In Brazil, some tile manufacturers have proposed a 10% (5.5°) slope between chords to minimize timber consumption. However, after simulating 21 slopes from 7% (4°) to 27% (15°), it was discovered that the axial strengths are inversely proportional to the slope, creating overly large dimensions for the bars competing for support. The results were obtained using software developed following the guidelines specified in the revised version of the ABNT NBR 7190 (2022) standard. Finally, it was found that the minimum slope until no reinforcement is needed for the string bars is 16% (9°).
In order to analyze the influence of moisture content variation on Cedrella odorata wood specie on strength and stiffness properties, considering 12% moisture content up to fiber saturation point (FSP). Most of strength and stiffness properties analyzed were significantly influenced by moisture content according statistical analysis. ANOVA, Anderson Darling and Multiple comparison tests were used at 5% significance level. Considering that most of properties were affected by moisture content, the equations to estimate wood properties according moisture decrease are quite precise, but most of estimations were higher than experimental values at 12% moisture content, indicating the need of a standard review for such estimators, which may lead to an unsafe timber structure design.
The Brazilian standard ABNT NBR 7190 (1997) governs the premises for the wood structure sizing through a table and the simplified method. Thus, this research aims to analyze whether the simplified method shown in the standard matches the resistance values of 72 Brazilian species, separated from class C20 to C60. In the end, it was possible to conclude that the value displayed by the standard between the ratio of shear and compression in the direction parallel to the fibers is half of what actually happens in Brazilian species, showing an urgent review in the standard premises.
The Brazilian standard ABNT 7190 (1997) establishes the strength classes C20, C30, C40 and C60 for the proper framework of the different wood types in the group of hardwoods. Associated with the strength class, which is based on the compressive strength characteristic value parallel to the fibers (fc0,k), the standard stipulates the respective values representing the stiffness (Ec0), with 19500 MPa being the reference value for the class C40, essential variables in structural design. For being the C40 class is the one with the greatest amplitude (20 MPa), it is possible that the value 19500 MPa is not the best representation of stiffness. This work aimed to verify the representativeness the stiffness value established by the Brazilian standard for C40 wood. The result obtained from the average confidence interval indicates the value of 14110 MPa as being the most representative, which may imply structures that are supposedly more rigid than they really are.
The present article aimed to characterize the wood specie Qualea albiflora (Mandioqueira), in order to enable its use for structural purposes. The tests to obtain the physical and mechanical characteristics were carried out according to the Brazilian standard ABNT NBR 7190, allowing the classification of the Qualea albiflora in the strength class C60, a wood species suitable for use in heavy constructions. After the characterization, it was verified with the aid of regression models (linear, logarithmic, exponential and geometric), that it is not possible to make use of the apparent density in the estimation of the other physical and mechanical characteristics, obtaining a bad adjustment in all the cases (R² < 50.00%) and the non-representativeness of the models adopted (P-Value> 0.05).
The present study deals with a production of pine particleboards using the sugarcane bagasse content and using castor-oil based bicomponent polyurethane resin and urea-formaldehyde resin. The influence of incorporation of sugarcane bagasse on the physical and mechanical properties of the composites was evaluated. The particleboards were produced according Brazilian standard ABNT NBR 14810, but performance requirements have been analyzed using Brazilian and international standards, as well. Treatment 2, using PU resin, were considered the best treatment using pine residue and sugarcane bagasse, presenting physical properties values 60% lower and mechanical properties 65% higher on average when compared with panel without sugarcane bagasse, indicating the good performance of sugarcane incorporation and the possibility of its use on commercial purpose for thermal and acoustic insulation. The addition of sugarcane bagasse improved physical and mechanical properties of particleboards when compared to panels manufactured from pine wood particles only. Statistical analysis indicated that moisture content and bagasse content were significant, enhancing properties when compared with reference treatments.
For safety reasons, wood strength values are calculated based on their characteristic values. Brazilian national standard (NBR, in Portuguese “Norma Brasileira Regulamentadora”) 7190 (1997) establishes ratios for characteristic strength estimation and three forms of wood characterization, with an emphasis on the simplified procedure for common species, which allows obtaining the strength characteristic values through equations correlating different mechanical properties. The present work evaluates the accuracy of the relation proposed by NBR 7190 (1997) of shear strength along the grain (fv0,k) to compression strength along the grain (fc0,k) (fv0,k=0.12 fc0,k). 960 experimental measurements of shear and compression strength values were performed for 40 hardwood species, and the precision of the relation proposed by the Brazilian standard was evaluated using the analysis of variance (ANOVA) method. Linear, exponential, logarithmic, and geometric regression models were used as an alternative to the NBR relation for shear strength estimation. The statistical analysis revealed that the geometric regression is the model of best fit.
This research aimed to characterize the wood species Goiabão (Planchonella pachycarpa), following the precepts set forth in the Brazilian standard ABNT NBR 7190, as well as to evaluate the possibility of estimating physical and mechanical properties, using the analysis of variance (ANOVA) as a function of apparent density, and also to estimate the stiffness properties as a function of the respective strength property. The physical and mechanical properties were considered adequate for the use of this wood for structural purposes, being classified in class C40. According to the results of the regression models, it is possible to estimate the tensile strength parallel to the fibers as a function of the apparent density. It was also possible to estimate the longitudinal elastic modulus in the compression parallel to the fibers as a function of the compressive strength parallel to the fibers.