Implications in the design of a method for visual grading and mechanical testing of hardwood structural timber for designation within the European strength classes

  • Guillermo Riesco Muñoz
  • Andrés Remacha Gete
  • Francisco Pedras Saavedra
Keywords: density, grading rule, MOE, MOR, testing procedure


The international strength class system (EN 338:2003) is based on a testing standard (EN 408:2004) that is not easy to use with hardwoods, although some of this type of timber, such as European oak (Quercus robur L.), is highly appreciated for construction purposes. This study proposes specifications for sampling design, visual grading and mechanical testing of oak wood. With this aim, 27 adult oaks were felled and sawn into pieces. A sample of quarter-sawn planks was selected, then air-dried and planed to 50x100x2,000 mm. The beams were visually graded in accordance with ten standards, and were mechanically tested, at an average wood moisture content of 21%. The Spanish visual grading standard UNE 56544:2007 was the most effective for categorizing the pieces. According to this standard, 39% of the sampled beams were suitable for structural use. The mean value of modulus of elasticity (11,702 N mm-2) and characteristic density (714 Kg m-3) enable preliminary designation of the wood in visual grade ME-2, to European strength class D40. However, the bending strength was too low for inclusion of the timber in the European strength classes. Criteria are proposed for elaborating visual grading rules for oak wood and for structural beam testing in order to allocate oak visual strength grades into strength classes.


Download data is not yet available.


Adell Almazán F.J., Hermoso Prieto E., Arriaga Martitegui F., Richter C., 2008. Comparison of the Spanish visual strength grading standard for structural sawn timber (UNE 56544) with the German one (DIN 4074) for Scots pine (Pinus sylvestris L.) from Germany. Holz als Roh-und Werkst 66(4), 253-258.

AENOR, 1972. UNE 56525:1972. Clasificación de la madera aserrada de construcción. AENOR, Madrid. 2 pp.

AENOR, 1978. UNE 56528:1978. Preparación de probetas para ensayos. AENOR, Madrid. 3 pp.

AENOR, 2005. EN 1912:2005+A2:2008. Madera estructural. Clases resistentes. Asignación de calidades visuales y especies. AENOR, Madrid. 22 pp.

AENOR, 2007a. UNE 56544:2007. Clasificación visual de la madera aserrada para uso estructural. Madera de coníferas. AENOR, Madrid. 26 pp.

AENOR, 2007b. UNE 56546:2007. Clasificación visual de la madera aserrada para uso estructural. Madera de frondosas.AENOR, Madrid. 24 pp.

AFNOR, 1992. NF B 52-001-4. Régles d'utilisation du bois dans les constructions. AFNOR, La Plaine Saint-Denis. 24 pp.

Argüelles R., Arriaga F., 1988. Curso de diseño y cálculo de estructuras de madera. Colegio Oficial de Arquitectos, Madrid, Spain. 173 pp.

Bermúdez J.D., 1997. La industria de transformación de la madera de Galicia. CIS Madera 0, 7-14.

Breyer D.E., Fridley K.J., Cobeen K.E., Pollock D.G., 2007. Design of wood structures-ASD/LRFD, 6th ed. McGrawHill Inc, New York, United States.

British Standards Institution, 2007. BS 5756: 2007. Visual grading of hardwood. Specification. BSI, London. 20 pp.

Collardet J., Besset J., 1992. Bois commerciaux (vol. II). Feuillus des zones tempérées. H Vial and CTBA, France. 399 pp.

Courchene T., Lam F., Barrett J.D., 1998. The effect of edge knots on the strength of SPF MSR lumber. For Prod J 48(4), 75-81.

Degron R., Nepveu G., 1996. Methodology of microdensitometric measurement for oak wood (Quercus robur L. and Quercus petraea Liebl): proposal for a representative sampling of oak wood density within ring. Holzforschung 50(6), 491-496.

Desch H.E., Dinwoodie J.M., 1996. Timber. Structure, properties, conversion and use. MacMillan Press Ltd, Hong-Kong. 306 pp.

European Committee For Standardization, 2002. EN 13183-1:2002. Moisture content of a piece of sawn timber - Part 1: Determination by oven dry method. CEN, Brussels. 8 pp.

European Committee For Standardization, 2004a. EN 384:2004. Structural timber. Determination of characteristic values of mechanical properties and density. CEN, Brussels. 17 pp.

European Committee For Standardization, 2004b. EN 408:2004. Timber structures. Structural timber and glued laminated timber. Determination of some physical and mechanical properties. CEN, Brussels. 33 pp.

European Committee For Standardization, 2010. EN 338:2009. Structural timber. Strength classes. CEN, Brussels. 12 pp.

Farmer R.H., 1972. Handbook of hardwoods, 2nd ed. Her Majesty's Stationery Office, London, UK. 243 pp.

Fernández-Golfín Seco J.I., Díez Barra M.R., Hermoso Prieto E., Conde García M., 2004. Mechanical characterization of timber from Spanish provenances of laricio pine according to European standards. Wood Sci Technol 38(1), 25-34.

Fernández-Golfín J.I., Díez M.R., Hermoso E., Baso C., Casas J.M., González O., 2007. Caracterización de la madera de Eucalyptus globulus para uso estructural. Boletín del CIDEU 4, 91-100.

Freas A.D., 1995. Wood properties. In: Wood engineering and construction handbook, 2nd ed (Faherty K.F., Williamson T.G., eds). McGrawHill Inc, New York, United States. pp. 1-29.

Green D.W., Kretschmann D.E., 1997. Properties and grading of southern pine timbers. For Prod J 47(9), 78-85.

Hermoso Prieto E., Fernández-Golfín Seco J.I., Díez Barra M.R., 2003. Mechanical characterization of timber according to European standards from Spanish provenances of Scots Pine. Invest Agrar: Sist Recur For 12(3), 103-110.

Iglesias A., 1998. Comercio exterior de industrias de la madera en los países de la UE: análisis del período 61-95 y modelización econométrica. Doctoral thesis. Universidad de Santiago de Compostela, Santiago de Compostela.

MARM, 2008. Anuario de Estadística Agroalimentaria y Pesquera 2007. Ministerio de Medio Ambiente, y Medio Rural y Marino, Madrid, Spain. 1002 pp.

Nassar D., 1996. La construcción de madera en España. El campo 134, 295-302.

Riesco Muñoz G., 2001. Estudio de las propiedades físico-mecánicas de la madera de roble (Quercus robar L.) de Galicia en relación con las variables del medio. Doctoral thesis. Universidad Politécnica de Madrid, Madrid.

Schaffer E.L., 1995. Preliminary design considerations. In: Wood engineering and construction handbook, 2nd ed (Faherty K.F., Williamson T.G., eds). McGrawHill Inc, New York, United States. pp. 30-60. PMid:7641455

United Nations. Economic Commission For Europe, 1988. Norme CEE recommandee pour le classement des sciages resineux selon la resistance. United Nations, Genève. 25 pp.

Van Acker J., Militz H., Stevens M., 1999. The significance of accelerated laboratory testing methods determining the natural durability of wood. Holzforschung 53(5), 449-458.

Vignote Peña S., Martínez Rojas I., 2006. Tecnología de la madera. Mundi-Prensa, Madrid, Spain. 687 pp.

Xunta De Galicia, 2001. O bosque galego en cifras. Consellería de Medio Ambiente, Santiago de Compostela, Spain. 226 pp.

Zhang S.Y., Nepveu G., Owoundi R.E., 1994. Intratree and intertree variation in selected wood quality characteristics of European oak (Quercus petraea and Quercus robur). Can J Forest Res 24(9), 1818-1823

How to Cite
Riesco MuñozG., Remacha GeteA., & Pedras SaavedraF. (2011). Implications in the design of a method for visual grading and mechanical testing of hardwood structural timber for designation within the European strength classes. Forest Systems, 20(2), 235-244.
Research Articles