charge cycle, allowing savings in time and energy in the operation of the equipment.

Contribution of oxygen related defects to the electronic transport in SnO2 sol-gel films

SnO2 deposited by sol-gel is a polycrystalline film with small grain size. Oxygen present at a less grain boundary traps electrons and then the depletion layer around the potential barrier of the grain boundary becomes wider, comparable to the grain size. We have modeled the conductivity taking into account the trapped charge at the depletion layer of the grain boundary and other scattering mechanisms such as ionized impurity and polar optical. Experimental data of photoconductivity of SnO2 sol-gel films are simulated considering the dominant scattering at grain boundary and crystallite bulk. The fraction of trapped charge at the grain boundary depends on temperature and wavelength of irradiating light, being as high as 50% for illumination in the range 500-600 nm for SnO2-2%Nb as grown sample annealed in air to 550°C. This fraction can be quite reduced depending on exposure to light and annealing under different oxygen partial pressure conditions.

Prospects for the use of municipal tree pruning wastes in particleboard production

The purpose of this study was to evaluate the physical and mechanical properties of particleboard made with pruning wastes from Ipê (Tabebuia serratifolia) and Chapéu-de-Sol (Terminalia catappa) trees. Particleboards were prepared with both wood species, using all the material produced by grinding the pruning wastes. The particleboards had dimensions of 45×45 cm, a thickness of approximately 11.5 mm and an average density of 664 kg/m3. A urea-formaldehyde adhesive was used in the proportion of 12% of the dry particle mass. The particleboards were pressed at a temperature of 130 C for 10 mins. The physical and mechanical properties analyzed were density, moisture content, thickness swelling, percentage of lignin and cellulose, modulus of resilience, modulus of elasticity and tensile strength parallel to the grain, accordingly to the standards NBR 14810 and CS 236-66 (1968). The particleboards were considered to be of medium density. The particle size significantly affected the static bending strength and tensile strength parallel to the grain. Ipê presented better results, demonstrating a potential for the production and use of particleboard made from this species. © The Author(s) 2013.

Comparação entre valores de ensaios experimentais e calculados da resistência ao embutimento da madeira de Pinus taeda L.

To design connections between timber parts with metal dowels (nails or bolts), two phenomena must be considered: bending of the metal dowel and the embedment strength in the wood. The Brazilian Standard ABNT NBR 7190:1997 proposes the methods used in the laboratory tests to determine the embedment strength with the metal dowell and, in the absence of testing, specifies relations to calculate the embedment strength from the compression strength. The aim of this research was to compare the embedment strength values obtained by experimental tests and calculated by the relationships established by the Brazilian Standard ABNT NBR 7190:1997. By the results of the hypothesis tests, it was possible to conclude that the estimate of the embedment strength parallel to the grain proposed by the Brazilian standard ABNT NBR 7190:1997, establishing equivalence with the strength compression results in the same direction, must be effective to the wood species Pinus taeda L., however, the same was not found in the perpendicular direction with respect to the grain, possibly explained by the alpha(e) values in the equation to calculed fe(90)

Fiberglass-reinforced glulam beams: Mechanical properties and theoretical model

The glued-laminated lumber (glulam) technique is an efficient process for making rational use of wood. Fiber-Reinforced Polymers (FRPs) associated with glulam beams provide significant gains in terms of strength and stiffness, and also alter the mode of rupture of these structural elements. In this context, this paper presents a theoretical model for designing reinforced glulam beams. The model allows for the calculation of the bending moment, the hypothetical distribution of linear strains along the height of the beam, and considers the wood has a linear elastic fragile behavior in tension parallel to the fibers and bilinear in compression parallel to the fibers, initially elastic and subsequently inelastic, with a negative decline in the stress-strain diagram. The stiffness was calculated by the transformed section method. Twelve non-reinforced and fiberglass reinforced glulam beams were evaluated experimentally to validate the proposed theoretical model. The results obtained indicate good congruence between the experimental and theoretical values.

Theoretical model and experimental analysis of glulam beam reinforced with FRP

This work present a study of glulam beams reinforced with FRP. It was developed a theoretical model that calculates strength and stiffness of the beams. The model allows for the calculation of the bending moment, the hypothetical distribution of linear strains along the height of the beam, and considers the wood has a linear elastic fragile behavior in tension parallel to the fibers and bilinear in compression parallel to the fibers, initially elastic and subsequently inelastic, with a negative decline in the stress-strain diagram. The stiffness was calculated by the transformed section method. Twelve non-reinforced and fiberglass reinforced glulam beams were evaluated experimentally to validate the proposed theoretical model. The results obtained indicate good congruence between the experimental and theoretical values.

AMS and grain shape fabric of the Late Palaeozoic diamictites of the Southeastern Paran Basin, Brazil

Diamictites interbedded with marine shales and turbidites onlap the eastern border of the Parana Basin (Southern Brazil). These poorly sorted sediments were deposited during the Permo-Carboniferous glaciation, and their matrix-supported clasts show no preferred orientation. These massive rocks have been studied using anisotropy of magnetic susceptibility (AMS) and grain shape fabric. Hysteresis loops and thermomagnetic measurements show that AMS depends mostly on the paramagnetic clays, but fine ferromagnetic particles also contribute to the anisotropy. The coarse silt to sand grain preferred orientation study supports the use of AMS in describing the diamictite fabric, at least regarding the orientation of the foliation. AMS and grain shape data reveal subhorizontal to weakly inclined magnetic and grain shape foliation parallel to the regional bedding. The magnetic lineations are normally scattered within the foliation plane in agreement with the oblate AMS ellipsoids found in these rocks. Both fabric patterns are consistent with deposition by subaqueous mudflows that were resedimented downslope, with elastic supply from continental sources. The off-vertical grain shape foliation poles suggest that the deposition of diamictites was controlled by the depocentre topography of the Rio do Sul sub-basin.

Physiological responses of the brown mussel Perna perna (Mollusca, Bivalvia) exposed to the anionic surfactant linear alkylbenzene sulphonate (LAS).

The effects of the Linear Alkylbenzene Sulphonate (LAS) were evaluated on the mussel Perna perna, using physiological and genotoxic biomarkers. The Micronuclei (MN) assay was used to estimate effects at nuclear level, whereas the physiological effects were evaluated by measuring the oxygen consumption and ammonia excretion rates. Significant effects were observed for the MN assay and the ammonia excretion rate, even in low concentrations. The oxygen consumption was not affected in the tested concentrations. For MN and ammonia excretion, the animals exposed to intermediate concentrations were not affected, but responded to the higher concentrations, indicating the existence of compensatory mechanisms at physiological level. However, parallel to this study other authors indicate the presence of progressive effects at the cellular level, suggesting that the organisms are not capable to recover of such increasing effects. Additionally, the results show that the levels of LAS observed for Brazilian coastal waters may chronically affect the biota.

Propriedades físicas e mecânicas de painéis LVL de Eucalyptus grandis

This paper mainly aimed to evaluate the physical and mechanical properties of LVL panels made from Eucalyptus grandis, from reforestation at the region of Senges, in Parana state, Brazil. LVL panels were manufactured using 23 veneers (2,4mm thick each one) in commercial dimension of 2.500 mm long and 1,200 mm wide. The properties of static bending were analyzed (strength and rigidity) in beams of the LVL, in the flatwise and edgewise positions. The properties of compression parallel to grain and shear parallel in the plans L-X and L-Y and density in this LVL panels were also analyzed according to ASTM-D 5456/4761 and ASTM-D 198 codes. The mean values to flatwise bending MOE and MOR were 13114 MPa and 88.76 MPa, respectively, and for edgewise bending MOE and MOR were 15871 MPa and 88.63 MPa, respectively. The density (12%) of the LVL panels and of the veneers were 690 kg/m(3) and 649 kg/m(3). The mean values to parallel compression MOE and MOR were 16856 MPa and 58.05 MPa, respectively. The mean values of the maximum resistance to shear parallel in the plans L-X and L-Y were 5.96 MPa and 591 MPa, respectively. All these values reached partially or they passed the medium limits of reference (normative codes, researches and commercial catalogs) established for LVL panels and original solid wood, attesting overall the quality of those panels produced with this wood.

Contribution to the embryology of Leiothrix fluitans (Eriocaulaceae : Poales)

This paper presents a contribution to the understanding of the embryology, especially microsporogenesis, the antipodal cell behavior, and the early stages of the micropylar seed operculum, in Leiothrix fluitans, to elucidate these aspects both within the subgenus Rheocaulon and within the genus in Eriocaulaceae. Contrarily to previous descriptions of this same species, our results show the following: microsporogenesis is of the successive type and results in isobilateral microspore tetrads; the antipodal cells gradually fuse together to form a conspicuous cyst; and the inner integument, which does not develop into an endothelium, shows evidence of the initiation of the seed operculum in its micropylar end. Such features are common to the family as a whole. Evidenced for the first time in the family, the chalazal end of the ovule differentiates into a hypostase closely associated to the antipodal cyst. These overall features of L. fluitalls point out previous misinterpretations on some of its embryological aspects, especially those concerning the only report of simultaneous microsporogenesis and proliferation of the antipodal cells. Furthermore, the results presented here allow us to reinforce the uniformity of the embryological aspects within the Eriocaulaceae, strengthening the cystic arrangement of the antipodal cells as a potential autapomorphy of the family within the other Poales (commelinids). (C) 2007 Elsevier B.V. All rights reserved.