Francisco Antonio Rocco Lahr | Universidade de São Paulo (original) (raw)

Papers by Francisco Antonio Rocco Lahr

BioResources

Particleboards were made using particles from sugarcane bagasse and eucalyptus residues of the pu... more Particleboards were made using particles from sugarcane bagasse and eucalyptus residues of the pulp industry. The particleboard properties were evaluated according to ABNT NBR 14810-1 (2013), ABNT NBR 14810-2 (2013), and ANSI A208.1 (1999) standards, which compared the efficiency of castor oil-based polyurethane resin (PU-Castor) and urea-formaldehyde resin (UF). The particleboards were composed of 60% wood particles and 40% bagasse, with a 10% adhesive dose based on the dry mass of particles. The following parameters were evaluated: apparent density, moisture content (MC), thickness swelling after 24 h, modulus of rupture (MOR), modulus of elasticity to static bending (MOE), and internal bond strength of panels (IB). The results obtained demonstrated the potential use of eucalyptus and sugarcane bagasse residues in the production of high-density particleboards. The panels produced with PU-Castor showed greater efficiency, and their physical and mechanical properties were compatible...

BioResources, 2019

Fast-growing species are gradually being used more in the Brazilian timber market. Such species a... more Fast-growing species are gradually being used more in the Brazilian timber market. Such species are more susceptible to deterioration and require conservative treatment to prolong their service life. This work analyzed the influence of the chromated copper arsenate oxide (CCA-A) treatment on the physical-mechanical properties of the tropical woods Simarouba amara (C20), Cedrelinga catenaeformis (C30), and Erisma uncinatum (C40), which were chosen to cover the three lower strength classes, as prescribed by Brazilian Standard Norm. The CCA-A was applied to the wood with the vacuum-pressure process, which could increase the amount of surface defects and weaken the wood properties. To investigate the influence of this process, complete characterization of the species with and without CCA-A was performed, and a Tukey’s multiple comparisons test (5% significance level) was applied. Also, scanning electron microscopy (SEM) images and energy dispersive spectra (EDS) were obtained to investi...

BioResources, 2019

Natural and artificial weathering treatments were studied to determine the change of wood propert... more Natural and artificial weathering treatments were studied to determine the change of wood properties as a function of exposure time. This paper aimed to provide general information about the mechanical performance of wood under natural and artificial weathering treatments and define a relationship between them. The eight strength classes of ABNT NBR 7190 (1997) were considered, in addition to a paired sampling approach. The modulus of elasticity and conventional strength value in static bending, strength in compression parallel to the grain, hardness perpendicular to the grain, and the elastic limit in the static bending test were investigated. Linear regression models for mechanical performances under artificial and natural aging treatments of the exposure time were made and tested using an analysis of variance. According to the results, 360 days of natural weathering provoked a change in mechanical performance of 15.72% that included a decrease in strength and modulus of elasticit...

Wood Research, 2020

For safety reasons, wood strength values are calculated based on their characteristic values. Bra... more 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 (f v0,k) to compression strength along the grain (f c0,k) (f v0,k =0.12 f c0,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.

Revista Facultad de Ingeniería Universidad de Antioquia, 2015

Experimental investigations were carried out for assessing the influence of thermal loadings on t... more Experimental investigations were carried out for assessing the influence of thermal loadings on the physical and mechanical properties of plain concrete after fire exposure. Cylindrical specimens were subjected to thermal loading at different temperatures inside a muffle furnace; while cubic specimens were exposed to direct flame following the ISO 834 standard curve. For both specimens' geometries the thermal loading was applied until it reached the selected temperature which was held for an hour. The specimens were tested for weight loss, optical microscopy, ultrasonic pulse velocity, residual compressive strength, X-ray diffraction and porosity. It has been observed that with the increase in the thermal loading, the physical and mechanical properties experienced significant detriment. The results suggested that the ultrasonic pulse velocity method is appropriate as an indicator of concrete compressive strength and microstructural properties after fire exposure.

Revista Ciência da Madeira - RCM, 2010

Resumo: O objetivo desse trabalho foi avaliar algumas propriedades da madeira de Eucalyptus uroph... more Resumo: O objetivo desse trabalho foi avaliar algumas propriedades da madeira de Eucalyptus urophylla, no sentido radial e em duas posições no sentido longitudinal. O material, com 6,3 anos, foi proveniente da Votorantim Metais Zinco S.A., localizada em Vazante, Minas Gerais,. Utilizaram-se seis árvores, das quais foram retiradas as duas primeiras toras da base, ambas com comprimento de três metros. As toras foram desdobradas e da parte superior de cada prancha diametral retirou-se uma amostra de madeira, com um metro de comprimento, de onde prepararam-se os corpos-de-prova para a determinação das propriedades estudadas. Avaliaram-se a massa específica básica e aparente a 12% de umidade, contrações totais e a 12% de umidade, dimensões de fibras e vasos, e os módulos de ruptura e elasticidade em flexão estática. Houve tendência de aumento, no sentido medulacasca, da massa específica, contração longitudinal total, comprimento das fibras, diâmetro dos vasos e dos módulos de ruptura e elasticidade. A contração longitudinal parcial, os coeficientes anisotrópicos e a frequência de vasos diminuíram nesse sentido. As contrações tangenciais e radiais, a largura, diâmetro do lume e a espessura da parede das fibras apresentaram outros padrões de variação. Somente a contração volumétrica parcial, contração radial parcial e frequência de vasos apresentaram diferenças significativas entre a primeira e segunda tora. As principais correlações observadas foram do módulo de ruptura e elasticidade com a massa específica e do diâmetro do lume das fibras com a massa específica básica, com contração longitudinal total e com o módulo de ruptura em flexão estática. Palavras-chave: eucalipto; massa específica; contração; anatomia da madeira; flexão estática.

CERNE, 2012

En Costa Rica, el concreto, el acero y los plásticos son los materiales más utilizados para const... more En Costa Rica, el concreto, el acero y los plásticos son los materiales más utilizados para construcción. Mientras que por otro lado la utilización de madera de plantaciones forestales se ha incrementado en los últimos años. Ante tal situación en el presente estudio, fueron determinadas las propiedades físicas y mecánicas de tableros terciados manufacturados con chapas de Gmelina arborea, Tectona grandis y Acacia mangium provenientes de plantaciones forestales para usos estructurales. Se analizaron tres tableros (plywood) de cada una de las especies, se realizó una caracterización general y se midieron sus principales propiedades físicas y mecánicas. Los resultados mostraron que los tableros producidos con árboles de T. grandis en general presentan propiedades físicas y de resistencia superiores a las de G. arborea y A. mangium. De acuerdo con las normas del Voluntary Products Standart PS 1-95 y PS 1-09 de los Estados Unidos, es posible producir tableros estructurales de grado 3 con...

TECNOLOGIAS AVANÇADAS E SUAS ABORDAGENS -V1

Os produtos resultantes do desenvolvimento tecnológico da madeira incorporam cada vez mais contro... more Os produtos resultantes do desenvolvimento tecnológico da madeira incorporam cada vez mais controle e precisão nos processos construtivos. Os painéis de CLT são uma alternativa bastante versátil, aplicável como um elemento estrutural rígido e autoportante. A modelagem numérica somada aos estudos experimentais, apresenta-se como uma ferramenta capaz de representar o comportamento mecânico dos painéis de CLT. Este capítulo tem como objetivo investigar a aplicação do método dos elementos finitos (MEF) em madeira lamelada colada cruzada (CLT). Para tanto, o estudo apresenta um breve histórico do emprego do material, bem como o desenvolvimento da tecnologia do sistema construtivo da CLT no Brasil e no mundo. Além da aplicação da simulação numérica em MEF como uma ferramenta na análise estrutural do produto. Conclui-se que o processo de fabricação é padronizado e a que a montagem é rápida, o que garante produtividade e racionalização da construção civil. Além disso, este tipo de método co...

TECNOLOGIAS AVANÇADAS E SUAS ABORDAGENS -V1

HOLOS

Ainda que o Brasil não sofra com catástrofes naturais e sejam incomuns episódios de terrorismo às... more Ainda que o Brasil não sofra com catástrofes naturais e sejam incomuns episódios de terrorismo às edificações, a crescente indústria da construção civil demanda práticas cada vez mais audaciosas que divergem do caminho da segurança e da integridade estrutural. Este fato tem gerado cada vez mais preocupação no meio técnico, uma vez que existem profissionais, por desconhecimento do colapso progressivo, negligencie a sua possibilidade e não anteveja os possíveis cenários de dano. Não obstante, a normas no cenário nacional carecem de explicações e de práticas de prevenção a este fenômeno. Isto posto, o presente trabalho tem função de analisar os métodos de aplicação genérica, podendo concluir qual o melhor método a ser utilizado. Um edifício didático foi modelado com a intenção de aplicar três diferentes métodos, chegando-se a conclusão que a metodologia adotada pela norma UFC 04-023-03 de 2009, além de resistir às solicitações típicas do fenômeno de colapso considerado, apresentou acré...

HOLOS

Revista Árvore

When wood is exposed outdoors, a combination of chemical and mechanical factors and solar radiati... more When wood is exposed outdoors, a combination of chemical and mechanical factors and solar radiation contribute to what is described as weathering, being the main degradation agent in this environment. This paper aims to investigate the effect of artificial weathering on mechanical and physical properties of Eucalyptus sp. and Cupiúba (Goupia glabra) woods simulating natural weathering effects. Samples were aged in UV radiation chamber with humidity and temperature control for 100, 200, 300 and 400 hours, considering aging cycles according to ASTM G154 (2006). Wood properties investigated were Conventional value of strength in static bending (fM), Modulus of elasticity in static bending (EM), strength in compression parallel to grain (fc0) and Janka Hardness (fH) according to ABNT NBT 7190 (1997). Effects of artificial weathering on wood properties were evaluated by statistical analysis at 5% significance level. Most of the wood properties investigated did not present significant cha...

Revista Árvore

WOOD RESEARCH 67(4) 2022

In Brazil, some tile manufacturers have proposed a 10% (5.5°) slope between chords to minimize ti... more 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°).

WOOD RESEARCH 67(4) 2022

European Journal of Wood and Wood Products

Given the need for durable and low-maintenance products, thermal modification has emerged as an e... more Given the need for durable and low-maintenance products, thermal modification has emerged as an environmentally friendly alternative, replacing chemical treatments. Although the literature reports a large number of articles related to the wood thermal treatment, nevertheless there is a much smaller number related to the thermal treatment of Oriented Strand Board (OSB) panels, which are scarce, limited or contradictory. This panel is used as a building material for internal and covered exterior functions in roofs, walls, floors, structural elements and other uses, currently being widely studied. Therefore, this research aims to present a bibliometric and systematic literature review on heat treatment of OSB panels published between 2000 and 2020 in the Scopus database, through extensive bibliographic review and using a simple and integrative systematic, containing its metrics and main findings. It was found that, despite the progressive growth of interest from the scientific community in relation to wood modification, thermal-based modifications still have much less studies compared to other techniques. At the end, gaps, opportunities and potential areas for future research related to thermal modification of panels are presented.

European Journal of Wood and Wood Products

SSRN Electronic Journal

Oriented strand board (OSB) consists of wood particles glued by resins, whose composite can be de... more Oriented strand board (OSB) consists of wood particles glued by resins, whose composite can be deteriorated by organisms due to construction uses in aggressive conditions. To improve the panel resistance against these organisms, especially when low natural durability woods are used, the panel treatment is necessary. This study evaluated physical and mechanical properties of OSB manufactured with Paricá (Schizolobium amazonicum), native low-density forest wood, whose strands were also treated by chromated copper borate preservative (CCB) and glued (8%, 10% and 12% content) with castor-oil based polyurethane adhesive. Panel performance was evaluated using the EN 300 and ABNT NBR 14810-2 requirements. From analysis of variance (5% significance level), the use of CCB promoted a significant reduction in the values of physical properties (thickness swelling and water absorption) and did not promote reduction in the mechanical properties of the manufactured panels. All composites manufactured showed highly satisfactory performance requirements. As the levels of adhesive resulted and composites with physical and mechanical properties statistically equivalent to each other, it can be concluded that the panels produced with 8% adhesive content and treated with CCB resulted in the best treatment, since it reaches the minimum standard with a smaller amount of resin (more economical).

BioResources

BioResources, 2019

Wood Research, 2020

Revista Facultad de Ingeniería Universidad de Antioquia, 2015

Revista Ciência da Madeira - RCM, 2010

CERNE, 2012

TECNOLOGIAS AVANÇADAS E SUAS ABORDAGENS -V1

HOLOS

Revista Árvore

WOOD RESEARCH 67(4) 2022

European Journal of Wood and Wood Products

SSRN Electronic Journal

A housing system that uses wood in its structure coincides with any construction process that int... more A housing system that uses wood in its structure coincides with any construction process that integrates, with coherence and balance, one or more set of elements and/or structural subsystems made with this raw material. Therefore, a wooden house is any system that uses this raw material in its structure and or walls, pure or mixed with other materials. Despite its popularity, wooden houses do not have a standardized classification to define and organize their main aspects. In the literature of wooden buildings, most authors emphasize structural systems for large spans (bridges, roofs, hangars, etc.). Thus, wooden housing classification reflects a tortuous theme of literature, considering many criteria and analysis of different aspects, along with few studies and limited subjects for this particular theme. This study was formed by two parts: the state of the art about the wooden housing techniques commercially produced worldwide, and the proposal of the standardized classification to cover and enclose the main aspects analyzed in this particular topic, i.e., manufacturing level and chronological origin. Sixteen construction typologies of wooden housing were analyzed and classified. This classification should assist in a better understanding of distinct wooden housing techniques commercially produced worldwide, diffusing their concepts and possibilities as forestry-timber products.

In wood structures, the elements subjected to bending stresses, such as the beams, present a frac... more In wood structures, the elements subjected to bending stresses, such as the beams, present a fracture initiated in the tensile region, and under these conditions, the use of laminated composite materials is presented as an alternative solution in the form of repair or reinforcement. This research aimed to evaluate the influence of the use of carbon fibers laminated composites in tensile reinforcement in the direction parallel to grain of Pinus elliotti and Manilkara huberi wood species. The Viapol two-component epoxy adhesive was used in the lamination and fixation of the unidirectional carbon fiber in the wood species. Ten specimens with no defects (reference) and 10 specimens were prepared for each crack length (25 and 50mm) with and without the reinforcement (60mm × 50mm) by the laminated composite. The tensile tests were performed in accordance with the requirements of the Brazilian standard ABNT NBR 7190 (1997). From the results of the statistical analysis, the use of the carbon fiber composite was able to restore the tensile strength of the cracked samples (partial or total) in relation to samples without defects, demonstrating the potential of the laminates in carbon fibers as an alternative solution in repair for both wood species.

Wood has several advantages as structural material. For this use to be applied in a safe way, it ... more Wood has several advantages as structural material. For this use to be applied in a safe way, it is necessary to know the statistical behavior of the mechanical properties. Some works and normative codes, such as the "Brazilian timber standard" (as well as its review project), accepts a normal distribution model for determining the characteristic value of compressive strength parallel to wood fiber, with the adoption of a coefficient of variation for this property equal to 18 %. This work evaluates the distribution model of compressive strength parallel to the fibers, as well as the coefficient of variation of this property. Tests and statistical treatment were performed in compression parallel to the fibers for 7 species of hardwood commonly found in Brazil. It was observed that the compressive strength of wood actually follows a normal distribution, and the adoption of an average coefficient of variation equal to 18 % is acceptable and in favor of safety.

Wood strength values are calculated based on the characteristic value, which corresponds to the 5... more Wood strength values are calculated based on the characteristic value, which corresponds to the 5 % percentile of a given probability distribution model. For a few number of samples (12 samples), the Brazilian standard establishes an estimator of the characteristic compressive strength parallel to grain of the wood, which may provide a different result when compared with the characteristic value coming from a suitable probability distribution model. Considering the strength results in the parallel compression to the grain of 45 wood species of the hardwood group, Normal, LogNormal, Weibull and Exponential probability distribution models were used for each specie with the purpose of determining the one with the highest adhesion. Calculated the characteristic values by the best probability model distribution, an analysis of variance (ANOVA) was performed in the estimation of the characteristic value of compressive strength, making it possible to identify the most significant terms of the models as well as the quality of the adjustment obtained on such models. The proposed regression model (R 2 adj= 96,56 %) proved to be equivalent to the empirical model of the Brazilian standard. The model proposed here only depends on the mean and the lowest value obtained from the compressive strength in the parallel direction to the grain.

To ensure the safety of wooden structures, estimation of wood strength is based on the characteri... more To ensure the safety of wooden structures, estimation of wood strength is based on the characteristic strength values. The Brazilian standard (NBR, in Portuguese Norma Brasileira Regulamentadora) 7190 proposes equations to estimate the strength properties with a simplified procedure, which allows obtaining the characteristic values through relations that correlate different mechanical properties. Using these equations, the values of tensile (f t0,k) and shear (f v0,k) strength can be calculated in a simplified way from the compressive strength (f c0,k) values. In the present work, 36 tropical hardwood species were evaluated for tensile, shear and compressive strength in the direction parallel to the grain, with a total of 1296 experimental measurements, and the precision of the relations defined by the Brazilian standard was assessed using the analysis of variance (ANOVA) method. Two-parameter regression models, based on linear, exponential, logarithmic and geometric functions, were used as an alternative proposal for the estimation of the strength properties. The statistical analysis validated the proposed relations, with the linear (f t0,k) and geometric (f v0,k) regression models being the models of best fit, with the coefficients of determination (R 2) equal to 63,02 % and 70,15 %, respectively. In addition, new simplified equations were suggested. The least squares method was used to determine the optimal coefficient (α) for validation of the Brazilian standard equations. The obtained coefficients validated the tensile strength relationship (f t0,k = f c0,k / 0,77), but failed to validate the shear strength relationship (f v0,k = 0,12• f c0,k). In the latter case, the obtained values were significantly higher (up to 91 % higher) when compared to those estimated by the Standard.

This research intends to evaluate the relation, aided by the Brazilian Standard and statistical a... more This research intends to evaluate the relation, aided by the Brazilian Standard and statistical analysis (Kruskal-Wallis ANOVA and bootstrap technique), between physical and mechanical properties of Cambará-Rosa wood harvested from three different regions: Vera, Mucajaí and South Rondonia. In addition, the possibility to estimate (regression models) physical and mechanical properties in function of apparent density was analyzed. Different climate and soil conditions which tree thrives may influence its growth and, consequently, its properties values. The results of ANOVA indicated an elevated equivalence index for all three regions. The bootstrap technique led to similar results for Vera and Mucajai regions, and for South Rondonia region, equivalence index equals to 89 %. The ANOVA results to estimate physical and mechanical properties in function of apparent density indicated that it is not possible to perform such estimates for Cambará-Rosa wood species.