Dynamic and static tests were performed on 523 lumber specimens of Norway spruce (Picea abies) of three different cross sectional sizes: 38 x 89 mm 2, 38 x 140 mm 2, and 38 x 184 mm 2. Specific material characteristics for the lumber are presented. The tests also enabled comparison between results from two testing methodologies. The mean value for the modulus of elasticity established from the dynamic tests was found to be approximately 10% higher than the corresponding value established from static tests. The statistical correlation between statically and dynamically established moduli is very strong. The dynamic E modulus was found to be as good a strength predictor as the static E modulus. Cross sectional size and the existence of the pith in the sawn lumber were found to significantly influence the material properties. In general terms, it was found that deeper beams correspond to lower values for the E modulus and for the bending strength. The reason for this tendency is believed to be a combination of a volumetric effect (in the case of strength) and a phenomenon related to the log selection and sawing process in the mills. Lumber that comprises the pith has been found to have generally lower values of the E modulus and bending strength while the shear modulus is higher, compared to lumber without pith sawn further out in the log. Mechonische Eigenschcrften von FichtenschnittholzAn 525 Schnittholzproben (Picea abies) wurden dynamische und statische Priifungen vorgenommen. Die Proben hatten drei verschiedene Querschnitte: 38 x 89 mm 2, 38 x 140 mm 2 und 38 x 184 mm 2. Anhand der vorgelegten Ergebnisse wurden auch zwei Priifmethoden verglithen. Die Mittelwerte der dynamischen MOE-Prfifung lagen etwa 10% h6her als die statisch ermittelten Werte. Die Korrelation beider MOE-Werte ist sehr streng. Beide Werte k6nnen zur Vorhersage der Festigkeit verwendetThe dynamic tests and subsequent evaluation and comparison between dynamic and static test data were made within a project concerning the determination of viscoelastic properties of anisotropic materials by modal testing, which is financially supported by the Swedish Research Council for Engineering Sciences (TFR) in grant No. 261-94-344; this is gratefully acknowledged. werden. Der Querschnitt und die Anwesenheit von Markanteilen beeinflussen das Ergebnis wesentlich. Je tiefer die Balken waren d.h. je n~iher sie der Markr6hre lagen, desto geringer waren E-Modul und Biegefestigkeit. Die Grfinde dafiir werden tells einem Volumeneffekt zugeschrieben (ira Falle der Festigkeit), tells auf das Auswahlverfahren der St~imme im S~igebetrieb zurfickgeffihrt. Schnittholz mit Markanteil hatte allgemein, einen geringeren E-Modul und niedrigere Biegefestigkeit als Proben aus iiufleren Stammbereichen; die Scherfestigkeit lag dagegen h6her.
This paper deals with the development of models for twist in structural timber. Twist was measured on 240 studs of Norway spruce (Picea abies). Several material parameters were also measured, such as spiral grain angle, shrinkage in all three directions, annual ring width and density. Twist in the studs was measured at four different times at different moisture contents. The amount of twist correlated well with the moisture content and was reversible throughout several moisture changes. When the moisture content decreased, the twist increased and vice versa. About 50% of the variation in twist could be explained by a single parameter, i.e. the average growth ring curvature. All studs with severe twist were cut with its centroid within a radius of 75 mm from the pith. A statistical analysis of the data shows that growth ring curvature and spiral grain angle together explained about 70% of the variation in twist. Other parameters, such as shrinkage strains, density and ring width, did not increase predictability. When using a model developed by Stevens and Johnston (1960), about 66% of the variation in twist could be explained. The model also explained twist quantitatively well. The model included curvature of the growth ring, spiral grain angle and the tangential shrinkage strain. Verwerfung von Fichtenschnittholz. Teil 2. Simulation der Verdrehung Diese Arbeit behandalt dia Entwicklung von Modellon fu Èr die Verdrehung in Schnittholz. Die Verdrehung wurde gemessen an 240 Fichtenkantho Èlzern (Picea abies). Mehrere Materialeigenschaften wurden ebenfalls gemessen, und zwar: Faserwinkel, Schwinden in drei Richtungen, Jahrringbreite und Dichte. Die Verdrehung der Kantho Èlzer wurde zu vier verschiedenen Zeitpunkten bei unterschiedlichen Feuchtegraden gemessen. Das Ausmaû der Verdrehung war gut korreliert mit der Feuchte. Mit abnehmender Feuchte stieg die Verdrehung und umgekehrt. Rund 50% der Verdrehungswerte sind durch einen einzigen Parameter erkla Èrt, na Èmlich die Jahrringkru Èmmung. Bei allen Kantho Èlzern mit starker Verdrehung lag die Mittelachse innerhalb eines Abstandes von 75 mm von der Markro Èhre. Die statistische Analyse ergab, daû Jahrringkru Èmmung und Faserwinkel zusammen ca. 70% der Variation der Verdrehung erkla Èren. Andere Parameter wie Schwindspannungen, Dichte und Jahrringbreite erho Èhten die Vorhersagbarkeit nicht. Mit Hilfe des Modells von Stevens und Johnson (1960) konnten rund 66% der Verdrehung erkla Èrt werden. Dieses Modell lieferte auch zufriedenstellende quantitative Ergebnisse. Beru Ècksichtigt werden dabei Jahrringkru Èmmung, Faserwinkel und tangentiale Schwindspannung.
Strength and stiffness together with some properties characterizing the stand and the growth of trees were studied. Specimens (45 • 70 x 2900 mm 3) were cut from different radial and longitudinal positions, from fast-grown trees from two stands in southern Sweden. These trees had relatively large annual rings (4-6 mm) and were not representative of Norway spruce in Sweden but are an example of the intensivelymanaged stands which will probably constitute a substantial part of the raw material supply in the future.The results indicate that the mean values for strength and stiffness were lowest for the core studs and increased further away from the pith. This radial variation in strength and stiffness appears to be associated with the variation in ring width. Density alone, on the other hand, does not explain the radial variation but should be used together with either ring width or knot area ratio to explain the stiffness and strength respectively. The increase in the strength and stiffness of the core studs from the butt logs to the top logs was significant. Density alone was found to be the best variable to explain the longitudinal variation between the butt logs and the top logs. The heartwood formation in the butt log juvenile core appeared not to have a positive effect on strength and stiffness. The occurrence of compression wood, the magnitude of grain angle and the margin knot area ratio had only a minor effect on strength and stiffness.
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