Influences of the growing area on the visual, physical and mechanical parameters based on the example of wood from alpine regions

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1 Influences of the growing area on the visual, physical and mechanical parameters based on the example of wood from alpine regions Roland Maderebner 1, Michael Flach 1, Alfred Teischinger 2, Martin Bacher 3 ABSTRACT It is often reported that the growing area of the tree has an influence on timber quality. However, this traditional knowledge is not always confirmed by sawmill owners. The objective of the work presented here is to detect the influence of the growing area on the visual, physical and mechanical properties of mountain spruce wood. Therefore a total of 476 timber beams from two mountain valleys in and Tyrol (Austria and Italy) were sorted by visual and machine strength-grading methods. Afterwards the physical and mechanical properties are determined by bending tests according to ÖNORM EN 408. The obtained results are compared with results of other investigations of spruce wood from deeper located growing areas. Furthermore, the influences of past cultivations in the growing area on the wood properties are also taken into account. KEYWORDS: Growing area, altitude level, knottiness, MOR, MOE, density, spruce wood, grading 1 INTRODUCTION 123 Due to its slow growth, special properties are often assigned to wood from alpine regions. This popular wisdom which exists in many alpine countries is, however, not confirmed by some sawmills; to some extent, they even report the opposite (Interreg IV Documentation, 2011). In this context, the general question is raised about the actual impact of the tree s location on wood properties (colloquially referred to as quality ), and whether, and via which parameters, these can be measured accordingly. In the course of an INTERREG IV project entitled Gebirgsholz Wald ohne Grenzen (Mountain timber Forest without Borders) (Maderebner, 2012), the possibilities to improve the market value of mountain timber from, East and Tyrol have been demonstrated. Besides a host of questions posed in the course of this project, also the general physical and mechanical properties of spruce timber (Picea abies) from alpine regions were examined. Moreover, also possible influences of the growing area, orientation, altitude and the different cultivation types on timber properties were of interest. The question as to the qualitative sortability of spruce timber from mountain valleys was treated in cooperation with partners from industry. The Timber Engineering Unit at the Faculty of Technical Sciences of the University of Innsbruck and the Institute of Wood Technology and Renewable Materials of the Vienna University of Natural Resources and Life Sciences (BOKU Wien) were commissioned with 1 University of Innsbruck, Austria, holzbau@uibk.ac.at 2 Institute of Wood Science and Technology, University of Natural Resources and Life Sciences of Vienna alfred.teischinger@boku.ac.at 3 MiCROTEC GmbH, martin.bacher@microtec.eu scientific project analysis. The results regarding the physical and mechanical properties gained from bending tests as well as selected visually perceptible properties are presented in this article. This paper is based on project reports (Maderebner, 2012 and 2015). 2 METHOD 2.1 Selection of locations and specimens The test material comes from the mountain valleys of Navistal in Tyrol (Austria) and Pustertal in Tyrol (Italy). Both valleys feature a pronounced East- West extension as well as roughly equal angles. For further location descriptions, see Maderebner, As displayed in Figure 1, the material was taken from overall 22 altitude levels at the north and south s of the mountain valleys mentioned above. When selecting the trees, a comparable optical quality of the spruce trees (comparable habit, age) was considered together with forest industry experts. Here, characteristics such as knottiness, taper, diameter at breast height as well as damages, if any, and/or injuries were documented. To avoid additional marginal influences, only trees from a single stock were considered for the selection. After the spruce trees had been felled and debranched, a tape measure and a calliper were used to determine the total length, the diameter and/or taper of the trees, and the annual rings were counted to determine the trees age (Table 1). To avoid red rot and reaction wood, in particular in the trunk area, the specimens were used for further tests at the selected trees only from the second log (central log) after a length of appr. 4.5 m (Figure 2). In order to perform an exact definition of the positions of the specimens in the trunk and to make them traceable down to the experimental tests, the trunks were marked at the mountain sides before felling and/or the ripping of the tree into individual logs. Based on all recordings for each individual tree as well as on the trunk location and

2 Figure 1: of the trees for the specimens the respective location s characteristics, consistent documentation is guaranteed and it is possible to arrive at a location-specific interpretation of results. Figure 2: Cut out the specimens of the logs Figure 3: Selection of the specimens of the joist Figure 4: Visual grades overall and depending on the orientation of the 2.2 Round timber cutting The specimens were cut four-post by way of a band saw (Figure 2), followed by technical drying to a wood moisture of appr. 12 %. For both sets, the mean value of the diameter at breast height was appr. 460 mm, while the diameter of the sample logs was, on average, appr. 350 mm. Due to the selection of this cutting, the share of juvenile timber is to be considered. The mountain-side markings of the individual logs were transferred to the wood clippings and numbered accordingly. Overall, 476 specimens were thus cut from the round timbers of the 22 locations, featuring dimensions of 48 mm x 4050 mm. This way, the timber could be assigned to the joist category (ÖNORM DIN , 2012). Of these overall 476 specimens, appr. 56 % were from the Tyrol set (268 pieces), while 44 % were from the Tyrol set (208 pieces). 2.3 Mechanical and visual grading After the wood had been dried technically, the joists were graded mechanically at the Theurl Holz company in Thal (East Tyrol) together with the Microtec company (grading machine: Goldeneye 706 combining vibration measurement of Viscan and X-ray scanning to determine dynamic modulus of elasticity, density and knots). In the course of the grading process, the timbers were cut back to a length of 4050 mm and planed from four sides to the final dimensions of 48 mm x 138 mm. The visual categorisation of the timber into grading classes was carried out according to the provisions of Austrian standard ÖNORM DIN (2012) applicable for macroscopic structure characteristics at the University of Innsbruck. The specimens were drygraded according to the grading criterias for joists and assigned to the corresponding classes S7, S10 and S13. By way of the grading classes determined visually, the

3 specimens can be assigned, according to ÖNORM EN 1912 (2013), to a system of strength classes according to ÖNORM EN 338 (2009). Based on this assignment, the quality of visual grading can be evaluated, using the results from the bending tests according to ÖNORM EN 408 (2012). 2.4 Cutting-to-size of specimens After visual grading and the exact documentation of the macroscopic timber properties, the specimens were cut to size on the basis of knot data and density measurements gained from mechanical and visual grading for the purpose of further performance of the bending tests according to ÖNORM EN 408. In this process, the 2630 mm long specimen was cut out of the 4050 mm long joist so that the weakest crosssection (= projected failure point) lies in the middle third (Figure 3). Due to load introductions in the third points of the specimens in the course of 4-point bending tests, the projected failure point is positioned in the area of constant bending moment load. After cutting-tosize, the markings for the mountain sides as well as for specimen numbers were, again, transferred, and the material was conditioned in standard reference atmosphere at (20 ± 3) C and (65 ± 5) % of relative air humidity until constant mass was achieved according to ÖNORM EN 408. The mean annual ring widths were measured for each joist in compliance with ÖNORM DIN RESULTS 3.1 General remarks In the following statements, a differentiation is made between the Tyrol (NT) and Tyrol (ST) sets, north (N) and south (S) orientations as well as between altitudes, respectively. 3.2 Visual grading results Figure 4 gives the yields of the grading classes from the visual grading of specimens featuring a length of 2630 mm with the parameters from the middle third for the purpose of compliance with the causality of measurements results and the comparability with bending test results. In this process, the key grading criterion is constituted by knottiness. Here, some 10 % are to be assigned to class S13, 45 % to S10 and 37 % to grading class S7. The share of specimens that cannot be assigned, i.e. grading classes REJ, accounts for 8 % (37 pieces). The two Tyrol and Tyrol sets exhibit roughly equal distributions in the individual grading classes. Yet the reject REJ is 6 % higher for the Tyrol set than at the Tyrol side (Table 2). Marked differences between the north and south exposures can be inferred from visual grading. At the north, a 8 % higher yield than at the south in grading class S13 is documented, and, in class S 10, an even 17 % higher yield than at the south is documented. Vice versa, grading class S7 exhibits a 14 % higher result at the south, and also with regard to reject REJ, a difference of 11 % is discernible (Table 2). Dependence of grading classes on altitude levels is represented in Figure Mean annual ring widths With regard to visual grading, the mean value achieved for annual ring widths, according to ÖNORM DIN , accounts for 2.14 mm (Figure 6). The highest value, i.e mm, as well as the lowest value, i.e mm, have occurred in the Tyrol south set (Table 1). For all sets, the maximum mean annual ring widths are observed in the lower altitude levels. As altitude of the growing area increases, annual ring width goes down. Also with regard to standard deviations from the mean value, a reduction has been observed as altitude increases. No differences can be inferred from the north and south orientations. The 1250-N (ST) location corresponds to 1250 m above sea level, north ( Tyrol), and exhibits a markedly higher mean value for annual ring widths when compared to neighbouring locations. This may be explained by the fact that this location had been registered in the historic cadastre up until the 1970s as an area used for grazing by cows and for litter utilisation (Maderebner, 2015). Also with regard to mechanical measurement results, differences have, again and again, been clearly identified. A similar correlation could be established also on the south side at the 1390-S (ST) location, corresponding to 1390 m above sea level, south ( Tyrol), bearing the locality name of Lana. Also here, pasture areas had been documented in the cadastre still until the 1950s (Maderebner, 2015). At the 810-S (ST) location, growing conditions have been subject to change due to clear-cutting around 1950 below the sample logs. From a location altitude of 1,600 m above sea level onwards, a decrease of annual ring widths on both sides of the s has been clearly observed. Table 1: Mean Annual ring-width tree age Annual ring width [mm] [years] Tyrol Tyrol Collective Tyrol Tyrol Collective Total XXL -Wood: (Teischinger, 2006) Holzknecht (DE; 100) (Holzknecht, 2010)

4 3.2.2 Knot parameters Overall, 7722 knots featuring the dimensions of 48 mm x 138 mm x 2630 mm have been documented exactly in terms of geometry at the 476 specimens. Table 3 and 4 as well as Figure 7 and 8 give the key results of the knot parameter tests. To ensure measurement data causality, here, again, only the knot data are represented over a range of ± 4 h (total length: 1104 mm), starting from the middle of the specimen. From the results achieved for knot parameters DEK as well as tkar it can be inferred that the gained specimens exhibit higher total knottiness values tkar and/or individual knot diameters DEK at the south s than those at the north s. In this process, the tkar parameter is not directly used as a value for visual grading, as this value is actually to be used as a grading criterion for research projects. However, as with this value, the characteristic features of knottiness are documented differently than with the DEK value, this value was used for an advanced analysis of the influence of the location. Similar to annual ring widths, also for knottiness the influence exerted by the location can be traced back very well. Accordingly, for example, also here, the 1390-S (ST) location, bearing the locality name of Lana (pasture areas), exhibits, at 0.51, the highest tkar value as well as the highest mean value, i.e As opposed to that, the 1010-N (ST) location bearing the locality name of Schattenwald exhibits the lowest value, i.e. 0.02, and also the lowest mean value of tkar, i.e At the 810-S (ST) location, the knottiness parameters are unremarkable. Also locations allow for the conclusion that, on south s, knottiness is more pronounced than on north s. A direct influence of altitude levels cannot be determined in statistical terms. Table 2: Visual grades S13 (C30) Visual grades [%] S10 (C24) S7 (C18) REJ Tyrol Tyrol Collective Tyrol Tyrol Collective Total Table 3: Knot parameter DEK Knot parameter DEK [-] Tyrol Tyrol Collective Tyrol Tyrol Collective Total Table 4: Knot parameter tkar Knot parameter tkar [-] Tyrol Tyrol Collective Tyrol Tyrol Collective Total Table 5: Strength classes based on the bending test results Sorting Combination [%] EN C30 C24 C18 REJ Tyrol Tyrol Collective Tyrol Tyrol Collective Total Table 6: Bending strength MOR MOR [N/mm²] Tyrol Tyrol Collective Tyrol Tyrol Collective Total Swiss spruce: Quality normal (Steiger, 1995) Teilprojekt 14: (dist. to mark: 137,5 mm) (Wegener, Glos, Tratzmiller) Holzknecht (DE; 100) (Holzknecht, 2010) Table 7: Modulus of elasticity in bending MOE MOE [N/mm²] Tyrol Tyrol Collective Tyrol Tyrol Collective Total Swiss spruce: Quality normal (Steiger, 1995) Teilprojekt 14: (dist. to mark: 137,5 mm) (Wegener, Glos, Tratzmiller)

5 Table 8: Density DEN DEN [kg/m 3 ] Tyrol Tyrol Collective Tyrol Tyrol Collective Total Swiss spruce: Quality normal (Steiger, 1995) Teilprojekt 14: (dist. to mark: 137,5 mm) (Wegener, Glos, Tratzmiller) Holzknecht (DE; 100) (Holzknecht, 2010) 3.3 Bending test results Assignment to strength classes In order to be able to evaluate the quality of visual grading for spruce timber from alpine regions, the results/yields are compared with the results from bending tests according to ÖNORM EN 408. By way of determination of yields according to ÖNORM EN (2013), categorisation into strength classes, according to ÖNORM EN 338 (2010), is performed, using grading combination C30-C24-C18 corresponding to S13-S10-S7, on the basis of the determined parameters of bending strength MOR, modulus of elasticity MOE and density DEN. By way of this so called perfect grading method, 84 % are assigned to strength grade C30, and 15 % of joists are assigned to grade C18 (Table 5). Reject REJ accounts for merely 1 % when compared with 8 % achieved for visual grading. Due to the grading combination C30-C24-C18, no joists remain for strength grade C24 so that all are assigned to strength grade C30. The reason for this lies in the grading combination (comment: insufficient distances between the individual classes) and, among other things, the more conservative assignment by way of visual grading techniques. In order to generate assignment of the specimens to strength grade C24 here, other grading combinations featuring bigger distances between the classes would have to be used which would, in turn, only be possible when using mechanical grading systems. Similar to visual grading, there is a correlation with altitude levels displayed in Figure 13 substantiated also by the bending test results and/or the strength classes inferred from them. When compared with visual grading, the Tyrol set exhibit a somewhat higher quality, with a 10 % higher yield in strength grade C30. A possible influence of different north-south orientations is, in turn, markedly put in perspective when considering the results of experimental tests in comparison with the yields gained for visual grading (Figure 5). At the 1250-N (ST) location, as with visual grading and when compared with neighbouring locations, there has been increased assignment to grade REJ, and with regard to 810-S (ST), strength grade C18 has emerged in large part Bending strength, MOR Bending strength values (ÖNORM EN 408, 2012) f m,150, converted to a reference height of 150 mm (ÖNORM EN 384, 2010), range between the dimensions of N/mm² and N/mm² at a span width of N/mm² (Table 6). On average, bending strength accounts for N/mm², with a variation coefficient of appr. 29 %, which is normal for spruce timber (Niemz, 1993). With regard to orientations and altitude levels, only minor differences accounting for 6 % could be observed in favour of the north sides. At the 1250-N (ST) location, a markedly smaller mean value, i.e N/mm², of f m,150 was observed on account of growing conditions and when compared to neighbouring locations (Figure 9). A similar result was established for the S (ST) as well as for the 810-S (ST) locations. Thus, a local influence on timber quality yielded by cultivation types is well identifiable (Maderebner, 2015) Modulus of elasticity in bending, MOE For the total set, the elasticity modulus accounts for N/mm², on average, and converted to a wood moisture of 12 % (ÖNORM EN 384, 2010), at a standard deviation of 2531 N/mm² (COV = 22 %) (Table 7). The lowest value of measured results has occurred at the 1250-N (ST) location which is again confirmed by knottiness results. With an average E m,g,12 value, the S (ST) set is markedly below the rigidity values exhibited by the other sets. Also for the MOE, similar to bending strength MOR, merely minor differences in the amount of overall 4 % have emerged in favour of the north sides regarding orientations. There is no evidence pointing towards a correlation with the altitude levels of the growing areas (Figure10). Yet also as regards the E-modulus, the influence of the location due to different cultivation types is plausible (Maderebner, 2015) Density, DEN When converted to a wood moisture of 12 % (ÖNORM EN 384, 2010), the total set exhibits mean density in the amount of ρ 12 of 415 kg/m³, with a variation coefficient of appr. 8 % (Table 8). There are only slight density variations between the individual sets. Decrease of the annual ring widths as altitude levels increase can, however, not be directly inferred from an increase of density (Figure11). As with the strength and rigidity parameters, also here, an influence of cultivation types (former pasture areas) is perceptible, even if it is not as pronounced as for strengths and rigidities.

6 4 Result analysis, discussion 4.1 Macroscopic properties Comparison of the mean annual ring widths with the values from other research projects (Steiger, 1995; Teischinger and Patzelt, 2006) has shown that the tested material is markedly below the values from these research projects, in particular for small annual ring widths (Table 1). When comparing these mean values to one another, the differences are, however, partly put in perspective. As the altitude level increases, scattering of annual ring widths becomes less pronounced (Figure 6). This decrease also has an impact on gross densities and results in some sort of homogenisation (Figure 11). As regards orientations, no differences have been determined, which can also be explained by pronounced East-West extensions found in the selected mountain valleys. It can be clearly observed to some extent that there is an impact of past cultivation types as annual ring widths increase. Also when analysing the knot parameters, this correlation with past cultivation types regarding the selected growing areas can be observed (Figure 7 and 8). Accordingly, areas that were used for grazing feature higher total knottiness values and often also bigger individual branches than this is the case for rather shady and primarily north-side locations that have always been wooded. This fact can also be inferred from the rigidity parameters and strength values. Unfortunately, no suitable values for comparisons with other research results could be found. 4.2 Strengths, rigidities and densities In spite of poor mean values of N/mm² for set S (ST), the tested sample material exhibits a relatively high bending capacity of N/mm² (Table 6). Comparison with bending strength results from other research projects shows that bending strength is relatively high for the tested sample material in spite of the low values exhibited by set S (ST). In this context, the maximum value, i.e N/mm², as well as the lowest value, i.e N/mm², have been observed at the north in Tyrol. This is a fact the substantiation of which is to be found in the past cultivation types prevalent at the respective locations (Maderebner, 2012). Dependencies of altitude levels have not been determined, but are masked by effects such as orientation and the past cultivation type prevalent at the location. As for the rigidity parameters, the same aspects as with bending strength have occurred. At a mean value of N/mm², it is in the same range as Swiss spruce timber (Steiger, 1995), furthermore, it appr. 10% below the indicated values achieved for the tests regarding subproject 14 (Wegener et al., 2008; Table 7). The partly low values of the MOE can be chiefly explained by the knottiness observed at certain locations. At 415 kg/m³, density is up to 16 % lower than the indicated values from intercomparison projects (Table 8). As the direct correlation between density and strength is frequently mentioned, mountain timber seems to exhibit a comparably high bending capacity here despite lower gross densities. Between the two examined locations of and Tyrol, basically no clear-cut differences could be identified. Yet some locations, in particular at the south in Tyrol, exhibited relatively poor mechanical parameters which is, however, explained by the basic selection of specimens (consideration of historic cadasters), and no conclusions are to be inferred from that. Figure 5: Average annual ring width dep. on the location and altitude Figure 6: Average annual ring width dep. on the location and altitude

7 Figure 7: DEK depending on the location and altitude Figure 10: MOE depending on the location and altitude Figure 8: tkar depending on the location and altitude Figure 11: Density depending on the location and altitude 5 Acknowledgement The project was co-financed by the European Regional Development Fund in the framework of the Interreg IV- A Italy-Austria programme and by national public contributions. Responsibility for the contents of this publication lies with the authors who would like to express their gratitude to project partners TIS innovation park, Cluster Holz und Technik (lead partner), proholz Tirol/Holzcluster as well as to the associated partners, i.e. the Office of the Provincial Government of Tyrol Forest Section, Tyrol Forest Association, Tyrol Timber Industry Section as well as the Microtec GmbH and Brüder Theurl GmbH companies for their support and excellent cooperation. Figure 9: Bending strength depinding on the location and altitude

8 Figure 12: Visual grades depending on the orientation of the and the altitude of the location Figure 13: Strength classes based on the bending tests depending on the orientation of the and the altitude of the location

9 6 REFERENCES Holzknecht, S.; (2010) Maschinelle Sortierung von Gebirgsholz. Diplomarbeit, Universität Innsbruck Maderebner, R.; (2015) Präsentationen und Besprechungen zur Dissertation Visuelle, physikalische und mechanische Eigenschaften von Fichtenholz aus Gebirgstälern. Dissertation (laufend, Stand Oktober 2015), Universität Innsbruck Maderebner, R.; (2012) Gebirgsholz Wald ohne Grenzen deutliche Verbesserung des Marktwertes Süd-, Ost- & Nordtiroler Gebirgshölzer und ausgewählter Holz-Nischenprodukte Maderebner, R. et al; (2016) Einfluss des Wuchsortes auf ausgewählte visuelle, physikalische und mechanische Eigenschaften am Beispiel von Fichtenholz aus alpinen Regionen (Teil I) in Ausgabe Institut für Holztechnologie Dresden gemeinnützige GmbH, Dresden 2016 ÖNORM EN (2013) Holzbauwerke Nach Festigkeit sortiertes Bauholz für tragende Zwecke mit rechteckigem Querschnitt Teil 2: Maschinelle Sortierung Zusätzliche Anforderungen an die Erstprüfung Steiger, R.; (1995) Biege-, Zug- und Druckversuche an Schweizer Fichtenholz. ETH Zürich, Birkhäuser Verlag Teischinger, A.; Patzelt, M.; (2006) XXL-Wood Materialkenngrößen als Grundlage für innovative Verarbeitungstechnologien und Produkte zur wirtschaftlich nachhaltigen Nutzung der Österreich Nadelstarkholzreserven Wegener, G.; Glos, P.; Tratzmiller, M.; (2008) Holzbau der Zukunft Teilprojekt 14 Hochwertige Bauprodukte aus Massivholz und Holzwerkstoffen aus starkem Stammholz Maderebner, R. et al; (2016) Einfluss des Wuchsortes auf ausgewählte visuelle, physikalische und mechanische Eigenschaften am Beispiel von Fichtenholz aus alpinen Regionen (Teil II) in Ausgabe Institut für Holztechnologie Dresden gemeinnützige GmbH, Dresden 2016 Niemz, P.; (1993) Physik des Holzes und der Holzwerkstoffe. DRWVerlag Weinbrenner GmbH & Co., Leinfelden Echterdingen ÖNORM EN 338 (2009) Bauholz für tragende Zwecke Festigkeitsklassen ÖNORM EN 384 (2010) Bauholz für tragende Zwecke Bestimmung charakteristischer Werte für mechanische Eigenschaften und Rohdichte ÖNORM EN 408 (2012) Holzbauwerke Bauholz für tragende Zwecke und Brettschichtholz Bestimmung einiger physikalische und mechanischer Eigenschaften ÖNORM EN 1912 (2013) Bauholz für tragende Zwecke Festigkeitsklassen Zuordnung von visuellen Sortierklassen und Holzarten ÖNORM DIN (2012) Sortierung von Holz nach der Tragfähigkeit Teil 1: Nadelschnittholz