BENDING STRENGTH AND STIFFNESS OF POLES OF ARGENTINEAN Eucalyptus grandis

E.a Torrán

Abstract


The present paper reports the results of an investigation regarding the determination of bending strength and stiffness in full-size poles of Argentinean Eucalyptus grandis. The importance of accurately knowing the mechanical properties of this material has increased with the increasing demand of utility poles of this species and with the use of modern procedures aimed at achieving a reliable and economical structural design. For this purpose an empirical research project with two samples containing new, green, untreated poles was carried out according to the procedures adopted by both the American standard ASTM D 1036 (2005) and the Argentinean standard IRAM 9529 (2004) for cantilever bending tests. Sample 1 enclosed 14 year-old poles with nominal length of 12 m and Sample 2 enclosed 11 year-old poles with nominal length of 8 m. The results found for the average circumference taper were similar to the values adopted by the American standard ANSI 05.1 (2002) and knot dimensions as well as knot ratio compared well with those permitted by this standard. The mean value found for maximum fi bre stress at ground line reached 62.9 N/mm2 for Sample 1 and 56.3 N/mm2 for Sample 2. These strength results are relatively high in comparison with values reported for seasoned sawn timber

of the same species and they compare well with those published by the American standard ANSI 05.1c (2004) for poles of different species. Both samples showed a coeffi cient of variation of 13 % for strength at ground line which is relatively low in comparison with those adopted by the American standard and may be considered an advantage of this material for structural purposes. The mean value found for modulus of elasticity reached 10935 N/mm2 for Sample 1 and 9546 N/mm2 for Sample 2, with a coeffi cient of variation of 14 % for both cases. Results also revealed signifi cant differences between mechanical properties values corresponding to the two samples containing poles with different sizes and age. The correlation coeffi cient between knot ratio and strength showed the insignifi cant values of 0.09 and 0.02 for Sample 1 and 2 respectively, and the corresponding results between modulus of elasticity and strength were 0.52 and 0.37.

Keywords: poles, Eucalyptus grandis, strength and stiffness


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