Tensile strength classes for hardwoods

Andriy Kovryga, Peter Stapel, Jan-Willem van de Kuilen

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Generally, for structural timber the main properties are listed in a strength class system. In Europe EN 338 (2016) lists available strength class and their respective characteristic properties. Depending on the product application the bending or the tension properties are of main interest. For glulam lamellas, tension classes are preferred as through tension classes the mechanical properties of glulam can be better predicted. Also, machine grading allows for a better prediction of tensile properties compared to bending properties. So far, tension grades were regulated in EN 14081- 4. Due to the increased demand on glulam products, the grades were recently analysed, and a tensile class table was introduced in EN 338 (2016). The new strength profiles are the preferred option for glulam production. The requirements for softwood glulam are regulated in EN 14080 (2013). So far, no tension classes exist for hardwoods. The EN 338 lists for hardwood specimens only so-called “D” classes based on the bending strength. The other properties, like tension strength, are assigned by the default on the safe side using the equations listed in EN 384. For those classes, the ratio tension strength to bending strength is declared on the safe side 0.6. However as shown by Burger & Glos (1997) for higher quality timber higher ratio can be expected. New tensile classes for hardwoods would allow utilising the properties of hardwoods more efficiently. Whereas the old European standards EN 1194 and EN 14080 (2005) did not regulate species, the most recent version of EN 14080 (2013) is restricted to softwoods only. This means that hardwood glulam producers in Europe face additional costs for obtaining approvals for their products.
Original languageEnglish
Title of host publicationInternational Network on Timber Engineering Research Proceedings
Subtitle of host publicationMeeting 49 Graz, Austria
EditorsR. Görlacher
PublisherKIT Scientific Publishing
Publication statusPublished - 2016
Event29th Meeting of the International Network on Timber Engineering Research - Graz, Austria
Duration: 16 Aug 201619 Aug 2016
Conference number: 49


Conference29th Meeting of the International Network on Timber Engineering Research
Abbreviated titleINTER 2016
Internet address


  • Structural timber
  • hardwoods
  • characteristic properties
  • EN 338
  • EN 384


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