ABSTRACT The use of wood is widespread in rural constructions, and the truss systems stand out among its various applications. This specific system has several typologies and requires a thorough study to determine the most advantageous model for each project. The present study aims to apply the Computational Intelligence concepts to determine the minimum viable cross-section of a Howe truss. For the computational simulation, methods like Finite Elements were used to obtain the loads and the Firefly Algorithm for the optimization process, focusing on minimizing the total weight of the structural part. Studies were conducted varying the spans of the elements and the height to span ratio. The design assumptions for establishing the optimization method’s constraints follow the recommendations of the Brazilian standard for wood design, ABNT NBR 7190 (1997). Weights between 95.42 kg and 653.57 kg were obtained, and all optimization processes presented feasible solutions for the design constraints.

ABSTRACT Brazilian flora has more than 12 thousand tropical wood species, which can be the raw material for the construction industry. Chromated copper borate (CCB) and chromated copper arsenate (CCA) are wood preservative chemicals, which can generate toxic waste. Particleboards are usually produced from Pinus sp. and Eucalyptus sp. wood particles and a polymeric matrix (often formaldehyde-based), and they are used as raw material mainly for the furniture industry. This study aimed to investigate the technical feasibility of particleboard production using caixeta wood (Simarouba amara Aubl.) particles and bicomponent castor oil-based polyurethane resin for tropical wood waste management, as well as study the impact of CCA/CCB treatments on the performance of these panels according to NBR 14810 standards. Analysis of variance (ANOVA) tests was performed to compare ten physical and mechanical properties of the panels produced with CCA, CCB, and non-treated caixeta wood particles. The performance of caixeta wood panels was similar to the usually produced boards (using Pinus sp. and Eucalyptus sp. wood). Furthermore, preservative treatments did not change significantly the mechanical performance of panels. However, water absorption increased and thickness swelling decreased in CCA/CCB treated samples.

ABSTRACT The use of alternative materials such as lignocellulosic residues in the production of particleboards has increased considering that these residues are produced in large volumes and often do not have an appropriate destination. This research studied the use of residues from cellulose industries, sugarcane bagasse, and castor oil-based polyurethane resin in the production of wooden panels and evaluated the influence of using these residues on the physical and mechanical properties of the panels. The products were manufactured according to the Brazilian standard ABNT NBR 14810 and the requirements of the panels were evaluated based on national and international standards. All treatments partially met the regulatory requirements. The addition of bagasse led to an improvement in physical and mechanical properties, with treatment 2 (50% wood residue and 50% bagasse) presenting the best performance, which indicates the possibility of using panels with residues with non-structural purpose in environments to improve the thermoacoustic performance of rural buildings. The statistical analysis indicated that the percentage of bagasse was significant, improving the evaluated properties.

ABSTRACT This research aimed to evaluate the effect of the number of fatigue cycles (NC, 0 – reference, 450, 4500, 45000, and 90000) for frequencies (Fr) of oscillation equal to 0.5 and 1.0 Hz on the modulus of elasticity (Em) and operating stress (σm) in the static bending of Pinus caribaea wood. Em and σm were determined taking into account three specimens (SPEC) manufactured for reference condition and another three for each of the four NC levels and each Fr level, resulting in 27 SPEC. Sixty experimental determinations were obtained, being the approximate total time of sample exposure to fatigue of 350 hours. The same specimens used to determine Em and σm for the reference condition were also used (via non-destructive tests) to obtain these properties for all fatigue cycles. The frequency and number of cycles significantly influenced both investigated properties. Reductions in Em and σm values were observed after 45000 cycles. The progressive increase in the number of fatigue cycles caused more marked reductions in mechanical properties when compared to the increase in the frequency of oscillation.

ABSTRACT Wood has been used for several purposes such as in civil and rural construction. Knowing wood mechanical behavior under short-term loading is essential for safer structural designs. However, wood toughness is a mechanical property little investigated for this purpose. Thus, this study aimed to evaluate, using exponential and polynomial regression models (linear, quadratic, and cubic), the possibility of estimating toughness as a function of apparent density, compression parallel to grain strength, and modulus of rupture in static bending. Thirty-six Brazilian tropical wood species from south of Roraima, Mato Grosso do Sul, and north and northeast of Mato Grosso were tested. Our results showed the significance and representativeness of all investigated fits, among which a cubic polynomial function is the most indicated for wood toughness estimates.

ABSTRACT The use of new wood species in construction requires knowledge of their properties for safer and more economical structural sizing. In Brazil, structural projects are carried out according to the standard document ABNT NBR 7190:1997. Tests required by this standard for the complete characterization of species require large machines with high costs, which are present only in large research centers. Considering the lack of experimental determination, this study aimed, with the help of analysis of variance of regression models, to investigate the possibility of estimating, through apparent density, wood properties obtained in tests where failure is considered fragile, allowing the estimation of properties of species still little used. Ten wood species belonging to the hardwood group (cambara, cedro, cedrorana, copaiba, angelim-araroba, castelo, oiticica-amarela, guarucaia, guaicara, and garapa), covering all strength classes established in the standard ABNT NBR 7190:1997, were used. The results showed that shear strength parallel to the grain (fv0) was the only property that could be estimated by apparent density (ρ12), with an R2 above 50%. Tensile strength normal to the grain (ft90) and splitting strength (fs0) showed poor fit quality.

ABSTRACT Wood is a material used for various purposes since ancient times and is mainly used in civil and rural construction and industry. Due to the predatory exploitation of known trees, it is necessary to characterize new species for use in urban and rural structures as alternatives of species commonly used. This study aimed to determine the physical and mechanical properties of Guarucaia wood (Peltophorum vogelianum Benth.) based on the Brazilian standard ABNT NBR 7190 (1997) and estimate the strength and stiffness as a function of apparent density using the analysis of variance and also estimate stiffness as a function of its strength. The mechanical properties of P. vogelianum were considered compatible for structural use when compared with others used for the same purpose, being classified in the class C50 of dicotyledon species and evidencing the possibility of its use for structural purposes. According to the results of the poor quality in the fit of regression models in the statistical analysis, the strength and stiffness could not be estimated as a function of apparent density nor stiffness properties as a function of their respective strengths.

ABSTRACT According to the ABNT NBR 7190: 1997 standard, tensile strength of wood samples shall be defined as the ratio between the ultimate strength from a stress test and the specimen cross-sectional area (350 mm2). However, due to the complex wood anatomy and experimental difficulties, the fractured surface in tested samples are not perpendicular to the loading direction; therefore, such fractured surface becomes larger than the sample cross section, overestimating tensile strength by this method. Using an alternative approach, we aimed to determine the approximate fracture surface of wood specimens subjected to tensile test. For this purpose, we used the least square method to estimate tensile strength of four hardwood species, which were equally divided into strength classes. Then, we determined the relationship between the cross-sectional areas of intact and fractured specimens. The results showed that the approximate area of a fractured surface was 2.14 higher than that of an intact sample. As a result, tensile strength estimates were 47% lower than those currently estimated, which is unfavorable for the safety of construction structures.

ABSTRACT Wood is one of the main materials used in the constructing of covering structures (roofs) because of its versatility. Under this situation, due to solar radiation incidence, the temperature can exceed 60 °C and, such as other environmental conditions, influence the mechanical properties of the wood in use. The aim of this research was to study the influence of exposure time of the wood of four different hardwood species at a temperature of 60 °C on the shear strength parallel to fibers. The wood of the following species was used: Cupiúba (Goupia glabra), Eucalyptus (Eucalyptus saligna), Garapeira (Apuleia leiocarpa), and Jatobá Tamarindo (Hymenaea sp.). In order to investigate the effect of exposure time (0, 168, 456, 720, and 2160 hours) of the wood species in an oven (60 °C) on the values of shear strength in the direction parallel to fibers, an analysis of variance (ANOVA) was carried out at 5% significance level. According to the results, the time the wood was exposed to the operating temperature significantly influenced the shear strength in the direction parallel to fibers. In addition, all species showed a decrease in shear strength after 456 hours of exposure at a constant temperature of 60 °C.

ABSTRACT For safety reasons, wood strength values, essential for structural dimensioning, are calculated based on the characteristic value, which corresponds to the 5% percentile of a given probability distribution model. For small samples, the Brazilian normative document ABNT NBR 7190 establishes an estimator of the characteristic wood strength, which can provide a significantly different result from the characteristic value coming from a suitable model of probability distribution. The main objective of this study was to evaluate the best probability distribution model (normal, lognormal, Weibull, and exponential) and the subsequent calculation of the characteristic value indicated by ABNT NBR 7190 (1997), allowing to evaluate its accuracy, being also investigated two relationships between characteristic values of the simplified characterization condition for woods of species already known. The best adhesion model was the normal model, which resulted in values statistically equivalent to the characteristic values according to ABNT NBR 7190 (1997). Among the evaluated relationships, the obtained results were significantly higher (up to 92%) when compared to those estimated by ABNT NBR 7190 (1997).

RESUMO Os painéis de madeira reconstituída são muito empregados em vários ramos da indústria da madeira, como nos setores moveleiros e vários segmentos da construção civil urbana e rural. No Brasil são gerados resíduos agrícolas e florestais abundantemente, tornando viável o estudo, desenvolvimento e aplicação de materiais alternativos e sustentáveis, produzidos a partir do aproveitamento destes resíduos. O objetivo deste trabalho foi produzir painéis de partículas homogêneos de alta densidade, com resíduos de madeira de Pinus elliottii e casca de aveia (Avena sativa), prensados com dois tipos de adesivo, poliuretano à base de óleo de mamona e melamina formaldeído, e avaliar o desempenho físico destes painéis. O desempenho físico dos painéis foi avaliado com base nas normas ABNT NBR 14810:2006, ANSI A208.1:1999 e BS EN 312:2003. Foi realizado uma análise de variância (ANOVA) para testar a influência dos fatores percentual de casca de aveia, percentual de adesivo e tipo de adesivo, e as interações entre estes fatores nas propriedades físicas dos painéis. Os resultados apontaram propriedades físicas, em alguns tratamentos superiores aos requisitos estipulados por normas consultadas. Conclui-se que os painéis produzidos com o adesivo poliuretano à base de óleo de mamona apresentaram melhor desempenho físico, se comparado aos painéis produzidos com o adesivo melamina formaldeído.

ABSTRACT Reconstituted wood panels are widely used in various branches of the wood industry, such as in the furniture sectors and various segments of urban and rural construction. In Brazil, agricultural and forestry residues are abundantly generated, making feasible the study, development and application of alternative and sustainable materials, produced from the use of these wastes. The aim of this study was to produce high-density homogenous panels with wood residues of Pinus elliottii and oat hulls (Avena sativa), pressed with two types of adhesive, castor oil-based polyurethane and melamine formaldehyde, and to evaluate the physical performance of these panels. The physical performance of the panels was evaluated based on the ABNT NBR 14810: 2006, ANSI A208.1: 1999 and BS EN 312: 2003 standards. Analysis of variance (ANOVA) was performed to test the influence of the factors percentage of oat hull, percentage of adhesive and type of adhesive, and the interactions between these factors on the physical properties of the panels. The results indicated physical properties, in some treatments superior to the requirements stipulated by the consulted standards. It was concluded that the panels produced with the castor oil-based polyurethane adhesive showed better physical performance when compared with the panels produced with the melamine formaldehyde adhesive.

ABSTRACT The aim of this research was to analysis the feasibility of production of wood particleboard with two alternative adhesives: epoxy ink waste and polyhydroxybutyrate polymer (BTH). Particleboard were produced with Pinus sp. wood specie wastes from sawmill process. For each alternative adhesive was proposed different combinations of parameters: time and temperature of press, pressure; alternative adhesive content and mass of wood particles. Two alternative adhesive contents were adopted, 10% and 20% replacing ureaformaldehyde adhesive. Mechanical properties (perpendicular tensile strength, pullout strengths of screw on face and top; modulus of elasticity and rupture) were determined according to ABNT NBR 14810:3 Brazilian Standard Code. The obtained results were compared to ABNT NBR 14810:3 and ANSI A.2018:1 Standard Codes requirements values. Particleboards produced with epoxy ink waste showed perpendicular tensile strength according to the minimum Standards requirements values. All proposed combinations to manufacture BTH polymer particleboards didn't show satisfactory mechanical properties in comparison to the Standard Codes values. Other combinations of wood species, time, pressure and temperature, epoxy ink waste and BTH polymer contents should be studied so that the requirements can be met.

ABSTRACT Over the years, the species of eucalyptus has become a multipurpose raw material. In addition, the most relevant aspect of the use for various purposes is related to the production of a high quality wood, coming from short duration plantations, which is fundamental to the current demand of the industries. However, its use in civil construction has not yet reached a level of importance, due to the low knowledge of many of its resistance properties and the consequent popular fear in the use of reforestation woods, in particular the Eucalyptus grandis. This research investigated its main mechanical properties, aiming to reinforce its constructive applications in wood structures. For this, two physical properties and fourteen mechanical properties, in two different moisture conditions of the samples were evaluated, according to the norm NBR 7190 (1997). In the first moisture content, the samples were stabilized at 30%, while the second level considered the content of 12%. It was obtained 3580 determinations for the sixteen properties. From the 14 mechanical properties, only 7 had significant increases with the moisture reduction (30% to 12%), consisting of the rupture modulus in the parallel and normal compressions, normal traction and static bending; modulus of elasticity in normal compression and static bending and in shear strength.

ABSTRACT: Eucalyptus urophylla consists in a wood-producing species, which offers a natural multiple raw material of good quality for applications in rural and civil constructions. However, Eucalyptus urophylla still has a small utilization as building parts and elements, resulting from the possible ignorance and low diffusion of its structural possibilities. Thereby, the present research aims to measure the main thirteen mechanical properties of Eucalyptus urophylla wood for two different moisture contents, 12% and 30% (green wood). Furthermore, in these two conditions of moisture content evaluation, volumetric mass densities were also evaluated. At the end of this evaluation, which included 2688 determinations, all the obtained results were statistically treated with t-test at a 5% of significance level in order to evaluate the influence of moisture content in the evaluated properties. Twelve mechanical properties were significantly affected by moisture content, and the behavior pattern consisted in increasing the values of the properties with the reduction of the moisture content.

ABSTRACT: Wood is a material that for years has been used by man for a variety of purposes, particularly in rural and civil constructions and furniture industry. The possibility of shortages of some wood species, the characterization of other unfamiliar species is an alternative source for use in civil and rural construction. This study aimed to determine, with the aid of Brazilian standard NBR 7190, physical and mechanical properties of Castelo (Calycophyllum multiflorum) wood specie. Twelve determinations were obtained by property, totaling 204 experimental values. In the characterization of wood, regression models were used to estimate the values of timber strength and stiffness as a function of apparent density, being density the physical property more simple to be obtained. The results of mechanical properties showed consistent with the performance of other species used in construction, which highlights the potential use of the Castelo wood in structural design. Regression models, apparent density was considered significant in the estimation of only 4 among the 14 properties for wood strength and stiffness.