European Journal of Wood and Wood Products

, Volume 76, Issue 3, pp 899–909 | Cite as

Unexplained site variance in machine strength grading of Norway spruce structural timber

  • Carolin Fischer
  • Geir I. Vestøl
  • Audun Øvrum
  • Olav A. Høibø


The aim of the study was to assess site effects in terms of unexplained site variance in machine strength grading of Norway spruce structural timber. The site effects were estimated for grading based on axial resonance frequency and timber length, and for grading based on dynamic modulus of elasticity. Timber was collected from 14 sites in Norway, and linear mixed models were developed based on 1188 boards. The study showed that strength grading based on axial resonance frequency and timber length leaves out effects of site that are related to altitude, latitude and site index. The variance could be reduced when the grading was based on dynamic modulus of elasticity. For both grading methods, the site effects were smaller for bending strength than for modulus of elasticity and density. Major parts of the site effects were explained by mass density, and simulations showed that it is possible to fulfil the requirements of the strength classes with a higher yield when the sorting is based on a combination of exclusion by mass density and exclusion by the frequency-based indicating property.



This study is part of the national project ‘Tresterk’, managed by the Norwegian Institute of Wood Technology (Treteknisk) and supported by the Research Council of Norway under grant number 208085/I10, Fondet for Treteknisk Forskning, Skogtiltaksfondet and Norwegian forest industries. The authors are grateful to the forest owners and forest owners’ associations for providing the timber and to Moelven Soknabruket AS, Begna Bruk AS and InnTre AS for processing the timber. We also want to thank Sebastian Knutsen, Runa Stenhammer Aanerod, and Friederike Mennicke for assisting in the lab.


  1. Atmer B, Thörnqvist T (1982) The properties of tracheids in spruce (Picea abies Karst.) and pine (Pinus sylvestris L.). Reports No. 134, Swedish university of agricultural sciences [in Swedish with English summary]Google Scholar
  2. Boström L (1997) Assessment of Dynagrade timber strength grading machine. Technical Report, Swedish National Testing and Research Institute Building TechnologyGoogle Scholar
  3. CEN (2016a) Report No. ITT/138/07/06. European committee for Standardization, BrusselsGoogle Scholar
  4. CEN (2016b) Report No. ITT/139/12/06. European committee for Standardization, BrusselsGoogle Scholar
  5. CEN (2016c) Report No. TC124/TG1. European committee for Standardization, BrusselsGoogle Scholar
  6. Chrestin H (2000) Mechanical properties and strength grading of Norway spruce timber of different origins. In: Proceedings from the World Conference on Timber Engineering, Whistler resort, British Colombia, Canada, July 31–August 3, 2000Google Scholar
  7. Colin F, Houllier F (1991) Branchiness of Norway spruce in north-eastern France: modelling vertical trends in maximum nodal branch size. Ann Sci For 48:679–693CrossRefGoogle Scholar
  8. Ericson B (1960) Studies of the genetical wood density variation in Scots pine and Norway spruce. Stockholm: Royal College of Forestry. Reports 4:1–52Google Scholar
  9. Fischer C, Vestøl GI, Øvrum A, Høibø O (2015) Pre-sorting of Norway spruce structural timber using acoustic measurements combined with site-, tree-, and log characteristics. Eur J Wood Prod 73(6):819–828CrossRefGoogle Scholar
  10. Hakkila P (1966) On the basic density of Finnish pine, spruce and birch wood. Commun Inst For Fenn 61:1–98Google Scholar
  11. Hanhijärvi A, Ranta-Maunus A (2008) Development of strength grading of timber using combined measurement techniques. Report of the Combigrade project—phase 2. VTT Publications 686, Espoo, FinnlandGoogle Scholar
  12. Hanhijärvi A, Ranta-Maunus A, Turk G (2005) Potential of strength grading of timber with combined measurement techniques. Report of the Combigrade project—phase 1. VTT Publications 568, EspooGoogle Scholar
  13. Hautamäki S, Kilpeläinen H, Verkasalo E (2013) Factors and models for the bending properties of sawn timber from Finland and North-Western Russia. Part I: Norway spruce. Baltic For 19:106–119Google Scholar
  14. Hoffmeyer P (1995) Styrkesortering ger mervärde. Del 2—Tilgængelig teknik [Strength sorting adds value. Part 2—Available technology]. Danmarks Tekniske Universitet, Teknisk Rapport 335Google Scholar
  15. Høibø OA (1991) The quality of wood of Norway spruce (Picea abies (L.) Karst) planted with different spacing. Dissertation, Agricultural University of NorwayGoogle Scholar
  16. Høibø O, Vestøl GI, Fischer C, Fjeld L, Øvrum A (2014) Bending properties and strength grading of Norway spruce: variation within and between stands. Can J For Res 44:128–135CrossRefGoogle Scholar
  17. Johansson K (2003) Influence of initial spacing and tree class on the basic density of Picea abies. Scand J For Res 8(1–4):18–27Google Scholar
  18. Klem GS (1965) Variations in the specific gravity of foreign softwood species and Norway spruce from South and West Norway. Medd Nor Skogforsøksvesen 74:137–169 (Norwegian with English summary) Google Scholar
  19. Kuçera B (1994) A hypothesis relating current annual height increment to juvenile wood formation in Norway spruce. Wood Fiber Sci 26:152–167Google Scholar
  20. Larsson D, Ohlsson S, Perstorper M, Brundin J (1998) Mechanical properties of sawn timber from Norway spruce. Holz Roh- Werkst 56(5):331–338CrossRefGoogle Scholar
  21. Littell RC (2006) SAS for mixed models. SAS Institute Inc., CaryGoogle Scholar
  22. Lukacevic M, Füssl J, Eberhardsteiner J (2015) Discussion of common and new indicating properties for the strength grading of wooden boards. Wood Sci Technol 49(3):551–576CrossRefGoogle Scholar
  23. Mäkinen H, Colin F (1998) Predicting branch angle and branch diameter of Scots pine from usual tree measurements and stand structural information. Can J Forest Res 28(11):1686–1696CrossRefGoogle Scholar
  24. Nagoda L (1985) Strength properties of Norway spruce (Picea abies (L.) Karst.) from Northern Norway tested on timber in structural sizes. Medd Nor Inst Skogf 38.17:1–31 (Norwegian with English summary) Google Scholar
  25. Olesen PO (1982) The Effect of Cyclophysis on Tracheid Width and Basic Density in Norway spruce. Forest Tree Improvement 15:80Google Scholar
  26. Olsson A, Oscarsson J, Johansson M, Källsner B (2012) Prediction of timber bending strength on basis of bending stiffness and material homogeneity assessed from dynamic excitation. Wood Sci Technol 46(4):667–683CrossRefGoogle Scholar
  27. Ranta-Maunus A (2009) Strength of European timber. Part 1. Analysis of growth areas based on existing test results. VTT Publications 706, EspooGoogle Scholar
  28. Ranta-Maunus A (2012) Determination of settings in combined strength, stiffness and density grading of timber. Eur J Wood Prod 70:883–891CrossRefGoogle Scholar
  29. Ranta-Maunus A, Turk G (2010) Approach of dynamic production settings for machine strength grading. In: Proceedings of the 11th world conference on timber engineering, Trentino, ItalyGoogle Scholar
  30. Ranta-Maunus A, Denzler JK, Stapel P (2011) Strength of European Timber. Part 2. Properties of spruce and pine tested in Gradewood project. VTT Publication 179. Espoo, FinlandGoogle Scholar
  31. Repola J (2006) Models for vertical wood density of Scots pine, Norway spruce and birch stems, and their application to determine average wood density. Silva Fennica 40(4):673CrossRefGoogle Scholar
  32. Rouger F (1997) A new statistical method for establishment of machine settings. In: Proceedings CIB-W18, Paper 30-17-1, Vancouver, CanadaGoogle Scholar
  33. Sandomeer M, Köhler J, Faber MH (2008) Probabilistic output control for structural timber—Modelling approach. In: Proceedings of CIB-W18, Paper 45-5-1, St. Andrews, CanadaGoogle Scholar
  34. Standard Norge (2009) Nordic visual strength grading rules for timber. Norsk Standard NS-INSTA-142Google Scholar
  35. Standard Norge (2010) Structural timber—determination of characteristic values of mechanical properties and density. Norsk Standard NS-EN384Google Scholar
  36. Standard Norge (2012a) Structural timber—strength classes—assignment of visual grades and species. Norsk Standard NS-EN1912Google Scholar
  37. Standard Norge (2012b) Timber structures—structural timber and glued laminated timber—determination of some physical and mechanical properties. Norsk Standard NS-EN408Google Scholar
  38. Standard Norge (2012c) Timber structures—strength graded structural timber with rectangular cross section. Part 2. Machine grading; additional requirements for initial type testing. Norsk Standard NS-EN, pp 14081–14082Google Scholar
  39. Standard Norge (2016) Structural timber—strength classes. Norsk Standard NS-EN 338Google Scholar
  40. Stapel P, van de Kuilen JWG (2013) Effects of grading procedures on the scatter of characteristic values of European grown sawn timber. Mater Struct 46(9):1587–1598CrossRefGoogle Scholar
  41. Stapel P, Denzler JK, van de Kuilen JWG (2015) Analysis of determination methods for characteristic timber properties as related to growth area and grade yield. Wood Mater Sci Eng. Google Scholar
  42. Tamminen Z (1964) Moisture content, density and other properties of wood and bark. II Norway spruce (Nr. R 47). Royal College of Forestry, StockholmGoogle Scholar
  43. Tveite B (1977) Site–index curves for Norway Spruce (Picea abies (L.) Karst.). Norwegian Res For Inst Rapp 33(1)Google Scholar
  44. Vestøl GI, Høibø O, Langsethagen KG, Skaug E, Skyrud REA (2012) Variability of density and bending properties of Picea abies structural timber. Wood Mater Sci Eng 7(2):76–86CrossRefGoogle Scholar
  45. Vestøl GI, Fischer C, Høibø O, Øvrum A (2016) Between-and within-site variation of density and bending properties of Picea abies structural timber from Norway. Scand J For Res 31(8):758–765CrossRefGoogle Scholar
  46. Wilhelmsson L, Arlinger J, Spangberg K, Lundqvist SO, Grahn T, Hedenberg O, Olsson L (2002) Models for predicting wood properties in stems of Picea abies and Pinus sylvestris in Sweden. Scand J For Res 17(4):330–350CrossRefGoogle Scholar
  47. Ziethén R, Bengtsson C (2011) Initial settings for machine strength graded structural timber. In: Proceedings of CIB W18, Paper 44-5-3, Alghero, ItalyGoogle Scholar

Copyright information

© Springer-Verlag GmbH Germany, part of Springer Nature 2017

Authors and Affiliations

  • Carolin Fischer
    • 1
  • Geir I. Vestøl
    • 1
  • Audun Øvrum
    • 2
  • Olav A. Høibø
    • 1
  1. 1.Faculty of Environmental Sciences and Natural Resource ManagementNorwegian University of Life Sciences (NMBU)ÅsNorway
  2. 2.Norsk VirkesmålingRudNorway

Personalised recommendations