PSI - Issue 5

Patrícia C. Raposo et al. / Procedia Structural Integrity 5 (2017) 1097–1101 Patrícia C. Raposo et al. / Structural Integrity Procedia 00 (2017) 000 – 000

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2.3.2. Results Fig. 7 presents the obtained stress-displacement curves, which show some dispersion of the breaking strength values of the four specimens. In Table 4 is shown the rupture strength of the specimens that have a mean value compression strength parallel to the fibers of 59.1 MPa, with an associated COV of 25.2 %, which validates the high dispersion observed in the graphic results (Fig. 7). Due to control system failure, the results of two specimens were considered infeasible.

90

Specimen 3 Specimen 4 Specimen 5 Specimen 6

Table 4. Obtained compressive rupture strength.

80

70

Specimen Rupture strength (MPa) Mean (MPa) COV (%) 3 82.20

60

50

30 Strength ( σ ) (MPa) 40

4 5 6

62.17 45.77 46.26

59.1

25.2

20

10

0

0

0.5

1

1.5

2

2.5

Displacement ( δ ) (mm)

Fig. 7. Compressive strength VS displacement curve.

3. Conclusions In the current work’s experimental campaign, the specimens weren’t all made with the direction perfectly parallel to the fibers due to deficiencies of the beam. The wood water content influences the behaviour and properties of wood, due to changes such as retraction or expansion of wood, and consequent distortions and warping, respectively, inducing the variation of the strength and the elastic modulus, although when the water changes occur above the fibers saturation point, the properties remain practically unchanged [8]. The wood rupture under tensile strength, in a direction parallel to the fibers, has a linear behaviour between near 1/10 and 1/3 of the breaking resistance (Fig. 5). The parallel to the fibers tensile strength (Table 3) is superior to the parallel to the fibers compressive strength (Table 4), for specimens made without defects, thanks to the buckling of the fibers under compression. Acknowledgements The authors express their gratitude to Mr. Antero de Sousa for allowing the visit and use of material from the case study building, to UTAD for providing the test facilities, to Mr. Armindo, for helping in the preparation of the wood specimens, and to Mr. Augusto Oliveira for the replacement of the wood beam used in experimental campaign. References [ 1] D. A. L. d. Silva, F. A. R. Lahr, O. B. d. Faria, and E. Chahud, "Influence of wood moisture content on the modulus of elasticity in compression parallel to the grain," Materials Research, vol. 15, no. 2, 2012. [2] W. Sonderegger, K. Kránitz, C.-T. Blues, and P. Niemz, "Agging effects on physical and mechanical properties of spruce, fir and oak wood," Journal of Cultural Heritage, vol. 16, no. 6, pp. 883-889, 2015. [3] T. Nilsson and R. Rowell, "Historical wood - structure and properties," Journal of Cultural Heritage, vol. 13, no. 3, pp. S5-S9, 2012. [4] D. Sousa, "Reabilitação de uma casa do século XIX, de Felgueiras/Caracterização, diagnóstico das anomalias construtivas e bases para o projeto de restauro e reabilitação," Escola de Ciências e Tecnologias, UTAD, Vila Real, 2013. [5] NP-616 Madeiras. Determinação da massa volúmica , 1973. [6] NP-614 Determinação do teor de água. Madeiras , 1973. [7] NP-618 Ensaio de compressão axial. Madeiras , 1973. [8] M. Nocetti, M. Brunetti, and M. Bacher, "Effect of moisture content on the flexural properties and dynamic modulus of elasticity of dimension chestnut timber," European Journal of Wood and Wood Properties, vol. 73, no. 1, p. 9, 2015. [9] P. B. Cachim, 2ª, Ed. Construção em madeira . 2014.