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Ambiente Construído

versão On-line ISSN 1678-8621

Ambient. constr. vol.19 no.2 Porto Alegre abr./jun. 2019

https://doi.org/10.1590/s1678-86212019000200319 

Artigos

Physical and mechanical properties of Eucalyptus saligna wood for timber structures

Propriedades físicas e mecânicas da madeira de Eucalyptus saligna para estruturas de madeira

Marta Cristina de Jesus Albuquerque Nogueira1 

Diego Henrique de Almeida2 

Victor Almeida de Araujo3 

Juliano Souza Vasconcelos4 

André Luis Christoforo5 

Tiago Hendrigo de Almeida6 

Francisco Antonio Rocco Lahr7 

1Universidade Federal do Mato Grosso. Cuiabá - MT - Brasil

2Universidade Federal de Rondônia. Porto Velho - RO - Brasil

3Universidade de São Paulo. Piracicaba - SP - Brasil

4Universidade Estadual Paulista. Botucatu - SP - Brasil

5Universidade Federal de São Carlos. São Carlos – SP - Brasil

6Universidade de São Paulo. São Carlos - SP - Brasil

7Universidade de São Paulo. São Carlos - SP - Brasil


Abstract

Due to its great availability in planted forests in Brazil, Eucalyptus saligna appears as a good species to be exploited, in order to assist in the consumption of wood for construction purposes. The aim of this research was to determine the physical and mechanical properties of Eucalyptus saligna wood species for its use in civil construction. The evaluation was based on 16 physical and mechanical properties obtained according to NBR 7190 (1997) standard. Two values of moisture content were considered: 30% (above the fiber saturation point) and 12% (equilibrium moisture content) according to NBR 7190 (1997). All obtained results obtained were statistically analyzed according to the t-test at the 5% level of significance. In addition, the characteristic strength properties were also determined, for batch classification in the strength classes recommended by the Brazilian standard. Eucalyptus saligna had an apparent density of 0.58 g/cm3 and a basic density of 0.73 g/cm3. The mechanical properties, presented fc0 and fc0,k equal to 46.80 and 32 MPa, respectively. The results indicated that Eucalyptus saligna wood can be used in the construction of timber structures as structural member

Keywords: Eucalypt; Strenght; Stiffness; Timber structures

Resumo

A fim de auxiliar no consumo de madeira pela construção civil, o Eucalyptus saligna surge como uma boa oportunidade a ser explorada, devido à sua grande disponibilidade em florestas plantadas no Brasil. O objetivo dessa pesquisa foi determinar as principais propriedades físicas e mecânicas da madeira de Eucalyptus saligna para sua utilização na construção civil. Esta avaliação baseou-se em 16 propriedades físicas e mecânicas obtidas de acordo com a norma NBR 7190 (1997). Dois valores de teor de umidade foram considerados: 30% (acima do ponto de saturação das fibras) e 12% (teor de umidade de equilíbrio) de acordo com a NBR 7190 (1997). Todos os resultados obtidos foram analisados estatisticamente de acordo com o teste t ao nível de 5% de significância. Além disso, também foram determinadas as resistências características para classificação do lote nas classes de resistência recomendadas pela norma. O Eucalyptus saligna apresentou densidade aparente igual a 0,58 g/cm3 e densidade básica igual a 0,73 g/cm3. Em relação às propriedades mecânicas, apresentou fc0 e fc0,k iguais a 46,80 e 32 MPa, respectivamente. De acordo com os resultados, foi possível concluir que o Eucalyptus saligna pode ser utilizado na construção de estruturas de madeira como elemento estrutural.

Palavras-chave: Eucalipto; Resistência; Rigidez; Estruturas de madeira

Introduction

Wood is a natural raw material obtained from natural or planted forests (MAZURANA et al., 2011; MATOS et al., 2012; TER STEEGE et al., 2016; TUISIMA-CORAL et al., 2017). In Brazil, Eucalyptus tree genus are utilized for a variety of applications, among them: pulp and paper, charcoal, essential oils, boards, firewood, construction, and furniture (GUIMARÃES JUNIOR et al., 2009, 2011; ALMEIDA; BRITO; PERRÉ, 2010; IWAKIRI et al., 2013; SOARES et al., 2015; MATTOS et al., 2014; NEIVA et al., 2015; BALLESTEROS et al., 2015).

For timber building structures, the knowledge of physical and mechanical properties of wood are very important, for its rational use (CALIL JUNIOR; LAHR; DIAS, 2003; CALIL JUNIOR; MOLINA, 2010; ANDRADE JUNIOR et al., 2014; LAHR et al., 2017a). The very purpose of wood characterization is to evaluate its possible use as a structural member (VIVIAN et al., 2010; CHEN; GUO, 2016, 2017; LAHR et al., 2017b). For this purpose, Brazilian Standard Code NBR 7190 (Associação Brasileira de Normas Técnicas (ABNT, 1997) presents all experimental procedures for the conduction of the testing of the specimens.

Another important characteristic of wood for timber structures is its moisture content (KOLMANN; CÔTÈ, 1968; HERZOG et al., 2000). In general, wood with higher moisture content presents lower mechanical properties (MATOS; MOLINA, 2016; ALMEIDA et al., 2016) and dimensional stability that is also influenced by moisture content (ALMEIDA et al., 2017).

Eucalyptus genus presents a fast growth that causes internal tension (growth stress) (BELTRAME et al., 2015), and besides this, the dry process, must be carefully performed to minimize the occurrence of drying defects, for examples, bows, crooks, top cracks, cups and twists (ELEOTÉRIO et al., 2014; REZENDE et al., 2015). These defect types influence the physical and mechanical properties of wood (LIMA et al., 2004).

Due to the scarce amount of reports available for this species, this research was aimed at determining the physical and mechanical properties of Eucalyptus saligna wood from different planted forests at two moistures content regimes (12 and 30%) for its use as structural timber.

Materials and methods

Eucalyptus saligna wood from a planted forest area in the State of São Paulo, Brazil was used for this research. 20-year old Eucalyptus saligna logs with an average 35 cm diameter were selected for the study. After the primary processing of the logs, the sawn timber boards were submitted to natural drying of the moisture contents adopted for this research: first above the fiber saturation point (30%) and at 12% moisture content as prescribed in NBR 7190 (1997).

Test specimens were prepared for physical and mechanical properties (Table 1) according to the Brazilian Standard, NBR 7190 (1997). For each property studied, moisture content was determined for 12 specimens according to NBR 7190 (1997) (except for the apparent density (ρap) which is always determined at 12% m.c). For this purpose, 372 specimens were prepared. Toughness tests were carried out in Charpy machine according to D143 (AMERICAN…, 1999) and, another test specimen was carried out in AMSLER with load capacity equal to 25,000 kgf.

Table 1 Physical and mechanical properties of Eucalyptus saligna 

Properties Symbol
Apparent density ρap
Basic density ρp
Compression parallel to the grain fc0
Compression perpendicular to the grain fc90
Tension parallel to the grain ft0
Tension perpendicular to the grain ft90
Modulus of rupture in static bending fM
Modulus of elasticity in compression parallel to the grain Ec0
Modulus of elasticity in compression perpendicular to the grain Ec90
Modulus of elasticity in tension parallel to the grain Et0
Modulus of elasticity in static bending EM
Shear parallel to the grain fv0
Cleavage parallel to the grain fs0
Parallel hardness fH0
Perpendicular hardness fH90
Toughness W

All the results from these sixteen physical-mechanical properties tests, with the exception of the apparent density (considered at 12% moisture content), were analyzed through t-test at a significance level of 5% (or P-value ≤ 0.05), investigating the moisture content influence.

The characteristic strengths were determined using Equation 1, according to NBR 7190 (1997). After determining the strength properties of 12 specimens, the results were placed in ascending order (f1 <f2 <f3 <fn) for the calculation of the characteristic strength of the wood (fk), the value of the characteristic strength could not be less than f1 and 70% of the average value of strength. Characteristic strength values were determined only to Eucalyptus saligna wood at 12% moisture content at 12%, according to NBR 7190 (1997).

fk=2.f1+f2+.+fn21n21fn2.1,1 Eq. 1

Results and discussions

Tables 2, 3, 4 and 5 present mean values (x), standard deviation (Sd), number of specimens (n) and P-values to physical and mechanical properties for each moisture content (MC), 12 and 30%, for Eucalyptus saligna.

Table 2 Densities of Eucalyptus saligna 

Properties MC (%) n x Sd P-value
ρap (g/cm3) 12 77 0.73 0.16 ---
ρb (g/cm3) 30 73 0.59 0.16 0.6670
12 77 0.58 0.12

Table 3 Strength properties of Eucalyptus saligna 

Properties MC (%) n x Sd P-value
fc0 (MPa) 30 75 37.70 7.90 0.0000
12 71 46.80 14.30
fc90 (MPa) 30 74 4.60 2.10 0.5711
12 75 4.80 2.20
ft0 (MPa) 30 74 74.50 33.40 0.0014
12 74 95.50 44.40
ft90 (MPa) 30 77 3.10 1.20 0.0000
12 77 4.10 1.70
fM (MPa) 30 73 74.10 14.10 0.0004
12 74 91.60 38.20

Table 4 Stiffness properties of Eucalyptus saligna 

Properties MC (%) n x Sd P-value
Ec0 (MPa) 30 75 13,076 4,021 0.0023
12 71 15,261 4,442
Ec90 (MPa) 30 74 458 212 0.5739
12 75 478 217
Et0 (MPa) 30 74 13,682 3,765 0.0018
12 74 15,981 4,939
EM (MPa) 30 73 12,306 2,640 0.0666
12 74 13,313 3,852

Table 5 Mechanical properties of Eucalyptus saligna 

Properties MC (%) n x Sd P-value
fv0 (MPa) 30 73 11.00 2.10 0.0000
12 73 14.00 3.90
fs0 (MPa) 30 75 0.65 0.18 0.0000
12 76 0.88 0.27
fH90 (kN) 30 73 5,160 1,330 0.0047
12 73 6,330 3,150
fH0 (kN) 30 76 5,580 1,830 0.0095
12 73 6,770 3,020
W (N∙m) 30 76 10.8 4.20 0.0018
12 76 13.3 5.40

Basic density decreased from 30 to 12% in about 1.69%. Through the t-test, the ρb not suffered the influence by the variation in moisture content (Table 2). Eucalyptus saligna wood studied in this research had an apparent density at 12% moisture content lower than the one determined by Müller (2014) for Eucalyptus benthamii wood (ρap = 0.61 g/cm3). However, the basic density of E. benthamiib = 0.52 g/cm3) was lower than the one in this study. The density values obtained in this study were close to those of other Eucalyptus wood species, such as: Eucalyptus grandisap = 0.57 g/cm3), and E. dunniiap = 0.77 g/cm3), E. urophyllaap = 0.55 g/cm3) and E. tereticornis (BHAT et al., 1987; EVANGELISTA et al., 2010).

The average density values obtained for Eucalyptus saligna wood species compare well with Brazilian native species, such as Cedro-amargo (Cedrela odorata), Cedro-doce (Cedrella sp.) and Cedrorana (Cedrelinga catenaeformis) (DIAS; LAHR, 2004).

The strength properties of Eucalyptus saligna indicated increases with the moisture content decrease (30 to 12%) such as 19.44% (9.1 MPa) compression parallel to grain, 0.2% (4.17 MPa) compression perpendicular to grain, 21.99% (21 MPa) tension parallel to grain, 24.39% (1 MPa) tension perpendicular to grain and 19.10% (17.5 MPa) in modulus of rupture in static bending. Thus, the t-test analysis showed ft0, ft90 and fc0 suffered influence in their mean values when these properties were submitted to the moisture decrease (P-value ≤ 0.05), similar to the results obtained by Almeida et al. (2016). This situation was not similar in fc90, because it did not present significant difference in their mean values with the decrease of moisture content (Table 3).

The modulus of elasticity of Eucalyptus saligna indicated increases with the moisture content decrease (30 to 12%) such as 14.31% (2,185 MPa) in compression parallel to grain, 4.15% (20 MPa) in compression perpendicular to grain, 14.39% (2,299 MPa) in tension parallel to grain and 7.56% (1,007 MPa) in EM. The analysis of t-test identified the Ec0 and Et0 had significant influence in their properties with moisture content decrease (P-value ≤ 0.05), whereas Ec90 and EM did not have any significant differences with regard to the decrease of moisture content (Table 4).

Finally, Table 4 revealed increases in the properties of shear parallel to the grain (20.74% or 3 MPa), cleavage parallel to the grain (26.14% or 0.23 MPa), perpendicular hardness (17.58% or 1.19 kN), parallel hardness (18.48% or 1.17 kN) and toughness (18.80% or 2.5 N∙m) with reduced moisture content from 30% to 12% (KOLMANN; CÔTÈ, 1968). The t-test, indicated that all these five properties had significant effect with the reduced moisture content (P-value ≤ 0.05).

The batch of Eucalyptus saligna wood presented a compression strength parallel to grain characteristic value (fc0,k) equal to 32 MPa (Table 6). Therefore, it was possible to classify this batch into class C30 of the dicotyledons according to the Brazilian Standard Code NBR 7190 (1997). The strength values of Eucalyptus saligna wood reported here was higher than that of Eucalyptus benthamii wood as determined by Müller et al. (2014).

Table 6 Average (x) and characteristic strength (fk) values of Eucalyptus saligna 

Properties x fk
fc0 (MPa) 46.80 32.00
fc90 (MPa) 4.80 3.40
ft0 (MPa) 95.50 66.00
ft90 (MPa) 4.10 3.00
fM (MPa) 91.60 64.00
fs0 (MPa) 0.88 0.60
fv0 (MPa) 14.00 12.00

The batch of Eucalyptus saligna wood presented a compression strength parallel to grain characteristic value (fc0,k) equal to 32 MPa (Table 6). Therefore, it was possible to classify this batch into class C30 of the dicotyledons according to the Brazilian Standard Code NBR 7190 (1997). The strength values of Eucalyptus saligna wood reported here was higher than that of Eucalyptus benthamii wood as determined by Müller et al. (2014).

Lima et al. (2014) reported basic density, compression parallel to the grain and shear parallel to the grain of Eucalyptus resinifera wood, equal to 0.74 g/cm3, 55.87 and 16.16 MPa, respectively, all of which are higher than those determined for Eucalyptus saligna wood.

Almeida and Dias (2016) determined the apparent density and the compression parallel to grain of Lyptus ® wood species (Eucalyptus hybrid) equal to 0.55 g/cm3 and 53.6 MPa, respectively. Even though the density was low when compared to Eucalyptus saligna, Lyptus presented a fc0 mean value higher than the batch of Eucalyptus saligna.

Conclusion

The present study concluded that:

  1. the batch of Eucalyptus saligna was classified under strength class C30 of the dicotyledons, after a large test campaign, and thus, it can be used safely as a structural member on timber structures;

  2. Eucalyptus saligna showed fc0 equal to 46.80 MPa and apparent density 0.58 g/cm3 at 12% m.c.; and

  3. at this reduced moisture content, 11 from 14 evaluated mechanical properties presented significant differences. Four strength properties showed an improvement in their mean values: fc0, ft0, ft90 and fM. Ec0 and Et0 showed an increasing trend in their average values with increasing m.c.

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Received: December 17, 2017; Accepted: July 14, 2018

Marta Cristina de Jesus Albuquerque Nogueira

Departamento de Arquitetura | Universidade Federal do Mato Grosso | Av. Fernando Corrêa da Costa, 2367, Boa Esperança | Cuiabá - MT - Brasil | CEP 78060-900 | Tel.: (65) 3615-8000 | E-mail: mcjanj@gmail.com

Diego Henrique de Almeida

Departamento de Engenharia Civil | Universidade Federal de Rondônia | Rodovia BR-364, km 9,5 | Porto Velho - RO - Brasil | CEP 76801-059 | Tel.: (69) 2182-2100 | E-mail: diegoestruturas@gmail.com

Victor Almeida de Araujo

Departamento de Ciências Florestais | Universidade de São Paulo | Av. Pádua Dias, 11 | Piracicaba - SP - Brasil | CEP 13418-900 | Tel.: (16) 97401-0030 | E-mail: victor@usp.br

Juliano Souza Vasconcelos

Departamento de Engenharia Rural | Universidade Estadual Paulista | Av. Universitária, 3780, Altos do Paraíso | Botucatu - SP - Brasil | CEP 18610-034 | Tel.: (14) 3880-7402 | E-mail: julianojsv@yahoo.com.br

André Luis Christoforo

Departamento de Engenharia Civil | Universidade Federal de São Carlos | Rodovia Washington Luís, km 235, SP-310 | São Carlos – SP – Brasil | CEP 13565-905 | Tel.: (16) 3361-2081 |E-mail: christoforoal@yahoo.com.br

Tiago Hendrigo de Almeida

Departamento de Engenharia de Materiais, Escola de Engenharia de São Carlos | Universidade de São Paulo | Av. João Dagnone, 1100, Jardim Santa Angelina | São Carlos - SP - Brasil | CEP 13563-120 | Tel.: (16) 3373-8677 | E-mail: tiago.hendrigo@gmail.com

Francisco Antonio Rocco Lahr

Departamento de Engenharia de Estruturas | Escola de Engenharia de São Carlos | Universidade de São Paulo | Av. Trabalhador São Carlense, 400, Centro | São Carlos - SP - Brasil | CEP 13566-590 | Tel.: (16) 3373-9479 | E-mail: frocco@sc.usp.br

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