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RESUMENEl objetivo del trabajo fue caracterizar la madera de Acacia melanoxylon R.Br en términos de densidad normal, contracción e hinchamiento máximos, anisotropía dimensional y contenido de humedad en el punto de saturación de las fi bras. En el marco de una investigación más amplia, se seleccionaron 10 árboles en dos sitios la Provincia de Buenos Aires, Argentina. Para la determinación de las propiedades físicas se emplearon las normas argentinas IRAM 9532 (1963), 9543(1966) y 9544(1973), y para el análisis de la varianza, modelos lineales mixtos. Los valores medios de los coefi cientes de contracción lineal para el conjunto de los árboles fueron de 0,16 y 0,30 en sus orientaciones radial y tangencial respectivamente. El punto de saturación de las fi bras correspondió a un contenido humedad del 24,7%. Los coefi cientes de anisotropía dimensional tomaron un valor de 2, por lo que se espera un comportamiento normal en el secado. El sitio no infl uyó signifi cativamente en la expresión de las propiedades físicas analizadas. En cambio, la varianza entre árboles para todas las propiedades contribuyó a la varianza aleatoria total con el 29,8-46,5%. La densidad normal promedio fue de 604 kg/m 3 , aumentando signifi cativamente desde la médula hacia la corteza. No hubo correlaciones signifi cativas entre densidad y cambios dimensionales.Palabras clave: Propiedades de la madera, densidad, contenido humedad, contracción, anisotropía. ABSTRACTThe aim of this research was to determine density, maximal swelling and shrinkage, anisotropy of swelling and shrinkage and fi bre saturation point on samples of Argentinean Acacia melanoxylon R Br. Ten trees were randomly selected from two sites located in Buenos Aires Province and samples were obtained at breast height. Physical properties were determined according to the Argentinean standards IRAM 9532 (1963), 9543(1966) y 9544(1973). Data were analysed by means of the analysis of variance according to a mixed linear model. Mean values of the coeffi cient of lineal shrinkage reached 0.16 and 0.30 for radial and tangential directions, respectively. Mean values for fi bre saturation point was 24.7 % and the factor of anisotropy was close to 2, which indicates that this species may normally perform drying processes. Site was not signifi cant for physical properties but highly signifi cant differences were found between trees. Tree variance component reached 29.8-46.5 % of the total random variation. The mean value for density reached 604 kg/m 3 and this property increases with the distance from the pith. The values found for the analysed properties are congruent with those reported for the same species by other researchers. No signifi cant correlation was found between density and dimensional changes.

The present paper reports on the results of an investigation regarding the determination of the embedding strength of sawn timber of Argentinean Eucalyptus grandis with dowel-type fasteners. The importance of accurately knowing this property has increased with the increasing demand for this material for structural purposes. An empirical research project with 294 specimens prepared for testing under the embedding action of rigid fasteners (nail, bolt and dowel) was carried out according to the procedures prescribed in EN 383 (2007). The results showed no significant influence of pre-drilling on the embedding strength for nailed joints, which is not in line with the European experience and the corresponding criterion adopted by the Eurocode 5 (2005). The characteristic values of the embedding strength estimated based on the timber density and by applying the corresponding equation from the Eurocode 5 (2005) for bolted joints were 45% and 176% greater than those obtained in this project for the specimens loaded parallel and perpendicular to the grain, respectively, and similar percentages were found for dowelled joints (45% and 126%). These results showed that the reliability of structural design may be strongly affected if the embedding strength of this timber species is estimated by following the procedures adopted by the Eurocode 5 (2005) for dowel-type connections. Lochleibungsfestigkeit von Vollholz ausEucalyptus grandis aus Argentinien. Analyse nach europäischen Normen Zusammenfassung Dieser Beitrag fasst die Ergebnisse einer Studie zusammen, in der die Lochleibungsfestigkeit von Vollholz aus Eucalyptus grandis aus Argentinien untersucht wurde. Das empirische Versuchsprogramm umfasste 294 Prüfkörper, die mittels steifen Verbindungsmitteln (Nagel, Bolzen und Stabdübel) nach EN 383 (2007) beansprucht wurden. Im Gegensatz zu der europäischen Erfahrung und dem entsprechenden Kriterium des Eurocodes 5 (2005) zeigten die Ergebnisse keinen deutlichen Einfluss der Vorbohrung auf die Lochleibungsfestigkeit von Nagelverbindungen. Die Abschätzung der charakteristischen Lochleibungsfestigkeit in Abhängigkeit der Rohdichte nach Eurocode 5 (2005) ergab Werte die 45 % und 176 % höher sind als die Ergebnisse dieser Untersuchung bei Beanspruchung in Richtung parallel bzw. rechwinklig zur Faser. Ähnliche Abweichungen wurden für die Stabdübelverbindungen gefunden. Diese Ergebnisse zeigten, dass die Zuverlässigkeit der Berechnung von Holzbauwerken stark vermindert werden kann, wenn die charakteristische Lochleibungsfestigkeit dieses Holzes nach dem Kriterium des Eurocodes 5 (2005) abgeschätzt wird.

The present paper reports the results of an investigation regarding the possibility of machine strength grading sawn timber of Argentinean Eucalyptus grandis. In order to assess the usefulness of each parameter for predicting the mechanical properties of this timber species, and to propose strength, stiffness and density profiles, an empirical research project with four samples of beams and one sample of boards subjected to bending, and another sample of boards subjected to tension parallel to the grain, was carried out. The results obtained with specimens in structural sizes reveal the more important single and combined parameters for machine strength grading this timber species, and allow to analyse strength, stiffness and density profiles in comparison with the international strength class system established in the European standard EN 338.